基于电流体动力学的马铃薯切片干燥特性变化

    Drying characteristics of potato slices via electrohydrodynamics

    • 摘要: 电流体动力学干燥作为一种新型干燥技术,以成本低、干燥均匀、高效节能等优势,为热敏性物料的干燥提供了新的方法。为探究电流体动力学作用下马铃薯切片的干燥特性和理化特征,该研究将马铃薯切片在0、14、18、22、26 、30 kV的交流电压下进行干燥,利用红外光谱和低场核磁共振技术分析电流体动力学干燥对马铃薯切片中分子结构、水分迁移的影响。结果表明,马铃薯切片在30 kV电压下的平均干燥速率、有效水分扩散系数、复水比分别为0.9228 g/(g·h)、2.2653×10−10 m2/s、4.78,明显优于其他电压下的试验结果。电流体动力学干燥后,马铃薯切片中的官能团没有发生明显变化,蛋白质以β-折叠结构为主。干燥可提高马铃薯切片内部自由水的流动性并降低组织对不易流动水的束缚力,从而促进水分的去除和迁移。电流体动力学干燥技术较好地保留了马铃薯的营养成分,该研究结果为马铃薯切片的干燥提供理论依据。

       

      Abstract: Potato has been one of the most favorite foods with the largest production and consumption in China. However, the potato tuber with high water content can easily germinate difficult to store, leading to a serious waste of resources. Drying can be used to effectively reduce the moisture content of potatoes, and then extend the storage period for the added value. The main drying methods are hot air drying, microwave vacuum drying, freeze drying, and infrared radiation drying at present. There is also some negative impact on the color, shrinkage, and nutrient content of dried products. The existing drying has one or more defects, such as equipment, energy consumption and quality. It is necessary to explore new drying technology. Electrohydrodynamic (EHD) drying without heat can be suitable for heat-sensitive food and biological products, due to the energy saving, low cost of equipment manufacturing, simple operation, rapid control of airflow speed, and sterilization. There was also excellent retention of the color, nutrient composition and shape of the material. However, it is still lacking on systematic studies on the drying and physicochemical characteristics of potatoes using EHD drying. In this study, the potatoes were dried by electrohydrodynamic drying. A systematic measurement was then carried out of the moisture content, drying rate, Rehydration ratio and effective moisture diffusion coefficient of potatoes under different drying voltages. The effects of electrohydrodynamic drying on the molecular structure, chemical composition and water transport of potatoes were also investigated by infrared spectroscopy and low-field nuclear magnetic resonance. Corona discharge was generated by a high-voltage electric field during drying. The voltage and current waveforms were plotted to obtain the outstanding filamentary discharge in half of the cycle. The higher the voltage in a single cycle was, the higher the discharge frequency and current amplitude were. The uneven discharge promoted the discharge, and then inhibited the discharge around, indicating positive feedback. High-voltage electric field discharge produced N+, N2+, O2-, and OH- ions. A large number of neutral particles were mixed to blow away from the needle electrode, and then form the ionic wind. As such, the ionic wind was also attributed to the main mechanism of electrohydrodynamic drying. A falling-rate period was then found when the electrohydrodynamic drying was acted mainly on the surface of the potatoes. The drying rate increased with the increase of voltage, whereas, the increment gradually decreased. Electrohydrodynamic drying significantly increased the effective moisture diffusion coefficient and Rehydration ratio of potatoes. The highest average drying rate, effective moisture diffusion coefficient and rehydration ratio were 0.922 8 g/(g·h), 2.265 3×10-10 m2/s, and 4.78 at 30 kV voltage. There were generally similar positions of characteristic peaks in the infrared spectra under different drying voltages. The characteristic peak intensity at 22 kV was the largest. Potato protein was dominated by β-sheet structure. The β-sheet structure shared an increasing trend with the increase in voltage. Thus, electrohydrodynamics led to the transformation of the protein's secondary structure from the order to the disorder. The internal structure of the potato was destroyed to reduce the binding force of less mobile water, particularly for the improved fluidity of free water. The migration and removal of three kinds of water were promoted in the potato, resulting in a decrease in water content. Infrared spectroscopy analysis showed that there was no significant change in the functional groups after drying. The finding can also provide the experimental and theoretical reference for electrohydrodynamic drying in potato processing.

       

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