Production of ghee-like product from vegetable oils blend enriched with red onion skin extract as a natural antioxidant

Production of ghee-like product from vegetable oils blend enriched with red onion skin extract as a natural antioxidant

Elsayed Hassan Atwaa, Elsayed Mohamed Abd El-Wahed

and MahetabFawzy Ramadan

Food Science Department, Faculty of Agriculture, Zagazig University, Zagazig 44519, Egypt

Abstract

This investigation was conducted to produce an acceptable quality ghee-like product from vegetable oils blend with a high degree of unsaturation, using blends of palm oil and sunflower oil. The blends containing palm oil: sunflower oil (70:30, w/w) had an acceptable color and texture but the oily flavor was detected in all blends. Boiling of different blends with fermented cream induced ghee-like flavor. This treatment was more effective in palm oil: sunflower oil (70:30, w/w). Although fermented cream was an effective flavoring agent, it did not enhance the oxidative stability of the blends. Addition of red onion skins extract (OSE) at concentrations of 200, 400, and 600 ppm to palm oil: sunflower oil blend treated with 3% fermented cream retarded the rate of oxidative changes during incubation at 63ºC for 21 days compared with a sample containing BHA and control sample. It could be concluded that palm oil: sunflower oil blend enriched with 3% fermented cream and OSE (400 ppm) to prepare ghee-like product resulted in products with high oxidative stability.

Introduction

Consumer demands of food products have dramatically changed. Consumers are becoming aware that food contributes directly to their health (Mollet&Rowaland, 2002). Today food is not intended to only satisfy hunger and to provide necessary nutrients for human, but also to prevent nutrition-related diseases and improve the physical and mental well-being of consumers (Menrad, 2003). Efforts have been made to formulate food with ingredients that help to lower health risk (Liong&shal, 2006). Particular attention has focused on the health benefits of reducing saturated fat by increasing monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA) in food products. Consequently, attempts have been made to use vegetable oils in food formulations as their use may offer health and dietary advantages associated with their MUFA and PUFA content (William 2006; and Ramadan, 2014). However, increasing the level of unsaturated fatty acids in food products was found to be complicated with their high sensitivity to oxidation and the development of rancidity (During et al., 2000a, ;and Ibrahim, 2003).

The onion (Allium cepa L.) is a most used vegetable from the Allium family. Onion is important throughout the world, not only for its taste but also as a source of many beneficial compounds. Flavonoids and other bioactive compounds are found in different varieties of onions (Lachman et al., 2003), which are located primarily in the skin. A high concentration of quercetin is found in onion skin than in the fleshy part (Wiczkowski et al., 2008). In addition, onion skin extracts had the high antioxidant capacity (Nuutila et al., 2002; and Cao et al., 2013). Onion peel and outer layers (skin) are waste materials, which have high antioxidant properties (Gawlik-Dziki et al., 2015).

Blending different vegetable oils gives new blends with improved functional characteristics. Mixing some oils, which tend to crystallize and change their clarity when cooled with higher and more unsaturated oils gives a more stable and clear mixture, which remains stable during storage (Roiaini et al., 2015). In addition, blending oils leads to changes in the oil physical properties such as solid fat contents, cloud points, smoke point, sensory quality, density and viscosity and triacylglycerol profile (Serjouie et al., 2010; and Bakhtiary, 2014).

Vegetable ghee service as a substitute for traditional ghee. Originally, vegetable ghee was prepared from a blend of vegetable oils, which hydrogenated to make it solid, and processed to mimic ghee texture and flavor. For years, hydrogenation was essential in the production process, however, trans fatty acids resulted from partial hydrogenation posing a health milk to coronary heart disease (CHD). Palm oil and its product with a wide range in its solid content can impart the required solid fats contact and texture without the need for hydrogenation. At present, palm, soybean, rapeseed, cottonseed and sunflower oils are the most commonly used oils for vegetable ghee production( Zaghlool  et al ,2009).

