ORIGINAL ARTICLE
 
Effect of UV-C Radiation at Low Temperatures on Postharvest Life of Fragaria vesca
 

iDMSc. Tania María Guzmán-ArmenterosIUniversidad UTE, Department of Agroindustry, Ecuador.

iDMSc. Yandi Fernández-OchoaIIUniversidad UTE, Department of Electromechanics, Ecuador.

 

IUniversidad UTE, Department of Agroindustry, Ecuador.

IIUniversidad UTE, Department of Electromechanics, Ecuador.

 

*Author for correspondence: Tania María Guzmán-Armenteros, e-mail: tania.guzman@ute.edu.ec

 

ABSTRACT

The effect of UV-C radiation on strawberry postharvest life was evaluated from a response surface central compound design (CCD). The postharvest life of strawberry (Fragaria vesca L) var Big Bear was modeled based on the UV-C dose (4-15 kJ/m2), time (15-30 min), and storage temperature (12-24 ℃) for a total of 19 experimental runs. The fruits were analyzed based on four key indicators of deterioration: firmness, weight, contamination, and color that defined the postharvest quality variable, expressed as the difference between controls and treatments when 10% quality losses were reached. The result of the ANOVA was a second-order mathematical model that predicts 92% of the variation of the postharvest life of Fragaria vesca with respect to the controls, from the study factors, with a coefficient of variation of 9.2%. Both coefficients indicate the validity of the model and its potential to be applied throughout the design space. It is concluded that the postharvest life of the strawberry (Fragaria vesca L) var Big Bear can be extended up to four days with doses of 15 kJ/m2 for 30 min at a temperature of 12 ℃. The model showed a zone of maximum response in the design space suggesting that a broader response could be found in design spaces that were not explored in the study.

Keywords: 
Deterioration Indicator; Firmness; Weight; Contamination; Color; Mathematical Model.
 
 
 
INTRODUCTION

Currently, there is a notable increase in the use of predictive models in the design of processes in the field of agronomy. These mathematical tools allow not only accurately describing the behavior of variables of interest, but also designing processes and evaluating transformations with different quality variables such as color, appearance, level of contamination, weight loss and fruit yield. With proper manipulation of the variables, these models can be compared and evaluated in practice easily and with a small margin of error. In this sense, their wide range of utility has allowed both the use of various pre-harvest systems for the control of pests and diseases and conservation treatments for the correct postharvest handling of fruits and vegetables (Díaz et al., 2019DÍAZ, P.M.; CARREÑO, O.Á.; SALINAS, A.J.-A.; CALLEJÓN, F.Á.-J.: ¨Application of Logistic Regression Models for the Marketability of Cucumber Cultivars¨, [en línea] Agronomy, 9(1): 17, 2019. Disponible en:https://www.mdpi.com/2073-4395/9/1/17 ; Bhattacharjee et al., 2020BHATTACHARJEE, P.; DEY, V.; MANDAL, U.K.: ¨Risk assessment by failure mode and effects analysis (FMEA) using an interval number based logistic regression model¨, [en línea] Safety Science, ISSN-0925-7535, DOI-https://dx.doi.org/10.1016/j.ssci.2020.104967, 132, 2020. ; Martin et al., 2021MARTIN, G.P.; SPERRIN, M.; SNELL, K.I.E.; BUCHAN, I.; RILEY, R.D.: ¨Clinical prediction models to predict the risk of multiple binary outcomes: a comparison of approaches¨, [en línea] Statistics in Medicine, ISSN-0277-6715, DOI-https://dx.doi.org/10.1007/s40098-021-00520-z, 40(2): 498-517, 2021. ).

The consequences of the decrease in the quality of the fruit are a risk, not only for the producers due to the obvious economic losses but also for the consumer due to the action of pathogenic microorganisms and toxin producers. Strawberry (Fragaria vesca) is one of the most important crops in Ecuador that stands out for its high nutritional value and sensory attributes, highly appreciated by consumers. However, the characteristics of the fruit cause its rapid postharvest deterioration (Idzwana et al., 2020IDZWANA, M.I.N.; CHOU, K.S.; SHAH, R.M.; SOH, N.C.: ¨The Effect Of Ultraviolet Light Treatment In Extend Shelf Life And Preserve The Quality of Strawberry (Fragaria x ananassa) cv. Festival¨, [en línea] International Journal on Food, Agriculture and Natural Resources, ISSN-2722-4066, DOI-https://dx.doi.org/10.46676/ij-fanres.v1i1.4, 1(1): 15-18, 2020. ; Pombo et al., 2011POMBO, M.A.; ROSLI, H.G.; MARTÍNEZ, G.A.; CIVELLO, P.M.: ¨UV-C treatment affects the expression and activity of defense genes in strawberry fruit (Fragaria× ananassa, Duch)¨, [en línea] Postharvest biology and technology, ISSN-0925-5214, DOI-https://dx.doi.org/10.1016/j.postharvbio.2010.08.003, 59(1): 94-102, 2011. ). This deterioration is due to factors of different nature (physical, chemical, and biological); however, the appearance of microorganisms is the factor that most reduces its postharvest useful life.

UV-C radiation is one of the minimum postharvest conservation treatments capable of substantially reducing the microbial load without affecting the organoleptic properties of the fruit (Idzwana et al., 2020IDZWANA, M.I.N.; CHOU, K.S.; SHAH, R.M.; SOH, N.C.: ¨The Effect Of Ultraviolet Light Treatment In Extend Shelf Life And Preserve The Quality of Strawberry (Fragaria x ananassa) cv. Festival¨, [en línea] International Journal on Food, Agriculture and Natural Resources, ISSN-2722-4066, DOI-https://dx.doi.org/10.46676/ij-fanres.v1i1.4, 1(1): 15-18, 2020. ; Urban et al., 2016URBAN, L.; CHARLES, F.; DE MIRANDA, A.M.R.; AARROUF, J.: ¨Understanding the physiological effects of UV-C light and exploiting its agronomic potential before and after harvest¨, [en línea] Plant Physiology and Biochemistry, ISSN-0981-9428, DOI-https://dx.doi.org/10.1016/j.plaphy.2016.04.004, 105: 1-11, 2016. ). UV-C has been used successfully in the postharvest of numerous fruits and vegetables such as strawberries, pineapple, peaches, tomatoes, cucumbers, and broccoli (Formica et al., 2017FORMICA, O.A.C.; MARTÍNEZ, H.G.B.; DÍAZ, L.V.; ARTÉS, F.; ARTÉS, H.F.: ¨Use of postharvest UV-B and UV-C radiation treatments to revalorize broccoli byproducts and edible florets¨, [en línea] Innovative Food Science & Emerging Technologies, ISSN-1466-8564, DOI-https://dx.doi.org/10.1016/j.ifset.2017.07.036, 43: 77-83, 2017. ; Liu et al., 2018LIU, C.; ZHENG, H.; SHENG, K.; LIU, W.; ZHENG, L.: ¨Effects of postharvest UV-C irradiation on phenolic acids, flavonoids, and key phenylpropanoid pathway genes in tomato fruit¨, [en línea] Scientia Horticulturae, ISSN-0304-4238, DOI-https://dx.doi.org/10.1016/j.scienta.2018.06.075, 241: 107-114, 2018. ; Yang et al., 2014YANG, Z.; CAO, S.; SU, X.; JIANG, Y.: ¨Respiratory activity and mitochondrial membrane associated with fruit senescence in postharvest peaches in response to UV-C treatment¨, [en línea] Food Chemistry, ISSN-0308-8146, DOI-https://dx.doi.org/10.1016/j.foodchem.2014.03.120, 161: 16-21, 2014. ). This conservation treatment produces resistance to deterioration not only due to its ability to inhibit microbial growth on the fruit surface but also due to the stimulation of metabolites that delay the senescence of the fruit at low doses of UV-C (hormonal effect) (Andrade et al., 2013ANDRADE, C.M.J.; MORENO, G.C.; CONCELLÓN, A.: ¨Efecto hormético de la radiación UV-C sobre el desarrollo de Rhizopus y Phytophthora en naranjilla (Solanum quitoense)¨, [en línea] Revista Iberoamericana de Tecnología Postcosecha, ISSN-1665-0204, DOI-https://dx.doi.org/10.1016/j.foodchem.2014.03.120, 14(1): 64-70, 2013. ; Liao et al., 2016LIAO, C.; LIU, X.; GAO, A.; ZHAO, A.; HU, J.; LI, B.: ¨Maintaining postharvest qualities of three leaf vegetables to enhance their shelf lives by multiple ultraviolet-C treatment¨, [en línea] LWT-Food Science and Technology, ISSN-0023-6438, DOI-https://dx.doi.org/10.1016/j.lwt.2016.05.029, 73: 1-5, 2016. ).

UV-C has a significant influence (p <0.05) in the main causes of deterioration of both fruits and vegetables, causing a delay in senescence. However, uneven surfaces of fruits and vegetables can vary the effectiveness of UV-C. Other factors of variation are the variety of the fruit, the season of the year, and the storage temperature (Cote et al., 2013COTE, S.; RODONI, L.; MICELI, E.; CONCELLÓN, A.; CIVELLO, P.M.; VICENTE, A.R.: ¨Effect of radiation intensity on the outcome of postharvest UV-C treatments¨, [en línea] Postharvest Biology and Technology, ISSN-0925-5214, DOI-https://dx.doi.org/10.1016/j.postharvbio.2013.03.009, 83: 83-89, 2013. ; Hakguder y Unluturk, 2018HAKGUDER, T.B.; UNLUTURK, S.: ¨Effect of postharvest UV-C treatment on the microbial quality of “Şalak” apricot¨, [en línea] Scientia Horticulturae, ISSN-0304-4238, DOI-https://dx.doi.org/10.1016/j.scienta.2018.02.012, 233: 370-377, 2018. ; Petrielli et al., 2019PETRIELLI, P.G.; USBERTI, C.Z.F.; ALVES, M.R.: ¨Effects of postharvest application of UV-C radiation on the control of microorganisms and maintenance of quality in strawberries¨, [en línea] Revista dos Trabalhos de Iniciação Científica da UNICAMP, ISSN-2596-1969, DOI-https://dx.doi.org/10.20396/revpibic262018489, (26), 2019. ). Combined UV-C treatments with gases, chemicals, modified atmospheres and light pulses can also increase the effectiveness of the UV-C response to fruit senescence (Allende et al., 2007ALLENDE, A.; MARÍN, A.; BUENDÍA, B.; TOMÁS, B.F.; GIL, M.I.: ¨Impact of combined postharvest treatments (UV-C light, gaseous O3, superatmospheric O2 and high CO2) on health promoting compounds and shelf-life of strawberries¨, [en línea] Postharvest Biology and Technology, ISSN-0925-5214, DOI-https://dx.doi.org/10.1016/j.postharvbio.2007.05.007, 46(3): 201-211, 2007. ; Xu et al., 2019XU, Y.; CHARLES, M.T.; LUO, Z.; MIMEE, B.; TONG, Z.; VÉRONNEAU, P.; AGUILERA, D.A.; ROLLAND, D.: ¨Ultraviolet‐C priming of strawberry leaves against subsequent Mycosphaerella fragariae infection involves the action of reactive oxygen species, plant hormones, and terpenes¨, [en línea] Plant, cell & environment, ISSN-0140-7791, DOI-https://dx.doi.org/10.1111/pce.13491, 42(3): 815-831, 2019. ; Kim et al., 2010KIM, J.Y.; KIM, H.J.; LIM, G.O.; JANG, S.A.; SONG, K.B.: ¨The effects of aqueous chlorine dioxide or fumaric acid treatment combined with UV-C on postharvest quality of ‘Maehyang’strawberries¨, [en línea] Postharvest Biology and Technology, ISSN-0925-5214, DOI-https://dx.doi.org/10.1016/j.postharvbio.2010.01.013, 56(3): 254-256, 2010. ; Lu et al., 2018LU, Y.; DONG, W.; ALCAZAR, J.; YANG, T.; LUO, Y.; WANG, Q.; CHEN, P.: ¨Effect of preharvest CaCl2 spray and postharvest UV-B radiation on storage quality of broccoli microgreens, a richer source of glucosinolates¨, [en línea] Journal of Food Composition and Analysis, ISSN-0889-1575, DOI-https://dx.doi.org/10.1016/j.jfca.2017.12.035, 67: 55-62, 2018. ; Marquenie et al., 2002MARQUENIE, D.; MICHIELS, C.W.; GEERAERD, A.H.; SCHENK, A.; SOONTJENS, C.; VAN IMPE, J.F.; NICOLAI, B.M.: ¨Using survival analysis to investigate the effect of UV-C and heat treatment on storage rot of strawberry and sweet cherry¨, [en línea] International Journal of Food Microbiology, ISSN-0168-1605, DOI-https://dx.doi.org/10.1016/S0168-1605(01)00648-1, 73(2-3): 187-196, 2002. ; Moreno et al., 2016MORENO, G.C.; ANDRADE, C.M.J.; TERÁN, G.A.; TÚQUERES, U.A.; CONCELLÓN, A.: ¨Efecto del uso combinado de radiación UV-C y atmósfera modificada sobre el tiempo de vida útil de mora de Castilla (Rubus glaucus) sin espinas¨, Revista Iberoamericana de Tecnología Postcosecha, ISSN-1665-0204, 17(1), 2016. ).

