Microbiological quality of pasteurized milk and stirred yoghurt during the stages of processing

The study was conducted to evaluate the microbiological quality of pasteurized milk and stirred yoghurt during the processing stages.  Pasteurized milk and stirred yoghurt were manufactured in a dairy plant and subjected to microbiological analyses, in addition to analyzing the air, personal swabs, and processing water. The results indicated that total viable bacteria count (TVBC) was highest (log₁₀ 5.02 cfu/ml) in the raw milk and lowest (log₁₀ 1.72 cfu/ml) in the buffer stage of processing.  E. coli count was highest (log₁₀ 4.54 cfu/ml) in raw milk and lowest (log₁₀ <1 cfu/ml) in the subsequent stages of processing. E. coli was detected in the mixing stage of yoghurt (log₁₀ 0.66 cfu/gm) and lowest (log₁₀ <1 cfu/gm) in the subsequent stages, while yeast and mould count was log₁₀ <1 cfu/gm in all stages.  TVB and yeast and mould counts were highest (log₁₀ 1.68 cfu/m² and log₁₀ 1.02 cfu/m², respectively) in the processing area and lowest (log₁₀ 1.42 cfu/m² and log₁₀ 0.68 cfu/m², respectively) in the laboratory.  TVBC was log₁₀ 0.92 cfu/m² and log₁₀ 0.79 cfu/m² in the swabs from operators and labours, respectively, while the count of E. coli and yeasts and moulds was log₁₀ <1 cfu/m².  There was a significant effect of water source on the total dissolved solids, pH, total hardness, and TVBC, while E. coli and yeast and mould counts were log₁₀ <1 cfu/ml. The study concluded that the pasteurized milk and stirred yoghurt were microbiologically acceptable and safe for human consumption because the processing conditions in the plant were acceptable.