Influence of Time of Harvest on ‘Adana Topagi’, ‘Gemlik’ Olives, Olive Oil Properties and Oxidative Stability
Olives and olive oil containing minor components are Mediterranean foods and they are very important in diet. Harvest time plays a key role in the quality and oxidative stability of olive oil. Adana Topagi and Gemlik were harvested at three different times and the oils were obtained on a laboratory scale. The results showed that as the fruit matured, the oil became less stable due to decreasing total polyphenol content, increasing polyunsaturated (mainly linoleic acid), and decreasing chlorophyll content. While pomological properties of olive fruits and oil content increased total phenol, chlorophyll carotenoid content and antioxidant activity was decreased depending on harvest date for Adana Topagi and Gemlik olives (p < 0.05). The best radical scavenging properties were obtained from Gemlik olives and Adana Topagi extracted olive oils. There was a strong interaction between total polyphenol content and DPPH radical scavenging activity for Gemlik and Adana Topagi olives. Chlorophyl and caretenoid content of Gemlik extracted olive oils were higher than Adana Topagi extracted olive oils during ripening (p ≤ 0.05). Gemlik olives were found to be effective antioxidants on DPPH inhibition and oxidative stability of refined olive oils (p < 0.05). It was found that variety and harvest time has significant effect on both some physical, chemical properties and antioxidant activity of olives and their olive oils.
Keywords: Gemlik, Adana Topagi, DPPH, oxidation, olives, olive oil
Journal of Food and Nutrition Research, 2013 1 (4),
Received July 31, 2013; Revised September 09, 2013; Accepted September 12, 2013Copyright © 2013 Science and Education Publishing. All Rights Reserved.
Cite this article:
- Keceli, Turkan Mutlu. "Influence of Time of Harvest on ‘Adana Topagi’, ‘Gemlik’ Olives, Olive Oil Properties and Oxidative Stability." Journal of Food and Nutrition Research 1.4 (2013): 52-58.
- Keceli, T. M. (2013). Influence of Time of Harvest on ‘Adana Topagi’, ‘Gemlik’ Olives, Olive Oil Properties and Oxidative Stability. Journal of Food and Nutrition Research, 1(4), 52-58.
- Keceli, Turkan Mutlu. "Influence of Time of Harvest on ‘Adana Topagi’, ‘Gemlik’ Olives, Olive Oil Properties and Oxidative Stability." Journal of Food and Nutrition Research 1, no. 4 (2013): 52-58.
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Olive oil production and consumption is highly concentrated in the Mediterranean region. Turkey is one of the most important olive oil producing countries, coming after Spain, Italy, Greece and Tunisia . Although olive varieties have considerable amount of oil content throughout ripening period, growers do not have a clue when to harvest their olives fruit for high oil quality and quantity. The majority of olive oil produced (94%) is not of the best commercial quality, as the fruit has not been picked at the optimal harvest time. Time of harvesting may have a significant effect on oil quality as well as, yield, oil stability and sensory characteristics. Riper olive fruits are more susceptible to hydrolytic and oxidative deterioration, which produces bitter oil. However, olives harvested before or after fruits reach optimum weight and size suffer from a substantial loss in quantity and quality [2, Int J Food Prop 2008, 11, 561-570.">3]. Cultivars, environmental conditions, degree of fruit ripeness, processing, storage, fruit health, some pigments and phenols affect oxidative and hydrolytic rancidity . Virgin olive oil has a high resistance to oxidative deterioration due to both a triacylglycerol composition low in polyunsaturated fatty acids and a group of phenolic antioxidants composed mainly of polyphenols and tocopherols . However, the oil antioxidant content is not constant; it depends on the cultivar, fruit ripening stage, agroclimatic conditions and olive growing techniques. The detailed composition of olives and their corresponding olive oils dependent on the nature of the cultivar used for its production, show great importance due to their health benefits and effect on oil shelf life . Taking into account the importance of minor compounds in olive oil production there is a need to select cultivars with virgin olive oil of good quality characteristics . Although ‘Adana Topagi and Gemlik’ is a very important Turkish olive cultivar, few works have described on Gemlik olives [6, 7, 8] and its oil composition [1, 7, 9, 10, 11]. However, the effect of the ripening on some properties of olives and their corresponding olive oil has not been studied in detail. To our knowledge this is the first study about Adana Topagi olive cultivar and its corresponding olive oil. This study aims to evaluate the effect of harvest time on quality, radical scavenging activity and stability of Adana Topagi and Gemlik olives and their corresponding olive oils grown in southeast of Turkey.
