Effect of caseinate glycation with oligochitosan and transglutaminase on the intestinal barrier function of the tryptic caseinate digest in IEC-6 cells
Oligochitosan was used in this study to glycate commercial caseinate under the catalytic action of transglutaminase (TGase), followed by trypsin-mediated digestion. The prepared tryptic digests from both caseinate and oligochitosan-glycated caseinate were assessed and compared for their effects on the intestinal barrier function of a cell model (IEC-6 cells). Both digests had similar chemical features in the nine amino acids (except for Met) and free amino group contents, but had different glucosamine contents. Both digests at 12.5–100 μg mL−1 promoted IEC-6 cell growth by 105.6–135.1% and more importantly improved intestinal epithelial barrier integrity via increasing trans-epithelial electrical resistance, decreasing paracellular permeability from 100% to 64.1–85.4%, reducing bacterial translocation, and enhancing antibacterial activity against Escherichia coli. The obtained qPCR and western-blot assay results also demonstrated that both digests had promoting effects on the expression levels of several tight junction proteins such as ZO-1, occludin, and claudin-1. The oligochitosan-glycated caseinate digest always showed higher effects than the caseinate digest in the cells to retain the intestinal epithelial barrier function. This study thus highlights that the used TGase-type glycation endowed the oligochitosan-glycated caseinate with a potential functional food ingredient to strengthen the epithelial barrier function, which might be a helpful event to intestinal health.