| With the rapid development of the social economy and the continuous improvement of people’s living standards,the ability to guarantee and supply nutrition has been significantly enhanced.At the same time,a series of health problems derived from over-nutrition and unbalanced metabolism are also increasing.The prevalence of chronic metabolic diseases such as diabetes,obesity,and cardiovascular diseases has become the most serious problems that affect the health of people in China.Based on the concept of dietary intervention,studying the interaction between food components to change the multi-scale structure of food,then regulating the digestibility of each component,and endowing it with nutritional functions such as regulating blood sugar,blood lipids,and gut microbiota,has become a research hotspot in the field of food nutrition and health in recent years.Starch and lipid are the most important nutrients for people,and the regulation of their digestive properties is crucial for management of human dietary nutrition and health.As a simple,environmentally friendly and low-cost thermal processing technology,microwave has been widely used in food processing.By orientating the polar molecules quickly,the original hydrogen bond structure between or within the chain of starch molecules could be destroyed.As a result,the formation of new helical structures and dense ordered structures can effectively regulate the digestibility of starch.Therefore,this thesis investigated the interaction between starch and lipid under microwave irradiation,the digestibility of starch-lipid complexes,and their impacts on gut microbiota,so as to clarify and establish the interrelationship among“microwave treatment and conditions-lipid structure and addition-the multi-scale structure of rice starch-lipid complexes-regulation of digestibility and gut microbiota”.Based on the study of the influences of microwave treatment parameters,oleic acid addition,and rice starch concentration on the digestibility of rice starch-oleic acid complex(SO),a prediction model for the anti-digestibility of SO was established by using the BP(back-propagation)artificial neural network.The prediction model was a 5-17-2 network topology using the Levernberg-Marquardt algorithm,with the learning rate lr of 0.50,the momentum coefficient mc of 0.10,and the number of iterations epochs of 1000.The predicted values of the model showed an average relative error of±3.46%compared with the measured values for the SDS(slowly digestible starch)(R~2=0.9775)and RS(resistant starch)(R~2=0.9687)of SO with high prediction accuracy.This indicates that the established model can accurately predict the changes of SDS and RS contents of SO,and has good generalization ability.The effects of fatty acid chain length and saturation,oil composition and addition,and starch concentration on the multi-scale structural evolution and digestibility of rice starch-fatty acid/oil complexes under microwave irridiation were systematically investigated.The correlation between complex structure and digestibility was established by Spearman correlation analysis.The in-vitro fermentation experiments were conducted to investigate the effects of the complex on the production of short-chain fatty acids(SCFAs),and the composition and distribution of the gut microbiota during fermentation.The results showed that microwave treatment promoted the movement and self-assembly of rice starch molecular chains,increasing short-and long-range ordered structures;the introduction of fatty acids/oils could interact with rice starch molecules through hydrophobic forces and hydrogen bonding to form single-helix complexes and dense ordered structural domains,thus preventing the hydrolysis of starch molecules by amylase,resulting in a significant increase in the anti-digestibility of the complexes.The longer carbon chains and less unsaturation of the fatty acid,the easier for it to interact with starch molecules to form more ordered structures,and the higher the RS content of the complexes;the higher the polyunsaturated fatty acid content in the oils,and the higher concentration of starch in the system,thus inhibiting the formation of ordered structures in the complexes.Spearman correlation analysis showed that the complexation rate,the degree of short-range ordering,single helix content,crystallinity,the density of nano-aggregates,and the enthalpy values were positively correlated with the RS content of rice starch-fatty acid/oil complexes;The results of the in-vitro fermentation experiments also showed that all complexes could produce SCFAs during fermentation,thus lowering the p H of the fermentation system,and the amount of SCFAs was positively correlated with the RS content of the complexes.The RS and total SCFAs contents of the rice starch-fatty acid complexes were in the following order:SS(rice starch-stearic acid complex)>SP(rice starch-palmitic acid complex)>SO>SL(rice starch-linoleic acid complex)>SD(rice starch-decanoic acid complex),and the RS and total SCFAs contents of the rice starch-oil complexes were in the following order:SOO(rice starch-olive oil complex)>SCO(rice starch-canola oil complex)>SMO(rice starch-maize oil complex)>SSO(rice starch-sunflower seeds oil complex).The fermentation of the complex reduced the biodiversity and the number of shared species of the gut microbiota,and increased the abundance of SCFAs-producing bacteria such as Prevotella and Bifidobacterium;SS with higher RS content could further promote the proliferation of Faecalibacterium and increase the content of acetate and butyrate,while SOO further promoted the growth of beneficial bacteria such as Weissella.The effect of higher oil content(20%,40%;wt%)on the oxidative stability and digestibility of oil in the oil-rice starch composite system under microwave irradiation,as well as its effect on the production of SCFAs and the composition of the gut microbiota during the in-vitro fermentation,were further investigated.The results showed that under microwave treatment,the complexation of oil and rice starch could inhibit the increase of acid value and peroxide value of oil during the accelerated oxidation process,and further reduce the peroxide value of MOS(maize oil-rice starch composite),SOS(sunflower seeds oil-rice starch composite),and OOS(olive oil-rice starch composite)with the increase of oil percentage of the system,but has no significant effect on the peroxide value of COS(canola oil-rice starch composite)except for promoting the production of its secondary peroxides.The interaction of oil and rice starch under microwave treatment would reduce the digestion extent and rate of oil component in the composite system;The continued increase in the oil content of the system further reduced the maximum release of fatty acids from OOS,but had no significant effect on the digestive behaviour of the oil in SOS,MOS and COS,which contained more polyunsaturated fatty acid contents.The p H of the oil-rice starch composite system digesta was significantly lower than that of the oil digesta after the in-vitro fermentation,and the total SCFAs contents were in followed order:OOS>MOS>COS>SOS;the dominant bacterial groups in the oil group and the oil-rice starch composite system group were significantly different,with the composite system group promoting the growth and reproduction of Megamonas and Bifidobacterium and inhibiting the growth and reproduction of pathogenic bacteria such as Escherichia-shigella,and also promoting the growth of Faecalibacterium by increasing the abundance of Bifidobacterium,thus increasing the content of butyrate.Among them,the effect of OOS is the most pronounced.In this thesis,a systematic study is carried out on the basic scientific issues related to the microwave-coupled lipid molecular interaction regulating the digestibility of rice starch-lipid complexes and their effects on the gut microbiota.The results have good innovation and academic value with practical significance,the established relationships and mechanisms among"microwave treatment and conditions-lipid structure and addition-the multi-scale structure of rice starch-lipid complexes-regulation of digestibility and gut microbiota"can provide a theoretical basis and a pathway for the regulation of starch and lipid nutritional functions and the creation of new high-quality nutritious and healthy food products. |
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