Characterization of Lactobacillus paracasei JSRL18-60 with probiotic properties as a starter in manufacturing fermented milk

In this study, eighty-eight lactic acid bacteria (LAB) were isolated from Korean traditional fermented foods for use as yogurt. Among the isolates, thirteen LAB strains with curd formation ability were selected. Among these, five LAB strains exhibited notable antibacterial activity against pathogens, such as Bacillus cereus, Staphylococcus aureus, and Listeria ivanovii. JSRL18-60 strain showed superior probiotic properties, such as high adhesion capacity to Caco-2 colorectal adenocarcinoma cells, and tolerance to low pH, temperature, and condition of the bile. Based on these results, JSRL18-60 strain was selected for further evaluation and identified by 16S rRNA sequencing as Lactobacillus paracasei. The maximum growth of L. paracasei JSRL18-60 was determined after 30 h of fermentation by measuring the optical density (1.74), viable cell number (9.61 log CFU/mL), and dried cell weight (2.30 g/L). Finally, we manufactured fermented milk using skimmed milk and L. paracasei JSRL18-60, and the optimal pH condition (pH 4.48) of the fermented milk was reached within 21 h of fermentation. Moreover, the log of the total cell count of L. paracasei JSRL18-60 was retained for at least 10 days at 9.48-9.36 log CFU/mL. The pH and acidity levels of the fermented milk containing L. paracasei JSRL18-60 were changed from pH 4.48 and 0.89% to pH 4.38 and 0.98%, respectively, in 10 days. These findings suggested that L. paracasei JSRL18-60 could be used as a starter for producing fermented milk with probiotic properties.