Influence of olive processing on virgin olive oil quality

Abstract

Virgin olive oil quality depends on different factors such as olive cultivar, olive tree cultivation and the operations of olive picking, storage and processing. Many investigations concerning these factors were carried out and, in particular, the influence of technological operations of olive processing on oil yields and quality was examined. Leaf-removal and olive washing are important operations for the mechanical safety of the olive extracting equipment which operates at high speed and for the organoleptic quality of olive oil. The leaves mixed with olives may increase, in fact, the organoleptic attributes of 'fresh-cut' grass or 'green', especially if metallic crushers are used to prepare olive paste. Olive crushing has an important influence on organoleptic and nutritional qualities of virgin olive oil. When mill stones are used, the obtained oils have a lower intensity of bitterness and pungency because this crushing method helps to produce oil with a lower content of phenolic substances. When metallic crushers are used oils have, due to the violent action, a higher content of phenolic compounds and are more bitter and pungent. Olive paste malaxation influences the oil yields and also the antioxidant content of oil. With prolonged malaxation oil yields, generally, increase while the phenol content of oils decreases. When 'difficult' olive pastes are processed, it is possible to increase oil yields by using technological co-adjuvants such as talc and enzymatic products during the malaxation. The separation of oil from solid and liquid phases of olive paste is performed by using either pressure, percolation or centrifugation systems. All systems may provide good-quality oil if olive fruits are sound and at the correct ripeness, but the centrifugation system helps to avoid or reduce the risk of an organoleptic contamination. The new centrifugal decanters, operating without adding water (or only a minimal amount of water) to olive paste, save heat energy and the oils obtained are more fruity and have a higher content of natural phenolic antioxidants.