Modulaion Of Gelation Of Polyuronates Based On Competitive Oligouronates

Polyuronate is a kind of food polysaccharides,which has been widely applied in the food industry.Pectin,alginate and gellan gum are typical polyuronates,which are used as thickener,stabilizer,gelling agent.These applications are based on ionic binding and gelation of polyuronates with metal ions,so it is important to figure it out.The ionic binding and modulation of gelation of polyuronates were mainly based on the molecular weight,monosaccharide composition,degree of esterification or acetylation,etc.Recently,oligouronates were found to be used to modulate gelation of polyuronates with metal ions,which provided a new way for the modulation of gelation of polyuronates.The different oligouronates were prepared by sodium alginate and pectin,which were characterized by various techniques.Their modulatory effects on the ionic binding and gelation of polyuronates with ions were investigated.Main conclusions are as follows:(1)The modulatory effect of oligoguluronate(GB)on the gelation of low methoxyl pectin(LMP)in the presence of different R(Ca/G)was characterized by rheological measurement,atomic force microscopic measurement(AFM)and water holding capacity measurement.In the lower calcium concentration regime(R<0.25),at a fixed calcium concentration of 1.8 mM or a fixed R of 0.10,the addition of GB increased the saturated storage modulus of 0.5% LMP.Therefore,the addtion of GB promoted the gelation of LMP.In the intermediate calcium concentration(0.25<R<0.60),the addition of GB decreased the network-forming ability of LMP.In the higher calcium concentration regime(R>0.60),GB turned to promote the lateral aggregation of LMP.The results together suggested that GB had a promotive effect on the calcium-induced gelation of LMP in the lower and higher calcium concentration regimes,while it tended to suppress the gelation of LMP in an intermediate calcium concentration regime.The promotive effect in the lower calcium concentration regime was attributed to the crosslinking of LMP under the mediation of GB.(2)The modulatory effect of oligogalacturonate(GaB)on the gelation of low methoxyl pectin(LMP)was characterized by rheological measurement,AFM and water holding capacity measurement.In the lower calcium concentration regime(R<0.6),at a fixed calcium concentration of 10.24 mM,the gelation rate and strength of ALG decreased with the addition of GaB.AFM results showed that the addition of GaB inhibited the gelation.This is because that GaB chelated Ca firstly and the Ca chelated by LAG decreased,so the addition of GaB inhibited the gelation.In the higher calcium regime(R>0.6),the gelation rate and strength of ALG increased with the addition of GaB.AFM results showed that the aggregation of ALG is obvious greatly.The water holding capacity of ALG increased in the presence of GaB.This indicated that the addition of GaB promoted the gelation.(3)The modulatory effect of GB on the gelation of low acyl gellan gum(LAGG)in the presence of ions was characterized by rheological measurement,AFM and Micro DSC.In calcium regime,GB could chelate calcium firstly because of its small size and high fluidity,then the calcium chelated by LAGG decreased,so the addition of GB tended to suppress the gelation of LAGG.In sodium and potassiumm regime,GB tended to promote the gelation of LAGG.The promotive effect on the gelation of LAGG was attributed to the brige between LAGG and GB.(4)The modulatory effect of GaB on the gelation of low acyl gellan gum(LAGG)in the presence of ions was characterized by rheological measurement,AFM and Micro DSC.In calcium regime,the addition of GaB increased the gelation of LAGG.AFM results showed that GaB tended to promote the network formation of LAGG.It was attributed to the crosslinking of LAGG under the mediation of GaB.In sodium,potassium regime,GaB tended to promote the gelation of LAGG.The promotive effect on the gelation of LAGG was attributed to the brige between LAGG and GaB.Interestingly,the addition of GaB resulted in the formation of irreversible gel of LAGG with the above three ions.