Thermal destruction of Escherichia coli O157:H7 in beef and chicken: determination of D- and z-values.

Thermal inactivation of a four-strain mixture of E. coli O157:H7 was determined in 90% lean ground beef, and lean ground chicken. Inoculated meat was packaged in bags which were completely immersed in a circulating water bath and held at 55, 57.5, 60, 62.5, and 65 degrees C for predetermined lengths of time. D-values, determined by linear regression, in beef were 21.13, 4.95, 3.17, 0.93 and 0.39 min, respectively (z = 6.0 degrees C). Using a survival model for non-linear survival curves, D-values in beef ranged from 20.45 min (D1; and there was no D2) at 55 degrees C to 0.16 min (D1) and 1.45 min (D2) at 65 degrees C. When E. coli O157:H7 four-strain cocktail was heated in chicken, D-values calculated by both approaches were consistently less at all temperatures. The heat resistance of E. coli O157:H7 was not altered after refrigerated or frozen storage of inoculated beef for 48 h. The results of this study will be beneficial to the food industry in designing HACCP plans to effectively eliminate E. coli O157:H7 in the meat products used in this study.

Bacterial Growth at Foodservice Operating Temperatures.

A search of current literature was conducted to determine the mean generation times (MGT) at various temperatures for growth of Staphylococcus aureus , Clostridium perfringens , Salmonella and total aerobes in various foods. The data were graphed and a regression line was plotted to begin to form a more definitive time-temperature basis for specification of safe foodservice recipe procedures and to increase sensory quality through control of spoilage organisms. The results show that generation times vary significantly over the range of temperatures normally found in foodservice, and pathogenic bacterial growth slows rapidly below 15-20 C. The results also show that data are quite limited and that there is need for additional studies.