Analytical Methods Effects of malaxation temperature and harvest time on the chemical characteristics of olive oils Olusola Samuel Jolayemi, Figen Tokatli ⇑ , Banu Ozen Izmir Institute of Technology, Department of Food Engineering, 35430 Urla-Izmir, Turkey article info Article history: Received 12 February 2016 Received in revised form 14 May 2016 Accepted 20 May 2016 Available online 20 May 2016 Keywords: Olive oil composition Malaxation temperature Harvest time Phenolic profile Fatty acid profile Oxidative stability Classification Multivariate regression abstract The aim of the study was to determine the effects of harvest time and malaxation temperature on chem- ical composition of olive oils produced from economically important olive varieties with a full factorial experimental design. The oils of Ayvalik and Memecik olives were extracted in an industrial two-phase continuous system. The quality parameters, phenolic and fatty acid profiles were determined. Harvest time, olive variety and their interaction were the most significant factors. Malaxation temperature was significant for hydroxytyrosol, tyrosol, p-coumaric acid, pinoresinol and peroxide value. Early and mid- harvest oils had high hydroxytyrosol and tyrosol (maximum 20.7 mg/kg) and pigment concentrations (maximum chlorophyll and carotenoids as 4.6 mg/kg and 2.86 mg/kg, respectively). Late harvest oils were characterized with high peroxide values (9.2–25 meq O 2 /kg), stearic (2.4–3.1%) and linoleic acids (9.3–10.4%). Multivariate regression analysis showed that oxidative stability was affected positively by hydroxytyrosol, tyrosol and oleic acid and negatively by polyunsaturated fatty acids. Ó 2016 Elsevier Ltd. All rights reserved. 1. Introduction The quality of virgin olive oil is equally affected by every step of production: agronomical (state of olive grove and olive fruits), technological (extraction system and malaxation conditions), and environmental (temperature and light during storage of olive oil). Use of healthy olive fruits at the time of extraction is a necessity in the production of virgin olive oils having considerable degree of chemical, nutritional and sensory characteristics. High quality raw material must be followed by the right operational choices in the production stage. Even healthy olive fruits are affected by adverse extraction conditions and result in poor quality olive oil. Type of extraction system and temperature-time combination in the malaxer, where the olives are crushed to form the oil part out of paste, are therefore significant parameters to be adjusted. Milling operation may seem to be a simple mechanical crushing process; however, it involves the act of several enzymes of olive, which play role in the overall quality of the final product (Clodoveo, 2012; Fregapane & Salvador, 2013). A strategic choice of appropriate agronomical parameters and processing conditions of olive fruits determine the overall degree of acceptability of olive oils. The parameters to be adjusted are var- ious. There are studies about some of the factors to evaluate their effects on the quality of olive oil. In the study of Monteleone, Caporale, Carlucci, and Pagliarini (1998), the olive ripening stage and storage, malaxation time and temperature effects on the total phenol and oxidative stability of olive oils were evaluated. In one study, the effect of three different extraction systems, maturity of olives and kneading temperature on the sterol composition was reported (Koutsaftakis, Kotsifaki, & Stefanoudaki, 1999). Ben- David et al. (2010) investigated the effect of olive type, tempera- ture, time, talc addition and different irrigation systems for a labo- ratory scale mill and determined oil yield, total phenol content and free fatty acidity. In other studies, researchers especially looked for the effect of oxygen in the head-space of malaxer and processing temperature with different cultivars (Catania, Vallone, Farid, & De Pasquale, 2015; Servili, Selvaggini, Taticchi, Esposto, & Montedoro, 2003). Nutritionally, olive oil has chemical compounds, responsible for its comparatively higher quality values than other vegetable oils (Frankel, 2011). The presence of high percentage of monounsatu- rated oleic acid makes olive oil much less susceptible to oxidation and contributes to high stability and long shelf life. Olive oil polyphenols, the other factor for its unique characteristics, belong to different classes based on their molecular weights and struc- tures: phenolic acids, phenyl ethyl alcohols (hydroxytyrosol and tyrosol), flavonoids, lignans and secoiridoids are the most charac- terized among others. Lately, the claims related to the support of http://dx.doi.org/10.1016/j.foodchem.2016.05.134 0308-8146/Ó 2016 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail addresses: olusolajolaym@iyte.edu.tr (O.S. Jolayemi), figentokatli@iyte. edu.tr (F. Tokatli), banuozen@iyte.edu.tr (B. Ozen). Food Chemistry 211 (2016) 776–783 Contents lists available at ScienceDirect Food Chemistry journal homepage: www.elsevier.com/locate/foodchem