等离子体辅助玉米醇溶蛋白电诱导沉积成膜的工艺优化

天然玉米醇溶蛋白（Zein）具有良好成膜特性，但其在成膜过程中蛋白无序排列导致膜结构不稳定，限制了实际应用。该研究基于玉米醇溶蛋白的电荷特性，将玉米醇溶蛋白置于平行匀强电场下，诱导蛋白有序自组装排列并沉积成膜，且在诱导液中引入低温等离子体预处理以提高诱导效率。分别探究了玉米醇溶蛋白浓度、溶液pH值以及电流密度对蛋白沉积率的影响，并通过Box-Behnken优化试验获得了最佳沉积工艺为Zein浓度139.5 mg/mL，Zein溶液pH 值为8.17，电流密度14.3 A/m2，在优化条件下，玉米醇溶蛋白的沉积率可达1.120 mg/cm2，显著高于未经等离子体处理的沉积率0.483 mg/cm2，表明等离子体辅助可有效提高电诱导中玉米醇溶蛋白的沉积率。扫描电子显微镜图像显示采用等离子体辅助电诱导制备的沉积膜表面更平整、光滑。傅里叶红外光谱分析表明，电诱导可使玉米醇溶蛋白二级结构中β-转角和无规则卷曲结构向β-折叠及α-螺旋结构转化。研究结果为电诱导玉米醇溶蛋白成膜技术提供参考，有利于拓展低温等离子体在蛋白质领域的应用。

Optimization of the preparation of electric induced deposited zein film assisted by plasma pretreatment

Abstract: Zein is one of the most important food compositions as-Generally Recognized As Safe (GRAS). Wet milling was often used to extract the zein from the processing byproducts of corn starch. The current zein is widely applied as the low-value feed protein, due mainly to the low water solubility and the less essential amino acids. A high proportion of hydrophobic amino acids and abundant disulfide bonds can be expected to greatly contribute to the better film-forming property of zein. However, the practical application of zein can be confined to the disordered arrangement in the form of random strands in the aqueous ethanol solution, leading to the unstable structure of zein film. Fortunately, the uniform electric induction assisted with the cold plasma pretreatment can be applied to induce the zein micelles to be self-assembly deposited on the Indium Tin Oxide (ITO) glass substrate using the amphoteric dissociation. Smaller particle size and better electrochemical characteristics can be achieved for the zein film after the cold plasma pretreatment. The deposition efficiency of zein can also be improved during the electric induction process. In this study, an optimal preparation was proposed for the electric-induced deposited zein film that was assisted by plasma pretreatment. Specifically, the plasma pretreatment conditions were set to obtain the proper particle size of zein micelles, with the generation voltage of 65 V, the input current of (1.0±0.2) A, and the treatment duration of 3 min. The influence of electric induction parameters was studied under the treatment condition of the zein concentration (30, 50, 100, 125, and 15.0 mg/mL), pH values (6, 7, 8, 9, and 10), and electric current density (5, 7, 10, 15, and 20 A/m2). A Box-Behnken experiment was also carried out to optimize the largest deposition rate on the ITO glass substrate. The single factor experiment showed that the deposition rate of zein film increased with the increasing concentration and pH of zein solution. The optimal conditions were achieved as follows: the zein concentration of 139.5 mg/mL, the zein solution pH of 8.17, and the electric current density of 14.3 A/m2. The deposition rate of zein reached 1.120 mg/cm2 under the optimal conditions, which was significantly higher than the sample without the plasma pretreatment (0.483 mg/cm2). It infers that the plasma treatment effectively enhanced the deposition rate of zein during electric induction. Scanning Electron Microscope (SEM) images indicated that smoother and much more uniform surface morphology was achieved in the electric-induced deposited zein film that was assisted by plasma pretreatment, compared with the untreated. Energy Dispersive Spectrum (EDS) analysis showed the In or Si element was not found in the electric-induced deposited zein film with the plasma pretreatment. More importantly, there was a similar profile of Fourier Transform Infrared spectroscopy (FTIR) spectra between the induced and untreated films, indicating no remarkable influence of the electric-induced deposition on the main structure of zein. The secondary structure of the protein was also drawn from the peak analysis of the amide I region (1 600-1 700 cm-1). It was found that the β-turn and random coil were transformed into the much more ordered β-folding and α-helix structure. In conclusion, the finding can lay the theoretical foundations to fabricate the zein film using electric induction. The high-value utilization of zein can be expected in the development of cold plasma in the protein modification field. The microstructure of electric-induced deposited zein film can also be further modified for specific use in the subsequent investigation.