Study On Extraction,Characterization And Retrogradation Of Millet Starch With Different Amylose/Amylopectin Ratios

It is reported that different amylose/amylopectin ratios in starch affect the molecular structure,physical and chemical properties of starch and the quality of its food produced.At present,the research on millet starch is becoming more and more comprehensive,but there are few studies on changing the amylose/amylopectin ratios through the extraction process.In this study,amylose/amylopectin ratios in millet starch was changed during extraction process.The physical and chemical properties and retrogradation of millet starches with different amylose/amylopectin ratios,were investigated.In this study,asymmetrical flow field-flow fractionation（AF4）coupled with multiangle light scattering（MALS）and differential refractive index detector（dRI）（AF4-MALS-dRI）was used to separate and characterize millet starch.The effects of dissolution temperature,injection volume,cross-flow rates,half-life,ionic strength and pH of the carrier liquid on the separation effect of the AF4 system were studied.The results showed that millet starch dissolved at 80°C under the conditions of injection concentration of 0.50 mg/mL,cross-flow rates of 1.2 mL/min,half-life of 3 minutes,and carrier solution of 10 mmol/L pH=7.00 NaNO₃,had better separation effect and repeatability,and the relative standard deviation of R_g is 3.4%,the relative standard deviation of M_w is 7.0%.The R_g/R_h result indicated that the millet starch has branched structures.Three different concentrations of alkaline glycerin were used to extract millet starch.Scanning electron microscopy（SEM）,fourier transform infrared spectroscopy（FTIR）,X-ray diffraction（XRD）,differential scanning calorimetry（DSC）,AF4-MALS-dRI and other methods were used to characterize the morphology and structure of millet starch with different amylose/amylopectin ratios.Retrogradation behavior of millet starch with different amylose/amylopectin ratios during storage for 7 days was studied.The results showed that the amylose/amylopectin of millet starch extracted with alkaline glycerin was lower than that of millet starch extracted by general method,but higher than that of waxy millet starch.Results indicated that the method use in this study can removed some amylose during the starch extraction process,leading to a change in amylose/amylopectin ratios.The granule size,morphology,and crystal structure of millet starches with six different amylose/amylopectin ratios were compared.Results revealed that the relative crystallinity,gelatinization and retrogradation behavior were different.Waxy millet starch with low amylose/amylopectin ratios has higher relative crystallinity,gelatinization temperature and slower retrogradation,while millet starch with high amylose/amylopectin ratios has the opposite effect.In this article,AF4-MALS-dRI was applied for studying retrogradation behavior of millet starch with different amylose/amylopectin ratios.AF4-MALS-dRI was proved to a useful tool for accurate separation and characterization of millet starch and study on its retrogradation behavior.Ultrasonic water bath extraction with alkaline glycerin can change the amylose/amylopectin ratios in starch.