The present work was carried out to produce a vegetable ghee-like product from oil blends with an increased level of PUFA using an accepted blend of palm oil and sunflower oil enriched with natural antioxidant extracted from red onion skin to improve the ghee oxidative stability.

Material and Methods

Materials and chemicals

Butylatedhydroxy anisole (BHA), 1,1-diphenyl-2-picrylhydrazyl (DPPH·), gallic acid and quercin were purchased from Sigma (St. Louis, MO, USA). Other chemicals and reagents were of the highest purity available. Palm oil and sunflower oil were obtained from Arma Company (10th of Ramadan City, Egypt). Red onion skin were obtained from the local market (Zagazig, Egypt), washed with distilled water and dried in an oven at 50˚C, before grinding to a powder and finally kept at 4˚C until the extraction.

Preparation of red onion skin extracts (OSE)

Dried red onion skin were extracted with ethanol (70%) at a ratio of 1:10 (w/v) in closed vessels by stirring at room temperature (25˚C) for 4 h followed by filtration through filter paper Whatman No. 1. The residues were re-extracted under the same conditions. All vessels were wrapped with aluminum foil to prevent light degradation during extraction (Yu et al., 2005). Ethanol extracts were evaporated in a rotary evaporator (Buchi-water bath-B-480, Switzerland) at 40˚C, and freeze-dried (Thermo Electron Corporation- Heto Power Dry LL 300 Freeze Dryer, Czech Republic). The dried OSE were stored at -20˚C.

Determination of total phenolic content (TPC) in OSE

    The concentration of TPC in OSE was measured using UV spectrophotometer (Jenway-UV-VIS spectrophotometer), based on a colorimetric oxidation/reduction reaction, as described by Skerget et al. (2005) using Folin-Ciocalteu reagent. 0.5 mL of diluted extract (10 mg in 10 mL solvent) was mixed with 2.5 mL of Folin-Ciocalteu reagent (diluted 10 times with distilled water) and 2 mL of Na₂CO3 (75 g/L). The sample was incubated for 5 min at 50˚C then cooled. For a control sample, 0.5 mL of distilled water was used. The absorbance was measured at 760 nm. TPC expressed as gallic acid equivalent (GAE) was calculated, and the results were expressed as an mg GAE g-¹ extract.

Determination of total flavonoid content in OSE

The total flavonoid content was determined by the aluminum chloride colorimetric method according to Lin and Tang (2007). The extract was dissolved in 80% methanol. Dissolved sample solution (0.5 mL) was mixed with 95% methanol (1.5 mL), 10% aluminum chloride (0.1 mL), 1 M potassium acetate (0.1 mL) and deionized water (2.8 mL). After 30 min, the absorbance was measured spectrophotometrically (Beckman DU 640B, Nyon, Switzerland) at 415 nm. Quercetin was used as the reference standard and the results were milligram quercetin equivalents (mg QE)/g extract. The assay was performed in triplicate.

Radical scavenging activity (RSA %) of OSE

RSA of OSE was measured by bleaching of the purple colored solution of DPPH· according to Hanato et al. (1988). One hundred µL of OSE (10 mg extract/10 mL solvent) was added to 3 mL of 0.1 mM DPPH· dissolved in ethanol. After the incubation period of 60 min at room temperature, the absorbance was determined against a control at 517 nm (Gulcin et al., 2004). Percentage of antioxidant activity of DPPH· was calculated as follows:

DPPH· scavenging activity (%) = [(A0- A1)/A0] × 100

where, A0 is the absorbance of the control reaction, and A1 is the absorbance in the extract. Samples were analyzed in triplicate.

HPLC analysis of bioactive compounds in OSE

For the characterization of active compounds in OSE, HPLC was used to identify and quanti­tative phenolic compounds. HPLC analysis was performed using an Agilent 1200 chromatograph (Agilent, Santa Clara, USA) and chromatographic separations were performed on a LUNA C-18 column (5 μm × 250 mm × 4.6 mm, Phenomenex, Torrance, USA). The composition of solvents and gradient elution conditions were described by Abdalbasit et al. (2010).

