THE EFFECT OF IRRADIATION AND PH ON LACTOBACILLUS-CURVATUS

Lactobacillus spp. display a higher radiation resistance than most bac teria and can withstand doses of between 2.5 and 5.0 kGy. This leads t o their dominance in the microflora of radurised meats. The lactobacil li are also acid-tolerant, with a pH range for growth of 7.-3.0. As th e 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) cell 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 bef ore irradiation had no effect on the survival rate of L. curvatus up t o a dose of 1.9 kGy. An increase in pH to 7.0 before irradiation led t o a marked decrease in survivors, over a dose range of 1.0-1.9 kGy. No further decrease was seen when the pH was increased to 7.5 prior to i rradiation. This effect was only observed when the pH was altered befo re radiation processing.