Survival of Unstressed and Acid-, Cold-, and Starvation-Stress-Adapted Listeria monocytogenes in Ham Extract with Hops Beta Acids and Consumer Acceptability of HBA on Ready-to-Eat Ham

Abstract

The efficacy of hops beta acids (HBA) against unstressed and stress-adapted Listeria monocytogenes in ham extract and the consumers' acceptability of HBA on ready-to-eat (RTE) hams were investigated. Unstressed or acid-, cold-, or starvation-stress-adapted L. monocytogenes was inoculated (1.3-1.5 log CFU/mL) into 10% ham extract, without (control) or with HBA (4.44 or 10.0 μg/mL). Survival/growth of the pathogen during storage (7.2°C, 26 days) was monitored periodically. Sensory evaluation (30 participants, 9-point hedonic scale) was performed with hams dipped into 0.05, 0.11, and 0.23% HBA solution. Ham extracts without HBA supported rapid growth of unstressed and stress-adapted cells with growth rates of 0.39-0.71 log CFU/mL/day and lag phases of 0-3.26 days. HBA inhibited growth of unstressed L. monocytogenes by slowing (P < 0.05) growth rate (0.24-0.29 log CFU/mL/day) and increasing (P < 0.05) length of the lag phase (3.49-12.98 days) compared to control. Acid-, cold-, or starvation-stress-adapted cells showed cross protection against HBA with greater (P < 0.05) growth rates (0.44-0.66 log CFU/mL/day) and similar or shorter lag phases (0-5.44 days) than unstressed cells. HBA did not (P > 0.05) affect sensory attributes of RTE ham. These results are useful for RTE meat processors to develop operational protocols using HBA to control L. monocytogenes.