Abstract
The overall quality of extra virgin olive oil (EVOO) strictly relates to the evolution of its oxidative state, which in turn depends on the amount of the oxygen availability during the product life, starting with the olive fruit milling. The issue of oil oxygenation during processing has been poorly studied. The few available literature assesses the relative contribution of three main processing steps (paste malaxation, decanter centrifugation, and vertical centrifugation) to the final dissolved oxygen concentration and the consequences on the oil quality decay during storage. Nevertheless, until now information about the contribution of the devices used to moves materials during processing, i.e. screw conveyor and pumps to move olive, olive paste and oil, to the amount of dissolved oxygen and in broader terms on the oil quality, are lacking. It can be reasonably assumed that the intact drupes handling during leaf-removal and washing before crushing, had a negligible effect on the final oil dissolved oxygen content, whereas from crusher to the decanter centrifuge by the malaxer, where olive paste handling occurs, a noticeable effect on the future oil characteristics could occur. The standard and widespread device used to move olive paste during processing, essentially from the crusher to the malaxer and from the malaxer to the decanter centrifuge, is the progressive cavity pump, commonly named mono-pump. Notices of other pumping devices used or proved in EVOO mills are missing. In the present work a peristaltic pump (roller pump) has been tested in comparison to the conventional mono-pump in a continuous centrifugal extraction plant. Specifically, the two pumps were alternatively used to feed the decanter centrifuge by empting the malaxation chambers. The oxygenation effect was assessed in terms of dissolved oxygen amount (DOA) in the produced EVOO, which were also compared for the main qualitative traits such as commercial parameters, phenolic and volatile profiles and phthalates occurrence being the peristaltic pump equipped with a phthalates-free tube. Basically, the qualitative effect of the two pumps significantly differs for the DOA with about 10% saving for the peristaltic pump. The latter also gives significantly (p<10%) higher concentration of trans-2-hexenal and lower concentration of trans-2-hexen-1-ol. Hence, it seems that the lower oxygenation effect reflects in a less advanced oxidative state of volatiles belonging to the LOX pathway. Finally, the peristaltic pump gives a quasi-significant reduction of phthalates, with mean values of about 15-45% lower than the mono-pump at p ranging from 24% to 36%. The lack of significance could rely in the presence of non- phthalates-free tube and piping in the processing devices other than the peristaltic pump.
