Fatty acid profile of olive oil extracted from irradiated and non-irradiated olive fruits

Abstract

Syrian Kaissy cv olive fruit (SKOF) was irradiated (0, 1, 2, and 3 kGy). Oils were extracted from irradiated and un-irradiated olive fruits. Fatty acid profiles of Syrian Kaissy cv olive oil (SKOO) were measured by gas chromatography immediately after irradiation and after 6, 12, 24, and 36 months of storage. Results of the study showed that composition of fatty acids of SKOO were determined as palmitic (C16:0) (14.69%), palmitoleic acid (C16:1) (1.18%), stearic (C18:0) (2.19), oleic (C18:1) (68.94%), linoleic (C18:2) (12.22%), and linolenic acid (C18:3) (0.79%). The fatty acid composition of SKOO contains a healthy mixture of all the types of saturated mono-unsaturated and poly-unsaturated fatty acids. The data showed an increase (p < 0.05) in the percentage of the total saturated fatty acids and decrease (p < 0.05) in the percentage of the total unsaturated fatty acids of SKOO during storage. In general, there were no significant (p > 0.05) differences in fatty acids compositions of both oils extracted from irradiated and un-irradiated SKOF.

KEYWORDS:

• Fatty acids
• Oleic acid
• Olive oil
• Gas chromatography
• Gamma irradiation
• Storage

Introduction

Vegetable oils are an indispensable part of everyday meal in most part of the world. Edible oils are constituted of triacylglycerol molecules, mainly formed by unsaturated (oleic (18:1), linoleic (18:2), linolenic (18:3) acids etc.) and saturated fatty acids (myristic (14:0), palmitic (16:0), stearic (18:0), archidonic (20:4) acids etc.) esterified to glycerol units.^[1] The majority of olive oil fatty acid chains contain 16 or 18 carbon atoms. Olive oil contains not only oleic acid, but also small amounts of other fatty acids, such as palmitic, palmitoleic, stearic, linoleic, and alfa linolenic acids and squalene.^[2] There are only a few types of fatty acids in olive oil, but the proportions of each strongly influence the characteristics and nutritive of the oil.^[3] The nutritional value and health functions of virgin olive oil (VOO) are ascribed to the presents of large amount of monounsaturated fatty acids (MUFAs) such as oleic acid (oleic acid is named after olive “olea”). and valuable minor components.^[4] Although fatty acids are relatively similar in structure, there are some variations that have a strong influence on the properties.^[5] Oil with higher monounsaturated fatty acids (MUFAs) and lower saturated fatty acids (SFAs) are preferred because of the proven beneficial effect of MUFAs on serum cholesterol levels.^[6] Fatty acid composition has been shown to influence the stability of oils, and polyunsaturated fatty acids have been found to contribute to the rancidification of several oils.^[7]

Syria has an important place in the world’s olive production, holds fifth position in world olive production.^[8] However, little studies have evaluated the physicochemical characteristics on composition of produced or marketed local cultivated olive oil in Syria.^[9]

Food irradiation has been identified as a new technology that can eliminate insects and microorganisms from raw food products extend shelf life and improve the quality and safety of food.^[10,11] Irradiation with ionizing energy is widely used to improve the physical, chemical, and biological properties of materials and commercial products.^[12,13] The effect of irradiation on locally stored foods is of utmost importance and an insight into these aspects of storage will help in understanding the shelf life of foods as well as its effects on sensitive nutrients.^[11] Lipids, including unsaturated fatty acids, are easily decomposed, saturated, and isomerized by gamma irradiation.^[14,15]

Radiation processing generates free radicals and hydrocarbon fragments and accelerates oxidation of unsaturated fatty acids that may induce some biochemical changes in food and influence its quality, such as the nutritional value.^[16,17] Although irradiation has been found to be a useful process to increase the longevity of several agricultural products, but the effect of gamma irradiation and storage on the fatty acids of Syrian olive oils has not been investigated. Therefore, this study was conducted to determine whether gamma irradiation could induce geometrical changes in fatty acids in olive oil extracted from Syrian Kaissy cv. olive fruits (SKOF) treated with 0, 1, 2, and 3 kGy doses of gamma irradiation.

