An improved microwave-assisted extraction of anthocyanins from purple sweet potato in favor of subsequent comprehensive utilization of pomace

In order to enhance the extraction efficiency of anthocyanins and subsequent comprehensive utilization of pomace from purple sweet potato (PSP), an improved microwave-assisted extraction (iMAE) of anthocyanins without dextrinization of starch was developed in this work. Firstly, the extraction conditions of PSP anthocyanins (PSPAs) were optimized by Response Surface Methodology (RSM) and the optimal parameters were as follows: solid-to-liquid ratio of 1:3 (g/mL), ethanol concentration of 30% with a small quantity of critic acid as regulating reagent of pH, microwave irradiation power of 320 w, extraction time of 500 s. Under the conditions, the yield of anthocyanins was 31.16 mg/100 g PSP (RSD = 1.45%, n = 3), which was a relative error of -4.88% compared with the predicted value (32.76 mg/100 g PSP) by model of Response Surface Methodology. By HPLC-ESI-MS/MS analysis, the composition of anthocyanins obtained by iMAE is basically the same as that of ultrasound-assisted extraction with citric acid aqueous. And the residue obtained by iMAE was in its original appearance and the total sugar content (TSC) in pomace was 88.2% of that in fresh PSP. The iMAE provided a method for the quick extraction of anthocyanins with some advantages of high efficiency as conventional MAE, but avoided gelatinization of starch which is useful for further utilization of starch in pomace. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.