TY - JOUR T1 - Action of a Ring-Cleaving Enzyme in Preventing Oxidative Darkening of Juices JF - American Journal of Enology and Viticulture JO - Am J Enol Vitic. SP - 221 LP - 226 DO - 10.5344/ajev.1969.20.4.221 VL - 20 IS - 4 AU - S. H. Kelly AU - B. J. Finkle Y1 - 1969/01/01 UR - http://www.ajevonline.org/content/20/4/221.abstract N2 - Catechol type compounds such as chlorogenic acid are the natural substrates for polyphenol oxidase in fruit juices, and these compounds are converted by the enzyme to polymers that result in a dark juice. When apple juice, in the presence of ascorbate, was treated with the enzyme protocatechuate 3,4-dioxygenas, darkening was permanently prevented since the enzyme oxidatively cleaves the benzene ring of the substrates to yield branched chain derivatives of muconic acid. The muconic acid derivatives cannot participate in the polyphenol oxidase browning reaction. ER -