Tailoring Freeze-Drying for Starter Cultures Preservation: A Case Study with Lactiplantibacillus plantarum

Freeze-drying is a crucial technique for preserving bacterial strains, yet its efficiency depends heavily on the precise selection of protective agents. This study aimed to optimize freeze-drying conditions for the commercially relevant, non-GMO strain Lactiplantibacillus plantarum K KKP/593/p. The cryoprotective effects of glycerol, dimethyl sulfoxide (DMSO), and trehalose were evaluated, alongside various carriers including skim milk powder, maltodextrin, inulin, and starch. Survival rates were determined using the plate count method on MRS agar, complemented by scanning electron microscopy (SEM) for microstructural analysis. Results indicated that skim milk powder was the superior carrier, significantly outperforming polysaccharides. Among the protective agents, glycerol exhibited the highest efficacy, while trehalose and DMSO were suboptimal. The most effective formulation 20% glycerol without prior incubation combined with skim milk powder at 0.75:1 (w/w, total mass) ratio maintained maximum viability with no statistically significant decrease. SEM observations confirmed that this synergistic combination ensured a stable, porous matrix favorable for rehydration. These findings emphasize that while synergistic multi-component systems are essential for maximizing post-process viability, cryoprotective formulations must be empirically tailored to specific bacterial strains to ensure industrial efficiency.