Reduction of Alicyclobacillus acidoterrestris Spores on Apples by Chlorine Dioxide in Combination with Ultrasound or Shaker

Alicyclobacillus acidoterrestris has recently become a major issue in the fruit juice industry due to its implication in the spoilage of pasteurized juices. The aim of this study was to determine the potential of combining chlorine dioxide (ClO2) with ultrasound or shaker processes to reduce A. acidoterrestris spores on the apple. Fuji apples were inoculated with a five-strain suspension of A. acidoterrestris spores and treated by ClO2, ultrasound and shaker, individually or combined. The results showed that ClO2 in combination with shaker was the most effective in reducing A. acidoterrestris spores on apples. After treatment with 200 mg/L ClO2 plus shaker (200 rpm) for 20 min, the viable spores remaining on the surface of the apple was reduced to undetectable levels (< 1.7 log(10) colony-forming unit (CFU)/apple). The inactivation efficiency of ClO2 was significantly decreased with the increase of pH in the range of 2.5-8.5; whereas, the alkaline condition was favorable to the spore detachment from apple surfaces. As for the artificially A. acidoterrestris-contaminated samples with spore concentrations of 3, 4, and 5 log CFU/apple, spores were reduced below the level of detection after combined treatment with ClO2 (50 mg/L, pH 2.5) and shaker (200 rpm) for 5, 10, and 20 min, respectively. This study demonstrates that the combination of ClO2 and shaker is an effective approach for controlling A. acidoterrestris spores on apples and minimizing the risk of contamination in apple juice.