| Resistant starch(RS)is a kind of starch which could not be hydrolyzed by amylolytic enzymes in the small intestine,but rather reaches the colon for fermentation where it behaves in a way similar to the dietary fiber.RS has drawn greater attention owing to its beneficial implications for obesity,type? diabetes and some intestinal diseases.In addition,RS shows improved crispness and expansion in certain products with better mouth feel,color and flavor,compared with the traditional fibers.Nowadays,the method for increase of the RS content efficiently is few,and the processing technology for RS production in a larger scale is hard to find,leading to the lack of commercial RS products.In this study,two methods(debranched-heating and heated-debranching)and three kinds of raw materials(the representatives of cereal starch,legume starch and tuberous root starch)were used to prepare RS.The content of RS was used as an evaluation index for selection of method and raw starch for RS preparation.Further more,the physicochemical properties,digestibility and fermentation properties of RS were studied.The changes of physical chemical characteristics,digestive characteristics and in vitro fermentation characteristics of the RS after treatment with simulated gastrointestinal fluids were investigated.This study could not only provide a basis for the selection of suitable raw material for RS production,but also provide the theoretical and practical experience for optimization of processing technology of RS.In addition,data supports for the investigation of relationship between structure and functionality in the gastrointestinal tract were also provided.This study could further promote the research and development on the interaction between RS and gut microflora,in order to provide some theoretical basis for the development and utilization of resistant starch and intestinal probiotics.The main research contents and results of this research are showed below:(1)The effects of improving the content of RS by debranched-heating or heated-debranching process were investigated,and the raw materials were corn starch(CS),mung bean starch(MS)and puerariae starch(PS).The results showed that debranched-heating method was better than heated-debranching to increase the content of RS(p<0.05).Moreover,MS was the best starch to increase the content of RS.Their contents were(13.70±0.20)%and(12.34±0.10)%respectively.The contents increased to(56.12±0.76)%and(53.39±1.85)%respectively after purification.The content of amylase and degree of polymerization(DP)were also indicated that brancing-heating method was better than heating-branching.(2)Gelatinization properties,thermal properties,crystallization,particle size and morphology of three raw starches and six kinds of RS were studied by technology of RVA,DSC,X-ray,Mastersizer laser particle size analyzer,SEM.The results showed that the gelatinization properties of six kinds of resistant starch were not detected below 100 ?.As for RS,the breakdown,the final viscosity and the melting temperature ranges were much lower than native starch,except ?H.This indicated that the crystal structure of RS was more uniform and better thermal stability.In addition,the particle size of RS was significantly higher(p<0.05).The crystal type was changed from native type A to type B and the crystallinity was lower than raw starch.The melting temperature range of debranched-heated RS was less than that of heated-debranched RS,but ?H was higher.The size of the debranched-heated RS was smaller than that of the heated-debranched RS.In addition,the smooth granules were replaced by rough and irregular particles during forming RS.(3)Three kinds of raw starch and six kinds of RS were treated by the simulated gastrointestinal liquid to compare the digestion rates of hydrolysis and the differences of RS physicochemical properties after digestion.The results showed that the hydrolysis rate of six kinds of resistant starch in simulated gastrointestinal liquid were in the range of 6%?8%,only about one-third of native starches.The content of amylose in resistant starch and DP decreased,especially puerariae RS(22.80%,21.92%and 11.93,5.01,respectively),debranched-heated RS reduced rapidly than heated-debranched RS.The RS melting temperature range decreased after digestion,which indicated the crystal structure was more uniform.However,the crystal type of RS did not change,so that the RS granule structure was looser treated by simulated gastrointestinal liquid.Through SEM showed that the tiny starch granule on the surface of the RS increased.In conclusion,it was speculated that the amylose molecular layer debranched-heated RS was thicker than heated-debranched RS.(4)Taken glucose as control sample,the fermentation characteristics of six kinds of digested RS in vitro on Escherichia coli,Lactobacillus casei and Bifidobacterium longum respectively from human colon were studied.The results showed that RS and glucose had a growth effect on three kinds of colonic bacteria.Moreover,the total colony counts of L.casei and B.longum by fermenting RS in the early stage increased obviously.Three kinds of colonic bacteria could ferment RS and glucose to produce acids making the reduction of pH,especially the reduction of pH on B.longum decreased rapidly in the late fermentation.As for the production of SCFAs,three kinds of exogenous bacteria preferentially utilized glucose to produce SCFAs.The main E.coli fermentation productions were acetic acid and butyric acid.L.casei mainly produced acetic acid.B.longum mainly produced acetic acid and improved the content of butyric acid by conversion.Thus,it was speculated that B.longum was able to decompose RS to produce long chain organic acids in the later stage of fermentation. |
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