Effect of high pressure homogenization applied individually or in combination with other mild physical or chemical stresses on Bacillus cereus and Bacillus subtilis spore viability

High pressure homogenization (HPH) has been proposed as an effective alternative to high hydrostatic pressure in the continuous sanitization of fluid food systems. In this study, we evaluated the influence of HPH treatment, applied individually (one, two or three cycles) or in combination with other mild physical or chemical stresses (mild heat treatment H2O2 and low pH), on the capability of Bacillus cereus and Bacillus subtilis spore, suspended in sterilized double distilled water, to form colonies. Although plate count only slightly decreased in all the strains when one cycle of HPH at 150 MPa was applied alone, the spores released significant levels of dipicolinic acid (up to 28%) that could indicate a possible disruption of spore layers. Three consecutive cycles of HPH determined high reduction of colony count (about 5 log CFU/ml) and high DPA release (52%). Among the stress conditions applied, it was observed that only the thermal shock after one HPH cycle reduced the colony count of 2.3 log CFU/ml and induced a DPA release up to 57%.These results suggested HPH as a novel application for B. cereus and B. subtilis control in fluid foods.