Wang Zebin, Narsimhan Ganesan
Biochemical and Food Process Engineering, Department of Agricultural and Biological Engineering, Purdue University, West Lafayette, Indiana 47907-2093, USA.
Langmuir. 2005 May 10;21(10):4482-9. doi: 10.1021/la047374g.
The ability of proteins to provide stability in foams is greatly influenced by their interfacial dilatational rheological properties. Surface tension response of a pulsatingbubble with an adsorbed layer of beta-lactoglobulin was measured for different frequencies and protein concentrations using a pulsating bubble tensiometer. A methodology, accounting for adsorption/desorption as well as variation of surface concentration due to expansion/contraction, was developed for the evaluation of surface dilatational elasticity and viscosity at different frequencies from these measurements. The adsorption rate constants were inferred from the surface pressure dynamics of protein adsorption using a Langmuir minitrough. The desorption rates were shown to be negligible for beta-lactoglobulin from the surface pressure response of a spread monolayer when subjected to compression in a Langmuir minitrough. The proposed model was employed to infer the interfacial dilatational viscosity and elasticity of an adsorbed beta-lactoglobulin layer at the air-water interface from experimental pulsating bubble data for protein concentrations in the range of 0.01-0.5 wt % at pH 7. As expected, the interfacial dilatational rheological properties were found to be higher at higher protein concentrations, this effect being less pronounced for dilatational elasticity. Heating at 80 degrees C for 30 min was found to result in higher interfacial dilatational viscosity and lower interfacial dilatational elasticity though this difference was within experimental error. The traditional approach for the inference of interfacial dilatational rheological properties is found to overpredict the interfacial dilatational elasticity whereas the viscosity values do not differ significantly from those obtained using the current analysis.
蛋白质在泡沫中提供稳定性的能力受到其界面膨胀流变特性的极大影响。使用脉动气泡张力仪，针对不同频率和蛋白质浓度，测量了带有β-乳球蛋白吸附层的脉动气泡的表面张力响应。开发了一种方法，该方法考虑了吸附/解吸以及由于膨胀/收缩导致的表面浓度变化，用于从这些测量结果评估不同频率下的表面膨胀弹性和粘度。使用Langmuir微型槽从蛋白质吸附的表面压力动力学推断吸附速率常数。当在Langmuir微型槽中进行压缩时，从铺展单分子层的表面压力响应来看，β-乳球蛋白的解吸速率可忽略不计。利用所提出的模型，根据pH为7时蛋白质浓度在0.01 - 0.5 wt%范围内的实验脉动气泡数据，推断空气 - 水界面处吸附的β-乳球蛋白层的界面膨胀粘度和弹性。正如预期的那样，发现较高蛋白质浓度下的界面膨胀流变特性更高，这种效应在膨胀弹性方面不太明显。发现在80℃加热30分钟会导致更高的界面膨胀粘度和更低的界面膨胀弹性，不过这种差异在实验误差范围内。结果发现，推断界面膨胀流变特性的传统方法高估了界面膨胀弹性，而粘度值与使用当前分析方法获得的值没有显著差异。
