Antimicrobial activities of spice extracts against pathogenic and spoilage bacteria in modified atmosphere packaged fresh pork and vacuum packaged ham slices stored at 4 °C

The antimicrobial activity of 14 spice extracts against four common meat spoilage and pathogenic bacteria (Listeria monocytogenes, Escherichia coli, Pseudomonas fluorescens and Lactobacillus sake) was screened in cultured media (experiment 1). The results showed that individual extracts of clove, rosemary, cassia bark and liquorice contained strong antimicrobial activity, but the mixture of rosemary and liquorice extracts was the best inhibitor against all four types of microbes. Subsequently, mixed rosemary/liquorice extracts were spray-applied to inoculated fresh pork in modified atmosphere packaging (experiment 2) and to inoculated ham slices in vacuum packaging (experiment 3). The meat samples were stored at 4 °C over a 28-day period and microbial growth was monitored regularly. The L. monocytogenes population on fresh pork by day 28 decreased 2.9, 3.1 and 3.6 logs, the MAB decreased 2.7, 2.9 and 3.1 logs, the Pseudomonas spp. count decreased 1.6, 2.1 and 2.6 logs and the total coliform count decreased 0.6, 0.8 and 1.2 logs, corresponding to 2.5, 5.0 and 10.0 mg/ml of spray, respectively, when compared to control (P < 0.05). The number of L. monocytogenes on ham slices decreased 2.5, 2.6 and 3.0 logs, the MAB plate counts decreased 2.9, 3.0 and 3.2 logs and the LAB counts decreased 2.4, 2.6 and 2.8 logs (P < 0.05), respectively, after 28-days, by the same levels of mixed rosemary/liquorice extract treatments. The results demonstrated strong potential of mixed rosemary and liquorice as a natural preservative in fresh pork and ham products.