Resumen Los materiales biocompuestos fabricados con matrices poliméricas biodegradables y reforzadas con fibras naturales son una propuesta ecológica para diversos sectores de aplicación. El objetivo de esta investigación fue dilucidar las propiedades físicas y mecánicas, así como la degradabilidad en el suelo de materiales elaborados a base de almidón de arroz y fibra de bagazo de caña. Se elaboraron seis biocompuestos de longitudes diferentes, que consideraron la aplicación o no de un tratamiento alcalino, que fueron sometidos a pruebas mecánicas de tracción, flexión y compresión, así como pruebas de absorción de agua y biodegradabilidad en el suelo. Los resultados mostraron que la resistencia mecánica del material fue afectada por el tratamiento alcalino de la fibra y la longitud de esta. La pérdida de peso de los seis biocompuestos, atribuible a su biodegradabilidad en el suelo, fue superior al 70 % después de cuatro semanas. El biocompuesto con longitud de fibra de 0.25 mm y con tratamiento alcalino mostró la mayor resistencia en todas las pruebas mecánicas y representa una propuesta ecológica prometedora para diversas aplicaciones.

Abstract Biocomposite materials made with biodegradable polymeric matrices and reinforced with natural fibers are an ecological alternative for various application sectors. The objective of this research was to elucidate the physical and mechanical properties, as well as the soil degradability, of materials made from rice starch and cane bagasse fiber. Six biocomposites of different lengths were elaborated, which considered whether or not to apply an alkaline treatment, and were subjected to mechanical tests of tensile, flexural and compression, as well as tests of water absorption and soil biodegradability. The results showed that the mechanical resistance of the material was affected by the alkaline treatment of the fiber and its length. The weight loss of the six biocomposites, attributable to their soil biodegradability, was greater than 70 % after four weeks. The 0.25mm fiber length biocomposite treated with alkaline, showed the highest strength in all mechanical tests and represents a promising ecological proposal for various applications.

Resumo: A quitosana é um biopolímero obtido a partir da desacetilação da quitina, tem múltiplas aplicações na agricultura como antifúngico, condicionador de solo, indutor de mecanismos de defesa, revestimento pós-colheita de frutos, folhas e sementes, entre outros. O objetivo desta pesquisa foi avaliar o efeito de revestimentos de quitosana misturados com fungicida (ditiocarbamato) na germinação e velocidade de germinação de sementes de feijão e milho armazenadas e determinar a capacidade de retenção do fungicida nas sementes revestidas sob diferentes tempos de embebição. Dois tratamentos de revestimento usando quitosana nas concentrações de 0,1 e 0,5% de quitosana em agua, dois tratamentos de revestimento usando quitosana nas concentrações de 0,1 e 0,5% de quitosana suplementados com fungicida 0,5% e um revestimento usando apenas 0,5% de fungicida em água foram aplicados como recobrimento em sementes de feijão e milho; e como controle foram utilizadas sementes embebidas em água destilada; após os tratamentos, a porcentagem de germinação e a velocidade de germinação foram determinadas, também a liberação de fungicida foi determinada em 0, 1, 2 e 6 h de embebição, e o efeito do tempo de armazenamento na germinação e na velocidade de germinação foi determinado a 30, 60, 90, 120, 150 e 180 dias de armazenamento a 4 °C e 45% de umidade relativa. O efeito da liberação do fungicida foi determinado pela inibição da germinação de conídios de Fusarium oxysporum. Não houve efeitos negativos dos revestimentos na germinação da semente após o armazenamento. O tratamento que proporcionou maior retenção do agente fungicida e liberou-o gradativamente foi a concentração de 0,5% de quitosana misturada ao fungicida. O recobrimento de sementes com quitosana misturadas com fungicida não causam mudanças negativas na germinação das sementes ou na taxa de germinação.

Abstract: Chitosan is a biopolymer obtained from deacetylation of chitin; it has multiple applications in agriculture as an antifungal, soil conditioner, inducer of defense mechanisms, fruits postharvest coating, leaves and seeds, among others. The objective in this research was to evaluate the effect of chitosan coatings mixed with fungicide (dithiocarbamate) on the germination and germination speed of bean and maize seeds in storage and to determine the retention capacity of the fungicide in the coated seeds under different times of imbibition. Two coating treatments at concentrations of 0.1 and 0.5% chitosan in water, two coatings treatments at 0.1 and 0.5% chitosan supplemented with 0.5% fungicide and a coating without chitosan using only 0.5% fungicide in water were used in bean and maize seed; and as control seeds imbibed in distilled water were used; after treatments, germination percentage and germination speed were determined, also fungicide release were determined at 0, 1, 2 and 6 h of imbibition, and the effect of storage time on germination and germination speed was determined at 30, 60, 90, 120, 150 and 180 days of storage at 4 °C and 45% relative humidity. The fungicide release effect was determined by inhibiting Fusarium oxysporum conidia germination. There were no negative effects of coatings on seed germination after storage. The treatment that provided both greater retention of the fungicidal agent and released it gradually, was 0.5% chitosan mixed with fungicide concentration. Chitosan coating seeds mixed with fungicide do not cause negative changes in seed germination or germination rate.

