Oyster, which is rich in protein and widely used as a marine traditional Chinese medicine, was believed to have good curative effects in health care and on chronic diseases. This study was designed to evaluate the anti-fatigue and anti-oxidant effects of oyster hydrolysate. Oyster meat (OM) was hydrolyzed with a complex protease, and oyster hydrolysate (OH) was separated by a 6 kDa ultrafiltration membrane into two fractions, OH-I (<6 kDa) and OH-II (≥6 kDa). The anti-fatigue effects of OM, OH, OH-I and OH-II groups were first investigated, and then the antioxidant activities of OH-I and OH-II were further analyzed. Anti-fatigue experimental results showed that OH-I displayed the strongest activity among the four groups. Compared to the control group, OH-I significantly prolonged swimming time (67.79%), increased the content of muscle glycogen (45.65%) and liver glycogen (49.01%), and reduced the content of blood urea nitrogen (BUN) (18.44%) (P < 0.05). Meanwhile, OH-I showed excellent chemical and cellular antioxidant activities, especially when the concentration increased; its antioxidant activity was significantly better than that of OH-II (P < 0.05). Results of an amino acid analysis showed that OH-I was rich in branched-chain amino acids (10.84 g per 100 g), Glu (8.63 g per 100 g), Tau (1.68 g per 100 g), Asp (5.02 g per 100 g) and Arg (3.61 g per 100 g), which were expected to contribute to its antioxidant and anti-fatigue activities.

Iron deficiency is a common nutritional disorder worldwide.

Casein phosphopeptides (CPPs) have been demonstrated to be calcium chelators. Unfortunately, few studies have been reported on the effects of CPPs on the mechanism of the uptake and absorption of Ca²⁺ and bone metabolism. In this study, a monomeric peptide fraction isolated by RP-HPLC (F6-1) that possessed high calcium transport capacity in Caco-2 cell monolayers was separated and characterized. The effects of F6-1 on the absorption mechanisms of Ca²⁺ in a Caco-2 monolayer model and bone metabolism in rats were investigated. F6-1 was isolated by preparative and analytical RP-HPLC. Results for calcium transport suggested that the rates of Ca²⁺ transportation by F6-1 were approximately 2.57, 2.87 and 2.38 times higher than those in the control group at 30, 60 and 120 min, respectively. Results of ultraviolet (UV) spectroscopy indicated that the intensity of UV absorption changed because of the binding of Ca²⁺ to F6-1. Analysis of transepithelial electrical resistance (TEER) and the expression of TRPV6 in Caco-2 cells showed that F6-1 was likely to influence the transcellular pathway of intestinal absorption of Ca²⁺ rather than the paracellular pathway. Furthermore, the F6-1 group (1% Ca, 0.03% F6-1) exhibited increases in serum Ca²⁺ levels, femur length and femur Ca and decreases in serum alkaline phosphatase (ALP) levels and urinary pyridinoline content in a Sprague-Dawley rat model, which implied that F6-1 was beneficial for bone calcification. Overall, our results suggested that F6-1 enhanced the transport of Ca²⁺ in Caco-2 cells by affecting the transcellular pathway by upregulating the expression of TRPV6. F6-1 also improved bone formation and prevented bone resorption to benefit bone health in rats, which provided a basis for using F6-1 in calcium supplements or functional foods.