Monitoring food safety for rendered fat product handling in the US and the informal vegetable value chain in Cambodia

Abstract

Food safety is a challenge across all food commodities, and the presence of bacterial pathogens in food is a major public health concern in all countries. In countries with more developed food safety infrastructures, food safety progress is often focused on emerging concerns. For example, it was long thought that finished rendered products were free of biological contamination. However, recent foodborne disease outbreaks associated with rendered products have highlighted the need to better understand pathogen transmission and survival in rendering environments to better eliminate pathogens in such products. The purpose of the first study was to evaluate the effects of moisture levels (0.0%, 0.5%, 1.0%, and 3.0%), storage temperatures (48˚C and 76˚C), and fat characteristics on the growth and survival of Salmonella enterica in choice white grease, beef tallow, and chicken fat samples. Samples were inoculated with a high concentration (~10⁸ CFU/mL) or low concentration (~10⁵ CFU/mL) Salmonella cocktail (S. Sentfenberg, S. Newport, S. Thompson and S. Infantis) and stored for up to 5 days at 48 ºC or 76 ºC. Remaining populations of Salmonella were evaluated daily with and without enrichment step. Bacterial death rates were calculated using the Weibull model for each temperature and moisture level. No significant effect between moisture and/or inoculum level were observed. Only temperature had a significant effect (P < 0.05) on Salmonella inactivation; when all products were challenged at 76˚C, Salmonella concentrations were below detectable limits after 24 hours. At 48˚C a progressive decline in Salmonella populations was observed within 3 days in both beef tallow and white grease when samples were inoculated with a high concentration Salmonella cocktail. Salmonella concentrations were below the detectable limit within 4 days in both fat types when a low concentration cocktail was applied. This research identified the effect of moisture and temperature in rendered fat samples contaminated with Salmonella and underlines the need to use time-moisture-temperature data to minimize microbial growth during transportation and storage. In low- and middle-income countries, food safety progress may begin with identifying which practices and points along the food chain are of the most concern for public health. Cambodia has introduced several initiatives to increase production and consumption of fresh produce throughout the country. Fresh produce, however, is often associated with foodborne disease; thus, understanding how foodborne pathogens enter and are transmitted throughout Cambodian produce production chains can help to ensure positive nutritional outcomes from increased produce consumption. The second study was conducted to provide a better understanding of transmission of foodborne pathogens throughout vegetable production chains in Cambodia with a focus on the distribution stage by assessing quantitative and qualitative aspects of Enterobacteriaceae, coliforms and generic Escherichia coli on tomatoes, cucumber, and lettuce sold through a produce distribution center in Battambang, Cambodia. Samples (n = 384) were collected over six-month period spanning (December 2019 - May 2020) and screened for the presence of Enterobacteriaceae, coliforms and E. coli. Lettuce samples were significantly (P < 0.05) more likely to carry Enterobacteriaceae and coliforms compared to cucumbers and tomatoes. Additionally, concentrations of Enterobacteriaceae were significantly (P < 0.05) higher in lettuce (4.71 ± 1.02 log₁₀ CFU/g) samples compared to cucumbers (3.44 ± 1.12 log₁₀ CFU/g), and tomatoes (2.79 ± 1.02 log₁₀ CFU/g). The same trend was observed for coliforms, where lettuce had a significantly higher concentration (P < 0.05; 4.36 ± 1.23 log₁₀ CFU/g), followed by cucumber (3.28 ± 1.32 log₁₀ CFU/g) and tomato (2.69 ± 1.45 log₁₀ CFU/g). The results of this study provide an initial assessment Enterobacteriaceae, coliforms and E. coli contamination in vegetables sold through Cambodian markets. These data can be used to identify sources of contamination and provide a baseline to assess the efficacy of interventions aimed at limiting contamination and ensuring the safety of fresh produce available to Cambodians.