Extraction of high-amylose starch from Radix Puerariae using high-intensity low-frequency ultrasound

High-amylose starch is in great demand in the food industry due to its unique functional properties but has very limited source. In this study, high-amylose starch was successfully extracted from Radix Puerariae using ultrasound extraction. The effects of ultrasound intensity (15.29, 20.38, 22.93, 24.46 and 25.38 kW/m²) and frequency (20 and 45 kHz) on extraction kinetics, and chemical compositions, crystallinity, in vitro digestion behaviour and gelling properties of starches were investigated. It was shown that with the increasing intensity, the extraction rate and content of amylose increased, but for starch the extraction rate increased initially until reached a plateau at an intensity of 24.46 kW/m². With the increasing low-frequency, the extraction rate and content of amylose increased, but the extraction rate of starch decreased. Based on statistical tests, the Logistic model was found to fit well to the extraction kinetics of amylose, and the Peleg model fit well to that of starch. The extraction yield of starch was not significantly affected by ultrasound conditions. The obtained starch has a high-purity with a content of more than 99% dry basis and an unchanged crystallinity. Moreover, the increased amylose content resulted in an increase of the content of slowly digestible starch, resistant starch, and gelling hardness. This study demonstrates that high-amylose starch can be obtained using ultrasound extraction from Radix Puerariae at high-intensity low-frequency.