| Slowly digestible starch (SDS) has the characteristics of slow digestion, absorption andcontinuously releasing energy. It can maintain the postprandial blood glucose level stable,reduce postprandial insulin secretion, and effectively improve the body’s sensitivity to insulin.Presently, the preparation of SDS products has several disadvantages with poor stability, lowSDS content, which limit the application of SDS products. Previous research has indicatedthat β-CD could interact with starch molecules to form complex, which transformed theinstantaneous nucleation type of starch to sporadic nucleation. This transformation suggestedthe β-CD-starch complex could be as an important material to prepare the SDS products withhigher thermal stability.In this study, three typical cyclodextrins: β-cyclodextrin (β-CD), maltosyl-β-cyclodextrin (Mal-β-CD) and hydroxypropyl-β-cyclodextrin (HP-β-CD) were chosen forour experiment. Based on the principle of β-CD-starch complex formation via hydrogen bondand Van der Waals forces, the selected CDs were used to modify starch for preparing the SDSproducts with higher thermal stability and SDS content. The method was established andverified for determination of the SDS content in vitro conditions. The results showed that theindica rice starch, screened from waxy rice, japonica rice, and indica rice starches, was mostsuitable for preparation of SDS during the CDs’ modification.The preparation conditions were optimized using single-factor test. The optimalconditions, using the indica rice starch as a material, were addressed below: CDs content,3%;water,80%; crystallization temperature,25oC; and crystallization time,2h. Under theseconditions, the maximum SDS content reached52.1%,48.9%, and45.8%, when β-CD,Mal-β-CD and HP-β-CD were presented, respectively.The thermal stability of the prepared SDS products was estimated using differentialscanning calorimetry (DSC) and thermogravimetric analysis (TGA). The results showed thatthree kinds of CDs could interact with starch molecules to form CDs-starch complex. Thepeak decomposition temperature (Tp) reached more than100oC, which was20oC～30oChigher than that of the SDS products prepared with retrogradation. Furthermore, thetemperature range (TC-T0) was positively correlated with SDS content, indicating that theSDS products mainly consisted of submicrocrystal (imperfect crystallites). The resultsobtained from TGA also demonstrated the formation of CDs-starch complex with higherdecomposition temperature.The driving force and crystalline properties of the formed CDs-starch complex werestudied using Fourier infrared spectrum (FT-IR) and X-ray diffraction (XRD). The resultsindicated that the surface crystalline area of the SDS products increased with the SDS content.The hydrogen bond and Van der Waals interaction was the major during force for the stability of the CDs-starch complex. The formed complex was characterized a V-type crystallinepattern. CDs were assumed to be included between starch molecules and they were notcontained in starch helixes.The digestion process of the CDs-starch complex was determined by in vitro simulationand scanning electron microscope (SEM). The results revealed that the hydrolysis rate wasreduced with the increasing of the SDS content. The predicted glycemic index (pGI) of ricestarches after physical modification with β-CD, Mal-β-CD and HP-β-CD reached57.2,67.9,and69.4respectively. The slow mechanism of the complex was attributed to the V-typeimperfect crystallites formed in the presence of CDs.The residual SDS content was measured at different time and heating environments. Theresults showed that the residual contents of SDS were78.2%,72.3%,70.6%after dry heatingat100oC for15min and were73.7%,69.5%,67.8%after moisture heating at90oC for15min. These results suggested that the prepared SDS products with higher thermal stability... |
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