INTRODUCTION
⌅The peanut (Arachis hypogaea L) is one of the most nutritious and important legumes worldwide, contributing to the agricultural and industrial development of the countries where it is grown, especially in developing nations (Guamán y Ellaury, 2004GUAMÁN, R.; ELLAURY, R. J.: Maní. Guía de cultivo para las zonas de Loja y el Oro, Boletín divulgativo, 314, Guayaquil, 2004.).
The high content of oil, protein, vitamins and minerals make this crop an excellent food source, both human and animal, which is why it is highly demanded by the candy and jam industry. The grains can be consumed raw, roasted and butter and oil of high nutritional and utilitarian value for the industry can also be made from peanut (Ayala, 2009AYALA, T. C. L.: Estudio de prefactibilidad para la producción y comercialización de maní (Arachis hypogaea L) en el cantón Jipijapa, provincia de Manabí, 69pp., Tesis (en opción al título de Ingeniero Agroempresas), Colegio de Agricultura, alimentos y nutrición, Universidad San Francisco de Quito, Ecuador, 2009.).
Because of its vegetable nature, peanut is an excellent food source, having multiple uses in human and animal nutrition, as well as contributing 30% of proteins and 50% of unsaturated fats that lower cholesterol. It is also very rich in vitamin E and provides minerals such as sodium, potassium, iron, magnesium, iodine, copper and calcium (Ayala, 2009AYALA, T. C. L.: Estudio de prefactibilidad para la producción y comercialización de maní (Arachis hypogaea L) en el cantón Jipijapa, provincia de Manabí, 69pp., Tesis (en opción al título de Ingeniero Agroempresas), Colegio de Agricultura, alimentos y nutrición, Universidad San Francisco de Quito, Ecuador, 2009.). Some nutrition experts believe that peanuts are beneficial for cardiovascular health and brain function due to their oleic and linoleic acid composition (Ayala, 2009AYALA, T. C. L.: Estudio de prefactibilidad para la producción y comercialización de maní (Arachis hypogaea L) en el cantón Jipijapa, provincia de Manabí, 69pp., Tesis (en opción al título de Ingeniero Agroempresas), Colegio de Agricultura, alimentos y nutrición, Universidad San Francisco de Quito, Ecuador, 2009.).
According to statistics for Latin American region (FAOSTAT, 2018FAOSTAT: Cultivos. Producción/Rendimiento de Manís (cacahuete) con cáscara en América del Sur + (Total) 1994 - 2016, [en línea] 2017, Disponible en:http://www.fao.org/faostat/es/#data/QC/visualize[Consulta: agosto, 2018].), Argentina has established itself as one of the main in-shell peanut producers in the world, after China, India, Nigeria and the United States. World in-shell peanut production oscillates around 45 654 t and is led by China (37% of total production) with around 17 000 t, followed by India (20% of the total) with around 9 000 (Blengino, 2015BLENGINO, C.: Maní, Organización de las Naciones Unidas para la Alimentación y la Agricultura, 2, 2015.).
Globally, China has managed to position itself as the world's leading producer and exporter of peanuts, taking advantage of its privileges in terms of soil conditions and production areas, yields and labor. This allows it to compete with prices well below the market average. However, it has not advanced in technology and quality as it has in other countries (Blengino, 2015BLENGINO, C.: Maní, Organización de las Naciones Unidas para la Alimentación y la Agricultura, 2, 2015.).
In Ecuador, peanut cultivation is traditional in the productive areas located in the provinces of Manabí, Loja, El Oro and Guayas. Currently, between 12 000 and 15 000 ha are cultivated, with an average yield of 700 kg/ha of peanuts in shell (Ayala, 2009AYALA, T. C. L.: Estudio de prefactibilidad para la producción y comercialización de maní (Arachis hypogaea L) en el cantón Jipijapa, provincia de Manabí, 69pp., Tesis (en opción al título de Ingeniero Agroempresas), Colegio de Agricultura, alimentos y nutrición, Universidad San Francisco de Quito, Ecuador, 2009.).
