Improving Oils Stability during Deep-Fat Frying using Natural Antioxidants Extracted from Olive Leaves using Different Methods

Middle East Journal of Applied Sciences ISSN 2077-4613

Volume : 05 | Issue : 01 | Jan.-Mar.| 2015 Pages: 26-38

Corresponding Author: Zahran, H. A., Fats and Oils Dept., National Research Centre, Dokki, Giza, Egypt E-mail: [email protected]

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Improving Oils Stability during Deep-Fat Frying using Natural Antioxidants Extracted from Olive Leaves using Different Methods

1Zahran, H. A., 2M. H. El-Kalyoubi, 2M. M., Khallaf and 1A. G. Abdel-Razek

1 Fats and Oils Dept., National Research Centre, Dokki, Giza, Egypt 2 Food Sci., Dept., Fac. Agric., Ain Shams Univ., Shoubra El-Kheima, Cairo, Egypt

ABSTRACT The aim of this study was to investigate the influence of natural antioxidants extracted from olive leaves using different solvent types and extraction assisted methods (dynamic ultrasonic & microwave) on some oils stability during deep-fat frying. Extraction was conducted at different temperatures (25, 60 °C & boiling) using two solvents: distilled water and mixture of water/ethanol at 1:1 (v/v). Total phenolic compounds were measured using the Folin-Ciocalteau method and antioxidant properties were determined by two methods, DPPH scavenging activity and inhibition of β-carotene bleaching. It was found that the total yield of the olive leaves extract (OLE) was higher being 46.6 % in the case of using water/ethanol (1:1, 30min/ultrasound/25 °C), than that when using water only. The antiradical scavenging activity (%) by DPPH was ranged between 56.09 and 77.33 %. Furthermore, It was found that the using of ethanol/water at ratio 1:1 for extraction of phenolic compounds from olive leaves at 25 °C using dynamic ultrasonic and microwave as assisted extraction methods significantly increased the yield and total phenolic content, as well as reducing the time of extraction by 83 %.The OLE which obtained by ethanol/water at ratio 1:1 was selected and its antioxidant efficiency was studied. Samples of sunflower oil (SFO), soybean oil (SBO) and their blend (1:1, w/w) mixed with OLE (at 1000 ppm) were used for intermittent deep-frying at 180±5°C for 5 h / day, for 4 consecutive days and had been assayed for stabilization of oil samples against control (antioxidant free sample) and 200 ppm butylated hydroxy toluene (BHT) containing sample. Results exhibited the efficiency of OLE in reducing the changes in the physicochemical properties of all oil samples during the frying at 180±5°C/20 h. Key words Natural antioxidant – Olive leaves – Phenolic compounds – Solvent extraction – Water extraction –

Deep-frying.

Introduction

Olive tree (Olea europaea) belongs to the family of Oleaceae, which is cultivated for its edible fruits. Olive fruits are consumed as table olives and used for producing olive oil. The traditional "Mediterranean diet" is considered to be one of the healthiest. In this diet, olive oil is the most popular dietary lipid. The leaves of the olive tree have also been widely used in folk medicine in regions around the Mediterranean (Soler-Rivas 2000).

Olive mill and olive processing residues are attractive sources of natural antioxidants. An important part of these residues is olive tree leaves (usually 5%, but possibly reaching up to 10% of the total olives’ weight depending on practices applied). In addition, during olive tree cultivation, the pruning step generates a considerable volume of olive leaves, which are usually used as animal feed, and which could also be used for antioxidant or olive-leaf extract production (Fki et al., 2005; Guinda 2006; De Leonardis et al., 2008; Lafka et al., 2011 and Taamalli et al., 2012).

In the past few years, the demand for olive leaf extract has increased to be used in foodstuffs, food additives and functional food materials. Although the antioxidant activities of some single phenolic compounds in olive leaf are well known, the antioxidant activities of its extract from various solvents, and especially from wild olive varieties for which higher phenolics content is expected have not been clearly investigated (Massei and Hartley 2000).

As each plant material has its unique properties in terms of phenolic extraction, it is very important to adjust the extraction conditions and afterwards the extract evaluation in terms of antioxidant activity and composition, as well as further utilization. Solvent extraction is a process designed to separate soluble phenolic compounds by diffusion from olive leaves (solid matrix) using a solvent (liquid matrix). Many factors contribute to the efficiency of the solvent extraction process, such as solvent type, temperature, and time of extraction (Chirinos et al., 2007 and Lafka et al., 2007 and Abaza et al., 2011).

In recent years, it has observed an increasing attention for new extraction techniques such as microwave-assisted extraction enabling accelerating and shortening extraction times, efficient extraction, automation, and reduction of organic solvent consumption (Spingo and Faveri 2009).

