Liu Shengnan, Xie Yun, Li Bingyi, Li Siqi, Yu Wenhua, Ye Aiqian, Guo Qing
College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China.
National Engineering Research Center for Fruit and Vegetable Processing, China Agricultural University, Beijing 100083, China.
Foods. 2023 Jul 3;12(13):2589. doi: 10.3390/foods12132589.
In this work, we extracted proteins from white quinoa cultivated in the northeast of Qinghai-Tibet plateau using the method of alkaline solubilization and acid precipitation, aiming to decipher how extraction pH (7-11) influenced extractability, purity and recovery rate, composition, multi-length scale structure, and gelling properties of quinoa protein isolate (QPI). The results showed that protein extractability increased from 39 to 58% with the increment of pH from 7 to 11 whereas protein purity decreased from 89 to 82%. At pH 7-11, extraction suspensions and QPI showed the similar major bands in SDS-PAGE with more minor ones (e.g., protein fractions at > 55 or 25-37 kDa) in suspensions. Extraction pH had limited effect on the secondary structure of QPI. In contrast, the higher-order structures of QPI were significantly affected, e.g., (1) emission maximum wavelength of intrinsic fluorescence increased with extraction pH; (2) surface hydrophobicity and the absolute value of zeta-potential increased with increasing extraction pH from 7 to 9, and then markedly decreased; (3) the particle size decreased to the lowest value at pH 9 and then increased to the highest value at pH 11; and (4) denaturation temperature of QPI had a large decrease with increasing extraction pH from 7/8 to 9/10. Besides, heat-set QPI gels were formed by loosely-connected protein aggregates, which were strengthened with increasing extraction pH. This study would provide fundamental data for industrial production of quinoa protein with desired quality.
在本研究中，我们采用碱溶酸沉法从青藏高原东北部种植的白藜麦中提取蛋白质，旨在解析提取pH值（7 - 11）如何影响藜麦分离蛋白（QPI）的提取率、纯度和回收率、组成、多尺度结构及凝胶特性。结果表明，随着pH值从7增加到11，蛋白质提取率从39%提高到58%，而蛋白质纯度从89%降至82%。在pH 7 - 11范围内，提取悬浮液和QPI在SDS - PAGE中显示出相似的主要条带，悬浮液中有更多的次要条带（如分子量> 55 kDa或25 - 37 kDa的蛋白质组分）。提取pH值对QPI的二级结构影响有限。相比之下，QPI的高阶结构受到显著影响，例如：（1）内在荧光发射最大波长随提取pH值增加；（2）表面疏水性和zeta电位绝对值在pH值从7增加到9时升高，然后显著降低；（3）粒径在pH 9时降至最低值，然后在pH 11时升至最高值；（4）QPI的变性温度随着提取pH值从7/8增加到9/10大幅下降。此外，热凝固的QPI凝胶由松散连接的蛋白质聚集体形成，随着提取pH值的增加而增强。本研究将为工业生产具有所需品质的藜麦蛋白提供基础数据。
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