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Enhancing Food Safety Through Control of Food-Borne Disease Agents

Harris, Linda
University of California - Davis
Start date
End date
  1. Pre-harvest reduction of food-borne pathogens in animals and the environment.
  2. Chemical and physical decontamination in food processing plant environments.
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NON-TECHNICAL SUMMARY: In recent years, fresh fruits and vegetables have increasingly contributed to the annual burden of foodborne illness in the U.S. This project examines routes of contamination of fresh fruits, vegetables, and tree nuts with foodborne pathogens and evaluates potential intervention strategies for reducing contamination.

APPROACH: Standardized methods developed elsewere for inoculation and recovery of foodborne pathogens into soils, and onto intact fresh fruits and vegetables and tree nuts will be used to 1) evaluate the behavior of foodborne pathogens in soils used to produce fresh produce and tree nuts under a variety of production management strategies and in a variety of soil types; 2) understand the behavior of foodborne pathogens inoculated onto fresh produce and tree nuts and onto food processing equipment using conditions that are typical for these products; 3) assess the efficacy of standard and novel chemical and physical decontamination methods for produce, nutmeats, and food processing equipment .

PROGRESS: 2000/10 TO 2006/09
A 2000/2001 outbreak of salmonellosis was associated with consumption of raw almonds. The objectives of this study were to determine the potential for growth of the outbreak strain Salmonella Enteritidis PT 30 in hull or shell slurries and to evaluate survival of S. Enteritidis PT 30 on wet almond hulls during drying. Both hull and shell slurries supported rapid growth of S. Enteritidis PT 30 at 24C; slurries containing hulls also supported growth at 15C. Maximum levels of 6.2 to 7.8 log CFU/ml were observed. Reductions of 1 to 3 log CFU/g of dry hull were observed during drying; reductions generally declined as incubation time increased. The data provide evidence that wet almonds may be a greater risk for high levels of Salmonella. These data among others were used to develop a quantitative microbial risk assessment of salmonellosis from consumption of raw almonds accounting for factors that can occur after almonds reach the processor. The risk associated with the consumption of raw almonds was estimated, as well as the risk reduction associated with almonds treated with a theoretical 5-log process or treated with propylene oxide (PPO) using a standard commercial process. Probability distributions were chosen to describe the chance of almond contamination, and the effects of storage time, storage temperature, and processing from currently available data. The application of a commercial PPO treatment reduced this risk to 0.01%. Hypothetical 5-log processes with different standard deviations (1, 0.5, 0.1, and 0) reduced the chance of predicted cases of salmonellosis per year to 0.69, 0.35, 0.30, and 0.21%, respectively. These results estimate that the risk of one or more U.S. cases of salmonellosis per year from consumption of raw almonds can be reduced from 78% to less than 1% by using a process achieving a 5-log reduction in Salmonella with a process standard deviation as large as 1 log, or by using a commercial PPO treatment. In a separate study, effects of whey protein isolate (WPI) coatings incorporating a lactoperoxidase system (LPOS) on the inhibition of Salmonella enterica and Escherichia coli O157:H7 on roasted turkey were studied by testing initial inhibition, as well as inhibition during storage. LPOS-WPI coatings with 7% and 4% of LPOS demonstrated initial 3- and 2-log CFU/g reductions of S. enterica and E. coli O157:H7, respectively. The antimicrobial effect was observed regardless of whether the turkey was inoculated before or after coating. Storage studies (5 (coating) and 3% (spreading) (w/w) LPOS) were conducted for 42 days at 4C and 10C. LPOS-WPI coatings inhibited the growth of both S. enterica and E. coli O157:H7 in turkey at both 4C and 10C for 42 days. The inhibition was more pronounced when the coating was formed on the surface of the turkey prior to inoculation than when the coating was formed on the inoculated surface. More effective inhibition of S. enterica and E. coli O157:H7 was observed with the LPOS-WPI coatings than with the LPOS solution-spread treatment. The growth of total aerobes was also retarded by LPOS-WPI coatings during storage.

IMPACT: 2000/10 TO 2006/09
Results from these studies have contributed to a better understanding of the ecology of Salmonella in almond orchards. One of the goals of the research was to provide a scientific basis for production management strategies that may reduce the persistence of Salmonella in almond orchards and thereby to reduce contamination of almonds. Information learned from this research has bearing on other tree nuts and row crops. Our results have lead to specific almond grower and processor recommendations for handling wet nuts that will reduce or prevent contamination of the crop with Salmonella and potentially other pathogens. Almond industry specifications for reduction of Salmonella in almond kernels were developed with the aid of a risk assessment model that depended upon key data from this research. Our other studies have furthered the understanding of antimicrobial coatings for foods. The coatings tested show potential for extending microbial stability and for inhibiting post-processing contamination pathogens on roasted turkey and other ready-to-eat products, thus potentially providing a novel means for improving the shelf life and microbial safety of those foods.

Funding Source
Nat'l. Inst. of Food and Agriculture
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Bacterial Pathogens
Nuts, Seeds