Water kefir grain polysaccharides: Ultrasonic-assisted extraction optimization, structural characterization, bioactivities, and application in goat yogurt

Polysaccharides from water kefir grains (WG) are functional, food-safe, and potential novel materials for functional food development. This study focused on the extraction process, structural characteristics, and in vitro biological activities of polysaccharides from WG (WPU), as well as the effects of WPU on goat yogurt (GY). WPU was optimally extracted from WG via ultrasound-assisted extraction (UE) under the conditions: 340 W (ultrasonic power), 42 min (ultrasonic time), 20 mL/g (liquid-to-solid ratio), and 80 °C (ultrasonic temperature), achieving a high yield of 27.64%. The monosaccharide composition of WPU-4 (the main purified fraction) was glucose (96.59 mol%), arabinose (0.23 mol%), galactose (0.66 mol%), and mannose (2.52 mol%). Its backbone was predominantly composed of 6-Glcp. Scanning electron microscopy (SEM) revealed that WPU-4 exhibited a sheet-like structure, with an uneven and loose porous network on its surface and a honeycomb-like morphology in its interior. In vitro assays showed WPU had superior antioxidant, α-glucosidase, and pancreatic lipase inhibitory activities compared to purified fractions. Adding 1.0 mg/mL WPU to GY enhanced its antioxidant, antidiabetic, and hypolipidemic activities. This research provides an efficient WPU extraction method and confirms bioactivity potential, offering technical support for WPU industrial applications as functional ingredients in foods and pharmaceuticals.