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High-pressure destruction kinetics of Clostridium sporogenes ATCC 11437 spores in milk at elevated quasi-isothermal conditions

Ramaswamy, Hosahalli S., Shao, Yanwen, Zhu, Songming
Journal of food engineering 2010 v.96 no.2 pp. 249-257
milk, food pathogens, Clostridium sporogenes, sterilizing, sterilized milk, bacterial spores, spore-forming bacteria, bacterial contamination, high pressure treatment, kinetics, food safety, predictive microbiology, mathematical models
The high-pressure sterilization establishment requires data on isobaric and isothermal destruction kinetics of baro-resistant pathogenic and spoilage bacterial spores. In this study, Clostridium sporogenes 11437 spores (10⁷ CFU/ml) inoculated in milk were subjected to different pressure, temperature and time (P, T, t) combination treatments (700-900MPa; 80-100°C; 0-32min). An insulated chamber was used to enclose the test samples during the treatment for maintaining isobaric and quasi-isothermal processing conditions. Decimal reduction times (D values) and pressure and temperature sensitivity parameters, ZT (pressure constant) and ZP (temperature constant) were evaluated using a 3×3 full factorial experimental design. HP treatments generally demonstrated a minor pressure pulse effect (PE) (no holding time) and the pressure hold time effect was well described by the first order model (R ² >0.90). Higher pressures and higher temperatures resulted in a higher destruction rate and a higher microbial count reduction. At 900MPa, the temperature corrected D values were 9.1, 3.8, 0.73min at 80, 90, 100°C, respectively. The thermal treatment at 0.1MPa resulted in D values 833, 65.8, 26.3, 6.0min at 80, 90, 95, 100°C respectively. By comparison, HP processing resulted in a strong enhancement of spore destruction at all temperatures. Temperature corrected ZT values were 16.5, 16.9, 18.2°C at 700, 800, 900MPa, respectively, which were higher than the thermal z value 9.6°C. Hence, the spores had lower temperature sensitivity at elevated pressures. Similarly, corrected ZP values were 714, 588, 1250MPa at 80, 90, 100°C, respectively, which illustrated lower pressure sensitivity at higher temperatures. By general comparison, it was concluded that within the range operating conditions employed, the spores were relatively more sensitive to temperature than to pressure.