RESUMO
D-values and z-values were determined for lean (2.0% fat) and fatty (30.5% fat) ground beef inoculated with approximately 107 Escherichia coli 0157:H7 cells per g. Inoculated ground meat was sealed in glass thermal death time tubes which were completely immersed in a circulating water bath and held at prescribed temperatures for predetermined lengths of time. Survival was determined by enumeration on plate count agar (PCA) containing 1% sodium pyruvate and by the 2-h indole test of Lee and McClain (7). D-values for fatty ground beef exceeded those for lean ground beef at the temperatures tested. D-values for lean and fatty ground beef at 125°F were 78.2 and 115.5 min, respectively, as enumerated on PCA plus pyruvate. D-values at 135°F were 4.1 and 5.3 min for lean and fatty beef. At 145°F D-values were determined to be 0.3 and 0.5 min. D-values calculated from 2-h indole test data for lean and fatty ground beef at 125°F were 80.1 and 121.0 min, respectively. D-values at 135°F were 4.0 and 7.4 min for lean and fatty beef and at 145°F a D-value of 0.2 min was calculated for lean beef only, due to insufficient survival of E. coli 0157:H7 in fatty beef at this temperature. The z-values determined for lean beef and fatty beef using PCA were 8.3 and 8.4°F respectively. The z-value for lean beef using the 2-h indole data was 7.8°F. No z-value for fatty beef using 2-h indole data could be determined.
RESUMO
D-Values and z-values for Listeria monocytogenes strain Scott A were determined in lean (2.0% fat) and fatty (30.5%) ground beef inoculated with approximately 107cells/g. Inoculated ground meat was sealed in glass thermal death time tubes which were completely immersed in a circulating water bath and held at prescribed temperatures for predetermined lengths of time. Survival was determined by enumeration on Columbia CNA agar base containing 1% sodium pyruvate with a CNA + 4% horse blood overlay (CBNA) and on Listeria Plating Medium (LPM). D-values for L. monocytogenes in lean and fatty ground beef at 125° were 81.3 and 71.1 min, respectively, as enumerated on CBNA plus pyruvate. D-values at 135°F were 2.6 and 5.8 min in lean and fatty beef. At 145°F, D-values were determined to be 0.6 and 1.2 min. D-values calculated from LPM recovery data from fatty ground beef at 125°F were 56.1 and 34.5 min, respectively. D-values at 135°F were 2.4 and 4.6 min in lean and fatty beef. At 145°F a D-value of 0.5 min was calculated in lean beef and a D-value of 1.1 min was determined in fatty beef. The z-values determined in lean beef and fatty beef using CBNA recovery data were 9.3 and 11.4°F, respectively. The z-value in lean beef using LPM recovery data was 9.8°F. The z-value in fatty beef using LPM recovery data was 13.2°F. A D-value for ground turkey meat at 160°F could not be determined under the conditions of this study. Problems encountered are discussed.
