Browning of media causing drying of explants is mainly due to

Browning of media causing drying of explants is mainly due to Tannins.
The underlying cause of tissue browning is the accumulation and subsequent oxidation of phenolic compounds in the tissue and culture media.
Tannins (commonly referred to as tannic acid) are water-soluble polyphenols that are present in many plant foods. It is mostly responsible for the browning of media and drying of explants in culture.