Effects of various processing techniques and interventions on beef safety and shelf-life

Abstract

Two experiments were conducted; the first evaluated decrease in log survival of pathogenic bacterial populations using three antimicrobial interventions (Peroxyacetic acid – PAA; Lactic Acid – LA; lactic/citric acid blend – LCA) applied at a spray cabinet used just before carcass chilling. Efficacy was evaluated using a Shiga-toxin producing Eschericia coli (STEC) inoculation cocktail that incorporated two strains of E. coli O157:H7 and 12 non-O157 STEC strains. In addition, this study was intended to validate the use of non pathogenic E. coli to serve as surrogates for the aforementioned STEC cocktail in plant operations. Influence of the carcass interventions on color stability of beef subprimals over a 30-day storage period was included to simulate effects on storage and display life. Each day, for three sampling days, 90 hot tissue samples from the plate subprimal were obtained immediately following slaughter. The tissue samples were evenly split into two inoculation groups (n = 45 samples/group): 1) STEC, or 2) surrogate. Within each inoculation group, samples were assigned randomly to one of nine treatments: i) 200 ppm PAA; ii) 1% LCA; iii) 1.5% LCA; iv) 2.5% LCA; v) 5% LA; vi) 8% LA; vii) 10% LA; viii) potable water; or ix) untreated control. Samples assigned to the surrogate inoculation group were further portioned into two equal sections for evaluation of the treatment influence on microbiological decrease in log survival and color. Samples were subjected to treatment using a custom-built, laboratory-scale spray cabinet to apply the intervention. Lightness (L*), redness (a*), and yellowness (b*) was evaluated before and immediately following spray application using a portable spectrophotometer. Following assessment of color immediately post-treatment application, the sample was further divided into three subsections that were vacuum packaged and stored for color evaluation at 10, 20, and 30 d. Among samples inoculated with STEC, log survival means with potable water and control were greater (P < 0.05) when compared to all other spray treatment groups. Likewise, the lower (P < 0.05) log survival means were observed for 8 and 10% LA treatment groups. No differences (P > 0.05) were observed among PAA, 1.5 and 2.5% LCA. Pairwise comparisons of surviving populations of STEC and surrogates revealed that the non-pathogenic strains could be effectively used as surrogates for the STEC cocktail. Color measures of L* values for samples spray treated with 8 or 10% LA were lower (P < 0.05) than for all other treatments, and declined over the 30 d storage period—indicating that the product darkened due to LA exposure and dark storage. Following 10 d dark storage, a* values were greater (P < 0.05) for untreated control samples than for samples sprayed with 1.5 or 2.5% LCA or for samples treated with any level of LA. Spectrophotometric b* values increased during dark storage (P < 0.05) suggesting product discoloration; however, no noticeable trends were observed among or between treatments. The second experiment monitored spoilage microorganisms, panelist and instrument color, and lipid oxidation changes during retail case display for three ground beef batches individually. After 7, 14, 18 or 21 d of vacuum-sealed, dark refrigerated storage (4C), three 73/27 ground beef batches (conventional - control; 25% inclusion of advanced meat recovery (AMR) product from plant one – BBFT 1; 25% inclusion of AMR product from plant two – BBFT 2) were separately fine ground, portioned into 454g loaves, and overwrapped with polyvinyl chloride (PVC) film for retail case display (4C) for 72 h. Sampling for aerobic plate count (APC), lactic acid bacteria (LAB) and 2-thiobarbituric acid reactive substances (TBAR) assay occurred every 24 h during retail case storage. Trained panelist-determined lean color, discoloration and redness intensity values, along with instrument L* (lightness), a* (redness) and b*(yellowness) measurements occurred every 12 h during retail case display. For each of the three products, neither least squares means for APC nor LAB exceeded 7 log CFU/g until after 21 d dark storage. Throughout retail case display, for all products, following all dark storage times, tan/brown discoloration means remained below 3%. With some exceptions, least squares means for panelist-determined lean color and redness intensity declined (P < 0.05) predictably, with greater retail case storage time. The L* means increased inconsistently depending on product or dark storage time; however, in several instances, L* values were highest (P < 0.05) toward the end of retail case storage. Conversely, a* values generally declined (P < 0.05) with increased storage times indicating a shift from bright red to dull blue color. Few noticeable trends among product and dark storage time were observed for CIE b* values throughout display. Least squares means for TBAR analyses were either similar (P > 0.05) or increased (P < 0.05) with retail case storage time.