Effect Of Starch Granule Properties On The Preparation And Digestibility Of Starch-lauric Acid Complexes

Starch-lipid complexes are formed by non-covalent bond between starch molecular chain and lipids through unique helical structure,which can significantly increase the content of slowly digestible starch and resistant starch during digestion process.Therefore,the research on the preparation method and digestibility of starch-lipid complexes will contribute to the development of nutritious and healthy starch-based foods,which is of great significance to the prevention of obesity,diabetes and other chronic metabolic diseases.In this paper,the effects of starch granule properties on the complexing index and structure of starch-lipid complexes were studied from three aspects,which were different granule size,different degree of gelatinization and different degree of debranching after gelatinization,based on wheat starch(A-type)and potato starch(B-type)as the research object and with the long chain fatty acid,lauric acid,as lipid ligand.Then,the digestive kinetics model was established by in vitro simulation to study its influence on the digestibility of the complexes.Firstly,wheat starch granules were divided into three fractions,by Stokes sedimentation method,and potato starch granules were divided into four fractions.Their average equivalent granule diameters were 5.81,11.09,24.21?m,and 9.37,17.62,27.10,51.98?m,respectively.Subsequently,the complexes were prepared with lauric acid to study the effect of granule size on structure and digestibility of the wheat starch-lauric acid complex.The experimental results showed that WS-L had a higher complexing index with lauric acid,while PS-VS had a higher complexing index.The phase transition temperature(T₀),crystal crystallinity and short-range ordered molecular structure of the wheat starch-lauric acid complexes were significantly increased,and the increasing range of the complexes gradually increased with the increase of granule size(P<0.05).The potato starch-lauric acid complexes with different granule size caused the destruction of the short-range ordered structure.The digestibility experiments showed that the crystal type and granule size of starch significantly affected the digestibility of complex.Compared with the native starch,the digestion rate of large granule wheat starch-lauric acid complexes decreased(k_{native starch}=0.0230 min^-1,k_complex=0.0189 min^-1).There was no significant difference in the digestion rate of starch-lauric acid complexes in medium granule wheat.The digestion rate of small granule wheat starch-lauric acid complexes increased(k_{native starch}=0.0296 min^-1,k_complex=0.0332min^-1).However,the result of potato starch digestion was the opposite.The digestion rate of starch-lauric acid complexes of very small granules and small granules decreased significantly(very small granules:k_{native starch}=0.0263 min^-1,k_complex=0.0233 min^-1;small granules:k_{native starch}=0.0253 min^-1,k_complex=0.0235 min^-1),while the digestion rate of starch-lauric acid complexes of large granules increased(k_{native starch}=0.0214 min^-1,k_complex=0.0231 min^-1).Secondly,wheat starch(25.52%,50.66%,100%)and potato starch(10.66%,24.65%,100%)with different gelatinization degrees were obtained by a Rapid Viscosity Analyzer,and then they were compounded with lauric acid,respectively.The effects of different gelatinization degrees on the structure and digestibility of starch-lauric acid complex were investigated.The results showed that the complexing index,enthalpy(?H),V diffraction peak intensity,and short-range ordered molecular structure of wheat starch and potato starch-lauric acid complexes increased with the increase of the degree of gelatinization.As for the wheat starch-lauric acid complexes,with the increase of starch gelatinization degree,the digestion rate was significantly decreased(k value decreased from 0.0412 to 0.0292),and the contents of resistant starch were significantly increased(P<0.05).For potato starch-lauric acid complex,when the degree of gelatinization was maximum,the digestion rate and the degree of hydrolysis of the complex decreased,the slowly digestible starch and resistant starch increased significantly(P<0.05).Finally,wheat starch and potato starch were treated with pullulanase for different time(0 h,1 h,2 h,4 h,6 h and 8 h)to prepare the complexes of wheat starch and potato starch with lauric acid to investigate the effects of different debranching time on the structure and digestibility of starch-lauric acid complexes.The results showed that the crystal structure of starch-lauric acid complexes changed significantly(P<0.05).Compared with the original starch,the intensity of V-typed diffraction peak was stronger,when the debranching time was 8 h.The melting enthalpy of starch-lauric acid complexes increased gradually with the prolonging of debranching time.Compared with the cooked starch,the hydrolysis rate of starch-lauric acid complexes decreased significantly(P<0.05),and gradually decreased with the prolonging of debranching time.The content of RS was increased by debranching treatment to a certain extent.The hydrolysis rate and resistant starch content of wheat starch-lauric acid complex after cooking and 8 h debranching treatment were 85.00%,14.77%and 48.91%,51.55%,respectively,and the hydrolysis rate and resistant starch content of potato starch were 84.06%,15.81%and 49.27%,51.37%,respectively.