Extraction and Functional Properties of Crude Prolamin from Amaranth

The objective of this study was to evaluate the structural, functional and morphological characterizations of ultrasonic-assisted extraction of crude prolamin from amaranth grain (Amaranthus hypochondriacus L.). A Box–Behnken design of response surface methodology (RSM) was employed to optimize the extraction parameters. The optimal extraction parameters included a solid/solvent ratio of 1:9 (g:mL), with 50% ethanol solution at 75 °C. Regarding the physicochemical characteristics, amaranth crude prolamin (ACP) possessed more orderly secondary structures (the proportions of α-helix and β-sheet were 43.65% and 25.52%, respectively), which is favorable for improving the object-holding capacity, such as higher oil- and water-holding capacity. The higher surface hydrophobicity of ACP was beneficial for self-assembly into microspheres at high ethanol concentrations. In general, ACP had a wider molecular weight distribution, higher zeta-potential and better emulsifying capacity (3.91 g VE/g prolamin). Thus, these results provide useful insight into the applications of amaranth prolamin.