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

摘要

Bacillus cereus strain CECF 148 was used as a model system to study of the behaviour of Bacillus under high pressure, at temp. over and below 0 degrees C and with ascorbic acid added to the culture. 3 different assays were carried out. The 1st assay was performed to observe how B. cereus reacted to pressure shift freezing (PSF) treatment at different subzero temp. (-8, -12, -20 and -17 degrees C) and pressures (120, 150, 210 and 350 MPa) in the vegetative form. The 2nd assay observed the effects of different concn. of ascorbic acid (1, 2, 5 and 20mM) on vegetative growth, and in the 3rd experiment, attempts were made to inactivate the vegetative and spore forms of B. cereus under at 210 MPa at room (20 degrees C) (HP) and at subzero (-20 degrees C) (PSF) temp., in the presence of ascorbic acid (20mM). Rresults confirmed that pressures of 210 and 350 MPa at low temp. (-20 and -17 degrees C) during PSF treatment were insufficient to inactivate Bacillus; only approx. 10% of B. cereus lost its growth capacity. The presence of ascorbic acid reduced B. cereus counts. Initial amounts of B. cereus in the vegetative form were in the range 108 to 109 cfu/ml. After HP (210 MPa at 20 degrees C) and PSF (210 MPa at -20 degrees C) treatments, counts of B. cereus decreased by 4 and 2 logarithmic units, respectively. However, in both treatments, the presence of ascorbic acid (20mM) reduced B. cereus growth capacity by approx. 5 logarithmic units. Presence of ascorbic acid in spore form decreased amounts of B. cereus by only 2 logarithmic units, but without the antioxidant, values remained close to controls.