2. Materials and Methods2.1. Materials
This investigation was carried out at Olive Gene Collection of the University of Cukurova, Turkey. The trees were spaced 7mX7 m; trickle irrigated and received routine horticultural care (standard pest, disease, fertilizer & irrigation programs). Representative olive trees of own rooted cvv Gemlik and Adana Topagi (extensively grown in Adana) were used in this research. Olive fruits were handpicked at three different harvest dates between the 20th August (1st harvest), the 19th October (2nd harvest), 19th November 2004 (3rd harvest). About 2 kg of olive drupes were collected from each cultivar at each harvesting date. All samples were stored at 4°C in darkness using plastic bags prior to analysis. Solvents were supplied by Sigma and Merck (Adana, Turkey). Folin-Ciocalteu reagent, 2,2-diphenyl-1-picrylhydrazyl free radical (DPPH), FAME’s standards were obtained from Sigma-Aldrich (Turkey). Refined olive oil purchased from a local market in Adana.2.2. Methods
2.2.1. Some Properties of Olives
Width and length was measured by using a caliper of 50 olive fruits and their pits. The fruit moisture was determined by weighing olives after drying in a chamber at 105°C according to method described by Lazzez et al. . For oil content determination, 30g of fruit samples were dried in an oven at 72°C to constant weight. The dry olives were extracted with petroleum ether using a Soxhlet apparatus . The results are expressed as percentage of the total olives [14, 15, 16].
2.2.2. Some Properties of Extracted Olive Oils
Free fatty acid (FFA), peroxide value (PV) and the IV of the oils was determined by AOCS Method Ca 5-40, Cd 8-53 and Cd 1-25 methods described in the American Oil Chemist’s Society recommendations . Each extracted olive oil sample (7.5 g) was dissolved in cyclohexane (25 mL) chlorophyll and carotenoid content of extracted olive oils were calculated from the absorption spectra following the method described by Allalout et al. . Base-catalyzed transesterification method was used  to analyze fatty acid methyl esters (FAMES). The FAMES mixture (1 μl) was injected on a Schimadzu 14 B Gas Chromatograph using a fused silica capillary column (DB 23; 60m x 0.25 mm i.d, Chrompack UK, Ltd). C. 17:0 was used as an internal standard. A mixed fatty acid standard containing 16:0, 16:1, 18:1 and 18:2 was also analyzed. Column temperature was set at 240°C and injector and detector temperatures were 250°C. The FAMES were identified by their retention times and the fatty acid composition of the extracted olive oils were determined.
2.2.3. Total Phenol Content and DPPH Radical Scavenging Activity (RSA) of Olives and Olive Oil
The extraction phenolic compounds from olives were performed according to the modified methods presented by Fernandez-Orozco et al. . 10 g of freeze-dried olive pulp with ethanol/water (80:20,v/v) containing 2% Nametabisulphite. Afterwards, it was treated with hexane to remove pigments and lipids. The extraction phenolic compounds from olive oils were done according to method proposed by Murkovic et al. . The total polyphenol content of the olives and olive oils were determined by a subsequent reaction with Folin-Ciocalteau reagent proposed by Gutfinger  with 0.5 ml of phenolic extract of olive (diluted 1:25, v/v with distilled water) or olive oil and mixture was incubated for 90 min in dark at RT. The phenol content was determined at 725 nm and the concentration was expressed as mg of caffeic acid equivalents per kg of olives or olive oil [12, 23]. The radical-scavenging activity (RSA) of olives and olive oil was evaluated by the DPPH assay. The RSA was measured, following the method of Brand-Williams et al. . Briefly, an aliquot 100 µl of methanol extract from the studied olives or olive oil (3.6 x 10-4 mol/L) was added to 2.9 ml of DPPH solution (6 x 10-5 mol/L in methanol) and the mixture was left in the dark at RT for 30 min. The absorbance of the mixture was measured at 515 nm against a blank solution. Triplicate measurements were made and RSA was expressed as inhibition percentage [14, 20].
