HEAT-RESISTANCE OF ALICYCLOBACILLUS-ACIDOTERRESTRIS SPORES AS AFFECTED BY VARIOUS PH VALUES AND ORGANIC-ACIDS

Alicyclobacillus acidoterrestris, a thermoacidophilic sporeformer, has caused spoilage of fruit juices which had been treated with thermal p rocesses intended to commercially sterilize the juice. The objective o f this research was to document the effect of pH, acid, and temperatur e on the heat resistance of spores of three fruit-juice isolates of A. acidoterrestris. The thermal resistance of spores of A. acidoterrestr is strains VF, WAC, and IP were studied in a model fruit-juice system composed of 12% glucose and 30 mM of either citric, malic, or tartaric acid, adjusted to selected pH values ranging from 2.8 to 4.0. Decimal reduction times (D values) and inactivation rates were determined. Sp ores of strains VF and WAC were similarly resistant to heat under acid ic conditions, while strain IP spores were less resistant. In the rang e of pH 2.8 to 4.0, a statistically significant effect of hydrogen ion concentration on heat resistance was observed at lower temperatures, but not at the higher temperatures. For example, at 91 degrees C and p H 3.1 and 3.7, D values were 31.3 and 54.3 min, respectively, while at 97 degrees C D values at pH 3.1 and 3.7 were 7.9 and 8.8 min, respect ively. The type of acid did not significantly affect the heat resistan ce. The z(D) values ranged from 5.9 to 10 degrees C, depending on the acid, pH, and the strain. The models generated from this research can be used to determine adequate thermal processes, accounting for the ac id type, pH, and temperature, to destroy A. acidoterrestris spores in beverages, since this organism is able to survive the typical hot-fill and hold process (2 min at 88 to 96 degrees C) currently used to proc ess fruit juice.