Although in Ecuador the cultivation of peanuts has become a family-type activity, the average annual production remains at approximately 591 to 909 kg/ha, not enough to cover the needs of internal consumption, which on average are about 1,150 kg. /ha, that is, around 225 t/year are produced, with a marked deficit for the oil, vegetable fat and confectionery industries, of around 450 kg/ha.
Worldwide for the Spanish and Virginia genotypes, respectively, yields are 2 031 and 1 932 kg/ha (Zapata et al., 2012ZAPATA, N.; VARGAS, M.; VERA, F.: "Crecimiento y productividad de dos genotipos de maní (Arachis hypogaea L.) según densidad poblacional establecidos en Ñuble, Chile", Idesia (Arica), ISSN 0718-3429, 30: 47-54, 2012.). The low productivity shown in peanut cultivation in Ecuador is basically due to the lack of improved varieties (Ivad, 2015IVAD: Producción actual de maní en Ecuador, rendimientos, y comercialización, [en línea] Disponible en:http://ivad1991.blogspot.com/2015/07/produccion-actual-de-mani-en-ecuador.html. [Consulta: 3 de marzo].).
Historically, in the province of Manabí, the plantations of this crop are concentrated in the cantons of Portoviejo, Tosagua, Chone, 24 de Mayo and part of Rocafuerte. In it, 9,000 ha are planted, of these, the largest volume of production is concentrated in the Calderón Parish, northeast of Portoviejo. There, 40% of Manabí crops are developed (Zambrano Casanova, 2018ZAMBRANO CASANOVA, D. E.: Propiedades físico mecánicas de los granos de maní (Arachis hypogaea L.) Que intervienen en la clasificación gravimétrica, 76pp., Tesis (para optar por al grado de Magister en Ing. Agrícola), Instituto de Postgrado, Universidad Técnica de Manabí, Manabí, Ecuador, 2018.).
Four varieties of peanuts are grown in this area, being: INIAP 380; Charapoto or Creole; Caramel or 382; and Rosita or 381. Criollo or Charapoto variety is the one that covers the largest planting area, since it has the greatest resistance to diseases and good adaptability to the rigors of the climate that are experienced in the territory, although the yields can be significant if appropriate agricultural practices are applied (Barros, 2015BARROS, C. J. C.: Comportamiento agronómico de tres variedades de maní (Arachís hipogaea l.) en el cantón Quinsaloma, 78pp., Tesis (en opción al titulo de Ing. Agropecuario), Unidad de Estudios a Distancia. Carrera Agropecuaria, Universidad Técnica de Quevedo (UTEQ), Quevedo, Ecuador, 2015.).
The Department of Productive Promotion of the Provincial Government of Manabí is developing several projects for the improvement of peanut production and the development of agribusiness in this sector, as well as supporting new ventures that will serve as a development axis for the province. As part of this action, the existence of a problem related to the selection and classification of peanut kernels has been identified, as this is detrimental to the final quality of the product.
In Ecuador, namely, the machines that are used for the classification of peanut grains have as a working principle the screening or selection by calibers, in this way the peanut grains are separated according to their size. This results in grains that are the same size, but when weighed do not have the same mass, showing differences in weight of up to 15%. That problem requires that, in the peanut benefit process, it is necessary to use a classifier whose principle of operation or separation is based on the mass of the grains (difference in mass).
Internationally, machines of this type have been developed, many of which are known as gravimetric or densimetric sorters, which guarantee greater uniformity in the mass of the kernels.
Currently in Ecuador this type of machines is not manufactured and their importation is expensive (MECALUX, 2016), with prices that can range between 12 000 and 15 000 USD, so it is convenient their local development.
As a previous step to the design of these machines, the determination of the physical-mechanical properties of the peanut kernels is required. Taking into account these aspects, as well as the fact that Criollo or Charapoto variety is the most cultivated in Manabí Province, it was decided to carry out the present work with the objective of determining the physical-mechanical properties of Criollo variety peanut kernels, required for the design of gravimetric grading machines.