Several studies of UV-C treatment in strawberries indicate a high sensitivity of the fruit to these treatments (Forges et al., 2018FORGES, M.; VÀSQUEZ, H.; CHARLES, F.; SARI, D.C.; URBAN, L.; LIZZI, Y.; BARDIN, M.; AARROUF, J.: ¨Impact of UV-C radiation on the sensitivity of three strawberry plant cultivars (Fragaria x ananassa) against Botrytis cinerea¨, [en línea] Scientia Horticulturae, ISSN-0304-4238, DOI-https://dx.doi.org/10.1016/j.scienta.2018.06.063, 240: 603-613, 2018. ; Ortiz et al., 2018ORTIZ, A.C.; RODONI, M.L.; DARRÉ, M.; ORTIZ, M.C.; CIVELLO, P.M.; VICENTE, A.R.: ¨Cyclic low dose UV-C treatments retain strawberry fruit quality more effectively than conventional pre-storage single high fluence applications¨, [en línea] LWT-Food Science and Technology, ISSN-0023-6438, DOI-https://dx.doi.org/10.1016/j.lwt.2018.02.050, 92: 304-311, 2018. ; Severo et al., 2015SEVERO, J.; DE OLIVEIRA, I.R.; TIECHER, A.B.; CHAVES, F.C.; ROMBALDI, C.V.: ¨Postharvest UV-C treatment increases bioactive, ester volatile compounds and a putative allergenic protein in strawberry¨, [en línea] LWT-Food Science and Technology, ISSN-0023-6438, DOI-https://dx.doi.org/10.1016/j.lwt.2015.06.041, 64(2): 685-692, 2015. ). However, few investigations include a mathematical model that can accurately predict the postharvest shelf life change of strawberries based on the treatment applied. The objective of the present work was to obtain a mathematical model that allows effectively evaluating the combined effect of different doses of UV-C radiation, storage time and temperature, on the postharvest shelf life of strawberries (Fragaria vesca L.) var. Big Bear.

MATERIALS AND METHODS

The fruits (Fragaria vesca) were selected without defects due to the uniformity of size, color, and degree of maturation from a systematic sampling (N = 20000; n = 380 and k = 52) according to the quality protocol of the packing plant "FRESTAR". The sample size was determined for a finite population (Montgomery, 2010MONTGOMERY, D.C.: Diseño y Análisis de experimentos, Ed. Limusa Wyley, segunda ed., México, 2010. ). Once selected, the fruits were placed in a 20 L radiation chamber containing a UV-C mercury lamp (15 W) and treated with a variable dose of 2-7 kJ/m2 at different exposure times (from 10 to 15 min). Subsequently, they were stored in plastic containers of approximately 0.35 L capacity at different storage temperatures in the 12-20 ° C range.

Every day all the fruits of each container (20) were analyzed according to four key indicators that characterize the deterioration process in the strawberry: firmness, weight, contamination, and color. The quality of the fruit (C) was determined as the percentage change rate (1) that establishes the average values of each of the four indicators defined as the average of the sum of the percentage ratio of each indicator.

 
Q%= IrIo100It  (1)
 

where:

If:

is the final measurement

Io:

is the initial measurement and

It:

is the total measurement

Firmness was determined, using the FHT200 brand digital fruit penetrometer (± 0.5% + 2 digits of precision), as the average of the maximum puncture force when drilling the sample on the radial and axial axes. To evaluate the weight, the digital scale EM-KBS2 was used with a precision of 0.01 g. The contamination level (CL) was determined using a subjective visual scale of five points that indicate by approximation the proportion of the contaminated area of the fruit (0: 100% of the surface without alteration, 1: CL < 10 % slight alteration, 2: 10 % ≤ CL <25 % moderate alteration, 3: 25 % ≤ CL ≤ 50 % severe alteration and 4: CL > 50 % very serious alteration). The color variation ΔE was determined using a digital photo colorimeter, using the CIE-L*a*b* system and the equation proposed by Chen & Ramaswamy (2002)CHEN, C.R.; RAMASWAMY, H.S.: ¨Color and texture change kinetics in ripening bananas¨, [en línea] LWT-food science and technology, ISSN-0023-6438, DOI-https://dx.doi.org/10.1006/fstl.2001.0875, 35(5): 415-419, 2002. :

 
ΔE= (ΔL2+Δa2+Δb2)1/2   (2)
 

where:

ΔL, Δa, and Δb represent the deviations of the individual color values (L- luminosity, a-red/green coordinate, and b-yellow/blue coordinate) of a fully ripe strawberry sample.

As for most foods, the relations of dependence of the variables in time obey to equations of the first-order and zero-order (Fu & Labuza, 1993FU, B.; LABUZA, T.P.: ¨Shelf-life prediction: theory and application¨, [en línea] Food Control, ISSN-0956-7135, DOI-https://dx.doi.org/10.1016/0956-7135(93)90298-3, 4(3): 125-133, 1993. ; Gacula Jr, 1975GACULA JR, M.C.: ¨El diseño de experimentos para el estudio de la vida útil¨, [en línea] Journal of Food Science, ISSN-0022-1147, DOI-: https://dx.doi.org/10.1111/j.1365-2621.1975.tb02211.x, 40(2): 399-403, 1975. ). To define the postharvest life of the strawberry, the change in quality (%) over time was considered as follows:

 
dQdt=-kQn   (3)
 

where;

k:

is the kinetic constant

Q:

is the quality of the fruit at a time t and

n:

is the order of the reaction

By integrating equation (3)dQdt=-kQn two equations of different order are obtained (4n=0 Q= Qo+kc t, 5n=1 lnQ=- kt+ln Qo ). Qo represents the quality of the fruit at the beginning when t = 0, and Q is the quality of the fruit at time t, with kc being the specific velocity constant for the zero-order reaction (n = 0) and k the specific velocity constant for the first-order reaction (n = 1). Both equations represent a straight line but first order equation (5)n=1 lnQ=- kt+ln Qo was considered as representing the best fit of our data (higher R2 coefficient (R2=0,87)):

 
n=0 Q= Qo+kc t  (4)
 

 
n=1 lnQ=- kt+ln Qo   (5)
 

 
t= lnQQ0k  (6)
 

To calculate the value of the specific rate constant k, expression 5n=1 lnQ=- kt+ln Qo was used, obtaining the value k (slope of the graph) from the experimental data of C. The limit value of C established for calculating postharvest life of the controls and treatments was 10% of quality, which is the time t in which ten percent of the postharvest quality has been lost (determined by the variation in the indicators: firmness, weight, contamination, and color), was defined as an indicator of quality loss. The value for t (10%) was selected as it represented the time when the quality losses of the strawberry, were visually appreciable (time in which 10% of the quality of the strawberry is lost by visual appreciation). This time was obtained through expression 6t= lnQQ0k.

The postharvest life (Pl) of the treated strawberries was expressed as the difference of t (10%) between controls and treatments, where tc represents the postharvest time of the strawberry when 10% of the quality of the controls has been lost, and tt represents the postharvest time of the strawberry when 10% of the quality in the treatments has been lost (5n=1 lnQ=- kt+ln Qo ). These values were obtained experimentally from triplicate tests.

 
Pl= tc-tt   (7)
 

Experimental Design

The Response Surface method was used in the statistical program Design Expert v.11 that uses the least-squares technique to fit the data obtained to first (8Y=B0+i=1 3BiXi+ε ) and second-order (9Y=Bo+i=13BiXi+i=13BiiXi2+i<1BijXiXj+ε) polynomial approximation equations. For this case, the full factorial Central Compound Design (CCD) was selected, whose matrix is composed of ten factorial points, five axial points, and four replicas in central points.

 
Y=B0+i=1 3BiXi+ε   (8)
 

 
Y=Bo+i=13BiXi+i=13BiiXi2+i<1BijXiXj+ε  (9)
 

The design matrix and the combination of factors, including the axial and central points with their replicas, resulted in 19 runs. The design was rotatory to guarantee consistent variance and orthogonal response (α = 1.681) (Table 1). For this purpose, the 19 experimental runs were randomly executed and, in order to respect the randomness, the execution order for the sequencing of experiments was taken exactly as indicated by the Design Expert program.

The analysis of variance (ANOVA) was used to evaluate the statistical significance of the models and the Fisher’s statistical test (F-test) determined which of the factors significantly affected postharvest life of Fragaria vesca. To this purpose the significance and the magnitude of the effects of each variable (UV-C dose, exposure time and temperature) and their possible interactions on the postharvest life were estimated. The variable effects with a p-value higher than 0.05 or with less than 95% of significance were discarded and a new analysis of variance was performed for the reduced model (Montgomery, 2010MONTGOMERY, D.C.: Diseño y Análisis de experimentos, Ed. Limusa Wyley, segunda ed., México, 2010. ).

 
TABLE 1.  Actual and coded factors levels in CCD Matrix
FactorNameUnits-1,683+1.6830-1+1
AUV-C dosekJ/m20.2518.759.54.0015.00
BExposure timemin9.8935.1122.515.0030.00
CTemperatureºC7.9128.0918.012.0024.00
 

RESULTS AND DISCUSSION
CCD Experimental Design Analysis

The results obtained showed average values ​​of postharvest life of the strawberry of 2.7 ± 1.12 days, indicating that the differences between treatments and controls are notable. This result also shows that UV-C treatments (in variable doses of 4-15 kJ/m2) and exposure times (15-30 min) take approximately 3.6 days to lose their quality attributes (depending on the weight, contamination, and indicators of color firmness) in relation to the controls (Table 2).

