Establishment of a stable complex formed from whey protein isolate and chitosan and its stability under environmental stresses.

This study aimed to investigate the stability of a complex formed with whey protein isolate (WPI) and chitosan under environmental stress. The optical density, particle size, zeta potential, chemical characteristics, electrostatic interactions, and surface morphology were evaluated for the stable complexes; the optimum conditions for the generation of the stable complex were 0.2% (wt/wt) whey protein with 0.05% (wt/wt) chitosan at pH 5.7. Under these conditions, the complex particle size was 217.8 ± 11.3 nm and the zeta potential was 16.7 ± 0.92 mV. The complex was formed through electrostatic interactions between the amine groups of chitosan (-NH3+) and carboxyl groups of whey protein (-COO-), and contained a porous network interspaced by heterogeneously sized vacuoles. The complex displayed stable physiochemical characteristics under environmental stresses including NaCl (0-75 mM) or sugar (0-5%) at ambient temperature and upon heating for 15 min at 25-65 °C, up to 65 °C for 30 min. Moreover, the complex could be stably stored for 30 d at 4 °C and for 20 d at 25 °C. The present results provide theoretical insights into the industrial production of chitosan-protein complexes and for microencapsulation of sensitive food or medicinal ingredients to increase their intestinal absorption.

l-Arginine induces antioxidant response to prevent oxidative stress via stimulation of glutathione synthesis and activation of Nrf2 pathway.

Arginine is a conditionally essential amino acid. To elucidate the influence of l-arginine on the activation of endogenous antioxidant defence, male Wistar rats were orally administered daily with l-arginine at different levels of 25, 50, 100 mg/100 g body weight. After 7 and 14 days feeding, the antioxidative capacities and glutathione (GSH) contents in the plasma and in the liver were uniformly enhanced with the increasing consumption of l-arginine, whereas the oxidative stress was effectively suppressed by l-arginine treatment. After 14 days feeding, the mRNA levels and protein expressions of Keap1 and Cul3 were gradually reduced by increasing l-arginine intake, resulting that the nuclear factor Nrf2 was activated. Upon activation of Nrf2, the expressions of antioxidant responsive element (ARE)-dependent genes and proteins (GCLC, GCLM, GS, GR, GST, GPx, CAT, SOD, NQO1, HO-1) were up-regulated by l-arginine feeding, indicating an upward trend in antioxidant capacity uniformly with the increasing consumption of l-arginine. The present study demonstrates that the supplementation of l-arginine stimulates GSH synthesis and activates Nrf2 pathway, leading to the up-regulation of ARE-driven antioxidant expressions via Nrf2-Keap1 pathway. Results suggest the availability of l-arginine is a critical factor to suppress oxidative stress and induce an endogenous antioxidant response.