EVALUATION OF CHEMICAL AND COLOR INDEX CHARACTERISTICS OF GOAT MILK, ITS YOGHURT AND SALTED YOGHURT

Abstract

Salted yoghurt (SY) is one of the most popular dairy products in Hatay region of Turkey.  It is made of goat milk, and known as ";yoghurt cheese"; or ";winter yoghurt"; due to its high solids content and long shelf life. Two different salting methods are traditionally used in manufacturing the SY: First by direct salting to the yogurt, and second by salting to whey removed yogurt before boiling. The SYs were manufactured using the direct salting method to compare the differences between the two salting methods in chemical parameters and changes in color values during salted yoghurt processing with reference to the original milk. Chemical composition and parameters such as total solids, fat, ash, salt and pH of the products were evaluated. The color characteristics of the samples were measured by the Minolta Chroma Meter CR-400 (Minolta Co., Ltd, Japan). Results showed that the mean chemical composition and indices of the original goat milk, regular yoghurt and SY were: total solids (%) 12.2, 12.0 and 31.9; total fat (%) 4.40, 4.20 and 10.20; ash (%) 0.58, 0.60 and 2.26; pH 6.53, 3.67 and 3.77, respectively. The slight decreases in total solids and fat contents of the regular yogurt may be due to the water from the yoghurt culture, where one-day old yogurt was used as starter culture. SY has substantially (P<0.001) higher fat and total solids contents compared to the original milk and regular yogurt, while pHs of both yogurts significantly (P<0.01) lower than that of original milk. Color values of the goat milk, regular yoghurt and SY were: L 85.2, 90.19, 92.07; a -3.38, -3.37, -7.33 and b 7.76, 7.33, 14.72, respectively. The mean L-value, lightness, was the lowest in milk. The a-value, an indicator of green color, was higher for milk and regular yoghurt. Yellowness (b-value) index was the highest in SY. The characteristics of color analysis revealed that yellowness increased two-fold during cooking of the yoghurt, and greenness decreased two-fold during cooking in comparison with those of regular yoghurt and milk samples. These color changes may be attributable to the caramelization of carbohydrates in the milk.