Characterization of the Probiotic Potential of Lactic Acid Bacteria Isolated from Kimchi, Yogurt, and Baby Feces in Hong Kong and Their Performance in Soymilk Fermentation

Background: There are several potential healthy or nutritional benefits from the use of lactic acid bacteria (LAB) in foods. This study aimed to characterize the LAB isolates from kimchi, yogurt, and baby feces in the Hong Kong area and evaluate their performance in fermented soymilk, which allowed us to assess their potential use in future experiments. Methods: General characteristics including tolerance to acid, NaCl, bile salts and phenol, antimicrobial activity to various pathogens, and adhesive ability to Caco-2 cells were evaluated using 18 LAB in this study. To further demonstrate the influence of such isolates in soymilk fermentation, we measured viability by plating and noting changes in pH, amino acid content, aglyconic isoflavones content and antioxidant capacities in vitro, such as scavenging ability, and iron chelating ability. Results: In this study, various LAB isolates belonging to Lactobacillus rhamnosus, Lactobacillus sakei, Lactiplantibacillus plantarum, and Leuconostoc mesenteroides isolated in Hong Kong were evaluated. L. plantarum isolates R7, AC12, and AC14.1, and L. rhamnosus AC1 showed higher tolerance to acid, NaCl, bile salts, and phenol as compared to the other isolates tested. L. plantarum isolates AC12, AC13 and AC14.1, and L. rhamnosus AC1 harbored strong antimicrobial activity. L. plantarum isolates R7, AC12, AC13 and AC14.1, and L. paracasei isolates R6 and R8 showed higher adhesive ability than the other tested isolates. In soymilk, the viable numbers of L. paracasei R5, L. plantarum R7, L. rhamnosus AC1, L. sakei AC2, and Leu. mesenteroides AC5 were much higher than the other tested isolates after 48 h of fermentation. The pH value measuring the lactic acid level in soymilk fermented by L. plantarum AC14.1 was the lowest in comparison to those in soymilk fermented by other isolates. In addition, the levels of free amino acids and isoflavones in the aglycone forms of L. rhamnosus AC1-fermented soymilk were the highest. L. rhamnosus AC1-fermented soymilk also showed the highest antioxidant potential, including DPPH scavenging ability and iron chelating ability. Conclusions: In general, L. plantarum isolates R7 and AC14.1 and L. rhamnosus AC1 exhibited higher tolerance to challenging conditions as compared to the other isolates. Moreover, L. rhamnosus AC1 exhibited superior performance in soymilk fermentation and potential as a starter and probiotic culture.