Effect of High Hydrostatic Pressure Treatment Combined with Alkaline Electrolyzed Water on the Injury and Growth Characteristics of Bacterial Spores

The characteristics of growth and injury of Bacillus subtilis spores whose heat resistance was reduced by the treatment of high hydrostatic pressure processing (HPP) combined with/without alkaline electrolyzed water (AlEW) were investigated. The delay in the lag phase of growth curve observed when used in combination with AlEW, especially at 50 MPa or less, and was prolonged by about 4 to 6 hours. However, the effects of temperature and time during treatment on the lag phase were not significantly different between solo-HPP and in combination with AlEW. The injury characteristics of the treated bacterial spores were evaluated by using antibiotics (penicillin G, rifampicin and chloramphenicol) supplemented trypticase soy broth. In the chloramphenicol supplemented TSB, although the lag phase of bacterial spores treated by HPP with AlEW was not prolonged as compared with the normal-TSB, the decrease in growth rate during logarithmic phase and increase in maximum growth amount were observed. This result could suggest due to a damage by combined treatment of HPP with AlEW such as the inhibition of protein synthesis. Furthermore, the combined treatment with AlEW increased the catalase activity by 1.45, 1.63 and 4.25 times at 30, 80 and 100 MPa, respectively, as compared with solo-HPP, therefore the combined treatment could cause high oxidative stress on bacterial spores.