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Impact of different water activities (a w) adjusted by solutes on high pressure high temperature inactivation of Bacillus amyloliquefaciens spores.

ABSTRACT: Much research has been conducted to comprehend the mechanisms of high pressure (HP) inactivation of spores in aqueous systems but for food model systems these information are scarce. In these systems spores can interact with ingredients which then could possibly lead to retarded or reduced inactivation, which can cause a problem for the sterilization process. The protective mechanism of a reduced a w-value is still unclear. HP processing might prove valuable to overcome protective effects of solutes and achieve shorter process times for sterilization under HP. To gain insight into the underlying mechanisms five a w-values (0.9, 0.92, 0.94, 0.96, 1) were adjusted with two different solutes (NaCl, sucrose). Solutions were inoculated with spores of Bacillus amyloliquefaciens and treated at 105, 110, and 115°C at 600 MPa. Further a thermal inactivation was conducted at the same temperatures for a comparison with the HP data. Afterward, the influence of HP high temperature treatment on the inactivation, the dipicolinic acid (DPA)-release and membrane constitution was assessed by plate count, HPLC and flow cytometry (FCM). The results show that during HP treatments sucrose and salt both have a protective effect, in which the influence of sucrose on the retarded inactivation is higher. The threshold water activities (a w), which is 0.94, here salt and sucrose have a significant influence on the inactivation. The comparison of thermal (105-115°C) and HP and high temperature (600 MPa, 105-115°C) treated samples showed that the time needed to achieve a 4-5 log10 inactivation is reduced from 45 (a w = 1) to 75 (a w = 0.9) min at 105°C to 3 (a w = 1) to 15 (a w = 0.9) minutes at 600 MPa and 105°C. The release of DPA is the rate limiting step of the inactivation and therefore monitoring the release is of great interest. The DPA-release is slowed down in high concentrated solutions (e.g., sucrose, salt) in comparison to a w 1. Since there is a difference in the way the solutes protect the spore it could be seen as an inner spore membrane effect. Maybe as shown for vegetative microorganism the solutes can interact with membranes, e.g., the inner spore membrane. Flow cytometry (FCM) measurement data show a similar trend.

SUBMITTER: Sevenich R

PROVIDER: S-EPMC4491632 | biostudies-literature | 2015

REPOSITORIES: biostudies-literature

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Impact of different water activities (a w) adjusted by solutes on high pressure high temperature inactivation of Bacillus amyloliquefaciens spores.

Sevenich Robert R Reineke Kai K Hecht Philipp P Fröhling Antje A Rauh Cornelia C Schlüter Oliver O Knorr Dietrich D

Frontiers in microbiology 20150706

Much research has been conducted to comprehend the mechanisms of high pressure (HP) inactivation of spores in aqueous systems but for food model systems these information are scarce. In these systems spores can interact with ingredients which then could possibly lead to retarded or reduced inactivation, which can cause a problem for the sterilization process. The protective mechanism of a reduced a w-value is still unclear. HP processing might prove valuable to overcome protective effects of sol ...[more]

PMID: 26217321

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Project description:Bacillus and Clostridium species form spores, which pose a challenge to the food industry due to their ubiquitous nature and extreme resistance. Pressurization at <300 MPa triggers spore germination by activating germination receptors (GRs), while pressurization at >300 MPa likely triggers germination by opening dipicolinic acid (DPA) channels present in the inner membrane of the spores. In this work, we expose spores of Bacillus licheniformis, a species associated with food spoilage and occasionally with food poisoning, to high pressure (HP) for holding times of up to 2 h. By using mutant spores lacking one or several GRs, we dissect the roles of the GerA, Ynd, and GerK GRs in moderately HP (mHP; 150 MPa)-induced spore germination. We show that Ynd alone is sufficient for efficient mHP-induced spore germination. GerK also triggers germination with mHP, although at a reduced germination rate compared to that of Ynd. GerA stimulates mHP-induced germination but only in the presence of either the intact GerK or Ynd GR. These results suggests that the effectiveness of the individual GRs in mHP-induced germination differs from their effectiveness in nutrient-induced germination, where GerA plays an essential role. In contrast to Bacillus subtilis spores, treatment with very HP (vHP) of 550 MPa at 37°C did not promote effective germination of B. licheniformis spores. However, treatment with vHP in combination with elevated temperatures (60°C) gave a synergistic effect on spore germination and inactivation. Together, these results provide novel insights into how HP affects B. licheniformis spore germination and inactivation and the role of individual GRs in this process.IMPORTANCE Bacterial spores are inherently resistant to food-processing regimes, such as high-temperature short-time pasteurization, and may therefore compromise food durability and safety. The induction of spore germination facilitates subsequent inactivation by gentler processing conditions that maintain the sensory and nutritional qualities of the food. High-pressure (HP) processing is a nonthermal food-processing technology used to eliminate microbes from food. The application of this technology for spore eradication in the food industry requires a better understanding of how HP affects the spores of different bacterial species. The present study provides novel insights into how HP affects Bacillus licheniformis spores, a species associated with food spoilage and occasionally food poisoning. We describe the roles of different germination receptors in HP-induced germination and the effects of two different pressure levels on the germination and inactivation of spores. This study will potentially contribute to the effort to implement HP technology for spore inactivation in the food industry.

Dataset Information

Impact of different water activities (a w) adjusted by solutes on high pressure high temperature inactivation of Bacillus amyloliquefaciens spores.

Publications

Impact of different water activities (a w) adjusted by solutes on high pressure high temperature inactivation of Bacillus amyloliquefaciens spores.

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