Effectiveness of thermal treatment on the bacterial spore counts in milk

Abstract

Untreated milk cannot be kept for long time due to microbial spoilage. The spore-formers are major contaminants as it significantly affects the shelf-life, quality, and wholesomeness of milk, which is treated with heat at different levels. Mesophilic and thermophilic spores can survive even post treatment. The comparison between the spore counts under different heating methods was performed on samples of different suppliers. 110 samples from six points were collected to analyze the effect of thermized and ultra-high temperature (UHT) on the spores. Samples were heated at 80 0C for 10 minutes to inactivate the vegetative cells. Plate Count Agar (PCA) was formulated and mesophilic spores were incubated at 30°C for 48 hours, while the Petri dishes for counting thermophilic spores were incubated at 55°C for 48 hours. Incubated culture plates were enumerated for spore-forming bacterial colonies. High heat resistant spores (Sporothermodurans) were not detected on milk of four suppliers. A significant difference (p<.0.05) was found to be among the spore counts of both thermophilic and mesophilic of raw, thermized and UHT milk. The reduction of spore-formers after thermization was higher on thermophilic than mesophilic. The study revealed that the most effective method for reduction of spore-forming bacteria was UHT