Department of Food, Bioprocessing, and Nutrition Sciences, North Carolina State University, Raleigh, NC 27695, USA.
J Dairy Sci. 2010 May;93(5):1890-9. doi: 10.3168/jds.2009-2780.
Whey proteins are a major ingredient in sports drink and functional beverages. At low pH, whey proteins are astringent, which may be undesirable in some applications. Understanding the astringency mechanism of whey proteins at low pH could lead to developing ways to minimize the astringency. This study compared the astringency of beta-lactoglobulin (beta-LG) at low pH with phosphate buffer controls having the same amount of phosphate and at similar pH. Results showed that beta-LG samples were more astringent than phosphate buffers, indicating that astringency was not caused by acid alone and that proteins contribute to astringency. When comparing among various whey protein isolates (WPI) and lactoferrin at pH 3.5, 4.5, and 7.0, lactoferrin was astringent at pH 7.0 where no acid was added. In contrast, astringency of all WPI decreased at pH 7.0. This can be explained by lactoferrin remaining positively charged at pH 7.0 and able to interact with negatively charged saliva proteins, whereas the negatively charged WPI would not interact. Charge interactions were further supported by beta-LG or lactoferrin and salivary proteins precipitating when mixed at conditions where beta-LG, lactoferrin, or saliva themselves did not precipitate. It can be concluded that interactions between positively charged whey proteins and salivary proteins play a role in astringency of proteins at low pH.
乳清蛋白是运动饮料和功能饮料的主要成分。在低 pH 值下，乳清蛋白具有收敛性，这在某些应用中可能是不理想的。了解低 pH 值下乳清蛋白的收敛性机制可能会导致开发出最小化收敛性的方法。本研究比较了低 pH 值下β-乳球蛋白（β-LG）与具有相同磷酸盐含量且 pH 值相似的磷酸盐缓冲液的收敛性。结果表明，β-LG 样品比磷酸盐缓冲液更具收敛性，这表明收敛性不是由酸单独引起的，而是蛋白质导致收敛性。在比较各种乳清蛋白分离物（WPI）和乳铁蛋白在 pH 3.5、4.5 和 7.0 时，乳铁蛋白在未添加酸的 pH 7.0 时具有收敛性。相比之下，所有 WPI 的收敛性在 pH 7.0 时降低。这可以解释为乳铁蛋白在 pH 7.0 时仍带正电荷，能够与带负电荷的唾液蛋白相互作用，而带负电荷的 WPI 则不会相互作用。电荷相互作用进一步得到了支持，因为当在β-LG、乳铁蛋白或唾液本身不会沉淀的条件下混合时，β-LG 或乳铁蛋白和唾液蛋白会沉淀。可以得出结论，带正电荷的乳清蛋白和唾液蛋白之间的相互作用在低 pH 值下蛋白质的收敛性中起作用。
