Internalization and thermal susceptibility of Shiga toxin-producing Escherichia coli (STEC) in marinated beef products.

This study evaluated the internalization and cooking susceptibility of seven individual Escherichia coli (STEC) serogroups in surface-inoculated (10(5)log CFU/cm(2)) and vacuum tumbled marinated (30 or 60 min) bottom sirloin steaks. After storage for 14 days (0 to 2°C), flaps were cooked to various endpoint temperatures (55, 60, 65, and 71°C) for evaluation of pathogen survival by direct plating or rapid PCR based detection (BAX®). Direct plating of cooked samples yielded no enumerable plates. The data indicate varied internalization, translocation, and heat susceptibility patterns among serogroups. Using the rapid PCR based detection method O26, O103, and O111 were detected in flaps after cooking to 55 and 60°C, while O157:H7 survived in flaps cooked to 60 and 65°C. However, STEC O145 was the only serogroup that survived in all cooking temperatures. Serogroup O121 was not detected by plating or PCR in any cooked products. Intriguingly, STEC serogroups can be internalized during marination and the internalized pathogens vary in thermal susceptibility.

The influence of beef quality characteristics on the internalization and thermal susceptibility of Shiga toxin-producing Escherichia coli (STEC) in blade-tenderized beef steaks.

The risk of Shiga toxin-producing Escherichia coli (STEC) survival in blade-tenderized beef is a concern for beef processors. This study evaluated the internalization and post-cooking survival of individual STEC serogroups (O157:H7, O26, O45, O103, O111, O121, and O145) in blade-tenderized beef steaks with different quality traits. Strip loins representing four combinations of USDA Quality Grade (Choice or Select) and pH category (High pH or Normal pH) were inoculated (10(6)logCFU/cm(2) attachment) with individual STEC serogroups before storage (14 days), blade tenderization, and cooking (50, 60, 71, or 85°C). Serogroup populations on raw steak surfaces and internal cores were determined. Rapid-based methods were used to detect the internal presence of STEC in cooked steaks. Internalization and post-cooking survival varied among STECs. All serogroups, except O45 and O121, were detected in the internal cores of steaks cooked to 50°C, while O103, O111, and O145 STEC were detected in steaks cooked to 50, 60, and 71°C.

Validation comparing the effectiveness of a lactic acid dip with a lactic acid spray for reducing Escherichia coli O157:H7, Salmonella, and non-O157 Shiga toxigenic Escherichia coli on beef trim and ground beef.

The objective of this research was to compare the effectiveness of two application methods (dip versus spray) of 4.4% lactic acid for reducing pathogens on inoculated beef trim and in ground beef. Beef trim inoculated with cocktail mixtures of E. coli O157:H7, non-O157 Shiga toxigenic E. coli (STEC), or Salmonella (10(5) to 10(6) CFU/g) at separate times was subjected to five treatments: lactic acid spray (LS), lactic acid dip (LD), water spray (WS), water dip (WD), and untreated control (CTL). Intervention effectiveness for pathogen reduction was measured at 1 and 20 h after treatment on beef trim. Trim was then ground and intervention effectiveness was measured 1 h, 24 h, 72 h, and 7 days after grinding. The LD treatment reduced all pathogens significantly (P < 0.05); E. coli O157:H7 was reduced by 0.91 to 1.41 log CFU/g on beef trim and ground beef, non-O157 STEC by 0.48 to 0.82 log CFU/g, and Salmonella by 0.51 to 0.81 log CFU/g. No other treatment significantly reduced any pathogen, although the WD treatment noticeably reduced (P > 0.05) both E. coli O157:H7 and non-O157 STEC populations compared with the CTL. The LS treatment reduced E. coli O157:H7 and Salmonella by up to 0.5 log CFU/g on beef trim, but these reduced counts did not significantly differ (P > 0.05) from the CTL counts. Overall, the LD treatment was most effective for reducing all pathogens and is the best of these options for improving the safety of beef trim and subsequently produced ground beef.

