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 (≈108 CFU ml−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, 600 MPa, 105 °C), and thermal processing (TP; 0.1 MPa, 105 °C) for 0 (come-up time), 0.5, 1, 3, and 5 min. Beef broth samples were also pressure treated (HPP; 600 MPa, 35 °C) for 3 and 5 min. Dormant spore survivors were enumerated by spread-plate technique. Heat shock (80 °C for 15 min) was used to enumerate the heat sensitive spores. A 5-min PATP reduced spore survivors counts to below 1-log CFU ml−1 (≈6.5–7.0 log reduction) in PPE and TPE as compared to 2.5-log and 3.1-log in DIW and HEPES buffer, respectively. 3 min PATP treatment reduced the spore survival to 3.58 and 2.1 log CFU ml−1 in beef broth and beef broth + natural extract, respectively. TP and HPP processing could inactivate the spores only by 0.5–1.2 log CFU ml−1. PPE and TPE are found to enhance the efficacy of PATP.