Influence of Different Centrifugal Extraction Systems on Antioxidant Content and Stability of Virgin Olive Oil

In the 1970s and 1980s, olive processing using the continuous centrifugation system, called a three-phase system, expanded to many countries of the Mediterranean area. The success of this system is due to the high working capacity and automation of the industrial plants leading to a reduction of manual labor and olive-processing costs ( Kapellakis et al., 2008 ). This system is called three-phase because the centrifugal decanter allows for the separation of three flows of matter; the olive oil, pomace (solid remains of olive) and vegetable waste water. However, this process requires lukewarm water to be added to dilute the olive paste. This causes the reduction of natural antioxidants in the oil and a considerable volume of vegetable waste water (80 – 100 L/100 kg of olives). At the beginning of the 1990s, olive oil plant manufacturers launched new models of decanters in the market. These were able to separate the oily phase from the olive paste without requiring the addition of lukewarm water and without producing vegetable waste water. These decanters have two exits producing oil and pomace only, and for this reason are called ‘ two-phase decanters ’ . They produce a very wet pomace, with water content between 65 and 70% by weight. However , the centrifugal three-phase decanters were improved to be able to separate oil employing only a small quantity of warm water (0 – 20 L/100 kg of olives) to dilute the olive paste. These decanters have the ability to separate a small volume of vegetable waste water (5 – 25 L/100 kg of olives) and a less wet pomace, with a water content between 55 and 60%. These decanters are called ‘ ARA ’ (Italian acronym meaning ‘ water saving decanter ’ ). The final manufacturing innovation regarding the de - canter centrifuges is called ‘ third generation ’ . They have an innovative design, which ensures greater strength and reliability due to a longer cylindrical part of the bowl and a shorter beach section, and a special bowl with a variable dynamic pressure (VDP) cone system. The VDP cone decanters allow for the adjustment of the process parameters for optimum extraction yield. This innovation makes the machine extremely flexible in order to adapt to the heterogenic rheological characteristics of the raw material. The different centrifugal decanters employed in olive processing influence oil yields, qualitative characteristics such as total phenols and induction time values, and composition of volatile compounds such as aldehydes, alcohols, esters, hydrocarbons, ketones, furans, and other compounds that are responsible for the unique and delicate flavor of olive oil ( Di Giovacchino et al., 2001 ). Total phenols as well as induction time values are higher in oils obtained by the centrifugal decanter of two-phases. The induction time is the length of time before the rate of lipid oxidation of an oil sample rapidly accelerates ( Pike, 1998 ). The induction time of olive oil samples, as measured by the Rancimat instrument, showed a significant correlation to the concentration of total phenolic compounds ( Baldioli et al., 1996 ). Dual-phase decanters work on the same principle as the three-phase decanters, except little or no water is added prior to centrifugation. This allows the retention of more polyphenols and volatiles ( Di Giovacchino et al., 2001 ). The ‘ third-generation ’ three-phase decanters allow for the improvement of oil yields without compromising the quality of the product. This is the best solution with respect to the two-phase decanters because it is possible to extract the oil without adding water to the process, thus obtaining dry pomace, which is more easily transportable and workable.