Survivability of Escherichia coli O157:H7 ATCC 43888 and Enterococcus faecium ATCC 8459 in a Hydrocolloid Gel Bar Model and Macronutrient Bar Model in Response to Vacuum Microwave Drying and Storage

This study aimed to investigate the microbial safety of Vacuum Microwave Drying (VMD) and 30 days storage at 25 °C on survivability of Escherichia coli O157:H7 ATCC 43888 and Enterococcus faecium ATCC 8459 in a nutritionally minimal bar model and macronutrient bar model. Sodium alginate hydrocolloid gel bars were inoculated with each microorganism and underwent processing in a 2 kW VMD and subsequent storage at 25 °C for 10 days in sealed bags to determine the impact of VMD on bacteria without the influence of a nutritionally dense food matrix. Additionally, the effects of macronutrient concentration on organism survivability during processing and storage were tested using a peanut butter banana bar formulated to contain high carbohydrate, high protein, or high-fat content. The macronutrient bars were inoculated with each microorganism and underwent VMD with subsequent storage at 25 °C for up to 30 days in sealed bags. Results of the hydrocolloid gel model showed that in a nutritionally minimal food matrix, both microorganisms were susceptible to VMD with additional loss of each microorganism during storage. Results showed the entire loss of E. coli O157:H7 by day 10 of storage. In the macronutrient bar study, E. faecium had minimal susceptibility to VMD and storage at 30 days while E. coli O157:H7 had minimal susceptibility to VMD with greater susceptibility to storage for 30 days. There was a significant difference (p < 0.05) in log loss comparing E. coli O157:H7 VMD processed and unprocessed bars and minimal significance comparing E. faecium VMD processed and unprocessed bars. Water activity and moisture content at storage timepoints had no observed correlation with pathogen survivability in either study.