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Radiofrequency-assisted thermal process validation of dairy powder considering the effect of storage time.

X. Wei


Radiofrequency-assisted thermal process validation of dairy powder considering the effect of storage time.
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 multistate foodborne outbreaks. Therefore, effective antimicrobial treatments need to be identified and validated to ensure the safety of dairy powders. Because storage time may influence the thermal resistance of Salmonella in dairy powders, this factor needs to be included in the process validation. The objectives of this study were to evaluate the effect of storage time on the thermal resistance of Salmonella in dairy powders; evaluate the suitability of Enterococcus faecium NRRL B-2354 as a non-pathogenic surrogate for Salmonella during thermal processing; and validate radiofrequency (RF)-assisted thermal processing as a suitable pasteurization process to inactivate Salmonella in dairy powders. Nonfat dry milk and whole milk powder were inoculated with a 5-strain Salmonella cocktail or E. faecium NRRL B-2354 and equilibrated to a low water activity (aw) level of 0.10 representing an extreme worst-case scenario (typical aw is 0.20). The samples were stored for 30, 60, and 90 d and decimal reduction values (D-values) were determined at 85�C. D-values were also determined at 90 and 95�C at 30 d of storage to identify the adequate thermal processing time and temperature combination for RF-assisted thermal processing. A custom-designed thermal death sandwich was used to conduct the isothermal treatments. Based on the determined processing conditions, RF heating of dairy powders was conducted in a 6-kW, 27.12-MHz pilot scale parallel plate RF heating system to achieve the target temperature and then transferred to a convective hot air oven for specific holding time. Results showed that storage time did not significantly (P > 0.05) affect the thermal resistance of Salmonella in dairy powders. E. faecium was a suitable surrogate for Salmonella due to its significantly (P < 0.05) higher thermal resistance (D-value) and similar inactivation kinetics during thermal treatment of dairy powders. RF studies are currently being conducted at 85, 90, and 95�C to validate at least a 5-log reduction of Salmonella in dairy powders.

Keywords: surrogate, thermal death time, dielectric heating.

Biography: Xinyao Wei is a Ph.D. 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 the lead author in three of these papers. He is certified in HACCP, Food Defense Awareness, and Preventive Controls for Human Food.