Electric field (EF) variables and electrode material are fundamental factors in ohmic heating (OH) processing. In this study, stainless steel, titanium and graphite were used as electrodes in conventional and OH (at 50 Hz and 20 kHz) treatments of whey protein isolate solutions at pH 3 and pH 7. The treated solutions were characterized in terms of UV absorbance, changes in intrinsic fluorescence, binding of a conformational probe and secondary structure (evaluated by circular dichroism). Differentiated structural features were induced by the different treatment conditions and were more evident at pH 7 and OH at 50 Hz. The metal leakage (quantified with ICP-MS) from the electrodes revealed to influence the equilibrium of early stages of protein aggregation, with stainless steel demonstrating to be the most electro-active material followed by titanium and finally graphite (that did not release metal). These findings highlight that structural properties of whey proteins may not only be influenced by the EF action but also by the leakage of metals from the electrodes.

Industrial relevance

OH is a recognized emerging processing technology and has a recognized potential to control and enhance protein functionality due its ability to influence protein structural features. Both electrode stability and protein structural changes are related with the EF operational parameters such as voltage, current or frequency. These parameters are decisive in the occurrence and extension of electrochemical phenomena and in the EF action mechanisms over protein structure. The confirmation of EF non-thermal effects at high and low frequencies (independently of the electrochemical phenomena) dissipated previous doubts regarding its effectiveness to modulate protein functionality. The understanding of the electrode material stability and influence of different electric parameters on the product's functionality, stability and safety are fundamental to design OH devices and to the establishment of operational protocols. The stability and material release from the electrodes is a fundamental factor during OH processing, imposing serious implications in equipment costs, maintenance, as well as in product quality and safety. This study highlights the influence of different electrode materials during OH at different electrical frequencies and its impacts on protein structural aspects.

中文翻译：

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揭示乳清蛋白结构方面欧姆加热效应的本质——电和电化学效应的影响

电场 (EF) 变量和电极材料是欧姆加热 (OH) 处理中的基本因素。在这项研究中，不锈钢、钛​​和石墨被用作在 pH 3 和 pH 7 的乳清蛋白分离物溶液的常规和 OH（50 Hz 和 20 kHz）处理中的电极。内在荧光的变化、构象探针的结合和二级结构（通过圆二色性评估）。不同的处理条件诱导了差异化的结构特征，并且在 pH 7 和 OH 50 Hz 时更加明显。来自电极的金属泄漏（用 ICP-MS 量化）显示影响蛋白质聚集早期阶段的平衡，不锈钢被证明是最具电活性的材料，其次是钛，最后是石墨（不释放金属）。这些发现强调，乳清蛋白的结构特性可能不仅受 EF 作用的影响，而且还受电极金属泄漏的影响。

工业相关性

OH 是一种公认​​的新兴加工技术，由于其影响蛋白质结构特征的能力，因此具有控制和增强蛋白质功能的公认潜力。电极稳定性和蛋白质结构变化都与电压、电流或频率等 EF 操作参数有关。这些参数对电化学现象的发生和扩展以及对蛋白质结构的 EF 作用机制具有决定性作用。EF 非热效应在高频和低频（独立于电化学现象）的确认消除了之前对其调节蛋白质功能有效性的怀疑。了解电极材料的稳定性以及不同电参数对产品功能的影响，稳定性和安全性是设计 OH 设备和建立操作协议的基础。电极的稳定性和材料释放是 OH 处理过程中的一个基本因素，对设备成本、维护以及产品质量和安全产生严重影响。这项研究强调了不同电极材料在不同电频率下 OH 期间的影响及其对蛋白质结构方面的影响。