Starch purification after pin milling and air classification of waxy, normal, and high amylose barleys

Abstract

Three barley cultivars with low (SB89528), normal (Condor), and high (Glacier) amylose starch contents were pin-milled and air-classified into coarse and fine fractions by two passes at a vane setting (particle-size cut) of 15 μm and a third pass at 30 μm. The coarse fractions from the final pass (C3) had 15-36% starch, 12-15% protein, and 13-24% β-glucan, whereas the fine fractions (F3) had 77-78% starch, 8-9% protein, and 6-8% β-glucan. The shifts in starch, protein, and β-glucan varied among the cultivars. Scanning electron microscopy of the pin-milled barleys and their air-classified fractions showed that the first two air-classifications separated small granule starch into fine I (F1) and fine 2 (F2) fractions ; the large granule starch was separated into coarse 1 (C1 and coarse 2(C2) fractions. The third pass yielded a fine fraction (F3) rich in large granule starch. Further purification of F3 fractions by a wet process yielded almost pure large granule starch with an extraction efficiency ∼30% higher than that obtained by conventional laboratory starch extraction from barley. Furthermore, the process yielded protein and β-glucan as by-products at high levels of purity.