Ultrasound-assisted extraction of polysaccharides from <i>Syzygium jambos (L.) Alston</i> fruit by deep eutectic solvent and its biological functions

<i>Syzygium jambos (L.) Alston</i> (<i>S. jambos</i>) fruit has been increasingly utilised as a functional food in diabetes management in recent years. As polysaccharides represent a key functional component in fruits with diverse biological activities, studies on extraction methods and antidiabetic effects of <i>S. jambos</i> polysaccharides remain limited. This study established a deep eutectic solvent (DES)-based ultrasound-assisted extraction method for polysaccharides from <i>S. jambos</i> fruit. The optimised extraction conditions determined to be a liquid-solid ratio of 17 mL/g, 6% water content in DES, an extraction time of 50 min, and an ultrasonic power of 200 W in the choline chloride-oxalate DES system (molar ratio of 2:1). The novel extraction method achieved a substantially higher extraction rate than traditional method (32.67% <i>vs</i>. 4.3%), demonstrating the potential for polysaccharides extraction from <i>S. jambos</i> fruits. Additionally, the biological evaluation <i>in vitro</i> revealed that purified polysaccharide TPS-1 moderately inhibited α-glucosidase and α-amylase activities, as well as scavenged DPPH· and ABTS⁺ radicals, suggesting its potential as a dual-functional antidiabetic and antioxidant agent. Moreover, monosaccharide analysis revealed that TPS-1, which comprised mannose, rhamnose, glucuronic acid, and galacturonic acid with a molar ratio of 5.49:11.79:41.25:30.95, differs significantly from the reported water-soluble polysaccharide of <i>S. jambos</i> fruits. However, the structure features of TPS-1 and its antidiabetic effects and mechanisms <i>in vivo</i> remain to be elucidated in future research.