Catherine N. Cutter

Opportunities for bio-based packaging technologies to improve the quality and safety of fresh and further processed muscle foods

It has been well documented that vacuum or modified atmosphere packaging materials, made from polyethylene- or other plastic-based materials, have been found to improve the stability and safety of raw or further processed muscle foods. However, recent research developments have demonstrated the feasibility, utilization, and commercial application of a variety of bio-based polymers or bio-polymers made from a variety of materials, including renewable/sustainable agricultural commodities, and applied to muscle foods. A variety of these bio-based materials have been shown to prevent moisture loss, drip, reduce lipid oxidation and improve flavor attributes, as well as enhancing the handling properties, color retention, and microbial stability of foods. With consumers demanding more environmentally friendly packaging and a desire for more natural products, bio-based films or bio-polymers will continue to play an important role in the food industry by improving the quality of many products, including fresh or further processed muscle foods.

Efficacy of Organic Acids Against Escherichia coli O157:H7 Attached to Beef Carcass Tissue Using a Pilot Scale Model Carcass Washer1

The efficacy of organic acids for controlling Escherichia coli O157:H7 attached to beef carcass tissue was determined using a pilot scale model carcass washer. Lean or adipose surface tissues from beef carcasses were inoculated with three strains of Escherichia coli O157:H7 or Pseudomonas fluorescens . After spraying either water, 1, 3, or 5% acetic, lactic, or citric acids at 24°C, tissues were incubated for 24 h at 4°C and bacterial populations enumerated. Statistical analyses of the data indicated that acid type was not a significant treatment factor (p ≥ = 0.05); however, concentration, tissue type, and bacterial strain were significant (p ≤ = 0.0001) factors that influenced the reduction of bacterial populations on lean or adipose tissue. Of the concentrations tested on lean tissue, spray treatments with 5% were the most effective for reducing populations of E. coli O157:H7 or P. fluorescens . Differences in the resistances of the E. coli O157:H7 strains to acid washing also were observed. The magnitude of bacterial population reductions was consistently greater on adipose versus lean tissue for all bacterial strains. Surface pH data indicated that reductions of bacterial populations may have been due to the effects of acidic pH. This study demonstrates that, while organic acids did reduce populations of E. coli O157:H7 on red meat, treatments did not completely inactivate the pathogen.

Antimicrobial effect of herb extracts against Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella typhimurium associated with beef.

The effects of plant extracts against pathogenic bacteria in vitro are well known, yet few studies have addressed the effects of these compounds against pathogens associated with muscle foods. A series of experiments was conducted to determine the effectiveness of a commercially available, generally recognized as safe, herb extract dispersed in sodium citrate (Protecta One) or sodium chloride (Protecta Two) against Escherichia coli O157:H7, Salmonella typhimurium, and Listeria monocytogenes associated with beef. In the first experiment, E. coli O157:H7, Salmonella typhimurium, and L. monocytogenes inoculated onto beef and subjected to surface spray treatments with 2.5% solutions of Protecta One or Protecta Two were not affected by immediate application (day 0) of the herbal extracts. However, after 7 days of storage at 4 degrees C, E. coli O157:H7 was reduced by >1.3 log10 CFU/cm2 by Protecta Two; L. monocytogenes was reduced by 1.8 and 1.9 log10 CFU/cm2 by Protecta One and Protecta Two, respectively; Salmonella typhimurium was not reduced >0.3 log10 CFU/cm2 by either extract by day 7. In the second experiment, 2.5% Protecta Two (wt/vol or wt/wt) added to inoculated lean and adipose beef trim, processed, and packaged as ground beef chubs (80% lean, 20% adipose), did not reduce pathogen populations >0.5 log10 CFU/g up to 14 days at 4 degrees C. In the third experiment, surface spray treatments of beef with 2.5% lactic acid or 2.5% solutions of Protecta One or Protecta Two, vacuum packaged, and stored up to 35 days at 4 degrees C did reduce E. coli O157:H7, L. monocytogenes, and Salmonella Typhimurium slightly. These studies suggest that the use of herb extracts may afford some reductions of pathogens on beef surfaces; however, the antimicrobial activity may be diminished in ground beef by adipose components.

