Phenolic Compounds, Antioxidant Activity and Fatty Acid Composition of Roasted Alyanak Apricot Kernel.

The oil recovery from Alyanak apricot kernel was 36.65% in control (unroasted) and increased to 43.77% in microwave-roasted kernels. The total phenolic contents in extracts from apricot kernel were between 0.06 (oven-roasted) and 0.20 mg GAE/100 g (microwave-roasted) while the antioxidant activity varied between 2.55 (oven-roasted) and 19.34% (microwave-roasted). Gallic acid, 3,4-dihydroxybenzoic acid, (+)-catechin and 1,2-dihydroxybenzene were detected as the key phenolic constituents in apricot kernels. Gallic acid contents varied between 0.53 (control) and 1.10 mg/100 g (microwave-roasted) and 3,4-dihydroxybenzoic acid contents were between 0.10 (control) and 0.35 mg/100 g (microwave-roasted). Among apricot oil fatty acids, palmitic acid contents ranged from 4.38 (oven-roasted) to 4.76% (microwave-roasted); oleic acid contents were between 65.73% (oven-roasted) and 66.15% (control) and linoleic acid contents varied between 26.55 (control) and 27.12% (oven-roasted).

assisted processing and thermos-analytical methods have significant advantages over conventional methods for edible oil extraction and characterization and they are widely used to increase oil quality and to assess the stability of vegetable oils 9 14 . Several studies have been conducted on chemical composition and phytochemical properties of apricot fruit and kernels 4,6,7 . However, comparative studies on roasting of apricot kernels using oven and microwave methods are still insufficient. The objective of current research was to investigate the effects of oven-and microwave-roasting on total phenolics, antioxidant activity, individual phenolic constituents and fatty acid composition of apricot kernels and their oil.

Moisture content
The initial moisture content of the apricot kernel was measured at 105 in an oven until a constant weight was reached.

Oven roasting
Apricot kernels 100 g were carefully roasted for 24 h at 70 using an oven. During roasting, they were stirred continuously to ensure the homogenous roasting.

Microwave heating
Microwave roasting was carried out in an oven Arçelik ARMD 580, Turkey with a power capacity of 720 W/25 min and working frequency of 2450 MHz. The microwave cavity of oven had dimension of 34.5 34.0 22.5 cm. Approximately 50 g of apricot kernel sample, kept in 50 mL beaker, and was placed at equal distances on a 28 cm diameter circumference of rotary plate in the oven during each treatment at 2450 MHz for 15 min. Once treated, samples were cooled down at room temperature and stored in sealed bottles at 25 under nitrogen before further chemical analyses. Samples were ground to a powder form prior to analyses 15 .

Extraction from apricot kernels
About 5 g powdered kernels sample was mixed with methanol 15 mL and then extraction was carried out in ultrasonic water-bath for 1 h followed by centrifugation at 6000 rpm for 10 min. n-Hexane 10 mL was added into filtered supernatant and mixed in a vortex. The methanol phases were collected from each step and evaporated at 50 to obtain a dried extract. The extract was then dissolved in 25 mL of methanol 16 . 2.2.5 Determination of total phenolic content Total phenolic contents in kernel extracts were evaluated as 750 nm wavelength using spectrophotometer Shimadzu, Japan after treating the extracts with Folin-Ciocalteu reagent following Yoo et al. 17 method. A 1 mL extract sample was mixed with I mL Folin-Ciocalteu reagent and after 5 min, 10 mL 7.5 Na 2 CO 3 solution was mixed. The final volume of the reaction mixture was made 25 mL using deionized water; incubation was carried out for 2 h at room temperature and absorbance values were recorded at 765 nm. Total phenolic contents were then reported as mg gallic acid equivalent GAE /100 g after comparing the sample results with those calibration curve of known concentration of gallic acid standard solutions.

Antioxidant activity
The antioxidant activity of apricot kernel was investigated according to a DPPH 1,1-diphenyl-2-picrylhydrazyl method as reported by Lee et al. 18 . The apricot kernel extract 1 mL was dissolved in 2 mL of methanolic solution of DPPH by vigorous shaking and kept at room temperature for 30 min. Absorbance of the mixture was measured spectrophotometrically at 517 nm after reacting the known quantities of sample extract with DPPH solution in metha-nol. Antioxidant activity was determined using following formula:

Antioxidant activity
∆A control 517 ∆A extract 517 ∆A control 517 100 2.2.7 Determination of phenolic compounds The determination of individual phenolic constituents in apricot kernel extracts was carried out using Shimadzu-HPLC, connected to a PDA detector and an Inertsil ODS-3 5 µm; 4.6 250 mm column. The mobile phase constituted 0.05 Acetic acid in water A and acetonitrile B mixture and its flow rate was set at 1 mL/min at 30 . Samples 20 µL were injected using autosampler and chromatograms were recorded at 280 and 330 nm wavelengths in PDA detector.

