Testing for total bacteria in dairy powder - Comparison of test incubation temperatures (a case study)

Abstract

The dairy industry uses the aerobic plate count (APC) to enumerate mesophiles (30 °C) and thermophiles (55 °C). However, there are some dairy-associated bacteria with optimal growth outside the temperature range used. Seventy milk powder samples were tested for APC at 30, 37, 55 and 65 °C. There was no significant difference (p > 0.05) between the number of bacteria capable of growth at 30 and 37 °C in all samples. However, bacterial growth at 55 °C (1.78 log cfu g−1) was significantly higher (p < 0.05) than growth at 65 °C (1.54 log cfu g−1). Bacillus licheniformis was found to be the dominant bacterium in the dairy powder samples when testing was done at 30 and 37 °C. Geobacillus stearothermophilus and Anoxybacillus flavithermus were found to be dominant in dairy powder samples when tested at 55 and 65 °C. These results indicate that the current testing temperatures are satisfactory.