A novel technique of ultrasound-assisted freeze-thaw pretreatment (UFP) was developed to improve the drying efficiency of maca and bioactive amide synthesis in maca. The optimal UFP conditions are ultrasonic processing 90 min at 30 °C with 6 freeze-thaw cycles. Samples with freeze-thaw pretreatment (FP), ultrasound pretreatment (UP), and UFP were prepared for further comparative study. A no pretreatment (NP) sample was included as a control. The results showed that UFP improved the drying efficiency of maca slices, showing the highest effective moisture diffusivity (1.75 × 10-9 m2 /s). This result was further supported by low-field nuclear magnetic resonance (LF-NMR) analysis and scanning electron microscopy (SEM). The rehydration capacity and protein content of maca slices were improved by UFP. More importantly, contents of bioactive macamides and their biosynthetic precursors were increased in 2.5- and 10-fold, respectively. In conclusion, UFP is an efficient technique to improve drying efficiency, physicochemical properties, and bioactive macamides of maca, which can be applied in the industrial manufacture of maca products.

中文翻译：

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采后超声辅助冻融预处理提高了玛卡 (Lepidium meyenii) 的干燥效率、理化性质和 Macamide 生物合成

开发了一种超声波辅助冻融预处理 (UFP) 新技术，以提高玛咖的干燥效率和玛咖中生物活性酰胺的合成。最佳 UFP 条件是在 30°C 下超声处理 90 分钟，并进行 6 次冻融循环。制备具有冻融预处理 (FP)、超声预处理 (UP) 和 UFP 的样品用于进一步的比较研究。无预处理 (NP) 样品作为对照。结果表明，UFP 提高了玛咖切片的干燥效率，表现出最高的有效水分扩散率（1.75×10-9 m2/s）。这一结果得到了低场核磁共振 (LF-NMR) 分析和扫描电子显微镜 (SEM) 的进一步支持。UFP提高了玛咖切片的复水能力和蛋白质含量。更重要的是，生物活性 macamides 及其生物合成前体的含量分别增加了 2.5 倍和 10 倍。综上所述，UFP 是一种提高玛咖干燥效率、理化性质和生物活性玛咖酰胺的有效技术，可用于玛咖产品的工业化生产。