Fruit juice and puree characteristics influence enrichment requirements for real-time PCR detection of Alicyclobacillus acidoterrestris

Background: Alicyclobacillus acidoterrestris is a key spoilage causing bacterium commonly found in fruit juices and purees. Commercial real-time PCR based assays to detect this organism are available, but reportedly require 48 hours of enrichment for detection. The underlying hypothesis of this study was that fruit juice and puree characteristics influence the enrichment requirements of this organism, and that in some matrices, the organism can be detected within 24 hours even when present at low initial contamination. Thirteen different store-purchased fruit juice and purees were inoculated with 10 CFU/ml of Alicyclobacillus acidoterrestris. The inoculated samples were enriched for 24 and 48 h. Aliquots from the un-enriched, 24 hour, and 48 hour enriched samples were taken, total community DNA extracted, and the real-time PCR assay performed using commercially available kits. Results: A. acidoterrestris was detected by real-time PCR within 24 h of enrichment in most matrices (except ketchup and orange concentrate) even from a low starting concentration (10 CFU/ml). Juice and puree samples with high soluble solids contents (i.e. Brix values) required longer incubation periods for lower A. acidoterrestris Ct values. Conclusions: The soluble solids (Brix) content of fruit juice and purees influence the enrichment requirements for real-time PCR detection of A. acidoterrestris. Samples with high Brix values should be diluted to reduce the inhibitors of A. acidoterrestris proliferation during enrichment.