Abstract:[Objective] This study aims to optimize the extraction process of polysaccharides from coffee peels and explore their structure and bioavailability. [Method] The composite enzymatic hydrolysis method was employed to extract polysaccharides from coffee peels. The polysaccharide structure was characterized from aspects such as infrared analysis, monosaccharide composition, molecular weight determination, and glycosidic linkage analysis. The bioavailability of the extracted polysaccharides was analyzed. [Result] The extraction process conditions were optimized as follows: a cellulase mass fraction of 2.6%, an alkaline protease mass fraction of 2.6%, a papain mass fraction of 2.6%, a pectinase mass fraction of 3.8%, an extraction temperature of 60 ℃, extraction time of 1.5 h, a solid-to-liquid ratio of 1 g∶100 mL, and pH 4. The composite enzymatic hydrolysis method effectively maintained the bioavailability of the polysaccharides. Structural characterization revealed that the coffee peel polysaccharides had a weight-average molecular weight of 1 626 765 and were composed of rhamnose, arabinose, galactose, glucose and galacturonic acid at a molar ratio of 4.39∶23.75∶28.03∶7.58∶36.25. It adopted an α-pyranose backbone and contained typical glycosidic linkages including →3)-Galp-(1→ and →4)-Galp-(1→. Galacturonic acid, as the major constituent, existed in the form of →4)-Galp-UA-(1→, which constituted the characteristic structural motif of the acidic polysaccharide. [Conclusion] This study provides a scientific reference for the in-depth research and development of coffee peels, a coffee by-product.
