Preparation and structural characteristics of polysaccharides from loquat peel waste, and their preliminary bioactivities

BACKGROUND: Loquat peel, often as food waste, is a valuable source of bioactive polysaccharides. However, study of such polysaccharides is insufficient, leaving a significant gap in understanding their preparation, structure and bioactivities. RESULTS: In this study, three types of loquat peel polysaccharides (LPWP, LPHP and LPNP) were sequentially extracted using hot water, HCl and NaOH solutions, respectively. Among them, LPWP was the purest, with a yield of 3.4% and molecular weight of 470.6 kDa, and it differed from LPHP and LPNP in structure, as evidenced by Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy, which demonstrated that LPWP consisted of more arabinose (Ara) but less galacturonic acid, rhamnose and galactose, with molar percentages of 71.3%, 23.3%, 3.5% and 1.9%, respectively. Besides, LPWP also exhibited superior antioxidant and antihyperglycemic activities in vitro, particularly in inhibiting α-amylase and α-glucosidase. Methylation and nuclear magnetic resonance analysis confirmed that LPWP was a methyl-esterified pectic polysaccharide rich in branched arabinan, as evidenced by the notable proportion of α-Ara residues, including T-α-Araf, 1,5-α-Araf and 1,2,3,5-α-Araf, with molar percentages of 27.1%, 23.1% and 10.2%, respectively. AFM imaging further revealed its branched-chain morphology and aggregation behavior. CONCLUSION: This study highlights the potential of loquat peel polysaccharides as a bioactive ingredient with significant antioxidant and antihyperglycemic properties, particularly LPWP, which was found as a methyl-esterified pectic polysaccharide with abundant-branched arabinan. Our work provides valuable insights into the application of loquat peel polysaccharides in functional foods. © 2024 Society of Chemical Industry.