Middle East J. Appl. Sci.., 5(1): 26-38, 2015

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Deep fat frying is one of the oldest cooking methods (dating back to 1600 A.C. in China) and is a very common and popular practice for the preparation and manufacture of foods. It is a fast, convenient, and energy efficient cooking procedure that increases palatability and provides crust formation together with pleasant flavors and odors (Gertz et al., 2000). This method, consisting in the immersion of the food in oil bath at temperature of 150°C - 190°C. Pedreschi et al., (2005) and Choe and Min (2007) provide many advantages, like very efficient heat transferring, crispy texture and typical flavor.

In order to overcome the stability problems of oils and fats, synthetic antioxidants, such as butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT) and tert-butyl hydroquinone (TBHQ) have been used as food additives. But, recent reports revealed that these synthetic antioxidants caused cancer and carcinogenesis (Hou 2003). Therefore, the most powerful synthetic antioxidant (TBHQ) is not allowed for food application in Japan, Canada and Europe. Similarly, BHA has also been removed from the generally recognized as safe (GRAS) list of compounds (Farag et al., 1989). Due to these safety concerns, there is an increasing trend to replace these synthetic antioxidants with natural ones, which, in general, are supposed to be safer. The effectiveness of different natural sources in stabilizing vegetable oils has been previously studied.

A consumer friendly way of improving oxidative stability of frying oils and fats is the addition of natural antioxidant components of plant origin. Several herbs, spices, and leaf extracts have been used as sources of natural antioxidants for the enrichment of oils used for frying; for example oregano powder in cottonseed oil (Houhoula et al., 2003) rosemary and sage extracts in palm oil (Che-Man and Jaswir 1999).

The objective of the present study is to shed light on the effect of natural antioxidants (from olive leaves extracted using different methods) on oil stability during deep-fat frying.

Materials and Methods Materials:

Potato was purchased from local market in Cairo, Egypt, washed and storage at 5 °C till used. Refined, bleached and deodorized sunflower oil (SFO) and soybean oil (SBO) free from additives were kindly supplied from Cairo Company for Oils and Soap, Ghamra, Cairo, Egypt. Olive leaves were obtained from Al-Raed Jet Master Company (olive oil extraction company). Chemicals and all reagents used were analytical grade and obtained from Merck Darmstadt, Germany.

Methods: Technological methods: Phenolic compounds extraction:

Olive leaves were washed and frozen at -20 °C for 24 h. then, dried in an oven at 40 °C for 4 days. Dried olive leaves were ground and put into polyethylene bags and kept in dark place. The extraction procedures were as follows: two g of dried ground leaves were weighed and put into a 100 ml quick-fit conical flask, the solvent was added to the sample at ratio of 5:1 (v/w), pH was adjusted to 2-3 (Theodora-Ioanna et al., 2011). The extraction methods are shown in Table (1) as follows:

Table 1: Phenolic compounds extraction methods from olive leaves:

Extraction solvent Assisted method

Temperature (°C) Time of extraction (min)

Water Stirring 25 180

Water Stirring 60 180 Water Dynamic ultrasonic 25 30 Water Dynamic ultrasonic 60 30 Water/Ethan

ol (1:1) Stirring 25 180

Water/Ethanol (1:1)

Dynamic ultrasonic 60 30

Water --- Boiling 10

Water Microwave --- 10 (sec.)

After extraction, the residual solution was filtered in 50 ml volumetric flask and completed to 50 ml by

extraction solvent. The extracts were collected and were ready for different analysis.


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Frying process: The experiment was designed to include: First: control, antioxidant free SFO, SBO and their blend.

Second: SFO, SBO and their blend with 200 ppm BHT. Third: SFO, SBO and their blend with OLE at a concentration of 1000 ppm. Fresh potato was washed, peeled and cut into slices (500 g), shelled shortly before frying, and were used throughout all frying sections. The oil (2.5 L) was placed in a covered stainless steel deep fryer, Model UEDF-194, 220-240V, 50/60Hz – 1800W. (EMJOY POWER) China, and heated to 180 ±5 ºC. Potato slices were fried in 100g batches at constant frying temperature. The batches were fried at 4-7 min intervals every 1h rate and for 5 h per day, for 4 consecutive days. A sample of oil (about 50 g) was taken every 2.5 h from the frying oil in a screw-cap vial and promptly kept frozen at -20º C until further analysis. Analytical methods: Polyphenols analysis: Total yield

About 10 g of ground olive leaves were weighed and put into a 100 ml quick-fit conical flask. Then, 50 ml of extracting solvent were added, after extraction as mentioned before, the residual solution was filtered in 100 ml round flask. The extract was disolventized under vacuum using rotary evaporator at about 40 °C to dryness and then weighted (Theodora-Ioanna et al. 2013)

