The combined effects of high pressure and nisin on germination and inactivation ofBacillusspores in milk

Abstract

Summary Aims: The aim of this work was to investigate the germination and inactivation of spores of Bacillus species in buffer and milk subjected to high pressure (HP) and nisin. Methods and Results: Spores of Bacillus subtilis and Bacillus cereus suspended in milk or buffer were treated at 100 or 500 MPa at 40°C with or without 500 IU ml−1 of nisin. Treatment at 500 MPa resulted in high levels of germination (4 log units) of B. subtilis spores in both milk and buffer; this increased to >6 logs by applying a second cycle of pressure. Viability of B. subtilis spores in milk and buffer was reduced by 2·5 logs by cycled HP, while the addition of nisin (500 IU ml−1) prior to HP treatment resulted in log reductions of 5·7 and 5·9 in phosphate buffered saline and milk, respectively. Physical damage of spores of B. subtilis following HP was apparent using scanning electron microscopy. Treating four strains of B. cereus at 500 MPa for 5 min twice at 40°C in the presence of 500 IU ml−1 nisin proved less effective at inactivating the spores of these isolates compared with B. subtilis and some strain‐to‐strain variability was observed. Conclusions: Although high levels of germination of Bacillus spores could be achieved by combining HP and nisin, complete inactivation was not achieved using the aforementioned treatments. Significance and Impact of the Study: Combinations of HP treatment and nisin may be an appealing alternative to heat pasteurization of milk.

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

“…First, spores are induced by high pressure to rapidly release Ca-DPA, and the partly hydrated spores are subsequently killed by the combination of pressure and heat due to their increased overall stress sensitivity (Margosch et al, 2004;Reineke et al, 2011). Most of existing mechanistic studies have also reported that the release of dipicolinic acid is accompanied by a loss of heat resistance of endospores during PATP (Black et al, 2008;Paidhungat et al, 2002). In our study, PATP with 3 min treatment resulted in a significant (P < 0.05) heat sensitive spore population among the survivors of B. amyloliquefaciens spores suspended in beef broth (Fig.…”

The development of high hydrostatic pressure processes as an alternative to other pathogen reduction methods

“…To increase the efficiency of HHP against pathogens including spores, some research works focus on its combination with other parameters, such as: the addition of antibacterial compounds such as nisin, xanthenes derivatives (Roberts and Hoover 1996; Gao and Ju 2007b; Black et al. 2008; Zhang and Mittal 2008) or the use of irradiation (Crawford et al.…”

Effect of Olive Powder and High Hydrostatic Pressure on the Inactivation ofBacillus cereusSpores in a Reference Medium

“…To solve this problem, the combination of HHP with other hurdle technologies (Leistner, 2000) has been investigated. One of these combinations with an interesting potential is the use of natural antimicrobials, such as nisin and=or sucrose laureate, which have been applied in some dairy products (Roberts and Hoover, 1996;Stewart et al, 2000;Black et al, 2008), to inactivate spores of B. cereus, Bacillus coagulans, B. subtilis, and Clostridium sporogenes. The inactivation of B. cereus spores has also been achieved by HHP combined with moderated temperatures (Raso et al, 1998;Ju et al, 2008).…”