Collagen and gelatin have been widely used in the food, pharmaceutical, and cosmetic industries due to their excellent biocompatibility, easy biodegradability, and weak antigenicity. Fish collagen and gelatin are of renewed interest, owing to the safety and religious concerns of their mammalian counterparts. The structure of collagen has been studied using various modern technologies, and interpretation of the raw data should be done with caution. The structure of collagen may vary with sources and seasons, which may affect its applications and optimal extraction conditions. Numerous studies have investigated the bioactivities and biological effects of collagen, gelatin, and their hydrolysis peptides, using both in vitro and in vivo assay models. In addition to their established nutritional value as a protein source, collagen and collagen-derived products may exert various potential biological activities on cells in the extracellular matrix through the corresponding food-derived peptides after ingestion, and this might justify their applications in dietary supplements and pharmaceutical preparations. Moreover, an increasing number of novel applications have been found for collagen and gelatin. Therefore, this review covers the current understanding of the structure, bioactivities, and biological effects of collagen, gelatin, and gelatin hydrolysates as well as their most recent applications.

Chronic over-exposure to UV radiation leads to the damage of skin tissue. The aim of this study was to investigate the effects of collagen peptide (CP) and antioxidant (astaxanthin, vitamin C (Vc), and vitamin E (Ve)) combinations on skin photoaging. Forty male UV-induced BALB/c mice were randomized and fed saline or CP and antioxidants for 7 weeks using gavage feeding. The results showed that oral administration of CP, CP combined with Vc and Ve (VCE) or Haematococcus pluvialis extract (HPE) significantly (P < 0.05) reduced a* of mouse skin and increased the content of Hyp and type I collagen to varying degrees, thereby improving skin integrity. Furthermore, the combination of CP, HPE, and VCE showed increased upregulation of antioxidant enzyme expression, reduced serum ROS, and decreased inhibition of metalloproteinase expression compared to the other treatment groups. Thus, this combination showed better effects in inhibiting collagen degradation and maintaining the redox balance. The Nrf2/ARE and TGF-β/Smad transcription systems are likely involved in these effects. Therefore, the results suggest that a diet containing CP, astaxanthin, and vitamins might be recommended to improve skin health and appearance.