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

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 1h) depletion of oleuropein and o-diphenols was estimated up to 90% and 77%, respectively. Results of Rancimat test (130°C and 20Lh-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. © 2013 Elsevier Ltd.