Abstract
Lactobacillus spp. display a higher radiation resistance than most bacteria and can withstand doses of between 2·5 and 5·0 kGy. This leads to their dominance in the microflora of radurised meats. The lactobacilli are also acid-tolerant, with a pH range for growth of 7·2–3·0. As the severity of radiation processing may be reduced by combination with other treatments, the effect of irradiation on Lactobacillus curvatus was examined over a range of pH values. Exponential phase cultures of L. curvatus, containing approximately 10 8 cells ml −1, were irradiated in de Man, Rogosa & Sharpe broth at doses of 0–1·9 kGy, at pH values ranging from 7·5 to 4·0. Lowering the pH from 4·6 to 4·3 and below before irradiation had no effect on the survival rate of L. curvatus up to a dose of 1·9 kGy. An increase in pH to 7·0 before irradiation led to a marked decrease in survivors, over a dose range of 1·0–1·9 kGy. No futher decrease was seen when the pH was increased to 7·5 prior to irradiation. This effect was only observed when the pH was altered before radiation processing.
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