Structural characterization and antioxidant activity of a glycoprotein isolated from shiitake mushrooms

In this paper, the shiitake mushroom glycoprotein (SGP) was extracted from shiitake mushrooms and its structure was characterized and its antioxidant activity was investigated. SGP contained 33.42 ± 1.75% protein and 42.59 ± 1.95% sugar, with 17 amino acids and eight monosaccharides at concentrations of 81.52 mg/g and 42.62 μg/mg, respectively. SGP contained abundant hydrophobic amino acids and monosaccharides in terms of variety and concentration, which can improve the chelation of SGP to metal ions and effectively improve its antioxidant capacity. Moreover, SGP belongs to the type of O-glycopeptide bond, wherein the secondary structure was mainly β-strands, the sugar chain had a pyran ring configuration, and the characteristic absorption peaks of polysaccharides and proteins appeared at 3383 cm−1 and 2929 cm−1. The O-glycopeptide bond and β-strand structure played a positive role in slowing the half-life of antioxidant active substances. In addition, the antioxidant capacity of SGP increased with increases in SGP concentration within a certain range, and the total antioxidant capacity reached a maximum of 4.4 ± 0.18 μmol/mL when the SGP concentration was 8 mg/mL. This study improved the understanding of the structure and antioxidant activity of SGP, and contributed to the study of structure-activity relationships in the food industry.