| potato starch slurry(20%,w/w)were subject to HVEF treatment at 10,20,30 and 40 k V,and the treatment time was 10,20,30,40,50 min respectively.Then,the modified starch was characterized by using X-ray diffraction(XRD),Fourier transformation infrared(FT-IR)spectroscopy,pasting behavior,water absorption capacity(WAC),light transmission and scanning electron microscopy(SEM).The results showed that HVEF caused a shift in the gelatinization range to lower temperatures,and a decrease in solubility,swelling power and crystallinity.HVEF was evidenced to change WAC and Light transmittance,with a tendence firstly increase and then decrease with the increasing of the treatment time.The SEM micrographs demonstrated that some roughness or damages emerged on the surface of potato starch granules after HVEF treatments.The X-ray diffraction showed that the decrease of crystallinity during the HVEF treatment.It was concluded that HVEF destroyed amorphous area and surface crystalline zone of starch.Native potato starch(NPS)was modified by ultrasonic(US),electric field(ES)and a combination of the two treatments: ultrasonic prior to the electric field(UES),electric field prior to the ultrasonic(EUS)and ultrasonic and electric field at the same time(UAES).Physicochemical properties,texture profile property and in vitro digestibility of potato starch were characterized.Compared to the NPS single and dual-modified potato starch granules displayed deep pitting on the surface and their shape was deformed.XRD results suggested that the characteristic peaks were not changed,whereas the relative crystallinity increased for all treatments except for the ES treatment.The ES granule also showed a relatively high average size distribution.The EUS exhibited the most desirable properties such as high light transmission,high water absorption capacity,solubility,swelling power and resistant starch content.Acetylation of native starch,US,ES,UES,EUS and UAES starch showed that the acetyl group substitution degree of starch increased after different pretreatment,and the acetylated starch obtained after EUS treatment had the highest degree of substitution(0.37).FT-IR showed that the acetyl group was successfully introduced into starch granules.XRD showed that the characteristic peaks of acetylated starch were not changed,but the relative crystallinity decreased.Through the analysis of its functional characteristics,it was found that with the increase of acetyl group content,the gelatinization temperature and the gelatinization enthalpy of acetylated starch decreased.The water absorption and oil absorption of acetylated starch granules increased.To understand the contribution of granule inner portion to the pasting property of acetylated potato starch under the electric field and ultrasonic treatment,these starches were subjected to chemical surface gelatinization by 4.0 mol/L Ca Cl2 to obtain remaining granules with pasting time 0,6,12,18,24,30 min,respectively.The structure of remaining granule was studied by the fitted distribution curve.The distribution curve of acetyl groups and amylose content showed that acetyl groups,both amylose and amylopectin populations were unevenly distributed.A large extent of acetylation took place in the outer lamellae.The SEM presented that the remaining potato starch granules had a rough surface with a lamella structure.The XRD and differential scanning calorimetry(DSC)showed that the acetylation was confirmed to mainly occur the amorphous region and only take place in the outer lamellae of crystalline regions of starch granule.Chemical gelatinization was a process of stepwise removal of the outer layer. |
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