Total phenol content (TPC):

The total polyphenols content of the olive leaves was determined colourimetrically at 725 nm using the Folin–Ciocalteau reagent according to the modified method described by Gutfinger (1981). To the solution of olive leaves extract (0.1–0.3 ml), 20 ml of deionized water and 0.625 ml of the Folin–Ciocalteau reagent were added in a 25 ml volumetric flask. After 3 min, 2.5 ml of saturated solution of Na2CO3 (35%) were added. The content was mixed and diluted to the volume with deionized water. After 1 h, the absorbance of the sample was measured at 725 nm against a blank using a double-beam ultraviolet–visible spectrophotometer Hitachi U-3210 (Hitachi, Ltd., Tokyo, Japan). Gallic acid served as a standard for preparing the calibration curve, and ranged from 2.5 to 20 µg/25 µl of assay solution.

Antioxidant activity: DPPH radical scavenging method:

The antioxidant activity of the phenol extracts was evaluated by using the stable 2,2-diphenyl-1-picryl-hydrazyl radical (DPPH) according to a modification method of Bandoniene et al. (2002). Methanolic solutions of phenol extracts (0.1 ml) and 3.9 ml methanolic solution of DPPH (0.0025 g/100 ml CH3OH) were placed in a cuvette and leave it to stand in dark place for 30 min, the absorbance at 515 nm was measured against methanol using a double-beam ultraviolet–visible spectrophotometer Hitachi U-3210 (Hitachi, Ltd., Tokyo, Japan). Simultaneously, the absorbance at 515 nm of the blank sample (0.1 ml methanol + 3.9 ml methanolic solution of DPPH) was measured against methanol. The radical scavenging activities of the tested samples, expressed as percentage inhibition of DPPH, were calculated according to the following formula:

% Inhibition = 100 X (A – A0) / A0 Where A0 is the absorbance at 515 nm of the blank sample at time t=0 min and A is the final

absorbance of the test sample at 515 nm.

Inhibition of β-carotene bleaching: The antioxidant activity of olive leave extracts were evaluated by the β-carotene linoleate model

system. A solution of β-carotene was prepared by dissolving β-carotene (2 mg) in chloroform (10 ml). Two ml of this solution were pipetted into a 100 ml round-bottom flask. After the chloroform was removed at 40 °C under vacuum, linoleic acid (40 mg), Tween 80 emulsifier (400 mg), and distilled water (100 ml) were added to the flask with vigorous shaking. Aliquots (4.8 ml) of this emulsion were transferred into different test tubes containing different concentrations of the olive leaves extracts (0.2 ml). The tubes were shaken and incubated at 50 ºC in a water bath. As soon as the emulsion was added to each tube, the zero time absorbance was measured at k = 470 nm using a spectrophotometer. Absorbance readings were then recorded at 20-min intervals until the control sample had changed its color. A blank, devoid of β-carotene, was prepared for background subtraction (Barros et al., 2007). Lipid peroxidation (LPO) inhibition was calculated using the following equation:


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LPO inhibition = (β-carotene content after 2 h of assay/initial β-carotene content) x 100 Frying oil samples analysis:

- Physical Properties: Refractive index (at 20°C) was estimated according to the procedures of the AOAC (2000). Relative viscosity value was determined using a Brookfield viscometer according to the method described in AOCS (1989).

- Chemical Quality Properties: Acidity % (as oleic acid) and iodine value were estimated by procedures described in AOAC (2000), while polar components in tested samples were determined by the method of Waltking and Wessels (1981).

- Oxidative Stability Properties: Peroxide value (PV) and anisidine value (AnV) were estimated by the procedures described in AOAC (2000). Totox value was calculated according to the equation, totox = AnV + 2PV.

Statistical analysis:

Results are representing the average and the standard deviation (SD) (in parenthesis) of three simultaneous assays carried out. Statistical significance of the differences between mean values was assessed by ANOVA; p ≤ 0.05 was considered statistically significant. The data obtained were exposed to proper statistical analysis according to Statistical Analysis System; Users Guide (SAS 1996).

Results and discussions Total yields of polyphenols:

Total yields of polyphenols of olive leaves obtained by different solvents and temperatures are shown in Table (2). The results indicated that means of total yield of polyphenols in olive leaves extracts expressed as dry matter (w/w) were ranged from 19.5 to 36.5 %. On the other hand, when using the dynamic ultrasound water bath as assistant method in the extraction for 30 min, the yields of polyphenols were ranged from 27.9 to 36.3 %. These results are comparable to those reported by Thoo et al. (2013). The statistical analysis of total yield of polyphenols indicated that both values were significantly (p≤ 0.05) affected by using the ultrasonic water bath extraction.