Abstract The respiratory metabolism of fruits is affected by multiple internal (product) and external (environmental) factors that often interact with each other. Among the external factors that have the greatest influence on respiration are temperature, air composition, moisture content, and illumination. This paper aims to elucidate the influence of environmental factors on the respiration rate of peach fruits based on transfer models obtained by dynamic regression modelling (ARIMAX). The fitted ARIMA models met the criteria of parsimony and white noise in residuals. The estimated coefficients of each model were statistically significant under the Durbin-Watson (DW), Akaike (AIC) and Schwarz (SBC) criteria. Transfer functions revealed 0.15% and 1.9% increase, and 0.001% decrease in the respiration rate of the peach fruit for each unit of change in temperature, relative humidity, and the illumination of the storage environment, respectively. The respiration rate response took place 1-8 minutes after the change in environmental variables had occurred. It was concluded that the dynamic regression modelling is reliable for predicting the physiological response of fruits the effect of external factors imposed continuously during postharvest handling.

Abstract: Prunus serotina is a species that grows wild or under cultivated conditions in several regions of the Americas, and is considered as a potential source of antioxidants. The study aimed to evaluate the concentration changes in compounds that contribute to the antioxidant capacity in capulin (Prunus serotina) fruit during the ripening process, in order to define when the maximum concentration is reached and thus establish a harvest index for the fruit. Antioxidant capacity was evaluated by spectroscopic methods. A completely randomized simple factor design was used for the statistical analysis. It was found that the content of total phenols and flavonoids decreased significantly at the S3 ripening stage (93 days after anthesis, DAA). Total anthocyanins increased significantly to 1.4 mg Cyanidin-3-glucoside gdb−1.The antioxidant capacity of the fruit had a maximum value of 63.7 µmol TE gdb−1 at the S3 ripening stage (93 DAA). Results indicated that the antioxidant capacity of the fruit is related to the content of total flavonoids and is higher before reaching the characteristic purple coloration, which is a consumption indicator.

Resumen: Prunus serotina es una especie que crece silvestre o en condiciones de cultivo en diversas regiones de América, y es considerada como una fuente potencial de antioxidantes. El objetivo de esta investigación fue evaluar los cambios de concentración en los compuestos que contribuyen a la capacidad antioxidante en frutos de capulin (Prunus serotina) durante el proceso de maduración, para definir el momento en que se alcanza la máxima concentración y así establecer el índice de cosecha de los frutos. La capacidad antioxidante se evaluó mediante métodos espectroscópicos. Para el análisis estadístico se utilizó un diseño de factor simple completamente aleatorizado. Se encontró que el contenido de fenoles y flavonoides disminuyó significativamente en la etapa de maduración S3 (93 DDA). Las antocianinas totales incrementaron significativamente hasta 1.4 mg Cyanidin-3-glucosido gbs−1 La capacidad antioxidante de los frutos tuvo un valor máximo de 63.7 µmol ET gbs−1 en la etapa de maduración S3. Los resultados indicaron que la capacidad antioxidante de los frutos está relacionada con el contenido de flavonoides totales y es mayor antes de alcanzar la coloración purpura característica, que es un indicador de consumo.

Abstract The huitlacoche (Ustilago maydis (DC) Corda) is a good source of nutrients in the diet. During post-harvest handling, the product shows a rapid senescence, attributed to the high rates of dehydration and respiration of the product, in addition to its composition. In order to prolong shelf life, the effect of high relative humidity and low storage temperature on the physical properties of huitlacoche (whole and in galls) and the presence of phytopathogenic fungi were evaluated. The results showed that at 3 ºC the dehydration rate decreased, maintaining the visual quality for longer, both the whole huitlacoche and in galls. Storage with high relative humidity at room temperature favored the proliferation of phytopathogenic host species such as Fusarium oxysporum, Rhizopus stolonifer and Penicillium expansum. The highest incidence and severity was shown by F. oxysporum inoculated with a wound in the gall, while R. stolonifer, although with a lower incidence than the other two species, was able to survive up to 10 ºC. The results demonstrate that the management of huitlacoche at 3 °C and high relative humidity in ambient air is feasible, as it counteracts the rate of dehydration and eliminates the risk of proliferation of host phytopathogenic fungi.

