Effect of high pressure treatment on microbial populations of sliced vacuum-packed cooked ham

In this study, culture-dependent and culture-independent approaches were used to reveal the microbial diversity and dynamic changes occurring in sliced vacuum-packed cooked ham after high pressure processing (HPP, 400 MPa or 600 MPa for 10 min at 22 °C) during refrigerated storage over 90 days. Direct extraction of genome DNA and total RNA from meat samples, followed by PCR-denaturing gradient gel electrophoresis (DGGE) and RT-PCR-DGGE on 16S rDNA V3 region, was performed to define the structure of the bacterial populations and active species in pressurized cooked ham. Results showed that HPP affected differently the various species detected. The predominant spoilage organisms of cooked ham, such as Lactobacillus sakei and Lactobacillus curvatus, were found to be very sensitive to pressure as they were unable to be detected in HPP samples at any time during refrigerated storage. Weissella viridescens and Leuconostoc mesenteroides survived HPP at 600 MPa for 10 min at 22 °C and were responsible for the final spoilage. An RNA-based DGGE approach clearly has potential for the analysis of active species that have survived in pressurized cooked ham. High pressure processing at 400 or 600 MPa for 10 min at room temperature (22 °C) has a powerful inhibitory effect on the major spoilage bacteria of sliced vacuum-packed cooked ham. High pressure treatment may lead to reduced microbial diversity and improve the productsʹ safety.