Prevalence, concentration, spoilage, and mitigation of Alicyclobacillus spp. in tropical and subtropical fruit juice concentrates

The presence of Alicyclobacillus in fruit juices and concentrates poses a serious problem for the juice industry. This study was undertaken to determine the (i) prevalence, concentration, and species of Alicyclobacillus in tropical and subtropical concentrates; (ii) efficacy of aqueous chlorine dioxide in reducing Alicyclobacillus spp. spores on tropical and subtropical fruit surfaces; and (iii) fate of and off-flavor production by Alicyclobacillus acidoterrestris in mango and pineapple juices. One hundred and eighty tropical and subtropical juice concentrates were screened for the presence and concentration of Alicyclobacillus spp. If found, the species of Alicyclobacillus was determined by 16S rDNA sequencing and analysis with NCI BLAST. Of these samples, 6.1% were positive for Alicyclobacillus, and nine A. acidoterrestris strains and two Alicyclobacillus acidocaldarius strains were identified. A five-strain cocktail of Alicyclobacillus spp. was inoculated onto the surface of fruits (grapefruit, guava, limes, mangoes, oranges and pineapple), which were then washed with 0, 50, or 100 ppm aqueous chlorine dioxide. Significant reductions due to chlorine dioxide were only seen on citrus fruits. A five-strain cocktail of A. acidoterrestris was inoculated into mango and pineapple juices. Microbial populations were enumerated over a 16-day period. Aroma compounds in the juice were analyzed by GC–olfactometry (GC–O) and confirmed using GC–MS. GC–O of mango juice identified previously reported medicinal/antiseptic compounds. GC–O of pineapple juice revealed an unexpected “cheese” off-aroma associated with 2-methylbutyric acid and 3-methylbutyric acid. ► Of the 180 tropical and subtropical juice concentrates screened, 6.1% were positive for Alicyclobacillus. ► In positive concentrates, Alicyclobacillus concentrations varied significantly. ► Chlorine dioxide significantly reduced Alicyclobacillus spore concentrations on the surface of citrus fruits. ► GC–O of pineapple juice following Alicyclobacillus growth yielded unexpected “cheese” off-aroma.