Oil extraction
Apricot kernels were ground to powder form in a small laboratory grinder followed by extraction of oil with petroleum ether in Soxhlet Apparatus for 5 h. The solvent was then removed by evaporation using a rotary evaporator at 50 19 .

Fatty acid composition
Evaluation of fatty acid composition of apricot kernel oil involved esterification of fatty acids using ISO-5509 20 method and then fatty acid methyl esters were analyzed in a gas chromatography Shimadzu GC-2010 system, which consisted of a flame-ionization detector FID and a capillary column Tecnocroma TR-CN100, 60 m 0.25 mm, film thickness: 0.20 µm . The temperature at injection block and detector was set at 260 , and nitrogen was used as carrier gas and its flow rate, total flow and split rates were set at 1.51 mL/min, 80 mL/min and 1/40, respectively 19 .

Statistical analysis.
The results were obtained after triplicate measurements of replicated roasting treatments applied to apricot kernels and the data was expressed as means standard deviation MSTAT C of independent roasting types 21 .

Results and Discussion
3.1 Moisture, oil, total phenolics and antioxidant activity of apricot kernels The moisture, oil contents, total phenolic contents, antioxidant activity values of unroasted, and oven and microwave roasted apricot kernels are presented in Table 1. The moisture contents of raw control and roasted kernels varied between 2.91 microwave-roasted and 21.64 control; unroasted . The oil contents ranged from 36.65 control and 43.77 microwave-roasted in apricot kernels. In addition, total phenol contents were detected between 0.06 oven and 0.20 mg GAE/100 g microwaveroasted while antioxidant activity varied between 2.55 oven and 19.34 microwave-roasted . It can be observed that the moisture contents of apricot kernels was reduced during roasting and the same time the recovery of oil was also partially enhanced. In addition, total phenolics and antioxidant activity values of roasted apricot kernels increased during roasting. However, the increase in antioxidant activity values of roasted apricot kernels may also be a result of Maillard reaction and caramelization products formed during roasting compared to control group unroasted apricot kernel . Significant p 0.05 differences were observed among chemical and bioactive properties of roasted and unroasted apricot kernels. Chandrasekara and Shahidi 22 determined that oil content was 41.30 to 42.58 in cashew nuts roasted at different temperatures. The oil yields of apricot kernels changed between 27.2 and 61. 4 w/w dry weight basis depending on the genotype 23 . Korekar et al. 24 determined 92.2 to 162.1 mg GAE/100 g total phenol in apricot kernels. Al-Juhaimi et al. 25 determined 54.41 mg GAE/100 g Soğancıoğlu to 59.61 mg GAE/100 g Hasanbey in apricot kernels. In addition, total phenolic contents in apricot kernel samples roasted at 720 W were determined between 27.41 mg G A E / 1 0 0 g Ç a t a l o ğ l u a n d 3 4 . 5 2 m g G A E / 1 0 0 g Soğancıoğlu in different varieties 25 . Goma 26 reported that total phenolic content and antioxidant activity value of sweet apricot kernel were identified as 3.290 mg/g and 59.53 mg/g, respectively. During the process of roasting, some chemical changes may occur in which sugars can condense with free amino acids, peptides, or proteins leading to the formation of Brown Maillard reaction products with potential antioxidant activity. Additionally, it has been stated that Folin-Ciocalteu reagent may not be precise for the determination of phenolic compounds as it may encounter certain analytical errors due to interaction and reaction with other non-phenolic components of samples being analyzed. Hence, chromatographic procedures HPLC may give better results during quantification of phenolic compounds 23,27 . Furthermore, this assay may be more useful in assessing the total antioxidants reducing capacity as being an electeon transfer-based assay it may measure the capacity of an antioxidant to reduce demonstrated by change in color an oxidant and the degree of color change is correlated with the sample s antioxidant concentrations 27,28 . Besides differences with those reported in literature, total phenolics and antioxidant activities of apricot kernel samples showed differences depending on roasting treatments applied in current study.

