A quantitative comparison of the extraction of protein fractions from wheat grain by different solvents, and of the polypeptide and amino acid composition of the alcohol‐soluble proteins

作者：Marjorie Byers, Benjamin J. Miflin, Susan J. Smith · 发表于：Journal of the Science of Food and Agriculture · 年份：1983 · DOI：10.1002/jsfa.2740340506 · 被引用次数：95 · 研究领域：Phytase and its Applications、Proteins in Food Systems、Food composition and properties

Abstract Using several cultivars, whole milled wheat grain was first extracted with 0.5M NaCl to remove non‐protein N, albumins and globulins: the amount of protein subsequently extractable by either 70% ethanol, 55% propan‐2‐ol, or 50% propan‐1‐ol (with or without the addition of acetic acid), was then compared. All solvents were tested at 4, 20 and 60°C both with and without the addition of 2‐mercaptoethanol (2‐ME) as a reducing agent. Raising the temperature, including a reducing agent, and repeated extractions, all combined to maximise protein extractability; least was extracted by 70% ethanol at 4°C and most by 50% propan‐1‐ol containing acetic acid and 2‐ME at 60°C. The differing polypeptide compositions of these alcohol‐soluble fractions illustrated why N solubility alone is not a sufficient guide to protein extraction, e.g. 35% of grain N was extractable by either 70% ethanol at 60°C or 70% ethanol containing 2‐ME at 4°C, but high mol. wt polypeptides (>60000) were found only in the 60°C extract. In contrast, the complete range of alcohol‐soluble polypeptides was extracted by all solvent mixtures based on propan‐1‐ol, even at 4°C. Amino acid analyses of these alcohol‐soluble fractions confirmed the low levels of lysine in fractions free from high mol. wt polypeptides. More glycine was found in all fractions containing high mol. wt polypeptides, but only those extracted by propan‐1‐ol mixtures had an increased lysine content, the amount of which increased linearly as t...