Produção de uvas-passas variedade Crimson: modelagem matemática e estudo experimental

Abstract

Brazil is the third largest producer of fruits in the world, among which the grapes rich in carbohydrates and source of iron, vitamins and minerals. The Brazilian production of grapes is concentrated in Rio Grande do Sul and in the region of the São Francisco Valley. The Crimson grape, object of this dissertation, is produced mainly in the city of Juazeiro do Norte (Bahia) and Petrolina (Pernambuco). It is considered a kind of table grapes, is apirénica and has reddish coloration. The raisins is obtained by drying, which reduces the amount of water and increases its shelf life. There is no record of raisins produced in Brazil on a commercial scale but the increase in the production recorded in recent years justifies the production of Brazilians raisins. Drying used to be produced through solar dryer or by using tray dryers. The production of raisins in these dryers allows a greater monitoring of the operation, which is not subject to climatic variations and allows a better control of the quality of the product. The optimization of the drying and improvement of the design of the dryers using mathematical models is efficient because allows to evaluate different scenarios that consider those properties of the food, the temperature and the velocity of drying air, the type of recirculation of this air. Which define the factors that more influence the process and ensure the improvement of the product quality. In this dissertation a phenomenological, unidimensional and transient mathematical model representative of the bed drying with constant and equivalent properties to the Crimson grapes, is developed and validated with experimental results obtained in a recirculation dryer. The phenomenon of shrinkage of the surface of this bed is considered in the development of the model. The specific heat, thermal conductivity, dry solid density and shrinkage coefficient of Crimson grapes were obtained experimentally and was compared with values reported in the literature. The other parameters were estimated through correlations. The mathematical model use partial differential equations that is solved using the discrete finite difference method. The simulate moisture, temperature and shrinkage results of a one-dimensional bed are consistent and qualitatively represent the drying of a set of raisins with oblato-spheroidal geometry. The quality of the product obtained was evaluated by sensory analysis techniques. The sensory attributes of Crimson variety raisins are considered to be good, indicating a positive consumer assessment.