Inactivation of Salmonella, Listeria monocytogenes and Enterococcus faecium NRRL B-2354 in a selection of low moisture foods Grzegorz Rachon MSc1, Dr Walter Peñaloza2 and Dr Paul A. Gibbs1 Leatherhead Food Research, Randall’s Road, Leatherhead, Surrey KT22 7RY; 2 Nestlé Research Center, Lausanne, Vers-Chez-Les-Blanc, 1000 Lausanne 26, Switzerland
Introduction Low moisture foods cannot support microbial growth. But, they have significantly contributed to the number of food-borne infections and outbreaks. • Public Health England reported 6,334 Salmonella gastrointestinal-infection cases in 2016. • RASFF (Rapid Alert System for Food and Feed) reported 457 alerts of Salmonella in 2016, 11% were related to low moisture foods and 17% related to feed and pet food. • The alerts of Listeria were 82 in 2016 with only two related to low moisture food (dried pork meat and sausages).
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Figure 1. RASFF number of intestinal infections related to Salmonella contamination in low moisture food in past 10 years.
The Salmonella notifications in low moisture foods indicate that current practices of harvesting, drying and primary processing are not efficacious to control the Salmonella risk or are not correctly implemented. Attention should therefore be focused on better understanding the ability of pathogens to survive in low moisture foods during both storage and validation of control measures to eliminate food-borne pathogens in ready to eat products. Purpose • Obtain survival and heat resistance data of Salmonella, Listeria monocytogenes cocktails and the surrogate Enterococcus faecium (NRRL B-2354) in low moisture foods (confectionery formulation, chicken meat powder, and savoury seasoning) during storage. • Test the Weibull model to express inactivation data and precisely calculate the minimum heating to achieve 5 log reduction.
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Figure 2. D80 of Salmonella (■), L. monocytogenes (■) and E. faecium NRRL B-2354 (■) in 2A; confectionery formulation, 2B; chicken meat powder, 2C; pet food and 2D savoury seasoning during 21 day storage. 3B 0.0
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Figure 3. Inactivation curves (-) and Weibull Model (-). Downward concave (3A; Salmonella in seasoning at 120˚C), upward concave (3B; Salmonella in confectionery formulation at 100˚C), (-) temperature. Calculated time required for 5log reduction 70°C
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TIME REQUIRED FOR 5 LOG REDUCTION (MIN)
Results • Salmonella, L. monocytogenes and E. faecium NRRL B-2354 survived very well at 16˚C for 21 days in all low moisture foods. • Overall, the D80 values remained stable during the 21 days of storage (Figure 2). • Inactivation trend in the low moisture foods was not log-linear (Figure 3). • The Weibull prediction was useful by including inactivation during the come up time and calculating more accurately the heating time for a 5 log reduction. • The surrogate E. faecium NRRL B-2354 for Salmonella and Listeria inactivation was suitable for low moisture foods except the sugar-containing confectionery formulation, where surrogate heat resistance was lower than Salmonella at the various temperatures (Figure 4).
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Methods • Dry foods were inoculated with 1% v/w of cell slurry inoculum. • Storage of inoculated samples was at 16˚C for 21 days (temporary storage before processing). During storage the D80 was determined. • The inactivation of each organism was evaluated in each low moisture food heated in thermal cells at various temperatures 70 - 140˚C. • The Weibull model was used to fit the inactivation data and calculate the minimum heating to achieve 5 log reduction.
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P1 - Confectionery powder; aw=0.565
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P2 - Culinary powder; aw=0.655
E.faecium Salmonella L. mono
P3 - Chicken meat powder; aw=0.383
E.faecium
P4 - Pet food powder; aw=0.653
Figure 4. Heating time required for 5 log reduction of Salmonella, L. monocytogenes and E. faecium NRRL B-2354 in confectionery formulation, chicken meat powder, pet food and savoury seasoning.
Salmonella, L. monocytogenes were inactivated by heating to 112˚C solid foods in sealed thermal cells. E. faecium NRRL B-2354 was a suitable surrogate in low moisture foods except confectionery powder (containing over 60 % sugar and carbohydrates). For further information please contact Grzegorz Rachon, E:
[email protected] or
[email protected]