Materials and methods

The studied olive cultivar was Kaissy, the most widespread in Syria. The olive fruits of good quality and in the mature firm condition were harvested during 2007/2008 growing season, from the trees grown in grove located at Deer Al Hajar research station, southeast Damascus, Syria (33o 21´ N, 36o 28´ E) at 617 m above sea level., under conventional agriculture practices. The climate of the area is sub-Mediterranean with average annual temperature between 19 and 36°C in July–August and a minimum of 3°C in January–February. Annual rainfall varies from 100 to 150 mm with most falling in winter. The supplementary water irrigation was managed to supply 2000 m³ he⁻¹ of water per tree over the period from mid-June to mid-September. Then, olive fruits were weighed as in the sampling plan and transferred into polyethylene pouches for irradiation. Each pouch of olive fruits (1 kg) was considered as a replicate. The samples were then divided into four groups (15 pouches for each group): group 1 (control) and groups 2, 3, and 4 were irradiated with 1, 2, and 3 kGy of gamma irradiation.

Irradiation treatments

Samples of olive fruits were exposed to gamma radiation at doses of 0, 1, 2, and 3 kGy in a ⁶⁰CO package irradiator (ROBO, Techsnabexport, Moscow, Russia). Irradiation was carried out in the stationary mode of operation with the possibility of varying dose rate (10.846 to 3.921 kGy h⁻¹) depending on the location and the distance from the source (10 to 40 cm). The samples were irradiated at place (15 cm from source) with a dose rate of 9.571 kGy h⁻¹. The irradiations were carried out at room temperature (18–25°C) and atmospheric pressure. The absorbed dose was determined using alcoholic chlorobenzene dosimeter.^[18]

Oil extraction

The oils from control and irradiated olive fruits were extracted from olives stored at ambient temperature for 0, 30, and 45 days after irradiation using a mechanical and physical processes.^[19] Olive fruits were crushed with hummer crusher and slowly mixed for about 30 min at 27°C, Then, the past mixed was centrifuged at 3000 rpm for 3 min without the addition of water to extract the oil. Finally, the oils were decanted and immediately transferred into dark glass bottles and stored at room temperature (18–25°C). Fatty acid determination analysis of oils extracted from irradiated and non-irradiated olive fruit samples was performed immediately after irradiation, and after 6, 12, 24, and 36 months of storage.

Fatty Acids (FA) determination

The fatty acid methyl esters (FAME) were prepared.^[15] The fatty acids (FAs) profile was determined by gas chromatography in a GC-17 A Shimadzu chromatograph (Shimadzu Corp., Koyoto, Japan) equipped with a flame ionization detector and a capillary column (CBP20-S25-050, Shimadzu, Australia). The selected chromatographic conditions were as follows: oven temperature at 190°C, detector temperature at 250°C, and injector temperature at 220°C; N2 was used as a carrier gas with split ratio 29:1; the sample volume injected was 1 μl. Peak areas were integrated and converted to FA percentages (direct area normalization) by means of the CLASS – VP 4.3 program (Shimadzu Scientific Instruments, Inc., Columbia, MD). The FA identification was carried out by retention times and by addition of standards.

