Preparation Of Starch Particles Delayed Digestion

As the most valuable segments of nutrition in starch, slowly digestible starch (SDS) isbecoming the research focus for its unique low glycemic index property. Through decreasingthe speed of energy release, this starch nutrition segments may be helpful for controlling andpreventing dietary metabolic disorders, including diabetes and obesity. There exist manymethods of preparing SDS, by different preparing processes, the properties of the starchproducts vary greatly. At present the research of preparation of slowly digestible starch wasmostly modified the starch, making the structure of starch charged, resulting in slowlydigestible starch increased. This study used microcapsule method to preparing the starchwhich still had high SDS content after cooking. Though physical effects could hinder theenzyme hydrolysis of starch, emulsion ionic cross-linking method was used to embed starchto obtain high slowly digestible starch content.(the SDS content in the thesis were alldetermined after stewing)By comparing the method of direct adding calcium ions and slow releasing calciumions(plan one and plan two), the latter method was used to preparing starch particles withbetter slow digestion property. Through particle morphology and particle size analysis,technological conditions were determined as follows: the oil/water ratio was6:1, emulsifiedtime was20min, and stirring rate was500r/min. On the basis of single factor experiment,response surface methodology was used to simulate the optimum conditions. With the addingof sodium alginate1.60%, calcium carbonate2.39%, emulsifier1.00‰, the starch particleswere well developed with12.40%SDS content and94.24%embedding rate. The factors thatinfluenced on SDS content and embedding rate of the starch particles were as follows: sodiumalginate concentration> calcium carbonate content> the emulsifier content.In order to improve the slow digestion performance, chitosan with differentconcentrations was cross-linked with the optimal result starch particles. With the increase ofchitosan concentration, the content of slowly digestible starch of starch particles was firstlyincreased and then decreased. After cross-linked with0.15%chitosan for1h, compared withthe native starch, SDS content of starch particles increased from2.27%to37.32%.The changing properties of embedding process on the particle size, crystalline,polarization cross, thermal characteristics of starch particles were investigated. The resultsshowed that: compared with the native starch, the particle size of starch particles increasedobviously, from42.5μm to141.0μm; Crystal form of the starch particles didn’t changethrough X-embedding diffraction. The polarization cross of the optimal result starch particles were weakened, after cross-linked with chitosan it almostly disappeared. Thermalcharacteristics of starch particles showed that the gelatinization temperature of the nativestarch increased after embedding process. The gelatinization temperature of starch particleswas further increased after cross-linked with chitosan, the enthalpy value was also increased.Enzyme-treated starch particles were investigated by scanning electron microscope. Theresults showed that the embedding process can improve the SDS content and the reason wasthat the hindrance of the outer surface of the starches hindered the contact between theenzymes and the starches and meanwhile the outer surface of the starch product’s calciumalginate layer and chitosan/alginate layer possessed slow-releasing property which delayedthe starting time of contacting between enzymes and starches.