Effect of olive paste kneading process time on the overall quality of virgin olive oil

The influence of the olive paste malaxation time on the composition and the industrial output of oil was investigated. To this purpose, three Italian olive varieties (Leccino, Dritta, Caroleo) were processed with a centrifugal system for six malaxation periods (0, 15, 30, 45, 60 and 75 min). The concentrations of the majority of the oil constituents changed during the malaxation. However, these changes were not significant for all of them: the contents of beta-carotene, the major xanthophylls, chlorophylls a and b, pheophytins a and b in the oils increased progressively with increasing malaxing times, whereas the contents of simple and hydrolysable phenols (secoiridoid derivatives), o-diphenols and total phenols decreased. A significant increase in total volatiles and green volatiles of the lipoxygenase cascade (C-6 aldehydes, C-6 alcohols, C-5 alcohols and C-5 carbonyls) was detected. An opposite trend was observed for the green C-6 esters. As a result, the global analytical quality, flavour, aroma and shelf-life of the oils were negatively affected. The oil yield increased substantially up to 45 min of paste malaxation times. Beyond 60 min, the yields tended to decrease.