Environmental stress adaptation enhances viability and freeze-dried survival of Lactobacillus acidophilus VAR1

This study examined the impact of environmental stress adaptation on the freeze-dried viability of Lactobacillus acidophilus VAR1. Cells were exposed to a range of stress conditions, including pH extremes (2.5–9), thermal stress (15˚C, 25˚C, 42˚C, and 47˚C), and CO₂ enrichment (1 to 24 hours), prior to freeze-drying. Results showed that extreme acidic (pH 2.5–3.5) and alkaline (pH 9) conditions significantly reduced cell viability, while moderate alkalinity (pH 8–8.5) had minimal short-term effects and supported improved freeze-dried survival (up to 5.5%). Thermal stress revealed that low temperatures (15˚C and 25˚C) enhanced survival, with freeze-dried viability reaching 53% and 65%, respectively. In contrast, high temperatures (42˚C and 47˚C) led to significant declines in both growth and freeze-dried survival. CO₂ enrichment also markedly improved freeze-dried viability in a time-dependent manner, with survival increasing from 9% after 1 hour to 25% after 24 hours of exposure. These findings, supported by experimental results, demonstrate that mild environmental stress adaptation significantly enhances the freeze-dried viability of L. acidophilus in the absence of cryoprotectants, offering a practical strategy for probiotic formulation.