Saccharomyces cerevisiae ATCC 2373 and Zygosaccharomyces bailii ATCC 36947 were exposed to hydrostatic pressures ranging from 1,500 to 3,000 atmospheres for 10, 20 and 30 min in 0.1 M citrate buffer at pH 3.0, 4.0 and 5.0 at 25 and 45°C. Inactivation of inoculated yeast cultures was achieved in spaghetti sauce with meat at 25°C with 3,000 atmospheres for 10 min and also at 45°C and 2,500 atmospheres for 10 min. Viable counts were determined on potato dextrose agar (PDA) incubated at 30°C for 48 h. Pressure-induced injury was demonstrated by plate count differential between PDA and PDA supplemented with glucose (PDAG). A reduction of 7-log₁₀ cycles colony forming units (CFU)/ml was seen for both strains at 3,000 atmospheres for 10 min at 25°C at all pH levels and at 2,250 atmospheres, pH 5.0 for 20 min at 45°C. At 2,000 atmospheres, pH 3.0 for 30 min, the increase in temperature from 25 to 45°C increased the inactivation of yeast by 6-log₁₀ cycles. Lowering the pH from 5.0 to 3.0 enhanced lethality up to 2-log₁₀ cycles at 2,250 atmospheres, 25°C for 30 min. Injury was most apparent at exposure parameters that produced 3- to 5-log₁₀ cycle reductions on PDA. This was achieved (99% injury) at 2,250 atmospheres, 25°C for 30 min. These data indicate that mild heat and acidity contribute to the effectiveness of the inactivation and injury of yeast by high hydrostatic pressure (HHP).

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Pandya Y, Jewett FF, Hoover DG

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