Centre National Interprofessionnel de l'Economie Laitière , F-75009 Paris , France.
Unité Matériaux et Transformations (UMET), UMR 8207, Ecole Nationale Supérieure de Chimie de Lille (ENSCL), Institut National de la Recherche Agronomique (INRA), Centre National de la Recherche Scientifique (CNRS) , Université de Lille , F-59000 Lille , France.
J Agric Food Chem. 2018 Oct 3;66(39):10274-10282. doi: 10.1021/acs.jafc.7b06147. Epub 2018 Sep 20.
During storage, a series of changes occur for dairy powders, such as protein lactosylation and the formation of Maillard reaction products (MRPs), leading to powder browning and an increase of insoluble matter. The kinetics of protein lactosylation and MRP formation are influenced by the lactose content of the dairy powder. However, the influence of lactose in the formation of insoluble matter and its role in the underlying mechanisms is still a subject of speculation. In this study, we aim to investigate the role of lactose in the formation of insoluble matter in a more comprehensive way than the existing literature. For that, two casein powders with radically different lactose contents, standard micellar casein (MC) powder (MC1) and a lactose-free (less than 10 ppm) MC powder (MC2), were prepared and stored under controlled conditions for different periods of time. Powder browning index measurements and solubility tests on reconstituted powders were performed to study the evolution of the functional properties of MC powders during aging. Proteomic approaches [one-dimensional electrophoresis and liquid chromatography-mass spectrometry (LC-MS)] and innovative label-free quantification methods were used to track and quantify the chemical modifications occurring during the storage of the powders. Reducing the amount of lactose limited the browning of MC powders but had no effect on the loss of solubility of proteins after storage, suggesting that the action of lactose, leading to the production of MRC, does not promotes the formation of insoluble matter. Electrophoresis analysis did not reveal any links between the formation of covalent bonds between caseins and loss in solubility, regardless of the lactose content. However, LC-MS analyses have shown that different levels of chemical modifications occur during the MC powder storage, depending upon the presence of lactose. An increase of protein lactosylation and acetylation was observed for the powder with a higher lactose content, while an increase of protein deamidation and dephosphorylation was observed for that containing lower lactose. The decrease of pH in the presence of lactose as a result of Maillard reaction (MR) may explain the difference in the chemical modifications of the two powders. In view of the present results, it is clear that lactose is not a key factor promoting insolubility and for the formation of cross-links between caseins during storage. This suggests that lactosylation is not the core reaction giving rise to loss in solubility.
在储存过程中，乳制品粉末会发生一系列变化，如蛋白质乳糖化和形成美拉德反应产物（MRP），导致粉末变褐和不溶性物质增加。蛋白质乳糖化和 MRP 形成的动力学受到乳制品粉末中乳糖含量的影响。然而，乳糖在不溶性物质形成中的作用及其在潜在机制中的作用仍然是推测。在这项研究中，我们旨在以比现有文献更全面的方式研究乳糖在不溶性物质形成中的作用。为此，我们制备了两种具有截然不同乳糖含量的酪蛋白粉末，即标准胶束酪蛋白（MC）粉末（MC1）和无乳糖（低于 10 ppm）MC 粉末（MC2），并在控制条件下储存不同时间。对再水合粉末进行粉末褐变指数测量和溶解度测试，以研究 MC 粉末在老化过程中功能特性的演变。采用蛋白质组学方法[一维电泳和液相色谱-质谱（LC-MS）]和创新的无标记定量方法来跟踪和定量储存过程中发生的化学修饰。减少乳糖的量限制了 MC 粉末的褐变，但对储存后蛋白质溶解度的丧失没有影响，这表明乳糖的作用导致 MRC 的产生并没有促进不溶性物质的形成。电泳分析没有显示出在酪蛋白之间形成共价键与溶解度丧失之间的任何联系，而与乳糖含量无关。然而，LC-MS 分析表明，取决于乳糖的存在，在 MC 粉末储存过程中会发生不同水平的化学修饰。对于含有较高乳糖含量的粉末，观察到蛋白质乳糖化和乙酰化的增加，而对于含有较低乳糖含量的粉末，则观察到蛋白质脱酰胺和去磷酸化的增加。由于美拉德反应（MR）导致乳糖的存在使 pH 值降低，可能解释了两种粉末中化学修饰的差异。鉴于目前的结果，显然乳糖不是促进不溶性物质形成和在储存过程中促进酪蛋白之间形成交联的关键因素。这表明乳糖化不是导致溶解度丧失的核心反应。
