## 5 Structure-Activity Relationship  
Polysaccharides have a complex structure. At present, most of the research on polysaccharide focuses on the primary structure, but the higher structure is relatively little. Therefore, the study on the structure-activity relationship of ginger polysaccharide is also very superficial. Based on the existing literature, the structure-activity relationship of ginger polysaccharide was sorted. On the one hand, it can reduce the duplication of research, and on the other hand, it can provide the direction for future research. Many studies have shown that the molecular weight of polysaccharides is closely related to a variety of biological activities. Proper molecular weight is one of the necessary conditions for polysaccharides to display pharmacological activities. The molecular weight and anti-oxidant activity of polysaccharides from ginger pomace (HW-GPP1, HW-GPP2, HW-GPP3, and UA-GPP1, UA-GPP2, UA-GPP3) extracted by two different extraction methods were different. The average molecular weight of HW-GPP1, HW-GPP2, and HW-GPP3, and UA-GPP1, UA-GPP2, and UA-GPP3 were calculated as 89.2, 939.8, 1007.9 and 40.6, 868.1, and 892.7 kDa, respectively. In anti-oxidant experiments, UA-GPP3 possessed the strongest scavenging ability on DPPH radicals, and UA-GPP2 exhibited the strongest scavenging ability on hydroxyl and superoxide radicals. It is reported in the literature that polysaccharides with lower molecular weights have more significant biological activity than higher molecular weight polysaccharides. Because polysaccharides with lower molecular weight are easier to enter the organism and play a role. When UA-GPP2 is compared with HW-GPP2, HW-GPP3, and UA-GPP3 in scavenging DPPH radicals, it was consistent with the view reported in the literature. When UA-GPP2 is compared with HW-GPP1 and UA-GPP1 in scavenging hydroxyl and superoxide radicals, it is contrary to this view [46]. Therefore, the relationship between molecular weight and activity needs to be further studied. It is well known that the monosaccharide composition of plant polysaccharides is an important factor affecting their biological activities. When the monosaccharide composition is different, the pharmacological effect is different. Using the same extraction method, two monosaccharide polysaccharides, GP1 and GP2, were extracted from the same raw material. The monosaccharide composition of GP1 is mannose, glucose, and galactose. GP2 is composed of arabinose, mannose, glucose, and galactose. GP1 might have anti-tumor activity, while GP2 displayed DPPH scavenging ability at concentration of 2 mg/mL, with a clearance rate of 67.2% [45]. When the monosaccharide composition is different, even if it has the same pharmacological effect, its strength is different. The study showed that the two ginger monosaccharides, ZOP and ZOP-1, had significant anti-oxidant effects, but the anti-oxidant activity of ZOP-1 was significantly higher than that of ZOP. When the concentration of ZOP and ZOP-1 is 1600 \(\mu\)g/mL, in the DPPH radical-scavenging assay, their maximum clearance rates were 72.7 and 95.2, respectively. In the hydroxyl radical assay, their maximum clearance rates were 33.6 and 99.1, respectively. The reason for this difference may be that the content of Gal in ZOP-1 is higher than that in ZOP. The composition and proportion of ZOP and ZOP-1 were Glc:GalA:Glc:Gal:Ara in a molar ratio of 1.97:1.15:94.33:1.48:1.07 and Glc:Gal:Ara in a molar ratio of 1.00:95.09:2.26, respectively. This speculation is consistent with the results of the anti-oxidant experiment of _Laminaria japonica_ Aresch polysaccharide [49]. When the composition of monosaccharide is the same, the different molar ratio will also affect the biological activity of polysaccharide. ASE-GSLP and HWE-GSLP in ginger polysaccharide are composed of Man, Rha, Glc, Gal, Xyl, Ara, GlcA, and GalA, with the proportions of 2.20:16.24:7.45:34.09:6.36:26.72:1.98:4.96 and 1.95:17.22:4.69:38.88:5.66:28.42:1.81:34, respectively, which have different anti-oxidant activities.