| The interaction between amylose and hydrocolloid plays an important role in regulating the properties of starch.In this study,high amylose corn starch,pea starch and cassava starch as raw materials to obtain debranched starch with a high debranching degree by pullulanase homogeneous debranching.The effects of hydrolysis time on the multi-scale structure and physicochemical properties of the three types of starch were investigated.The composite gel system of debranched starch-konjac glucomannan was constructed by three kinds of debranched starch with a high debranching degree and konjac powder(KGM)were mixed with in different proportions,and the effects of the weight-average degree of polymerization and proportion of debranched starch on the assembly behavior of amylose and KGM were investigated.On this basis,a variety of characterization methods were used to reveal the correlation between total mass fraction and the two-phase behavior,gel properties and antidigestibility of the composite gel system.In addition,the microstructure and gel properties of the composite gels with different freezing treatment methods were compared,and the changes of the composite gels during short-term storage in different food systems were analyzed.It provides ideas for designing functional food with new structure,further expanding and explaining the starch-hydrocolloid system and promoting the practical application of starchbased composite gels in the food industry.Firstly,the molecular structure and physicochemical properties of high amylose corn starch,pea starch and cassava starch were investigated by pullulanase hydrolysis at different time.The granular morphology,microstructure and crystal structure of the three types of starch were changed after pullulanase modification.The three kinds debranched starch with loose and porous structure were mainly amorphous region.The weight-average molecular weight,branching degree,water holding capacity and modulus showed a decreasing trend,while the relative debranching degree and solubility of the three kinds of debranched starch showed an increasing trend with the prolongation of debranching time(high amylose corn starch was hydrolyzed for 4 h-12 h,pea starch and cassava starch were hydrolyzed for 4 h to 20 h).In the same time(4 h,8 h and 12 h),the relative debranching degree of debranched cassava starch was the highest among the three kinds of debranched starch.Compared with the native starch,the short-range and long-range ordering of the debranched starch decreased.The degradation temperature of all the debranched starch ranged from 316.78°C to 318.69°C,and the weight loss rate ranged from 83.61% to 87.49%.Starch-based materials with specific physical and chemical properties could be obtained by controlling the structure and the content of various components of starch by controlling the debranching time.Secondly,the amylose-konjac glucomannan composite gel system was established by mixing three kinds of amylose with different weight-average degree of polymerization(711.728,1322.222 and 2045.062)in debranched starch with a high debranching degree with KGM(10248.765)at different mass ratios(1:1,2:1,3:1,4:1 and 5:1)with the total mass fraction was 4%.As the mass ratio of amylose to KGM decreased,the network structure of the three kinds of non-composite gels became denser,the pore size became smaller and uniform,the content of non-freezable water increased,the mobility of water molecules weakened,the gel properties(rheological properties,texture properties and freeze-thaw stability)further improved,but the long-term order decreased.When the mass ratio of amylose to KGM was 1:1 and 2:1,respectively,the associative phase separation appeared in the medium degree of amylose-konjac glucomannan composite gel and the high degree of amylose-konjac glucomannan composite gel.The three kinds of amylose-konjac glucomannan composite gel networks have different structures,and KGM was a continuous phase forming the three-dimensional network structure.Low weight-average degree of polymerization amylose with better mobility was relatively short.Low weight-average degree of polymerization amylose could enhance the network structure of the composite gel without impeding the interconnection between KGM molecular chains.Under the same proportion,low weight-average degree of polymerization amylose has stronger compatibility with KGM,and low degree of amylose-konjac glucomannan composite gel has good gel properties.However,the high weight-average degree of polymerization of amylose with longer molecular chains tended to form ordered crystal structures with KGM.Then,in order to investigate the effect of concentration on the assembly behavior,composite gel properties and anti-digestion properties,the high weight-average degree of polymerization amylose was prepared by homogenous debranching cassava starch with wide source and low price through pullulanase for 20 h,and the high weight-average degree of polymerization amylose-konjac glucomannan composite gel was prepared with mass ratio of amylose to KGM was 5:1.The network structure of composite gel became denser,the mobility of water molecules weakened,the content of non-freezing water in the system increased,and the gel properties(rheological properties,texture properties and freeze-thaw stability)further improved with the increase of the total mass fraction(from 3% to 10%).The crystallinity of composite gel increased first and then decreased,and the estimated glycemic index showed an opposite trend.When the total mass fraction was 6%,the estimated glycemic index(74.59)and crystallinity(25.66%)of composite gel were the lowest and the highest.When the total mass fraction was higher than 6%,the crystallinity of composite gel began to decrease and the system was incompatible.When the total mass fraction was higher than 8%,the results of confocal laser scanning microscope and thermal degradation analysis showed that the associative phase separation appeared locally in the high weight-average degree of polymerization amylose-konjac glucomannan composite gel.The storage modulus of composite gel decreased significantly after the addition of hydrogen bond cracking agent(urea),which verified that the interaction between amylose and KGM was mainly by hydrogen bonding.The mass fraction could affect the assembly behavior of amylose and KGM,and composite gel properties.Finally,the structure and gel properties of the high weight-average degree of polymerization amylose-konjac glucomannan composite gel(total mass fraction was 6%,mass ratio of starch to KGM was 5:1)were studied under different freezing conditions(-18°C,-48°C and-80°C).Compared with the unfrozen composite gel,the pore size of the frozen composite gel increased obviously,the rheological properties and texture properties further improved due to the concentration and squeezing effect,and the crystallinity and degradation temperature decreased.With the decrease of the treatment temperature,the water molecules in the composite gel system were easier to flow,the syneresis rate increased,and the pore size of the network structure became smaller and uniform.The storage modulus of two kinds(unfrozen and frozen at-18°C)of high weight-average degree of polymerization of amylose-konjac glucomannan composite gel increased to a certain extent after soaking in sucrose solution(mass fraction was 20%),salt solution(mass fraction was 10%),edible soya oil and lactic acid solution(p H=4)for a certain time(1,3,5 and 7 days)at 60°C,and the texture properties of the two kinds of composite gels changed differently.The hardness,cohesion,elasticity and adhesiveness of the frozen composite gel are obviously higher than those of the unfrozen composite gel with the same soaking method and time. |
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