Resumen El huitlacoche (Ustilago maydis (DC) Corda) es una buena fuente de aporte de nutrientes en la alimentación. Durante el manejo poscosecha, el producto muestra una rápida senescencia, atribuida a las altas tasas de deshidratación y respiración del producto, además de la composición del mismo. Con la finalidad de prolongar la vida de anaquel, se evaluó el efecto de alta humedad relativa y baja temperatura de almacenamiento sobre las propiedades físicas del huitlacoche (entero y agalla) y la presencia de los hongos fitopatógenos. Los resultados mostraron que a 3 ºC la tasa de deshidratación disminuye, manteniendo la calidad visual por más tiempo, tanto del huitlacoche entero como en agalla. El almacenamiento con alta humedad relativa a temperatura ambiente favoreció la proliferación de especies fitopatógenas hospederas como Fusarium oxysporum, Rhizopus stolonifer y Penicillium expansum. La mayor incidencia y severidad la presentó F. oxysporum inoculada con herida en agalla, mientras que R. stolonifer, aunque con menor incidencia que las otras dos especies, fue capaz de sobrevivir hasta 10 ºC. Los resultados demuestran que es viable el manejo del huitlacoche a 3 °C y alta humedad relativa en el aire del ambiente, ya que contrarresta la velocidad de deshidratación y elimina el riesgo de proliferación de hongos fitopatógenos hospederos de la superficie.

The mechanical damages constitute one of the principal causes of losses post-harvest of fruits and vegetables. Sapodilla fruits ( Manilkara zapota L. P. Royen ) are very perishable susceptible to mechanical damage and attack of pathogenic during the post-harvest. It was Examined the physiological behavior and mechanic under axial compression with an Instron Universal Testing Machine 3382, with capability of 100 kilo Newton and a velocity of crossbeam of 20 mm/ minute. The parallel plates compressed the fruit once only, checking a curve force-deformation for each fruit evaluated, in analysis were used two types of fruit (I and II), two positions of compression and three displacements of crossbeam. The evolution of the respiratory activity, and production of ethylene were determined during five days, mechanical variables were gotten from test for each fruit. The two types of sapodilla showed physiological sensibility to the application of external loads (mechanical damage). The production of ethylene and the velocity of respiration increased significantly for the load applied at the vertical position, which accelerated the deterioration. With the obtained results, it can be inferred than the mechanical parameters for protection of the fruits in harvest, transportation and storage, they should be based in the behavior of the fruits to compression at the horizontal position, with the second displacement of crossbeam, if compression can be reduced for down the doorsteps before referred, it would be possible to reduce the levels of damage and consequently showing a fresh fruit of quality.

Los daños mecánicos constituyen una de las principales causas de pérdidas postcosecha de los productos hortofrutícolas. Los frutos de chicozapote (Manilkara zapota L. P. Royen), son muy perecibles, susceptibles a daño mecánico y ataque de patógenos durante la postcosecha. Se analizó el comportamiento fisiológico y mecánico bajo compresión axial con un equipo Instron Universal Testing Machine 3382, con capacidad de 100 kilo Newton y una velocidad de cruceta de 20 mm/ minuto. Los platos paralelos comprimieron una sola vez el fruto, registrándose una curva fuerza-deformación para cada fruto evaluado, en el análisis se utilizaron dos tipos de fruto (I y II), dos posiciones de compresión y tres desplazamientos de cruceta. La evolución de la actividad respiratoria, y producción de etileno fueron determinadas durante cinco días, variables mecánicas fueron obtenidas a partir de la prueba para cada fruto. Los dos tipos mostraron sensibilidad fisiológica a la aplicación de cargas (daño mecánico). La producción de etileno y la velocidad de respiración se incrementaron significativamente por la carga aplicada en la posición vertical, lo que aceleró la senescencia. Con los resultados obtenidos, se puede inferir que los parámetros mecánicos para protección de los frutos en cosecha, transporte y almacenamiento, deben ser basados en el comportamiento de los frutos a compresión en la posición horizontal, con el segundo desplazamiento de cruceta, si la compresión puede ser reducida por abajo de los umbrales antes referidos, sería posible reducir los niveles de daño y por consiguiente presentar un fruto fresco de calidad.