Determination of the Most Suitable Time for Harvesting Olive (Olea europea L.) Fruits 'Yellow' and 'Arbequina' Cultivars Based on Physiologic Characteristics

IntroductionOlive (Olea europea L.) fruit ripening is a slow and long process and has a great impact on fruit quality, including the amount of oil. Also, interrupting the harvest and extraction of olive oil causes unfavorable conditions in this fruit. Therefore, it is important to determine the best time to harvest the fruit. Olive oil has unsaturated fatty acids and has an antioxidant activity. The analysis of maturation stages is a prerequisite for fruit harvest time in each cultivar and quality of olive products. The time of harvest and maintenance after harvest is two important factors in the quality and quality of olive fruit oil. The exact determination of olive harvest time depends on the geographical area, cultivar and climate, agronomic and fruiting conditions. Study on different olive cultivars in different regions of Iran and the world revealed that fruit harvest time plays an effective role on the morphological, physiological and metabolic parameters of fruit. The approximate time of olive fruit harvest is in different geographical points, November and October. The purpose of this study was to investigate the right time of olive fruit harvesting 'Arbequina' and 'Yellow' cultivars for obtaining maximum quality of fruit and oil. Materials and MethodsA factorial experiment containing two factors; cultivar in two levels ('Yellow' and 'Arbequina') and harvest time in six levels (24th and 31th October, and 7th, 14th, 21th and 28th November) based on a completely randomized block design with two factors in 12 treatments, 3 replicates and 36 experimental units was done to determine the appropriate harvest time and its effect on oil quality. Physiologic parameters; percentage of oil, amount of phenolic compounds, degree of peroxidation, amount of oleic acid, force of separation of fruit from tail and acidity were evaluated. This research was conducted at the olive research station in Rudbar city in southern Guilan province using the removed olives from the Manjil ETKA station. The 6 trees from two cultivars; 'Arbakkin' and 'Yellow' (from each 3 tree) which were similar in terms of height, age, crown diameter, mean conditions and irrigation were evaluated. Trees were planted at 6 × 8 m intervals. After selecting trees, from each tree, 2 to 3 kg of olive was randomly harvested. In fruits with tail, the force needed to separate the tail of the fruit was measured by the force assessment device. Standard method numbers 4178 and 4179 standard institutes and industrial research of Iran were used to measure acidity and olive oil peroxide, respectively. Polyphenols were measured with spectrophotometer. To determine the percentage of oil, saccule was used. For measurement of oleic acid, gas chromatography (GC) was used. Data were analyzed using SAS software and their average comparison was done by Duncan.   Results and Discussion Mean comparison of the interaction effect between cultivar and harvest time showed that the highest acidity of the fruit was obtained in 'Arbequina' cultivar, respectively harvested at two times 31th and 24th October. The highest fruit peroxide value and the highest percentage of oleic acid were calculated in 'Yellow' cultivar in 24th October. The highest value of polyphenol was obtained in 'Yellow' cultivar on 7th November. The highest percentage of fruit oil was obtained in 'Arbequina' cultivar on 31th October. The lowest force to separate the tail from the fruit was applied in 'Arbequina' cultivar on 31th October. The results showed that the best time to harvest 'Yellow' cultivar is 7th November and for 'Arbequina' cultivar is 14th November. The study on several olive cultivars in China showed that the most suitable fruit harvest time was in late October until mid-November. There was an adverse significant correlation between changes in total sugar content in fruit and leaf and oil accumulation in the fruit. The quality of fruit depends mainly to the type of cultivar, genetic characteristics, maturity and environmental conditions. Study on some olive cultivars showed that the ratio between sugars is different in various stages of fruit maturity and between different cultivars of olive fruit. Some studies have shown that the most suitable time of olive fruit harvest for canned preparation is early September and for extraction of oil, late September. Fruits should be harvested when they have the highest oil accumulation. The study on 'Koroneiki' and 'Mission' cultivars in Gorgan region showed that the amount of oil in the dry matter and the percentage of free fatty acids increased with increasing degree of maturity, while peroxide value was reduced. One of the causes of peroxide value reduction during maturity is reduction in lipoxygenase enzyme activity. This enzyme increases the peroxide value by effect on linolenic acid and linoleic acid. Based on these results, the best time to harvest for the above cultivars is early in December. ConclusionsHarvest time and proper storage after harvest are two important factors of olive oil quantity and quality. In both cultivars, a longer delay in harvesting compared to the mentioned-above dates increases the percentage of oil, but it has a negative effect on the reproductive stages of the next year, and perhaps one of the causes of olive aging is excessive delay in harvesting. It is important to pay attention to the above two items.