Effects Of Fatty Acid Types And Starch Sources On Structures And Digestibility Of Their Complexes

Starch is the most important energy sources in human diet,and the regulation of its digestibility is of great significance to dietary nutrition and human health.The complexes formed by starch and lipids are considered as type 5 resistant starch(RS),which can significantly improve the starch resistance to digestion,and have attracted great attention of researchers.The structure and digestibility of starch-lipid complexes have been widely investigated.However,few systematic studies concerning the regulation mechanism of lipid and starch structures on the multiscale structures and digestibility of starch-lipid complexes are available.Therefore,the effects of fatty acid(FA)types,starch sources and debranching degrees on the multiscale structures and digestibility of complexes were systematically investigated using FAs as lipid ligands in this study.The objective of this study was to construct the complexes with adjustable digestibility by changing the structures of FA and starch,which can provide a theoretical basis for the research and development of functional foods.The main research contents are displayed as follows:(1)The effects of various types of FAs on the fine structures and digestibility of complexes were investigated using maize starch(MS)as raw materials.The results showed that MS-FA complexes showed V-type crystalline structures,and the hydrogen bond and hydrophobic interactions between MS and FA were enhanced.However,the complexes formed by various types of FAs and MS displayed different V₆-type polymorphs.The complexes with 14-carbon FAs displayed the highest RS content(26.31%)and possessed better thermal stability.Nevertheless,the complexes with 10-carbon FAs exhibited the highest slowly digestible starch(SDS)content(28.99%),and their amylose single helices displayed disordered arrangement.Compared with other FAs,the intermolecular interactions between the FAs with a chain length of 10-14 carbons and MS were obviously enhanced,and the formed complexes possessed more long-range ordered structures(relative crystallinity:14.14%-16.72%).The 18-carbon FAs incompletely combined with the amylose helices of MS,and their carboxyl groups were fully exposed outside the amylose helices.Compared with18-carbon saturated FAs,the unsaturated FAs showed stronger intermolecular interactions with MS,and the SDS and RS content of the formed complexes were significantly increased.(2)The complexation behavior between starch from various sources and 14-carbon myristic acid(MA),and digestibility of the complexes were investigated using MA as ligands,and MS,waxy maize starch(WS),high amylose maize starch(HMS),rice starch(Ri S),cassava starch(CS)and potato starch(PS)as raw materials.The results showed that amylose content and inclusion capacity of starch were closely related to the complex degrees of complexes.HMS-MA complexes displayed the highest complex degrees,followed by MS-MA complexes,whereas WS-MA complexes displayed the lowest complex degrees.The RS content and degrees of structural order of MS-MA and HMS-MA complexes were significantly higher than those of other complexes,while WS-MA and Ri S-MA complexes displayed lower RS content and degrees of structural order.MS and HMS possessed stronger interactions with MA molecules than other starch.Both MS-MA and HMS-MA complexes contained MA molecules displaying a lower complex degree with amylose helices,whose carboxyl groups were fully exposed outside the amylose helices.WS-MA and PS-MA complexes showed lower thermostability,and the MA molecules were mainly physically embedded outside the amylose helical structure in these complexes.The content of physically embedded MA in CS-MA complexes was the highest,and its binding force with CS is stronger.The weight-average relative molecular weight of amylose,average chain length of amylopectin side chains,and relative content of chain segments with degree of polymerization6-12 and 25-36 could affect their interactions with MA molecules.(3)MS was debranched by pullulanase to improve the digestion resistibility of complexes,and the effects of debranching degrees on the structures and digestibility of MS-MA complexes were investigated.The results showed that with increasing degrees of debranching,the amylose content of complexes significantly increased,relative content of?-1,6-glycosidic bond decreased,and apparent structures gradually changed from small aggregates to large aggregates.The RS content of the complexes was significantly increased by debranching modification,but SDS content was significantly decreased.The RS content of MS_{6 h}-MA complexes was the highest(33.41%),but SDS content was the lowest(2.08%).Debranching modification enhanced the intermolecular interactions between MS and MA,and greatly improved the degrees of long-range molecular order;however,the thermal stability of the complexes reduced,and degrees of short-range molecular order significantly decreased.Besides,the degrees of long-range(relative crystallinity:19.92%)and short-range molecular order and complex were higher than those of other debranched starch-MA complexes.(4)In order to further improve the digestion resistibility of complexes,the fine structures of the complexes formed by various types of FAs and debranched starch,and the changes of their digestibility were investigated using starch with low(MS_{1 h})and high(MS_{6 h})debranching degrees as raw materials.The results showed that the complexes formed by different FAs and debranched starch displayed a mixture of V_6III-type and B-type crystalline structures.The formation of the complexes greatly increased the degrees of long-range molecular order of debranched starch,but significantly decreased the degrees of its short-range molecular order.Compared with unsaturated FAs,the saturated FAs showed stronger intermolecular interactions with starch with different debranching degrees,and they could obviously improve the thermal stability of debranched starch.The complex degrees of MS_{1 h}-FA complexes were lower,and FA molecules were primarily physically embedded in the starch matrix.Nevertheless,the complex degrees of MS_{6 h}-FA complexes were higher,and FA molecules mainly weakly bound with the amylose helices,and the degree of their hydrocarbon chains entering into helical structure was smaller.The RS content and degrees of long-range structural order of both MS_{1 h}-FA and MS_{6 h}-FA complexes significantly increased with the increase of FA chain length;the increment of MS_{6 h}-FA complexes was larger than that of MS_{1 h}-FA complexes.The maximum RS content and relative crystallinity were 38.90%and 24.23%,respectively,while the maximum RS content and relative crystallinity of MS_1h-FA complexes were 35.74%and 21.79%,respectively.The degrees of FA unsaturation had less effects on the RS content and long-range structural order of the complexes.