Olive oil filtration is a critical process that takes place before the bottling stage of extra virgin and virgin olive oil. The unfiltered extra virgin and virgin olive oils, which are received after centrifugation from the olive mills, contain significant amounts of suspended solid particles, moisture and “margarines”, which are white and solid “margarinoid” masses, formed in olive oils at low temperatures and derive from wax complexes with triglycerides. These compounds can affect the chemical and sensory characteristics of olive oil and therefore can lead to quality degradation.
The filtration process under investigation includes two different sequential stages. The first one aims at the retention of solid impurities and margarines with the operation of a leaf filtering type device, based on the formation of a precoating filtering material (diatomaceous earth) to retain particles, while allowing the lipid phase to pass through. The second one includes the leaf filtered olive oil supply on a filter press and aims at the retention of a percentage of moisture content. Chemical parameters of unfiltered and filtered specimens of extra virgin olive oils, such as the acidity expressed as oleic acid (FFA%), the peroxide value expressed as meqO2/ kg (PV) and the K232 and K270 indices, which are associated with primary and secondary oxidation, the moisture and the solid content (% w/w), the concentration of chlorophyll (ppm) and carotenoids (ppm) and the lipid profile (C16:0 – C22:0), were quantified. The concentration of waxes and sterols (in ppm) of the unfiltered specimens were also taken into consideration. The K232, K270 and PV value increase is related to inlet pressure increase during filtration and the moisture content decrease, after both filtration stages, is up to 61,5%. The chlorophyll and carotenoid concentration of most specimens is up to 15,7% decrease. All the above chemical parameters were also statistically correlated with operational parameters of the filtration process, such as the quantity of the filtering material (kg), the operational time (min), the filtration performance (%) and the manometric inlet pressure (bar).