Purpose: This study was undertaken to determine the presence and survival of pathogens of importance in selected low aw foods.
Methods: Sixty household low aw foods were examined for the presence of selected pathogens using conventional methods and a simulative study was conducted using a high sugar, low aw macadamia butter to determine the survival of Bacillus cereus and Staphylococcus aureus ATCC 25923.
Results: Results obtained from 60 low aw household samples had some significant differences (P≤ 0.05) within food categories. There were no significant differences (P≥0.05) amongst the different food groups; except for spices and nuts, which had significant differences in their colony counts compared to those of other food categories. Spices had the highest number of aerobic bacteria, aerobic sporeformers, anaerobic sporeformers and S. aureus. Mean aerobic colony counts for nuts and spices were 2.30 log CFU/g and 4.40 log CFU/g, respectively. Pathogens such as Escherichia coli and Cronobacter sakazakii were present in nuts, whilst Salmonella spp. were present in chocolates. In the simulative study, temperature and high sucrose concentrations played a significant role in the survival of B. cereus and S. aureus. Bacillus cereus was found to be more osmotolerant at both reduced and elevated temperatures (18 to 25°C) in the butter samples with 12% sucrose; whilst, S. aureus seemed to grow better in sucrose free samples at both temperatures. After 28 days of storage of 20% sucrose sample, S. aureus was not detected and there was four-log reduction of B. cereus.
Significance: This work implied that certain low aw foods may present a public health risk. The simulated work also signified that B. cereus, being a spore forming bacterium, can be osmotolerant at both reduced and elevated temperatures.