Heat resistance and outgrowth of clostridium perfringens spores as affected by the type of heating medium, and heating and cooling rates in ground pork

摘要

The survival and germination of Clostridium perfringens spores in differentheating media and at different heating rates was studied to determine the fate of C.perfringens spores during abusive cooking and cooling of pork products. The heatresistance (HR) of C. perfringens spores from three strains that were either previouslyheat shocked (HS) or non-heat shocked (NHS) was determined individually and as acocktail in phosphate buffer solution (pH 7.4) (PBS), beef gravy (BG), ground pork (GP)and cured ground pork (CGP) at 75?C. The effect of the heating rate on HR, germinationand outgrowth of C. perfringens spores in CGP was determined by increasing thetemperature from 20 to 75?C at a rate of 4, 8, and 12?C/h prior to heating and holding at75?C for 48 h. Heating rates at 4?C/h in GP and CGP were repeated with additionalcooling from 54.4 to 7.2?C within 20 h (temperature abuse).Linear survival curves were observed on NHS spores in the four heating media,whereas HS spores showed linear curves when heated in PBS and BG, and biphasiccurves when heated in GP and CGP. In general, HS spores were more heat sensitive than NHS spores. NHS spores heated in GP had greater HR than spores heated in CGP, BGor PBS.There were no significant differences (P>0.05) on the HR of C. perfringensspores in CGP heated from 20 to 75?C at 4, 8, or 12?C/h. Heating rates of 8 and 12?C/hshowed no difference in germination and outgrowth of inoculated spores, whereas at4?C/h, growth of C. perfringens occurred between 44 and 56?C.Temperature abuse during cooling of GP resulted in 2.8 log CFU/g increase of C.perfringens counts. In CGP, C. perfringens counts decreased by 1.1 log CFU/g duringcooling from 54.4 to 36.3?C and then increased by 1 log CFU/g until the product reached7.2?C. However, with an initial inoculum in raw CGP of 5 log CFU C. perfringensspores/g, C. perfringens counts did not exceed 3.4 log CFU/g during a 20 h abusivecooling. These results suggest there is no risk associated with C. perfringens in curedpork products under the conditions tested. Results from the present study indicate thatdifferent behavior may be expected with different meat products.