[5] Common foods producing the enzyme include mushrooms (Agaricus bisporus),[6][7] apples (Malus domestica),[8][9] avocados (Persea americana), banana (Musa (genus)),[10] and lettuce (Lactuca sativa).
[11] Fruits high in flavan-3-ols, but low in PPOs (notably berries) are commonly combined with banana in smoothies, resulting in reduced bioavailability of flavan-3-ols and other polyphenols.
The substrate preference of tyrosinases and catechol oxidases is controlled by the amino acids around the two copper ions in the active site.
[24] The most common UV/Vis spectrophotometry assay involves the monitoring of the formation of o-quinones, which are the products of polyphenol oxidase-catalysed reactions, or the consumption of the substrate.
[32] PPO has importance to the food industry because it catalyzes enzymatic browning when tissue is damaged from bruising, compression or indentations, making the produce less marketable and causing economic loss.
[32] Examples in which the browning reaction catalyzed by PPO may be desirable include avocados, prunes, sultana grapes, black tea, and green coffee beans.
[citation needed] Catechol oxidase-type PPO is located in the chloroplasts of mango skin cells and its phenolic substrates in the vacuoles.
[36] Due to an increase in consumer demand for pre-prepared fruits and vegetables, a solution for enzymatic browning has been a targeted area of research and new product development.
[40] Ascorbic acid/protease combinations constitute a promising practical anti-browning method as treated apricot purees preserved their color.
[citation needed] Damage in the skin tissue of potato tuber causes a disruption of cell compartmentation, resulting in browning.
The brown or black pigments are produced from the reaction of PPO quinone products with amino acid groups in the tuber.
[42][43] A monomeric catechol oxidase from Populus nigra converts caffeic acid to quinone and melanine at injured cells.
[46] Hemocyanin is homologous to the phenol oxidases (e.g. tyrosinase) since both enzymes sharing type copper active site coordination.