Effect of Source of Heat and Storage Period on Physicochemical and Microbiological Characteristics of Goat Milk

Abstract

This investigation was conducted to evaluate the effect of heat treatment of goat milk with charcoal, gas and microwave on the physicochemical and microbiological characteristics during the storage period. Raw goat milk was heated with char- coal, gas and microwave at 99°C for 12 min followed by storage at 4°C for 10 days. Physicochemical and microbiological characteristics were determined at 1, 3, 7 and 10-day intervals. The results showed a significant effect of source of heat on the physicochemical characteristics under study except fat content and pH. The highest protein (3.62%), lactose (4.97%) and solids-non-fat (SNF) (9.31%) contents were high in milk heated with charcoal, while fat (5.68%) and total solids (TS) (14.26%) contents were high in milk treated with microwave and the acidity (0.19%) was high in milk treated with gas. The total viable bacteria (TVB) and lactic acid bacteria (LAB) were significantly (P<0.001) higher (log 2.31 cfu/ml and log 2.26cfu/ml, respectively) in milk heated with charcoal. The protein, TS, lactose, SNF and acidity increased during the stor- age period, while fat and ash decreased. TVB and LAB increased during the storage period. Bacillus and Staphylococcus genera survived the heat treatment and were isolated in heated milk till day 7 of the storage period, and then Staphylococcus was not detected at day 10.