2.2.4. Oxidative Stability of Refined Olive Oil Enriched with Olive Extracts
Duplicate samples of refined olive oil (20g) without (control) or with olive extracts or BHT at a level of 100 ppm stored in beakers covered by aluminum foil and stored in an oven at 60C to measure oxidative stability by using Schaal Oven Test method. Aliquots of each sample was removed periodically for Cd-8-53 peroxide value (PV), according to AOCS Official Methods  during 10 days of storage in the oven.
2.2.5. Statistical Analysis
The results were evaluated by analysis of variance (ANOVA by using SPSS 13 for windows. According to the results of ANOVA test Duncan’s multiple range test was used to determine the significance at p < 0.05 levels.
3. Results and Discussion3.1. Some Properties of Olives
Table 1 shows some pomological properties of Adana Topagi (AT) and Gemlik (GE) olives during ripening. Harvest time has significant effects on fruit weight, fruit width and length (p < 0.05). The results showed that Adana Topagi olives had higher pit and fruit weight, fruit width and length values than Gemlik olives during ripening process (p < 0.05). The pit and fruit weight values (g) of the olives ranged from 1.2 to 1.3 and 5.2 to 6.4 for Adana Topagi and 0.6 to 0.7 and 4.5 and 5.9 for Gemlik olives, respectively (Table 1). Tanilgan et al.  reported that the fruit and pit weight as 3.5 and 3.9 and 0.3 to 0.5 g respectively for edible oil olives. However, the results obtained here are in the range of previously reported values for Gemlik olives by Arslan and Schreiner .
Table 2 shows some properties of olives during ripening.The maturity stage is well known to affect the oil yield in olive, which is reported to increase during ripening. The oil content in fruit often depends on growth conditions and product ripening level, but the oil accumulation is cultivar dependent. In a great number of cultivars, the most amount of oil is cumulated before perfect ripening .
The result shows that there was significant increase in oil percentage as ripening progressed for both variety (p < 0.05). Total oil content increased progressively from 9 to 16% and 10 to 20% for Adana Topagi and Gemlik olives, respectively during ripening (Table 2) indicating that Gemlik had higher oil content than Adana Topagi (p < 0.05). The oil content was increasing towards the end of the harvest season suggested that both variety should be harvested late at season to get higher oil content. Our results were in agreement that oil content of olives is increased during ripening [2, 12, 16, 25, 26, 27, 28]. Oil contents in mature fruits have been recorded to vary between 20–70%, based on dry weight, depending on cultivars, geographical region, health of the fruits and growing conditions . Recently, Espinola et al.  found that Picual olives had oil content changed from 13 to 23% and 18 to 22% for two campaigns. Previous studies have reported that oil content of Gemlik olives was changed between 25 and 30% [7, 11]. Our results were lower than the values reported by Uylaser et al.  since harvest date and growth conditions and maturation index could affect the oil content of the same olive cultivar. To our knowledge Adana Topagi oil content were not reported elsewhere before. It is obvious that Gemlik had more oil content than Adana Topagi. In fact, Adana Topagi is generally processed for table olive and Gemlik are used for both table olive and olive oil production in Turkey .
