Serotonin is a neurotransmitter that is primarily produced in the gut and is produced by lactic acid bacteria (LAB). It plays a crucial role in regulating mood and mental health disorders via the gut-brain axis using the enteric nervous system. Exopolysaccharides (EPS) are complex metabolic end products of probiotic LAB that contribute to health-promoting activities in the intestine. Interactions between LAB and components in the food matrix, such as the milk fat globule membrane (MFGM), may alter the production of serotonin and EPS in the gastrointestinal tract. The objectives of this work were to determine if supplementing LAB growth medium with MFGM increases serotonin and EPS production and to uncover the impact of the bacterial secretome on intestinal cell differentiation. We screened 137 strains of LAB for serotonin production, and the top 10 highest producing strains received supplementation with MFGM, and their growth curves were measured spectrophotometrically. Samples were collected during the growth, early stationary, and late stationary phases. The cell-free supernatant (CFS) samples were evaluated for serotonin as well as EPS. These CFS were used to treat Caco-2 intestinal cell lines for 6 h on d 0 and 7 of confluency. From Caco-2 cells, RNA was extracted with TRIzol and used for RT-qPCR analysis of occludin tight junction protein expression. Protein was extracted using RIPA lysis buffer and used for detection of alkaline phosphatase using an analysis kit and for sucrase-isomaltase and dipeptidyl peptidase 4 using antibody detection with slot blot. The results of this project demonstrate that MFGM tended to increase the production of serotonin and significantly increase EPS production from select LAB strains during the later stages of growth. We further observed that upon the presence of low concentrations of the metabolites in the secretome of some strains, there was a significant increase in the expression of occluding from Caco-2 cells. These results indicate that there is a high potential of the use of MFGM for intestinal health such as prevention of 'leaky gut syndrome' and warrants further research on this subject.