 
TABLE 2.  Levels (highs and lows), factors (A: UV-C dose, B: time, C: temperature), and response variable (postharvest life) in the experimental design CCD
RunA: UV-C dose (kJ/m2)B: time (min)C: Temperature (ºC)Postharvest life (days)
19.535.118.03.01
21530.024.03.54
31530.012.04.01
4415.024.01.27
59.522.518.03.54
69.522.518.03.44
718.722.518.04.54
81515.012.03.87
9430.012.01.82
10430.024.01.37
119.522.518.03.55
129.522.507.93.02
131515.024.03.34
140.2522.518.00.46
15415.012.01.58
169.522.518.03.58
179.522.518.03.25
189.522.528.01.51
199.509.818.02.48
 

Similar studies determined that the UV-C dose of 9 kJ/m2 and UVB at 72 h/15 °C improved the stability of broccoli flowers (Formica et al., 2017FORMICA, O.A.C.; MARTÍNEZ, H.G.B.; DÍAZ, L.V.; ARTÉS, F.; ARTÉS, H.F.: ¨Use of postharvest UV-B and UV-C radiation treatments to revalorize broccoli byproducts and edible florets¨, [en línea] Innovative Food Science & Emerging Technologies, ISSN-1466-8564, DOI-https://dx.doi.org/10.1016/j.ifset.2017.07.036, 43: 77-83, 2017. ; Lu et al., 2018LU, Y.; DONG, W.; ALCAZAR, J.; YANG, T.; LUO, Y.; WANG, Q.; CHEN, P.: ¨Effect of preharvest CaCl2 spray and postharvest UV-B radiation on storage quality of broccoli microgreens, a richer source of glucosinolates¨, [en línea] Journal of Food Composition and Analysis, ISSN-0889-1575, DOI-https://dx.doi.org/10.1016/j.jfca.2017.12.035, 67: 55-62, 2018. ). The same effect of UV-C has been observed in pears, pineapples, blueberries, amaranth, spinach, leeks, onion, tomato, persimmon, and cucumber in doses that vary between 1.7 kJ/m2 to 39.6 kJ/m2, and storage temperatures of 4-24 ºC (Liu et al., 2018LIU, C.; ZHENG, H.; SHENG, K.; LIU, W.; ZHENG, L.: ¨Effects of postharvest UV-C irradiation on phenolic acids, flavonoids, and key phenylpropanoid pathway genes in tomato fruit¨, [en línea] Scientia Horticulturae, ISSN-0304-4238, DOI-https://dx.doi.org/10.1016/j.scienta.2018.06.075, 241: 107-114, 2018. ; Petrielli et al., 2019PETRIELLI, P.G.; USBERTI, C.Z.F.; ALVES, M.R.: ¨Effects of postharvest application of UV-C radiation on the control of microorganisms and maintenance of quality in strawberries¨, [en línea] Revista dos Trabalhos de Iniciação Científica da UNICAMP, ISSN-2596-1969, DOI-https://dx.doi.org/10.20396/revpibic262018489, (26), 2019. ; Gogo et al., 2018GOGO, E.; FÖRSTER, N.; DANNEHL, D.; FROMMHERZ, L.; TRIERWEILER, B.; OPIYO, A.; ULRICHS, C.; HUYSKENS-KEIL, S.: ¨Postharvest UV-C application to improve health promoting secondary plant compound pattern in vegetable amaranth¨, [en línea] Innovative Food Science & Emerging Technologies, ISSN-1466-8564, DOI-https://dx.doi.org/10.1016/j.ifset.2018.01.002, 45: 426-437, 2018. ; Imaizumi et al., 2018IMAIZUMI, T.; YAMAUCHI, M.; SEKIYA, M.; ALONSO, Y.; TANAKA, F.: ¨Responses of phytonutrients and tissue condition in persimmon and cucumber to postharvest UV-C irradiation¨, [en línea] Postharvest Biology and Technology, ISSN-0925-5214, DOI-https://dx.doi.org/10.1016/j.postharvbio.2018.06.003, 145: 33-40, 2018. ; Sari et al., 2016SARI, K.L.; SETHA, S.; NARADISORN, M.: ¨Effect of UV-C irradiation on postharvest quality of ‘Phulae’pineapple¨, [en línea] Scientia Horticulturae, ISSN-0304-4238, DOI-https://dx.doi.org/10.1016/j.scienta.2016.09.049, 213: 314-320, 2016. ).

In strawberries, exposure to UV-C (250 nm) in doses of 0.4-15 kJ/m2 has shown substantial changes in the visible characteristics that limit their postharvest life (Jin et al., 2017JIN, P.; WANG, H.; ZHANG, Y.; HUANG, Y.; WANG, L.; ZHENG, Y.: ¨UV-C enhances resistance against gray mold decay caused by Botrytis cinerea in strawberry fruit¨, [en línea] Scientia Horticulturae, ISSN-0304-4238, DOI-https://dx.doi.org/10.1016/j.scienta.2017.06.062, 225: 106-111, 2017. ) and delay contamination fungal. This effect at the same time produces an increase in the expression of genes related to the defense of the host against attacks by microorganisms (Forges et al., 2018FORGES, M.; VÀSQUEZ, H.; CHARLES, F.; SARI, D.C.; URBAN, L.; LIZZI, Y.; BARDIN, M.; AARROUF, J.: ¨Impact of UV-C radiation on the sensitivity of three strawberry plant cultivars (Fragaria x ananassa) against Botrytis cinerea¨, [en línea] Scientia Horticulturae, ISSN-0304-4238, DOI-https://dx.doi.org/10.1016/j.scienta.2018.06.063, 240: 603-613, 2018. ). If the UV-C doses are increased, this effect is cyclically enhanced at different times of the postharvest (Hakguder y Unluturk, 2018HAKGUDER, T.B.; UNLUTURK, S.: ¨Effect of postharvest UV-C treatment on the microbial quality of “Şalak” apricot¨, [en línea] Scientia Horticulturae, ISSN-0304-4238, DOI-https://dx.doi.org/10.1016/j.scienta.2018.02.012, 233: 370-377, 2018. ; Ortiz et al., 2019ORTIZ, O.L.C.; ORTIZ, C.M.; DARRÉ, M.; RODONI, L.M.; CIVELLO, P.M.; VICENTE, A.R.: ¨Role of UV-C irradiation scheme on cell wall disassembly and surface mechanical properties in strawberry fruit¨, [en línea] Postharvest Biology and Technology, ISSN-0925-5214, DOI-https://dx.doi.org/10.1016/j.postharvbio.2019.01.002, 150: 122-128, 2019. ).

 
TABLE 3.  ANOVA results to the reduced quadratic model
SourceSum of SquaresdfMean SquareF-valuep-value
Model22,5763,76111,73< 0.0001significant
A-Dose (UV-C)17,78117,78528,00< 0.0001
B-Time exposure0,180810,18085,370,0390
C-Temperature1,3511,3540,20< 0.0001
1,3211,3239,09< 0.0001
0,684310,684320,320,0007
2,1112,1162,81< 0.0001
Residual0,4040120,0337
Lack of Fit0,331480,04142,280,2221not significant
Pure Error0,072740,0182
Cor Total22,9818
Std. Dev.0,1835 0,9824
Mean2,80 Adjusted R²0,9736
C.V. %6,56 Predicted R²0,9296
Adeq Precision34,4567
 

In the ANOVA test, the effect of each variable on the postharvest life of Fragraria vesca was obtained (Table 3). Once the terms of the quadratic model that were not significant (p> 0.05), (AB, AC, and BC) were eliminated, the terms (A, C, B, A², B², C²) significant (p <0.05) were obtained. The F value (111.73) obtained implies that the quadratic model is significant (p <0.05), its F value for lack of fit (2, 28) was not significant (p> 0.05) in relation to the pure error and there is a 22.21% probability that an out-of-fit F-value occurs due to noise (this implies a good fit of the model to the data).

 
FIGURE 1.  Predicted response values versus the actual response values and normality of residuals
 

The predicted R² model of 0.92 is in reasonable agreement with the adjusted R² of 0.97; (the difference is less than 0.2) indicating that in the model space the factors UV-C dose, temperature, and exposure time can explain 97% of the postharvest life variations. The precision measure (AP = 34, 45) was higher than 4, which indicates an adequate signal. The coefficient of variation (CV = 6.56) reveals the reliability of the experiments (Table 3). The predicted response values ​​versus the actual response values ​​(experimental values) show that at each point, the model correctly predicted the corresponding values ​​(Figure 1a). The normal probability indicates that the residuals follow a straight line with little scatter data; therefore, they follow a normal distribution. (Figure 1b). In general, the relationship between the predictions and the experimental values ​​and the diagnosis of the residuals were adequate (R² = 0.92), which implies that the model obtained can be used to navigate through the design space. (Fig 1 a, and b).

Mathematical model, the second-order (in actual and coded terms)

  • a) Postharvest life = 3,465 + 1,140A + 0,115B -0,314C -0,3105A2 -0,223B2 -0,393C2.

  • b) Postharvest life = -4,389 + 0,402 UVC-Dose-C + 0,194time + 0,341Temperature -0,010 UVC-Dose-C^2 -0,003 (time)2 -0,010 (Temperature)2

The mathematical expression in terms of coded factors can be used to make predictions about postharvest life for given levels of each factor (a). The coded expression is useful to identify the relative impact of the factors (UV-C dose, temperature, and time) by comparing the coefficients of the factors. It is observed that temperature (C) has a linear negative effect on postharvest life (coefficient preceded by a negative sign -0.314), while UVC dose and exposure time (A; B) have a linear positive effect (coefficients preceded by positive signs 0.14 and 0.11, respectively) on postharvest life, negative quadratic terms (A; B) indicate a curvature where the values ​​of the factors determined the response to the maximum value. From this point on, the response values ​​could begin to gradually increase or begin to decrease (design limit)

The expression obtained in terms of actual factors (b) can be used to make predictions about postharvest life for given levels of each factor, such as UV-C dose, temperature, and exposure time, provided the levels are specified in the original factor units for each. However, this expression should not be used to determine the relative impact of each factor because the coefficients are scaled to accommodate the units of each factor and the intersection is not in the center of the design space (Table 5).

In the statistical program, the numerical optimization maximized the postharvest life response to a limit lower than 10 (minimum acceptable value) and a limit higher than 20 (Montgomery, 2010MONTGOMERY, D.C.: Diseño y Análisis de experimentos, Ed. Limusa Wyley, segunda ed., México, 2010. ) Under these conditions, maximum desirability of 73% is obtained in the following factorial coordinates (A, B, C) = (15; 24, 4; 15, 5). At this theoretical point, three experimental replicas were carried out. The results obtained are compared with the results of expression b (Table. 4) and show a good agreement between the calculated (4.30) and experimental (3.78) values, which confirms that this model can be used to navigate for the design space (Cote et al., 2013COTE, S.; RODONI, L.; MICELI, E.; CONCELLÓN, A.; CIVELLO, P.M.; VICENTE, A.R.: ¨Effect of radiation intensity on the outcome of postharvest UV-C treatments¨, [en línea] Postharvest Biology and Technology, ISSN-0925-5214, DOI-https://dx.doi.org/10.1016/j.postharvbio.2013.03.009, 83: 83-89, 2013. ).

 
TABLE 4.  Theoretical and experimental optimum response values
FactorsValues
A- UV- C Dose 15
B-Time exposure30
C-Temperature12
Optimized response*4,37
Experimental response**3,78

*Equation b results **Mean value of three experimental measurements.

 

The overall mean response for all executions was adequate. The coefficients are properly adjusted around an average value (when the factors are orthogonal, the variance inflation factor (VIF) is 1; if VIF is greater than 1, it indicates multicollinearity (the higher the VIF, the more severe the correlation of factors). This indicates that the expected change in postharvest life per unit changes in value by one factor when all the remaining factors remain constant (Table 5).

 
TABLE 5.  Coefficients in terms of coded factors
FactorCoefficient EstimateDfStandard Error95% CI Low95% CI HighVIF
Intercept3,4710,08203,293,64
A-Dose (UV-C)1,1410,04971,031,251,0000
B-exposure time0,115110,04970,00690,22321,0000
C-Temperature-0,314810,0497-0,4230-0,20661,0000
-0,310510,0497-0,4187-0,20231,04
-0,223910,0497-0,3321-0,11571,04
-0,393610,0497-0,5018-0,28541,04
 

The response surface, the contour lines and the cube graphs show that the postharvest life of the strawberry increases as the dose increases and the exposure to UV-C as the temperature decreases (Fig 2). A maximum zone is verified where the best postharvest life conditions are obtained (4.37 days). At this point, the designed system verifies the best conditions of the study variables to extend the postharvest life of the strawberry (Figure 2).

 
FIGURE 2.  Response surface, contour lines and “view of the cube” in quadratic model
 

The observed changes are representative of the ranges of the study system and indicate that, under optimal conditions, the treated fruits take around four days to lose 10% of their quality compared to the controls. The upward curvature of the model allows inferring that the maximum value obtained is not absolute and other areas with better response behavior could be found by increasing the UV-C dose. This implies that the postharvest life of the strawberry could be extended at higher doses of UV-C and lower temperatures.

