The browning reaction needs the presence of oxygen, polyphenol
oxidases (PPO) and phenolic compounds and is generally
triggered by the enzymatic oxidation of monophenols into odiphenols
and quinones, which further undergo non-enzymatic
polymerization leading to the formation of pigments (Gao, Zhao,
Duan, & Tao, 2014; Pizzocaro, Torreggiani, & Gilardi, 1993).