Quality of olives: A focus on agricultural preharvest factors

More than 11 million ha of olives (Olea europaea L.) are currently grown worldwide, 98% of which are localized in the Mediterranean Basin, with olives being one of the most important fruit trees in the area. The olive fruit is a very particular drupe since it not may be directly consumed but must instead be processed. Table olives and virgin olive oil are the two main processed products derived from olive fruits. Both are considered staple foods of the Mediterranean Diet and have been produced in the area for centuries, presumably since olive domestication occurred approximately 6.000 years ago. Despite their long history and economic importance, the focus on quality is quite recent. The presence of various and copious amounts of bioactive compounds, some of which are exclusive to olives, is drawing attention to the nutraceutical value of these products. This review aims to integrate the available information regarding the quality of table olives and olive oil with a focus on how preharvest factors may affect quality. The first part of the review describes the main quality attributes considered for each product from different perspectives, including the legal, organoleptic and nutritional points of view, among others. The physiological mechanisms involved in fruit development and ripening, which significantly affect the quality of the fruits, i.e., the raw material for obtaining both products, are also discussed. The review also addresses the potential of both the considerable number of traditional olive cultivars and recent olive breeding programs to obtain products with distinct quality attributes (in terms of sensorial profile and bioactive compounds). Finally, the most recent literature concerning the effect of environmental (soil and climate) and agronomical factors (irrigation, fertilization, canopy management and harvesting) is extensively reviewed.