Rheological And Gelation Properties Of Polysaccharide From Dendrobium Officinale And Its Application

Dendrobium officinale is a medicinal and edible plant with a variety of bioactivity activities,including immunomodulatory effect,antioxidant activity,antitumor,etc.Previous researches indicated that polysaccharide was the main substance for biological activities.At present,there are few reports on the rheology of polysaccharide solution from Dendrobium officinale(DOP),and the gel formation and properties of DOP are still unclear.In this thesis,the physicochemical properties,the rheological and gelation formation and properties of DOP were studied,and the possible mechanism of gel formation was proposed.In addition,the application of DOP-Xanthan gum(DOP-XG)in jelly food was explored.The main results of this paper are as follows:(1)Polysaccharide of Dendrobium officinale was extracted by hot water extraction,and successively deproteinized by Sevag method,and finally analyzed its molecular weight distribution and physicochemical properties by various optimal methods.The results showed that the total sugar content of DOP after deproteinization was 89.38%,the glyoxylic acid content was 2.19%,the protein content was 0.39%,the content of acetyl group was 3.43%.The results of HPGPC showed that DOP was composed of two molecular weight polysaccharides(43.6 k Da and 64.7 k Da).The results of FT-IR indicated that DOP contained acetyl groups in its structure.The results of XRD showed that DOP as a whole presented a relatively amorphous state.The results of DSC showed that DOP had good stability in the range of 30?200?.The results of SEM showed that the solid morphology of the DOP was a relatively uniform and smooth flake.(2)The effects of mass concentration,metal ion type and concentration,temperature and p H on the rheological properties of DOP were evaluated.The results showed that the DOP aqueous solution exhibited shear-thinning flow behavior under different concentration,temperature,inorganic cation type and solution p H.The viscosity of DOP solution increased with its increasing concentration.The viscosity of DOP solution decreased with the increasing of temperature in the range of 5?75?.The viscosity of DOP solution significantly increased with the increasing of Na⁺concentration.However,the viscosity of DOP solution was decreased when K⁺,Ca²⁺,Al³⁺were added respectively and the change trend was related to the metal ions concentration and valence.DOP extracted with hot water had good stability in the range of p H 2.0?6.8.However,the viscosity of DOP solution significantly increased under alkaline conditions and the gelation of solution will be occurred under alkaline conditions(p H>10.0).The dynamic rheological results showed that the gelation of DOP was enhanced with the increasing of polysaccharide mass concentration.(3)This study observed for the first time that DOP could form gel under certain conditions,and the effects of various factors on the texture properties and water-holding capacity of DOP gel were analyzed.The results showed that the gel properties of DOP were significantly affected by the polysaccharide mass concentration,temperature,alkali type and concentration,Na⁺and urea.The higher the mass concentration of polysaccharide,the higher the strength and water-holding capacity of the DOP gel.In the range of 40?100?,the gel strength and water-holding capacity of DOP decreased gradually with the increasing of temperature.With the mass concentration of alkali in the solution increasing,the strength of the gel increased first and then decreased,and the water holding property of the gel decreased gradually.Under the condition of the same alkali addition,the order of the gel strength formed was Na₂CO₃>K₂CO₃>Na OH>KOH.The addition of Na⁺increased the gel strength and water-holding capacity.However,the gel strength and water-holding capacity were decreased when urea was added.The crystallinity(XRD)and thermal stability(DSC)of the DOP gel formed by adding Na₂CO₃were analyzed.The results of XRD showed that after gelation,DOP appeared new diffraction peaks at 2?=26.05°and 27.55°.The results of DSC showed that the peak temperature and enthalpy value of the water absorption peak increased after gelation.The results of FT-IR spectroscopy and chemical titration showed that deacetylation was an important factor affecting the phenomenon of gelation.After deacetylation,the interaction of polysaccharide molecular was strengthened and a stable gel network structure was formed.(4)The optimum process formula of DOP jelly was obtained by single factor and orthogonal experiment:the ratio of DOP to XG was 4:6,the amount of gelling agent was1.5%,the amount of honey was 9.0%,the amount of citric acid was 0.5%,and the amount of rose was 2.0%.The DOP jelly prepared under these conditions has the best score of sensory evaluation.DOP could compensate the deficiency of xanthan gum properties.This study clarified the rheological and gelation properties of DOP,and proposed possible gel formation mechanisms.The research results can provide theoretical references for the study on the physical and chemical properties,product processing and chemical modification of DOP.