Structural characterisation and antioxidant and prebiotic activities of Ophiopogon japonicus polysaccharides obtained by enzymatic pretreatment followed by simultaneous microwave-ultrasound-assisted extraction.

In this study, response surface methodology was used to optimize a sequential two-stage process comprising enzymatic pretreatment followed by simultaneous microwave-ultrasound-assisted extraction of Ophiopogon japonicus polysaccharides. At the unrounded model optimum (208.492 W microwave power, 300.945 W ultrasonic power, 25.207 min enzymatic hydrolysis, and 30.100 min microwave-ultrasound extraction), the predicted crude polysaccharide extract yield was 43.999% (44.0% when rounded). Two fractions, OJP-1 and OJP-2, were obtained by DEAE-52 and Sephadex G-100 chromatography. Structural analyses showed differences in their monosaccharide composition, spectral properties, surface morphology, thermal stability, and HPGPC molecular-mass profiles. In vitro, OJP-2 showed stronger radical-scavenging and probiotic growth-promoting responses than OJP-1, whereas both fractions resisted hydrolysis in the simulated digestion systems. OJP-2's stronger responses were accompanied by distinct compositional, morphological, thermal, and HPGPC molecular-mass-profile characteristics.