P2-07 Evaluation of Thermal Resistance of Salmonella Enteritidis PT30 and Enterococcus faecium NRRL B-2354 in Wheat Flour and Peanut Butter Using TAC and TDT Cell

Tuesday, August 2, 2016
America's Center - St. Louis
Jie Xu, Washington State University, Pullman, WA
Roopesh Syamaladevi, Washington State University, Pullman, WA
Shuxiang Liu, Washington State University, Pullman, WA
Ravi Kiran Tadapaneni, Washington State University, Pullman, WA
Juming Tang, Washington State University, Pullman, WA
Mei-Jun Zhu, Washington State University, Pullman, WA
Shah Devendra, Washington State University, Pullman, WA
Introduction: Salmonella outbreaks in low-moisture foods have created great concerns among consumers, research communities and food processing industry. Enterococcus faecium NRRL B-2354 is considered to be an effective surrogate microorganism for Salmonella Enteritidis PT30 in validating thermal processing technologies and systems. This research evaluated two factors, namely, food composition and water activity (aw) on the thermal resistance of Salmonella Enteritidis and E. faecium in two food models.

Purpose: Using wheat flour and peanut butter as separate model food products inoculated with either Salmonella Enteritidis or E. faecium: A) Assess inactivation kinetics with aw=0.45±0.05 at 80 ℃; B) Determine and compare D80, 0.45 values by using two types of test cells (TDT and TAC cells); C) Explore and find factors (water activity, food types) that influence thermal resistance; D) Identify desorption isotherms (aw changes with temperature) which influence thermal resistance.

Methods: Organic wheat flour (carbohydrate rich) and peanut butter (oil rich) were inoculated separately with Salmonella Enteritidis and E. faecium culture (1010 CFU/ml), and conditioned to aw 0.45 with final bacterial populations 108 CFU/g after equilibration. Inactivation studies were conducted at 80℃ using TAC and TDT cells in parallel. The TAC cell was able to maintain a constant aw, while the TDT cell maintained a constant sample moisture content, allowing the elevation of aw during the heating treatment.

Results: In wheat flour, D80, 0.45 values (4.25±0.45 min for Salmonella Enteritidis, and 5.56±0.49 min for E. faecium) by using TDT cells were significantly lower than those (7.28±1.17 min for Salmonella Enteritidis, and 9.96±1.06 min for E. faecium) by using TAC cells; in peanut butter, D80, 0.45 values were similar irrespective of the test cells used (TDT: 6.84±0.46 min, TAC: 8.03±0.68 min for Salmonella Enteritidis; TDT: 36.12±1.17min, TAC: 37.42±1.68 for E. faecium).

Significance: Water activity (aw) and food type are essential factors influencing the thermal resistance of bacteria. Such factors should considered in further thermal inactivation studies and validation for industrial applications.