Synergy between high-pressure, temperature and ascorbic acid on the inactivation of Bacillus cereus

B. cereus strain (CECF 148) was used as a model system in the study of the behaviour of bacillus under high pressure, at temperatures over and below 0 degrees C and with ascorbic acid added to the culture. Three different assays were carried out in the present experiment. The first assay was performed to observe how B. cereus reacted to pressure shift freezing (PSF) treatment at different subzero temperatures (-8, -12, -20 and -17 degrees C) and pressures (120, 150, 210 and 350 MPa) in their vegetative form. In the second assay, we observed how different concentrations of ascorbic acid (1, 2, 5 and 20 mM) added to the growing brought decreased B. cereus on its vegetative form. Finally, we tried to inactivate the vegetative and spore form of B. cereus under pressure of 210 MPa at room (20 degrees C) (HP) and at subzero (-20 degrees C) (PSF) temperatures, in presence of ascorbic acid (20 mM), added to the growing culture (TSB). The results confirmed that pressures of 210 and 350 MPa at low temperatures (-20 and -17 degrees C) in the PSF treatment were not enough to inactivate bacillus and only about 10% of B. cereus at the assayed conditions (350 MPa at -17 degrees C) lost its growth capacity. The presence of ascorbic acid reduced the amount of B. cereus. The initial amount of B. cereus in the vegetative form was 10(8) to 10(9) cfu/mL. After HP (210 MPa at 20 degrees C) and PSF (210 MPa at -20 degrees C) treatments, the amount of B. cereus decreased by 4 and 2 logarithmic units, respectively. However, in both treatments, the presence of ascorbic acid (20 mM concentration) reduced the B. cereus growth capacity in about 5 logarithmic units. The presence of ascorbic acid in the spore form decreased the amount of B. cereus only by 2 logarithmic units, but without the antioxidant, the values remained close to control. The present research is a contribution to elicit the safety standards of food treated by high pressure.