Heat resistance of Listeria monocytogenes strains V7 and Scott A in chicken gravy and changes in heat resistance during refrigerated storage were studied. After chicken gravy was made, it was cooled to 40°C, inoculated with 105 CFU L. monocytogenes per ml of gravy, and then stored at 7°C for 10 d. Gravy was heated at 50, 55, 60, and 65°C immediately after inoculation and after 1, 3, 5, and 10 d of refrigerated storage. The D values for strains Scott A and V7 in gravy heated at 50°C at day 0 were 119 and 195 min and at day 10 they were 115 and 119 min, respectively, whereas at 65°C comparable values at day 0 were 0.48 and 0.19 min and at day 10 they were 0.014 and 0.007 min. Heat resistance (expressed as D values) was greater at day 0 than at the end of refrigerated storage. The z values ranged from 3.41 to 6.10°C and were highest at the early stages of chill storage and then decreased at the later stages. Strain V7 was more heat resistant than Scott A at 50°C. Strain Scott A always had a higher z value than did strain V7 at the same storage interval. A heat treatment greater than the 4-D process recommended by the U.S. Department of Agriculture was required to inactivate the large numbers of L. monocytogenes that developed in chicken gravy during refrigerated storage.
Survival of Listeria monocytogenes in chicken gravy during processing by the cook‐chill method was studied because this pathogen is of major concern in the safety of refrigerated foods in foodservices. Cooked gravy (70 to 77C) was poured into 1.9, 3.8 or 5.7L. pans and refrigerated at 7C. When cooled to 40C, gravy was inoculated with L. monocytogenes strain Scott A to give ca. 104 CFU/ml. Samples (59.1 ml) were taken every 6 h. during the first 24 h, then once a day for the subsequent 11 days and numbers of L. monocytogenes were determined. Time required to cool 1.9, 3.8 and 5.7 L. of gravy from 70–77C to 7C averaged 12, 20 and 26 h, respectively. Populations of L. monocytogenes ranged from 1.0 × 105 to 3.2 × 106 CFU/ml after 24 h of refrigeration and growth rates in different volumes of gravy were significantly (P < .001) different. Maximum growth (≥ 108 CFU/ml) of L. monocytogenes was reached 4 to 6 days after inoculation, depending on the volume of gravy. The population remained at 108–109 CFU/ml during the rest of chilled storage. There was no decrease in populations of L. monocytogenes even after extended refrigerated storage of the gravy. Hazardous conditions can occur easily if cooling and storage conditions in an actual foodservice operation are similar to those used in this study.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.