The results showed that the mixture of ethanol/water at 1:1 extracts had the highest amount of total yields, while water extract contained the lowest amount. However, using of ultrasonic extraction was the most efficient than traditional method. Furthermore, using the ultrasonic reduced the time of extraction from 180 min to 30 min.

While the total yield of polyphenols were 31.2 and 29.4 % as extracted by boiling water and microwave respectively. The results are similar to that obtained by Japon et al. (2006). The results demonstrated that using the ultrasound and microwave can dramatically accelerate the extraction rate and reduce the extraction time. Data revealed also ultrasonic extraction was faster and more efficient than traditional methods. This drastic acceleration can be attributed to the increased surface area between the solid and liquid phase by particle disruption.

The recovery of polyphenols from plant materials is influenced by the solubility of the phenolic compounds in the solvent used for the extraction process. Furthermore, solvent polarity will play a key role in increasing phenolic solubility.

From the equilibrium view point, an elevated temperature could increase the extraction rate and thus reduce the extraction time needed to reach the maximum recovery of phenolic compounds (Ho et al., 2007). However, elevated temperature may not be suitable for all types of phenolic compounds (Thoo et al., 2013). Total phenol content (TPC):

The means of TPC of olive leaves extracts in terms of g GAE kg–1 DM were ranged from 14.01 to

22.84 g/kg, Table (2). These results are agreement to those reported by Stavros et al. (2011). It could be noticed also the mixture of ethanol: water gave the highest of TPC (22.1 g/kg). In addition when using ultrasonic with ethanol/water mixture gave the highest TPC levels (22.84 g/kg). However, using of traditional extraction method (stirring/3h) at 25 ºC and using water/ethanol mixture, gave the lowest amounts of TPC being 14.01 and 14.22 g/kg respectively. The results revealed that the mixture of ethanol/water 1:1 with ultrasound-assisted method was the most effective for polyphenols extraction from olive leaves. These data are in accordance with those reported by Jerman et al. (2010). The statistical analysis indicated that the obtained values were significantly (p≤ 0.05) affected by using ultrasound extraction.


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Concerning the efficiency of the solvent used Ho et al. (2008) reported that the absolute alcoholic solvents decrease extraction yield of olive leaves. So, application of water combined with other organic solvents makes it a moderately polar medium ensuring the optimal conditions for extraction of polyphenols. Besides that, using water in combination with alcohols leads to an increase in swelling of plant materials and the contact surface area between the plant matrix and the solvent which finally, improves the extraction yield (Chirinos et al., 2007). The temperature used in polyphenol extraction from olive wastes has to be chosen very carefully, since the process may be affected in a non-desirable way. It is true that higher temperatures (40 ºC) may increase the solubility of phenolics (Japon et al., 2006), but too high (60 ºC) may cause their degradation. Table 2: Total yields %, total phenol content (TPC, g/kg) and antioxidant activity of polyphenols in olive leaves extracted by different

solvents:

Extraction solvent Total yield %* TPC (g/kg)*

Antioxidant activity

DPPH* Inhibition of β-carotene*

Water (25ºC)/stirring/3h

19.5 ±1.8d

14.01 ±0.01c

59.28 ±1.20c

52.14 ±0.70b

Water (60ºC)/stirring/3h

29.8 ±0.7c

16.18 ±0.01b

56.15 ±1.48d

47.28 ±0.66b

EtOH:Water, 1:1 (25ºC)/stirring/3h

36.5 ±0.8a

14.22 ±1.58c

59.51 ±0.17cd

52.23 ±1.15b

Water (25ºC)/ultrasonic/30min

27.9 ±0.4c

16.58 ±0.22b

56.09 ±1.65d

48.92 ±1.17b

Water (60ºC) /ultrasonic/30min

33.9 ±0.8b

22.10 ±0.10a

74.66 ±0.17b

60.08 ±3.23a

EtOH:Water, 1:1 (25ºC)/ultrasonic/30min

36.3 ±0.2a

22.84 ±1.16a

77.33 ±1.59a

59.61 ±3.77a

Boiling water /10 min 31.2 ±0.3c

17.86 ±0.11b

72.04 ±0.85b

51.61 ±1.07b

Water/ microwave/10 sec

29.4 ±0.7c

14.36 ±0.16c

62.41 ±2.51c

50.02 ±0.10b

* Means with the same letter in the same column are not significant at (p≤ 0.05)

Antioxidant activity assessment: DPPH assay:

Antioxidant activity of OLE using DPPH radical was measured and ranged between 56.9 to 77.33 %, Table (2). Olive leaves extracted by the mixture of ethanol/water at ratio 1:1, with and without ultrasound clearly showed the highest activity being 77.33 % and 74.66 %, respectively, followed by OLE using boiling water/10 min (72.04 %) then by using microwave/10 sec (62.71 %). However, moderate antiradical activity (%) was observed for water at 25 and 60 ºC with and without ultrasonic using stirring for 30 min and 3 h, respectively, which ranged between 56.09 to 59.28 %. These results are in agreement with those reported by Stefania et al. (2008).

