Estudo da fluidodinâmica de inertes em secador rotatório não-convencional e sua relação com a secagem da polpa de camu-camu

Abstract

Camu-Camu is a fruit native to the Amazon region, recognized for being the largest natural source of vitamin C, and an important source of bioactive compounds with a beneficial potential for health. Despite this, the high perishability and cultivation non-domesticated are still factors that hinder its commercialization outside the local market and in the post-harvest period. In this context, the rotary dryer with inert filling (SRRI) presents itself as an alternative to the use of camu-camu pulp when obtaining a product in the form of powder and high quality in the sense of less degradation of bioactive agents. In the operation of this dryer, the dynamics of the aggregates play a fundamental role in the processing efficiency, the successive collisions are responsible for the fragmentation of the already dried pulp and the formation of dust. The present work aimed to study the effects of operational variables of an SRRI on the drying performance of the pulp in terms of yield, bioactive content (phenolic, flavonoids and ascorbic acid) and the antioxidant capacity of the product. As inert, calcite porcelain spheres with diameters of 25.40, 19.05 and 12.70 mm were used. The dynamics of these aggregates were evaluated by applying Lagrangean modeling using the discrete element method (DEM), whose contact law allowed to obtain information on how the particles interact with each other and with the equipment. Six central composite plans (PCC) were carried out, three of them evaluating the drum loaded with aggregates of only one diameter, and the others evaluating the loading with the binary combination between aggregates of different diameters. The independent variables were rotation speed (R), filling degree (E) and the fraction between inerts (FI), the responses were collision force and number of particle-particle and particle-wall collisions obtained through simulation. With the results, an optimization was carried out in order to simultaneously maximize the two DEM responses in each CCP, obtaining six conditions for SRRI operation. Such conditions were tested experimentally and the highest drying efficiency verified (86.66%) resulted from the use of 25.40 and 12.70 mm aggregates, which combined the effect of the greater collision force given by the 25.40 mm aggregate and a greater number of collisions due to the 12.70 mm inert. This configuration was then explored in the drying of the pulp from a PCC in which the temperature was evaluated as the fourth independent variable. Regarding the responses, the yield and the content of bioactive compounds were determined. In all evaluated conditions, the product showed water activity below 0.28, indicating an inhibition of microbial growth. As for yield, the main effects were identified by the filling and temperature variables, in which the higher levels of the two variables contributed to the increase in the experimental response. It was found that a greater proportion of the particle of 12.70 mm compared to 25.40 mm favors the yield (greater number of collisions), while the rotation has little influence. As for bioactives, the main effect was verified for temperature. Higher temperature levels led to a greater degradation of bioactive compounds, reducing the levels of total phenolics, flavonoids and ascorbic acid, and resulting in a lower antioxidant capacity of the product. It was also found that the conditions of greater collision force resulted in greater degradation of bioactive substances. When performing a multi-response optimization, the calculation resulted in an IF of 26.28%, filling of 49.83%, and rotation of 74.82 RPM conditions associated mainly with a higher process yield and a temperature of 44.30 °C aiming at less degradation of bioactive compounds.