Application of thermo-ultrasonic treatments for the inactivation of osmotolerant yeasts suspended in media with reduced water activity

Abstract

Ultrasound (US) is an alternative to inactivate pathogenic and spoilage microorganisms in food. However, US alone is not very effective because long treatment times are required. Coupling US with heat is an effective tool for microbial inactivation, reducing the treatment temperature and the processing time, translating into important energy savings during food processing. This research aimed to study mild heat treatment intensified by ultrasound to inactivate Saccharomyces cerevisae, Zygosaccharomyces bailii, and Zygosaccharomyces rouxii at different aw to obtain the thermal death kinetics. Yeasts inactivation was performed by heat application (45, 50, or 55°C) and/or low frequency ultrasound (20 kHz/ 75 µm) in culture broth (aw 0.99, 0.97 or 0.95, and pH 3.5). First-order kinetics were used to describe the inactivation behavior of yeasts (D and z values). Log reductions of yeasts by the treatments oscillated between 0.2 to 3, the more resistant yeast was Z. bailii. US intensified yeast's inactivation at mild temperatures reducing D values.