Inoculation of cv. Arbequina olives with fungi isolated from leaves and its effect on the extracted oils' stability and health-related composition

Abstract

Cv. Arbequina fruits were inoculated during one day with suspensions of Aureobasidium pullulans, Epicoccum nigrum or both species (104 spores/g olives), isolated from olive leaves, aiming to increase the phenolic content of the olive oils. Oils were extracted from non-inoculated (control) and inoculated olives, being evaluated for their oxidative stability, and phenolic composition. Compared to the control oils, those extracted from inoculated olives showed higher oxidative stability (+1629%), phenolic acids contents (up to+37%), phenolic alcohols (up to+101%), flavonoids (up to+154%) and secoiridoid derivatives (up to + 12%). These positive effects could be attributed to the hydrolytic activity of enzymes secreted by the studied fungi on the fruit cellular membranes and extracted phenolics, increasing the extractability and, consequently, altering the phenolic concentration. Considering the two fungi species, E. nigrum inoculation had a more significant positive impact on the contents of tyrosol, oleuropein, and ligstroside derivatives, showing an inhibition effect regarding the oleacein formation. Contrary, A. pullulans inoculation mainly resulted into an accentuated increase of luteolin and oleacein contents (3 and 12-times higher compared with control oils, respectively). Overall, no enhanced positive synergetic effect could be attributed to the inoculation with a suspension containing both fungi. The significant changes observed on the phenolic contents, due to the fungal inoculation, allowed the successful discrimination of the four types of extracted oils using an electronic tongue. This device acts as an artificial taste device allowing anticipating an impact at the oils basic taste sensations due to the fungi inoculation.