METHODS
⌅The experimental investigation was carried out in the controlled conditions of the physics laboratories of the Institute of Basic Sciences (ICB) of the Technical University of Manabí.
The program of the experimental investigations is shown (Table 1), where the object of study, order of execution, the aspects analyzed and the place where each task was carried out are established. The same were carried out in the period included in the year 2021, first semester.
| Task | Object of study | Aspects to be analyzed | Place |
|---|---|---|---|
| 1 | Physical properties of peanuts | Laboratory of the Research Institute, Technical University of Manabí | |
| 2 | Mechanical properties of peanut kernels | Physics laboratory. Institute of Basic Sciences, Technical University of Manabí |
Methodology to determine the physical properties of peanut kernels (Arachis hypogea)
⌅The physical properties of peanut kernels investigated were: length; equatorial diameter and peanut mass which agree with the properties proposed by KURT y ARIOGLU (2018)KURT, C.; ARIOGLU, H.: "Physical and mechanical properties of some peanut varieties grown in Mediterranean environment", Sciendo, e-ISSN 2067-1865, Vol. LI(2): 27-34, 2018., to define kernel dimensions.
The preparation of samples as a previous step to determine physical properties, consisted on the selection of 10 kg of certified seed, coming from the experimental areas of the National Institute of Agricultural Research (INIAP) in Portoviejo. The measurements of physical properties involved taking 50 samples (kernels) at random, during the determination of each of the properties. Figure 1, shows the preparation of the sample of peanut kernels subjected to the test.
Methodology for the determination of length (L). The measurement of this variable was carried out with a WEZU Vernier caliper of 250 mm ± 0.05 mm of error, the measurement comprised the distance between both ends of the peanut (Figure 2).
Methodology for the determination of the equatorial diameter (d). The measurement of the equatorial diameter was carried out with the previously described Vernier caliper, taking as a measure the cross section of the kernels (Figure 3).
Methodology for the determination of mass (m). The mass of the peanuts was determined on an Ohaus Pionner precision balance model PA512 510 g X 0.01 g, 180 mm plate, with a capacity of 510 g and a precision of 0,001 g. The precision balance is shown (Figure 4).
Experimental determination of the mechanical properties of peanut kernels. The mechanical properties of the peanuts that were determined during the experimental investigations are related to the contact and relative sliding of peanuts with the surface of the sorter, as well as the rolling resistance.
Static friction angle (ϕ). It was determined by using an inclined plane (Akcali et al., 2006AKCALI, I. D.; INCE, A.; GUZEL, E.: "Selected Physical Properties of Peanuts", International Journal of Food Properties, ISSN: 1094-2912, 9(1): 25-37, 2006.). This plane allows variations of inclination of the sliding surface from 0 to 90 degrees. It has a scale that makes it possible to take readings of the angle of inclination. Different types of sliding surfaces were used, such as: Stainless steel type AISI 301; Aluminum; Rubber and Wood. Figure 5 shows, images of the inclined plane used in the experimental investigations.
Static friction was determined by placing the peanut kernel longitudinally on the sliding surface, which was varied in inclination to the point where any increase in the weight component (m∙g∙sin (ϕ)) acting perpendicular to the sliding plane causes sliding. The grain will be in a state of imminent motion. In the case of imminent motion of the peanut kernel, the summation of forces acting on both axes equal zero, since the body is at rest.
Dynamic friction angle (ϕd). The same procedure and equipment used during the determination of static friction was used, with the difference that, in this case, an impact was exerted on the sliding surface so that the peanut kernels could overcome the inertia force that keeps them in static equilibrium.
Static (α) and dynamic (αd) rolling angle. It was determined by placing the peanut grain transversely on the inclined plane, in such a way that, by varying the inclination of the surface, the grain begins to roll on it. In the same way as in the previous case, an impact was exerted on the sliding surface in the case of the dynamic angle.
