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Effect of storage time on olive oil quality
This work reports changes in the major quality parameters of Turkish extra virgin olive oils stored at room and refrigerator temperatures in dark and monitored for 14 months. Peroxide values, specific absorbance values, total phenol content, free fatty acidity, fatty acid and phenolic profiles of extracted (Erkence and Ayvalık-Edremit) and commercial extra virgin olive oil samples (Altınoluk, Ezine, Bayındır and Ortaklar) from South and North of the Aegean were determined. The acidity and K232 values of samples were within the acceptable limits, the peroxide and K270 values exceeded the limits after 7 and 9 months storage. Hydroxytyrosol, tyrosol, caffeic acid, vanillic acid, vanilin, p-coumaric acid, ferulic acid, m-coumaric acid, cinnamic acid, luteolin, and apigenin were determined as the major phenolics in Turkish extra virgin olive oils. The concentration of hydroxytyrosol and tyrosol increased, while a decrease was observed in the amounts of other phenolics during storage.The highly unsaturated flaxseed oil was mixed with olive oil at 5-15 % levels and stored at room and refrigerator temperature to examine the effect of olive oil on the oxidative stability of flaxseed oil. 15% olive oil addition to flaxseed oil increased its oxidative stability. Fourier Transform (FT-IR) spectral data were used to predict the oxidative quality parameters, total phenol content and the fatty acid compositions by partial least square analysis (PLS). FT-IR spectra of samples subjected to accelerated oxidation were examined to determine the bandwidths, which can be considered as the finger-prints of the oxidation phenomenon (2924, 2852, 1746-1743, 1163 and 967-976 cm-1).