Study On Digestibility And Physicochemical Properties Of Starch-galactomannan Complexes

Galacotomannan(GM)is a class of water-soluble polysaccharides existing in the endosperm of various legumes,and it's composed of a ?-(1,4)-D-mannose backbone and single D-galactose units attached to the main chain through ?-(1,6)glycosidic bond.Besides,the ratio of mannose to galactose residues ranges from 1 to 4,due to the different plant sources of the polysaccharides.Heat-moisture treatment(HMT)refers to the process of heat treatment of starch at low moisture content(?30%)and relatively higher temperature(90~120?),usually can help starch to form a more stable structure.Nowadays,the digestibility of starch,which is closely related with human health,has become a research hotspot,cause starch is the main source of energy for the human body.In this thesis,high-amylose,normal and waxy maize starches,and Guar,Tara and LBG gums with mannose/galacose residue raitos of about 2,3,4 in order were used as raw materials.The morphology,structure,digestibility and other physicochemical properties of the native starch-galactomannan complex(NS-GM)paricles prepared with or without HMT were studied,and the effects of the three galactomannans,amylose content and HMT on the composite systems were compared and analyzed.The normal maize starch(NMS)was blended with 0,0.5%,1%,and 2%(w/w)galactomannan respectively,and the products were obtained after heat-moisture treating under the condition of water content of approximately 20% and temperature of 120? for 4h.Following analyzing their properties,it was found that the distribution of the three galactomannans and the resistant starch content in the HMT NMS-GM composite particles were related to the ratio of galactose/mannose residues in the galactomannan.The distribution of LBG,Tara and Guar on the surface of starch granules was attachment,sticking and wrapping into gather in order,and the phenomina became more obvious with the increase in the addition amount of the gums.The resistant starch content was in the order of HMT NMS-LBG < HMT NMS-Tara < HMT NMS-Guar,and that of HMT NMS-Tara/Guar composite significantly increased with the amount of gum increased.In addition,the resistant fragment in the resulting composites was more than that in the native and HMT starches,due to the physical barrier action on the surface of starch granules and the noncompetitive inhibitory effect on the enzyme activity of the added galactomannan.Moreover,adding galactomannan could significantly increase the gelatinization temperature and decrease the enthalpy of the HMT composites;the value of ?T(gelatinization temperature range)significantly increased when the addition amount of gum reached 2%.Besides,HMT NMS-2%Guar composite had the highest Tp,which means its crystalline was the most stable;HMT NMS-GM formed relatively looser recrystallization structure after freezing-thaw.Cause HMT NMS-2%Guar composite had the most resistant fragment,2% Guar has been chosen to be blended respectively with three kinds of maize starches with different amylose content,and the mixtures were devided into two portions,one of which was subjected to HMT and the other was not.Then the properties of the products were studied,and the results showed that HMT could make the distribution of guar on the surface of the starch granules more uniform,decrease the relative crystallinities of the composites,and the decrease range increased with the amylose content increased;high amylose starch-Guar also tended to form more stable crystalline after HMT.Differ from the other mixtures,the high amlose maize starch-Guar without HMT had the crystalline of B+V style,which means that high amylose starch might form a complex with guar gum directly.Besides,the anti-digestibillity of blend particles decreased with the decrease in amylose starch content;after HMT,the HMT normal maize starch-Guar composite showed the highest resistance,due to the wrapping of guar gum and the change in the composites' crystalline structure.Furthermore,HMT could significantly decrease the complx systems' hygroscopicity,and also decrease the gelatinization enthalpy of the composites in the order of waxy starch-Guar >normal starch-Guar>high amylose starch-Guar,and help slow down the normal/waxy-Guar's long-term ageing.Additionally,(HMT)normal maize starch-Guar is the most resistant to moisture in the lower humidity(45%)environment,and has the lowest gelatinization temperature and the minimum ?T.