The research conducted on olive composition highlights that the polyphenols are remarkably variable according to the variety, the agronomic conditions, the state of ripeness, and the technology of conservation [25, 31]. Adana Topagi and Gemlik olives had 296 and 373 mg kg-1 CAE total phenols, at 3rd harvest date. These results indicated that Gemlik olives had higher total phenols than Adana Topagi (p < 0.05). The total phenol levels of both Adana Topagi and Gemlik olives progressively increased until they reached a maximum at 2nd harvest date after which they decreased (Table 2). Similar trend were also observed for Cornicabra , Chetoui  Arbequina , Roghani, Zard, Lechino , Chemlali  variety during ripening. The increase of polyphenols at the latest maturity stage is might be due to decrease of humidity during ripening. This event could affect imperfect extraction of polyphenol compounds. There was significant increasing of polyphenol contents at low level of humidity and vice versa . This is in agreement with our findings that the moisture content of Adana Topagi and Gemlik olives dropped from 73 and 74 to 51 and 57%, respectively (Table 2). Arslan and Schreiner  reported the total phenolics content of Halhali olive variety from the Hatay region of Turkey ranged between 178 and 231 mg kg-1. Boskou et al.  found that total phenol content of Greek table olives between 52 to 171 mg 100 g-1 of olives as expressed as caffeic acid. Recently,  found the total phenolic contents of olives from 3 different regions of Turkey between 133 and 216 mg kg-1 CAE. The results were in the range reported in the literature.3.2. Corresponding Olive Oil Properties
Some properties of olive oils can be found at Table 3. The free acidity of the studied oils did not exceed the limit of 0.8% which is established for the best commercial quality olive oil, designated as extra virgin olive oil except for Adana Topagi olive oil at 3rd harvest time (Table 3). Olives at a later stage of maturity give oils with higher level of free acidity since they undergo an increase in enzymatic activity, especially by lypolitic enzymes [26, 27, 28].
There are published studies which report that free acidity increases with ripeness or harvest time . The results showed that harvest time significantly affected PV and IV of both variety and FFA of Adana Topagi oils at the last harvest time (p < 0.05). Peroxide values (PV) were rather high and decreased with harvesting period for Adana Topagi and Gemlik olive oils. Gemlik oils had slightly higher PV than Adana Topagi oils (p < 0.05). This could be due to the extraction of oil by Soxhlet method by using high temperatures. Iodine value olive oils ranges between 80 and 96 and 92 to 103 for for Adana Topagi and Gemlik extracted olive oils.
Table 4 shows fatty acid content of Adana Topagi and Gemlik oils during ripening. Fatty acid analysis indicated that individual fatty acids vary considerably during fruit maturation (p < 0.05).
This is of importance to olive oil producers in selecting oil with good stability and a superior nutritional fatty acid profile. Olive oil is considered to be a highly nutritional and stable oil due, in part, to the high level of monounsaturated oleic acid . Palmitic acid is a saturated fat and as such provides stability. Palmtic acid content of Gemlik oils were higher than Adana Topagi oils at same harvest times (p < 0.05) and decresed during ripenning. Adana Topagi had slightly higher oleic acid than Gemlik variety throughout ripening period (Table 4). Oleic acid content decreased from 72.4 to 69%, 65.7 to 64.8% for Adana Topagi and Gemlik, respectively during maturation. This fall in oleic acid levels has also been observed by [35, 36] for Souri, Barnea and Cheteoui olive cultivars during ripening. Shelf life and oil stability are closely related to the degree of unsaturation of oils, linoleic and linolenic acids, despite their perceived nutritional benefits are both susceptible to oxidation as they are polyunsaturated in nature . Table 4 showed that the lionleic acid (C18:2) content of olive oils slightly increased depending on ripening time for both variety (p < 0.05). Gemlik variety had higher linoleic acid (12%) than Adana Topagi (11%) at the 3rd harvest date. Decrease in palmitic and increase in linoleic acid were also shown by [Int J Food Prop 2008, 11, 561-570.">3, 35, 36, 37, 38] during maturation for Souri, Barnea, Memecik, Domat, Nabali and Chetoui olive cultivars. The increase in linoleic acid content could be due to the transformation of oleic acid into linoleic acid by the oleate desaturase activity which is active during the triacylglycerol biosynthesis . This opposite trend of oleic and linoleic acids may involve a rise of the oxidative susceptibility at higher ripeness index. This should affect the oxidative stability of olive oil, but the latter is also affected by the concentrations of natural antioxidants . Concerning linolenic acid, which is more susceptible to oxidation decreased from 1 and 1,4 to 0,7% for Adana Topagi and Gemlik olive oils, respectively during ripening (Table 4). However, the levels of fatty acids for Adana Topagi and Gemlik variety are below the limits established for extra virgin olive oil (Oleic acid 55-83%, palmitic acid 7,5-20%, linoleic acid 3,5-21%, linolenic acid ≤ 1%) according to IOOC and the EEC Regulation [39, 40]. Recently, Uylaser et al.  found the fatty acid composition of Gemlik olive oils obtained from 4 different districts in Turkey were determined 71.7% oleic, 12.8% palmitic, 11.7% linoleic, 0.7% palmitoleic and 2.3% stearic acids.
