Determination of harvest time of Gemlik olive cultivars by using physical and chemical properties

Abstract

Olive fruits are subjected to various chemical and physical changes during maturation. Therefore, the total phenol content, radical scavenging activities, L*, a*, b* values, and color dex, detachment index, firmness, ripening index values were monitored during the ripening of Gemlik olive cultivars grown in Osmaniye. The ripening indices of the olives increased from 0.970 to 4.480 during the harvest period and firmness decreased from 4.463 to 1.341 N. Color values of L*, b* and color index decreased from 68.00 to 39.620, from 31.840 to -7.850, and from 36.590 to -5.332 respectively. The total phenol contents (mg GAE/kg) and RSA (%) reached to the highest level along with the b* value approaching 0. Gemlik olives had a total phenol content of 3330.8 mg GAE/kg and radical scavenging activity as 87.47% in the 4th harvesting period, and then, both values decreased. The moisture and oil content of olives increased during the ripening period, reached maximum values in the 6th harvesting period. The average weight of Gemlik olives changed from 2.871 to 4.564 g during the harvesting period. There were close relationships between color-ripening indices and color-detachment indices of olive cultivars. The sigmoidal model found significant relationship between color and detachment indices of Gemlik olive cultivars depending on the regression coefficients and RMSE (%). Color index value of -4.792 could be suggested as the threshold value of Gemlik olive cultivars for determining the harvesting time which could present a reliable, non-destructive and time-saving instrument to evaluate the optimal harvesting time.