A new method to isolate and separate small and large starch granules from barley and malt

Abstract

Large lenticular and small spherical starch granules are present in small grains in varying quantities and have different characteristics, affecting how the cereals perform during processing. Separation and isolation of these granules for characterisation is challenging, especially for germinating or malted cereals, because the latter can contain up to a 1000-fold higher α-amylase activity. In this work, a new but simple method is described to isolate starch from barley and malt and separate it in small and large starch granules while avoiding α-amylase activity. A protease treatment at pH 8.0 in the presence of 0.1 M EDTA is used to degrade the protein matrix around the starch granules in an aqueous cereal suspension. After sieving over a 38 μm sieve, highly pure (90.2–95.1 dm%) starch is obtained. Next, sequential sieving over 10 μm and 5 μm sieves results in isolated large and small starch granule fractions with a respective starch purity of 89.8%–93.8% and 76.8%–86.2% and a volume-based granule-type purity higher than 92.9%. Residual EDTA concentration and α-amylase activity in the isolated starch fractions are reduced to a minimum, preventing their interference during the further determination of the starch properties.