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Reassembling of Alkali-Treated Casein Micelles by Microbial Transglutaminase
Journal of Agricultural and Food Chemistry ( IF 5.7 ) Pub Date : 2018-10-12 00:00:00 , DOI: 10.1021/acs.jafc.8b04000 Anja Duerasch 1 , Jana Wissel 1 , Thomas Henle 1
Journal of Agricultural and Food Chemistry ( IF 5.7 ) Pub Date : 2018-10-12 00:00:00 , DOI: 10.1021/acs.jafc.8b04000 Anja Duerasch 1 , Jana Wissel 1 , Thomas Henle 1
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In milk, caseins interact to form nanoparticles called casein micelles. Under weak alkaline conditions, casein micelles swell reversibly and are disrupted at pH values above 8.5. The enzyme microbial transglutaminase (mTG) is widely used in food industry to modify the functional properties of proteins. Here, we evaluated the potential of mTG as a stabilizer for alkaline disrupted casein micelles. Hence, enzymatic cross-linking of casein micelles as well as sodium caseinate was studied at the natural milk pH 6.8 and under alkaline conditions at pH 7.9 by analyzing oligomerization via size exclusion chromatography, monomeric caseins via RP-HPLC-UV, and extra-micellar protein via Bradford assay. Additionally, alkaline swelling as well as enzymatic reconstruction of casein micelles was observed via scanning electron microscopy and dynamic light scattering. The results showed that the extent of cross-linking is mainly influenced by protein conformation and not by pH value. However, micellar αs2-casein was much more cross-linked at pH 7.9 compared to pH 6.8, whereas an opposite tendency was determined for micellar κ-casein. This leads to the conclusion that αs2-casein is mainly located in the inner center of casein micelles and is only accessible for enzymatic cross-linking after alkaline swelling of the micelle. Alkaline disrupted casein micelles are reassembled due to intramicellar cross-linking by mTG. On the basis of the results, an enhanced model of the structure of casein micelles was developed.
中文翻译：
微生物转谷氨酰胺酶对碱处理过的酪蛋白胶束的重组装
在牛奶中，酪蛋白相互作用形成称为酪蛋白胶束的纳米颗粒。在弱碱性条件下，酪蛋白胶束可逆溶胀，并在pH值高于8.5时被破坏。微生物转谷氨酰胺酶（mTG）在食品工业中广泛用于修饰蛋白质的功能特性。在这里，我们评估了mTG作为碱性破坏酪蛋白胶束的稳定剂的潜力。因此，在天然牛奶pH 6.8和碱性条件下在pH 7.9的条件下，通过大小排阻色谱分析低聚反应，RP-HPLC-UV色谱分析单体酪蛋白和胶束外胶，研究了酪蛋白胶束和酪蛋白酸钠的酶促交联。通过Bradford分析获得蛋白质。此外，通过扫描电子显微镜和动态光散射观察到酪蛋白胶束的碱性溶胀和酶促重建。结果表明，交联的程度主要受蛋白质构象的影响，而不受pH值的影响。但是，胶束αS2 -酪蛋白是更在相比pH 6.8的pH值7.9的交联，而被确定为胶束κ酪蛋白相反的倾向。这导致这样的结论：α S2 -酪蛋白主要位于酪蛋白胶束的内部中心，并且仅用于碱性胶束溶胀后酶促交联访问。碱性干扰的酪蛋白胶束由于mTG的胶束内交联而重新组装。基于结果，开发了酪蛋白胶束结构的增强模型。
更新日期：2018-10-12
中文翻译：
微生物转谷氨酰胺酶对碱处理过的酪蛋白胶束的重组装
在牛奶中，酪蛋白相互作用形成称为酪蛋白胶束的纳米颗粒。在弱碱性条件下，酪蛋白胶束可逆溶胀，并在pH值高于8.5时被破坏。微生物转谷氨酰胺酶（mTG）在食品工业中广泛用于修饰蛋白质的功能特性。在这里，我们评估了mTG作为碱性破坏酪蛋白胶束的稳定剂的潜力。因此，在天然牛奶pH 6.8和碱性条件下在pH 7.9的条件下，通过大小排阻色谱分析低聚反应，RP-HPLC-UV色谱分析单体酪蛋白和胶束外胶，研究了酪蛋白胶束和酪蛋白酸钠的酶促交联。通过Bradford分析获得蛋白质。此外，通过扫描电子显微镜和动态光散射观察到酪蛋白胶束的碱性溶胀和酶促重建。结果表明，交联的程度主要受蛋白质构象的影响，而不受pH值的影响。但是，胶束αS2 -酪蛋白是更在相比pH 6.8的pH值7.9的交联，而被确定为胶束κ酪蛋白相反的倾向。这导致这样的结论：α S2 -酪蛋白主要位于酪蛋白胶束的内部中心，并且仅用于碱性胶束溶胀后酶促交联访问。碱性干扰的酪蛋白胶束由于mTG的胶束内交联而重新组装。基于结果，开发了酪蛋白胶束结构的增强模型。
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