α-Lactalbumin (α-LA) is the second most abundant bovine whey protein. It has been intensively studied because of its readiness to populate the molten globular (MG) state, a partially folded state with native levels of secondary structure but loss of tertiary structure. The MG state of α-LA exposes a significant number of hydrophobic patches that could be used to bind and stabilize small hydrophobic molecules such as vitamin D₃ (vitD). Accordingly, we tested the ability of α-LA to stabilize vitD in a pH interval from 7.4 to 2; over this pH interval, α-LA transitions from the folded state to the MG state. The MG state stabilized vitD better than the folded state and was superior to the major bovine whey protein β-lactoglobulin (β-LG), which is known to stabilize vitD. At pH 7.4, β-LG and α-LA stabilized vitD to the same extent. Tryptophan fluorescence quenching measurements indicated that α-LA has one binding site at pH 7.4 but acquires an additional binding site when the pH is lowered to pH 2 to 4. Stability measurements of the vitD in the α-LA–vitD complex at different temperatures suggest that UHT processing would lead to little loss of vitD. This study demonstrates the potential of α-LA as a component in vitD fortification, particularly for low pH applications.

α-乳清蛋白（α-LA）是第二丰富的牛乳清蛋白。由于其易于填充熔融球状（MG）状态（具有天然二级结构水平但丧失三级结构的部分折叠状态），因此对其进行了深入的研究。α-LA的MG状态暴露出大量疏水斑点，可用于结合和稳定小的疏水分子，例如维生素D ₃（vitD）。因此，我们测试了α-LA在7.4到2的pH范围内稳定vitD的能力。在此pH间隔内，α-LA从折叠状态转变为MG状态。MG状态比折叠状态更好地稳定了vitD，并且优于已知的稳定vitD的主要牛乳清蛋白β-乳球蛋白（β-LG）。在pH 7.4时，β-LG和α-LA可将vitD稳定在相同程度。色氨酸荧光猝灭测量表明，α-LA在pH 7.4处具有一个结合位点，但在pH降低至pH 2至4时获得了另一个结合位点。在不同温度下对α-LA-vitD复合物中vitD的稳定性测量表明UHT处理几乎不会导致vitD损失。这项研究证明了α-LA作为vitD强化成分的潜力，特别是在低pH应用中。