Effect Of Pyruvate Group On Synergistic Effect And Gel Properties From Mixtures Of Xanthan And Konjac Glucomannan

Xanthan gum(XG),a common polysaccharide from microbial fermented,is widely applied in food industry,daily chemical and petroleum fields.It has high viscosity,which isn't sensitive to pH and still has great high temperature resistance under the effect of salt ions.However it does not form true gels.Xanthan could form thermoreversible gels in mixtures with konjac glucomannan(KGM)and have a significant impact on the texture of food products.Pyruvate is one of the substituents on xanthan gum side chain,and has a vital effect on its structure,which it turn affects the synergistic between XG and KGM.This paper major studied the effect of pyruvate content on the synergistic effect and gel properties of mixed system of XG and KGM,and provided a basis for its food texture design.Main conclusions are as follows:1.The xanthan gum with different pyruvate content was prepared by acid heat treatment,and the results were characterized.Compared with oxalic acid,hydrochloric acid promoted the removal of pyruvate groups;in the concentration range of 0.01-1 mol/L,the pyruvate content is lowest at 0.1 mol/L hydrochloric acid;increasing temperature,the pyruvate content was lower.The samples of XG1,XG2,XG3,XG4,XG5 were respectively obtained from 0.1 mol/L hydrochloric acid solution under different temperature of 80?,85?,90?,95?,98?.The corresponding pyruvate content of them were 2.39%.1.3%?0.69%?0.34%?0.12%.The pyruvate content of untreated XG gum was 5.93%,recorded as XG0.The pyruvate-based signal peak at 1.5 ppm of XG5 disappeared,while the other characteristic peaks except for 1726.50 cm-1 in Fourier transform infrared spectroscopy(FTIR)were unchanged,indicating that other structures did not change under the process of depyruvate reaction.Rheological test results showed that the pyruvate content decreased,the viscosity of the xanthan gum solution was lower,the shear thinning behavior gradually disappeared,the storage modulus G' decreased,and the ordered-ordered conformation temperature shifted to higher temperature.Besides,the optical microscopy showed that the aggregation of xanthan gum disappeared and the dispersibility increased while the pyruvate content decreased.2.The xanthan gums were mixed with KGM at the ratio of 1:1,and the influence of pyruvate content on XG/KGM thermoreversible gel was measured by MCR320 rheometer.Steady-state scanning at 60 ? showed that the XG/KGM mixed system exhibited shear thinning behavior,the pyruvate content decreased,the consistency coefficient k decreased,and the flow index n increased and was trend to 1,indicating that the pyruvate content was reduced,the fluid resistance of the XG/KGM mixed system decreased.Cooling scan showed that the elastic modulus G' of XG/KGM mixed system with different pyruvate content increased with the decrease of temperature,indicating that the three-dimensional network of gel was formed between XG and KGM through hydrogen bonding and so on.The initial gel pointe(Tm)of XG/KGM mixed system was decreased from 60? to 41 ?,and G' was lower;indicating that the synergy between XG and KGM was weakened and sol-gel temperature was lower as pyruvate content decreasing.All the storage modulus G' levelled out towards constant values between 0.1 rad/s and 100 rad/s,suggesting that XG mixed with KGM could form a true gel.As the pyruvate content decreasing,tan8 increased and G' decreased,solid-like property was weaker.3.Three factors,different radio,temperature,salt ion,were used to explore the effect of pyruvate content on the sensitivity to environment factors of XG/KGM mixed system.The result showed that the strength of mixed system was changed as the mixing radio of XG with KGM.Improving the temperature and the addition salt ions were weaken the synergy between XG and KGM.The optimal synergistic ratio of XGO and KGM is 5:5.With the reduction of pyruvate content,the synergy effect between XG and KGM was enhanced by increasing KGM content.The optimal synergy ratio of XG5 and KGM is 3:7.G' of XG/KGM mixed gel gradually decreased as improving temperature.The downward trend became steep as the pyruvate content decreasing,suggesting that XG/KGM mixed gel with low pyruvate content is sensitive to temperature.With the addition of salt ions,G' of the XG/KGM mixed gel decreased;the pyruvate content decreased,the G' decline trend became flat;it suggested that the weakening reason of salt ion for the synergistic effect of XG and KGM is mainly to weaken the electrostatic shielding at XG side chain,thereby increasing the stability of XG structure,reducing the contact area between XG and KGM,reducing the number of intermolecular hydrogen bonds;so,the synergy effect between XG and KGM was weaken;As the reduction of pyruvate content,XG/KGM complex gel is less sensitive to salt ions.4.The effect of pyruvate content on the transparency,gel strength,water holding capacity and swelling kinetics of XG/KGM mixed gel were studied,the results showed that the transparency of the XG/KGM mixed gel increased first and then decreased with decreasing pyruvate content in xanthan gum.The transparency was the best when the pyruvate content was 0.34%.As the pyruvate content decreasing,the synergy effect between XG and KGM was weak,the gel strength was decreased,the network structure was loose,and the binding capacity of water molecules was weakened,so that the water holding capacity decreased.As the pyruvic acid content decreasing,the swelling rate of the XG/KGM mixed gel decreased first and then increased,while the equilibrium swelling ratio gradually decreased.As the pyruvate group decreased,the FTIR spectrum showed that the hydrogen bonding between XG and KGM is weakened,and the stability of combined water was weaken in the DSC test.