Alterações das propriedades físico-químicas do suco de maracujá (Passiflora edulis f. flavicarpa Deg.) para diferentes técnicas de congelamento inicial, ao longo do período da armazenagem frigorificada.

Abstract

Juice of yellow passion fruit, pure and sweetened, submitted to two methods of initial freezing, in freezer at -22,6 ° C and for immersion in liquid nitrogen at -196 °C, were stored by 180 days at -22,6 ° C . It was determined the kinetic o f cooling and freezing of these juices and the alterations of some physical-chemical (ascorbic acid, acidity, pH, reducers sugar, non-reducers sugar, totals sugar and soluble solids) and sensorial characteristics (appearance, color, aroma and flavor) during the storage period, seeking to verify the influence of the initial freezing in the quality of the same ones. For the juices frozen at -22,6 °C, the cooling, crystallization and powder-freezing phases were of 1.200, 5.700 and 14.400 seconds, respectively for the pure juice and 1.500, 5.700 and 14.100 seconds for the sweetened juice. The average effective thermal diffusivity considering the phases 1 and 3 was 0,54.mm2.s"1 for de pure juice and 0,25.mm2.s"1 for the sweetened juice. For the juices frozen at -196.°C in the phases of cooling, crystallization and powderfreezing, the time were 60, 20, and 190 seconds for the pure juice and 40, 30 and 300 seconds for the sweetened juice. The thermal effective average considering the phases 1 and 3 was 30,81 mm2.s"' to the pure juice and 26,21 mm2.s"' for the sweetened juice. The values of ascorbic acid, pH, reducers sugar and totals sugar, appearance, color and flavor, showed to be stable for all the treatments, indicating that the freezing types were efficient in the preservation of the quality of the two types of juices along the storage. In the sweetened juices a larger tendency of maintenance of acidity was observed during the storage. In the juices without sugar a larger stability was verified in the texts of total sugars and non reducers, as well as a larger preference, second sensorial analysis, for the parameters appearance and color in relation to the sweetened juices.