Aj. Pontius et al., HEAT-RESISTANCE OF ALICYCLOBACILLUS-ACIDOTERRESTRIS SPORES AS AFFECTED BY VARIOUS PH VALUES AND ORGANIC-ACIDS, Journal of food protection, 61(1), 1998, pp. 41-46
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.