Keith Vorst

Transfer of Listeria monocytogenes during mechanical slicing of Turkey Breast, Bologna, and Salami

A commercial delicatessen slicer was used as the vector for sequential quantitative transfer of Listeria monocytogenes (i) from an inoculated slicer blade (approximately 10(8), 10(5), or 10(3) CFU per blade) to 30 slices of uninoculated delicatessen turkey, bologna, and salami, (ii) from inoculated product (approximately 10(8) CFU/cm2) to the slicer, and (iii) from inoculated product (10(8), 10(5), or 10(3) CFU/cm2) to 30 slices of uninoculated product via the slicer blade. Cutting force and product composition also were assessed for their impact on L. monocytogenes transfer. Five product contact areas on the slicer, which were identified from residue of product bathed in Glow-Germ, were also sampled using a 1-ply composite tissue technique after inoculated product had been sliced. After being sliced with inoculated blades, each product slice was surface or pour plated on modified Oxford agar and/ or enriched in University of Vermont medium. Greater transfer (P < 0.05) occurred from inoculated turkey (10(8) CFU/cm2) to the five slicer contact areas from an application force of 4.5 kg as compared with 0 kg. On uninoculated product sliced with blades inoculated at 10(8) CFU per blade, L. monocytogenes populations decreased logarithmically to 10(2) CFU per slice after 30 slices. Findings for the inoculated slicer blade and product (10(5) CFU per blade or cm2) were similar; L. monocytogenes concentrations were 102 CFU per slice after 5 slices and enriched samples were generally negative for L. monocytogenes after 27 slices. For uninoculated product sliced with blades inoculated at 10(3) CFU per blade, the first 5 slices typically produced L. monocytogenes at approximately 10 CFU per slice by direct plating, and enrichments were negative for L. monocytogenes after 15 slices. The higher fat and lower moisture content of salami compared with turkey and bologna resulted in a visible fat layer on the blade that likely prolonged L. monocytogenes transfer. As a result of cross-contamination, those delicatessen-sliced meats that allow growth of L. monocytogenes during prolonged refrigerated storage likely pose an increased public health risk for certain consumers.

Improved Quantitative Recovery of Listeria monocytogenes from Stainless Steel Surfaces Using a One-Ply Composite Tissue

Four sampling devices, a sterile environmental sponge (ES), a sterile cotton-tipped swab (CS), a sterile calcium alginate fiber-tipped swab (CAS), and a one-ply composite tissue (CT), were evaluated for quantitative recovery of Listeria monocytogenes from a food-grade stainless steel surface. Sterile 304-grade stainless steel plates (6 by 6 cm) were inoculated with approximately 106 CFU/cm2 L. monocytogenes strain Scott A and dried for 1 h. The ES and CT sampling devices were rehydrated in phosphate buffer solution. After plate swabbing, ES and CT were placed in 40 ml of phosphate buffer solution, stomached for 1 min and hand massaged for 30 s. Each CS and CAS device was rehydrated in 0.1% peptone before swabbing. After swabbing, CS and CAS were vortexed in 0.1% peptone for 1 min. Samples were spiral plated on modified Oxford agar with modified Oxford agar Rodac Contact plates used to recover any remaining cells from the stainless steel surface. Potential inhibition from CT was examined in both phosphate buffer solution and in a modified disc-diffusion assay. Recovery was 2.70, 1.34, and 0.62 log greater using CT compared with ES, CS, and CAS, respectively, with these differences statistically significant (P < 0.001) for ES and CT and for CAS, CS, and CT (P < 0.05). Rodac plates were typically overgrown following ES, positive after CS and CAS, and negative after CT sampling. CT was noninhibitory in both phosphate buffer solution and the modified disc-diffusion assay. Using scanning electron microscopy, Listeria cells were observed on stainless steel plates sampled with each sampling device except CT. The CT device, which is inexpensive and easy to use, represents a major improvement over other methods in quantifying L. monocytogenes on stainless steel surfaces and is likely applicable to enrichment of environmental samples.

