THERMAL-RESISTANCE OF BACILLUS-STEAROTHERMOPHILUS HEATED AT HIGH-TEMPERATURES IN DIFFERENT SUBSTRATES

The effect of mushroom extract, with or without acidification with glu cono-delta-lactone, and the overnight incubation of the spores in CaCl 2, on the heat resistance of B. stearothermophilus ATCC 12980 spores w as studied. The temperature range considered was 121 to 140 degrees C for mushroom extract and CaCl2 and 121 to 145 degrees C for double-dis tilled water as a reference substrate. The results indicated that mush room extract without added acid significantly reduces the thermal resi stance of the spores in comparison to the double-distilled water. Acid ification of the mushroom extract reduces the heat resistance of spore s of B. stearothermophilus at 121 degrees C. However, above 130 degree s C lowering of the pH did not significantly reduce the thermal resist ance of the spores, and so no generalizations should be made with rega rd to the effect of the pH when high temperature-short time (HTST) pro cesses are being considered. Overnight incubation in CaCl2 and subsequ ent heat treatment lead to increased heat resistance at 121 degrees C compared to that observed in double-distilled water. However, at 130 d egrees C and above CaCl2 did not increase the apparent heat resistance of the spores.