INFLUENCE OF GROWTH-MEDIUM ON THERMAL-RESISTANCE OF PEDIOCOCCUS SP NRRL B-2354 (FORMERLY MICROCOCCUS-FREUDENREICHII) IN LIQUID FOODS

Pediococcus sp. is a nonpathogenic heal-resistant spoilage organism th at has been used as a test organism in milk pasteurization studies. Th ese characteristics make this bacterium an attractive test organism to study the mode of bacterial thermal inactivation in a food pilot plan t, We report here the effect of growth medium on the thermal D value o f this organism in skim milk, whole Liquid egg, 10% glucose solution, pineapple juice, apple juice, tomato juice, and water at 60 degrees C. Thermal inactivation was done in a submerged coil; D values were calc ulated from the linear portion of the survival curves by linear regres sion analysis. The range of D values of stationary-phase cells grown a t 28 degrees C in tryptone glucose yeast extract (TGY) or tryptic soy broth (TSB) was 0.14 to 12.05 min in all heating menstrua tested. The TSB-grown cells exhibited the highest thermal resistance with skim mil k and 10% glucose solution as the heating menstrua. Survival curves of the TGY-grown cells indicated the presence of a cell population heter ogeneous in thermal resistance. The TSB-grown cells exhibited a cell p opulation uniform in thermal resistance and with a lag time for therma l inactivation. When compared to TGY-grown cells, Pediococcus sp, grow n in TSB showed a significant (P < 0.05) increase in D values by up to eightfold in all heating menstrua. Results from this study suggested that thermal inactivation of Pediococcus sp. was dependent on the grow th medium and on the heating menstruum with respect to both pH and com position.