Inhibition of β-carotene bleaching:

The antioxidant activities of the studied extracts varied significantly (p ≤ 0.05) with the type of solvent used and temperature (Table 2). The antioxidant activities (%) in OLE measured by inhibition of ß-carotene bleaching ranged between 47.28 to 60.08 %. The results revealed that olive leaves extracted by the mixture of ethanol/water at ratio (1:1) with and without ultrasound showed clearly the highest activity being 59.61 and 60.08 %, respectively. However, moderate antiradical activity (%) was observed for OLE obtained by boiling water/10 min., microwave/10 sec., water/stirring for 3h, at 25 and 60 ºC, water/stirring for 30 min with ultrasound at 25 and 60 ºC, which ranged between 47.58 to 52.23 %, these values were no significant differences (p ≤ 0.05) as shown in Table (2). The obtained results are in agreement with those reported by Stefania et al. (2008).

From the aforementioned results, it could be concluded that the best OLE was by using water/ethanol at ratio of 1:1 with dynamic ultrasonic method. So, in this study this extract was used in frying experiment to evaluate its efficiency to increase the stability of some edible oils against thermal oxidation. Physicochemical properties of oils during deep-fat frying: Relative viscosity:

Fig (1) reveals that the relative viscosity of fried oil samples (SFO and SBO) increased with increasing the time of frying at 180±5°C, the control oil (antioxidant free sample) showed the highest values at each


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heating period. On the other hand, the obtained values decreased with the addition of OLE, as well as the sample containing BHT which had values similar to that of sample containing OLE. Furthermore, the values of sample containing BHT and OLE decreased with blending SFO and SBO at ratio of 1:1.

The relative flow time reflects the magnitude of oil viscosity and is generally considered as an adequate indicator of the resistance to the oil flow affecting by the reactions which may be occurred in it (Badawy and Ismail 1990). This means that the addition of OLE to SFO, SBO and their blend induced the least changes on viscosity.

Fig. 1: Changes in relative viscosity of SFO, SBO and their blend treated with OLE compared to control oils

and oils treated with BHT during deep-frying at 180±5°C for 20h. Refractive index:

Fig (2) shows that the refractive index of tested samples increased with increasing the time of frying at 180±5°C, the control oils (antioxidant free sample) exhibited the highest values at each heating period. It was noticed that, these values decreased with the addition of OLE, or BHT to oil samples which showed similar values. However, the values of control oils and samples containing BHT or OLE of SBO and blend oils were the same, however, these values decreased with blending SFO and SBO at ratio 1:1.

The refractive index is considered one of the most important physical characteristics of oils, as it is useful for estimating the degree of their saturation as well as for identification processing purposes, establishing their purity and observing the progress reaction such as catalytic hydrogenation, oxidation and isomerisation. Since the OLE protect the oil from oxidation (Amro et al., 2002 and De Leonardis et al., 2007). Therefore, samples containing OLE at 1000 ppm exhibited lower refractive index values as compared with control and BHT containing samples. Free fatty acids (FFA):

Fig (3) reveals the changes occurred in the % acidity of the control and antioxidant treated oil samples during frying at 180±5°C for 20 h. The graphs showed that the FFA content of all samples increased with increasing the heating time, while at each heating time and after 20 h of the intermittent heating the control sample exhibited the highest FFA content, followed by the samples containing OLE and BHT. Moreover, the values of oil samples containing BHT or OLE decreased with blending SFO and SBO at ratio 1:1.

The acidity (as % oleic acid) is considered a good indicator for the hydrolysis extent takes place in oils (Frega et al., 1999). It could be noticed that BHT and OLE at levels of 200, 1000 ppm reduced the hydrolysis of


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the triglycerides which resulted in low free fatty acid content and low acidity than the control sample. This indicated that the phenolic compounds in OLE decreased the oil hydrolytic rancidity. In this respect (Farag et al., 2003) reported that total and free polyphenols obtained from both leaves and fruits of olive cultivar possessed anti-hydrolytic activity and increased with concentration.

Fig. 2: Changes in refractive index of SFO, SBO and their blend treated with OLE compared to control oils and

oils treated with BHT during deep-frying at 180±5°C for 20h.

