Cinética de congelamento, análise físico-química e sensorial do leite de cabra armazenado em diferentes temperaturas.

Abstract

This work was developed with the objective of studying the effect of goat milk freezing under temperatures of -20, -30, -170 and -196 ° C. The physicochemical characteristics of frozen goat milk were analyzed concerning to the following parameters: moisture, protein, ash, lactose, density, total titratable acidity, lipids, non fat solids, pH and total dry extract. The analysis of goat milk were also determined during storage for (0, 30, 45, 60, 75 and 90) days under -20 ° C of temperature. Such as the kinetics of freezing of goat milk under temperatures of -20, -30,every five minutes, and under -170°C in intervals of 60 seconds; while under the temperature of -196°C it was done every 5s, using, respectively, conventional freezer, nitrogen steam and immersion in nitrogen. The of sensory attributes of goat milk analyzed during the storage for 90 days were: appearance, color, flavor and aroma. The results of the characterization of the goat milk frozen in physicochemical parameters of protein, ash and titratable acidity of all samples are in accordance with current legislation, as well as the values of the lactose samples frozen under -170 and -196 ° C temperatures, the values of densities of the samples frozen under - 30, -170 and -196 0 C temperatures, and the values of non fat solids of the samples frozen under -30 and -170 ° C. The values of moisture and ash of the samples showed a tendency of stability by the end of the storage. But the values of total soluble solids and pH had increased by the end of the storage for all samples. The values of the physicochemical protein (-20, -170 and -196 ° C), density (-20 and -196 ° C), acidity (-20, -30 and -170 ° C), total dry extract (-20 ° C) and lipids (-170 and-196 ° C) increased by the end of the storage; however the values of lactose (-20 ° C), fat (-20 and -196 ° C) and dry extract (- 196 ° C) decreased, while the values of protein (-30 ° C), lactose (-30, -170 and -196 ° C), density (-30 ° C), lipids (-30 ° C), total dry extract (-30 and -170 ° C) and acidity (-196 0 C) have not changed by the end of the storage based on the initial values. In the kinetics of freezing of the frozen samples under -20 ° C and -30 ° C were observed the three well defined phases of freezes, while under -170 and -196 ° C these three phases were not well defined. The values of average effective diffusivity of the samples frozen under -20, -30, - 170 and -196 ° C were, respectively, equal to 0.306, 0.538, 14.688, 121.888 mm2 s"1. Samples evaluated for appearance and color are among the scales, "indifferent" and " I liked it slightly" and "creamy white" and "white", respectively. On the other hand the smell is in the scale of "light milk odor " and "odor of milk," while the flavor is in the scale "mild characteristic flavor of milk" and "characteristic taste of milk."