In this study, the combined effect of ultrasound (US) and pulsed electric field (PEF) techniques was analyzed for the quality improvement and microbial safety of spinach juice. The spinach juice was treated with US at frequency of 40 kHz, radiating power of 200 W below 30 ± 2 °C temperature for 21 min in ultrasonic bath cleaner, and PEF treatment (pulse frequency: 1 kHz, flow rate: 60 mL/min, temperature: 30 ± 2 °C, time: 335 µs, electric field strength 9 kV/cm) was done. In results, the combined (US-PEF) treatment attained the highest value of minerals and total free amino acids as compared to US or PEF treatment alone. US-PEF treatment significantly reduced the total plate count (3.83 to 1.97 log CFU/mL), E. coli/Coliform (1.90 to 0.75 log CFU/mL) and yeast and mold (4.23 to 2.22 log CFU/mL). Fourier-transform infrared spectroscopy (FT-IR) spectra showed that all nonthermal treatments led to a higher concentration of carbonyl compounds rather generate new carbonyl compounds. US-PEF treatment significantly reduced the particle size. The rheology of spinach juice was drastically changed by all nonthermal techniques, indicating non-Newtonian modal accompanied by a decrease of consistency index (K), apparent viscosity (η), and increase of flow behavior (n). Overall, the improved quality of spinach juice shows the suitability of both technologies for industrial applications despite the variations in rheological properties. PRACTICAL APPLICATION: Nowadays, nonthermal technologies like US and PEF are being used to enhance the nutritional quality and stability of different fruits and vegetable juices. The current research shows that US-PEF application can enhance the free amino acids and mineral contents while significantly decrease microbial activities and particle size. The rheology of spinach juice can be dramatically changed, through the reduction of consistency index (K), apparent viscosity (η) and elevation of flow behavior (n). The results of this research proposed that US-PEF treatment can be a more suitable nonthermal application to enhance the quality of spinach juice at an industrial scale.

中文翻译：

---

新加工技术和菠菜汁：质量和安全改进

本研究分析了超声 (US) 和脉冲电场 (PEF) 技术对菠菜汁质量改进和微生物安全性的综合影响。菠菜汁在超声浴清洁器中以 40 kHz 频率、200 W 辐射功率、200 W 辐射功率处理菠菜汁 21 分钟，PEF 处理（脉冲频率：1 kHz，流速：60 mL/min , 温度: 30 ± 2 °C, 时间: 335 µs, 电场强度 9 kV/cm) 完成。结果，与单独的 US 或 PEF 处理相比，联合 (US-PEF) 处理获得了最高的矿物质和总游离氨基酸值。US-PEF 处理显着降低了总菌落数（3.83 至 1.97 log CFU/mL）、大肠杆菌/大肠菌群（1.90 至 0.75 log CFU/mL）以及酵母和霉菌（4.23 至 2.22 log CFU/mL）。傅里叶变换红外光谱 (FT-IR) 光谱表明，所有非热处理都会导致更高浓度的羰基化合物，而不是生成新的羰基化合物。US-PEF 处理显着减小了粒径。所有非热技术都极大地改变了菠菜汁的流变性，表明非牛顿模态伴随着稠度指数 (K)、表观粘度 (η) 的降低和流动行为 (n) 的增加。总体而言，菠菜汁质量的提高表明，尽管流变特性存在差异，但这两种技术都适用于工业应用。实际应用：如今，US 和 PEF 等非热技术正被用于提高不同水果和蔬菜汁的营养质量和稳定性。目前的研究表明，US-PEF 应用可以提高游离氨基酸和矿物质含量，同时显着降低微生物活性和颗粒大小。通过降低稠度指数 (K)、表观粘度 (η) 和提高流动行为 (n)，菠菜汁的流变学可以发生显着变化。这项研究的结果表明，US-PEF 处理可以是一种更合适的非热应用，以在工业规模上提高菠菜汁的质量。