Physical Treatments Of Millet Starch And Its Phy Sicochemical Properties

As the green and efficient modification methods,ultrasound and microwave have a very broad application space in the starch deep processing field.In this paper,millet starch was treated by ultrasonic and microwave technology respectively,and the differences between these two modification methods were compared.The following research results were obtained.The extraction conditions of millet starch were as follows:-alkali concentration was 0.3%,the solid-liquid ratio was 1:3,soaking time was 24 h,nillet starch yield was 95.1 0%.After ultrasound treatment,the breakdown value,swelling power,transparency,initial gelatinization temperature(To),enthalpy and short-range order of millet starch increased first and then decreased,and the average diameter(D50)and relative crystallinity of starch continued To decrease.The concentration factor had the greatest influence on the peak viscosity of millet starch.When the concentration of starch slurry was 20%,the peak viscosity decreased by 6.95%.The time factor had the greatest influence on the disintegration value and transparency of starch,after treatment for 75 min,breakdown value and transparency decreased by 40.38%and 3.89%respectively.The frequency factor had the greatest influence on the swelling power of starch,and the starch swelling power increased by 11.31%after 25+80 kHz treatment.The temperature factor had the greatest influence on the relative crystallinity of starch,after treatment for 60oC,the relative crystallinity was reduced by 24.20%.Microwave treatment significantly reduced the peak viscosity,disintegration value,swelling power and relative crystallinity of starch,and the change degree of the starch slurry was greater than that of dry starch.Microwave treatment significantly increased the digestibility of the starch.In the FT-IR spectrum,the peak of the hydroxyl bond shifted To ward a lower wavenumber direction.Microwave caused deep cracks and central voids on the surface of the granules,and the original shape of the starch gradually disappears and a rough?surfaced gel block or a fine sheet gel were formed.The effect of microwave on starch was much greater than that of ultrasound.The peak viscosity and relative crystallinity of millet starch milk with 20%concentration decreased by 72.59%,91.8%and 6.41%and 15.16%after 120 s microwave and 75 min ultrasound treatment,respectively.The viscosity,transparency,swelling power and short-range orderliness of starch were decreased by microwave,while those properties were increased by ultrasonic at 20 kHz,300 W or 15 min.The infrared characteristic peaks of starch after ultrasound treatment did not change significantly,however,the width and intensity of the infrared characteristic peaks became wider and lower after microwave,and the position of the peaks moved forward obviously.Ultrasound treatment only resulted voids,cracks,and partial particle damage in the surface,while microwave treatment would cause serious damage to starch granules even gelatinized.