Quantitative determinations of selected bacteria in ground beef extended with varying levels of textured vegetable protein

The objective of this study was to determine the influence of various levels of textured vegetable protein (TVP) on selected groups of bacteria present in ground beef. This influence was assessed by five selected bacteriological assays: aerobic count, psychrophilic-mesophilic count, coliform count, KF (fecal streptococci) count and the counts of Staphylococcus aureus. Samples were prepared by extending ground beef to contain by weight 0, 5, 10, 20 and 40 percent of hydrated TVP. The samples were stored at 6°C for 4 days, at 0°C for 10 days and at -16°C for 90 days. The bacteriological determinations of the TVP revealed that this material contained very small numbers of bacteria as determined by the selected assays. Variation among replications during storage at the three selected temperatures was highly significant (P < 0.01). Highly significant (P < 0.01) or significant (P < 0.05) increases in logarithmic counts were observed with increased time of storage at 6°C and 0°C, but not at -16°C, in all assays except those for Staphylococcus aureus. Highly significant (P < 0.01) decreases were observed with time in logarithmic counts of Staphylococcus aureus at all storage temperatures. With the exception of percent protein, highly significant (P < 0.01) changes were observed in proximate analyses with increasing levels of TVP. Percent moisture and the unanalyzed fraction increased while the percent ether extract decreased. The protein analyses varied little. Highly significant (P < 0.01) increases in logarithmic aerobic and psychrophilic-mesophilic counts accompanied increased level of TVP during storage at 6°C and 0°C, but not at -16°C. The increases in the logarithmic counts of these bacteria at higher levels of TVP commenced early and proceeded rapidly during storage. The interaction between levels of TVP and storage time was observed to be significant (P < 0.05) or highly significant (P < 0.01) at storage temperatures of 6°C and 0°C respectively. No significant differences in logarithmic coliform counts or logarithmic counts of Staphylococcus aureus attributable to varying levels of TVP were observed during storage at any of the selected temperatures. Although highly significant (P < 0.01) increases in logarithmic KF counts due to varying levels of TVP were observed during storage at 0°C, the magnitudes of change as well as observed numbers were small. Coagulase-positive staphylococci were observed in all of the initial samples.