| Starch is the major carbohydrate and engery source for human, Englyst devided the starch into three group by their digestion characteristics and bio-avaliablity. Rapidly digestible starch(RDS), could be fully digested and quickly absorbed in the small intestine within 20 minutes. Slowly digestible starch(SDS), could be completely digested and slowly absorbed in the small intestine in 20~120 minutes. Resistant starch(RS), could not be digested and absorbed in the small intestine, it would be excrected to large intestine and be used by the microorganism in the large intestine, which is similar to the diet fiber. SDS is able to release the energy steadily and to keep the blood glucose at the stable level after the meal, which will reduce the secretion of the insulin, prevent and control the chronic disease such as the diabetes. In order to maintain the SDS and high-RS content starch, several modified methods were used to improve the digestibility of the starch.Waxy rice starch(WRS), potato starch(PS) and cassava starch(CS) were submitted to the esterification reaction with citric acid to improve their digestibility, otherwise, the reaction time, temperature and starch type were studied to learn their effect on the formation of citrate starch.(a) Waxy rice starch is easier to react with citric acid, and to obtain the citrate starch with high resistence-digestibility and high thermodynamic stability. The optimal reaction condition is 130, 5 h, and the SDS and RS content of the cooked starch sample is up to 82.1%.(b) Citrate starch would loss the polarization cross and the swelling property, its X-ray diffraction spectrum showed a dispersed peak, which is the characteristic of typical amorphous structure.The starch was pretreated with alkali first before it reacted with citric acid to obtain the citrate starch with high-degree substitution, which will increase the RS content inside the starch. Moreover, the degree of pretreatment was studied to learn its effect on the esterification reaction, the result showed that the higher degree of pretreatment will increase the RS content inside the starch but decrease the water solubility, it will also cause fold or even unregular structure on the surface of the starch. A new absorption peak was observed on the FTIR on the CWRS.A reaction was conducted by dry heating waxy rice starch and konjac glucomanan(KGM) to produce the SDS, the reaction condition is 130, 5 h and the ratio of KGM to WRS is 3:100(g/g), the SDS and RS content of the above SDS sample is up to 31.1% and 15.8%. Obvious fragment and adhesion could be seen on the surface of the WRS-KGM compound made through dry heat method, the starch compound kept the polarization cross. In the Brabender test, the pasting temperature, peak viscosity and the breakdown viscosity of the WRS-KGM compound would drop, besides, the To and the H in the DSC test would also drop. The X-ray diffraction spectrum showed that the WRS-KGM is the A-type crystal structure, and its relative crystalinity increased.In order to obtain the starch-lipid complex, waxy rice starch, potato starch and cassavo starch were submitted to the reaction with lauric acid in the ethanol-water solvent at the temperature higher than the gelatinization point. The result showed the potato starch-lipid complex contained up to 51.8% SDS while the cassaco starch-lipid complex contained up to 29.1%, however, the digestibility of waxy rice starch is hardly affected, so the potato starch was more suitable for the reaction. The DSC heat flow curve of potato starch-lauric acid complex and cassavo starch-lauric complex showed two endothermic melting peak, and the peak in the range of 90~110 is caused by the fusion of typical II starch-lipid. The characteristic absorption peak of V-type crystal structure could be seen on the X-ray diffraction spectrum of potato starch-lauric acid complex and cassavo starch-lauric complex. |
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