| With the improvement of living standard and changes of diet diversity and disease spectra,foods with the nutritional functions such as physiological accommodation and disease prevention have attracted more and more attention.Therefore,designing a personalized health food with specific nutritional function has been one of the hotspots in the field of food science.Rice,as one of the most widely consumed staple food,is mainly composed of starch.And modulating digestion and nutritional function of rice starch is closely associated to human health.Considering the status quo and development trend of manufacturing nutritional and healthy food,a method combined heat-moisture treatment(HMT)with fatty acid complexation to modulate the digestion and nutritional function of rice starch was developed and the mechanism of altering the multi-scale structure was revealed in this thesis.This research is of great significance in modulating the nutrition function of rice starch and manufacturing new types of starchy health food.Since digestion of rice starch is a pivotal factor influencing its nutritional function,HMT,a green,efficient and low-cost method was employed to treat rice starch.The effects of HMT conditions on the digestion of rice starch were investigated,and moisture content was confirmed to be the key factor on modulating digestion of rice starch.By response surface methodology,the HMT conditions were optimized.Under the optimum conditions,the content of resistant starch(RS)in HMT rice starch granules could increase to 15.9%.Further,fatty acids were added while heat-moisture treating rice starch.The effects of different kinds of fatty acids and their additive amount on the digestion of rice starch were discussed.The results showed that the formation of rice starch-fatty acid complex during HMT greatly promoted the increase of RS,however,inhibited the increase of rapidly digested starch(RDS)and the decrease of slowly digested starch(SDS).In addition,RS levels for the complex could increase to 23.2% and 30.8% when the additive amount of rice fatty acid and linoleic acid were 4% and 8% respectively.Using modern analytic technologies,the synergistic effect of HMT and fatty acid complexation on multi-scale structure in rice starch such as molecular weight and distribution,helical structure,crystalline structure,lamellar structure and granule morphology were systemically explored.Then physical models describing the relationship among processing conditions,changes of multi-scale structure and modulation of digestion of rice starch were constructed.From the view of molecular level and molecular interaction,the mechanism of modulating the digestion of rice starch was discussed.It was revealed that the thermal energy and water molecules during HMT could degrade starch molecules,unravel double helices,reduce relative crystallinity and decrease the ordered degree of lamellar structure and short-range ordered molecular structure,thus resulting in the improvement of RDS and the decline of SDS significantly.Accompanying the structural disorder and degradation,some molecular rearrangements and orientation occurred to probably form densely packed starch fractions such as perfectly arranged double helix and A-type crystallite,the single helix and V-type complex,new ordered molecular aggregation architecture and aggregated granules with low specific surface area,which improved the content of RS at different levels.Under dual effects of HMT and fatty acids complex,the multi-scale structure of rice starch were further disorganized and thus transformed from ordered hierarchical structure to disordered one.The addition of fatty acids induced the formation of single helix complex between fatty acid and amylose or long side chains of amylopectin,which formed more V-type crystallite,resulting in higher ordered degree of molecular chain aggregations in amorphous amylose background regions,reducing the amorphous lamella and making double helix and A-type crystallite perfectly arranged.These structural alternations inhibited the molecular interactions(e.g.,binding ability,catalyzed location)between rice starch and amylase,which eventually increased the content of RS and decreased the content of SDS.And these changes were more obvious with the increased saturation degree of fatty acids.Heat moisture treated rice starch and the complex with different fatty acid with well-controlled digestion were chosen for animal experiments.The nutritional function of rice starch modified by HMT and fatty acid complex were evaluated on the levels of physiological indexes such as blood glucose,serum lipids,oxidative stress,etc.in high-fat diet rats,and proliferation and distribution of intestinal microflora were also studied.The results indicated that the changes of physiological and biochemical indexes in tested rats depended on the total content of SDS and RS,while the composition and distribution of intestinal microflora were affected by RS levels.Because of the decline of SDS levels in rice starch treated by HMT,thus the decline of total content of SDS and RS,the blood glucose,serum lipids,oxidative stress and liver function metabolic indexes in HMT group were worse than those of rice starch group.However,the increase content of RS in HMT rice starch altered the diversity and species abundance of intestinal microflora.Also,the high RS level in HMT group could promote the growth of probiotics(e.g.,Bifidobacterium and Lactobacillus genus)and inhibit the growth of pathogenic bacterium(e.g.,S24-7 Bacteroides and Parabacteroides genus).Furthermore,the physiological and biochemical indexes in HMT rice starch-fatty acid complex group were better than those of rice starch.Specially,heat moisture treated rice starch-linoleic acid complex showed an excellent function on preventing the disorder of blood glucose and lipid metabolism.Although heat moisture treated rice starch-linoleic acid complex had high RS content,the diversity and species abundance of intestinal microflora reduced.It could promote proliferation of beneficial bacteria that produced short chain fatty acid such as Turicibacter genus,as well as pathogenic bacteria such as Lachnospira genus and so on.The mechanism of regulating rice starch digestion by HMT and fatty acid complex was revealed from the view of hierarchical structural changes at molecular level,and nutritional functions of treated rice starch were investigated as well.The relationship among HMT and fatty acid complexation conditions-starch structure-starch digestibility-nutritional function was established and effective techniques in modulating rice starch digestion through HMT and fatty acid complex were obtained,which will be beneficial to provide technical support and theoretical basis for producing rice starchy health foods with the functions of regulating and controlling blood glucose,lipid metabolism and intestinal microflora. |
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