An amino acid of towel gourd will accelerate oxidation at high temperature, denature and cause blackening.

To avoid blackening, you should cook it quickly or heat it by isolating oxygen (making soup, water will isolate oxygen), because the starch content in loofah is relatively high, and it will react with oxidation after contacting with air. If you want to eat it fresh, it will still be oxidized and denatured for a long time, resulting in blackening.