Iodine value:

Fig (4) illustrated the changes occurred in the iodine values of the control and antioxidant treated oil samples during frying at 180±5°C for 20 h. The graphs showed that the iodine values of all oils decreased with increasing the frying time, while at each frying time the control samples exhibited the lowest iodine values, followed by oils containing OLE & BHT,

The iodine value is considered a good index for the unsaturation extent of fatty acids in oils. The OLE reduced the changes of iodine values by the same way which affects acidity, these results are in agreement with those reported by Anwar et al. (2006). Peroxide value:

Fig (5) showed the changes occurred in the peroxide values (PV) of the control oil samples and antioxidant treated samples during frying at 180±5°C for 20 h. Results indicated that the peroxide values of all oil samples increased with increasing the frying time, while at each frying time and the end of frying, the control samples exhibited the highest peroxide values, followed by oils containing OLE and BHT.

Peroxide value is known as an indicator of the extent of forming the hydroperoxides and peroxides. Also, it is a valuable measure of the early stages of rancidity occurring in food under ambient conditions. The OLE at level 1000 ppm reduced the PV during frying since it reduced the hydroperoxide formation and the consequence of its degradation to peroxides. Anisidine value:

The changes occurred in the AnV of the control and antioxidant treated oil samples during frying at 180±5°C for 20 h are shown in Fig (6). Anisidine value of all samples increased with increasing the frying time,


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0.000 0.500 1.000 1.500

02.55

7.510

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110.00112.00114.00116.00118.00120.00122.00124.00126.00

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Fig. 3: Changes in % acidity of SFO, SBO and their blend treated with OLE compared to control oils and oils

treated with BHT during deep-frying at 180±5°C for 20 h.

Fig. 4: Changes in iodine value of SFO, SBO and their blend treated with OLE compared to control oils and oils

treated with BHT during deep-frying at 180±5°C for 20h.


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0.001.002.003.004.005.006.007.008.009.00

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while at each frying time and after 20 h of the intermittent frying, the control sample exhibited the highest AnV, followed by oil samples containing OLE and BHT. Furthermore, the values of oils containing BHT and OLE decreased with blending of SFO and SBO at ratio 1:1.

Anisidine value is a measurement of aldehyde content in an oil, principally 2,4-dienals and 2-alkenals (AOCS 1992). Aldehydes are secondary oxidation products produced during the oxidation of lipids. The OLE reduced the AnV during frying since it reduced the hydroperoxide formation and the consequence degradation of it to peroxides.

Fig 5: Changes in peroxide value of SFO, SBO and their blend treated with OLE compared to control oils and

oils treated with BHT during deep-frying at 180±5°C for 20h.

Totox value:

Results in Fig (7) showed that the totox value of all samples increased with increasing the frying time, while at each frying time and after 20 h of the intermittent frying the control sample exhibited the highest totox values, followed by the oil samples containing OLE and BHT. Furthermore, the values of samples containing BHT and OLE decreased with blending of SFO and SBO at ratio 1:1.

Peroxide value and p-anisidine value may be combined to form an oxidation value or “Totox” value. The Totox value is calculated by the formula AV + 2PV to indicate oil’s overall oxidation state. The lower the totox value, the better the quality of oil. Polar compounds:

The changes in polar compounds Fig (8) indicated that the polar compounds of all samples were

increased gradually with increasing the frying time, while at each frying time, the control samples exhibited the highest polar compounds followed by the samples containing OLE and BHT.

It has been reported that the polar compounds content is considered a reliable indicator of the state of the edible oils deterioration (Gere 1982). The results took the same trend of the other chemical quality properties which indicate that OLE can act as a good antioxidant in protecting SFO, SBO and their blend as reported by Lumley (1988).


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Fig. 6: Changes in anisidine value of SFO, SBO and their blend treated with OLE compared to control oils and

oils treated with BHT during deep-frying at 180±5°C for 20 h.

Fig. 7: Changes in totox value of SFO, SBO and their blend treated with OLE compared to control oils and oils

treated with BHT during deep-frying at 180±5°C for 20h.


36

0.00

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Fig. 8: Changes in % polar compounds of SFO, SBO and their blend treated OLE compared to control oils and oils treated with BHT during deep-frying at 180±5°C for 20h.

Conclusion

From the obtained results, it could be concluded that ethanol/water at ratio 1:1, v/v using dynamic ultrasonic method at 25 ºC/30 min was the most efficient extraction method for phenolic compounds from olive leaves, and enhances not only the rate of extraction but also the yield of polyphenols as well as reducing the time of extraction. Olive leaves is a valuable and economic source of phenolic compounds that can be used in many of the food, pharmaceutical and therapeutic applications. It could be concluded also, that olive leaves extract at 1000 ppm can effectively stabilize sunflower, soybean oils and their blend as compared with BHT at its legal limit during the deep-frying at 180 ± 5°C. Olive leaves extract can be recommended as a potent source of antioxidants for the stabilization of oil food systems, especially unsaturated vegetable oils.

