Effect of gelatinisation of starch with casein proteins on incretin hormones and glucose transporters in vitro.

Foods that have a low glycaemic index or foods that contain slowly digestible starch are beneficial in controlling fluctuations in blood glucose and insulin levels. The study hypothesis is that gelatinisation of starch in structured casein networks provides a method for decreasing the digestion rate of the starch and, hence, minimising postprandial glucose fluctuations. This study examined the effect of starch gelatinisation with or without casein on (1) gene expression and peptide secretion levels of the incretin hormones glucagon-like peptide 1 and glucose-independent insulinotropic polypeptide and (2) gene expression of the sodium-glucose cotransporter and GLUT-2 in intestinal cell culture systems. The intestinal epithelial cell line, STC-1, and the enteroendocrine colonic cell line, Caco-2, were exposed to in vitro digested foods (starch gelatinised with α-casein, starch gelatinised with β-casein and gelatinised starch alone). The encapsulation of starch with casein before in vitro digestion lowers levels of incretin hormone secretion. Digestion of starch gelatinised with casein also releases less glucose than starch alone as indicated by significantly (P < 0·05) lower levels of glucose transporter mRNA transcripts. Some subtle cellular response differences were observed following exposure to starch gelatinised with α- compared to β-casein. Fractionation of α-casein and β-casein by reverse-phase HPLC identified that fractions that differed in hydrophobicity differed significantly (P < 0·05) in their ability to promote secretion of the incretin hormones. Evidence suggests that gelatinisation of starch with casein may be a functional food ingredient that minimises blood glucose fluctuations.