Ultrasound-assisted hot water extraction of yellow leaves of Pu’er tea polysaccharides: Extraction process, characterization, antioxidant and hypoglycemic activity
Aobo Zhao, Lina Sun, Fu Xu, Wendie Gan, Bao Lin Guo, Lianzhou Jiang, Xia Wu
Abstract
Yellow leaves of Pu’er tea are classified as lower-grade Pu’er tea, and polysaccharides being its principal active components. Pu’er tea polysaccharides (PTPS) were optimally extracted from yellow leaves of Pu’er tea using ultrasound-assisted hot water extraction with the following parameters: solid-to-liquid ratio of 1:25 (w/v), ultrasonic temperature of 70 °C, ultrasonic power of 500 W, and ultrasonic time of 40 min. Two fractions, PTPS-4A and PTPS-5A, were clearly isolated and purified. Their antioxidant and hypoglycemic effects were compared in a lab after examining their structural features. PTPS-4A and PTPS-5A were mostly composed of fucose, rhamnose, arabinose, galactose, glucose, mannose, and glucuronic acid. They manifested as flexible chains and assumed a linear spline curve suggestive of an earthworm-like conformation. The nuclear magnetic resonance investigation found α- and β-glycosidic linkages ( δ 4.30–5.95 ppm and δ 4.29–4.97 ppm, respectively) in PTPS-4A and PTPS-5A. PTPS-4A had enhanced DPPH and hydroxyl radical removal, with IC 50 values of 1.79 ± 0.07 mg/mL and 6.42 ± 0.16 mg/mL, respectively. The intermediate concentration value of 5.22 ± 0.08 mg/mL of PTPS-4A indicated a stronger inhibitory impact on α-glucosidase. PTPS-4A and PTPS-5A did not affect α-amylase in any way. The PTPS-4A fraction from this study may be further processed to create polysaccharide-based hypoglycemic and antioxidant products.