Effect of solvent and temperature on the size distribution of casein micelles measured by dynamic light scattering
Effect of solvent and temperature on the size distribution of casein micelles measured by dynamic light scattering
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DOI：
10.3168/jds.2008-1467
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发表时间：
2009-05-01
影响因子：
3.5
通讯作者：
Moraru, C. I.
中科院分区：
文献类型：
--
作者：
Beliciu, C. M.;Moraru, C. I.
本研究的目的是调查在不同温度下的动态光散射（DLS）的酪蛋白胶束粒度测定的准确性的溶剂的影响，并建立一个明确的协议，这些测量。使用90 Plus纳米颗粒尺寸分析仪（Brookhaven Instruments，霍尔茨维尔，NY）在6、20和50 ℃下进行动态光散射分析。生脱脂乳和巴氏杀菌脱脂乳被用作酪蛋白胶束的来源。模拟牛奶超滤液，超滤水，并通过使用10 kDa的截止膜的脱脂牛奶的超滤得到的渗透物被用作溶剂。测定了所有溶剂的pH值、离子浓度、折射率和粘度。通过DLS评价溶剂，以确保它们对粒度测量结果没有显著影响。实验方案的开发，在所有溶剂和实验条件下的颗粒尺寸的准确测量。所有的测量具有良好的重现性，与变异系数小于5%。溶剂和温度对酪蛋白胶束的有效直径有显著影响。以超滤透过液为溶剂时，酪蛋白胶束的粒径和多分散性随温度的升高而减小。来自用超滤渗透物稀释的生脱脂乳的酪蛋白胶束的有效直径在6 ℃下为176.4 +/-5.3nm，20 ℃下为177.4 +/-1.9nm，50 ℃下为137.3 +/-2.7nm。随着温度的升高，疏水键的强度增加，证明了这种趋势。总的来说，本研究的结果表明，酪蛋白胶束的DLS分析的最合适的溶剂是酪蛋白耗尽的超滤渗透液。用水稀释导致胶束解离，这显著影响DLS测量，特别是在6和20 ℃下。模拟牛奶超滤液似乎只有在20 ℃下才能给出准确的结果。在模拟牛奶超滤液中获得的结果，在6摄氏度不能解释的基础上，已知的温度对酪蛋白胶束的影响，而在50摄氏度，沉淀的无定形磷酸钙影响DLS测量。
The objectives of this study were to investigate the effect of the solvent on the accuracy of casein micelle particle size determination by dynamic light scattering (DLS) at different temperatures and to establish a clear protocol for these measurements. Dynamic light scattering analyses were performed at 6, 20, and 50 degrees C using a 90Plus Nanoparticle Size Analyzer (Brookhaven Instruments, Holtsville, NY). Raw and pasteurized skim milk were used as sources of casein micelles. Simulated milk ultrafiltrate, ultrafiltered water, and permeate obtained by ultrafiltration of skim milk using a 10-kDa cutoff membrane were used as solvents. The pH, ionic concentration, refractive index, and viscosity of all solvents were determined. The solvents were evaluated by DLS to ensure that they did not have a significant influence on the results of the particle size measurements. Experimental protocols were developed for accurate measurement of particle sizes in all solvents and experimental conditions. All measurements had good reproducibility, with coefficients of variation below 5%. Both the solvent and the temperature had a significant effect on the measured effective diameter of the casein micelles. When ultrafiltered permeate was used as a solvent, the particle size and polydispersity of casein micelles decreased as temperature increased. The effective diameter of casein micelles from raw skim milk diluted with ultrafiltered permeate was 176.4 +/- 5.3 nm at 6 degrees C, 177.4 +/- 1.9 nm at 20 degrees C, and 137.3 +/- 2.7 nm at 50 C. This trend was justified by the increased strength of hydrophobic bonds with increasing temperature. Overall, the results of this study suggest that the most suitable solvent for the DLS analyses of casein micelles was casein-depleted ultrafiltered permeate. Dilution with water led to micelle dissociation, which significantly affected the DLS measurements, especially at 6 and 20 degrees C. Simulated milk ultrafiltrate seemed to give accurate results only at 20 degrees C. Results obtained in simulated milk ultrafiltrate at 6 degrees C could not be explained based on the known effects of temperature on the casein micelle, whereas at 50 degrees C, precipitation of amorphous calcium phosphate affected the DLS measurement.