2.5 Measurement of starch and storage protein composition
Refined rice samples were milled into flour in the liquid nitrogen, and the starch was purified according to the instructions of Tran et al. (2011). The starch molecules are completely dissolved by the protease, sodium bisulfate, DMSO/LiBr (0.5%) ethanol solution, and the proteins, fats, and non-starch polymers are removed without starch degradation. Starches were further debranched with isoamylase and dissolved in DMSO/LiBr solution and physicochemical properties of starch were identified from the milled rice. The total starches were determined by using the protocols described in our previous study by Yang et al. (2016).
According to the solubility of protein components in different solvents, albumin, globulin, prolamin, and glutelin can be extracted with distilled water, dilute hydrochloric acid, ethanol, and dilute alkali in sequence, and the extracts are collected separately. The biuret colorimetric method was used to determine the remaining species using the Coomassie brilliant blue colorimetric method (Sapan et al., 1999).