Abstract The interaction of the water molecules from the environment with foods and other materials can be evaluated using sorption isotherms. Films and biodegradable films are susceptible to changes in their functional characteristics due to adsorbed water. The amount of moisture that biodegradable films can adsorb depends on the temperature, relative humidity of the storage area and chemical composition. Several mathematical models can be used to describe the behavior of sorption isotherms in biodegradable films and some of them have been modified to include the temperature parameter into the equation. In this research, the original and modified BET, GAB, Halsey, Henderson and Oswin models were assessed to determine their suitability describing the behavior of moisture adsorption isotherms of chitosan films at 15, 20, 25 and 30 °C. The modified models of GAB, Oswin and Halsey gave the best fit to the experimental sorption data of the chitosan films, with R2 values higher than 0.97 demonstrating that those models describe better the sorption isotherms at the temperatures studied.

Abstract Kinetic parameters of thermal inactivation of pectin methylesterase (PME) in a partially purified mango enzyme extract were determined. The PME of mango partially purified by salting out showed different patterns of thermal inactivation, indicating the presence of a thermostable fraction at 70 °C and a thermolabile fraction at lower temperatures. The inactivation of the thermostable fraction exhibited a linear behavior that yielded a z-value of 9.44 °C and an activation energy (Ea) of 245.6 kJ mol-1 K-1 using the Arrhenius model. The thermostable mango PME fraction represented 17% of total crude enzyme extract, which emphasizes the importance of residual enzyme activity after heat treatment.

Abstract Cooked crabmeat has been reported to produce weak gels after a three-cycle washing process. Adding microbial transglutaminase (MTGase) can improve the mechanical properties in these gels. The objective of this work was to determine if a single washing treatment combined with adding of MTGase could improve the mechanical properties of crabmeat gels. Blue crabs (Callinectes sapidus) were obtained from Laguna Madre Tamaulipas, México and cooked at 120 °C for 20 min to separate the cooked meat from the shell. Cooked meat was homogenized in a cutter with 0 (control), 0.5 % and 1 % MTGase and stuffed in stainless steel tubes and incubated at 40 °C for 30 min before cooking at 90 °C for 15 min. Gels were also obtained by cooking directly at 90 °C for 15 min without previous incubation. Changes on the texture profile analysis were evaluated. The single washing step was enough to improve the mechanical properties of the crabmeat gels and MTGase improved such properties especially when gels were incubated to 40 °C previous to their cooking at 90 °C. The results obtained indicate that it is feasible to produce restructured products from cooked crabmeat by reducing the number of washing cycles if MTGase is added.

RESUMEN La carne de jaiba cocida sometida a un ciclo de tres lavados puede gelificar, produciendo geles débiles. La adición de transglutaminasa (TGasa) microbiana puede mejorar las propiedades mecánicas de estos geles. El objetivo del presente trabajo fue determinar si la aplicación de un solo ciclo de lavado, combinado con la adición de la enzima TGasa microbiana, mejora las propiedades mecánicas de los geles de jaiba. La jaiba azul (Callinectes sapidus) se obtuvo de la Laguna Madre, Tamaulipas, México y se coció a 120 °C por 20 min para separar manualmente la carne del exoesqueleto. La carne cocida se homogenizó en una cortadora de carne y se mezcló con 0 (control), 0.5 % y 1 % de TGasa microbiana. Posteriormente, se introdujo en tubos de acero inoxidable y se incubó a 40 °C por 30 min antes de cocerla a 90 °C por 15 min. También se obtuvieron geles mediante la cocción directa a 90 °C por 15 min, sin incubación previa. Se evaluaron los cambios en el análisis del perfil de textura (APT) de los geles obtenidos. El empleo de un solo ciclo de lavado de la carne de jaiba fue suficiente para mejorar las propiedades mecánicas de los geles de jaiba y la adición de TGasa microbiana incrementó esas propiedades, especialmente cuando los geles se incubaron a 40 °C antes de cocerlos a 90 °C. Los resultados obtenidos indicaron que es factible obtener productos reestructurados a partir de carne de jaiba previamente cocida, si se emplea un solo ciclo de lavado y se adiciona la enzima TGasa microbiana.

Abstract Composite films of chitosan, fish gelatin and microbial transglutaminase (MTgase) were developed. Films were produced by the casting method and dried at room temperature for 30 h, conditioned for 7 days at 30 °C at a relative humidity (RH) from 11 to 90%, and characterized. Chitosan:fish gelatin films in different proportions (100:0, 75:25, 50:50) with MTgase, were subjected to tensile properties and water vapor transmission (WVT) testing. The results showed that tensile strength decreased with an increase in RH and with an increase in gelatin content. Percent of elongation also increased with increasing RH and gelatin concentration. Water vapor transmission showed an increase proportional to an increase in RH with the presence of gelatin being unfavorable for reducing WVT. Results in this work allowed studying the effect of relative humidity on tensile and water vapor properties of chitosan and fish gelatin films.