Several causes are attributed to the delay of senescence induced by UV-C, among them there are compounds called phenylpropanoids, which prevent the direct action of microorganisms on the cell parenchyma (Liu et al., 2018LIU, C.; ZHENG, H.; SHENG, K.; LIU, W.; ZHENG, L.: ¨Effects of postharvest UV-C irradiation on phenolic acids, flavonoids, and key phenylpropanoid pathway genes in tomato fruit¨, [en línea] Scientia Horticulturae, ISSN-0304-4238, DOI-https://dx.doi.org/10.1016/j.scienta.2018.06.075, 241: 107-114, 2018. ). Other bioactive compounds involved are phytoalexins and polyamines that cause the inactivation of enzymes that soften the tissues of the fruit, generating mechanisms that can slow down its senescence (Severo et al., 2015SEVERO, J.; DE OLIVEIRA, I.R.; TIECHER, A.B.; CHAVES, F.C.; ROMBALDI, C.V.: ¨Postharvest UV-C treatment increases bioactive, ester volatile compounds and a putative allergenic protein in strawberry¨, [en línea] LWT-Food Science and Technology, ISSN-0023-6438, DOI-https://dx.doi.org/10.1016/j.lwt.2015.06.041, 64(2): 685-692, 2015. ). Causally, there are several mechanisms that describe the action of UV-C on biological systems that in turn can delay the damage due to the cold weather and soft rot of fruit caused by microorganisms (Formica et al., 2017FORMICA, O.A.C.; MARTÍNEZ, H.G.B.; DÍAZ, L.V.; ARTÉS, F.; ARTÉS, H.F.: ¨Use of postharvest UV-B and UV-C radiation treatments to revalorize broccoli byproducts and edible florets¨, [en línea] Innovative Food Science & Emerging Technologies, ISSN-1466-8564, DOI-https://dx.doi.org/10.1016/j.ifset.2017.07.036, 43: 77-83, 2017. ; Petrielli et al., 2019PETRIELLI, P.G.; USBERTI, C.Z.F.; ALVES, M.R.: ¨Effects of postharvest application of UV-C radiation on the control of microorganisms and maintenance of quality in strawberries¨, [en línea] Revista dos Trabalhos de Iniciação Científica da UNICAMP, ISSN-2596-1969, DOI-https://dx.doi.org/10.20396/revpibic262018489, (26), 2019. ).

UV-C has been shown to generate mutations in the DNA molecule of microorganisms by directly inhibiting microbial growth, but at the same time, it also stimulates certain genomic regions of the fruit. (Pombo et al., 2011POMBO, M.A.; ROSLI, H.G.; MARTÍNEZ, G.A.; CIVELLO, P.M.: ¨UV-C treatment affects the expression and activity of defense genes in strawberry fruit (Fragaria× ananassa, Duch)¨, [en línea] Postharvest biology and technology, ISSN-0925-5214, DOI-https://dx.doi.org/10.1016/j.postharvbio.2010.08.003, 59(1): 94-102, 2011. ). These regions encode enzymes that slow fruit senescence (Urban et al., 2016URBAN, L.; CHARLES, F.; DE MIRANDA, A.M.R.; AARROUF, J.: ¨Understanding the physiological effects of UV-C light and exploiting its agronomic potential before and after harvest¨, [en línea] Plant Physiology and Biochemistry, ISSN-0981-9428, DOI-https://dx.doi.org/10.1016/j.plaphy.2016.04.004, 105: 1-11, 2016. ). On the other hand, there are components of the membrane (phospholipids, glycolipids, proteins and lignin) that are sensitive to the short wave ultraviolet range, where they absorb energy promoting permanent metabolic changes. In these conditions, the cell walls of the fruit are reinforced, offering greater firmness (Ortiz et al., 2019ORTIZ, O.L.C.; ORTIZ, C.M.; DARRÉ, M.; RODONI, L.M.; CIVELLO, P.M.; VICENTE, A.R.: ¨Role of UV-C irradiation scheme on cell wall disassembly and surface mechanical properties in strawberry fruit¨, [en línea] Postharvest Biology and Technology, ISSN-0925-5214, DOI-https://dx.doi.org/10.1016/j.postharvbio.2019.01.002, 150: 122-128, 2019. ).

The effect of cold also affects the delay of the metabolism of the fruit (Andrade et al., 2013ANDRADE, C.M.J.; MORENO, G.C.; CONCELLÓN, A.: ¨Efecto hormético de la radiación UV-C sobre el desarrollo de Rhizopus y Phytophthora en naranjilla (Solanum quitoense)¨, [en línea] Revista Iberoamericana de Tecnología Postcosecha, ISSN-1665-0204, DOI-https://dx.doi.org/10.1016/j.foodchem.2014.03.120, 14(1): 64-70, 2013. ). As the temperature drops, microbial growth is inhibited thus preventing contamination of the fruit. Low temperatures also regulate respiratory processes that directly influence ripening (Liao et al; 2016LIAO, C.; LIU, X.; GAO, A.; ZHAO, A.; HU, J.; LI, B.: ¨Maintaining postharvest qualities of three leaf vegetables to enhance their shelf lives by multiple ultraviolet-C treatment¨, [en línea] LWT-Food Science and Technology, ISSN-0023-6438, DOI-https://dx.doi.org/10.1016/j.lwt.2016.05.029, 73: 1-5, 2016. ), delaying the deterioration of the fruit and the senescence process (Liao et al., 2016LIAO, C.; LIU, X.; GAO, A.; ZHAO, A.; HU, J.; LI, B.: ¨Maintaining postharvest qualities of three leaf vegetables to enhance their shelf lives by multiple ultraviolet-C treatment¨, [en línea] LWT-Food Science and Technology, ISSN-0023-6438, DOI-https://dx.doi.org/10.1016/j.lwt.2016.05.029, 73: 1-5, 2016. ).

In this study, the combined effect of low temperatures and UV radiation-induced favorable changes in strawberry postharvest life. The adequate combination of the study factors probably induced a cascade mechanism on the plant tissue, which led to the prolongation of the postharvest life of strawberry (Formica et al., 2017FORMICA, O.A.C.; MARTÍNEZ, H.G.B.; DÍAZ, L.V.; ARTÉS, F.; ARTÉS, H.F.: ¨Use of postharvest UV-B and UV-C radiation treatments to revalorize broccoli byproducts and edible florets¨, [en línea] Innovative Food Science & Emerging Technologies, ISSN-1466-8564, DOI-https://dx.doi.org/10.1016/j.ifset.2017.07.036, 43: 77-83, 2017. ).

CONCLUSION

  • It was demonstrated that the Design of the Central Compound is a good tool to evaluate the effects and interactions of UV-C dose, temperature and time, in the postharvest life of Fragaria vesca.

  • The empirical model obtained was statistically significant and showed good agreement between the experimental and predicted values, obtaining a maximum response of 4 days above the controls.

  • The model indicates that a better response could be found by increasing the UV-C dose.

  • The applications of this work emphasize the importance of the combined effect of UV-C and low temperatures in the postharvest life of the strawberry.

 
 
 

 

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MORENO, G.C.; ANDRADE, C.M.J.; TERÁN, G.A.; TÚQUERES, U.A.; CONCELLÓN, A.: ¨Efecto del uso combinado de radiación UV-C y atmósfera modificada sobre el tiempo de vida útil de mora de Castilla (Rubus glaucus) sin espinas¨, Revista Iberoamericana de Tecnología Postcosecha, ISSN-1665-0204, 17(1), 2016.
ORTIZ, A.C.; RODONI, M.L.; DARRÉ, M.; ORTIZ, M.C.; CIVELLO, P.M.; VICENTE, A.R.: ¨Cyclic low dose UV-C treatments retain strawberry fruit quality more effectively than conventional pre-storage single high fluence applications¨, [en línea] LWT-Food Science and Technology, ISSN-0023-6438, DOI-https://dx.doi.org/10.1016/j.lwt.2018.02.050, 92: 304-311, 2018.
ORTIZ, O.L.C.; ORTIZ, C.M.; DARRÉ, M.; RODONI, L.M.; CIVELLO, P.M.; VICENTE, A.R.: ¨Role of UV-C irradiation scheme on cell wall disassembly and surface mechanical properties in strawberry fruit¨, [en línea] Postharvest Biology and Technology, ISSN-0925-5214, DOI-https://dx.doi.org/10.1016/j.postharvbio.2019.01.002, 150: 122-128, 2019.
PETRIELLI, P.G.; USBERTI, C.Z.F.; ALVES, M.R.: ¨Effects of postharvest application of UV-C radiation on the control of microorganisms and maintenance of quality in strawberries¨, [en línea] Revista dos Trabalhos de Iniciação Científica da UNICAMP, ISSN-2596-1969, DOI-https://dx.doi.org/10.20396/revpibic262018489, (26), 2019.
POMBO, M.A.; ROSLI, H.G.; MARTÍNEZ, G.A.; CIVELLO, P.M.: ¨UV-C treatment affects the expression and activity of defense genes in strawberry fruit (Fragaria× ananassa, Duch)¨, [en línea] Postharvest biology and technology, ISSN-0925-5214, DOI-https://dx.doi.org/10.1016/j.postharvbio.2010.08.003, 59(1): 94-102, 2011.
SARI, K.L.; SETHA, S.; NARADISORN, M.: ¨Effect of UV-C irradiation on postharvest quality of ‘Phulae’pineapple¨, [en línea] Scientia Horticulturae, ISSN-0304-4238, DOI-https://dx.doi.org/10.1016/j.scienta.2016.09.049, 213: 314-320, 2016.
SEVERO, J.; DE OLIVEIRA, I.R.; TIECHER, A.B.; CHAVES, F.C.; ROMBALDI, C.V.: ¨Postharvest UV-C treatment increases bioactive, ester volatile compounds and a putative allergenic protein in strawberry¨, [en línea] LWT-Food Science and Technology, ISSN-0023-6438, DOI-https://dx.doi.org/10.1016/j.lwt.2015.06.041, 64(2): 685-692, 2015.
URBAN, L.; CHARLES, F.; DE MIRANDA, A.M.R.; AARROUF, J.: ¨Understanding the physiological effects of UV-C light and exploiting its agronomic potential before and after harvest¨, [en línea] Plant Physiology and Biochemistry, ISSN-0981-9428, DOI-https://dx.doi.org/10.1016/j.plaphy.2016.04.004, 105: 1-11, 2016.
XU, Y.; CHARLES, M.T.; LUO, Z.; MIMEE, B.; TONG, Z.; VÉRONNEAU, P.; AGUILERA, D.A.; ROLLAND, D.: ¨Ultraviolet‐C priming of strawberry leaves against subsequent Mycosphaerella fragariae infection involves the action of reactive oxygen species, plant hormones, and terpenes¨, [en línea] Plant, cell & environment, ISSN-0140-7791, DOI-https://dx.doi.org/10.1111/pce.13491, 42(3): 815-831, 2019.
YANG, Z.; CAO, S.; SU, X.; JIANG, Y.: ¨Respiratory activity and mitochondrial membrane associated with fruit senescence in postharvest peaches in response to UV-C treatment¨, [en línea] Food Chemistry, ISSN-0308-8146, DOI-https://dx.doi.org/10.1016/j.foodchem.2014.03.120, 161: 16-21, 2014.

 

NOTES

The mention of trademarks of specific equipment, instruments or materials is for identification purposes, there being no promotional commitment in relation to them, neither by the authors nor by the publisher

 
 

Received: 23/01/2021

Accepted: 20/09/2021

 
 

Tania María Guzmán-Armenteros, Profesora, Universidad UTE, Department of Agroindustry, Ecuador, e-mail: tania.guzman@ute.edu.ec

Yandi Fernández-Ochoa, Profesor, Universidad UTE, Department of Electromechanics, Ecuador, e-mail: yandi.fernandez@ute.edu.ec

The authors of this work declare no conflict of interests.

