Effect of pre-freezing regimes and reactivation conditions on the viability of lyophilized Saccharomyces cerevisiae strains

Abstract

Long-term preservation of Saccharomyces cerevisiae by lyophilization is highly important for scientific research and for the biotechnological and food industries. Maintaining cell viability and genetic stability is essential for reproducible results and consistent product quality. Lyophilization includes rapid freezing of microbial cultures followed by water removal through sublimation under vacuum. Therefore, pre-freezing temperature is a key factor affecting post-lyophilization survival, as it influences ice crystal formation, membrane integrity, and intracellular stability. Higher pre-freezing temperatures cause slower freezing and larger ice crystals, leading to irreversible cell damage and reduced viability. Lower temperatures ensure faster freezing, smaller and more uniform ice crystals, less mechanical injury, and higher survival rates. The aim of this study was to evaluate the influence of pre-freezing temperature and reactivation time on the survival capacity of Saccharomyces cerevisiae yeasts after 13 years of storage in a lyophilized state.