The different pathways of spore germination and inactivation of Bacillus subtilis under high pressure and elevated temperatures

摘要

High pressure combined with elevated temperatures could produce commercially sterile and shelf stable lowacid foods. Depending on the applied temperature and pressure level, bacterial endospores pass throughdifferent physiological pathways, which can induce germination or a subsequent inactivation. To improve theunderstanding of spore inactivation Bacillus subtilis spores and isogenic strains, which lack the gens forencoding the germinant receptors, were pressure treated. Therefore, the strains FB114 and FB115 and its wildtype strain (PS832) were processed from 1 s up to 24 h in a pressure-temperature range of 200 – 1000 MPaand 30 - 80 °C under isothermal and isobaric conditions during dwell time in pressure stable ACES buffersolution. Afterwards, aliquots of each sample were mild heat treated and the released amount of DPA wasquantified by HPLC, to estimate the amount of germinated spores. Further, two model approaches weretested to derive a global model from the kinetic data. It was confirmed for both FB-strains, that sporegermination above 500 MPa is possible without germinant receptors and even at 300 MPa germination ofthese spores was detected. Furthermore, no spore inactivation occurred for pressures below 700 MPa andtemperatures up to 50 °C. Whereas The behavior of PS832 was contrary, here an inactivation of more than3 log_(10)-cycles was detected at 300 MPa after 30 min dwell time at 40 °C and no inactivation was observed at550 MPa, 37 °C, 120 min. Possibly, spores with nutrient receptors could proceed through stage II ofgermination at low pressure levels, whereas this germination step is retarded at higher pressures. Moreover,above 300 MPa both germination mechanisms interfere with each other, whereas above 500 MPa the openingof the Ca~(2+)-DPA-channels is dominant. For all strains a strong acceleration of germination with increasingpressure and temperature was detected, whereas above a certain threshold pressure (p > 600 MPa) thetemperature played the dominant role for spore inactivation.