Extraction Of Quinoa Starch And Analysis Of Physicochemical Properties After Modification

In this study, quinoa was chosen as experiment materials, from which the starch was extracted by dilute alkali method, and the optimum extraction process was determined. The starch extracted was modified by physical method ( heat-moisture treatment) and chemical method (acetic acid esterification). Then, we made an in-depth exploration of the starch before and after the treatment though modern instruments, and the structure,physicochemical properties and vitro digestibility of the modified starch were studied systematically. We had the findings as follows:(1) According to the national standard method, the basic components of quinoa were determined, which contained 19.87 g protein, 9.78 g water, 53.20 g starch, 6.28g fat, and 1.60 g ash of quinoa per 100.00g.(2) Aqueous alkali was used for extracting the quinoa starch, and the extraction conditions were obtained as follows: concentration of NaOH was 0.25%, extraction time was 6h and extraction temperature was 50 ℃. Based on the single-factor experiments,Box-Behnken central composite experiment design was used,and the optimum extraction condition were obtained as follows: concentration of NaOH was 0.26%, extraction time was 380 min and extraction temperature 53 ℃.. Finally, starch extraction yield we obtained was 49.44%.(3) After heat-moisture treatment at lower moisture content and shorter time, the grain morphology, crystal type and molecular structure of the starch were not changed, however,the intensity of the diffraction peak decreased and the crystal type was still A type. With the moisture content increased and heat treatment time extended, starch granules had the aggregation and adhesion, and surface of some starch particles appeared shrinkage, pits and holes, and a small amount of starch was found melting deformation. Structure of starch changed from A type to A + V type, and the ratio of (1045/1022) cm-1 increased. After heat-moisture treatment, the gelatinization temperature, T0, Tp of starch were increased with the increase of moisture content and heat treatment time. However, the end viscosity,disintegration value, peak viscosity, recovery value,△H,solubility, swelling and freeze-thaw stability of starch were reduced.The content of RDS decreased, but the content of SDS and RS of starch which was treated of heat-moisture increased with the moisture content increasing. After 20 min of enzymolysis, the hydrolysis rate of starch decreased. When the starch was hydrolyzed at 20 min, more deeper and larger pores appeared on the native starch surface than the HMT-12h starch. Most of the starch at 120 min was hydrolyzed and lost the original morphological characteristics.(4) The degree of substitution of acetate starch was proportional to the reaction time.After esterification, the starch particles aggregated into large clusters, and the structure became loose and porous. X-ray diffraction was used to observe the diffraction peaks of starch at 9° and 20°. The results of FT-IR showed that the absorption peak of OH stretching vibration was decreased at 1740 cm-1 with the increase of the degree of esterification.Analysis with TGA showed that the thermo stability of starch after esterification was enhanced,which indicates that there was a new phase formed in the starch.