T3-06 Isothermal Inactivation of Salmonella and Enterococcus faecium in Dates Impacted by Water Activity Variation at Elevated Temperature

Monday, August 1, 2016: 9:45 AM
241 (America's Center - St. Louis)
Shuxiang Liu, Washington State University, Pullman, WA
Roopesh Syamaladevi, Washington State University, Pullman, WA
Mei-Jun Zhu, Washington State University, Pullman, WA
Juming Tang, Washington State University, Pullman, WA
Introduction: Temperature and water activity (aw) are highly affecting the thermal inactivation efficiency of microorganisms in low-moisture foods; however, the influence of aw at elevated temperatures on thermal resistance of Salmonella and its surrogate Enterococcus faecium (E. faecium) in dates is not yet available.

Purpose: (1) To compare thermal resistance of E. faecium with a Salmonella Enteritidis PT30 (Salmonella PT30) on date surfaces in the same thermal treatments, and (2) to understand the relationship between temperature-induced changes in aw and thermal resistance of Salmonella.

Methods: Dates were inoculated with E. faecium or Salmonella PT30 and equilibrated to different aw, 25°C (0.30, 0.45 and 0.60±0.02) to establish 8.5±0.1 CFU/piece. The samples were vacuum-sealed in thin plastic bags, heated isothermally at 75, 80 and 85°C, cooled after treatment, and enumerated to obtain D-values. Equilibrium water sorption isotherms (moisture content vs. aw) for dates at 20 to 80ºC were generated using a vapor sorption analyzer and a thermal cell with relative humidity sensor, and compared using ANOVA.

Results: E. faecium showed equal or higher thermal resistance than Salmonella PT30 at all aw levels (e.g., at aw,25°C=0.45±0.02, 80°C, DE. faecium=4.22±0.72 min, DSalmonella PT30 =2.60±0.42 min). A flat isotherm curve was observed for dates below aw,25°C=0.5, indicating constant moisture content and same aw at elevated temperatures. It may explain the statistically same D85°C with different initial aw (e.g. DE. faecium, aw,25°C=0.30=1.64±0.86 min, and DE. faecium, aw,25°C=0.45=1.60±0.80 min).

Significance:  Improved understanding of the relationship between temperature-induced changes in aw of dates and the thermal resistance of Salmonella and E. faecium is critically important in designing and validating thermal processing for ensuring dates' safety.