Impact of water regimes on the chemical composition, antioxidant activity and quality of olive oil (Olea europaea L.) under semi-arid conditions in Tunisia

Abstract

Water scarcity is the main challenge in irregular olive oil production in Tunisia. In olive orchards the use of deficit irrigation technique is the main method to optimize water saving and achieve sustainable olive production. The aim of this study was to assess four levels of drip irrigation (100% ETc, 60% ETc, 50% ETc and 40% ETc (evapotranspiration)) on ‘Chemlali’ and ‘Koroneiki’ olive oil varieties, in semi-arid conditions, for two consecutive crop years. The quality parameters, antioxidant compounds, and antioxidant properties against DPPH and ABTS cation radicals of oils, were evaluated. Moreover, the fatty acid composition of ‘Chemlali’ and ‘Koroneiki’ oils was determined through gas chromatographic analysis. The result showed that irrigation regimes had a moderate effect on the standard quality parameters (free fatty acids, peroxide value, K232 and K270) of virgin olive oil as well as on the composition of the fatty acids. The oil obtained from trees treated with 50% ETc irrigation strategy was characterized by a high content of oleic acid (approximately 61% for ‘Chemlali’ and 78% for ‘Koroneiki’), a low level of palmitic acid, a high content of phenolic compounds (217.44 and 198.99 mg of eq catechin kg-1 of oil for ‘Chemlali’ and ‘Koroneiki’, respectively), O-diphenols, chlorophyll and carotenoids and high antioxidant properties for both olive cultivars. Therefore, this method is considered the best irrigation strategy to optimize water management and improve the quality, the antioxidant content and properties of oil.

Keywords

• antioxidant compounds
• fatty acids
• irrigation treatments
• olive oil
• quality parameters