RESULTS AND DISCUSSION
⌅The results of the determination of the physical properties of the peanut kernels show the main statistics for each of the properties investigated (Table 2). They reflect the mean values and deviations of the dimensional and mass characteristics of the peanut kernels, as well as the ranges and deviations of their magnitudes.
| Statistics | m, g | L, mm | d, mm |
|---|---|---|---|
| Count | 100,00 | 100 | 100 |
| Average | 0,49 | 13,56 | 8,01 |
| Median | 0,49 | 13,0 | 8,0 |
| Mode | 12,0 | ||
| Geometric Mean | 0,49 | 13,4586 | 7,92 |
| Variance | 0,008 | 2,8802 | 1,47 |
| Standard Deviation | 0,09 | 1,6971 | 1,21 |
| Coefficient of Variation, % | 18,06 | 12,51 | 15,16 |
| Standard Error | 0,009 | 0,169 | 0,12 |
| Minimum | 0,26 | 10,00 | 5,50 |
| Maximum | 0,77 | 20,00 | 12,00 |
| Range | 0,51 | 10,00 | 6,50 |
| Sum | 49,97 | 1356,00 | 801,00 |
| Sum of squares | 25,78 | 18672,50 | 6562,00 |
For the specific case of the mass of peanut grains, the results show that Criollo variety reaches average values of 0,49 ± 0,009 g, within a range of mass values that vary from 0,26 ± 0,009 g to a maximum of 0,77 ± 0,09 g. The standard deviation did not exceed 0,09 g. The coefficient of variation shows the great natural variability of the mass in this variety. The mass of the grains of this variety are similar to that of other varieties that are harvested in Ecuador, since it is within the range registered for the INIAP-380 varieties; INIAP-281 (INIAP, 1996INIAP: INIAP-380. Nueva variedad de Maní de alto potencial. En: INIAP (ed.) Estación Experimental, Boliche. Ecuador, Vol. pp. 5, 1996., 2012INIAP: INIAP-381. Nueva variedad de Maní precoz para zonas semisecas. En: INIAP (ed.) INIAP: Estación Experimental Boliche, Ecuador, Vol. pp. 10, 2012.). Similarly, these observed mass ranges agree with those reported by (Akcali et al., 2006AKCALI, I. D.; INCE, A.; GUZEL, E.: "Selected Physical Properties of Peanuts", International Journal of Food Properties, ISSN: 1094-2912, 9(1): 25-37, 2006.; Iraj et al., 2011IRAJ, B.; SAYED, H. P.; FATEMEH, R.-A.: "Mechanical behavior of peanut kernel under compression loading as a function of moisture contents", Elixir Agriculture, ISSN 2229-712X, 36: 3552-3557, 2011.), although they differ from the 66,80 g reported by Sarmiento (2013)SARMIENTO, C. L. M.: Evaluación Agronómica de un cultivar de maní (Arachys hipogaea L.) tipo Valencia, en el Valle de Casanga, Provincia de Loja, 126pp., Tesis (en opción al grado previo a la obtención del Título de Ing. Agronomo), Area de Agropecuaria y Recursos Naturales y Renovables, Universidad Nacional de Loja, Loja, Ecuador, 2013..
In the case of seed length, the results show that this variety has an average length of 13,6 ± 0,17 mm, varying from a minimum length of 10 ± 0,17 to maximum values of 20 ± 0,17. mm. The standard deviation of 1,7 mm and the coefficient of variation reaffirm the natural variability of the physical properties of peanut kernels in this variety (Gojiya et al., 2020GOJIYA, D.; DOBARIYA, U.; PANDYA, P.; GOJIYA, K.: "Studies on Physical and Engineering Characteristics of Peanut Kernel", International Journal of Nutritional Science and Food Technology, ISSN 2471-7371, 6(2): 22-27, 2020.).
