ABSTRACT

The investigation concerned the effect of three methods of thawing frozen products at 18-20°C (room temperature), 2-4°C (conditions of a domestic refrigerator), and in a microwave oven, on the quality of fruit of bilberry, raspberry, black- and redcurrant, and strawberry. Physico-chemical indices applied as the criteria of the estimate were the content of dry matter, volatile acids, vitamin C, and anthocyanins, the amount of cell sap exuded after thawing, and the results of organoleptic evaluation. after harvest fruits were kept in a cold store and processed within 24 h. Frozen products were stored at about — 30°C up to the time of degustation. From the practical point of view the applied techniques of thawing insignificantly affected the level of the physico-chemical indices. Only in the case of fruit affected by microwaves the content of vitamin С (blackcurrant) and anthocyanins (bilberry, raspberry, and blackcurrant) was smaller, though maximum diiTerences did not exceed 10%. The amount of cell sap exuded in the course of thawing depended on the fruit species and method of thawing. Blackcurrant exuded trace amount of sap, greater ones were noted, in the increasing order, with bilberry, raspberry, and strawberry, and the greatest with redcurrant. of the thawing techniques tested the smallest amount of sap exuded at 2-4°C, at 18-20° it was by 30% and in the microwave oven by 63% greater. The highest organoleptic value was assessed in fruit thawed at 2-4°C with a final average score of 4.44, a slightly lower one at 18-20°C, and in the microwave oven the lowest with an average score of 4.13. Blackcurrant did not distinctly respond to the method of thawing while the reaction of raspberry was strong.