Preparation of palm oil: sunflower oil blends

Different blends were prepared from palm oil and sunflower oil at different ratios (Table 1). The blends were heated with 3% fermented cream at 125°C for 2 min and examined for flavor, texture and appearance. The blending ratio of 70: 30 palm oil and sunflower oil (w/w) boiled with 3% fermented cream was selected for further characterization. This ratio of blending gave a blend with good texture, appearance and flavor. The degree of unsaturation and fatty acid composition of this blend was determined.

GC analysis of fatty acids in oil blends

The fatty acid methyl esters were analyzed using Thermo Ultra Trace GC series gas chromatography and Thermo DSQ mass spectrometer from Thermo Fisher Scientific (Waltham, MA, USA). SGE BP x 70 column 25 m x 0.25 mm, 0.25 μm film thicknesses (65% methyl-35%- phenyl silicone) was used. The library search was carried out using NIST and Wiley GC-MS libraries (Tong et al., 2007). The area under each fatty acid peak relative to the total area of all fatty acid peaks was used to quantify the fatty acids identified. Results are reported as g fatty acid/100 g of total fatty acids (Lutterodt et al., 2011). All samples were analyzed in triplicate.

Degrees of unsaturation of oil blends

Iodine value was determined as an index for the degree of unsaturation according to AOAC (2007).

Preparation of oil blends enriched with OSE

Boiling oil blend with fermented cream was found to be effective in enhancing its flavor and simulating ghee-like flavor. A farther attempt has been done to enhance the oxidative stability of the vegetable oils blends using natural antioxidants extracted from red onion skin. OSE was added to oil blend (palm oil: sunflower oil, 70/30 w/w) at concentrations of 200, 400 and 600 ppm (treatments T1, T2 and T3). In addition, BHA was added at a concentration of 200 ppm (C1), while sample without additives was serving as control (C). All samples were incubated at 63 ±1˚C for 21 days to accelerate the lipid autoxidation. Samples were analyzed every week until the end of the incubation period (21 days) for peroxide value, acid values, thiobarbituric acid (TBA) test and Rancimat test. All experiments were triplicated.

Oxidative stability indices

Peroxide value (PV) and acid value (AV) of ghee-like product from oils blend enriched with different concentrations of OSE were determined according to AOAC (2007). TBA was determined according to Keeny (1971). In the Rancimat test, resistance to auto-oxidation was measured using 743 (Metrohm, Herisau, Switzerland) instrument at 120°C with an airflow rate of 20 L/h. The oxidative stability was expressed as induction period (h) or oxidative stability index (h). A 3.0 g of completely melted sample was weighed accurately into each reaction vessel. The vessels were placed in the heating block of the Rancimat apparatus. The reaction vessels were connected to the measuring vessels via connecting tube. 60 mL of deionized water was measured into each measuring vessel, containing the electrodes. The measuring vessels were placed in the Rancimat apparatus. All parts were connected to the apparatus as per the operating instructions, and the test was carried out until the endpoints of all the samples were reached, with a maximum allowable limit of 48 h according to AOCS (1997).

Statistical analysis

All the results of the present study were subjected to analyses of variance (ANOVA) using software (SAS Institute, 1990). Differences between means were collected by the least significant differences (LSD) at p < 0.05. All measurements were carried out in triplicate.  