 

This is an open-access article distributed under the terms of the Creative Commons Attribution License


 
 
ARTÍCULO ORIGINAL
 
Efecto de la radiación UV-C a bajas temperaturas en la vida poscosecha de Fragaria Vesca
 

iDMSc. Tania María Guzmán-ArmenterosIUniversidad UTE, Department of Agroindustry, Ecuador.

iDMSc. Yandi Fernández-OchoaIIUniversidad UTE, Department of Electromechanics, Ecuador.

 

IUniversidad UTE, Department of Agroindustry, Ecuador.

IIUniversidad UTE, Department of Electromechanics, Ecuador.

 

*Author for correspondence: Tania María Guzmán-Armenteros, e-mail: tania.guzman@ute.edu.ec

 

RESUMEN

Se evaluó el efecto de la radiación UV-C en la vida poscosecha de la fresa a partir de un diseño compuesto central (DCC) de superficie de respuesta. La vida poscosecha de la fresa (Fragaria vesca L) var Oso Grande se modeló en base a la dosis de UV-C (4-15 kJ/m2), tiempo (15-30 min) y temperatura de almacenamiento (12-24 ℃) para un total de 19 corridas experimentales. Los frutos se analizaron en base a cuatro indicadores claves de deterioro: firmeza, peso, contaminación y color que definieron la variable de calidad poscosecha, expresada como la diferencia entre controles y tratamientos cuando se alcanza el 10% de pérdidas de calidad. El resultado del ANOVA fue un modelo matemático de segundo orden que predice el 92% de la variación de la vida poscosecha de Fragaria vesca con respecto a los controles, a partir de los factores de estudio, con un coeficiente de variación de 9.2%. Ambos coeficientes indican la validez del modelo y su potencial para ser aplicado en todo el espacio de diseño. Se concluye que la vida poscosecha de la fresa (Fragaria vesca L) var Oso Grande puede extenderse hasta cuatro días con dosis de 15 kJ/m2 durante 30 min a una temperatura de 12℃. El modelo mostró una zona de máxima respuesta en el espacio de diseño que sugiere que se podría encontrar una respuesta más amplia en los espacios de diseño que no se exploraron en el estudio.

Palabras clave
indicador de deterioro; firmeza; peso; contaminación; color; modelo matemático.
 
 
 
INTRODUCCIÓN

Actualmente existe un notable incremento en el uso de modelos predictivos en el diseño de procesos en el campo de la agronomía. Estas herramientas matemáticas, permiten no solo describir con precisión el comportamiento de variables de interés, sino diseñar procesos y evaluar transformaciones con diferentes variables de calidad como color, apariencia, nivel de contaminación, pérdida de peso y rendimiento de frutos. Con una adecuada manipulación de las variables, estos modelos se pueden comparar y evaluar en la práctica de forma sencilla y con un pequeño margen de error. En este sentido, su amplia gama de utilidad ha permitido tanto el uso de diversos sistemas precosecha para el control de plagas y enfermedades como tratamientos de conservación para el correcto manejo poscosecha de frutas y hortalizas (Díaz et al., 2019DÍAZ, P.M.; CARREÑO, O.Á.; SALINAS, A.J.-A.; CALLEJÓN, F.Á.-J.: ¨Application of Logistic Regression Models for the Marketability of Cucumber Cultivars¨, [en línea] Agronomy, 9(1): 17, 2019. Disponible en:https://www.mdpi.com/2073-4395/9/1/17 ; Bhattacharjee et al., 2020BHATTACHARJEE, P.; DEY, V.; MANDAL, U.K.: ¨Risk assessment by failure mode and effects analysis (FMEA) using an interval number based logistic regression model¨, [en línea] Safety Science, ISSN-0925-7535, DOI-https://dx.doi.org/10.1016/j.ssci.2020.104967, 132, 2020. ; Martin et al., 2021MARTIN, G.P.; SPERRIN, M.; SNELL, K.I.E.; BUCHAN, I.; RILEY, R.D.: ¨Clinical prediction models to predict the risk of multiple binary outcomes: a comparison of approaches¨, [en línea] Statistics in Medicine, ISSN-0277-6715, DOI-https://dx.doi.org/10.1007/s40098-021-00520-z, 40(2): 498-517, 2021. ).

Las consecuencias de la disminución de la calidad de la fruta son un riesgo, no solo para los productores por las evidentes pérdidas económicas, sino también para el consumidor por la acción de microorganismos patógenos y productores de toxinas. La fresa (Fragaria vesca) es uno de los cultivos más importantes del Ecuador que destaca por su alto valor nutricional y atributos sensoriales, muy apreciado por los consumidores. Sin embargo, las características del fruto provocan su rápido deterioro poscosecha (Idzwana et al., 2020IDZWANA, M.I.N.; CHOU, K.S.; SHAH, R.M.; SOH, N.C.: ¨The Effect Of Ultraviolet Light Treatment In Extend Shelf Life And Preserve The Quality of Strawberry (Fragaria x ananassa) cv. Festival¨, [en línea] International Journal on Food, Agriculture and Natural Resources, ISSN-2722-4066, DOI-https://dx.doi.org/10.46676/ij-fanres.v1i1.4, 1(1): 15-18, 2020. ; Pombo et al., 2011POMBO, M.A.; ROSLI, H.G.; MARTÍNEZ, G.A.; CIVELLO, P.M.: ¨UV-C treatment affects the expression and activity of defense genes in strawberry fruit (Fragaria× ananassa, Duch)¨, [en línea] Postharvest biology and technology, ISSN-0925-5214, DOI-https://dx.doi.org/10.1016/j.postharvbio.2010.08.003, 59(1): 94-102, 2011. ). Este deterioro se debe a varios factores de diferente naturaleza (físicos, químicos y biológicos); sin embargo, la aparición de microorganismos es el factor que más disminuye su vida útil poscosecha.

La radiación UV-C es uno de los tratamientos mínimos de conservación poscosecha capaces de reducir sustancialmente la carga microbiana sin afectar las propiedades organolépticas de la fruta (Idzwana et al., 2020IDZWANA, M.I.N.; CHOU, K.S.; SHAH, R.M.; SOH, N.C.: ¨The Effect Of Ultraviolet Light Treatment In Extend Shelf Life And Preserve The Quality of Strawberry (Fragaria x ananassa) cv. Festival¨, [en línea] International Journal on Food, Agriculture and Natural Resources, ISSN-2722-4066, DOI-https://dx.doi.org/10.46676/ij-fanres.v1i1.4, 1(1): 15-18, 2020. ; Urban et al., 2016URBAN, L.; CHARLES, F.; DE MIRANDA, A.M.R.; AARROUF, J.: ¨Understanding the physiological effects of UV-C light and exploiting its agronomic potential before and after harvest¨, [en línea] Plant Physiology and Biochemistry, ISSN-0981-9428, DOI-https://dx.doi.org/10.1016/j.plaphy.2016.04.004, 105: 1-11, 2016. ). La UV-C se ha utilizado con éxito en la poscosecha de numerosas frutas y verduras como fresas, piña, melocotones, tomates, pepinos y brócoli (Formica et al., 2017FORMICA, O.A.C.; MARTÍNEZ, H.G.B.; DÍAZ, L.V.; ARTÉS, F.; ARTÉS, H.F.: ¨Use of postharvest UV-B and UV-C radiation treatments to revalorize broccoli byproducts and edible florets¨, [en línea] Innovative Food Science & Emerging Technologies, ISSN-1466-8564, DOI-https://dx.doi.org/10.1016/j.ifset.2017.07.036, 43: 77-83, 2017. ; Liu et al., 2018LIU, C.; ZHENG, H.; SHENG, K.; LIU, W.; ZHENG, L.: ¨Effects of postharvest UV-C irradiation on phenolic acids, flavonoids, and key phenylpropanoid pathway genes in tomato fruit¨, [en línea] Scientia Horticulturae, ISSN-0304-4238, DOI-https://dx.doi.org/10.1016/j.scienta.2018.06.075, 241: 107-114, 2018. ; Yang et al., 2014YANG, Z.; CAO, S.; SU, X.; JIANG, Y.: ¨Respiratory activity and mitochondrial membrane associated with fruit senescence in postharvest peaches in response to UV-C treatment¨, [en línea] Food Chemistry, ISSN-0308-8146, DOI-https://dx.doi.org/10.1016/j.foodchem.2014.03.120, 161: 16-21, 2014. ). Este tratamiento de conservación produce resistencia al deterioro no solo por su capacidad para inhibir el crecimiento microbiano en la superficie del fruto, sino también por la estimulación de metabolitos que retrasan la senescencia del fruto a bajas dosis de UV-C (efecto hormonal) (Andrade et al., 2013ANDRADE, C.M.J.; MORENO, G.C.; CONCELLÓN, A.: ¨Efecto hormético de la radiación UV-C sobre el desarrollo de Rhizopus y Phytophthora en naranjilla (Solanum quitoense)¨, [en línea] Revista Iberoamericana de Tecnología Postcosecha, ISSN-1665-0204, DOI-https://dx.doi.org/10.1016/j.foodchem.2014.03.120, 14(1): 64-70, 2013. ; Liao et al., 2016LIAO, C.; LIU, X.; GAO, A.; ZHAO, A.; HU, J.; LI, B.: ¨Maintaining postharvest qualities of three leaf vegetables to enhance their shelf lives by multiple ultraviolet-C treatment¨, [en línea] LWT-Food Science and Technology, ISSN-0023-6438, DOI-https://dx.doi.org/10.1016/j.lwt.2016.05.029, 73: 1-5, 2016. ).

La UV-C influye significativamente (p <0,05) en las principales causas de deterioro tanto de frutas como de hortalizas, provocando un retraso en la senescencia. Sin embargo, las superficies no uniformes de frutas y verduras pueden variar la eficacia de UV-C. Otros factores de variación son la variedad de la fruta, la estación del año y la temperatura de almacenamiento (Cote et al., 2013COTE, S.; RODONI, L.; MICELI, E.; CONCELLÓN, A.; CIVELLO, P.M.; VICENTE, A.R.: ¨Effect of radiation intensity on the outcome of postharvest UV-C treatments¨, [en línea] Postharvest Biology and Technology, ISSN-0925-5214, DOI-https://dx.doi.org/10.1016/j.postharvbio.2013.03.009, 83: 83-89, 2013. ; Hakguder y Unluturk, 2018HAKGUDER, T.B.; UNLUTURK, S.: ¨Effect of postharvest UV-C treatment on the microbial quality of “Şalak” apricot¨, [en línea] Scientia Horticulturae, ISSN-0304-4238, DOI-https://dx.doi.org/10.1016/j.scienta.2018.02.012, 233: 370-377, 2018. ; Petrielli et al., 2019PETRIELLI, P.G.; USBERTI, C.Z.F.; ALVES, M.R.: ¨Effects of postharvest application of UV-C radiation on the control of microorganisms and maintenance of quality in strawberries¨, [en línea] Revista dos Trabalhos de Iniciação Científica da UNICAMP, ISSN-2596-1969, DOI-https://dx.doi.org/10.20396/revpibic262018489, (26), 2019. ). Los tratamientos combinados UV-C con gases, productos químicos, atmósferas modificadas y pulsos de luz también pueden aumentar la eficacia de la respuesta UV-C a la senescencia de la fruta (Allende et al., 2007ALLENDE, A.; MARÍN, A.; BUENDÍA, B.; TOMÁS, B.F.; GIL, M.I.: ¨Impact of combined postharvest treatments (UV-C light, gaseous O3, superatmospheric O2 and high CO2) on health promoting compounds and shelf-life of strawberries¨, [en línea] Postharvest Biology and Technology, ISSN-0925-5214, DOI-https://dx.doi.org/10.1016/j.postharvbio.2007.05.007, 46(3): 201-211, 2007. ; Xu et al., 2019XU, Y.; CHARLES, M.T.; LUO, Z.; MIMEE, B.; TONG, Z.; VÉRONNEAU, P.; AGUILERA, D.A.; ROLLAND, D.: ¨Ultraviolet‐C priming of strawberry leaves against subsequent Mycosphaerella fragariae infection involves the action of reactive oxygen species, plant hormones, and terpenes¨, [en línea] Plant, cell & environment, ISSN-0140-7791, DOI-https://dx.doi.org/10.1111/pce.13491, 42(3): 815-831, 2019. ; Kim et al., 2010KIM, J.Y.; KIM, H.J.; LIM, G.O.; JANG, S.A.; SONG, K.B.: ¨The effects of aqueous chlorine dioxide or fumaric acid treatment combined with UV-C on postharvest quality of ‘Maehyang’strawberries¨, [en línea] Postharvest Biology and Technology, ISSN-0925-5214, DOI-https://dx.doi.org/10.1016/j.postharvbio.2010.01.013, 56(3): 254-256, 2010. ; Lu et al., 2018LU, Y.; DONG, W.; ALCAZAR, J.; YANG, T.; LUO, Y.; WANG, Q.; CHEN, P.: ¨Effect of preharvest CaCl2 spray and postharvest UV-B radiation on storage quality of broccoli microgreens, a richer source of glucosinolates¨, [en línea] Journal of Food Composition and Analysis, ISSN-0889-1575, DOI-https://dx.doi.org/10.1016/j.jfca.2017.12.035, 67: 55-62, 2018. ; Marquenie et al., 2002MARQUENIE, D.; MICHIELS, C.W.; GEERAERD, A.H.; SCHENK, A.; SOONTJENS, C.; VAN IMPE, J.F.; NICOLAI, B.M.: ¨Using survival analysis to investigate the effect of UV-C and heat treatment on storage rot of strawberry and sweet cherry¨, [en línea] International Journal of Food Microbiology, ISSN-0168-1605, DOI-https://dx.doi.org/10.1016/S0168-1605(01)00648-1, 73(2-3): 187-196, 2002. ; Moreno et al., 2016MORENO, G.C.; ANDRADE, C.M.J.; TERÁN, G.A.; TÚQUERES, U.A.; CONCELLÓN, A.: ¨Efecto del uso combinado de radiación UV-C y atmósfera modificada sobre el tiempo de vida útil de mora de Castilla (Rubus glaucus) sin espinas¨, Revista Iberoamericana de Tecnología Postcosecha, ISSN-1665-0204, 17(1), 2016. ).

