Lactose-Free Fermented Milk Production Using Lactococcus lactis NK24 and NK34 with Immune-Enhancing Effects on RAW 264.7 Cells

This study aimed to produce lactose-free fermented milk using probiotic Lactococcus lactis strains and to investigate the immune-enhancing effects of fermented milk. Lactose-free milk was fermented using Laticaseibacillus rhamnosus GG (LGG), L. lactis NK24, and L. lactis NK34. The pH, TA, viable lactic acid bacterial counts, and physicochemical properties of lactose-free fermented milk were recorded over 28 days under refrigeration. Each water-soluble extract of lactose-free fermented milk stimulated NO production, phagocytic activity, and induced morphological changes in RAW 264.7 cells, similar to the LPS treatment group. Additionally, the mRNA levels of inducible nitric oxide (iNOS), cyclooxygenase-2 (COX-2), and proinflammatory cytokines increased. Furthermore, each sample promoted protein expression of iNOS, and COX-2 and phosphorylation of p38, p65, JNK, and ERK. Therefore, lactose-free milk fermented by L. lactis NK24 and L. lactis NK34 can enhance the immune response via nuclear factor-kB (NF-kB) and mitogen-activated protein kinase (MAPK) activation and has the potential for development as a functional food.