Peracetic Acid Effects on Shelf Life and Survival of Escherichia coli on Beef Steaks
Type of DegreeMaster's Thesis
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A study was conducted to determine the effectiveness of peracetic acid (PAA) against Escherichia coli O157:H7 in beef. In this study, 150 slices of beef ball tips (IMPS: 185B) weighing 100g each were inoculated with either a high (106 CFU/mL) or a low (102 CFU/mL) inoculation of a cocktail made of five strains of E. coli O157:H7. After a 30 minute attachment time at ambient temperature, the inoculated samples were treated with either 0.012% (120ppm) PAA, 0.04% (400ppm) PAA, or were left untreated as the control. The amount of peracetic acid solutions applied to each sample was approximately 3mL in total. After a 5-minute treatment time, samples (including control samples) were sprayed with approximately 1mL of sodium thiosulfate to neutralize the reaction. The neutralized samples were plated onto Cefixime Tellurite Sorbitol MacConkey agar (CT-SMAC) and incubated for 24 hours at 35° C. Three replications were conducted. For the low (102 CFU/mL) inoculation level of E. coli O157:H7, the 120ppm treatment of PAA reduced bacterial numbers by 0.067 log CFU/g, which was not different (P>0.05) from the control. The 400ppm treatment for the low inoculation level of E. coli O157:H7 reduced (P<0.05) the bacterial numbers by 0.568 log CFU/g. When treatment was applied to the high (106 CFU/mL) concentration of E. coli O157:H7, both the 120ppm treatment and the 400ppm treatment of PAA reduced (P<0.05) the bacterial numbers (reductions were 0.12 log CFU/g and 0.19 log CFU/g, respectively). While both 120ppm PAA and 400ppm PAA reduced the overall amount of E. coli O157:H7 when compared to the positive controls, not all reductions were significant, and treatment with 400ppm PAA was the most effective at reducing E. coli O157:H7 on the samples. Sensory analysis was performed by treating samples with 0.04% (400ppm) or 0.012% (120ppm) peracetic acid, with some samples left untreated as a control. Total volume of peracetic acid solution applied was approximately 3mL per sample. Samples were cooked to an internal temperature of 160° F, then cut (2.54cm x 1cm x 1cm) and placed into plastic cups labeled with random 3-digit codes. Panelists evaluated samples one at a time using an 8-point hedonic scale for initial and sustained tenderness, initial and sustained juiciness, flavor intensity, and off-flavor intensity. Results from the sensory analysis showed no difference between treatments (P>0.05) in any of these characteristics. Data from Warner-Bratzler shear force measurements indicated no difference (P>0.05) between treatment with 400ppm peracetic acid and the control, or between treatment with 120ppm or 400ppm peracetic acid, but did indicate an increase (P<0.05) in tenderness between treatment with 120ppm peracetic acid and the control. It is of note that the shear force values for treatment with 400ppm peracetic acid were lower than the values for the control, indicating that they were slightly more tender when treated; however, this difference was not significant (P>0.05). In a shelf-life study, 100g slices of beef ball tips (n=108) were inoculated with 100μL of the high (106 CFU/mL) inoculum. Following a 30-minute bacterial attachment time, samples were sprayed with 0.012% (120ppm) PAA, 0.04% (400ppm) PAA, or left untreated as a positive control. Total volume of peracetic acid solution applied was approximately 3mL per sample. After a 5-minute treatment time, samples were sprayed with approximately 1mL of 0.1% sodium thiosulfate to neutralize any remaining reaction from the PAA. Samples were packaged in a Styrofoam tray with overwrap and placed in a walk-in cooler. On days 1, 3, 5, and 7, color was analyzed using a Hunterlab L* a* b* colorimeter, then samples were plated in duplicate onto CT-SMAC, Plate Count Agar, Coliform petrifilms, and Yeast/Mold petrifilms. Plates were incubated 24 hours following the manufacturers’ instructions. This process was repeated on different days for a total of three replications. Results showed that, although there were some interactions for color by day and replication of the study, there is no difference (P>0.05) in L*, a*, or b* color values between treatment values alone with 120ppm peracetic acid, 400ppm peracetic acid, or the control. Furthermore, results indicate that a treatment of 400ppm peracetic acid is more effective (P<0.05) at controlling bacterial growth than 120ppm peracetic acid or the control. In summary, peracetic acid may be viable for use in a multi-hurdle approach to the control of E. coli O157:H7 without negative effects to shear force or quality or sensory attributes.