Survivability of Escherichia Coli in Commercial Powder Goat Milk during Four Months Storage at Two Different Temperatures

Abstract

Bacteria in low moisture environments are not favorable for growth, but can survive and cause a possible food safety risk for consumers. A study was conducted to evaluate survivability of Escherichia coli and storage stability of commercial powdered goat milk (PGM) products. Three batches of whole milk PGM samples were purchased at a local outlet, and divided into two halves to assign non-inoculated control and E. coli inoculated groups, then stored at 4 and 22°C for 0, 2, and 4 months. Results showed that significant reduction (P<0.05) in E. coli counts occurred at 22°C treatment group by more than 2 log CFU/g at 2 months storage, then further decreased by an additional 0.37 log CFU/g at 4 months storage. The survival of E. coli was significantly higher at 4°C, suggesting that E. coli could survive better at 4°C by extending a longer latent period than at higher temperature (22°C) under the low water activity condition. E. coli counts had negative correlations with water activity at both temperature treatments for all three storage periods except for 0 and 2 months at 22°C, indicating that the survivability of the E. coli would decrease in powdered whole goat milk for 4 months of storage because of decrease in water activity. It was concluded that Escherichia coli survival and storage stability of the commercial PGM products were significantly (P<0.05) affected by storage temperature and time.