Spoilage characteristics of ground beef with added lactic acid bacteria and rosemary oleoresin packaged in a modified-atmosphere package and displayed at abusive temperatures.

Lactic acid bacteria (LAB) can reduce Escherichia coli O157:H7 and Salmonella spp. in ground beef during storage. Furthermore, the addition of rosemary oleoresin (RO), a natural antioxidant, to ground beef has been shown to increase shelf life and is commonly used in modified-atmosphere packaged (MAP) ground beef. This study evaluated the effects of LAB and RO treatment on the shelf life and stability of MAP ground beef displayed at abusive (10°C) temperatures for 36 h. Subjective and objective sensory analyses were conducted to determine spoilage endpoints. Trained and consumer panel responses and Hunter lightness (L*), redness (a*), and yellowness (b*) values were not affected (P = 0.62, 0.66, 0.45) by LAB addition, although RO inclusion improved (P < 0.05) lean color. Ground beef with LAB and RO had significantly less (P < 0.0001) thiobarbituric acid reactive substance values than control ground beef, indicating decreased lipid oxidation. Additionally, RO inclusion reduced (P < 0.0001) off odors, as determined by trained and consumer odor panelists. Overall, the addition of LAB did not negatively affect beef color, odor, or oxidative rancidity, suggesting that LAB can be added to ground beef in MAP packaging as a processing intervention without detrimentally affecting shelf life or stability.

Shelf life and stability traits of traditionally and modified atmosphere packaged ground beef patties treated with lactic acid bacteria, rosemary oleoresin, or both prior to retail display.

Previous research indicates that lactic acid bacteria (LAB) can inhibit pathogenic bacteria. This research evaluated effects of LAB inclusion on the shelf life of traditionally packaged ground beef patties; as well as the effects and possible interaction of LAB and rosemary oleoresin (RO) on the stability of high oxygen MAP ground beef during display. In both package types, trained and consumer evaluations indicated no effect (P>0.05) of LAB on lean color and off-odor. Display affected trained and consumer sensory evaluations and indicated declined stability over time. Thiobarbituric acid values were lower for traditionally packaged ground beef with LAB (P<0.05) and MAP ground beef with RO or RO and LAB (P<0.05). Overall, LAB had no effect on the shelf life and stability of traditionally or high-oxygen MAP packaged ground beef patties. Therefore, utilization of LAB in ground beef to reduce pathogenic bacteria is viable without alteration of spoilage indicators.

Spoilage characteristics of traditionally packaged ground beef with added lactic acid bacteria displayed at abusive temperatures.

Growth of pathogenic organisms such as Escherichia coli O157:H7 and Salmonella spp. can be inhibited in ground beef through the addition of certain lactic acid-producing bacteria (LAB; Lactobacillus acidophilus NP51, Lactobacillus crispatus NP35, Pediococcus acidilactici, and Lactococcus lactis ssp. lactis). This study evaluated the effects of LAB inclusion on the organoleptic and biochemical properties typically associated with spoilage in traditionally packaged ground beef displayed at abusive (10°C) temperatures for 36 h. Trained and untrained panelist evaluations of lean color and off-odor, as well as instrumental color analyses, did not indicate an effect on spoilage traits due to LAB utilization (P > 0.05). However, display length affected each variable independently and was indicative of decreased stability and acceptability as display time (h) increased (P < 0.05). Thiobarbituric acid values were decreased for ground beef with added LAB (P < 0.05), but likely can be related to bacterial degradation of lipid oxidation by-products because no reduction in organoleptic traits due to oxidation was noted between treatments. Overall, LAB did not adversely influence the spoilage characteristics of traditionally packaged ground beef displayed at abusive temperatures for up to 36 h. Furthermore, biochemical and sensory indicators of spoilage were present for all treatments at the conclusion of display. Therefore, LAB can be added to ground beef in traditional packaging as a processing intervention without masking or delaying the expected spoilage characteristics.