Polysaccharides from Trifolium repens L. extracted by different methods and extraction condition optimization

Four different extraction methods, including hot water extraction (HWE), ultrasonic-assisted extraction (UAE), enzyme-assisted extraction (EAE) and ultrasonic-enzyme-assisted extraction (UEAE), were applied to extract polysaccharides from Trifolium repens L. (TRPs). In addition, response surface methodology (RSM) was performed to optimize the extraction conditions of TRPs. The results showed that different extraction methods had significant effects on the extraction yields and antioxidant activities of TRPs. TRPs extracted by the EAE method (10.57%) and UEAE method (10.62%) had significantly higher extraction yields than TRPs extracted by the HWE method (8.35%) and UAE method (9.43%) (P < 0.05). However, there was no significant difference between the extraction yields of the EAE method and UEAE method (P > 0.05). TRPs extracted by the EAE method had a higher content of uronic acid and exhibited better antioxidant capacities. Therefore, EAE was selected as the optimal extraction method to extract TRPs. The optimal extraction conditions of EAE to extract TPRs were liquid–solid ratio 30 mL/g, enzymolysis time 87 min, enzyme-complex dosage 1.6% and pH 6, leading to a TRPs yield of 13.15%.