Chemical and physical analysis of oils

Acidity value (AV) in terms of (oleic acid %) and peroxide value (PV) in terms of mEq O₂ kg₋₁ oil were determined according to standard methods.^[20]

Statistical analysis

The four treatments and five storage periods were distributed in a completely randomized design with three replicates. Data were subjected to the analysis of variance test (ANOVA) using the SUPERANOVA computer package (Abacus Concepts Inc, Berkeley, CA, USA; 1998). The p value of less than 0.05 was considered statistically. The degree of significance was denoted as: p < 0.05*, p < 0.01**.^[21]

Results and discussion

Fatty acid composition profile of Syrian Kaissy cv. Olive Oil (SKOO)

Fatty acid profiles of Syrian Kaissy cv. olive oil (SKOO) were measured by gas chromptography. Table 1 depicts fatty acid profile of SKOO which included palmitic (C16:0) (14.69%), palmitoleic acid (C16:1) (1.18%), stearic (C18:0) (2.19), oleic (C18:1) (68.94%), linoleic (C18:2) (12.22%), and linolenic acid (C18:3) (0.79%). SKOO samples contained the oleic and linoleic acids, which can be classified in oleic-linoleic acid group.

Table 1. Fatty acid composition of Syrian Kaissy cv. olive oil (SKOO) and the allowable fatty acid ranges for extra-virgin and virgin olive oil according to (IOC, 2015).

Fatty acid	Carbon number	Allowable range % (IOC, 2015)	SKOO %
Palmitic	C16:0	7.50–20.00	14.69
Palmitoleic acid	C16:1	0.30–3.50	1.18
Stearic	C18:0	0.50–5.00	2.19
Oleic	C18:1	55.00–83.00	68.94
Linoleic	C18:2	2.50–21.00	12.22
Linolenic	C18:3	≤ 1	0.79

Fatty acid composition profile of SKOO composition data differs from those reported by Jbara et al.^[9] However, the fatty acid composition varies considerably depending on where the crop is grown. It has been shown that environmental factors play an important role in the fatty acid composition.^[22]

The absence of arachidonic acid and low levels of linolenic and stearic acids in authentic olive oil allow these compounds to serve as a signal for adulteration with other vegetable oils.^[22] The International Olive Council^[23] has produced a list of the allowable levels for each of the fatty acids to be acceptable as extra virgin and virgin olive oil (Table 1). Although the IOC allows such a wide range of fatty acids in olive oil, growers are encouraged to select cultivars that have the highest levels of the best fatty acids. Based on the desire to increase the nutritionally preferred fatty acids, SKOO has low saturated palmitic (C16:0) and high monounsaturated oleic (C18:1) which is considered a nutritionally desirable alternative. The fatty acid composition of SKOO contains a healthy mixture of all the types of saturated mono-unsaturated and poly-unsaturated fatty acids. However, lipids of SKOO had the highest content of unsaturated fatty acids (UFA) reaching 83.12% of the total fatty acids, and the oleic acid (an essential fatty acid) was the most abundant monounsaturated fatty acid (MUFA), while linoleic was the predominant polyunsaturated fatty acids (PUFA). Meanwhile, the total saturated fatty acids (SFA) reached 16.88% and the predominant SFA were palmitic and stearic acids (Table 5). The high level of UFA in SKOO was due to their high levels of oleic acid. This showed that these oils are good source of UFA, mostly MUFA with oleic acid being the most abundant. Oleic acid is the most important essential fatty acid for it must be got from food.^[24] It was shown that monounsaturated-rich diet reduced the susceptibility of low density lipoprotein peroxidation and may be of therapeutic value in the treatment of hypercholestrolemia.^[25,26] The USFA/SEA index of SKOO which is associated to the impact in the human health is also high (4.93) (Table 5) which makes them the most suitable edible oils for mass consumption.

Effect of storage time on fatty acid profile of virgin olive oil

The effect of storage time on individual saturated, monounsaturated, and polyunsaturated fatty acids of Syrian Kaissy cv olive oil (SKOO) is shown in Tables, 2, 3, and 4 respectively, while the effect of storage time on total saturated (S), total unsaturated (US), and US/S ratio of SKOO is shown in Table 5.