Varios estudios de tratamiento con UV-C en fresas indican una alta sensibilidad de la fruta a estos tratamientos (Forges et al., 2018FORGES, M.; VÀSQUEZ, H.; CHARLES, F.; SARI, D.C.; URBAN, L.; LIZZI, Y.; BARDIN, M.; AARROUF, J.: ¨Impact of UV-C radiation on the sensitivity of three strawberry plant cultivars (Fragaria x ananassa) against Botrytis cinerea¨, [en línea] Scientia Horticulturae, ISSN-0304-4238, DOI-https://dx.doi.org/10.1016/j.scienta.2018.06.063, 240: 603-613, 2018. ; Ortiz et al., 2018ORTIZ, A.C.; RODONI, M.L.; DARRÉ, M.; ORTIZ, M.C.; CIVELLO, P.M.; VICENTE, A.R.: ¨Cyclic low dose UV-C treatments retain strawberry fruit quality more effectively than conventional pre-storage single high fluence applications¨, [en línea] LWT-Food Science and Technology, ISSN-0023-6438, DOI-https://dx.doi.org/10.1016/j.lwt.2018.02.050, 92: 304-311, 2018. ; Severo et al., 2015SEVERO, J.; DE OLIVEIRA, I.R.; TIECHER, A.B.; CHAVES, F.C.; ROMBALDI, C.V.: ¨Postharvest UV-C treatment increases bioactive, ester volatile compounds and a putative allergenic protein in strawberry¨, [en línea] LWT-Food Science and Technology, ISSN-0023-6438, DOI-https://dx.doi.org/10.1016/j.lwt.2015.06.041, 64(2): 685-692, 2015. ). Sin embargo, pocas investigaciones incluyen un modelo matemático que pueda predecir con precisión el cambio de vida útil poscosecha de la fresa en función del tratamiento aplicado. La presente investigación tiene como objetivo obtener un modelo matemático que permita evaluar eficazmente el efecto combinado de diferentes dosis de radiación UV-C, tiempo de almacenamiento y temperatura, en la vida útil poscosecha de la fresa (Fragaria vesca L.) var. Oso Grande.

MATERIALES Y MÉTODOS

Los frutos (Fragaria vesca) fueron seleccionados sin defectos por la uniformidad de tamaño, color y grado de maduración a partir de un muestreo sistemático (N=20000; n=383 y k=52) según protocolo de calidad de la planta empacadora “FRESTAR”, el tamaño de muestras se determinó para una población finita (Montgomery, 2010MONTGOMERY, D.C.: Diseño y Análisis de experimentos, Ed. Limusa Wyley, segunda ed., México, 2010. ). Una vez seleccionados, los frutos se colocaron en una cámara de radiación de 20 L que contenía una lámpara UV-C de mercurio (15 W) y se trataron con una dosis variable de 4-15 kJ/m2 en diferentes tiempos de exposición (de 15 a 30 min). Posteriormente se conservaron en envases plásticos de aproximadamente 0,35 L de capacidad a diferentes temperaturas de almacenamiento en el rango de 12-24°C.

Diariamente se analizaron todos los frutos de cada envase (20) según cuatro indicadores clave que caracterizan el proceso de deterioro en la fresa: firmeza, peso, contaminación y color. La calidad de la fruta (C) se determinó como la tasa de cambio porcentual (1) que establece los valores promedio de cada uno de los cuatro indicadores definidos como el promedio de la suma de la razón porcentual de cada indicador.

 
C%= IfIo100It  (1)
 

donde:

If:

es la medida final

Io:

es la medida inicial

It:

es la medida total

La firmeza se determinó, utilizando penetrómetro digital para frutas marca FHT200 (± 0.5 % + 2 dígitos de precisión), como el promedio de la fuerza de punción máxima al perforar la muestra sobre los ejes radial y axial. Para evaluar el peso se utilizó la báscula digital EM-KBS2 con una precisión de 0.01 g. El nivel de contaminación (NC ) se determinó mediante una escala visual subjetiva de cinco puntos que indica por aproximación, el porcentaje del área contaminada del fruto (0: 100% de la superficie sin alteración, 1: NC <10% leve alteración, 2:10% ≤ NC <25% alteración moderada, 3:25% ≤ NC ≤ 50% alteración severa y 4: NC > 50% alteración muy grave). La variación de color ΔE se determinó mediante un fotocolorímetro digital, utilizando el sistema CIE-L * a * b * y la expresión propuesta por (Chen y Ramaswamy, 2002CHEN, C.R.; RAMASWAMY, H.S.: ¨Color and texture change kinetics in ripening bananas¨, [en línea] LWT-food science and technology, ISSN-0023-6438, DOI-https://dx.doi.org/10.1006/fstl.2001.0875, 35(5): 415-419, 2002. ):

 
ΔE= (ΔL2+Δa2+Δb2)1/2  (2)
 

donde:

ΔL, Δa y Δb representan las desviaciones de los valores individuales del color (L- luminosidad, a-coordenada rojo/verde y b-coordenada amarillo/azul) de una muestra completamente madura de fresa.

Como ocurre con la mayoría de los alimentos, las relaciones de dependencia de las variables en el tiempo obedecen a ecuaciones de primer orden y orden cero (Fu y Labuza, 1993FU, B.; LABUZA, T.P.: ¨Shelf-life prediction: theory and application¨, [en línea] Food Control, ISSN-0956-7135, DOI-https://dx.doi.org/10.1016/0956-7135(93)90298-3, 4(3): 125-133, 1993. ; Gacula Jr, 1975GACULA JR, M.C.: ¨El diseño de experimentos para el estudio de la vida útil¨, [en línea] Journal of Food Science, ISSN-0022-1147, DOI-: https://dx.doi.org/10.1111/j.1365-2621.1975.tb02211.x, 40(2): 399-403, 1975. ). Para definir la vida poscosecha de la fresa (3dcdt=-kCn ), se consideró el cambio en la calidad (%) a lo largo del tiempo de la siguiente manera:

 
dcdt=-kCn   (3)
 

k:

es la constante cinética

C:

es la calidad de la fruta en un momento (t)

n:

es el orden de la reacción

Al integrar la expresión (3)dcdt=-kCn se obtuvieron dos ecuaciones de diferente orden (4n=0 C= Co+kc t , 5n=1 lnC=-kt+ ln Co ). Donde Co representa la calidad de la fruta al principio cuando t = 0, y C es la calidad de la fruta en el tiempo t, siendo kc la constante de velocidad específica para la reacción de orden cero (n=0) y k la velocidad específica constante para la reacción de primer orden (n=1). Ambas ecuaciones representan una línea recta, pero se consideró que la expresión de primer orden (5n=1 lnC=-kt+ ln Co ) representaba el mejor ajuste de nuestros datos (coeficiente R2 más alto (R2=0,87)):

 
n=0 C= Co+kc t   (4)
 

 
n=1 lnC=-kt+ ln Co   (5)
 

 
t= lnCC0k  (6)
 

Para calcular el valor de la constante de velocidad específica k se utilizó la expresión 5n=1 lnC=-kt+ ln Co , obteniendo el valor k (pendiente de la gráfica) a partir de los datos experimentales de C. El valor límite de C establecido para el cálculo de la vida poscosecha de los controles y tratamientos fue un 10% de calidad, que es el momento t en el que se ha perdido el diez por ciento de la calidad poscosecha (determinado por la variación en los indicadores: firmeza, peso, contaminación y color) se definió como un indicador de pérdida de calidad. Se seleccionó el valor para t (10%) que representa el tiempo cuando las pérdidas de calidad de la fresa son apreciables visualmente (tiempo en que se pierde el 10% de la calidad de la fresa por apreciación visual). Este tiempo se obtuvo mediante la expresión 6t= lnCC0k.

La vida poscosecha (Vp) de las fresas tratadas se expresó como la diferencia de t (10%) entre controles y tratamientos, donde tc representa el tiempo poscosecha de la fresa cuando se ha perdido el 10% de la calidad en los controles, y tt representa el tiempo de poscosecha de la fresa cuando se ha perdido el 10% de la calidad en los tratamientos (7Pl= tc-tt ). Estos valores se obtuvieron experimentalmente a partir de ensayos por triplicado.

 
Pl= tc-tt   (7)
 

Diseño experimental

Se utilizó el método de Superficie Respuesta en el programa estadístico Design Expert v.11 que emplea la técnica de mínimos cuadrados para ajustar los datos obtenidos a ecuaciones de aproximación polinomial de primer (8Y=B0+i=1 3BiXi+ε ) y segundo orden (9Y=Bo+i=13BiXi+i=13BiiXi2+i<1BijXiXj+ε ). Para este caso, se seleccionó el Diseño Compuesto Central (DCC) factorial completo, cuya matriz está compuesta por diez puntos factoriales, cinco axiales y cuatro réplicas en puntos centrales.

 
Y=B0+i=1 3BiXi+ε   (8)
 

 
Y=Bo+i=13BiXi+i=13BiiXi2+i<1BijXiXj+ε   (9)
 

La matriz de diseño y la combinación de factores, incluidos los puntos axiales y centrales con sus réplicas, dieron como resultado 19 experimentales. El diseño fue rotativo para garantizar una varianza consistente y una respuesta ortogonal (α = 1.681) (tabla 1). Para ello, las diecinueve corridas experimentales se ejecutaron de forma aleatoria, y para respetar la aleatoriedad, el orden de ejecución para la secuenciación de experimentos se tomó exactamente como lo indica el programa Design Expert.

