Extraction, structural characterization and in vitro antioxidant activity of porcine small intestinal glycoproteins from heparin processing wastewater

In this study, porcine small intestinal glycoproteins (PSIG-1) was extracted and purified from the heparin-processing wastewater of porcine small intestines; its structure was characterized, and its antioxidant activity was evaluated. The optimized extraction conditions were 0.3 mol/L NaOH, liquid-solid ratio of 1:20, and extraction at 60 °C for 3.5 h. The extraction yield reached 11.46 ± 1.73 %. PSIG-1 consists of 83.52 ± 0.39 % proteins and 12.42 ± 0.41 % polysaccharides. PSIG-1 was primarily composed of a 70 kDa glycoprotein. Structural analysis revealed that PSIG-1 possesses the O-glycopeptide linkage and the pyranose cyclic sugar chain conformation that protects its antioxidant activity, with its secondary structure predominantly comprising random coils. In cellular experiments, PSIG-1 significantly enhanced the activities of glutathione peroxidase, superoxide dismutase, and catalase while reducing intracellular malondialdehyde levels in RAW264.7 cells subjected to H 2 O 2 -induced oxidative damage, demonstrating strong antioxidant activity. This study reveals that PSIG-1 has potential applications as an antioxidant in functional foods. • A method was developed for the extraction and purification of porcine small intestinal glycoproteins (PSIG-1) • PSIG-1 was mainly composed of 70 kDa glycoproteins • PSIG-1 possesses the O-glycopeptide bond and the pyranose cyclic sugar chain conformation • PSIG-1 have excellent antioxidant properties in RAW264.7 cells