Natural acidifying agents (yuzu juice and organic acids)-assisted alkali extraction process for naked oat (Avena sativa L.) proteins

This study aimed to determine the optimal alkali extraction conditions—including alkaline pH, isoelectric precipitation pH, and enzyme treatment—for enhancing protein yield and crude protein content when using yuzu juice in the alkali extraction of naked oat proteins. First, unsoaked oat grains showed lower protein loss than soaked grains. Furthermore, the use of yuzu juice as the precipitation agent resulted in higher crude protein content and extraction yield than the use of citric acid alone. When oat proteins were extracted at alkaline pH 11 followed by isoelectric precipitation at pH 6 using a combination of organic acid and yuzu juice, the process achieved the highest values: crude protein content of 17.72%, extraction yield of 54.36%, and total amino acid content of 203.7 mg/g. To further improve extraction efficiency, three types of enzymes—starch hydrolyzing/ saccharifying enzymes, fiber-degrading enzymes, and proteases—were evaluated. Enzymatic treatment significantly increased protein extraction yield compared to the non-enzyme control. Among them, the treatment with Enzyme Ⅱ showed the highest crude protein content and extraction yield. Taken together, the most optimal conditions for oat protein extraction were identified as follows: enzymatic pretreatment with a starch hydrolyzing/saccharifying enzyme, alkali extraction at pH 11, and subsequent isoelectric precipitation at pH 6 using yuzu juice as the natural acidifying agent.