Effects of soluble polylactic acid and gamma irradiation on ground beef inoculated with Escherichia coli 0157:H7 and legal classification of irradiation as a food additive

Ground beef samples were inoculated with stationary phase E. coli 0157:H7 cells to a concentration of 107 cfu/ml and allowed to incubate for 24 hours. The samples were treated with a 2% solution of soluble polylactic acid (SPLA) and exposed to gamma radiation in doses ranging from 7--125 krads at a dose rate of 17.1 krads/hr.; After 2 days of storage at 4°C there was an overall reduction in E. coli 0157:H7 populations of 0.70 log10 CFU/ml. (30%) in ground beef treated with SPLA only. Gamma irradiation was effective in reducing E. coli 0157:H7 populations in ground beef and resulted in an overall reduction of 4.55 log10 CFU/ml after 125 krads. SPLA in combination with gamma radiation was less effective than gamma radiation alone in reducing populations of E. coli 0157:H7 in ground beef and resulted in a reduction in E. coli 0157:H7 populations of 3.80 log10 CFU/ml after 125 krads. SPLA was protective at the 2% level and may act to prevent the cleavage of DNA molecules. Refrigerated storage of irradiated ground beef at 4°C for 7 days had no significant effect on E. coli 0157:H7 populations. SPLA treatment had a significant effect (p < 0.01) on the pH of ground beef but had no effect on water activity and moisture content.