부산대학교 도서관

Polyphenol oxidase (PPO) is an enzyme and has a catalytic property for the oxidation of aromatic phenolic substances into quinones, which are recognized as highly reactive compounds. PPOs are considered as copper-containing class of enzymes (tyrosinase, catechol oxidase, and laccase) that have the ability to oxidize/catalyze O-hydroxylation of monophenols to O-diphenols with the involvement of oxygen. PPOs are broadly disseminated in lower organisms to higher mammals, including microbes (bacteria and fungi), animals, and plants. Damaged/injured tissues of fresh vegetables as well as fruits often become brown due to oxidation of phenolic substances and as a result considerably lose quality. The process of enzymatic browning is primarily attributed to the activity of PPO. Enzymatic browning is a significant concern for apples due to their high concentration of polyphenols, which makes them highly susceptible to discoloration. Nonetheless, extensive applications of PPOs were noticed in the medical field (pharmaceutical), cosmetic, environmental, as well as food industries. Several reports of PPOs were highly described in plants. It has been recognized that very less and scanty review reports were noticed on fungal and bacterial PPOs. Hence, this chapter focuses on PPOs from bacteria. Initially, this chapter discussed an overview of PPOs and the mechanism of phenol oxidation by the involvement of the same enzymes. Next, this chapter explored three PPOs (tyrosinase, catechol oxidase, and laccase) from bacteria. Finally, this chapter has given extensive reports on applications of bacterial PPOs such as laccase and tyrosinase enzymes in the bioremediation of a variety of xenobiotic compounds.