Pouliot Yves, Guy Marie-Michèle, Tremblay Mélanie, Gaonac'h Anne-Cécile, Chay Pak Ting Bertrand P, Gauthier Sylvie F, Voyer Normand
STELA Dairy Research Center, Institute of Nutraceuticals and Functional Foods (INAF), Université Laval, Quebec City, Quebec, Canada G1V 0A6.
J Agric Food Chem. 2009 May 13;57(9):3760-4. doi: 10.1021/jf803539f.
Spontaneous precipitation of a peptide mixture has been observed during the concentration by reverse osmosis of a tryptic hydrolysate of whey protein. The precipitated material collected by centrifugation could not be solubilized by urea, mercaptoethanol, or sodium dodecyl sulfate. However, a complete solubilization of the aggregates was observed when the pH of the solution was lowered to 2.0. Analysis of the insoluble fraction has allowed the identification of beta-lactoglobulin (beta-lg) fragment 1-8 as the major peptide involved in the formation of aggregates. Peptide beta-lg f1-8 accounted for >94% of the peptide content in the precipitate washed twice with distilled water. The investigation of the secondary structure using circular dichroism evidenced that the peptide beta-lg f1-8 isolated from the flocculated peptide mixture is under random coil conformation at acidic and neutral pH and tends to adopt a beta-sheet conformation at basic pH. The findings of this study provide evidence that peptide beta-lg f1-8 forms aggregates via an efficient self-assembly process.
在对乳清蛋白胰蛋白酶水解产物进行反渗透浓缩过程中，观察到肽混合物的自发沉淀现象。通过离心收集的沉淀物质不能被尿素、巯基乙醇或十二烷基硫酸钠溶解。然而，当溶液pH值降至2.0时，观察到聚集体完全溶解。对不溶部分的分析已确定β-乳球蛋白（β-lg）片段1-8是参与聚集体形成的主要肽段。用蒸馏水洗涤两次后的沉淀物中，肽β-lg f1-8占肽含量的94%以上。使用圆二色性对二级结构进行研究表明，从絮凝肽混合物中分离出的肽β-lg f1-8在酸性和中性pH值下呈无规卷曲构象，在碱性pH值下倾向于采用β-折叠构象。本研究结果证明，肽β-lg f1-8通过高效的自组装过程形成聚集体。
