The Effect of Harvest Time on Quality of Virgin olive Oils produced in Adana region of Turkey
Turkan Mutlu Keceli, Fatma Begum Gokkaya, Merve Degirmen, Muge Akmanlar,
Berra Nil Mercankaya, Onur Ozdemir, Sebnem Guler, Melek Gamze Kartal, Adalet Dishan, Feyza Ozturk, Gulbahar Alis
The University of Cukurova, Faculty of Agriculture., Department of Food Engineering 
Adana, Turkey

Harvesting plays a major role in the virgin olive oil production. Optimal harvesting time is the most important factor that determines the olive oil quality and quantity. Olive oil quality is influenced by a great number of factors including the cultivar and the fruit maturity stage the composition of fatty acids, and the levels of polyphenols, tocopherols, sterols and pigments change with maturation. The changes are reflected in the quality grade, sensory characteristics, oxidative stability and nutritional value of the product. Olive oils were collected from 3 different olive oil mills in Adana, Turkey in September and November at 2014. Peroxide value (16-33 meq O2/kg) acidity (5 and 7 % expressed as oleic acid), K232 (1,8 and 2,5) and K270 values (0,15 and 0,5) significantly increased. Oxidative stability was significantly reduced depending on harvest times (p≤0.05). Thiobarbutiric acid values increased from 0,6 to 1,5 malonaldehyde /kg oil. It was found that chlorophyll (6 and 3,5 mg/kg oil), karotenoid (4 and 2 mg/kg oil),  tocopherol (148-83 mg/kg) and  total phenol contents ( 970 to 400 mg/kg) and antioxidant activity (16 to 7 %) were significantly reduced as a result of differences of harvest time from September to November (p<0.05).  The colour values of the oils (L, a, and b) also changed depending on harvest time.  The oxidative stability was also evaluated at both 60 and 100 C by Schall oven test. The result showed that  depending on harvest time the oil becomes less stable due to an increase in polyunsaturated fatty acids and a decrease in total polyphenol and tocopherol content. These changes are of high commercial importance as they dramatically influence the sensory characteristics of the oil, as well as its shelf life. Oil yield is of prime economic importance to the grower and as such, should be considered together with the quality indices for harvest timing. 

Acknowledgement: This research has been financed by the project FYL-2014-2839 from the University of Cukurova (Adana,Turkey)