| Dioscorea opposita Thunb.,a traditional Chinese medicine withlarge amounts biologically active substances,not only can decrease blood glucose,but also it has the function of strengthen the immune system.D.opposita Thunb.starch is widely used in food industry for its high gel strength and high retrogradation value.Heat-moisture treatment and high-pressure homogenization are effective physical methods in starch modification.With a view to that,This paper mainly studied the physicochemical properties of D.opposita Thunb.starch and Compare the result of these two methods systematically.the causes of starch's Modification were analyzed.The results of the research are summarized below:Heat-moisture treatment and high-pressure homogenization significantly changed in the birefringence of the starch and particle morphology.The surface of Dioscorea opposita starch granule was obviously damaged and the intensity of birefringence was reduced when pressure higher than 80MPa.After the particle surface starch gelatinization appears adherent to each other and left the crater.Starch granules were clearly breached and the intensity of birefringence was reduced when the starch under moisture content higher than 20%heat-moisture treatment.After heat moisture treatment,D.opposita Thunb.starch partly gelatinized and crystalline structure was damaged too.After the high-pressure homogenization,the starch particle size decreases and then increases.At low pressure(40-60MPa)high pressure homogenization,mechanical crushing phenomenon occurs mainly.At a pressure higher than 80 MPa,starch gelatinization appeared.Heat-moisture treatment increases the particle size of the starch granules and decreased the apparent density of the power.After homogenization and heat moisture treatment,the starch content yam amylose were increased to varying degrees.It proves that these two physical methods enables degradation of starch molecules into amylose.High-pressure homogenization treatment reduced the gelatinization temperature and gelatinization enthalpy of starch.Heat-moisture treatment significantly increased the yam starch pasting temperature and reduced gelatinization enthalpy of this starch.Part of the sample can hardly gelatinized under atmospheric conditions.The solubility and swelling of starch tended to increase while the transmittance increased with the pressure increasing.The solubility,swelling and transmittance of the starch decreased after heat-moisture treatment.The crystal type was not changed while the crystalline decreased from 26.45%to 19.88%with the decreasing FTIR absorption peaks at 3233.42?1164.01?1081.90?1050.27 and 1015.81cm-1.The in vitro digestibility showed that the amount of resistant starch decreased from 81.68%to 52.60%,while the contents of rapidly digestible starch and slowly digestible starch increased from 11.32%and 7.00%to 30.34%and 17.06%respectively with the increasing of homogenization pressure.High-pressure homogenization treatment did not change crystalline type of yam starch while heat-moisture treatment changed the C-type to A-type.Rapidly digestible starch and slowly digestible starch increased to 39.23%and 30.98%when the moisture content above to heat-moisture treatment.Slowly digestible starch content increased by 4 times compared to native starch.High-pressure homogenization and heat-moisture treatment can improve starch digestibility. |
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