Assessment of phenolic compounds in virgin olive oil by response surface methodology with particular focus on flavonoids and lignans

This work deals with the combined effect of agronomical and technological variables on the content of virgin olive oils in phenolic compounds with special attention to flavonoids (luteolin and apigenin) and lignans (pinoresinol and 1-acetoxypinoresinol). Olives from irrigated or rainfed trees at different fruit ripening were studied using Response Surface Methodology. Relevant variables included malaxation temperature (20-60 °C); time (20-60 min); and talc dosage (5-25 g/kg g olives). According to the models, the highest concentrations were 7.83, 289.4, 38.0 and 4.70 mg/kg of hydroxytyrosol, oleocanthal, luteolin and pinoresinol, respectively. Results show that the content of phenolic compounds is mostly affected by the malaxation temperature, increasing when the temperature rises; however, the time exerts an irregular influence, while the dosage of adjuvant has little influence. The flavonoid content, both luteolin and apigenin, decreased with increasing temperature and malaxation time. The pinoresinol content increased with temperature and malaxation time. Non-irrigated olive oils have a higher content in phenolic compounds. The flavonoid contents presented a maximum around maturity index 4. Moreover, the contents usually were higher for olives coming from rainfed. Pinoresinol content decreased with the increase of the index of maturity, the oils from fruits grown in rainfed containing more pinoresinol.