References Abaza, L., N. Youssef, H. Manai, F. Haddada, K. Methenni and M. Zarrouk, 2011. Chétoui olive leaf extracts:

Influence of the solvent type on phenolics and antioxidant activities. Grasas Y Aceites, 62, 96–104. Abdel-Razek, A. G., G. H. Ragab and H. S. Ali, 2012. Pretreatments and frying time on physical and chemical

properties of cottonseed oil. J. of Applied Sci. Res., 8(11): 5381-5387. Amro, B., T. Aburjai and S. Al-Khalil, 2002. Antioxidative and radical scavenging effects of olive cake extract.

Fitoterapia, 73: 456-461. Anwar, F., A. Jamil S. Iqbal and M. Sheikh, 2006. Antioxidant activity of some plant extracts for edible oils at

ambient and accelerated conditions. Grasasy y Aceites, 57(2): 189-197. AOAC, 2000. Official Methods of Analysis. Association of Official Analytical Chemists. Published by the

AOAC. International 17th ed., Washington, D.C. AOCS, 1989. Official and Recommended Practices of the American Oil Chemists` Society, 5th ed.; Champaign,

IL. AOCS, 1992. Official Methods and Recommended Practices of the American Oil Chemists’ Society, 4th edn.,

AOCS Press, Champaign ,Additions and Revisions, Method Cd 18–90. Badawy, H. and A.I. Ismail, 1990. Changes in physical and chemical properties of sunflower seed oil used for

frying and heating. Egypt. J. Appl. Sci., 5(8): 371-379.


37

Bandoniene, D., M. Murkovic,W. Pfannhauser, P. R. Venskutonis and D. Gruzdiene, 2002. Detection and activity evaluation of radical scavenging compounds by using DPPH free radical and on-line HPLC–DPPH methods. European Food Research Technology, 214, 143–147.

Barros, L., P. Baptista and I. C. Ferreira, 2007. Effect of Lactarius piperatus fruiting body maturity stage on antioxidant activity measured by several biochemical assays. Food and Chemical Toxicology, 45, 1731–1737.

Che-Man, Y. B. and I. Jaswir, 1999. Effects of natural and synthetic antioxidants on changes in refined bleached and deodorized palm olein during deep-fat frying of potato chips. Journal of Agricultural and Food Chemistry, 76, 331–339.

Chirinos, R., H. Rogez, D. Campos, R. Pedreschi and Y. Larondelle, 2007. Optimization of extraction conditions of antioxidant phenolic compounds from mashua (Tropaeolum tuberosum Ruíz & Pavón) tubers. Sep. Purif. Technol., 55, 217–225.

Choe, E. and D. B. Min, 2007. Chemistry of Deep-Fat Frying Oils. Journal of Food Science, Vol. 72, pp. R77- R86.

De Leonardis, A., A. Aretini, G. Alfano, V. Macciola and G. Ranalli, 2008. Isolation of a hydroxytyrosol-rich extract from olive leaves (Olea Europaea L.) and evaluation of its antioxidant properties and bioactivity. Eur. Food Res. Technol., 226, 653–659.

De Leonardis, A., V. Macciola, G. Lembo, A. Aretini and A. Nag, 2007. Studies on oxidative stabilization of lard by natural antioxidants recovered from olive oil mill wastewater. Food Chemistry, 100: 998-1004.

Farag, R. S., A. Z. Badei and G. S. El Baroty, 1989. Influence of thyme and clove essential oils on cottonseed oil oxidation. J. American Oil Chemists Society, 66(6): 800-804.

Farag, R. S., G. S. El-Baroty and M. A. Basuny, 2003. The influence of phenolic extracts obtained from the olive plants (cvs) picual and Kronakii ) on the stability of sunflower oil. J. Food Sci. Techn., 55: 81-87.

Fki, I.; N. Allouche, and S. Sayadi, 2005. The use of polyphenolic extract, purified hydroxytyrosol and 3,4-dihydroxyphenyl acetic acid from olive mill wastewater for the stabilization of refined oils: A potential alternative to synthetic antioxidants. Food Chem., 93, 197–204.

Frega, N., M. Mozzon and G. Lercker, 1999. Effect of free fatty acids on the oxidative stability of vegetable oils. J. American Oil Chemists Society, 76: 325-329.

Gere, A., 1982. Studies of the changes in edible fats during heating and frying. Die Nahrung, 26: 923-932. Gertz, C., S. Klostermann and S. Kochhar, 2000. Testing and Comparing Oxidative Stability of Vegetable Oils

and Fats at Frying Temperature. European Journal of Lipid Science and Technology, Vol. 102, No. 8-9, pp. 543- 551.

