β-酪蛋白耗竭的酪蛋白胶束的研究：胶束稳定性，酶交联和作为纳米载体的适用性,Journal of Agricultural and Food Chemistry

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β-酪蛋白耗竭的酪蛋白胶束的研究：胶束稳定性，酶交联和作为纳米载体的适用性
Journal of Agricultural and Food Chemistry ( IF 5.7 ) Pub Date : 2020-11-17 , DOI: 10.1021/acs.jafc.0c00904
Anja Duerasch ₁ , Pia Herrmann ₁ , Konstantin Hogh ₁ , Thomas Henle ₁

Affiliation

β-酪蛋白是两亲蛋白，因此被认为在酪蛋白胶束中是多边结合的。它的极性分子部分（尤其是磷酸丝氨酸残基）可以与胶体磷酸钙（CCP）发生静电相互作用，形成纳米簇，其非极性分子部分通过与其他酪蛋白形成疏水键来增强胶束稳定性。由于冷却减弱了疏水相互作用，因此可以通过重复的耗竭步骤，包括冷却和随后的超速离心，从酪蛋白胶束中不可逆地除去大部分的β-酪蛋白。尽管数十年来冷却对胶束β-酪蛋白浓度的影响已广为人知，但耗竭对酪蛋白胶束主要特征的影响尚未得到研究。因此，我们旨在分析β-酪蛋白耗竭对酪蛋白胶束稳定性和功能的影响，以评估与天然酪蛋白微胶粒作为纳米载体相比耗竭的情况。通过反复冷却和超速离心步骤不可逆地从天然酪蛋白胶束中分离出高达43.2％的总β-酪蛋白。分别通过动态光散射（DLS）和纳米粒子跟踪分析（NTA）进行测量，耗竭对胶束悬浮液的尺寸分布以及多分散性和颗粒浓度没有影响。此外，胶束对乙醇或螯合剂乙二醇-双（β-氨基乙基醚）-的稳定性通过反复冷却和超速离心步骤不可逆地从天然酪蛋白胶束中分离出2％的总β-酪蛋白。分别通过动态光散射（DLS）和纳米粒子跟踪分析（NTA）进行测量，耗竭对胶束悬浮液的尺寸分布以及多分散性和颗粒浓度没有影响。此外，胶束对乙醇或螯合剂乙二醇-双（β-氨基乙基醚）-的稳定性通过反复冷却和超速离心步骤不可逆地从天然酪蛋白胶束中分离出2％的总β-酪蛋白。分别通过动态光散射（DLS）和纳米粒子跟踪分析（NTA）进行测量，耗竭对胶束悬浮液的尺寸分布以及多分散性和颗粒浓度没有影响。此外，胶束对乙醇或螯合剂乙二醇-双（β-氨基乙基醚）-的稳定性N，N，N '，Nβ-酪蛋白耗竭不影响'-四乙酸（EGTA）。尽管如此，耗竭的胶束对微生物转谷氨酰胺酶（mTG）的酶促交联的敏感性较小，表明由于耗竭而导致的水通道变窄。另外，加载实验表明，与天然胶束一样，可以向枯竭的胶束中加载亚油酸（LA）的强度更高，因此，LA可以从天然胶束中置换高达81.3％的β-酪蛋白。我们的结果证实，耗竭不会增强酪蛋白胶束充当疏水性物质的纳米载体的能力，但可以支持对酪蛋白胶束结构的理解。基于观察到的针对EGTA的不变稳定性，受阻的酶促交联以及LA对β-酪蛋白的有效置换，我们建议，胶束β-酪蛋白的主要部分被疏水地结合到胶束结构中，而不会影响磷酸钙纳米簇的形成。因此，β-酪蛋白对酪蛋白胶束结构的主要作用可能是促进内部的高水合作用，从而促进酪蛋白胶束的高渗透性。

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Study on β-Casein Depleted Casein Micelles: Micellar Stability, Enzymatic Cross-Linking, and Suitability as Nanocarriers

β-Casein is an amphiphilic protein and thus considered as multilaterally bound in casein micelles. Its polar molecule part, in particular the phosphoserine residues, can interact electrostatically with colloidal calcium phosphate (CCP) to form nanoclusters and its nonpolar molecule part enhances micellar stability by forming hydrophobic bonds to other caseins. Because cooling weakens hydrophobic interactions, a substantial portion of β-casein can be irreversibly removed from the casein micelle by repeated depletion steps, including cooling and subsequent ultracentrifugation. Although this effect of cooling on the micellar β-casein concentration has been well known for decades, the influence of depletion on the main characteristics of casein micelles has been less investigated yet. Therefore, we aimed to analyze the consequences of β-casein depletion on the stability as well as the functionality of casein micelles to evaluate the suitability of depleted compared to native casein micelles as nanocarriers. Up to 43.2% of the total β-casein was irreversibly sequestered from native casein micelles by repeated cooling and ultracentrifugation steps. Depletion showed no effect on size distribution as well as polydispersity and particle concentration of micelle suspensions as measured via dynamic light scattering (DLS) and nanoparticle tracking analysis (NTA), respectively. Furthermore, the stability of the micelles against ethanol or the chelating agent ethylene glycol-bis(β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid (EGTA) was not influenced by β-casein depletion. Notwithstanding, depleted micelles were less susceptible to enzymatic cross-linking by microbial transglutaminase (mTG), indicating narrowed water channels due to depletion. Additionally, loading experiments showed that depleted micelles could be loaded with linoleic acid (LA) as intensively as native micelles, whereupon LA displaces up to 81.3% of β-casein from native micelles. Our results confirm that depletion does not enhance the ability of the casein micelle to act as a nanocarrier for hydrophobic substances but could support the understanding of the casein micelle structure. Based on the observed unchanged stability against EGTA, the hindered enzymatical cross-linking, and the efficient displacing of β-casein by LA, we suggest that the major portion of micellar β-casein is hydrophobically incorporated into the micelle structure without impact on the formation of calcium phosphate nanoclusters. The main role of β-casein for the casein micelle structure, therefore, might be to facilitate the high hydration of the interior and thus the high permeability of casein micelles.

更新日期：2020-11-25

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