ABSTRACT
Collagen is de’ned as proteinous components with a triple helical structure in the extracellular matrix. Collagen forms a family consisting of closely related but different gene products and divided into two groups: ’brillar and non’brillar collagens (van der Rest and Garrone, 1991; Heino, 2007). In mammalian and avian tissues, the ’brillar collagen includes type I, II, III, V, and XI collagens (Sato et al., 1989; Zylberberg et al., 1992). Type I and II collagens are major constituents in skin, bone, tendon (type I), and cartilage (type II) in vertebrates, including ’sh, and type V collagen is codistributed with type I collagen as minor components in ’sh (Sato et al., 1989). In cartilage, type XI collagen is codistributed with type II collagen (Kelly et al., 1988). Thus, type I and II collagens are mainly used for collagen-related food ingredients. The collagens speci’cally consist of hydroxyproline (Hyp) and hydroxylysine (Hyl), posttranslational modi’ed amino acids of proline (Pro) and lysine (Lys), respectively. The triple helical domain of the ’brillar collagen has a Gly-X-Y repeating motif, where X and Y are frequently occupied by Pro and Hyp, respectively (van der Rest and Garrone, 1991). The triple helical structure will be lost by heating the solution and converted into a globular structure. The denatured form of collagen is referred to as gelatin, which can be dissolved in hot water, yielding a viscous solution, and gel formation occurs by cooling the gelatin solution. Gelatin has long been used as a food ingredient as well as in folk medicine in Asia to improve blood circulation and arrest bleeding (Yao et al., 1989). In Western countries, gelatin consumption has been believed to improve joint condition by reducing pain (Moskowitz, 2000). Recently, partially hydrolyzed gelatin products have been prepared by enzymatic hydrolysis in order to increase their solubility in cold water. These are referred to as collagen peptides, and in some cases, simply as collagen in commercial products. Large amounts of collagen peptide preparations have been obtained from bone and skin of cattle, pig, chicken, etc. However, after the prevalence of bovine spongiform encephalopathy, much interest has been focused on production of collagen peptides from ’sh scales, skin, bone, etc. Episodes suggesting that ingestion of the collagen peptide would improve subjective skin conditions are widely prevalent in Japan and other countries. In Japan, annual sales of collagen peptide as a food supplement reached approximately US$300 million in 2007. Recent human
10.1 Introduction .......................................................................................................................... 125 10.2 Effect of Collagen Peptide Ingestion on Skin Condition ...................................................... 126 10.3 Metabolic Fate of Collagen Peptide in Humans ................................................................... 128 10.4 Possible Mechanism for Bene’cial Effect of Collagen Peptide Ingestion ............................ 129 10.5 Conclusion ............................................................................................................................ 130 References ...................................................................................................................................... 130
trials using placebo control also have revealed that daily ingestion of collagen peptides increases skin surface water content and improves skin condition (Ohara et al., 2009; Koyama, 2009). Some animal experiments also have revealed the bene’cial effects of collagen peptides on skin (Matsuda et al., 2006; Tanaka et al., 2009; Zhuang et al., 2009). In contrast, it has been believed that collagen peptides might be degraded into amino acids during digestion and absorption processes. Collagen predominantly consists of nonessential amino acids: Gly, Ala, Pro, Gln, Asn, etc. (van der Rest and Garrone, 1991). Hence the bene’cial effect of collagen peptide could not be explained by supplementation of amino acids for collagen synthesis. In 2005, our group demonstrated the occurrence of 25-60 µM levels of food-derived collagen peptides in human peripheral blood after ingestion of chicken collagen peptides (Iwai et al., 2005). This ’nding was a breakthrough for elucidation of the mechanism of the bene’cial effect of collagen peptide by ingestion.
