The use of collagen hydrolysates (CHs) as a nutraceutical agent in skin aging has gained increasing attention. Here, the effects of various doses and molecular weights of CH from silver carp skin on photoaging in mice were investigated. The ingestion of CH at 50, 100 and 200 mg per kg body weight led to a dose-dependent increase in the hydroxyproline, hyaluronic acid and moisture contents of the skin, but it had no significant effect on the mice body weight, or on the spleen or thymus index. Furthermore, ingesting CH with lower (LMCH, 200-1000 Da, 65%) and higher molecular weight (HMCH, >1000 Da, 72%) significantly increased the skin components and improved the antioxidative enzyme activities in both serum and skin (p < 0.05); LMCH performed better than HMCH. By contrast, gelatin (>120 kDa) ingestion did not bring a significant change compared to model mice. These results indicated that LMCH exerted a stronger beneficial effect on the skin than did either HMCH and gelatin, which supported the feasibility of using LMCH as a dietary supplement from silver carp skin to combat photoaging.

Applying antioxidants to attenuate skin photoaging has received great attention. In this study, antioxidant collagen peptides (ACPs) with different activities were prepared using different proteases, called high (HCP), medium (MCP) and low antioxidant collagen peptides (LCP). The effects of ACPs, tea polyphenols (TP) and casein peptides (CP) on the photoaged skin of mice were evaluated and compared. Ingestion of ACPs significantly alleviated UV-induced abnormal alterations of skin components and antioxidative indicators in both serum and skin (p < 0.05). In addition, HCP had the best effect on protecting skin from photoaging among the three collagen peptides, with no significant differences between MCP and LCP (p > 0.05). TP and CP, with higher antioxidant activity in vitro, only significantly increased hydroxyproline content (only in the TP group) and CAT activity and decreased protein carbonyl content at week 2, showing a much weaker effect than that of the ACP groups. The histological analysis result further demonstrates that ACPs exerted a stronger beneficial effect on normalizing skin structure and collagen arrangement than TP and CP. Accordingly, ACPs have potential for nutraceuticals as anti-skin-photoaging ingredients.