El análisis de varianza (ANOVA) se utilizó para evaluar la significancia estadística de los modelos y la prueba estadística de Fisher (prueba F) determinó cuáles de los factores afectan significativamente la vida poscosecha de Fragaria vesca. Para ello, se estimó la significancia y la magnitud de los efectos de cada variable (dosis de UV-C, tiempo de exposición y temperatura) y sus posibles interacciones en la vida poscosecha. Se descartaron los efectos de la variable con un valor p superior a 0,05 o con menos del 95% de significación y se realizó un nuevo análisis de varianza para el modelo reducido (Montgomery, 2010MONTGOMERY, D.C.: Diseño y Análisis de experimentos, Ed. Limusa Wyley, segunda ed., México, 2010. ).

 
TABLA 1.  Matriz del diseño con niveles de factores reales y codificados
FactorNameUnits-1,683+1.6830-1+1
ADosis UV-C kJ/m20.2518.759.54.0015.00
BTiempo de exposiciónmin9.8935.1122.515.0030.00
CTemperaturaºC7.9128.0918.012.0024.00
 

RESULTADOS Y DISCUSIÓN
Análisis de diseño experimental DCC

Los resultados obtenidos muestran valores promedio de vida poscosecha de la fresa de 2,7±1.12 días indicando que las diferencias entre tratamientos y controles son notables. Este resultado también muestra que los tratamientos UV-C (en dosis variables de 4-15 kJ/m2) y los tiempos de exposición (de 15-30 min) tardan aproximadamente 3,6 días en perder sus atributos de calidad (dependiendo de la firmeza, peso, contaminación e indicadores de color) en relación a los controles (Tabla 2).

 
TABLA 2.  Diseño experimental DCC con niveles (máximos y mínimos), factores (A: dosis de UV-C, B: tiempo, C: temperatura) y variable de respuesta (vida poscosecha)
CorridasA: Dosis UV-C -(kJ/m2)B: Tiempo de exposición (min)C: Temperatura (ºC)Vida poscosecha (días)
19.535.118.03.01
21530.024.03.54
31530.012.04.01
4415.024.01.27
59.522.518.03.54
69.522.518.03.44
718.722.518.04.54
81515.012.03.87
9430.012.01.82
10430.024.01.37
119.522.518.03.55
129.522.507.93.02
131515.024.03.34
140.2522.518.00.46
15415.012.01.58
169.522.518.03.58
179.522.518.03.25
189.522.528.01.51
199.509.818.02.48
 

Estudios similares determinaron que la dosis de UV-C de 9 kJ/m2 y UVB a 72 h /15°C mejoró la estabilidad de las flores de brócoli (Formica et al., 2017FORMICA, O.A.C.; MARTÍNEZ, H.G.B.; DÍAZ, L.V.; ARTÉS, F.; ARTÉS, H.F.: ¨Use of postharvest UV-B and UV-C radiation treatments to revalorize broccoli byproducts and edible florets¨, [en línea] Innovative Food Science & Emerging Technologies, ISSN-1466-8564, DOI-https://dx.doi.org/10.1016/j.ifset.2017.07.036, 43: 77-83, 2017. ; Lu et al., 2018LU, Y.; DONG, W.; ALCAZAR, J.; YANG, T.; LUO, Y.; WANG, Q.; CHEN, P.: ¨Effect of preharvest CaCl2 spray and postharvest UV-B radiation on storage quality of broccoli microgreens, a richer source of glucosinolates¨, [en línea] Journal of Food Composition and Analysis, ISSN-0889-1575, DOI-https://dx.doi.org/10.1016/j.jfca.2017.12.035, 67: 55-62, 2018. ). El mismo efecto de UV-C se ha observado en peras, piñas, arándanos, amaranto, espinacas, puerros, cebolla, tomate, caqui y pepino en dosis que varían entre 1,7 kJ/m2 a 39,6 kJ/m2, y temperaturas de almacenamiento de 4-24 ºC (Liu et al., 2018LIU, C.; ZHENG, H.; SHENG, K.; LIU, W.; ZHENG, L.: ¨Effects of postharvest UV-C irradiation on phenolic acids, flavonoids, and key phenylpropanoid pathway genes in tomato fruit¨, [en línea] Scientia Horticulturae, ISSN-0304-4238, DOI-https://dx.doi.org/10.1016/j.scienta.2018.06.075, 241: 107-114, 2018. ; Petrielli et al., 2019PETRIELLI, P.G.; USBERTI, C.Z.F.; ALVES, M.R.: ¨Effects of postharvest application of UV-C radiation on the control of microorganisms and maintenance of quality in strawberries¨, [en línea] Revista dos Trabalhos de Iniciação Científica da UNICAMP, ISSN-2596-1969, DOI-https://dx.doi.org/10.20396/revpibic262018489, (26), 2019. ; Gogo et al., 2018GOGO, E.; FÖRSTER, N.; DANNEHL, D.; FROMMHERZ, L.; TRIERWEILER, B.; OPIYO, A.; ULRICHS, C.; HUYSKENS-KEIL, S.: ¨Postharvest UV-C application to improve health promoting secondary plant compound pattern in vegetable amaranth¨, [en línea] Innovative Food Science & Emerging Technologies, ISSN-1466-8564, DOI-https://dx.doi.org/10.1016/j.ifset.2018.01.002, 45: 426-437, 2018. ; Imaizumi et al., 2018IMAIZUMI, T.; YAMAUCHI, M.; SEKIYA, M.; ALONSO, Y.; TANAKA, F.: ¨Responses of phytonutrients and tissue condition in persimmon and cucumber to postharvest UV-C irradiation¨, [en línea] Postharvest Biology and Technology, ISSN-0925-5214, DOI-https://dx.doi.org/10.1016/j.postharvbio.2018.06.003, 145: 33-40, 2018. ; Sari et al., 2016SARI, K.L.; SETHA, S.; NARADISORN, M.: ¨Effect of UV-C irradiation on postharvest quality of ‘Phulae’pineapple¨, [en línea] Scientia Horticulturae, ISSN-0304-4238, DOI-https://dx.doi.org/10.1016/j.scienta.2016.09.049, 213: 314-320, 2016. ).

En las fresas, la exposición a UV-C (250 nm) en dosis de 0,4-15 kJ/m2 ha mostrado cambios sustanciales en las características visibles que limitan su vida poscosecha (Jin et al., 2017JIN, P.; WANG, H.; ZHANG, Y.; HUANG, Y.; WANG, L.; ZHENG, Y.: ¨UV-C enhances resistance against gray mold decay caused by Botrytis cinerea in strawberry fruit¨, [en línea] Scientia Horticulturae, ISSN-0304-4238, DOI-https://dx.doi.org/10.1016/j.scienta.2017.06.062, 225: 106-111, 2017. ) y retrasan la contaminación fúngica. Este efecto al mismo tiempo produce un aumento en la expresión de genes relacionados con la defensa del huésped ante los ataques de microorganismos (Forges et al., 2018FORGES, M.; VÀSQUEZ, H.; CHARLES, F.; SARI, D.C.; URBAN, L.; LIZZI, Y.; BARDIN, M.; AARROUF, J.: ¨Impact of UV-C radiation on the sensitivity of three strawberry plant cultivars (Fragaria x ananassa) against Botrytis cinerea¨, [en línea] Scientia Horticulturae, ISSN-0304-4238, DOI-https://dx.doi.org/10.1016/j.scienta.2018.06.063, 240: 603-613, 2018. ). Si las dosis de UV-C se incrementan, este efecto se potencia cíclicamente en diferentes momentos de la poscosecha (Hakguder y Unluturk, 2018HAKGUDER, T.B.; UNLUTURK, S.: ¨Effect of postharvest UV-C treatment on the microbial quality of “Şalak” apricot¨, [en línea] Scientia Horticulturae, ISSN-0304-4238, DOI-https://dx.doi.org/10.1016/j.scienta.2018.02.012, 233: 370-377, 2018. ; Ortiz et al., 2019ORTIZ, O.L.C.; ORTIZ, C.M.; DARRÉ, M.; RODONI, L.M.; CIVELLO, P.M.; VICENTE, A.R.: ¨Role of UV-C irradiation scheme on cell wall disassembly and surface mechanical properties in strawberry fruit¨, [en línea] Postharvest Biology and Technology, ISSN-0925-5214, DOI-https://dx.doi.org/10.1016/j.postharvbio.2019.01.002, 150: 122-128, 2019. ).

 
TABLA 3.  Resultados del ANOVA para el modelo cuadrático reducido
TérminosSuma de cuadrados glCuadrado medioValor FValor p
Modelo22,5763,76111,73< 0.0001
A-Dosis (UV-C)17,78117,78528,00< 0.0001
B-Tiempo de exposición0,180810,18085,370,0390
C-Temperatura1,3511,3540,20< 0.0001
1,3211,3239,09< 0.0001
0,684310,684320,320,0007
2,1112,1162,81< 0.0001
Residual0,4040120,0337
Falta de ajuste0,331480,04142,280,2221
Error Puro0,072740,0182
Cor Total22,9818
Desv. Est0,1835 0,9824
Media2,80 R²Ajustado0,9736
C.V. %6,56 R² Predicho0,9296
A.P.34,4567
 

En la prueba ANOVA se obtuvo el efecto de cada variable en la vida poscosecha de Fragraria vesca (Tabla 3). Una vez eliminados los términos del modelo cuadrático que no eran significativos (p >0, 05), (AB, AC y BC) se obtuvieron los términos (A, C, B, A², B², C²) significativos (p <0, 05). El valor F (111,73) obtenido implica que el modelo cuadrático es significativo (p <0, 05), su valor F de falta de ajuste (2, 28) no fue significativo (p >0, 05) en relación con el error puro y hay una probabilidad del 22,21% de que se produzca un valor F de falta de ajuste debido al ruido (esto implica un buen ajuste del modelo a los datos).

El modelo R² predicho de 0,92 está razonablemente de acuerdo con el R² ajustado de 0,97; (la diferencia es inferior a 0,2) indicando que en el espacio del modelo los factores: dosis de UV-C, temperatura y tiempo de exposición pueden explicar el 97% de las variaciones de vida poscosecha La medida de precisión (A.P =34,45) fue superior a 4, lo que indica una señal adecuada, por su parte, el coeficiente de variación (CV=6.56) revela la fiabilidad de los experimentos (Tabla 3). Los valores de respuesta predichos frente a los valores de respuesta reales (valores experimentales) muestran que en cada punto, el modelo predijo adecuadamente los valores correspondientes (Fig. 1a). La probabilidad normal indica que los residuos siguen una línea recta con pocos datos de dispersión, por lo tanto, siguen una distribución normal. (Fig. 1b). En sentido general la relación entre las predicciones y los valores experimentales y el diagnóstico de los residuos, fueron adecuados (R²= 0,92), lo que implica que el modelo obtenido se puede utilizar para navegar por el espacio del diseño. (Fig. 1 a y b).

 
FIGURA 1.  Valores de respuesta predichos frente a los valores de respuesta reales y normalidad de los residuos.
 

Modelo matemático, de segundo orden (en términos reales y codificados).

  • a) Vida poscosecha = 3,46598 + 1,14094 * A + 0,115059 * B -0,314824 * C -0,310513 * A^2 -0,223893 * B^2 -0,393598 * C^2.

  • b) Vida poscosecha = -4,38928 + 0,402478 * Dose UV-C + 0,194455 * tiempo + 0,341128 * Temperatura -0,0102649 * Dosis UV-C^2 -0,00398032 * tiempo^2 -0,0109333 * Temperatura^2

La expresión matemática, en términos de factores codificados se puede utilizar para hacer predicciones sobre la vida poscosecha para niveles dados de cada factor (a). La expresión codificada es útil para identificar el impacto relativo de los factores (dosis de UV-C, temperatura y tiempo) comparando los coeficientes de los factores. Se observa que la temperatura (C) tiene un efecto lineal negativo en la vida de poscosecha (coeficiente que va precedido de un signo negativo -0,314), mientras que la dosis UVC y el tiempo de exposición (A; B) tienen un efecto lineal positivo (coeficientes que van precedidos por signos positivos 0,14 y 0,11 respectivamente) sobre la vida de poscosecha, los términos cuadráticos negativos (A; B) indican una curvatura donde los valores de los factores aumentan la respuesta al valor máximo. A partir de este punto, los valores de respuesta podrían comenzar a aumentar o comenzar a disminuir gradualmente (límite de diseño)

La expresión obtenida en términos de factores reales (b) se puede utilizar para hacer predicciones sobre la vida poscosecha para niveles dados de cada factor, como la dosis de UV-C, la temperatura y el tiempo de exposición, siempre que los niveles se especifiquen en el original unidades para cada factor. Sin embargo, esta expresión no debe usarse para determinar el impacto relativo de cada factor porque los coeficientes se escalan para acomodar las unidades de cada factor y la intersección no está en el centro del espacio de diseño (tabla 5).

