Isolation and Characterization of Starch from the Purple Yam (Dioscorea alata) Anthocyanin Extraction Residue Obtained by Ultrasound-Assisted Extraction

Abstract Purple yam ( Dioscorea alata ) is a tuber crop found in tropical countries that could be a valuable source of anthocyanins and starch. After anthocyanin extraction, the starch from the extraction residue was isolated using steeping in acid pH (AS), steeping in alkaline pH (KS), and steeping in water (WS). The starch yield was higher in AS (50.86 ± 1.23%), followed by KS (45.90 ± 0.68%) and WS (41.23 ± 4.92%). WS starches presented softer round-oval forms, and AS and KS presented some layers in the spherical structures. Diffractograms showed a characteristic of a B type of starch with crystallinity between 43 and 48% for all isolation methods. Enthalpy of gelatinization was higher in the AS (302.52 ± 29.26 J g −1 ) than KS (211.40 ± 35.09 J g −1 ) and WS (265.03 ± 26,58 J g −1 ). Monomodal distributions with mean volume diameter ranging between 35.58 µm and 36.05 µm were obtained for all isolation methods. As expected, the swelling power (SP) and water solubility index (WSI) increases as temperature increases for starches isolated using AS, KS, and WS. The isolation of starch from the residue of the extraction of anthocyanins from purple yam is suitable using AS, KS, and WS. Although no significant differences among isolation methods were observed in almost physicochemical parameters, AS isolation method produces starches with higher extraction yield and purity. Graphical Abstract