Storage time caused a significant (p < 0.05) difference between the fatty acid composition of the SKOO. The presented data show an increase in the percentage of the total saturated fatty acids (including palmitic acid (C16:0)) and decrease in the percentage of the total unsaturated fatty acids (including (C16:1), linoleic (C18:2), and (C18:3)). Moreover, the oleic (C18:1) fatty acid remained unaffected during storage. The ratio between total unsaturated fatty acids and saturated ones (U/S ratio) was 4.93 for SKOO, while it decreased gradually in parallel with storage time. The increase in SFA and the decrease in USFA during storage were probably due to the preferential cleaving double bonds. Storage may cause the saturation of double bonds of palmitoleic (C16:1), linoleic (C18:2), and linolenic acid (C18:3). Present results are in good agreement with those of Mexis et al.,^[27] who reported an increase in saturated fatty acids with parallel decrease in unsaturated fatty acids in ground almonds during storage. The decrease in the unsaturated fatty acid content and the concomitant increase in the saturated fatty acid content are explained by De Camargo et al.,^[28] who stated that the ratio of the oxidation rates of stearic, oleic, linoleic, and linolenic acids was 1: 10: 100: 200. Another study suggested that the decrease in unsaturated fatty acids during storage of oil is mainly due to a molecular structure change in fatty acids.^[29]

Effect of gamma irradiation on fatty acid of olive oil

The changes in individual saturated, monounsaturated, and polyunsaturated fatty acids of olive oil extracted from treated Syrian Kaissy cv olive fruits (SKOF) with 0, 1, 2, and 3 kGy of gamma irradiation and stored for different time after extraction (0, 6, 12, 24, and 36 months) are given in Tables 2, 3, and 4, respectively, while the effect of gamma irradiation treatments on total saturated (S), total unsaturated (US), and US/S ratio of SKOO is shown in Table 5. The results indicate that oil samples extracted from irradiated and non-irradiated SKOF contained the same fatty acids. However, small changes were observed in total saturated and unsaturated fatty acids compositions in all irradiation treatments at all storage times. In general, there were no significant (p > 0.05) differences in fatty acids compositions of both oil extracted from irradiated and un-irradiated SKOF. This can be due to the relative stability of olive oil’s fatty acids against oxidation reaction during the processing.^[30] Our results are in good agreement with those of^[31] whose data confirm that SFA and USFA of almond oil were not affected by irradiation doses of 1, 2, and 3 kGy. Golge and Ova^[32] did not find significant changes in fatty acids composition of pine nuts irradiated at gamma irradiation doses up to 5 kGy. Minami et al.^[33] reported that the fatty acid composition of soybean oil was not markedly changed by irradiating at 10 kGy under aerobic conditions. Abd El-Aziz and Abd El-Kalek^[24] reported that, at low irradiation doses (1, 3, and 6 kGy), small changes were observed in saturated and unsaturated fatty acids compositions, and the changes in fatty acids composition of oil extracted from irradiated seeds were not significant (p > 0.05). Although irradiating even up to 60 kGy did not affect the fatty acid composition in chilled or frozen beef.^[16] According to the literature, irradiation of high moisture content foods results in high hydroxyl radical concentration, which triggered fat oxidation, leading to changes in fatty acid composition of fatty foodstuff. Such reactions are expected to be slower in dry foodstuff such as nuts.^[34,35] Given the high moisture content of olive fruits and the relatively low irradiation doses applied, it is most probable that no free fatty acids were produced through triglycerides hydrolysis. Among the natural antioxidants present in virgin olive oil, tocopherols and polyphenols, they are important antioxidants that protect the oil against damages by reacting with free radicals and driving the oxidative reactions toward their final stages.^[5,36]

Table 2. Saturated fatty acids (palmitic (C16:0) and stearic (C18:0)) content (%) on olive oil produced from olive fruits treated with gamma irradiation.

