Abstract: Sialoglycoprotein from Carassius auratus eggs (Ca-SGP) is a novel sialic acid glycoprotein which has the functions of improving bone metabolism and regulating immunity. However, as a large molecular mass substance (195.35 kDa), how Ca-SGP is digested and absorbed by the gastrointestinal tract is yet not clear. This paper aims to study the degradation of Ca-SGP by simulated gastrointestinal fluids and colonic intestinal flora, which is expected to provide theoretical support for further exploration of the mechanism of action of Ca-SGP in vivo. The degradation of Ca-SGP by simulated gastrointestinal fluid and intestinal flora in vitro was evaluated by detecting the molecular mass, pH, sialic acid content and reducing sugar content at different stages of digestion. The results showed that the molecular mass of Ca-SGP decreased, the content of sialic acid declined and the content of reducing sugar increased after gastrointestinal digestion, which indicated that the simulated gastrointestinal fluids can degrade Ca-SGP, and the gastrointestinal digestive enzymes can cause the active factor sialic acid to fall off the end of the Ca-SGP sugar chain. The molecular mass of Ca-SGP and the reducing sugar content were reduced after fermentation by the intestinal bacteria, indicating that Ca-SGP can be continuously fermented and utilized by microorganisms, and the pH gradually decreased as fermentation proceeded, which may be related to the production of acidic substances such as short-chain fatty acids. Hence, the simulated gastrointestinal fluids can degrade Ca-SGP, and the intestinal microflora can further degrade it and utilize its degradation products.

Key words: sialoglycoprotein from Carassius auratus eggs; in vitro digestion; intestinal flora; molecular mass; sialic acid