Institut National de la Recherche Agronomique, Laboratoire de Recherches de Technologie Laitière, 65 rue de Saint-Brieuc, 35042 Rennes Cedex, France.
Biotechnol Bioeng. 1997 Nov 20;56(4):391-7. doi: 10.1002/(SICI)1097-0290(19971120)56:4<391::AID-BIT5>3.0.CO;2-J.
The selective precipitation of alpha-lactalbumin (alpha-LA) at a pH around its isoelectric point (4.2) under heat treatment is the basis for a fractionation process of whey proteins. In these conditions, beta-lactoglobulin remains soluble, whereas bovine serum albumin and immunoglobulins co-precipitate. Knowledge of the mechanism governing the alpha-LA precipitation influences the choice of operating conditions and enables optimization of the fractionation process. alpha-LA is a calcium metallo-protein and its isoelectric precipitation is governed by the protein-calcium complexation equilibrium. Citrate, a sequestrant of calcium, decreases the free calcium concentration and displaces the precipitation phenomenon to a lower temperature range. A study of the effect of citrate on the precipitation phenomena of whey proteins is presented. Whatever the citrate content, precipitation curves for bovine serum albumin (BSA) and alpha-LA intersect at a temperature around 45 degrees C. For a temperature of heat treatment lower than 40 degrees C, a selective enrichment in alpha-LA of the precipitated phase is observed. As addition of citrate leads to high alpha-LA precipitated fractions at a temperature around 35 degrees C, the precipitation step may be performed at this temperature. It results in a reduced heat denaturation of whey proteins and in a higher alpha-LA purity in the precipitated fraction. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 391-397, 1997.
在热处理条件下，当 pH 值接近其等电点（4.2）时，乳清蛋白中的α-乳白蛋白（α-LA）选择性沉淀，这是乳清蛋白分级分离的基础。在这种条件下，β-乳球蛋白保持溶解状态，而牛血清白蛋白和免疫球蛋白则共同沉淀。对控制α-LA 沉淀机制的了解会影响操作条件的选择，并能使分级分离过程得到优化。α-LA 是一种钙金属蛋白，其等电沉淀受蛋白-钙络合平衡的控制。柠檬酸是钙的螯合剂，能降低游离钙浓度，并将沉淀现象推向更低的温度范围。本文研究了柠檬酸对乳清蛋白沉淀现象的影响。无论柠檬酸的含量如何，牛血清白蛋白（BSA）和α-LA 的沉淀曲线在 45°C 左右相交。对于热处理温度低于 40°C 的情况，沉淀相中α-LA 的选择性富集。由于在 35°C 左右的温度下添加柠檬酸可得到高含量的α-LA 沉淀，因此可以在该温度下进行沉淀步骤。这样可以降低乳清蛋白的热变性程度，并使沉淀相中α-LA 的纯度更高。（c）1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 391-397, 1997.
