The Effect Of Structural Modification On The Emulsifying Properties Of Artemisia Argyi

Artemisia sphaerocephala Krasch. (ASK) is an important natural plant resource with a great planting area in northwest of China. Artemisia sphaerocephala Krasch. polysaccharide (ASKP) is a natural water-soluble heteropolysaccharide extracted from the outer layer of ASK seeds. When soaked in water, ASKP can form a viscous solution and demonstrate the ability to reduce the surface tension of oil/water interface. ASKP has great potential to be processed into the polysaccharide emulsifier.In the present study, xylanase from Trichoderma viride, glucanase from Acidothermus cellulolyticus. protease from Bacillus licheniformis and acetylation were used to conduct the structural modifications on ASKP and its two fractions-high molecular weight fraction (60P) and low molecular weight fraction (60S). Molecular characteristic, rheological property, emulsifying activity and emulsifying stability were measured to evaluate the effects of structural modifications on the emulsifying property of ASKP. The results are illustrated as follows:(1) Effects of structural modifications on molecular characterizations, rheological properties and emulsifying properties of hydrocolloidsAfter hydrolyzed by polysaccharase, the molecular weights and radiuses of gyration of ASKP,60P and 60S decreased and the conformations of 60P and 60P in ASKP trended to be looser with random coils. The apparent viscosities of ASKP and 60P solutions decreased while the surface tensions at oil/water interface decreased with significant difference (p<0.05). Differently,60S solution maintained a low apparent viscosity, as well as the surface tensions at oil/water interface decreased with no significant difference (p<0.05). After hydrolysis, ASKP and 60P were conferred better emulsifying properties while 60S lost the excellent ability.After deproteinization with the protease, the molecular weight and radius of gyration of 60P in ASKP decreased, as well as the conformation trended to be looser with random coils. The apparent viscosity of ASKP solution decreased while the surface tensions at oil/water interface increased with no significant difference (p<0.05). The procedure of deproteinization was harmful for the emulsifying property of ASKP.For the degradation during acetylation, the molecular weights and radiuses of gyration of 60P and 60S in ASKP decreased. With the increase of substitution degree (DS). the molecular weights and radiuses of gyration of acetylated ASKPs increased and exceeded those of ASKP. After acetylation, the conformations of acetylated ASKPs trended to be more compact, which tended to curl up into balls. Low DS conferred acetylated ASKPs low viscosities. With the increase of DS. the apparent viscosities of acetylated ASKPs increased and exceeded that of ASKP. Compared with ASKP, acetylated ASKPs could reduce the surface tension significantly (p<0.05). The emulsifying properties of acetylated ASKPs increased with the increase of DS.(2) Structure-activity relation of the emulsifying property of ASKPMolecular weight and radius of gyration were the important factors for the emulsifying property of ASKP. Lower molecular weight and smaller radius of gyration were beneficial to improve the emulsifying properties of ASKP and 60P and bad for that of 60S.The existence of protein in ASKP played an important role in the maintenance of 60P's high molecular weight structure and was essential to the emulsifying property of ASKP.The addition of acetyl groups could improve the emulsifying property of ASKP and the effect was more obviously than those of molecular weight and radius of gyration.The conformations of samples showed the smaller effects.In the current study, the basic structure-activity relation between structural characteristic and emulsifying property of ASKP was discussed. It provides the experimental and theoretical supports for the development of emulsifiers with ASKP.