Effect of lactose and milk protein on thermal resistance of Enterococcus faecium NRRL B-2354 and Salmonella in dairy powders

Microbial challenge studies using nonpathogenic surrogates provide a practical means for validating thermally based pathogen controls for low-moisture foods. Because the relative thermal resistance, or kill ratio, of Enterococcus faecium NRRL B-2354 (a nonpathogenic surrogate) to Salmonella is great...

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Main Authors: Ahmad, Nurul Hawa, Marks, Bradley P., Ryser, Elliot T.
Format: Article
Published: International Association for Food Protection 2022
Online Access:http://psasir.upm.edu.my/id/eprint/101118/
https://www.sciencedirect.com/science/article/pii/S0362028X22110781
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spelling my.upm.eprints.1011182023-05-23T08:04:14Z http://psasir.upm.edu.my/id/eprint/101118/ Effect of lactose and milk protein on thermal resistance of Enterococcus faecium NRRL B-2354 and Salmonella in dairy powders Ahmad, Nurul Hawa Marks, Bradley P. Ryser, Elliot T. Microbial challenge studies using nonpathogenic surrogates provide a practical means for validating thermally based pathogen controls for low-moisture foods. Because the relative thermal resistance, or kill ratio, of Enterococcus faecium NRRL B-2354 (a nonpathogenic surrogate) to Salmonella is greatly influenced by food composition, this study assessed relative thermal resistance of a five-strain Salmonella cocktail and E. faecium in skim milk powder (SMP), lactose-free skim milk powder (LSMP), 90% milk protein isolate (MPI), and lactose powder (LP). The impact of sugar composition (lactose versus glucose-galactose) on resuscitation of bacterial survivors, by using SMP and LSMP, was also determined. Dairy powders were inoculated with agar-grown cultures, mixed, preequilibrated at 0.25 water activity (aw), ground to achieve homogeneity, reequilibrated, and subjected to isothermal treatment. After enumeration on nonselective differential media, log-linear and Bigelow models were fit to the survivor data via one-step global regression. The aw changes and glass transition temperature were assessed at elevated temperatures by using uninoculated, equilibrated powder samples. Estimated D90°C-values were approximately two times higher for E. faecium (P < 0.05) than for Salmonella in SMP, LP, and MPI, but statistically similar (P > 0.05) in LSMP. Addition of sugars to recovery media did not influence survivor resuscitation from heat-treated SMP and LSMP, confirming that microbial inactivation was impacted primarily by the thermal treatment, not the recovery step. Thermally induced changes in aw were seen only for LP and MPI, with the glass transition temperature observed only for SMP and MPI. In conclusion, rather than always requiring greater lethality of E. faecium than Salmonella, these findings suggest that sufficient pathogen controls for low-moisture foods can also be validated by thoroughly documenting the appropriate kill ratios of E. faecium to Salmonella. International Association for Food Protection 2022-09-29 Article PeerReviewed Ahmad, Nurul Hawa and Marks, Bradley P. and Ryser, Elliot T. (2022) Effect of lactose and milk protein on thermal resistance of Enterococcus faecium NRRL B-2354 and Salmonella in dairy powders. Journal of Food Protection, 85 (12). pp. 1865-1874. ISSN 0362-028X; ESSN: 1944-9097 https://www.sciencedirect.com/science/article/pii/S0362028X22110781 10.4315/JFP-22-111
institution Universiti Putra Malaysia
building UPM Library
collection Institutional Repository
continent Asia
country Malaysia
content_provider Universiti Putra Malaysia
content_source UPM Institutional Repository
url_provider http://psasir.upm.edu.my/
description Microbial challenge studies using nonpathogenic surrogates provide a practical means for validating thermally based pathogen controls for low-moisture foods. Because the relative thermal resistance, or kill ratio, of Enterococcus faecium NRRL B-2354 (a nonpathogenic surrogate) to Salmonella is greatly influenced by food composition, this study assessed relative thermal resistance of a five-strain Salmonella cocktail and E. faecium in skim milk powder (SMP), lactose-free skim milk powder (LSMP), 90% milk protein isolate (MPI), and lactose powder (LP). The impact of sugar composition (lactose versus glucose-galactose) on resuscitation of bacterial survivors, by using SMP and LSMP, was also determined. Dairy powders were inoculated with agar-grown cultures, mixed, preequilibrated at 0.25 water activity (aw), ground to achieve homogeneity, reequilibrated, and subjected to isothermal treatment. After enumeration on nonselective differential media, log-linear and Bigelow models were fit to the survivor data via one-step global regression. The aw changes and glass transition temperature were assessed at elevated temperatures by using uninoculated, equilibrated powder samples. Estimated D90°C-values were approximately two times higher for E. faecium (P < 0.05) than for Salmonella in SMP, LP, and MPI, but statistically similar (P > 0.05) in LSMP. Addition of sugars to recovery media did not influence survivor resuscitation from heat-treated SMP and LSMP, confirming that microbial inactivation was impacted primarily by the thermal treatment, not the recovery step. Thermally induced changes in aw were seen only for LP and MPI, with the glass transition temperature observed only for SMP and MPI. In conclusion, rather than always requiring greater lethality of E. faecium than Salmonella, these findings suggest that sufficient pathogen controls for low-moisture foods can also be validated by thoroughly documenting the appropriate kill ratios of E. faecium to Salmonella.
format Article
author Ahmad, Nurul Hawa
Marks, Bradley P.
Ryser, Elliot T.
spellingShingle Ahmad, Nurul Hawa
Marks, Bradley P.
Ryser, Elliot T.
Effect of lactose and milk protein on thermal resistance of Enterococcus faecium NRRL B-2354 and Salmonella in dairy powders
author_facet Ahmad, Nurul Hawa
Marks, Bradley P.
Ryser, Elliot T.
author_sort Ahmad, Nurul Hawa
title Effect of lactose and milk protein on thermal resistance of Enterococcus faecium NRRL B-2354 and Salmonella in dairy powders
title_short Effect of lactose and milk protein on thermal resistance of Enterococcus faecium NRRL B-2354 and Salmonella in dairy powders
title_full Effect of lactose and milk protein on thermal resistance of Enterococcus faecium NRRL B-2354 and Salmonella in dairy powders
title_fullStr Effect of lactose and milk protein on thermal resistance of Enterococcus faecium NRRL B-2354 and Salmonella in dairy powders
title_full_unstemmed Effect of lactose and milk protein on thermal resistance of Enterococcus faecium NRRL B-2354 and Salmonella in dairy powders
title_sort effect of lactose and milk protein on thermal resistance of enterococcus faecium nrrl b-2354 and salmonella in dairy powders
publisher International Association for Food Protection
publishDate 2022
url http://psasir.upm.edu.my/id/eprint/101118/
https://www.sciencedirect.com/science/article/pii/S0362028X22110781
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