Inactivation of Bacillus subtilis spores by combined pulsed light and thermal treatments.

The combined effect of pulsed light (PL) and heat processing was evaluated on the inactivation of Bacillus subtilis spores. Those processes were applied separately and the time between both treatments was modified to evaluate whether the effect of the first treatment is maintained for a long time. B. subtilis spores subjected to sublethal pre-treatments were more sensitive to subsequent treatments (PL or thermal treatments) than untreated spores. Heating followed by PL was the most effective combination in reducing B. subtilis counts. Bacterial spores remained sensitized to subsequent treatment for at least 24 h of storage in water, whatever the temperature was (4 or 30°C). Sensitivity of B. subtilis cells to PL or heat processing increased after germination in a nutrient broth, being equally sensitive from 3 to 24 h. Vegetative cells maintained their enhanced sensitivity to subsequent processing after spore germination. The results of this work demonstrate that the combination of heating and PL treatment is a promising preservation method for microbial inactivation.

Influence of ß-lactoglobulin and ß-casein on Listeria innocua inactivation by pulsed light.

The effect of ß-lactoglobulin and ß-casein on the pulsed light (PL) inactivation of Listeria innocua was evaluated. For low protein concentrations (ß-lactoglobulin and ß-casein up to 10 mg/mL), the lowest fluences applied (0.2 J/cm(2)) induced more than 7 Log reductions in cell counts. However, higher fluences were needed to induce similar reduction in L. innocua counts when this bacterium was suspended in solutions of higher protein concentration. The fluence required to induce similar microbial inactivation was lower in ß-casein than in ß-lactoglobulin solutions. For all protein solutions, the inactivation curves followed first order kinetics. The specific inactivation rate for L. innocua inactivation in protein solutions depended on the quantity of light transmitted in the range 230-290 nm by protein solutions. This work shows that PL technology could be used for the decontamination of high protein content solutions like whey or even higher protein concentration solutions.