Water Activity Effect on Microbial Behavior During Hyperbaric Storage at Room Temperature of Watermelon Juice as a Case Study

Hyperbaric storage (HS) is a novel technology for storing foods under mild pressures that, when used at room temperature (RT), offers much lower energy costs and greenhouse gas emissions than conventional refrigeration (RF). Watermelon juice (WJ), with interesting associated health benefits, is highly perishable due to its pH (5.20-6.70) and water activity (a_W, 0.97-0.99). This work investigated a_W's impact on WJ's preservation by HS/RT, studying the behavior of <i>Escherichia coli</i>, <i>Listeria monocytogenes</i>, and <i>Saccharomyces cerevisiae</i> inoculated in WJ at a_W 0.930-0.971 stored at 25-75 MPa for up to 28 days, along with RT and RF atmospheric pressure controls. The results showed that HS could control microbial growth, and, during storage, inactivation was also observed, and that HS's impact depended on the a_W level, microorganism, and storage pressure. Inactivation was often increased at 50-75 MPa and at a_W 0.930-0.950, while growth mostly occurred at a_W 0.971. The inactivation curves were mathematically described by the first-order and Weibull kinetic models, with the Weibull model frequently obtaining better fits. These findings support HS's potential for food preservation, showing better overall WJ growth control and inactivation effects than RF, without temperature control, making HS environmentally friendlier.