#18-100

Complete

Date Full Report Received

12/01/2019

Date Abstract Report Received

12/01/2019

Investigation

Institution:
Primary Investigator:

A growing number of outbreaks caused by human enteric pathogens is an increasing concern for pork processors and regulatory agencies because of their negative impacts on consumers’ health and their trust in the U.S. food system. Despite both pre- and post-harvest critical control measures employed by commercial pork operations, recently, approximately 531,000 lbs. of pork products (from the whole hog to pork trimming) were recalled due to Salmonella contamination (USDA/FSIS 2015; USDA/FSIS 2016). The current industry’s approach focuses primarily on antimicrobial intervention immediately during harvest such as pre-stunning wash, hot water scalding, hot water wash, and singeing (burning hair); however, safety and interventions for further processed pork products, especially pork trimming used for ground pork and sausages are lacking. The 2018 National Pork Board’s RFP cited an under-reviewed, NPB-funded study reporting a great risk of Salmonella contamination in pork trimming and suggesting that the industry must focus on pork trimming. This concern by the pork industry is confirmed by USDA/FSIS data from Raw Pork Products Exploratory Sampling Program Phase II from July 1, 2015 to June 30, 2017, reporting a steady increase in Salmonella incidence rate in comminuted pork, from 21.24% in 2015 to more than 30.93% in 2017. These data indicate that current methods to reduce microbial load on pork carcasses do not prevent recurrence of Salmonella in pork trimming. Therefore, we proposed a project to use 3% acetic acid in potential combination with heat-shock and natural antioxidants as a clean-label hurdle to control Salmonella in pork trimming used for ground pork and pork sausage production. Our overall goal is to provide the pork industry, especially processors using pork trimming, with a hurdle, clean-label approach to reduce Salmonella counts in pork trimming and to make meat products safer. The beef industry has been using 3% acetic acid to control E. coli. Acetic is a GRAS organic acid (generally recognized as safe). Our preliminary data indicated a marked reduction of fluorescence signal of lux-modified Salmonella Typhimurium inoculated in pork trimming exposed to 3% acetic acid, 55⁰C hot water, and ice slurry. Our three objectives were: (1)to determine the efficacy of acetic acid dipping and heat shock in reducing nalidixic acid-resistant (to exclude background microflora) Salmonella in pork trimming in a benchtop trial, (2) to determine the efficacy of natural antioxidant in maintaining protein functionality and preventing lipid oxidation in pork trimming post-treatment, and (3) to determine the efficacy of acetic acid dipping and heat shock in reducing nalidixic acid-resistant Salmonella in pork trimming in a pilot scale.

We purchased pork loins and trimming from a local purveyor. We cut the pork loin into 2.5 cm (L) × 2.5 cm (W) × 1.3 cm (H) cubes and packaged pork trimming into 2.3-kg chubs (5 lbs.). We conducted three experiments to fulfill objective 1. We inoculated pork cubes with nalidixic acid- resistant Salmonella at 5 log for XLD-agar plating or lux-modified Salmonella at 8 log for bioluminescent imaging method. In the first experiment, pork cubes were dipped into 3% acetic acid at room temperature (21°C) or 50°C for 15 s to determine whether temperature had an impact on efficacy. In the second experiment, we conducted a heat-shock treatment from cold (ice-cold water) to hot (50°C) and vice versa to determine if heat shock had an impact on Salmonella survival. In the third experiment, we tested both temperature and dipping duration (15, 45, and 75 s). We confirmed that dipping pork trimming in 3% acetic acid at 50°C for 75 s was the best treatment to reduce Salmonella (up to 1.4-log reduction). Although heat shock for 2 min resulted in 0.4-log reduction in Salmonella culture, heat shock did not affect Salmonella survival on pork cubes, although warm acetic acid was more effective than room-temperature acetic acid. Therefore, we decided not to include heat-shock in our final application because it would add significant water and disposal costs and result in almost no meaningful reduction of Salmonella. To fulfill objective 2, we also tested meat quality under the effects of temperature and time when dipping pork cubes in 3% acetic acid. No meaningful effect was found except that surface color was paler; however, such an effect only occurred on the surface. Underneath the surface, the analysis of cross-sections had similar color and myoglobin composition to surface before treatment application. We do not think surface color will have much of an impact on ground meat or sausage color because the inside of pork trimming is still not affected. All quality attributes include lipid oxidation and protein quality (solubility and water-holding capacity) were not impacted by treatment application. We also concluded that no antioxidant is needed because acidic conditions on the surface did not have enough time to induce oxidation. Choosing 3% acetic acid at 50°C for 75 s for scale-up application, we aimed to answer the question whether a dipping application would be effective in reducing Salmonella if the contaminated pieces were to be buried within pork trimming bulks. It is a physics question of acetic acid penetration, not a biological question of acetic acid efficacy. We inoculated a pork cube with 5 log of nalidixic acid-resistant Salmonella and buried it at the geometrical center of a 2.3-kg pork chub, shaped in a plastic bag placed in a perforated cylindrical canister to mimic the trimming container in the industry. We tested both simple submersion and submersion with shaking. Both methods resulted in only 0.2- to 0.3-log reduction, not a microbiologically meaningful reduction. Therefore, we do not recommend dipping large bulks of pork trimming in acetic acids because while the surface pieces may be adequately treated, the core pieces may not be treated because of lack of acetic acid penetration. We recommend that the processors find ways to treat core pieces of trimming bulks, e.g., spreading trimming on conveyor for a dipping or spraying application, or loosening the trimming bulks to allow for penetration of acetic acid. It is interesting that the inoculated pork cubes at the center did not cross-contaminate the surrounding pieces in a meaningful way after Salmonella was allowed to attach to the meat surface.

In conclusion, we confirm that 3% acetic acid at 50°C for 75 s is effective in reducing Salmonella in pork trimming without negative impacts on meat quality. Acetic acid is also volatile and will evaporate after treatment and during storage; therefore, it is unlikely to affect meat quality. Application for the industry will need to consider whether acetic acid can penetrate the center of trimming bulks, through either spreading the trimming on a conveyor or in smaller, more loosened bulks to allow better penetration or a spray application. We also recommend processors validate a spray application to ensure sufficient contact time (75 s).

Contact information:
Thu Dinh
Department of Animal and Dairy Sciences
Mississippi State University
Mississippi State, MS 39762
Phone: (662) 325-7554
Fax: (662) 325-8873
Email: thu.dinh@msstate.edu

Key Findings:
• Acetic acid at 3% and 50°C provides adequate control of Salmonella, more than 1.4-log reduction at 75 s. This is the recommended application temperature and time.
• Heat-shock application on inoculated pork cubes does not reduce Salmonella; however, because warm temperature does seem to enhance the efficacy of acetic acid. Heat-shock application does reveal that we allowed adequate time for Salmonella attachment because there was no wash-out effect.
• There was no meaningful impact of treatment on meat quality of pork trimming. Oxidation was not detected in pork trimming; therefore, antioxidants are not needed. Protein quality and water-holding capacity that are important for ground meat binding and meat juiciness are not impacted.
• Dipping large bulks of pork trimming in acetic acids is not recommended because while the surface pieces may be adequately treated, the core pieces may not be treated because acetic acid may not penetrate deep into a large meat bulk. It is recommended that the processors find ways to treat core pieces of trimming bulks, e.g., spreading trimming on conveyor for a dipping or spraying application, or loosening the trimming bulks to allow for penetration of acetic acid. Salmonella after attaching to meat surface did not cross-contaminate the surrounding pieces in a meaningful way.