Finally, the analysis to determine the equatorial diameter of the grains in this variety showed that the average equatorial diameter takes values of 8.01 ± 0.12 mm, with a standard deviation of 1.21 mm and extreme values of 5 .50 ± 0.12 mm and 12.0 ± 0.12 mm, as minimum and maximum equatorial diameters, respectively.
The analysis of the frequency histograms (Figure 6), showed that the most probable values of the investigated variables are in the order of m=0,26 to 0,6 g; L=10 to 15 mm; d=5,50 to 9,1 mm.
Mechanical properties of peanut kernels involved in the design of gravimetric sorting surfaces
⌅The results of the determination of the angles of friction due to sliding and rolling resistance without sliding showed, the highest values for the static cases, a result that agrees with the classical theories of sliding and rolling of the bodies (Figure 7). That is because the force required to overcome the inertia that keeps the grains in static equilibrium will be greater than the force required to keep them in motion (Ospina, 2002OSPINA, M. J. E.: Características físico mecánicas y análisis de calidad de granos, edit. Universidad Nacional de Colombia, pp. 101, ISBN: 958-701-182-1, Bogotá, Colombia, 2002.).
In the case of friction or sliding friction (static), the highest values of the friction angle were observed when the kernels slid on rubber and wood surfaces with ϕ= 35,7 ± 0,10 and ϕ= 22,9 ± 0,12 degree, respectively. On both surfaces the values were significantly higher (Table 3), compared to aluminum and stainless steel, respectively ϕ= 35,3 ± 0,075 and ϕ= 22,9 ± 0,075 degree, respectively. These results agree with the results obtained by several researchers (Olajidea y Igbekab, 2003OLAJIDEA, J. O.; IGBEKAB, J. C.: "Some physical properties of groundnut kernels", Journal of Food Engineering, ISSN 0260-8774, 58(2): 201 - 204, 2003.; Akcali et al., 2006AKCALI, I. D.; INCE, A.; GUZEL, E.: "Selected Physical Properties of Peanuts", International Journal of Food Properties, ISSN: 1094-2912, 9(1): 25-37, 2006.; Iraj et al., 2011IRAJ, B.; SAYED, H. P.; FATEMEH, R.-A.: "Mechanical behavior of peanut kernel under compression loading as a function of moisture contents", Elixir Agriculture, ISSN 2229-712X, 36: 3552-3557, 2011.).
The recorded values for stainless steel surfaces and aluminum did not show statistically significant differences for 95% confidence level. The magnitude of the observed values agrees with those found by other authors for other peanut varieties (Akcali et al., 2006AKCALI, I. D.; INCE, A.; GUZEL, E.: "Selected Physical Properties of Peanuts", International Journal of Food Properties, ISSN: 1094-2912, 9(1): 25-37, 2006.; Iraj et al., 2011IRAJ, B.; SAYED, H. P.; FATEMEH, R.-A.: "Mechanical behavior of peanut kernel under compression loading as a function of moisture contents", Elixir Agriculture, ISSN 2229-712X, 36: 3552-3557, 2011.; KURT &ARIOGLU, 2018KURT, C.; ARIOGLU, H.: "Physical and mechanical properties of some peanut varieties grown in Mediterranean environment", Sciendo, e-ISSN 2067-1865, Vol. LI(2): 27-34, 2018.). Although the values obtained for wood were lower than those reported by Olajidea y Igbekab (2003)OLAJIDEA, J. O.; IGBEKAB, J. C.: "Some physical properties of groundnut kernels", Journal of Food Engineering, ISSN 0260-8774, 58(2): 201 - 204, 2003.; Akcali et al. (2006)AKCALI, I. D.; INCE, A.; GUZEL, E.: "Selected Physical Properties of Peanuts", International Journal of Food Properties, ISSN: 1094-2912, 9(1): 25-37, 2006. as in these cases they found values from 24 to 26 degree.
