Comprehensive evaluation of extraction process, physicochemical properties and bioactivities of hawk tea polysaccharides: comparison of ultrasonic and hot water extraction

Hawk tea (HT) is a long-established substitute tea, rich in polysaccharides and other biologically active ingredients, with research value in food science and medicine. Therefore, this study, utilized ultrasonic extraction (UAE) to extract HT polysaccharides (UHTP). The disparities in extraction yield, energy consumption, and HT structure between UAE and hot water extraction (HWE) were contrasted to elucidate the extraction mechanism. Subsequently, the physicochemical properties and in vitro activities of the UHTP and polysaccharides extracted by hot water (HTP) were examined and evaluated to reveal the correlation between physicochemical properties and bioactivities. The results manifested that under optimal UAE conditions, the polysaccharide yield was 11.08 ± 0.07%. Compared to HWE, UAE had a 17.00% higher extraction yield, 42.66% less energy consumption, and 42.67% lower CO₂ emissions. The improved UAE efficiency stemmed from its greater capacity to modify cell wall composition, disrupt microstructure, and reduce particle size, facilitating mass transfer. Moreover, compared with HTP, UHTP exhibits lower molecular weight and apparent viscosity, higher content of uronic acid (36.81% increase). UAE notably induced polysaccharide chain degradation, yielding UHTP with more homogeneity, smaller particle size, and rougher surface. Ultimately, UHTP demonstrates stronger antioxidant, hypoglycemic and prebiotic activities. Overall, this study offers a theoretical foundation and new prospects for the highly efficient extraction mechanism and the correlation between physicochemical properties and bioactivities of HT polysaccharides.