Guinda, A., 2006. Use of solid residue from the olive industry. Grasas Y Aceites, 57, 107–115. Gutfinger, T., 1981. Polyphenols in olive oils. Journal of the American Oil Chemists Society, 58, 966–968. Ho, S., L. S. Hwang, Y. Shen and C. Lin, 2007. Suppressive effect of a proanthocyanidin-rich extract from

longan (Dimocarpus longan Lour.) flowers on nitric oxide production in lps-stimulated macrophage cells. J. Agric. Food Chem., 55, 10664-10670.

Ho, C. H., J. E. Cacace and G. Mazza, 2008. Extraction of lignans, proteins and carbohydrates from flaxseed meal with pressurized low polarity water. LWT – Food Science and Technology, 40 (9): 1637-1647.

Hou, D.X., 2003. Potential mechanism of cancer chemoprevention by anthocyanin. Current Advancements in Molecular Medicines, 3: 149-159.

Houhoula, D. P., V. Oreopoulou and C. Tzia, 2003. Antioxidant efficiency of oregano during frying and storage of potato chips. J. of the Sci. of Food and Agric., 83, 1499–1503.

Japon, R.; J. M. Luque-Rodriguez and M. D. Luque de Castro, 2006. Dynamic ultrasound-assisted extraction of oleuropein and related biophenols from olive leaves. Journal of Chromatography A, 1108, 76–82.

Jerman, T., P. Trebše, B. Mozetic and A. Vodopivec, 2010. Ultrasound-assisted solid liquid extraction (USLE) of olive fruit (Olea europaea) phenolic compounds Food Chemistry, 123, 175–182.

Lafka, T. I., V. J. Sinanoglou and E. S. Lazos, 2007. On the extraction and antioxidant activity of phenolic compounds from winery wastes. Food Chem., 104, 1206–1214.

Lafka, T. I., A. E. Lazou, V. J. Sinanoglou and E.S. Lazos, 2011. Phenolic and antioxidant potential of olive oil mill wastes. Food Chem., 125, 92–98.

Lumley, I. D., 1988. Polar compounds in heated oils. In: Frying of Food, Principles. Changes, New Aproaches (Ed. G. Varela, A. Bender and I.D. Morton), VCH publishers Ltd, London, pp: 166-173.

Massei, G. and S. E. Hartley, 2000. Disarmed by domestication? Induced responses to browsing in wild and cultivated olive. Oecologia, 122, 225–231.

Pedreschi, F., P. Moyano, K. Kaack and K. Granby, 2005. Colour Changes and Acrylamide Formation in Fried Potato slices. Food Research International, Vol. 38, No. 1, pp. 1-9.

Soler – Rivas, C., C. Espin and H. J. Wichers, 2000. Oleuropein and related compounds. Journal of Food and Agriculture, 80 (7), 1013-1023.


38

Spingo, G. and D. M. D. Faveri, 2009. Microwave-assisted extraction of tea phenols, a phenomenological study. J. Food Eng., 93, 210 – 217.

Stavros, L., A. Vasilios, G. Olga, B. Maria, G. Ioannis, T. John and B. Filippos, 2011. Enrichment of table olives with polyphenols extracted from olive leaves. J. of Food chemistry, 127, 1521-1525.

Stefania, M., K. Elias, P. Dimitris and K. Panagiotis, 2008. Optimisation of the extraction of olive (Olea europaea) leaf phenolics using water/ethanol-based solvent systems and response surface methodology Anal Bioanal Chem, 392, 977–985.

Taamalli, A., D. Arráez-Román, M. Zarrouk, J. Valverde, A. Segura-Carretero and A. Fernández-Gutiérrez, 2012. The occurrence and bioactivity of polyphenols in Tunisian olive products and by-products: A review. J. Food Sci., 77, 83–92.

Theodora-Ioanna, L., E. L. Andriana, J. S. Vassilia and S. L. Evangelos, 2011. Phenolic and antioxidant potential of olive oil mill wastes. Food Chemistry, 125, 92–98.

Theodora-Ioanna, L., E. L. Andriana, J. S. Vassilia and S. L. Evangelos, 2013. Phenolic Extracts from Wild Olive Leaves and Their Potential as Edible Oils Antioxidants. J. of Foods, 2, 18-31.

Thoo, Y. Y., S. Y. Ng, M. Z. Khoo, W. M. Wan-Aida and C. W. Ho, 2013. A binary solvent extraction system for phenolic antioxidants and its application to the estimation of antioxidant capacity in Andrographis paniculata extracts International Food Research Journal, 20(3): 1103-1111.

Waltking, A. E. and H. Wessels, 1981. Chromatographic Separation of polar and non polar components of components of frying fats. J. Assoc. of Chem., 64(6): 1329-1330.

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Improving Oils Stability during Deep-Fat Frying using Natural Antioxidants Extracted from Olive Leaves using Different Methods