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

Abstract 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‐Ara f , 1,5‐α‐Ara f and 1,2,3,5‐α‐Ara f , 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.