Physicochemical Characteristics of Functional Goats? Milk Yogurt as Affected by some Milk Heat Treatments

摘要

Background: The use of milk with particular nutritional properties as goats? milk alone or in combination with bacterial strains having probiotic properties represents one of the technology options for manufacturing new dairy functional products. Objective: This study aimed to study the possibility of preparation and properties of functional goats' milk yogurt using commercial yogurt and probiotic starter cultures for enhancing nutritional and functional values of these products with the emphasize on the effect of different heat treatment of the milk use in the manufacture on the physico chemical properties and sensory quality attributes during storage, in attempts to achieve a goats? milk yogurt that was typical of yogurt product as potentially functional dairy foods. Materials and Methods: Functional Goats? Milk Yogurt (FGMY) were made from goats? milk thermally treated at 63, 85 and 95°C for 30 min, whereas the control was pasteurized on 72°C for 15 sec, using Yo-Fast 1 ( Lactobacillus delbrueckii ssp., bulgaricus and Streptococcus thermophilus ) and ABT-2 ( Lactobacillus acidophilus , Streptococcus thermophilus and bifidobacteria) as yoghurt and probiotic starters, respectively used for the fermentation process. The physicochemical, sensory properties as surviving starter microorganisms were followed in yogurt during storage period (9 days at 6±0.5°C). Results: Goats? milk yogurt treatments differed (p≤0.05) in their properties; depending on heat treatment s, type of starter used and storage period. Results showed that, the effect of goats? milk heat treatment on the chemical composition of the resultant products was more pronounced than the type of starter culture. Meanwhile, the control sample was characterized by the highest index of syneresis and this index was decreased while, firmness of curd and dynamic viscosity increased in all treatments till the end of storage period. Also, the treatments made with Yo-Fast 1 showed higher total solids, protein and ash contents but lower carbohydrate content, pH and dynamic viscosity values than those made with probiotic starter. Also, S. thermophilus were the most prevalent viable microorganisms in all treatments while bifidobacteria cells showed the lowest counts. The counts of viable cells in all FGMY were maintained at an acceptable level to be considered as functional foods until the end of storage period. In terms of yogurt preference, sensory evaluation showed that all yogurt treatments were accepted by the panelists. Conclusion: In conclusion, the highest thermally treated goats? milk used in the manufacture yogurt treatments had good significant impact on the physio chemical properties , with higher dynamic viscosity values, lowest whey separation and strong curd compared with other treatments as well as the control throughout storage period especially when fermented with probiotic starter and could be considered as product with functional properties and health benefits.