Preparation of wheat gluten hydrolysates with high opioid activity

The opioid activity of wheat gluten hydrolysates (WGHs) prepared with several proteases was investigated in vitro by the contraction of guinea pig ileum (GPI), and WGHs with high opioid activity were further obtained through desalting and ultrafiltration (UF). The opioid activity varied with different wheat gluten hydrolysates. AWGH (WGH prepared with Alcalase), PPWGH (WGH prepared with Pepsin followed by Pancreatin) and PWGH (WGH prepared with pepsin) had relatively stronger inhibitory effects on the contraction of GPI with IC(50) values of 1.21 +/- 0.25, 1.29 +/- 0.38 and 1.57 +/- 0.21 mg protein/ml, respectively. Subsequently, AWGH and PPWGH were desalted using cation exchange resin and anion exchange resin, with high nitrogen recovery (88.51 and 89.28%, respectively) and high desalting ratio (84.67 and 85.20%). The resultant hydrolysates were further fractionated by UF performed with a 3 kDa molecular weight cut-off membrane. Compared with AWGH and PPWGH, the 3 kDa-permeates have higher opioid activities with high protein content above 90% and low ash content about 1.5%. The molecular weight distributions of the two 3 kDa-permeates were concentrated below 2,000 Da.