Effect Of The Degree Of Amylopectin Polymerization On The Gelatinization And Retrogradation Properties Of Jackfruit Starch

Starch retrogradation is of great interest since the foods made of starch inevitably happen to retrograde after pasting and storage when the amorphous starches recrystallize,which results in the undesirable taste and texture qualities.However,the effect of the degree of amylopectin polymerization on the gelatinization and retrogradation properties has not yet been reported.The relationship between gelatinization and retrogradation properties and structure need to be further investigated.Therefore,in this paper,jackfruit amylopectin with different degree of polymerization and amylose of the same jackfruit cultivar were studied.The molecular structure,fine structure,micromorphology,freezing-thawing stability,double helix structure,pasting properties,short-range molecular order,particle size distributions,textural properties,recrystallization nucleation ways,rate of retrogradation,degree of retrogradation,and crystallization structure were taken as indicators to study the effects of different degree of amylopectin polymerization on the gelatinization and retrogradation process of jackfruit starch(Jfs).The theoretical model of the effect of amylopectin polymerization degree on Jfs retrogradation was established,which can be used to interpret the relationship between gelatinization or retrogradation properties and different degree of amylopectin polymerization.Those studies can provide the theoretical principle for the correlation between degree of amylopectin polymerization and gelatinization or retrogradation properties of Jfs.Starch was extracted from five jackfruit cultivars(M1,M5,M6,M11,and X17)and separated into amylose and amylopectin.The values for weight-average molar mass(Mw)and average radius of gyration(Rg)of the Jfs were 1.74×107 g/mol-4.61×107 g/mol and 115.40nm-144.20 nm,respectively.Compared with the other four cultivars,starch from the M1 cultivar exhibited the highest Mw and Rg of amylose(3.79×106 g/mol and 69.10 nm)and the lowest Mw and Rg of amylopectin(3.07×107 g/mol and 114.10 nm).But starch from the X17 cultivar exhibited the lowest Mw and Rg of amylose(1.42×106 g/mol and 55.30 nm)and the highest Mw and Rg of amylopectin(6.99×107 g/mol and 132.80 nm).The amylose of the M1 cultivar and the amylopectin of the X17 cultivar showed more compact structures than did the other four starches identified.M1 cultivar had the lowest weight-average degree of amylopectin polymerization(189506),while X17 cultivar had the highest weight-average degree of amylopectinpolymerization(431481).The Jfs exhibited higher proportions of A and B1 chains,lower proportions of B2 and B3+ chains and shorter average chain lengths(33.89%-38.33%,39.06%-39.58%,17.13%-18.43%,4.96%-8.62% and DP 18.27-19.71,respectively).The proportions of B2 and B3+ chains increased with the increased of amylose Mw and Rg,while the proportions of A and B1 chains decreased with the increased of amylopectin Mw and Rg.The same cultivar of amylose(M1,30%)was mixed with five different types of amylopectin(M1,M5,M6,M11 and X17,70%)to prepare gelatinized Jfs(GJfs: G-M1,G-M5,G-M6,G-M1,and G-X17)with different degree of amylopectin polymerization.The five GJfs samples showed significant variations in micro-morphology variing from a compact structure(G-M1)to a loose structure(G-X17).High syneresis(22.73-45.56%)formed a compact structure(G-M1),and low syneresis(19.71-40.47%)formed a loose structure(G-X17).As the degree of amylopectin polymerization increased,the gelatinization enthalpy,peak viscosity,trough viscosity,breakdown,final viscosity,setback,absorbance ratios,average particle size,hardness,adhesiveness and chewiness of the five GJfs samples decreased from 3.75 J/g,2229 c P,996 c P,0.39,11.69 μm,1911.25 g,-118.93 g.sec,and 204.54 m J(G-M1)to 1.26 J/g,1503 c P,824 c P,0.34,3.39 μm,1036.36 g,-150.26 g.sec and 166.70 m J(G-X17),respectively.However,the transition temperatures,pasting temperature,springiness,cohesiveness,gumminess and resilience increased from 48.14 °C,59.43 °C,68.45 °C,50.15 °C,8.26%,0.26,193.28 and 0.27(G-M1)to 50.56 °C,61.49 °C,69.93 °C,57.50 °C,12.55%,0.47,283.52 and 0.70(G-X17)respectively.The thermal properties,pasting properties,short-range molecular order structure,average particle size distributions,and textural properties were consistent with the results of micro-morphology and syneresis.After starch gelatinization,the amorphous molecules recrystallize during storage to form retrograded Jfs(retrograded Jfs,RJfs: R-M1,R-M5,R-M6,R-M11 and R-X17)with different degree of amylopectin polymerization.The five RJfs samples showed significant variations in micro-morphology and varied from a compact structure(R-M1)to a loose structure(R-X17).Increasing the degree of amylopectin polymerization led to a decreased recrystallization rate of the five RJfs samples from 0.14(R-M1)to 0.10(R-X17)and an increased Avrami exponent from0.77(R-M1)to 0.96(R-X17).The freeze-thaw stability was consistent with the results of the micro-morphology.R-M1 sample had the highest syneresis(58.24-75.39%)formed a compactstructure,while R-X17 sample had the lowest syneresis(55.16-67.14%)formed a loose structure.As the degree of amylopectin polymerization increased,the transition temperatures,springiness,cohesiveness,gumminess and resilience increased from 51.84 °C,60.83 °C,71.43 °C,6.99%,0.05,101.71 and 0.19(R-M1)to 57.16 °C,65.49 °C,74.83 °C,10.01%,0.39,205.74 and 0.68(R-X17),respectively.However,the retrogradation enthalpy,degree of retrogradation,relative crystallinity,absorbance ratios,average particle size,hardness,adhesiveness and chewiness decreased from 10.92 J/g,68.16%,11.58%,0.55,10.01 μm,2858.76 g,-100.58 g.sec and355.28 m J(R-M1)to 7.03 J/g,56.33%,7.29%,0.49,1.51 μm,2002.31 g,-132.22 g.sec and247.84 m J(R-X17),respectively.The results of the thermal properties,crystalline structure,short-range molecular order,particle size distributions,and textural properties confirmed the retrogradation behavior of RJfs with different degrees of polymerization.In summary,this experiment starts from the molecular structure and fine structure,the effect of different degree of amylopectin polymerization on the gelatinization and retrogradation properties of Jfs was analyzed,and the relationship between the gelatinization and retrogradation properties of Jfs and the degree of amylopectin polymerization was revealed.All the results indicated that the degree of amylopectin polymerization is an important structural factor that can affect the gelatinization and retrogradation properties of Jfs in the process of storage.