Growth of Escherichia coli O157:H7 and Listeria monocytogenes in Packaged Fresh-Cut Romaine Mix at Fluctuating Temperatures during Commercial Transport, Retail Storage, and Display

Temperature abuse during commercial transport and retail sale of leafy greens negatively impacts both microbial safety and product quality. Consequently, the effect of fluctuating temperatures on Escherichia coli O157:H7 and Listeria monocytogenes growth in commercially-bagged salad greens was assessed during transport, retail storage, and display. Over a 16-month period, a series of time-temperature profiles for bagged salads were obtained from five transportation routes covering four geographic regions (432 profiles), as well as during retail storage (4,867 profiles) and display (3,799 profiles). Five different time-temperature profiles collected during 2 to 3 days of transport, 1 and 3 days of retail storage, and 3 days of retail display were then duplicated in a programmable incubator to assess E. coli O157:H7 and L. monocytogenes growth in commercial bags of romaine lettuce mix. Microbial growth predictions using the Koseki-Isobe and McKellar-Delaquis models were validated by comparing the root mean square error (RMSE), bias, and the acceptable prediction zone between the laboratory growth data and model predictions. Monte Carlo simulations were performed to calculate the probability distribution of microbial growth from 8,122,127,472 scenarios during transport, cold room storage, and retail display. Using inoculated bags of retail salad, E. coli O157:H7 and L. monocytogenes populations increased a maximum of 3.1 and 3.0 log CFU/g at retail storage. Both models yielded acceptable RMSEs and biases within the acceptable prediction zone for E. coli O157:H7. Based on the simulation, both pathogens generally increased <2 log CFU/g during transport, storage, and display. However, retail storage duration can significantly impact pathogen growth. This large-scale U.S. study-the first using commercial time/temperature profiles to assess the microbial risk of leafy greens-should be useful in filling some of the data gaps in current risk assessments for leafy greens.

Effect of recycled poly(ethylene terephthalate) content on properties of extruded poly(ethylene terephthalate) sheets

Sixty (60) polyethylene terephthalate (PET) sheets containing 0—100% recycled-PET (RPET) bottle flake were produced using industrial extruders. The PET/RPET sheets were characterized using differential scanning calorimetry, ultraviolet— visible spectroscopy, mechanical testing, and inductively coupled plasma—atomic emission spectroscopy (ICP—AES). The absorbance at 350 nm, %crystallinity, crystallization temperature, and crystallization peak offset were found to be both unaffected by a silicone mold release coating and reasonably valid indicators of %RPET. Mechanical testing determined that incorporating recycled content into virgin resin will significantly alter the composite mechanical properties; analysis indicated that there was approximately a 2-, 3-, and 30-MPa increase in stress at the proportional limit, stress at yield, and Young’s modulus, respectively, in the machine direction at 40% RPET concentration when compared to virgin resin. The ICP—AES determined that PET/RPET sheets can be safely used for food packaging as according to California Health and Safety Code.

Survey of heavy metal contamination in recycled polyethylene terephthalate used for food packaging

Polyethylene terephthalate food-product containers made with post-consumer materials have been found contaminated with heavy metals due to the recycling and sorting process. The increased use of recycled plastic flake from international suppliers, and subsequent commingling with electronic waste, has been suspected as the source of the increased levels of heavy metal contamination. In this study, nickel, chromium, cadmium, antimony, and lead were quantified in post-consumer polyethylene terephthalate extruded sheet and thermoformed samples, using inductively coupled plasma-atomic emission spectrometry. Recycled polyethylene terephthalate samples were digested using trace-metal grade hydrochloric, perchloric, and nitric acids. Samples were analyzed per ASTM E1613-04, standard test method for determination of lead by inductively coupled plasma atomic emission spectrometry, flame atomic absorption spectrometry, or graphite furnace atomic absorption spectrometry techniques. Two hundred samples were tested of which 29 were found to be contaminated with heavy metals. Chromium and cadmium were found in all 29 sample replicates. Nickel was found in 96.4% of the sample replicates and when it was found, the concentration averaged 11.59 ppm. Lead was found in 90.4% of the sample replicates and the average concentration was 0.15 ppm. Antimony was found in 97.6% of the sample replicates and concentrations were higher in rigid recycled polyethylene terephthalate containers compared to films. It was noted that the total contamination in all 29 samples was well below the threshold level set for the incidental presence of heavy metals in packaging materials as set forth in California’s Toxics in Packaging Prevention Act of 2006. The percentage of each heavy metal that would actually leach from the plastics to contaminate food products during normal processing, packaging, marketing, and consumer use was not determined in this study.

Characterization of Current Environmentally-Friendly Films

The purpose of this study was to evaluate the physical and mechanical properties of environmentally-friendly films for fresh-cut lettuce. This objective was achieved by determining the gas transmission rates for oxygen, water vapor, carbon dioxide, and the thermal and mechanical properties of the films following ASTM standards D3985, F1249, F2476-05, D3418-03, and D882-02, respectively. Electromechanical testing and thermal analysis determined that biodegradable polypropylene (BPP) possessed similar mechanical and thermal properties when compared to the industry standard. This study suggests that BPP films may be used in place of traditional petroleum-based films currently used to package fresh-cut produce.

