Optimization Culture and Freeze-Drying Conditions for High-Density Powder Production of Lacticaseibacillus rhamnosus L22-FR28

Probiotic lactic acid bacteria require robust culture and freeze-drying processes to maintain high viability for functional food applications. In this study, the culture and freeze-drying conditions were optimized to produce a high-density freeze-dried powder of the Lacticaseibacillus rhamnosus L22-FR28 (KACC 92513P). The strain was cultivated in a food-grade medium containing 2.5% yeast extract, 1%-2% peptone, and the antioxidant L-cysteine, with glucose concentrations of 3% (BC3) and 5% (BC5).<br/>Cultivation was carried out in 5 L fermenters with the pH maintained at 5.7. After cultivation, the cells were harvested by centrifugation, resuspended in a cryoprotectant mixture [2% (v/v), based on culture volume], rapidly frozen, and freeze-dried to obtain probiotic powders. The freeze-dried powder produced in 5% glucose medium showed a viable cell count of 3.74 × 10¹¹ CFU/g and a freeze-drying survival rate of 81.66%, which were significantly higher than those obtained in the 3% glucose medium (1.91 × 10¹¹ CFU/g and 63.88%, respectively). These results suggest that the optimized culture and freeze-drying conditions established in this study enable the production of high-density, high-viability L. rhamnosus L22-FR28 powder and may be useful for manufacturing industrial-scale probiotics.