Isolation of Alicyclobacillus acidoterrestris from Fruit Juices

Abstract

K agar, a novel isolation medium developed for the food industry, was compared with other acidified media for isolation of Alicyclobacillus acidoterrestris spores. Spores were inoculated into apple juice, orange juice, and a fruit juice blend and then isolated on the following media: K agar, pH 3.7; semi-synthetic medium, pH 4.0; orange serum agar, pH 3.5; and minimal salts medium, pH 4,0. Media were incubated at 24, 35, 43, and 55°C. Highest recovery of spores was obtained with either K agar or semi-synthetic medium, incubated at 43°C. The effect of heat shocking spores at different times was also determined; heat shocking at 80°C for 10 min was considered appropriate. Peptone, previously shown to inhibit A, acidoterrestris, was not inhibitory when present in K agar. A collaborative trial with 9 laboratories was undertaken to determine the repeatability and reproducibility of counts on K agar. K agar prepared from individual components was compared with dehydrated K agar prepared by International BioProducts (Redmond, WA). There were no significant differences between log mean counts for the 2 media for each of the juices analyzed at both the high and the low inoculum levels. Repeatability and reproducibility values were not significantly different either within juices, within trials, or across all samples tested in both trials. K agar is suitable for isolation of A, acidoterrestris spores from fruit juices.