Treatment	Control	1 KGY	2 KGY	3 KGY	p-level
Storage period/(Months) C16:0
0	14.69 ± 0.68bC	15.23 ± 0.67abA	15.69 ± 0.64abB	16.02 ± 0.23aA	NS
6	15.41 ± 0.29aB	15.11 ± 0.64aA	15.51 ± 0.47aAB	15.28 ± 0.36aA	NS
12	16.29 ± 0.33aA	15.75 ± 0.93aA	16.21 ± 0.42aAB	15.44 ± 1.07aA	NS
24	15.33 ± 0.1aBC	15.62 ± 0.41aA	15.71 ± 0.69aB	15.52 ± 0.69aA	NS
36	15.68 ± 0.12dAB	15.96 ± 0.06cA	16.60 ± 0.06aA	16.34 ± 0.02bA	**
p-level	**	NS	*	NS
C18:0
0	2.19 ± 0.09aA	2.15 ± 0.11abAB	2.10 ± 0.13aA	2.16 ± 0.05aAB	NS
6	1.73 ± 0.06aC	1.86 ± 0.25abB	2.25 ± 0.48aA	1.96 ± 0.05aB	NS
12	2.14 ± 0.08aA	2.59 ± 0.61aA	2.50 ± 0.49aA	3.21 ± 1.37aA	NS
24	1.99 ± 0.04aB	2.06 ± 0.14aAB	1.99 ± 0.09aA	1.79 ± 0.26aB	NS
36	2.13 ± 0.00bcA	2.21 ± 0.03aAB	2.06 ± 0.06cA	2.12 ± 0.01bAB	**
p-level	**	NS	NS	NS

^abc Mean values in the same column not sharing a superscript are significantly different.

^ABC Mean values in the same row not sharing a superscript are significantly different.

NS: not significant.

* Significant at p < 0.05.

** Significant at p < 0.01.

Table 3. Monounsaturated fatty acids (palmitoleic (C16:1) and oleic (C18:1) content (%) on olive oil produced from olive fruits treated with gamma irradiation.

Treatment	Control	1 KGY	2 KGY	3 KGY	p-level
Storage period/(Months)
C16:1
0	1.18 ± 0.11aB	1.11 ± 0.16aA	1.20 ± 0.14aB	1.37 ± 0.18aA	NS
6	1.48 ± 0.15aA	1.31 ± 0.24aA	1.46 ± 0.13aA	1.30 ± 0.08aAB	NS
12	1.24 ± 0.11aB	1.31 ± 0.21aA	1.24 ± 0.01aB	1.19 ± 0.1aAB	NS
24	1.13 ± 0.08aB	1.14 ± 0.05aA	1.09 ± 0.10aB	1.16 ± 0.13bAB	NS
36	1.13 ± 0.02bB	1.16 ± 0.04bA	1.21 ± 0.03aB	1.15 ± 0.03bB	**
p-level	**	NS	*	NS
C18:1
0	68.94 ± 0.41aA	68.40 ± 0.21abB	67.85 ± 0.19bB	68.29 ± 0.59abBC	*
6	69.13 ± 0.75aA	68.94 ± 1.10aAB	69.50 ± 0.87aA	69.17 ± 0.52aAB	NS
12	68.69 ± 0.67aA	68.34 ± 0.48aB	65.98 ± 0.71bC	67.91 ± 0.38aC	**
24	69.15 ± 0.12bA	69.20 ± 0.55abAB	68.89 ± 0.19bA	70.02 ± 0.67aA	NS
36	69.09 ± 0.10bA	69.60 ± 0.06aA	68.86 ± 0.14cbA	69.70 ± 0.21aA	**
p-level	NS	NS	**	**

^abc Mean values in the same column not sharing a superscript are significantly different.

^ABC Mean values in the same row not sharing a superscript are significantly different.

NS: not significant.

* Significant at p < 0.05.

** Significant at p < 0.01.

Table 4. Polyunsaturated fatty acids (linoleic (C18:2) and Linolenic (C18:3) acids) content (%) on olive oil produced from olive fruits treated with gamma irradiation.

