Abstract
During the thermal processing of dairy products, the Maillard reaction occurs between milk proteins and lactose, resulting in the formation of various products including glycated proteins. In this study, lactose-glycated casein was generated through the Maillard reaction between casein and lactose and then hydrolyzed by a trypsin preparation. The anti-inflammatory effect of the resultant glycated casein hydrolysate (GCH) was investigated using the lipopolysaccharide (LPS)-sitmulated rat intestinal epithelial (IEC-6) cells as a cell model and corresponding casein hydrolysate (CH) as a control. The results indicated that the preformed glycation enabled lactose conjugation to casein, which endowed GCH with a lactose content of 12.61 g/kg protein together with a lower activity than CH to enhance the viability value of the IEC-6 cells. The cells with LPS stimulation showed significant inflammatory responses, while a pre-treatment of the cells with GCH before LPS stimulation consistently led to a decreased secretion of three pro-inflammatory mediators, namely, IL-6, IL-1β and tumor necrosis factor-α (TNF-α) but an increased secretion of two anti-inflammatory mediators, including IL-10 and transforming growth factor-β (TGF-β), demonstrating the anti-inflammatory potential of GCH in LPS-stimulated cells. In addition, GCH up-regulated the expression of TLR4, p-p38, and p-p65 proteins in the stimulated cells, resulting in the suppression of NF-κB and MAPK signaling pathways. Collectively, GCH was mostly less efficient than CH to exert these assessed anti-inflammatory activities in the cells and more importantly, GCH also showed an ability to cause cell inflammation by promoting IL-6 secretion and up-regulating the expression of TLR4 and p-p65. The casein lactose-glycation of the Maillard-type was thereby concluded to attenuate the anti-inflammatory potential of the resultant casein hydrolysate. It is highlighted that the casein lactose-glycation of the Maillard-type might cause a negative impact on the bioactivity of casein in the intestine, because the glycated casein after digestion could release GCH with reduced anti-inflammatory activity.