Microbiological efficacy of pressure assisted thermal processing and natural extracts against Bacillus amyloliquefaciens spores suspended in deionized water and beef broth

Abstract

Effect of aqueous extracts of pomegranate peel (PPE) and tamarind pulp (TPE) on lethality of pressure assisted thermal processing (PATP) against Bacillus amyloliquefaciens Fad 82 spores was investigated. B. amyloliquefaciens spores (≈108CFUml−1) were suspended in deionized water (DIW), 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) buffer PPE, and TPE (1% w/v in DIW, pH-6) and beef broth with or without PPE and TPE (0.45% w/v). Samples were subjected to pressure assisted thermal processing (PATP, 600MPa, 105°C), and thermal processing (TP; 0.1MPa, 105°C) for 0 (come-up time), 0.5, 1, 3, and 5min. Beef broth samples were also pressure treated (HPP; 600MPa, 35°C) for 3 and 5min. Dormant spore survivors were enumerated by spread-plate technique. Heat shock (80°C for 15min) was used to enumerate the heat sensitive spores. A 5-min PATP reduced spore survivors counts to below 1-logCFUml−1 (≈6.5–7.0log reduction) in PPE and TPE as compared to 2.5-log and 3.1-log in DIW and HEPES buffer, respectively. 3min PATP treatment reduced the spore survival to 3.58 and 2.1logCFUml−1 in beef broth and beef broth+natural extract, respectively. TP and HPP processing could inactivate the spores only by 0.5–1.2logCFUml−1. PPE and TPE are found to enhance the efficacy of PATP.