Treatment	Control	1 KGY	2 KGY	3 KGY	p-level
Storage period/(Months)
C18:2
0	12.22 ± 0.57aA	12.31 ± 0.68aA	12.39 ± 0.55aAB	11.32 ± 1.06aA	NS
6	11.31 ± 0.55aAB	11.93 ± 1.41aAB	10.49 ± 0.25aC	11.38 ± 0.21aA	NS
12	10.97 ± 0.95bA	11.27 ± 1.21bAB	13.17 ± 0.59aA	11.40 ± 0.28bA	*
24	11.82 ± 0.11aAB	11.37 ± 0.74aAB	11.64 ± 0.54aB	10.82 ± 0.62aAB	NS
36	11.42 ± 0.05aAB	10.54 ±0.02cB	10.63±0.07bC	10.15 ± 0.03dB	**
p-level	NS	NS	**	*
C18:3
0	0.79 ± 0.07aA	0.80 ± 0.03aA	0.77 ± 0.03aB	0.84 ± 0.04aA	NS
6	0.78 ± 0.07aA	0.80 ± 0.03aA	0.77 ± 0.03aB	0.84 ± 0.04aA	NS
12	0.67 ± 0.06bAC	0.74 ± 0.18abAB	0.91 ± 0.05aA	0.85 ± 0.10abA	NS
24	0.57 ± 0.05bBC	0.62 ± 0.04abBC	0.68 ± 0.04bC	0.69 ± 0.07aB	NS
36	0.55 ± 0.02bB	0.54 ± 0.02bC	0.65 ± 0.02aC	0.64 ± 0.03aB	**
p-level	**	**	**	**

^abc Mean values in the same column not sharing a superscript are significantly different.

^ABC Mean values in the same row not sharing a superscript are significantly different.

NS: not significant.

* Significant at p < 0.05.

** Significant at p < 0.01.

Table 5. Total saturated fatty acids (SFA), total unsaturated fatty acids (USFA), and (TUSFA/SFA) on olive oil produced from olive fruits treated with gamma irradiation.

Treatment	Control	1 KGY	2 KGY	3 KGY	p-level
Storage period/(Months) SFA
0	16.88 ± 0.59bC	17.38 ± 0.56abAB	17.79 ± 0.52abB	18.18 ± 0.31aAB	NS
6	17.15 ± 0.31abC	16.97 ± 0.39bB	17.75 ± 0.56aB	17.24 ± 0.32abC	NS
12	18.43 ± 0.43aA	18.34 ± 1.08aA	18.70 ± 0.23aA	18.65 ± 0.33aA	NS
24	17.32 ± 0.07aBC	17.67 ± 0.37aAB	17.70 ± 0.33aB	17.31 ± 0.94aBC	NS
36	17.81 ± 0.12dB	18.17 ± 0.05 cB	18.66 ± 0.07aA	18.46 ± 0.02bA	**
p-level	**	*	*	*
USFA
0	83.12 ± 0.59aA	82.62 ± 0.56abAB	82.22 ± 0.52abA	81.82 ± 0.31bAB	NS
6	82.71 ± 0.50aAB	82.97 ± 0.48aA	82.22 ± 0.61aA	82.70 ± 0.27aA	NS
12	81.57 ± 0.25aC	81.66 ± 1.08aB	81.30 ± 0.23aB	81.35 ± 0.33aB	NS
24	82.68 ± 0.07aAB	82.33 ± 0.37aAB	82.30 ± 0.33aA	82.69 ± 0.94aA	NS
36	82.19 ± 0.12aBC	81.83 ± 0.05bB	81.34 ± 0.07cB	81.64 ± 0.20bB	**
p-level	**	*	*	*
USFA/SFA
0	4.93 ± 0.21aA	4.76 ± 0.19abAB	4.63 ± 0.16abA	4.50 ± 0.09bAB	NS
6	4.83 ± 0.12aA	4.89 ± 0.14aA	4.64 ± 0.18aA	4.80 ± 0.11aA	NS
12	4.43 ± 0.07aC	4.47 ± 0.33aB	4.35 ± 0.07aB	4.36 ± 0.09aB	NS
24	4.77 ± 0.02aABC	4.66 ± 0.12aAB	4.65 ± 0.11aA	4.79 ± 0.32aA	NS
36	4.62 ± 0.02aC	4.50 ± 0.02bB	4.36 ± 0.02dB	4.42 ± 0.02cB	**
p-level	**	*	*	*

^abc Mean values in the same column not sharing a superscript are significantly different.

