EFFICACY OF HEAT AND ETHANOL SPORE TREATMENTS FOR THE ISOLATION OF PSYCHROTROPHIC CLOSTRIDIUM SPP. ASSOCIATED WITH THE SPOILAGE OF CHILLED VACUUM-PACKED MEATS

Psychrotrophic Clostridium spp. associated with chilled meat spoilage are difficult to isolate and culture. In this study the kinetics of he at and ethanol spore inactivation was determined as a first step towar ds optimising the recovery of psychrotrophic clostridial spores from m eat and environmental samples. To determine heat inactivation, spores of nine isolates associated with spoiled chilled or frozen meat and a psychrotrophic reference strain Clostridium algidicarnis NCFB 2931, su spended in phosphate buffer, were exposed to temperatures between 75 d egrees C and 95 degrees C for 0 to 120 min using a submerged tube proc edure. Survivors after various temperature-time combinations were enum erated on Peptone Yeast Extract Glucose Starch (PYGS) agar containing lysozyme. D-values and z-values for each spore suspension were determi ned from their respective survival curves. To determine ethanol inacti vation, similar phosphate buffer spore suspensions were mixed with equ al volumes of absolute ethanol, incubated at 20 degrees C and survivor s enumerated on lysozyme-containing PYGS agar after 0 to 300 min. Base d on spore heat inactivation, the 10 isolates could be grouped as havi ng either heat-sensitive or heat-resistant spores. For heat-sensitive spore types, 60 min ethanol treatment gave maximum spore recovery wher eas for heat-resistant spore types, heat treatment at 80 degrees C for 10 min gave the best recovery. When the spore heat-resistance type is unknown, as would be the case when attempting an isolation from spoil ed product, both an ethanol treatment and a separate heat treatment sh ould be used, to ensure maximum spore recovery. (C) 1998 Elsevier Scie nce B.V.