Effects Of Small Molecular Sugars On The Retrogradation Characteristics Of Lotus Seed Starch

During the processing,the lotus seed is prone to retrogradation,since it contains high starch content and of which the amylose molecule is more than 40%.That seriously affects the commercial value of its processed products.Thus,the study on retrogradation and anti-retrogradation of lotus seed starch?LS?has important scientific significance and practical applications.Small molecular sugars mainly include monosaccharides,disaccharides and oligosaccharides with a degree of polymerization less than 10.The glucose,sucrose and maltooligosaccharides have been reported to have the effect of delaying starch retrogradation.Based on this,LS was adopted as research object in this paper,the effects of small molecular saccharides?monosaccharides,disaccharides and oligosaccharides?on the crystal structure,short-range ordered structure and double helix structure of LS were studied using X-ray diffraction?XRD?,nuclear magnetic resonance?NMR?and fourier infrared?FTIR?spectroscopy,combined with the differences of molecular weight and microstructure for the blended system,the effects of small molecular sugars on short-term and long-term retrogradation characteristics of LS were analyzed in-depth.The results of this study would provide a theoretical basis for the study of the effect of different saccharides on starch retrogradation and its mechanism.?1?Effect of monosaccharides on the retrogradation characteristics of LSThe effects of different monosaccharides?glucose and fructose?on the retrogradation of LS were studied.The results of XRD,NMR and FTIR showed that glucose and fructose could inhibit LS recrystallization during short-term and long-term retrogradation,causing the crystallinity,double helix structure and short-range ordered structure decreasing and the proportion of amorphous region increasing in the composite system.The glucose was better in retarding starch retrogradation,which might be related to the enhancement of glucose-water interaction.The results of gel permeation chromatography showed that the molecular weight M_n and M_wof LS with glucose addition were significantly increased,while those of LS with fructose addition were significantly decreased.It was suggested that the molecular weight of starch increased by glucose was the key factor affecting the retrogradation of system.The observation of scanning electron microscope?SEM?showed that the microstructure of LS added with glucose or fructose was more loose,with more porous cross-linking structure,which proved that the presence of glucose and fructose could hinder the retrogradation of starch molecules,and the effect of glucose was more obvious than that of fructose.?2?Effect of disaccharides on the retrogression characteristics of LSThe effects of disaccharides?sucrose and maltose?on the retrogradation of LS were studied.The results showed that,similar to monosaccharides,addition of sucrose and maltose caused the significant decreases in the relative crystallinity,short-range ordered structure R_{1 047/1022}of LS composite system and an increase in the proportion of amorphous area P_C4 value?p<0.05?,suggesting sucrose and maltose could inhibiting the recrystallization?retrogradation?process of LS under the autoclaving treatment,with good ability of retrogradation.The P_C4values of LS added with maltose were the highest,while R_1047/1022 value was the lowest,indicating that maltose inhibited the retrogradation of lotus seed starch more effectively than sucrose.At the same time,the results of SEM also displayed that the maltose groups of 1 and 7-day retrograded samples were more loose with obvious porous structure when compared with the sucrose group.Maltose was more effective than sucrose in preventing recrystallization and the formation of ordered structure of LS,which was highly consistent with the results of XRD,NMR and FTIR.The higher inhibitory effect of maltose on retrogradation might be influenced by the presence or absence of fructose molecules in its structure,in addition to the increase of molecular weight in the composite system.?3?Effect of oligosaccharides on the retrogression characteristics of LSThe effects of different oligosaccharides?maltotrisaccharides,raffinose and stachyose tetrahydrate?on the retrogradation characteristics of LS were studied.The results showed that the addition of maltotrisaccharide could significantly reduce relative crystallinity of LS composite system,as well as R_{1 047/1 022} and R_{995/1 022,}values,and increase the P_C4 values?p<0.05?.It suggested that maltotrisaccharides had the potential to delay the short-term and long-term retrogradation of starch.Compared with monosaccharide and disaccharide group,maltotrisaccharide had weaker inhibition than maltose on recrystallization of LS.In contrast,the addition of raffinose and stachyose tetrahydrate increased the proportion of crystal area,relative crystallinity,R_1047/1022and R_995/1022values of the composite system,and decreased the P_C4 values,especially the stachyose tetrahydrate.The results showed that raffinose and stachyose tetrahydrate could promote recrystallization?retrogradation?of LS,and the effect of stachyose tetrahydrate was more stronger.The promoting effect of raffinose and stachyose tetrahydrate on the retrogradation of LS might be related to the plasticization of saccharides.