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Modeling the effect of temperature and water activity on thermal resistance of Salmonella in dairy powders.

X. Wei




Modeling the effect of temperature and water activity on thermal resistance of Salmonella in dairy powders.
X. Wei*1, B. Chaves1, M.-G. Danao1, S. Agarwal3, J. Subbiah2. 1University of Nebraska Lincoln, NE, 2University of Arkansas Fayetteville, AR, 3Mars Wrigley Chicago, IL.

Salmonella persistence in dairy powders has caused several foodborne outbreaks. The selection of pasteurization processing conditions requires determination of the thermal inactivation kinetics of Salmonella in dairy powders. The objectives of this study were to 1) determine the thermal inactivation kinetics of dairy powders at different fat content and water activity (aw); 2) evaluate multiple models for describing the effect of temperature, aw, and fat content on inactivation of Salmonella in dairy powders. Two types of dairy powders, nonfat dry milk (0.62% fat content, wt/wt) and whole milk powder (29.46% fat content) were inoculated with a 5-strain Salmonella cocktail and equilibrated to 3 aw levels (0.10, 0.20 and 0.30) for the isothermal treatment at 75, 80 and 85�C to obtain the D- and z-values. Response surface and modified Bigelow models were used to fit the collected data. The thermal resistance of Salmonella significantly increased (P < 0.05) as aw decreased, which suggested that a higher temperature or longer processing time would be required to achieve the desired inactivation of Salmonella at lower aw. Fat content did not have a significant impact on thermal inactivation kinetics and therefore, data from both dairy powders were pooled to develop a combined model. Response surface model was compared with modified Bigelow model. Modified Bigelow model performed well to predict D-values (root-mean-square error (RMSE) = 1.47 min) and log reductions (RMSE = 0.47 log cfu/g), when compared with the response surface model (RMSE = 1.61 min and 0.48 log cfu/g). This study provides guidance to the dairy industry to understand the influence of temperature and aw on the thermal inactivation of Salmonella in dairy powders and identify the proper temperature and time combinations for the development and implementation of the pasteurization process to ensure food safety.

Keywords: modified Bigelow model, response surface model, D and z values.

Biography: Xinyao Wei is currently a Ph.D. Candidate in the Food Science and Technology graduate program at the University of Nebraska-Lincoln and is being co-advised by Dr. Jeyamkondan Subbiah and Dr. Mary-Grace Danao. His main research interests lie in the enhancing implementation of pasteurization technologies for improving low moisture food safety. To date, he has published six papers in peer-reviewed journals (Journal of Food Protection, Food Control, Food Microbiology, Journal of Food Science) and was lead author in three of these papers. He is certified in HACCP, Food Defense Awareness, and Preventive Controls for Human Food