Microbial Decontamination of Beef and Sheep Carcasses by Steam, Hot Water Spray Washes, and a Steam-Vacuum Sanitizer

Three separate studies were conducted to determine the effectiveness of various temperature water spray washes (Wt), wash and steam combinations (WtS), and vacuum and wash combinations (VWt) for reducing fecal bacteria on sheep and beef carcasses. Wt of 15.6, 54.4, and 82.2°C were administered to sheep carcasses contaminated with feces, using a hand-held spray nozzle. Initial carcass bacterial populations of approximately 2.5, 4, and 6 log CFU/cm2 were subjected to all wash combinations. W82.2 and W82.2S reduced 6 log CFU/cm2 bacterial populations as much as 4.0 log cycles. When carcasses were subjected to WtS and W82.2, the initial contamination levels (4 and 6 log CFU/cm2) had little effect on final bacterial levels (2.7 to 3.3 log CFU/cm2). However, uninoculated carcasses with initial bacterial populations of 2.5 log CFU/cm2 experienced a 1.5-log-cycle reduction when subjected to WtS and W82.2. It is possible that hydration of a carcass before and during interventions affords some protection to bacteria. The next study used a commercial carcass washer to apply a hot water (72°C), low pressure (20 psi) wash in combination with a high pressure (125 psi), warm water (30°C) wash (W72/30). Reductions on beef of 2.7, 3.3, and 3.4 log cycles for aerobic plate count (APC), coliforms, and E. coli populations, respectively, were observed. When a commercial steam-vacuum was used in conjunction with W72/30, reductions of 3.1, 4.2, and 4.3 log cycles for APC, coliforms, and E. coli populations, respectively, were achieved. Implementation of these interventions could reduce the amount of trimming needed on carcass-processing lines and would increase the microbial safety of beef carcasses.

Population reductions of gram-negative pathogens following treatments with nisin and chelators under various conditions

When used in combination with chelating agents (EDTA, EGTA, citrate, phosphate), the bacteriocin nisin is effective for reducing populations of gram-negative bacteria in vitro. This study examined parameters (buffers, temperature presence of divalent cations) that affect nisin inhibition of Escherichia coli O157:H7 and Salmonella typhimurium . Approximately 7 log10 colony-forming units (CFU) per ml of E. coli and S. typhimurium were treated in PBS or MOPS buffers containing 50 μg/ml of purified nisin, alone or in combination with 500 mM lactate, 100 mM citrate, 50 mM EDTA, and 1% (wt/vol) sodium hexametaphosphate (pH 7.0) at 37°C for 60 min or 5°C for 30 min. Surviving bacterial populations were compared to untreated controls (buffers without nisin). Data indicated that treatments with nisin in buffers resulted in reductions of 4.30 and 2.30 log10 CFU/ml of E. coli and S. typhimurium , respectively, as compared to untreated controls. Population reductions ranging from 2.29 to 5.49 log10 CFU/ml were observed when cells were treated with nisin and chelator combinations at either 37°C for 60 min or 5°C for 30 min. The addition of magnesium and calcium to buffers with nisin decreased inhibition. Data obtained from spectrophotometric experiments indicated that treatments were causing the release of cellular constituents. However, transmission electron microscopy (TEM) analyses were inconclusive, since cellular membranes did not appear to be disrupted.

