Inactivation of Listeria monocytogenes Scott A 49594 in Apple Juice Supplemented with Cinnamon

Abstract

Normal (pH 3.7) and adjusted (pH 5.0) pasteurized apple juice containing cinnamon (0, 0.1, 0.2, and 0.3%) was inoculated with Listeria monocytogenes Scott A 49594 at 104 CFU/ml and stored at 5 and 20°C for 7 days. Counts on tryptic soy agar (TSA), modified Oxford (MOX) medium, and thin agar layer (TAL) were determined at 1 h and 1, 3, and 7 days. The TAL method (MOX medium overlaid with TSA) was used for the recovery of injured cells. In apple juice, both at normal and adjusted pH, with any doses of cinnamon, no L. monocytogenes (a 4.6-log CFU/ml reduction) was detected after 1 h of storage at both temperatures, and no growth occurred at any points of storage. Therefore, cinnamon by itself (regardless of pH) had a pronounced killing effect. A further enrichment step with brain heart infusion agar showed that L. monocytogenes was completely inactivated in apple juice stored at 20°C, except in pH 5.0 samples with 0.1% of cinnamon. The TAL method was as effective as TSA in recovering injured cells of L. monocytogenes. Cinnamon considerably inactivates L. monocytogenes in apple juice and thus enhances the safety of this product.