Thermal inactivation kinetics of Salmonella and Enterococcus faecium NRRL B-2354 on dried basil leaves. (June 2021)

• Record Type: Journal Article
• Authors: Verma, Tushar; Chaves, Byron D.; Howell, Terry; Subbiah, Jeyamkondan
• Is Part Of: Food microbiology. Volume 96(2021)
• Publication Date: 2021-06
• Subjects: Validation -- Spices -- Surrogate -- Thermal lethality -- Low moisture food -- Salmonella; Food Microbiology -- Periodicals; Aliments -- Microbiologie -- Périodiques; Food -- Microbiology; Periodicals; Food -- Microbiology -- Periodicals; Food contamination -- Periodicals; 664.001579
• DOI: 10.1016/j.fm.2020.103710
• Languages: English
• ISSNs: 0740-0020

Abstract

Abstract: 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 (aw : 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 °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 AICc showed that the log-linear model fits well for thermal inactivation of both microorganisms. As the aw decreases from 0.70 to 0.40 at 75 °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 AICc 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. Highlights: Thermal resistance of Salmonella and E. faecium increased with decrease in aw . Log-linear model fitted the thermal inactivation data better than Weibull model. Modified Bigelow model fitted better than the RSM for both microorganisms. Modified Bigelow model can predict the D -value at different aw and temperatures. E. faecium was found to be a conservative surrogate for Salmonella.