Effects of Acetic Acid, Lactic Acid and Trisodium Phosphate on the Microflora of Refrigerated Beef Carcass Surface Tissue Inoculated with Escherichia coli O157:H7, Listeria innocua, and Clostridium sporogenes†

The microbial profiles of inoculated beef carcass tissue (BCT) were monitored during prolonged refrigerated vacuum-packaged storage following antimicrobial treatment. An industrial spray wash cabinet was used to deliver water (W), 1.5 and 3.0% lactic (LA) or acetic (AA) acid, or 12% trisodium phosphate (TSP) washes. Fresh unaltered bovine feces spiked with antibiotic-resistant strains of Escherichia coli O157:H7, Listeria innocua , and Clostridium sporogenes were used to inoculate BCT prior to all treatments. The effect of treatments on bacterial populations was tracked by monitoring levels of specific-antibiotic-resistant(marked) bacteria along with mesophilic aerobic bacteria (APC), lactic acid bacteria (LAB), and pseudomonads for up to 21 days of storage at 5°C. Initial APC levels of approximately 5.6 log CFU/cm2 were reduced by 1.3to 2.0 log CFU/cm2 by LA, AA, and TSP treatments. Marked bacteria were reduced to <1.3 log CFU/cm2, remaining that way throughout the 21-day storage. TSP treatments were not different in effectiveness from acids for controlling growth of E. coli O157:H7 and C. sporogenes , but were less effective for APC, L. innocua , or LAB. The aerobic bacteria, L. innocua , and LAB had counts ≥7 log CFU/cm2 by 7 days in all but one case and by 14 days all had counts >7 log CFU/cm2 on the untreated controls and water-washed samples. Treatments generally added a degree of safety regarding the foodborne pathogens and pathogen models used for the present study when beef tissue was stored up to 21 days and in no case did the treatments appear to offer any competitive advantage to select microorganisms on BCT.

Microbial Control by Packaging: A Review

Referee: Dr. Mildred Rivera-Betancourt, Microbiologist, USDA, ARS, R.L. H. Meat Animal Research Center, P.O. Box 166, State Spur 18D, Clay Center, NE 68933 Since early man first used a variety of natural containers to store and eat foods, significant developments in food packaging materials have provided the means to suppress microbial growth as well as protect foods from external microbial contamination. Throughout this progression, packaging materials have been developed specifically to prevent the deterioration of foods resulting from exposure to air, moisture, or pH changes associated with the food or the surrounding atmosphere. Both flexible and rigid packaging materials, alone or in combination with other preservation methods, have been developed to offer the necessary barrier, inactivation, and containment properties required for successful food packaging. Examples of flexible packaging used to inactivate microorganisms associated with foods include controlled atmosphere, vacuum, modified atmosphere, active, and edible packaging. Additionally, the combination of rigid packaging materials made from metal, glass, or plastic with heat provides the most effective and widely used method for inactivating microorganisms. As with all food products, it is necessary to integrate a HACCP-based program to assure quality throughout the packaging operation. In addition to packaging improvements, other novel technologies include the development of detectors for oxygen levels, bacterial toxins, and microbial growth, or the integration of time-temperature indicators for detection of improper handling or storage.

The effectiveness of triclosan-incorporated plastic against bacteria on beef surfaces.

Triclosan is a nonionic, broad-spectrum, antimicrobial agent that has been incorporated into a variety of personal hygiene products, including hand soaps, deodorants, shower gels, mouthwashes, and toothpastes. In this study, plastic containing 1,500 ppm of triclosan was evaluated in plate overlay assays and meat experiments as a means of reducing populations of bacteria. Plate overlay assays indicated that the triclosan-incorporated plastic (TIP) inhibited the following organisms: Brochothrix thermosphacta ATCC 11509, Salmonella Typhimurium ATCC 14028, Staphylococcus aureus ATCC 12598, Bacillus subtilis ATCC 6051, Shigella flexneri ATCC 12022, Escherichia coli ATCC 25922, and several strains of E. coli O157:H7. In meat experiment 1, irradiated, lean beef surfaces inoculated with B. thermosphacta, Salmonella Typhimurium, E. coli O157:H7, or B. subtilis were covered with TIP, vacuum packaged, and stored for 24 h at 4 degrees C. Of the organisms tested, only populations of B. thermosphacta were slightly reduced. In meat experiment 2, prerigor beef surfaces were inoculated with E. coli O157: H7, Salmonella Typhimurium, or B. thermosphacta incubated at 4 degrees C for 24 h, wrapped in TIP or control plastic, vacuum packaged, and stored at 4 degrees C for up to 14 days. There was a slight reduction in the population of the organisms after initial application with TIP. However, bacterial populations following long-term, refrigerated (4 degrees C), vacuum-packaged storage up to 14 days were not statistically (P< or =0.05) or numerically different than controls. In meat experiment 3, even TIP-wrapped, vacuum-packaged beef samples that were temperature abused at 12 degrees C did not exhibit significant (P< or =0.05) or sustainable reductions after 14 days of 4 degrees C storage. Another study indicated that populations of E. coli O157:H7 or B. thermosphacta added directly to TIP were not affected after 2 h of refrigerated storage or that the antimicrobial activity could be extracted from the plastic. Additional experiments suggest that presence of fatty acids or adipose may diminish the antimicrobial activity of TIP on meat surfaces. This study demonstrates that while antimicrobial activity is detected against bacterial cultures in antimicrobial plate assays, plastic containing 1,500 ppm of triclosan does not effectively reduce bacterial populations on refrigerated, vacuum-packaged meat surfaces.

