Temperature or Ethylene Regulate Browning in Lotus Root by Modulating Polyphenols and Starch Metabolism

Browning is the major physiological cause of quality loss in lotus root. This study explored the effects of temperature (4 °C, 25 °C, 35 °C) or ethylene (ET) on quality, especially browning, as well as polyphenol and starch metabolism in lotus root. Low temperature (4 °C) reduced browning and color changes (L*, a*), while retaining water and vitamin C (Vc) content. ET maintained Vc and soluble protein, while high temperature (35 °C) promoted total soluble solids (TSS) and soluble sugar accumulation. ET or 35 °C upregulated polyphenol metabolism-related genes including NnPAL1/4, NnCHS1, NnF3H and NnANR, increased total phenolic and flavonoid content, and enhanced antioxidant capacity. Moreover, 35 °C increased PAL activity, and ET also upregulated NnUGT88B1. Furthermore, 4 °C downregulated NnGBE1-1/2, promoted starch accumulation, while ET upregulated NnSSI, downregulated NnGBE1-1/2, and delayed starch decline. Meanwhile, ET elevated NnETR and NnEBF1-2 and mediated ethylene signaling transduction. In conclusion, 4 °C storage was optimal for delaying browning and starch metabolism of lotus root. Meanwhile, ET treatment or 35 °C were more beneficial to obtain more phenolics and flavonoids.