Physicochemical Properties And Applications Of Mucilage From Dioscorea Opposita Thunb.

Mucilage from animals or plants has attracted much attention due to its unique physicochemical properties,functions and biological activities.Mucilage from Chinese yam（Dioscorea opposita Thunb.）is riched in nutrients and active substances.However,there are few studies on the functional properties and applications of mucilage,which limits the application of mucilage in process design and product developemt.Therefore,in order to develop the application of mucilage from D.opposita（DOM）,the compositions,antioxidant activity,rheological,emulsification and film-forming properties were studied.The main research contents and results are as follows:DOM,extracted by water extraction,mainly obtained polysaccharide and protein.The total carbohydrate content was approximately 45.18%,and monosaccharides in DOM were mainly glucose,mannose and galactose.The protein content was approximately 10.35%.The molecular weight（Mw）was1.43×10⁵ Da with a wide range of Mw distribution,indicating complex structure of mucilage.Meanwhile,the antioxidant activity was studied,and DOM had ability to scavenge hydroxyl free radicals and DPPH·free radicals,which is expected to be developed as a natural antioxidant.The effects of different concentration,temperature,p H,salt ions,sugar,freeze-thaw conditions on the rheological properties were investigated.DOM dispersions exhibited a pseudoplastic（shear-thinning）behaviour that well fitted with the Power Law model.The viscosity of DOM increased with the increase of concentration and decreased with the increase of temperature（25-65°C）.The viscosity decreased in both acidic and alkaline environments,which may be related to the ionization of carboxyl group,conformation change and molecular interaction.The addition of Ca²⁺and sugar could enhance the network structure of DOM,leading to increasing the viscosity.Therefore,DOM presents appropriate rheological properties and provides theoretical support for use as thickening or gelling agent.Based on our previous study on the emulsification of DOM,the DOM-polysaccharide emulsions were prepared by high pressure homogenization method with DOM,polysaccharide[Guar gum（GG）,Xanthan gum（XG）and pectin（Pec）]and different oil phase[medium chain triglyceride（MCT）,soybean oil（SO）,orange oil（OO）,fish oil（FO）],and the stability mechanisms of DOM-polysaccharide emulsions were speculated,which provides theoretical foundation for medical preparations of suspensions or emulsions.The particle size,zeta-potential,microstructure,turbidity,interfacial tension were studied,the results showed that the emulsions made by GG,XG and Pec alone exhibited larger particle sizes and lower zeta-potential,while DOM-polysaccharide emulsions with MCT or SO presented smaller particle sizes and the absolute zeta-potential values were greater than 30 m V,and exhibited higher turbidity and lower interfacial tension,indicating that the complex emulsions were stable.In particular,the particle sizes of emulsions prepared by DOM and pectin were smallest,which may be associated with the molecular weight and structure.DOM and 0.4%w/v polysaccharides showed better stability and lower creaming index during 21 days.The emulsions made by OO and FO showed larger particle size,and the droplets easily flocculate until creaming,which may be caused by the chain length of fatty acids and the polarity of the oil.The results suggested that DOM and polysaccharide had synergistic effect to improve the stability of emulsions.Therefore,DOM has good potential for applications in the pharmaceutical area and food industry as natural emulsifier.The DOM-Zn O NPs films and DOM-Ag NPs films were prepared by casting method based on the thickening and film-forming properties of DOM.The addition of Zn O NPs and Ag NPs decreased the transparency,and addition of DOM enhanced the cross-linking network and reduced the water vapour permeability（WVP）.The films with DOM and nanoparticles increased the elongation at break,reduced the tensile strength,and improved the flexibility of the composite film.Moreover,films were characterized by FTIR,SEM and AFM.The results showed that films had compact network structure with smooth surface.The antibacterial activity and acute toxicity of films were further studied.The non-toxic film-forming solutions containing 2.0 g Zn O NPs and Ag NPs respectively presented significantly antibacterial activities on S.aureus and E.coli,and accelerated wound healing.Therefore,DOM is expected to be developed as film-forming agent which can be used as biodegradable packaging materials and wound dressing.This study investigated the physicochemical properties of DOM including rheology, emulsification,and film-forming properties,providing novel prospectives for the applications of mucilage.