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The qualitative effects of vertical centrifugation (VC), i.e., the last step of the extra virgin olive oil (EVOO) extraction process, were investigated on an industrial scale by sampling EVOOs before and after VC. Several parameters were determined to evaluate EVOO quality. Vertical centrifugation results in a marked loss of volatile aromatic compounds, whereas only a slightly variation was recorded in the hydrophilic phenols concentration.

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Influence of the extraction process on dissolved oxygen in olive oilThe influence of the olive oil processing steps [paste malaxation (PM), decanter centrifugation (DC), and vertical centrifugation (VC)] on the dissolved oxygen (DO) concentration in virgin olive oil (VOO) right after production was investigated at industrial plant scale for two successive years. The influence of this parameter on quality decay during shelf life, assessed by peroxide value (PV) analysis, was also monitored. The VC step showed the higher oxygenation effect (50% increase in comparison to the control), and a good linear regression (r 2 = 0.83) was found between the initial DO concentration and the PV after 2 days. An 18-months shelf life test, performed on VOO sampled before and after the VC, indicated the slowest decay kinetics in the oils with the lower initial DO concentration, i.e. the non-centrifuged oils.

The relationship between olive paste malaxation temperature and the concentration of olive oil hydrophilic phenols (HP), i.e. simple phenols, secoiridoids and lignans, was investigated. Malaxation experiments were performed at laboratory scale for 45 min at 21, 24, 27, 30, 33 and 36 7C. A significant (p ,0.05) increment of total phenols concentration was found with a maximum at 27 7C, whereas for higher temperatures (30-36 7C) a progressive decrement was observed. A similar pattern was recorded approximately for all the secoiridoid compounds, i.e. a quasi-linear increment of concentrations with increasing temperature until 30 7C, followed by a marked decrease in correspondence with the higher malaxation temperature (33 and 36 7C). The amount of simple phenols increased linearly with increasing temperature and no decrements were observed up to the maximal temperature investigated (36 7C), while no significant differences were found for lignans. A small increment of peroxide values and total chlorophyll was recorded as a function of the increasing malaxation temperature, whereas no differences were observed in the free acidity. The results highlight that there is not a univocal relationship between HP concentration and malaxation temperature. An equilibrium between degradation (chemical and biochemical oxidation and hydrolysis) and transfer (partitioning) phenomena was hypothesized.