Different processing parameters affect antioxidant properties and shelf life of ‘Oblica’ virgin olive oils

Extra virgin olive oil is obtained by mechanical processing of olive fruits at temperature up to 27 ºC in each processing step, as a guarantee of the highest oil quality. With prolonged malaxation time the oil yield can increase, but the quality of obtained oil is usually lower. In this paper the influence of different processing conditions (temperature and malaxation time) in monovarietal olive oils from 'Oblica' has been studied, in order to determine better overall quality, antioxidant characteristics and longer shelf life. Different malaxation temperatures (26, 36, 46 ºC) were applied during olive processing on laboratory scale using Abencor mc2 system. For each temperature, the influence of several malaxation times were also examined (30, 45, 60 min). The analyses of free fatty acid, peroxide value, UV spectrophotometric indices was perforemd according to official EEC methods (2568/91). Total phenols content (TPC) was determined using the Folin–Ciocalteau method (Gutfinger, 1981). The sensory evaluation of olive oils was performed according IOC (2007) method. Oxidative stability was measured using Rancimat apparatus while antioxidant activity was detected using DPPH antioxidant assay following the method described by Kalantzakis et al. (2006). Both oxidative stability and antioxidant activity was carried out in fresh oils and during 12 months of oil storage in dark place at the room temperature. Prolonged malaxation had the strongest influence on K-numbers, especially at the temperature of 46 ºC so oils obtained under this conditions were in the category of lampante non-edible oils. Strangely and unexpected, these same oils had very high TPC. The best overall quality was detected in oils obtained 26oC and during shortest malaxation time (30 min.). Same oils had the highest TPC and the best oxidative stability. Sensory analyses of investigated oils showed the highest score for oils processed at 26 ºC and 36 ºC and 30 min of malaxation. The fastest degradation of overall quality was noticed in oils produced at 46 oC i 45 min of malaxation.