Purpose: The objectives of this work were to assess homogeneity, stability and thermal resistance of Enterococcus faecium atomized into ground black pepper and oat flour over a 42-day storage period.
Methods: Plate harvested cells (10 mL) were atomized onto black pepper and oat flour (1000 g) using a Sonic Model CV24 ultrasonic atomizer to achieve an initial inoculum level of approximately 8 log CFU/g. The inoculated matrices were kept in a 32% relative humidity chamber at ambient (23±2ºC) temperature. Triplicate samples of each matrix were obtained throughout the 42 day storage period to evaluate stability and thermal resistance of E. faecium. Thermal resistance was evaluated by immersing aluminum test cells containing the food matrices in an oil bath. Differences between treatments were verified with a two-tailed t-test.
Results: Initial E. faecium populations in black pepper and oat flour were 7.93 (± 0.13) and 8.08 (± 0.19) log CFU/g, respectively and after 42-days storage, were 7.88 (± 0.10) and 8.12 (± 0.12) log CFU/g, respectively (p-value > 0.05).The D85ºC-value for the organism decreased from 2.59 minutes to 2.26 minutes after 42 days of storage of inoculated black pepper, and decreased from a D90ºC-value of 2.58 minutes to 2.37 minutes after storage of inoculated oat flour (p-value > 0.05). There were no statistical differences in the stability and thermal resistance of E. faecium in black pepper and oat flour after the 42-day storage period.
Significance: Atomization of E. faecium into food matrices creates homogenous and stable test samples for use in validation of preventative controls for low water activity foods.