Postharvest Ultrasound‐Assisted Freeze‐Thaw Pretreatment Improves the Drying Efficiency, Physicochemical Properties, and Macamide Biosynthesis of Maca (Lepidium meyenii)

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.