Polyphenol oxidase and enzymatic browning in apricot (Prunus armeniaca L.): Effect on phenolic composition and deduction of main substrates

In this study, we investigate the effect of enzymatic browning on the phenolic composition of apricot in vivo and in vitro. The in vitro browning was caused by the recombinant latent apricot polyphenol oxidase (L-PaPPO). Successful heterologous expression of PaPPO in Escherichia coli yielded substantial amounts of enzyme containing both copper ions in the catalytic active site. The expressed L-PaPPO was characterized with regard to its molecular mass (56531.3 Da), pH optimum (7.0), activation by SDS, and enzyme kinetics. LC-MS/MS was used to compare the phenolic profiles of brown and non-brown apricots. The browning reactions did significantly decrease total phenolics and antioxidant capacity (measured with DPPH and CUPRAC assays). Catechin, epicatechin, and B-type procyanidins were the individual phenolics most affected by browning, followed by chlorogenic and neochlorogenic acid. These phenolics are most likely the main endogenous substrates of L-PaPPO, as they were oxidized much faster than the other identified phenolics. [Display omitted] •Enzymatic browning greatly reduces the amount of phenols in apricots.•This decrease in phenols causes a marked reduction of the antioxidant capacity.•Apricot phenols do not contribute evenly to enzymatic browning.•Catechins and (neo)chlorogenic acids are the main endogenous substrates of PaPPO.