4.7 Article

Thermal inactivation kinetics of Salmonella and Enterococcus faecium NRRL B-2354 on dried basil leaves

Journal

FOOD MICROBIOLOGY
Volume 96, Issue -, Pages -

Publisher

ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD
DOI: 10.1016/j.fm.2020.103710

Keywords

Validation; Spices; Surrogate; Thermal lethality; Low moisture food; Salmonella

Funding

  1. National Institute of Food and Agriculture, U.S. Department of Agriculture [2015-68003-23415]

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This study aimed to investigate the effect of water activity on thermal inactivation of Salmonella in dried basil leaves and evaluate Enterococcus faecium as an appropriate surrogate for Salmonella. The results indicated that the log-linear model fits well for thermal inactivation data, while the modified Bigelow model is better for fitting the D-values.
The enhanced heat resistance of Salmonella developed at low water activity makes it a serious challenge to eliminate them during thermal processing. The objectives of this research are to (i) investigate the effect of water activity on thermal inactivation of Salmonella cocktail (Agona, Tennessee, Mbandaka, Montevideo, and Reading) in dried basil leaves, and (ii) evaluate Enterococcus faecium NRRL B-2354 as an appropriate surrogate for Salmonella in dried basil leaves. Dried basil leaves, inoculated with a Salmonella cocktail and E. faecium separately, were equilibrated to different water activities (a(w): 0.40, 0.55, and 0.70) in a humidity-controlled chamber. The basil samples were packed (1.6 +/- 0.1 g) in aluminum pouches and thermally treated at 70, 75, and 80 degrees C using a dry heating method for 0-180 min to obtain the thermal death curve. The microbial survival data was fit using two primary models (Log-linear and Weibull model). Results from AIC(c) showed that the log-linear model fits well for thermal inactivation of both microorganisms. As the a(w) decreases from 0.70 to 0.40 at 75 degrees C, the D-value increases from 3.30 to 9.14 min for Salmonella and 6.53 to 14.07 min for E. faecium. Based on the AIC(c) values, the modified Bigelow model fits the D-values better than the response surface model for both the microorganisms. The kill ratio of surrogate to pathogen ranged from 1.4 to 2.8, indicating that it is a conservative surrogate for Salmonella for performing validation of the thermal pasteurization process. The identification of suitable surrogate and development of modified Bigelow model will help the spice industry in developing the thermal processes for improving the safety of basil leaves.

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