Short-term effects of a low dose of olive mill wastewater on pomological characteristics of olive fruits and on oil quality: Olive oil quality is negatively affected by OMW application

The present work was aimed at evaluating, under natural situations (field of olive trees, Olea europea cv Chemlali), the effects of one-year agronomic application of an olive mill wastewater (OMW) biologically derived compost. The experimental study was carried in 2014 in an olive orchard situated at Jammel (region of Monastir-Tunisia). An experimental plot (TM, 50 olive trees) was amended on February 2014 (the 'Off year) with 50 m3/ha. The plot TC (50 olive trees) was not amended and served as a control. After one year of OMW application, at harvest, olive fruits were collected and pomological characteristics were determined. Olive oil was extracted and biochemical parameters were studied. Statistical analyses showed that short-term field application of OMW affected negatively carpometric characteristics of olive fruits and oil content. Oil produced from TM had a decreased pigment content and oxidative stability. Moreover, the level of MUFA, particularly oleic acid, as well as C18:1/C18:2 and MUFA/PUFA ratios were negatively influenced by OMW amendment which affects negatively olive oil quality and nutritional value. These findings must be taken into consideration when developing strategies for oil quality enhancement, especially in an exporting country like Tunisia.