Identification and characterization of acid-tolerant spore-forming spoilage bacteria from acidified and low-acid pasteurized sauces

Abstract

To improve the microbial stability of mildly processed acidified sauces, which are threatened by acid-tolerant spore-forming spoilage bacteria (ATSSB), this study investigated the individual effect of pH, water activity (aw), temperature and organic acids on the growth from ATSSB spores and their spoilage potential. The pH of nine commercial sauces was gradually increased (3.8–5.6), and 81 strains were isolated from each sauce with the lowest pH allowing microbial growth. After heat treatment and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, ten selected strains were identified to the Bacillus subtilis and Bacillus cereus species group by 16S rRNA gene sequencing. The selected isolates with three acid-tolerant reference strains all exhibited enzymatic spoilage activity (amylase, protease, lipase or lecithinase) and had D95°C -values between 0.8 and 6.4 min. None of the 13 strains grew below 10 °C, while the minimum growth pH varied from 4.1 to 5.4 and the minimum aw varied from 0.89 to 0.96. Moreover, the minimum inhibitory concentrations of benzoic, sorbic, acetic and lactic acids were 0.04–0.07, 0.05–0.10, 0.11–0.30 and 0.20–1.05 g/100g, respectively. This work demonstrated that the ATSSB spores were sensitive to organic acids and refrigeration, contributing to more accurate strategies to preserve the mildly pasteurized sauces with reduced acids and salts.