Edible coating effect study and intermittent drying on the dried mango quality

The main objective of this work was to investigate the methods of drying mango into pieces from the combination of edible coatings and intermittent drying, in order to reduce the time and energy consumption of the operation and to improve the quality of the dried product in relation to the conventional drying. Firstly, we aimed to study the thermal intermittence applied to the convective drying process of mango slices (Mangifera indica L.), a tropical fruit with a high nutritional content and that has wide acceptance in the market. The thermal intermittent consisted of using a higher temperature at the beginning of the drying, while the surface of the fruit is predominantly saturated, which made its temperature remain low due to the intense evaporation of the water. The configurations were combinations of 95 °C (40 min) and 80 °C (40 min) in the first stage with 70 °C and 60 °C in the second stage. The time of the first stage was set in such a way that the sleeves did not exceed 60 °C during the period. Control dryings were continuous at 70 °C and 60 °C. The influence of these configurations on drying kinetics, drying rates, energy consumption (calculated by enthalpy balance), color retention and carotenoids were evaluated. The intermittency increased drying rates, reducing the time and energy consumption of the total process. Intermittent drying at 95 °C in the first stage showed the lowest energy consumption and similar values for the 60 °C and 70 °C temperatures applied to the second stage. The color parameters did not change significantly with the different operating conditions, and the carotenoid content was positively influenced by the intermittence, being that the 95 °C / 60 °C combination was the one that best protected this nutrient. Subsequently, edible films have been developed, which have shown to be promising in many applications aimed at improving food quality, both by the protective effect and by the ability to load and release substances of interest. Formulations of isolated soybean protein (SPI) and high methoxylation pectin (PEC) films were selected based on the zeta potential of the filmogenic solution, which indicates conditions of probable coacervation. In this work, two films formed by SPI, obtained at pH 11 and 3, and four films composed of SPI and PEC at pH 3 were characterized by their structural properties (FTIR and X-ray) and their optical, mechanical, solubility, morphology and permeability to water vapor and oxygen. It was found that the pH and the concentration of PEC added to the SPI solution significantly influenced the transparency and oxygen permeability of the films. The increase of the added PEC content did not significantly alter the solubility and the permeability to water vapor, however, it increased the transparency and reduced the permeability to oxygen, even in relation to the films formed only by SPI. Edible films, which have different applications, were evaluated in the present study as edible coatings. Mango pieces were coated with the formulation of lower oxygen permeability, 5% SPI + 2% PEC, and then dried until the fruit reached 9% ± 1% of moisture, through intermittent drying in two stages (95 ° C for 40 minutes and second stage at 60 ° C) and continuous drying (60 ° C), preselected conditions based on the first part of the research. The influence of this edible coating and the thermal intermittence on the drying efficiency and on the physical (color) and nutritional (carotenoid and vitamin C) qualities of the fruit were evaluated. It was found that the thermal intermittence increased the drying rates, reducing the drying time of the sleeves, as well as reducing energy consumption for air heating and maintain or even improve the quality of the dried fruit in relation to the continuous drying. Regarding the influence of the coating, this did not increase the resistance to drying, and still reduced the degradation of bioactive compounds of the mango. Therefore, it was possible to prove that the application of thermal intermittence and edible coatings can be quite efficient. (AU)