| Starch prepared through mild gelatinization treatment is a new type of modified starch. Its inner porous network structure can form embedding space for guest molecules. Because of this property, it can be used to encapsulate functional materials to provide protection while allowing their slow-release. As an antioxidant, EGCG plays an important role in inhibition of cardiovascular diseases and cancer. However, its application is limited to a greater extent because it can be oxidized and it is characterized by low stability. In this study, mild gelatinization treatment combined with freeze drying was utilized to prepare modified starch, and the changes in their physicochemical properties and granule structure were investigated. Thereafter, the modified starch was used as a carrier to embed EGCG to prepare modified starch-EGCG complex, and the stable structure and digestion characteristics of the complex were studied.In this study, to prepare slight gelatinization-freeze dried starch with high adsorption rate, strong mechanical as well as high retention rate for original characteristics, cassava starch, potato starch and corn starch were selected as experimental materials and the adsorpion rates for water/oil together with intact particle structure were set as selection criteria. Other parameters which were investigated including starch types, temperature and reaction time. Results from the study were as follows: among the three kinds of starches, cassava starch displayed the highest adsorption properties, the best modification conditions were obtained when the starches were both treated at 62°C and 70°C for 1 min. Under these conditions, adsorption rates for water of modified starches were 168.7%, 179.6%, respectively, increasing by 58.3%, 68.5% compared with native starch, adsorption rates for oil were 189.1%, 228.2%, increasing by 80.6%, 117.9%, respectively. The prepared modified starches had intact granule structure and good mechanical strength, also the particle distribution and rheological properties showed no obvious change suggesting that the original characteristis were retained to a great degree.The amylose content of cassava starch samples prepared under various reaction temperature was measured and results showed that the percentage of amylose increased with temperature increasing; molecular weight was decreasing; results on X-ray diffraction showed that starch type maintained A-type after treatment, and with reaction temperature increasing, the relative degree of crystallinity was subjected to a small decrease, with the damage of crystalline regions; results on Fourier transform infrared spectroscopy showed no groups were introduced or moved, and there was a strong relationship between R value(A1047/A1022) in FITC with the crystallinity results in X-ray. TGA results indicated that pyrolysis temperature increased from 330°C to 339°C after modification, suggesting the stronger ability of heat tolerance. Results on DSC analysis showed that the melt temperature of chain-chain crystal was enhanced, and enthalpy increased from 211.4 J/g to 247.1 J/g, with thermal stability being enhanced, indicating that the structure in crystalline regions became more ordered, double helix structure more stable, crystalline region more perfect.The modified starch was used as a carrier to embed EGCG to prepare modified starch-EGCG complex, and the adsorption curve showed that the maximum embedding capacity was up to 101.76 mg/g. Results on the analysis of the stable structure of the complex showed that modified starch and EGCG had strong binding force through hydrogen bond, with the increase of relative crystallinity and thermal stability. After five weeks of storage, the radical scavenging capacity of EGCG embedded by modified starch decreased from 87% to 75%, while that of EGCG which was not embedded decreased from 90% to about 40%, indicating starch provided great protection for EGCG. After digestion for 1 h, it was observed that free EGCG released 50% to simulated intestinal fluid. However, it took 4 h to release the same level of EGCG in the complex, suggesting great controlled-release of modified starch to EGCG. In the presence of EGCG, the digestion rate of starch decreased, and release rate of glucose showed obvious decline, content of resistant starch changed from original 33.67% to 57.36%. During the digestion process, changes in starch structure showed that EGCG was decreasing the release rate of glucose, inhibiting the sudden rise, slowing down the rate of granule collapse, decreasing granule size and molecular weight was decreasing as a result of the inhibition of the hydrolysis of middle-length chain molecules to short chain molecules of starch. |
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