Treatments with nisin and chelators to reduce Salmonella and Escherichia coli on beef

Salmonella typhimurium ATCC 14028 or Escherichia coli O157:H7 attached to lean beef tissue were treated with citrate, lactate, sodium hexametaphosphate, or EDTA, alone or in combination with nisin in simple buffers, and incubated at 4°C for up to 3 days. Lactate with nisin reduced S. typhimurium attached to beef by 040 log10 CFU/cm2, while EDTA and nisin reduced E. coli O157:H7 by 0.42 log10 CFU/cm2. Unlike earlier in vitro studies in which treatments with nisin and chelating agents resulted in reductions of > 4 log10 CFU/cm2, such reductions were not observed in situ.

Interventions for the reduction of Salmonella Typhimurium DT 104 and non-O157:H7 enterohemorrhagic Escherichia coli on beef surfaces.

A study was conducted to determine if slaughter interventions currently used by the meat industry are effective against Salmonella Typhimurium definitive type 104 (DT 104) and two non-O157:H7 enterohemorrhagic Escherichia coli (EHEC). Three separate experiments were conducted by inoculating prerigor beef surfaces with a bovine fecal slurry containing Salmonella Typhimurium and Salmonella Typhimurium DT 104 (experiment 1), E. coli O157:H7 and E. coli O111:H8 (experiment 2), or E. coli O157:H7 and E. coli O26:H11 (experiment 3) and spray washing with water, hot water (72 degrees C), 2% acetic acid, 2% lactic acid, or 10% trisodium phosphate (15 s, 125 +/- 5 psi, 35 +/- 2 degrees C). Remaining bacterial populations were determined immediately after treatments (day 0), after 2 days of aerobic storage at 4 degrees C, and after 7, 21, and 35 days of vacuum-packaged storage at 4 degrees C. In addition to enumeration, confirmation of pathogen serotypes was performed for all treatments on all days. Of the interventions investigated, spray treatments with trisodium phosphate were the most effective, resulting in pathogen reductions of >3 log10 CFU/cm2, followed by 2% lactic acid and 2% acetic acid (>2 log10 CFU/cm2). Results also indicated that interventions used to reduce Salmonella Typhimurium on beef surfaces were equally effective against Salmonella Typhimurium DT 104 immediately after treatment and again after long-term, refrigerated, vacuum-packaged storage. Similarly, E. coli O111:H8 and E. coli O26:H11 associated with beef surfaces were reduced by the interventions to approximately the same extent as E. coli O157:H7 immediately after treatment and again after long-term, refrigerated, vacuum-packaged storage. It was also demonstrated that phenotypic characterization may not be sufficient to identify EHECs and that the organisms should be further confirmed with antibody- or genetic-based techniques. Based on these findings, interventions used by the meat industry to reduce Salmonella spp. and E. coli O157:H7 appear to be effective against DT 104 and other EHEC.