Study On The Modification Of Starch With Octenyl Succinic Anhydride In Ionic Liquid Systems And Its Applications

As an important biopolymer,starch is not only a major source of carbohydrates in the human diet but also a green bio-based material that is renewable,biodegradable,and biocompatible.The functions properties of native starch can be improved by modifying native starch for better application in food or non-food industries.The dense structure of native starch and the presence of a large number of intra-/inter-molecular hydrogen bonds make it difficult to process in traditional solvents.Ionic liquids(ILs)have been used as an important“green solvent”for starch dissolution and modification in recent years due to their excellent physicochemical properties such as non-volatility,thermal stability,designability,and recyclability.However,the high cost and high viscosity of pure ionic liquids limit their industrial applications.In this thesis,maize starch and potato starch were used as the study objects,and the different mass ratios of ionic liquid-water mixed solution was used as the solvent to study the dissolution behavior and the octenyl succinic anhydride(OSA)modification mechanism of starches in ionic liquid-water solvents systems.The complex interaction mechanism of OSA starch with lipids and protein was systematically explored.Meanwhile,the nutritional properties of the complexes such as in vitro digestion and fermentation were comprehensively characterized.The main contents and conclusions of the full thesis are as follows:(1)The dissolution behavior of maize and potato starches in the solvent system of 1-ethyl-3-methylimidazolium acetate([Emim][OAc]):water mixtures at room temperature was investigated.The long-and short-range molecularly ordered structures and granule morphology of both starches were disrupted progressively with increasing mass ratios of ionic liquid:water.The multiscale structure of maize starch was disrupted completely after treatment with[Emim][OAc]:water mixture of 6:4,indicating good dissolution performance of this mixture solution for maize starch.This mixture seemed to provide a balance between viscosity of the solvent and availability of ions to disrupt starch H-bonds.The different dissolution behavior of maize starch and potato starch in[Emim][OAc]:water mixtures were attributed to structural differences of the granule surfaces.These results showed that the dissolution behavior of starches was affected by both starch sources and properties of[Emim][OAc]:water mixtures(2)Granular maize and potato starch esters with OSA were homogeneous synthesized in aqueous ionic liquid solutions at 35 ℃.The reaction efficiency(RE)of maize starch esterification and the degree of substitution(DS)of granular OSA-maize starches prepared in the mixture of IL:water of 2:8(w/w)were increased significantly by 35.3%and 35.6%,respectively.The pasting,textural,and emulsion properties of the OSA-starches were improved greatly.The results showed that both the DS and the structural changes of starch following esterification determined the functional properties of OSA-starches,and that OSA-potato starches presented different functional properties compared with OSA-maize starches.Compared with other mass ratios of IL:water mixtures,the optimum RE and DS for both maize and potato starches were obtained with a 2:8(w/w)IL:water mixture.Meanwhile,the effect of different mass ratio of aqueous ionic liquid on OSA was investigated by Attenuated Total Reflectance Fourier Transform Infrared(ATR-FTIR)Spectroscopy to reveal in-depth the modification mechanism of OSA starch in aqueous ionic liquid with different mass ratios.(3)The effect of OSA starch on the formation of starch-lipid complexes was investigated.The complexing index(CI)showed that native maize starch(NMS)formed more complexes with monopalmityl glycerol(MPG)than with palmitic acid(PA),whereas dipalmityl glycerol(DPG)was not effective in forming complexes with NMS.After OSA modification,the complexation between OSA-starch and lipids was greatly enhanced,especially for PA and DPG,and the CI values increased from 79.6 to 93.3%for OSA-starch-PA and from 80.3 to93.2%for OSA-starch-DPG complexes with increasing DS of OSA-starch.Structural analyses showed that OSA-starch-lipid complexes had higher degree of long-and short-range molecular order than the corresponding NMS-lipid complexes.This study showed for the first time that DPG can form complexes with OSA-starch,which was attributed to the increased dispersion of DPG in water by the emulsifying ability of OSA-starch.And the rod-like morphological structure of the binary complexes was demonstrated using Confocal Laser Scanning Microscopy(CLSM).Meanwhile,the delivery system of OSAMS-LA binary complex emulsion encapsulated quercetin was constructed.(4)The interaction mechanism of binary or ternary complexes prepared by monoglycerides with different chain lengths and beta lactoglobulin(βLG)OSA starch,and the effect of OSA-starch on the in vitro digestion of the complexes were investigated.And the multi-scale structure and functional properties of the complexes were characterized using various techniques.The MTT assay and LIVE/DEAD survival assay demonstrated that OSA starch prepared by aqueous ionic liquid has good biocompatibility and the IL can be recovered efficiently and has good functional properties.The ternary complexes of amylose-monoglyceride-protein were prepared using OSA starch,and the formation mechanism of the ternary complexes was demonstrated by molecular dynamics simulations and CLSM.The binary or ternary complexes were formed by OSA starch with monoglycerides andβLG,and the enthalpy value of the complexes increased gradually with decreasing monoglyceride chain length.Compared with the binary or ternary complexes prepared from natural starch,OSA starch could significantly promote the interaction between amylose,monoglycerides andβLG,and form the complexes with more stable V-type crystal structures and increase the number of type II complexes.In particular,it significantly promoted the formation of type II binary or ternary complexes of amylose with long chain monoglycerides(MPG and MSG).In vitro digestion experiments showed that the binary or ternary complexes prepared from OSA starch had stronger enzyme resistance and lower digestion than the complexes prepared from the corresponding native starch.(5)A composite resistant starch(RS4+RS5)based on OSA starch-lipid binary complex was constructed using OSA starch and its multiscale structure was characterized and analyzed.The fermentation characteristics of the composite resistant starch were studied by in vitro fermentation model to reveal the interrelationship between the structure of the composite resistant starch,metabolites and gut microbiota.The results showed that different structural types of resistant starch had significant differences on the abundance and composition structure of gut microbiota.Compared with NPS-MLG traditional resistant starch(RS5),OSAPS-MLG composite resistant starch(RS4+RS5)significantly promoted the proliferation of Firmicutes and reduced the relative abundance of Bacteroidetes.Meanwhile,OSAPS-MLG samples also effectively increase the relative abundance of various beneficial bacteria such as Megamonas,Parabacteroides,Dialister,Megasphaera,and Blautia,which produce more short-chain fatty acids and significantly modulate the abundance and composition of intestinal microorganisms and improve the function and expression of potential host genes,thus performing important physiological functions to regulate human intestinal health.To sum up,this thesis focuses on OSA starch synthesized by novel green and sustainable methods and its corresponding binary or ternary complexes.The formation mechanisms of OSA starch,OSA starch-lipid,and OSA starch-lipid-protein was investigated in terms of the multiscale structures,functional properties,and in vitro digestion and fermentation characteristics of starch-based derivatives,and constructs an emulsion delivery system and a composite resistant starch model based on OSA starch-lipid binary complexes.The results and conclusions of which are of great theoretical significance and application value for the precise design of encapsulation carrier materials or other starch-based products with desirable probiotic properties.