Plackett-Burman Design Combined with Response Surface Methodology to Recover Polysaccharides with Cardiovascular Protective Potential from Waste Zizania latifolia Bracts

Zizania latifolia is the second aquatic vegetable in China. The circular valorization of its waste bracts remains ongoing concern. In this work, the cellulase-microwave-assisted extraction (CMAE) of polysaccharides from waste Z. latifolia bracts (PWZLBs) was explored. Seven parameters were selected via single-factor test, of which three significant parameters were screened out using Plackett-Burman design, followed by response surface methodology optimization. The optimal CMAE for PWZLBs were: cellulase addition of 0.5%, microwave time of 7 min, and microwave power of 425 W, resulting in a yield of 0.82 ± 0.08%. Four polysaccharide fractions (PWZLBs-1 ~ 4) were isolated from PWZLBs, of which PWZLBs-1 accounted for major proportion and exerted higher scavenging capacities on diphenyl picryl hydrazinyl and hydroxyl radicals. More importantly, PWZLBs-1 elicited anticoagulation via prolonging thrombin time and prothrombin time, exhibiting potential for cardiovascular protection. Various characterizations confirmed that PWZLBs-1 is a heteropolysaccharide containing uronic acids and sulfates, with galactose (34.3%) as the predominant monosaccharide, and has a molecular weight of 8061 kDa. This work provides clues for the circular valorization of waste Z. latifolia bracts and offers potential opportunities for the development of new cardiovascular protective drugs.