The effect of malaxation temperature on the virgin olive oil phenolic profile under laboratory-scale conditions

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 degrees C. A significant (P < 0.05) increment of total phenols concentration was found with a maximum at 27 degrees C, whereas for higher temperatures (30-36 degrees C) 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 degrees C, followed by a marked decrease in correspondence with the higher malaxation temperature (33 and 36 degrees C). The amount of simple phenols increased linearly with increasing temperature and no decrements were observed up to the maximal temperature investigated (36 degrees C), 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.