Mechanism Of Amylopectin Retrogradation Induced By Crystal Seeds

Starch retrogradation is a common phenomenon in the storage of high-starch products,and it affects product quality to a large extent.It is generally believed that the short-term retrogradation based on amylose and the long-term retrogradation based on amylopectin jointly determine the starch retrogradation process,and the rapid retrogradation of amylose in the short-term retrogradation process provides seed source for the retrogradation of amylopectin in the long-term retrogradation process,therefore promoting the retrogradation of amylopectin.However,in the absence of amylose to provide the seed source,the pure amylopectin system will also spontaneously retrograde,and the characteristic changes in the starch retrogradation process are mainly due to the retrogradation of amylopectin.Plus,there are many types of amylopectin and the system is complex.The question of how the amylopectin system retrograde has not been systematically explained.Based on these,this topic constructs amylopectin seed crystals,by introducing the seed crystals into the pure amylopectin system to interfere with its retrogradation and simplify the retrogradation research system to analyze the common mechanism of amylopectin retrogradation.Different amylopectin crystal seeds were prepared with amylopectin as raw material,and the crystalline structure of the crystal seeds was characterized.The glutinous rice flour was purified by ethanol to obtain amylopectin.Then the amylopectin samples were treated by regenerative method and acidolysis method respectively to obtain three kinds of amylopectin crystal seeds,which were named RA,RA-AH and A-AH seed,respectively.Dynamic light scattering scanning results showed that the calibrated particle sizes of three kinds of crystal seeds were 311.26,226.17 and163.32 nm,respectively,which were all nanometer size.XRD results showed that RA and RA-AH seeds were hexagonal and B-type crystals,while A-AH seed was monoclinic and A-type crystal.Combined with Jade 6.0 software analysis,the c axes of the three kinds of crystal seeds were all longer than the a axes and the b axes.All three crystal seeds were in the shape of rods.But the axes of the A-AH crystal seed were all longer than the other two kinds of crystal seeds and its cell volume was the largest.Small angle X-ray diffraction showed that the crystal structure of A-AH seed was perfect and the lamellar thickness was 8.655 nm,and the crystal structure of RA and RA-AH seeds were not perfect,and the lamellar thickness were 17.654 and 12.368 nm,respectively.Crystal seeds were added to the amylopectin system to analyze the nucleation characteristics of amylopectin recrystallization induced by crystal seeds.Avrami equation was used to analyze the effects of crystal seed on amylopectin regrowth kinetic parameters.The results showed that the introduction of RA and RA-AH seeds increased the regrowth rate constant k from 0.035 to 0.038 and 0.045,respectively,which promoted starch recrystallization.However,the addition of A-AH seed reduced k value to 0.032 and inhibited starch recrystallization.Under the influence of RA and RA-AH seeds,the n value decreased from 1.75to 1.68 and 1.53,respectively,and the recrystallization nucleation mode of starch tended to be instantaneous rod-like nucleation.The addition of A-AH seed had no significant effect on n value.The results of DSC showed that the enthalpy of the retrograded starch with RA and RA-AH seeds increased from 4.05 J/g to 4.36 and 5.19 J/g,respectively,which promoted the regeneration.The effect of A-AH seed on the enthalpy was not significant.The addition of three kinds of seed increased T_o,T_p and T_c values,and the crystal stability of the retrograded starch increased,while RA and RA-AH seeds reduced the（T_c-T_o）value of the retrograded sample,indicating that the two kinds of seed induced amylopectin to form more homogeneous starch crystals,and the induction effect of RA-AH seed was stronger.The crystal structure transformation process of amylopectin recrystallization induced by crystal seeds was studied.XRD results showed that the samples of both control group and experimental group were B-type crystals,which indicated that the addition of crystal seed did not change the crystal type of retrograded starch.The addition of RA and RA-AH seeds increased the crystallinity of retrograded starch by 2.16%and 4.73%,respectively,indicating that the addition of RA and RA-AH seeds promoted the recrystallization of retrograded starch,and the long-range order degree of retrograded starch was improved.The addition of A-AH seed had no significant effect on the crystallinity.Fourier transform infrared spectroscopy showed that the ratio of 1047 cm^-1/1022 cm^-1 and 995 cm^-1/1022 cm^-1 of retrograded starch increased with the addition of RA and RA-AH seeds.Confocal Raman spectroscopy showed that RA and RA-AH seeds reduced the full width at half maximum height of retrograded starch from 19.1 to 18.0 and 16.9 at 480 cm^-1,respectively.These results indicated that the molecular chain of amylopectin was more orderly and the short-range order of the restored starch was improved.¹³C nuclear magnetic resonance results showed that the content of the double helix structure of retrograded starch increased from 14.98%to 24.23%,27.86%and 19.79%after the addition of RA,RA-AH and A-AH seeds,respectively.In combination with the results of XRD,RA and RA-AH seeds induced the ordered arrangement of adjacent amylopectin molecular chains to form the double helix structure and further promoted the ordered accumulation of the double helix structure.Jade 6.0 software analysis results showed that after adding RA and RA-AH seeds,the cell volume of retrograded starch increased.Small angle X-ray diffraction results showed that RA and RA-AH seeds increased the lamellar thickness of regenerated starch.These results indicated that they promoted the arrangement of amylopectin molecular chains,thus promoting starch recrystallization.In conclusion,the introduction of amylopectin crystal seeds increased the rate of amylopectin recrystallization.The crystal nucleus was dominated by instant rod-shaped nucleation,which promoted the orderly arrangement of amylopectin molecular chains and promotes retrogradation.Therefore,it is speculated that the common mechanism of retrogradation of pure amylopectin system is that the molecular chains of amylopectin instantly nucleate to generate B-type crystal nuclei,which induces the orderly arrangement of adjacent molecular chains to promote retrogradation.