^ABC Mean values in the same row not sharing a superscript are significantly different.

NS: not significant.

* Significant at p < 0.05.

** Significant at p < 0.01.

Effect of gamma irradiation and storage period on acid value of olive oil

Table 6 details averaged results obtained for the acid value (AV) (free fatty acids) indices and their respective standard deviations after irradiation and during the whole storage time. The values of initial acidity of olive oils studied (0.53%) are below the maximum levels established by the international regulations.^[37] The international olive council^[23] has defined the quality of olive oil, based on free fatty acid (FFA) content. Olive oils are classified into extra-virgin olive oil 0.8 (max), virgin olive oil 2.0 (max), and ordinary virgin olive oil 3.3 (max). Science the FFA content of our olive oil was (0.53%) little lower than 0.8 it could be classified as extra-virgin olive oil. It is clear that AVs significantly (p < 0.01) changed due to irradiation doses and storage time, and it was always below its threshold value (0.8%) (Table 6). After gamma irradiation treatment, the significant (p < 0.01) increase in acid value in samples treated with lower doses of gamma irradiation (1 and 2 kGy) was confirmed. After storing the oil samples for 36 months, a similar increase in AVs in both irradiated and un-irradiated EVOOs was observed, although the increase in the acid value was less marked in control samples comparing with irradiated ones. These results agree with the study performed by Mendez and Falque^[37] who indicated that during storage that confirmed the increase in acidity in olive oil over time and gradual loss of quality of olive oil during storage. As far as we know, there is no literature about the relationship between the acid value of EVOO and the gamma irradiation treatment.

Table 6. Effect of gamma irradiation and storage period on acid value (free fatty acid) (%) of olive oil.

Treatment	Control	1 KGY	2 KGY	3 KGY	p-level
Storage period/(Months) Acid value (Free Fatty Acid) (% oleic acid)
0	0.53 ± 0.03cA	0.77 ± 0.03aB	0.58 ± 0.04bD	0.48 ± 0.05dE	**
6	0.52 ± 0.01cB	0.81 ± 0.09aB	0.72 ± 0.01bB	0.53 ± 0.01cCD	**
12	0.43 ± 0.01dC	0.82 ± 0.01aB	0.70 ± 0.004bA	0.51 ± 0.01cB	**
24	0.42 ± 0.02dAD	0.85 ± 0.06aB	0.75 ± 0.03bBC	0.59 ± 0.01cAC	**
36	0.50 ± 0.01E	1.01 ± 0.01aA	0.78 ± 0.02bC	0.72 ± 0.02cA	**
p-level	**	**	**	**

^abc Mean values in the same column not sharing a superscript are significantly different.

^ABC Mean values in the same row not sharing a superscript are significantly different.

* Significant at p < 0.05.

** Significant at p < 0.01.

Conclusion

The results of this study demonstrated that the studied Syrian olive cultivar (Kaissy) shows the best fatty acid composition (lowest palmitic acid, which is the major saturated fat and it has high levels of mono-unsaturated fat and mono-unsaturated oleic acid). The samples were found to contain oleic acid (C18:1) ranging from 67.25% to 71.34%. Post-harvest storage of olives has been shown to increase the concentration of saturated fatty acids and decrease the unsaturated fatty acids leading to reduce the index. The results of this study showed that gamma irradiation at 1, 2, and 3 kGy did not significantly alter the fatty acid composition of Syrian Kaissy cultivar olive oil.

Acknowledgments

The authors wish to express deep appreciation to the Director General of the Atomic Energy Commission of Syria (AECS) and the staff of the division of food irradiation.