En el programa estadístico, la optimización numérica maximizó la respuesta de vida poscosecha a un límite inferior a 10 (valor mínimo aceptable) y un límite superior a 20 (Montgomery, 2010MONTGOMERY, D.C.: Diseño y Análisis de experimentos, Ed. Limusa Wyley, segunda ed., México, 2010. ). En estas condiciones, se obtiene una deseabilidad máxima de 73% en las siguientes coordenadas factoriales (A, B, C) = (15; 24, 4; 15, 5). En este punto teórico se realizaron tres réplicas experimentales. Los resultados obtenidos se comparan con los resultados de la expresión b (tabla. 4) y muestran una buena concordancia entre los valores calculados (4,30) y experimentales (3,78), lo que ratifica que este modelo se puede utilizar para navegar por el espacio de diseño (Cote et al., 2013COTE, S.; RODONI, L.; MICELI, E.; CONCELLÓN, A.; CIVELLO, P.M.; VICENTE, A.R.: ¨Effect of radiation intensity on the outcome of postharvest UV-C treatments¨, [en línea] Postharvest Biology and Technology, ISSN-0925-5214, DOI-https://dx.doi.org/10.1016/j.postharvbio.2013.03.009, 83: 83-89, 2013. ).

 
TABLA 4.  Valores de respuesta óptimos teóricos y experimentales
FactoresValores
A- Dosis UV- C 15
B-Tiempo de exposición30
C-Temperatura12
Respuesta optimizada*4,30
Respuesta experimental**3,78

*Resultados de la expresión b **Valores medios de los tres tratamientos experimentales.

 

La respuesta media general de todas las ejecuciones fue adecuada. Los coeficientes se ajustan apropiadamente alrededor de un valor promedio (cuando los factores son ortogonales, el factor de inflación de la varianza (FIV) es 1; si el FIV es mayor que 1 indican multicolinealidad, cuanto mayor es el FIV, más grave es la correlación de factores). Esto indica que el cambio esperado en la vida poscosecha por unidad cambia en el valor un factor cuando todos los factores restantes permanecen constantes (Tabla 5).

 
TABLA 5.  Coeficientes en términos de factores codificados
FactorCoeficiente EstimadoGlError Estándar95% IC Bajo95% IC AltoFIV
Intercepto3,4710,08203,293,64
A-Dosis (UV-C)1,1410,04971,031,251,0000
B-Tiempo de exposición0,115110,04970,00690,22321,0000
C-Temperatura-0,314810,0497-0,4230-0,20661,0000
-0,310510,0497-0,4187-0,20231,04
-0,223910,0497-0,3321-0,11571,04
-0,393610,0497-0,5018-0,28541,04
 

La superficie de respuesta y las curvas de nivel muestran que la vida poscosecha de la fresa aumenta a medida que aumenta la dosis y la exposición a la UV-C, en tanto la temperatura disminuye (Fig 2). Se verifica una zona máxima donde se obtienen tiene las mejores condiciones de vida poscosecha (4,37 días). En este punto, el sistema diseñado verifica las mejores condiciones de las variables de estudio para extender la vida poscosecha de la fresa (Fig 2).

 
FIGURA 2.  Superficie de respuesta, y contorno en el modelo cuadrático.
 

Los cambios observados son representativos de los intervalos del sistema de estudio e indican que, en condiciones óptimas, los frutos tratados tardan alrededor de cuatro días en perder el 10% de su calidad en comparación con los controles. La curvatura hacia arriba del modelo, infiere que el valor máximo obtenido no es absoluto y se podrían encontrar otras áreas con mejor comportamiento de respuesta, al aumentar la dosis de UV-C. Esto implica que la vida poscosecha de la fresa podría extenderse a dosis más altas de UV-C y temperaturas más bajas.

Varias causas se atribuyen al retraso de la senescencia inducida por UV-C, entre ellas se encuentran compuestos denominados fenilpropanoides, que evitan la acción directa de los microorganismos sobre el parénquima celular (Liu et al., 2018LIU, C.; ZHENG, H.; SHENG, K.; LIU, W.; ZHENG, L.: ¨Effects of postharvest UV-C irradiation on phenolic acids, flavonoids, and key phenylpropanoid pathway genes in tomato fruit¨, [en línea] Scientia Horticulturae, ISSN-0304-4238, DOI-https://dx.doi.org/10.1016/j.scienta.2018.06.075, 241: 107-114, 2018. ). Otros compuestos bioactivos implicados son las fitoalexinas y poliaminas que provocan la inactivación de enzimas que ablandan los tejidos del fruto, generando mecanismos que pueden ralentizar su senescencia (Severo et al., 2015SEVERO, J.; DE OLIVEIRA, I.R.; TIECHER, A.B.; CHAVES, F.C.; ROMBALDI, C.V.: ¨Postharvest UV-C treatment increases bioactive, ester volatile compounds and a putative allergenic protein in strawberry¨, [en línea] LWT-Food Science and Technology, ISSN-0023-6438, DOI-https://dx.doi.org/10.1016/j.lwt.2015.06.041, 64(2): 685-692, 2015. ). Causalmente, existen varios mecanismos que describen la acción de UV-C sobre los sistemas biológicos que a su vez pueden retrasar el daño por frío y la pudrición blanda de la fruta causada por microorganismos (Formica et al., 2017FORMICA, O.A.C.; MARTÍNEZ, H.G.B.; DÍAZ, L.V.; ARTÉS, F.; ARTÉS, H.F.: ¨Use of postharvest UV-B and UV-C radiation treatments to revalorize broccoli byproducts and edible florets¨, [en línea] Innovative Food Science & Emerging Technologies, ISSN-1466-8564, DOI-https://dx.doi.org/10.1016/j.ifset.2017.07.036, 43: 77-83, 2017. ; Petrielli et al., 2019PETRIELLI, P.G.; USBERTI, C.Z.F.; ALVES, M.R.: ¨Effects of postharvest application of UV-C radiation on the control of microorganisms and maintenance of quality in strawberries¨, [en línea] Revista dos Trabalhos de Iniciação Científica da UNICAMP, ISSN-2596-1969, DOI-https://dx.doi.org/10.20396/revpibic262018489, (26), 2019. ).

Se ha demostrado que la UV-C genera mutaciones en la molécula de ADN de los microorganismos al inhibir directamente el crecimiento microbiano, pero a la vez también estimula ciertas regiones genómicas de la fruta (Pombo et al., 2011POMBO, M.A.; ROSLI, H.G.; MARTÍNEZ, G.A.; CIVELLO, P.M.: ¨UV-C treatment affects the expression and activity of defense genes in strawberry fruit (Fragaria× ananassa, Duch)¨, [en línea] Postharvest biology and technology, ISSN-0925-5214, DOI-https://dx.doi.org/10.1016/j.postharvbio.2010.08.003, 59(1): 94-102, 2011. ). Esta regiones codifican a enzimas que ralentizan la senescencia de frutos (Urban et al., 2016URBAN, L.; CHARLES, F.; DE MIRANDA, A.M.R.; AARROUF, J.: ¨Understanding the physiological effects of UV-C light and exploiting its agronomic potential before and after harvest¨, [en línea] Plant Physiology and Biochemistry, ISSN-0981-9428, DOI-https://dx.doi.org/10.1016/j.plaphy.2016.04.004, 105: 1-11, 2016. ). Por otra parte, existen componentes de la membrana (fosfolípidos, glicolípidos, proteínas y ligninas) que son sensibles al rango ultravioleta de onda corta, donde absorben energía promoviendo cambios metabólicos permanentes. En estas condiciones de las paredes celulares del fruto se refuerzan, ofreciendo mayor firmeza (Ortiz et al., 2019ORTIZ, O.L.C.; ORTIZ, C.M.; DARRÉ, M.; RODONI, L.M.; CIVELLO, P.M.; VICENTE, A.R.: ¨Role of UV-C irradiation scheme on cell wall disassembly and surface mechanical properties in strawberry fruit¨, [en línea] Postharvest Biology and Technology, ISSN-0925-5214, DOI-https://dx.doi.org/10.1016/j.postharvbio.2019.01.002, 150: 122-128, 2019. ).

El efecto por frío también inciden en el retraso del metabolismo del fruto (Andrade et al., 2013ANDRADE, C.M.J.; MORENO, G.C.; CONCELLÓN, A.: ¨Efecto hormético de la radiación UV-C sobre el desarrollo de Rhizopus y Phytophthora en naranjilla (Solanum quitoense)¨, [en línea] Revista Iberoamericana de Tecnología Postcosecha, ISSN-1665-0204, DOI-https://dx.doi.org/10.1016/j.foodchem.2014.03.120, 14(1): 64-70, 2013. ). A medida que baja la temperatura, se inhibe el crecimiento microbiano evitando así la contaminación de la fruta. Las bajas temperaturas también regulan los procesos respiratorios que influyen directamente en la maduración (Liao et al., 2016LIAO, C.; LIU, X.; GAO, A.; ZHAO, A.; HU, J.; LI, B.: ¨Maintaining postharvest qualities of three leaf vegetables to enhance their shelf lives by multiple ultraviolet-C treatment¨, [en línea] LWT-Food Science and Technology, ISSN-0023-6438, DOI-https://dx.doi.org/10.1016/j.lwt.2016.05.029, 73: 1-5, 2016. ), retrasando el deterioro del fruto y el proceso de senescencia (Cote et al., 2013COTE, S.; RODONI, L.; MICELI, E.; CONCELLÓN, A.; CIVELLO, P.M.; VICENTE, A.R.: ¨Effect of radiation intensity on the outcome of postharvest UV-C treatments¨, [en línea] Postharvest Biology and Technology, ISSN-0925-5214, DOI-https://dx.doi.org/10.1016/j.postharvbio.2013.03.009, 83: 83-89, 2013. ).

En este estudio, el efecto combinado de las bajas temperaturas y la radiación UV indujo cambios favorables en la vida poscosecha de la fresa. La adecuada combinación de los factores de estudio probablemente indujeron un mecanismo en cascada sobre el tejido vegetal, que condujo a la prolongación de la vida poscosecha de la fresa (Formica et al., 2017FORMICA, O.A.C.; MARTÍNEZ, H.G.B.; DÍAZ, L.V.; ARTÉS, F.; ARTÉS, H.F.: ¨Use of postharvest UV-B and UV-C radiation treatments to revalorize broccoli byproducts and edible florets¨, [en línea] Innovative Food Science & Emerging Technologies, ISSN-1466-8564, DOI-https://dx.doi.org/10.1016/j.ifset.2017.07.036, 43: 77-83, 2017. ).

CONCLUSIONES

  • El diseño del central compuesto resultó ser una buena herramienta para evaluar los efectos e interacciones de la dosis de UV-C, la temperatura y el tiempo, en la vida poscosecha de Fragaria vesca.

  • El modelo empírico obtenido fue estadísticamente significativo y mostró una buena concordancia entre los valores experimentales y predichos, obteniéndose una respuesta máxima de 4 días por encima de los controles.

  • El modelo indica que se podría encontrar una mejor respuesta aumentando la dosis de UV-C.

  • Las aplicaciones de este trabajo enfatizan la importancia del efecto combinado de UV-C y bajas temperaturas en la vida poscosecha de la fresa.

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