Individual phenolic compounds of apricot kernels
The phenolic compounds of unroasted and oven 70 for 24 h and microwave 720 W for 15 min roasted apricot kernels are shown in Table 2. The amounts of individual phenolic compounds were significantly p 0.05 affected by roasting processes. The extracts from roasted and unroasted apricot kernels were analyzed chromatographically and it was observed that the gallic acid contents varied from 0.53 mg/100 g control to 1.10 mg/100 g microwaveroasted ; 3,4-dihydroxybenzoic acid contents were between 0.10 control and 0.35 mg/100 g microwaveroasted ; -catechin contents remained between 0.15 mg/100 g microwave-roasted and 0.32 mg/100 g ovenroasted ; 1,2-dihydroxybenzene contents changed from 0.08 mg/100 g control to 0.17 mg/100 g oven-roasted ; kaempferol contents were between 0.03 mg/100 g ovenroasted and 0.24 mg/100 g control and isorhamnetin contents varied from 0.04 mg/100 g microwave-roasted to 0.18 mg/100 g control . The unroasted apricot kernel control was found to contain higher contents of syringic acid, caffeic acid, rutin-trihydrate, p-coumaric acid, transferulic acid, apigenin-7-glucoside, resveratrol and quercetin than the roasted ones, which, may also be attributed to the sensitivity of these compounds to microwave and thermal processing. In general, the phenolic compounds showed differences in their contents depending on roasting types. Chandrasekara and Shahidi 22 reported that the roasted cashew contained 0.251 mg/g of gallic acid, 0.867 mg/g of syringic acid, 0.112 mg/g of p-coumaric acid, 15.646 mg/g of -catechin, 8.368 mg/g of -epicatechin and 6.544 mg/g of epigallocatechin. Al-Juhaimi et al. 24 reported that the gallic acid contents of apricot kernels roasted at 540 W were higher 21.17 mg/100 g than that of unroasted kernels 15.35 mg/100 g . Certain variations in results of phenolic compounds contents from those in literature can also be due to ripening time, roasting method, roasting temperature, microwave power and analytical conditions 25 . By adding the contents of 16 phenolic compounds as presented in Table 2 it was observed that that unroasted kernels had a total of 2.6 mg/100 g of these compounds which was higher than microwave 2.34 mg/100 g and oven 3.35 mg/100 g roasted kernels. Hence, the higher total phenolic contents and better antioxidant activity of microwaveroasted kernels may be due to certain other antioxidants, which also interfered with Folin-Ciocalteu reagent during analysis. Therefore, this analytical method alone may not be correct to identify actual contents of phenolic compounds 27, 28 .

Fatty acid composition of apricot kernel oil
The fatty acid composition of oil samples from unroasted, oven-, and microwave-roasted apricot kernels are presented in Table 3. Palmitic, oleic, and linoleic acids were the key fatty acids in apricot kernel oils. Microwave 720 W  control ; linoleic acid contents ranged from 26.55 control to 27.12 oven-roasted and linolenic acid contents were between 0.10 and 0.11 . Roasting had no effect on arachidic and arachidonic acids of kernel oils. The palmitic and oleic acid contents in microwave-roasted kernels were partially higher than oil from oven-roasted kernels. In addition, the palmitic, oleic and linolenic acid contents in control oil from unroasted kernels were partially higher in oil from oven-roasted kernels. However, arachidic, linolenic, behenic and arachidonic acid contents of roasted apricot kernel oils were found similar in both systems. Statistical significant p 0.05 differences were observed among palmitic, oleic and linoleic acids of roasted and unroasted apricot kernel oils. Velickovska et al. 29 reported that sweet apricot oil contained 6.0 palmitic, 3 25 . Ogungbenle and Afolayan 30 determined 58.7 oleic, 18.9 linoleic and 12.1 palmitic acids in cashew nut roasted in an oven. The oleic and linoleic acids were the two key fatty acids of apricot kernel oils; however, their content is affected meaningfully by the variety and amounted to 38.5-67.2 and 26.4-54.8 , respectively 31 . The present study shows that apricot kernels are a rich source of oil containing appreciable amounts of oleic and linoleic acids. Furthermore, bioactive properties, fatty acid composition and phenolic compounds of unroasted and roasted apricot kernel and oils may change depending on analytical conditions, variety, geographical origin and roasting methods 32 36 .

Conclusions
The recovery of oil from apricot kernels roasted in microwave was higher compared to that from unroasted control kernels. Significant differences were observed among bioactive properties, fatty acid composition and phenolic compounds in apricot kernels roasted using either conventional thermal or microwave ovens. Microwave-720 W, 15 min and oven-roasting 70 , 24 h caused differences in fatty acid contents in apricot kernel oils which varied from those in unroasted kernels in certain cases. Microwave processing of foods is considered a new technique and it is gaining increased applications in household and industrial food processing. Present study demonstrate certain beneficial outcomes of applying microwave roasting to apricot kernels such as better recovery of oil and improved biological properties due to liberation of more phenolics and other bioactive compounds from kernel matrix. More studies can elaborate further the effects of microwave roasting on phenolic constituents and other biologically important molecules.