Microbiological and Physicochemical Characteristics of Sheep Milk Heated with Charcoal, Gas and Microwave

Aims: This investigation was conducted to study the effect of heat treatment on the physicochemical and microbiological characteristics of sheep milk.

Methodology: Samples were collected from different farms in Shambat, Khartoum State. Raw sheep milk was heated using charcoal, gas and microwave at 99°C/12 min, then cooled to 4°C and stored for 10 days. Physicochemical and microbiological characteristics were determined at 1, 3, 7 and 10-day intervals.

Results: Milk treated with charcoal had higher values for all physicochemical characteristics except lactose and acidity which were higher in milk treated with microwave. The storage period significantly affected all physicochemical characteristics except protein and ash contents. Total viable bacteria (TVB) and lactobacilli counts were significantly higher in milk treated with charcoal and gas. During the storage period, total viable bacterial and lactobacilli counts significantly increased towards the end. The identification of bacteria of the genus level revealed that Streptococcus, Enterococcus, Staphylococcus and Bacillus were found during storage.

Conclusion: The method of heating milk significantly affected fat, protein, total solids [TS] contents, TVB and lactobacilli counts, while the storage period significantly affected all physicochemical and microbiological characteristics of milk except protein and ash contents. The genera Staphylococcus, Bacillus and Enterococcus were identified. The results indicated that gas and microwave heating of milk resulted in the reduction of the nutritive value of milk, although milk from these two methods was safer to the consumer.