| Cases | Mean | Homogeneous groups | |
|---|---|---|---|
| αd - Stainless Steel | 50 | 8,39 | X |
| αd - Aluminum | 50 | 8,4 | X |
| α - Aluminum | 50 | 9,72 | X |
| α - Stainless Steel | 50 | 9,72 | X |
| ϕd - Aluminum | 50 | 13,51 | X |
| ϕd - Stainless Steel | 50 | 13,54 | X |
| ϕ - Aluminum | 50 | 14,72 | X |
| ϕ- Stainless Steel | 50 | 14,73 | X |
| αd - Wood | 50 | 16,48 | X |
| α - Wood | 50 | 19,97 | X |
| ϕd - Wood | 50 | 20,64 | X |
| ϕ - Wood | 50 | 22,93 | X |
| αd - Rubber | 50 | 24,41 | X |
| α - Rubber | 50 | 25,98 | X |
| ϕd - Rubber | 50 | 31,44 | X |
| ϕ - Rubber | 50 | 35,73 | X |
This same behavior was observed (Figure 7) during the determination of the dynamic friction angle (ϕd), since the values shown varied from ϕd =13,51 ± 0,07 degree (aluminum surface) to ϕd =31,44 ± 0,13 degree (rubber surface). In this case, the dynamic friction angle values observed were slightly higher on the aluminum surface than on the stainless-steel surface, although this difference was not statistically significant at the 95% confidence level (Table 3). Similar results were found by López (2015)LÓPEZ, A.: Determinación de las propiedades físico-mecánicas de los rizomas de Sagú (Maranta Arundinacea, L) requeridas para el diseño de las máquinas extractoras de almidón, 71pp., Tesis (en opción al título académico de Máster en Ing. Agrícola), Departamento de Ing. Agrícola, Universidad Central de Las Villas, Santa Clara, Cuba, 2015. during the determination of the mechanical properties of Sago.
The results of the static rolling angle determination showed higher values (α=25,98 ± 0,11 degree) for the rubber surface compared to the rest of the investigated surfaces (Figure 7), the lowest values were observed (α=9,72 ± 0,09) for the stainless steel and aluminum surfaces. The comparison between the rolling angles observed on each of the surfaces ratified that there are statistically significant differences between the values recorded on the surfaces analyzed, except for the stainless steel and aluminum surfaces which showed the same values (Table 3).
Finally, the dynamic rolling angle (αd) showed a similar response to the rest of the variables analyzed for each of the surfaces (Figure 7), since the maximum values were observed on the rubber surface αd =24,41 ± 0,08 degree and the smallest for the stainless steel surface αd =8,39 ± 0,11 degree. Statistical analysis showed that there are no statistically significant differences between the observed values of this angle on stainless steel and aluminum surfaces for a 95% confidence level (Table 3). However, these values have statistically significant differences with those observed on wood and rubber surfaces, respectively.
CONCLUSIONS
⌅The physical properties of Criolla peanut kernels, which characterize their size, shape and mass, showed that for the peanut variety investigated the most probable values are: m=0,26 to 0,6 g; L=10 to 15 mm; d=5,50 to 9,1 mm.
Both, the angle of friction due to sliding and rolling without sliding showed the highest values for the static cases, compared to the dynamic ones, regardless of the type of sliding or rolling surface.
The stainless steel and aluminum sliding surfaces showed the lowest values of the static and dynamic friction angle (ϕ=14,731 ± 0,07 and ϕd =13,51 ± 0,07 degree). The maximum values of these angles were observed during the use of the rubber surface with ϕ= 35,73 ± 0,10 and ϕd= 31,44 ± 0,13.
The static and dynamic rolling angle of the grains exhibited a response similar to that observed in the friction angle in each of the investigated rolling surfaces, reaching maximum values in the rubber surface (α=25,98 ± 0,11 and αd=24,41 ± 0,08 degree) and minimum values on the stainless steel surface (αd=8,39 ± 0,11and αd =9,72 ± 0,09) degree.