Table 5 shows chlorophyl, carotenoid and total phenol content of olive oils during ripening. The stages of maturity significantly affect chlorophyll and carotenoid concentrations in virgin olive oil .
Gemlik oil had the significantly higher level of chlorophyll and carotenoid content than Adana Topagi during ripening (p < 0.05). Chlorophyll and carotenoid contents of the oils of Adana Topagi and Gemlik were high at 1st harvest time and rapidly decreased with time as the fruit ripened (p < 0.05). These results agree with the findings by other authors indicating rapid decrease of colour pigment of olive oils [1, 26, 41] during ripenning. The color change in olive oils during maturity and progressing harvest times can be due to the reduction of the pigment concentration, a natural breakdown, which parallels that of phenols and formation of other colored compounds such as anthocyanins .
The amount of phenolic compounds in extra virgin olive oil is an important factor when evaluating olive oil quality, given that the natural phenols improve its resistance to oxidation, and nutritional properties and flavor of olive oil [31, 35]. Total polyphenols provide a good indication of the olive oil stability without the need for expensive and time- consuming analysis of individual polyphenols [28, 34]. The results showed that Adana Topagi olive oils had higher total phenolic content than Gemlik olive oils (p < 0.05) during ripenning. Total phenol content of Adana Topagi and Gemlik olive oils progressively increased until they reached a maximum at 2nd harvest date after which they decreased significantly (p < 0.05) same as their corresponding olives (Table 2). The polyphenol content of olive oils changed from 128 to 227 and 103 to 140 mg caffeic acid kg -1of oil during ripenning. The amount of total phenols extra virgin olive oils normally ranges between 50 and 1000 mg kg–1, depending on various factors . Ayton et al.  reported that the total phenolic content of olive oils between 70 and 800 mg kg-1 of oil for Mission, Pragon Corregiola varieties. Lazzez et al.  found that total phenol content ranged between 67 and 123 mg kg-1 of oil for Chemlali olive cultivar during maturation process. So our results were in the range reported for olive oils in the literature. However, our results were higher than the results of Keceli  who found the total phenol content of extra virgin olive oils between 44 and 97 mg caffeic acid per kg of oil for Nizip, Halhali, Hasabi, Ayvalik and Odemis varieties harvested at the same time. Our results were also supported that total phenol content of oils preliminary increased then decreased depending on ripening previously reported by [12, 16, 34, 35, 36].
Table 6 shows the radical scavenging activity of olive and olive oils during ripening. RSA activity changed depending on olive cultivar (p < 0.05). Gemlik olives had higher RSA than Adana Topagi olives at 1st harvest time (p < 0.05) and showed similar activity during ripening (p>0.05) at 100 and 200 ppm concentration (Table 6). This is interesting although Gemlik olives have significantly higher total phenol content than Adana Topagi olives they showed similar RSA during ripening. It was found that Gemlik and Adana Topagi olives had better RSA than BHT (p < 0.05). Although harvest time significantly reduced the RSA of both olives theye were still effective than BHT even at the 3rd harvest time (p < 0.05).
Similarly, Rotondi and Magli  found that antioxidant activity shown by the ARP index appears to follow a decreasing trend from 4.02 at the first stage of ripeness to 2.05 at the last harvest date. In addition, Zullo et al.  found that total ORAC decreases with the increase in fruit maturity.
