Effects of polyphenol enzymatic-oxidation on the oxidative stability of virgin olive oil

•Enzymatic phenol oxidation may occur in virgin olive oil in contact with vegetables.•Laccase oxidation of polyphenols within the virgin olive oil (VOO) was studied.•Laccase led to a significant reduction of oleuropein and o-diphenols fraction.•Controversial results were found during the accelerated oil oxidation trials.•Enzymatic phenol oxidation into VOO may be exploited also for analytical purposes.

Activity of laccase from Trametes versicolor was assayed directly in virgin olive oil (VOO) samples. Laccase-treated oils led to the formation of insoluble precipitate and to significant qualitative and quantitative changes of their polyphenol composition. At the extreme condition of oil/laccase incubation (60 °C for 1 h) depletion of oleuropein and o-diphenols was estimated up to 90% and 77%, respectively. Results of Rancimat test (130 °C and 20 L h− 1) and oven-test (60 °C) evidenced controversial effects on the VOO oxidative stability. At high temperature, induction time of laccase-treated oils was found to be similar or even lower than the one recorded in the chemically-dephenolized oils; therefore, enzyme treatment induced a pro-oxidant effect. Conversely, during the storage at 60 °C, all the laccase-treated oils showed an improvement on their oxidative stability compared to the fresh oil counterparts. Experimental data suggest that polyphenol enzymatic-oxidation generated oil by-products which manifest higher radical scavenging or conversely pro-oxidant property, depending on the treatment temperature and storage conditions of the oils.