Results and Discussion

Characterization of OSE (TPC, total flavonoid compounds, RSA and phenolic compounds)

In our study, the TPC of ethanolic OSE was 434.6 mg/g. Total flavonoid compounds of ethanolic OSE was 218.4 mg/g, while the RSA (%) of ethanolic OSE was 84.6%. These results agree with that previously reported (Singh et al., 2009; Cheng et al., 2013; Lee et al., 2014; Burri et al., 2017; Singh et al., 2017; and Viera et al., 2017) who studied antioxidant activity of red onion skin and peel extracts. Therefore, OSE could be a good source of bioactive compounds with high antioxidant potential.Table 2

Table 3 shows the phenolic and flavonoids compounds in OSE. The phenolic compounds in OSE ranged from 4.8 to 512.2 µg/g DW. The predominant compound in OSE was quercetin (512.2 µg/g DW). These results are similar to those reported by Cheng et al. (2013), Lee et al. (2014) and Burri et al. (2017).), who found that the phenolic compounds in OSE ranged from 12.20 to 1779.8 µg/g DW.

Characterization of oils and oil blend (degrees of unsaturation, and fatty acid composition)

In the present study, palm oil had a low iodine value (52.4) than sunflower oil (126.8). Blending palm oil with sunflower oil increased iodine value of blend to 82.6, which mean that blending of palm oil with 30% sunflower oil increased the levels of unsaturated fatty acids in the blend. The fatty acid composition of palm oil (PO), sunflower oil (SFO) and blend of PO: SFO is shown in Table 4. The results indicated that SFO contained 17.8% saturated fatty acids (SFA), 21.5% MUFA and 60.6% PUFA. PO contained 47.2% SFA, 43.50% MUFA, and 9.50% PUFA. The blending of SFO with PO increased the contents of PUSFA from 9.30% to 33.80%. These results were in agreement with the data obtained by Chugh and Dhawan (2014).

Oxidative stability of oils blend

Peroxide value (PV)

Results given in Table 5 showed that the PV of control vegetable oils and blend samples increased during the accelerated incubation up to the end of the incubation period (21 days). BHA treated sample recorded 11.04 meq O₂/kg at the end of incubation period. OSE enriched samples at different concentrations 200, 400 and 600 ppm showed PV values 12.12, 10.66 and 10.00 meq O₂/kg at the end of the incubation period, respectively. OSE significantly (p <0.05) lowered the PV throughout 21 days of storage at 63°C as compared to the control. The obtained results were in agreement with Pawar et al. (2014),who reported that addition of the ethanol extracts of vidarikand (Puerariatuberosa), shatavari (Asparagus racemosus) and ashwagandha (Withaniasomnifera) extracts  to ghee was more effective in preventing the development of the PV under accelerated conditions ,alsoTaghvaei and Jafari (2015) found that addition of the ethanol extracts of green tea, sesames  to edible oils was more effective in preventing the development of the PV under accelerated conditions. The PV of OSE enriched samplesat a rate of 400 and 600 ppm was significantly (p >0.05) lower than the samples enriched with BHA and control sample throughout 21 days of storage. These results agree with Chugh et al. (2014)and Asha et al, (2015), who found that supplemented of butter oil with orange peel extract preventing the development of the PV. Also, Nadeem et al. (2017) found that supplemented of margarine with chia oil preventing the development of the PV. The results highlighted the effect of OSE as natural antioxidants in retarding of lipid oxidation in oils blend.

Thiobarbituric (TBA) test

It is well known that TBA values are taken as an index to evaluate the advance of oxidation changes occurred in oils and fats. The addition of OSE to oils blend retarded the oxidative changes during accelerated storage at 63˚C/21days (Figure 1). This means that the formation of malonaldehyde, which affects the formation of pink color intensity from the reaction of TBA material with malonaldehyde, took place at a relatively lower rate in treated oils blend samples. The OSE-enriched samples at concentrations of 400 and 600 ppm showed lower TBA values throughout the accelerated incubation period at 63˚C/21days than control and BHA-enriched sample. It seems that there is a relationship between the antioxidant efficiency and the chemical composition of fats. OSE contains phenolic compounds which can be used as antioxidants or oxidation inhibitors. These results agree with previous studies (Pankaj et al., 2013; Atwaa et al. 2015; Taghvaei and Jafari, 2015; and Nadeem et al., 2017), they found that fortification of some fatty products such as ghee, edible oils and margarine with some natural antioxidants e.g. Arjuna bark, olive leaves and green tea extracts lowering TBA values throughout the accelerated incubation to these fatty products.