Use of one-ply composite tissues in an automated optical assay for recovery of Listeria from food contact surfaces and poultry-processing environments.

A novel one-ply composite tissue (CT) method using the Soleris (formerly BioSys) optical analysis system was compared with the conventional U.S. Department of Agriculture (USDA) environmental sponge enrichment method for recovery of Listeria from food contact surfaces and poultry-processing environments. Stainless steel and high-density polyethylene plates were inoculated to contain a six-strain L. monocytogenes cocktail at 10(4), 10(2), and 10 CFU per plate, whereas samples from naturally contaminated surfaces and floor drains from a poultry-processing facility were collected with CTs and environmental sponges. CT samples were transferred into Soleris system vials, and presumptive-positive samples were further confirmed. Sponge samples were processed for Listeria using the USDA culture method. L. monocytogenes recovery rates from inoculated stainless steel and polyethylene surfaces were then compared for the two methods in terms of sensitivity, specificity, and positive and negative predictive values. No significant differences (P > 0.05) were found between the two methods for recovery of L. monocytogenes from any of the inoculated stainless steel and polyethylene surfaces or environmental samples. Sensitivity, specificity, and overall accuracy of the CT-Soleris for recovery of Listeria from environmental samples were 83, 97, and 95%, respectively. Listeria was detected 2 to 3 days sooner with the CT-Soleris method than with the USDA culture method, thus supporting the increased efficacy of this new protocol for environmental sampling.

The Relevance of Drop Tester Accuracy

ASTM D 5276-98 “Standard Test Method for Drop Test of Loaded Containers by Free Fall,” [1] was written as the general test specification for permitting free-fall drop tests for packaged products. One of the fundamental characteristics for drop testers used to perform ASTM D 5276 is that they must produce a flat drop with tolerance limit set at ±2 deg. For drops other than flat drops, such as edges and corners, tolerance limits of ±5 deg have been specified. Although most drop testers are calibrated during manufacturing, they are often not checked for accuracy at their lab locations. This is primarily due to the lack of a calibration standard. This paper investigates the importance of drop test accuracy and reports observations, measurements, and documentation of changes in acceleration and velocity change measured on a test specimen as it is subjected to drops with increasing deviation from the desired impact orientation. A statistical analysis of accelerations as impact orientations deviated is provided and statistical trends in the data as impact angles change are reported. The results suggested that the existing tolerances for performing drops within ±2 deg as recommended by ASTM D 5276 are acceptable for flat drops and the tolerances for performing edge and corner drops within ±5 deg are not acceptable as they can result in larger deviations as the offset is increased beyond ±2 deg.

Determination of ε-Caprolactam Concentration in Water and a White Wine Simulant during Simulated Transport and Storage of Lidded Cups

Under normal sealing and storage conditions, nylon-6, poly (caprolactam)-based plastic laminates may release impurities to packaged foods and liquids, and the application of heat for cooking often increases the rate of migration. Epsilon-caprolactam is one of the main contaminates found to migrate from a nylon-6 poly (caprolactam) plastic film. The objectives of this study were to determine the effects of solvent, transportation, and storage time on the concentration of e-caprolactam from a nylon-6-based lidding material in water or a white wine substitute (12 % ethanol) in poly (propylene) cups lidded with a nylon-6-based film. Cups were filled, sealed, packaged, stacked, and exposed to a simulated 3-day cross-country shipment. Cups were sampled with or without simulated shipment after 0, 7, 14, or 28 days at 20.6°C. Epsilon-caprolactam was determined using a gas chromatograph (GC) equipped with flame ionization detector and Restek Rtx 1301 megabore column. Results of the study indicated release of e-caprolactam into containers at the time of sealing with significantly higher levels (4.42 ppm average) occurring in 12 % ethanol versus water (0.01 ppm average). After the cups were sealed, neither simulated cross-country shipment nor storage increased levels of e-caprolactam in either solvent. It is not understood how the alcohol, whether as liquid or vapor, interacted with the lidding material to increase e-caprolactam release at the time of sealing. No delamination of the poly (propylene) layer of the lidding material was observed when cups were sealed. Future research needs to be conducted to study the effects of alcohol, alcohol vapor, sealing time, and temperature on potential e-caprolactam release.