Zhang Ruijia, Luo Lan, Yang Zhi, Ashokkumar Muthupandian, Hemar Yacine
School of Food and Advanced Technology, Massey University, Auckland 0632, New Zealand.
School of Food and Advanced Technology, Massey University, Auckland 0632, New Zealand.
Ultrason Sonochem. 2021 Dec;81:105852. doi: 10.1016/j.ultsonch.2021.105852. Epub 2021 Dec 3.
In this work, oil-in-water emulsions stabilised by milk protein concentrate (MPC70) were investigated. The MPC70 concentration was kept constant at 5% (close to the protein content found in skim milk) and the oil volume fraction was varied from 20 to 65%. Sonication was performed at 20 kHz and at a constant power of 14.4 W for a total emulsion volume of 10 mL. Under certain oil concentration (≥35%) and sonication times (≥3s) the emulsion aggregated and formed high-viscosity pseudo plastic materials. However, the viscosity behaviour of the emulsion made with 35% oil reverted to that of a liquid if sonicated for longer times (≥15 s). Confocal laser scanning microscopy showed clearly that the oil droplets are aggregated under the sonication conditions and oil concentrations indicated above. An attempt to explain this behaviour through a simple model based on the bridging of oil droplets by the MPC70 particles and, taking into account the oil droplet and MPC70 particle sizes as well as the oil volume fraction, was made. The model fails to describe in details the aggregation behaviour of these emulsions, likely due to the inhomogeneous protein layer, where both free caseins and casein micelles are adsorbed, and to the packing of the oil droplets at concentrations ≤55%. Nonetheless, this work demonstrates the potential of ultrasound processing for the formation of dairy emulsions with tailored textures.
在这项工作中，对由浓缩乳蛋白（MPC70）稳定的水包油乳液进行了研究。MPC70浓度保持在5%不变（接近脱脂牛奶中的蛋白质含量），油相体积分数在20%至65%之间变化。超声处理在20kHz、14.4W恒定功率下进行，乳液总体积为10mL。在一定的油浓度（≥35%）和超声处理时间（≥3s）下，乳液会聚集并形成高粘度假塑性材料。然而，如果超声处理时间更长（≥15s），含35%油的乳液的粘度行为会恢复为液体的粘度行为。共聚焦激光扫描显微镜清楚地显示，在上述超声处理条件和油浓度下，油滴会聚集。我们尝试通过一个基于MPC70颗粒桥接油滴的简单模型来解释这种行为，并考虑了油滴和MPC70颗粒的大小以及油相体积分数。该模型未能详细描述这些乳液的聚集行为，这可能是由于蛋白质层不均匀，其中游离酪蛋白和酪蛋白胶束都被吸附，以及在浓度≤55%时油滴的堆积。尽管如此，这项工作证明了超声处理在形成具有定制质地的乳制品乳液方面的潜力。