RSA activity increased from 26 to 42% and 17 to 20% for Adana Topagi and Gemlik olive oils during ripening, respectively (Table 6). Adana Topagi oils had higher RSA than Gemlik oil (p>0.05) during ripening (Table 6). This could be due to the fact that Adana Topagi oils had higher total phenol content than Gemlik oils. Similarly, Kıralan and Bayrak  who showed that Memecik oils had higher total phenol and RSA activity than Ayvalik oils. Kıralan et al.  found RSA of oils from Halhalı, Hasebi, Kilis and Nizip between 30 to 96%. On the other hand Nenadis et al.  found the RSA of olive oils as low as 15 and 27%. Recently, Keceli  found the total RSA activity between 68.5 to 80% for Hasebi, Ayvalik, Nizip, Halhali and Odemis extra virgin olive oils. The results were in the range that obtained by others depending on variety of oils. RSA activity of olives were similar or better than BHT (p ≤ 0.05) and oils showed similar or lower RSA than BHT (p≥0.05). The results found in this study in accordance with previous research is quite important finding since there are some health concern about the potent antioxidants such as BHT and BHA and Gemlik and Adana Topagi olives can be very important source of phenolics showing comparable or even better activity than BHT.
Table 7. The effect of olives extracts on the oxidative stability of bulk oil stored at 60°C for 10 days
Table 7 shows the oxidative stability of refined olive oils at 60°C enriched with olive extracts from Adana Topagi and Gemlik obtained at different harvest times. Initial PV of refined olive oil was 27 meq/kg. At the end of 10 days, PV of the oils enriched with Adana Topagi olive extracts increased from 27 to 123 and 120 meq O2 kg-1, while of the oils enriched with Gemlik olive extracts varied from 96 to 113 meq O2 kg-1 depending on harvest time. PV of olive oils enriched with BHT increased from 27 to 64 meq O2 kg-1 during storage at 60°C for 10 days. Addition of BHT to olive oil enhanced the oxidative stability at 56% and was more effective than both olive extracts obtained from Adana Topagi and Gemlik (Table 7).
PV of oils enriched with Adana Topagi olive extracts increased more than refined olive oils enriched with Gemlik olive extracts at different harvest times. Therefore Gemlik olive extracts were more effective protecting refined olive oil against oxidation than Adana Topagi olive extracts at 100 ppm (p ≤ 0.05). However, protective ability of olive extracts decreased depending on ripeness stage. This could be due to higher total phenol content of Gemlik olives than Adana Topagi olives at different harvest times (Table 2). In fact, Gemlik olives had higher total phenol content, higher RSA activities and higher protective ability of olive oils than Adana Topagi olives. These relations between oxidation stability, antiradical activity, total phenol, confirm the findings reported by Kıralan and Bayrak . This study also confirmed the strong relationship between total phenol content and oxidative stability of olive oils during olive maturation as stated before by Morello et al. .
As the maturation process continues, a number of changes, both physical and chemical, occur within the fruit and their corresponding olive oils. Modification of those components can be commercially relevant as they have a significant effect on the radical scavenging activity, stability (shelf life potential) and sensory characteristics of the olive oil. The results of this study can be considered useful for providing information about Adana Topagi and Gemlik olives and olive oil in relation to the olive ripening degree. The result showed that some quality parameters of these two varieties were similar but variations in the fatty acid profile, changes in total phenolic compound levels and decreases in pigments, antiradical activity and oxidation stability of these cultivars were different (p < 0.05). The Adana Topagi olive oil was shown to be the most effective at scavenging DPPH radicals and also had higher polyphenol concentrations that are expected to contribute to oil RSA. However, Gemlik olives had higher total oil content, higher chlorophyll and carotenoid content, higher RSA which was comparable to that of BHT at all harvest times and better protective ability to refined olive oil. These results improve knowledge of the effect of ripening on the antioxidant content that could help to establish the optimum fruit harvesting date according to the nutritional, sensorial and commercial advantages. Finally the results could be great interest to the local industrial sector, the international olive oil business and to consumers.
This study was funded by the Scientific Research Projects Office of The University of Cukurova (BAP) Adana Turkey. Author would like to thank Dr. Ilknur Unsal Ekinci for fatty acid analysis of extracted olive oils.
The authors have no competing interests.
AT: Adana Topagi, GE: Gemlik
TPC: total phenol content
CAE: Caffeic acid equivalents
RSA: radical scavenging activity
IOOC: International Olive Oil Council
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