Acid value (AV)

Table 6 shows clearly that there were significant differences (p <0.05) between oils blend treatments through the incubation period. The results given indicated that there was a significant increase (p < 0.05) in AV with the increase in storage time. The AV of vegetable oils blend without antioxidant was 0.74 mg KOH/g at zero time, and increase to 2.92 mg KOH/g after 21 days of storage. At the end of the experiment, AV of oils blend enriched with BHT (200 ppm) and OSE was 2.32, 2.26, 2.14 and 1.98 mg KOH/g at a concentration of 200, 400 and 600 ppm, respectively. Considerable increases of AV were observed until the end of the incubation period of vegetable oils blend for all samples. Blend samples enriched with OSE at 400 and 600 ppm showed a lower increase in AV compared blend sample enriched with synthetic antioxidants’ referring to the high efficiency of OSE in delaying hydrolysis. Red onion skin extracts were favorable as an antioxidant agent (Singh et al., 2017; Viera et al., 2017). These results agreed with Atwaa et al. (2015) and Taghvaei and Jafari (2015), they found that fortification of some fatty products such as ghee, edible oils with some natural antioxidants e.g. Arjuna bark and olive leaves extracts lowering AV values throughout the accelerated incubation to these fatty products.

Rancimat test

The effect of OSE and BHA enrichment on the oxidative stability of oils blend containing high-level PUFA was evaluated by Rancimat equipment and the results are presented in Figure 2. The induction time (h) was used as an indicator of the antioxidative potential of added antioxidants. The induction period (IP) known also as oxidative stability index (OSI) determine the time required to reach an end point of oxidation corresponding to either a level of detectable rancidity or a fast change in the rate of oxidation (Presa-Owens and

Lopez-Sabater, 1995).

The OSE was found to be more effective in stabilizing oils blend against oxidative deterioration as compared to a control sample. The IP of oils blends enriched with OSE was found to be significantly higher (p < 0.05) than that of the control sample. Nahak and Sahu (2010) reported that phenolics compounds are considered to be the most important antioxidant components of plant materials, wherein a good correlation existed between the concentrations of phenolics and the total antioxidant capacities. The antioxidative traits of oils blend containing OSE were found to be significantly high (p <0.05) followed by blend enriched with BHA and finally control blend. The antioxidant activity of OSE and BHA in vegetable oils blend as measured by Rancimat test was in the following order: blend enriched with OSE (600 ppm)> blend enriched with OSE (400 ppm)> blend enriched with BHA> blend enriched with OSE (200 ppm)> control blend. The results agree with Pawar et al. (2014); El-Shourbagy and El-Zahar (2014); Taghvaei and Jafari (2015); Nadeem et al. (2017).

Conclusion

Vegetable ghee with acceptable flavor and oxidative stability could be produced from a blend of vegetable oil consisting of 70% palm oil and 30% sunflower oil after boiling with 3% fermented cream. The addition of OSE at concentrations of 400 or 600 ppm to the blend could enhance both flavor and oxidative stability of the product.

Table 1. Preparation and the sensory properties of Palm oil: sunflower oil blends

             ++Good, +Bland, - Unaccepted oily flavor

Table (2).     Total phenolic, flavonoid compounds and radical scavenging activity of rice bran extract (RBE).

Table 3. Phenolic and flavonoid compounds in OSE

Table 4. Fatty acid composition of palm oil, sunflower oil and oilsblend

SFO (sunflower oil), PO (palm oil), PO+SFO (palm oil 70% + sunflower oil 30%)

Table 5. Peroxide value (meq O₂/Kg) of oil blend during incubation at 63˚C for 21 days

The same letters in the column means significant differences

C: control without antioxidants                

C1:  vegetable oils blend with 200 ppm BHA (positive control)

T1: vegetable oils blend with 200 ppm OSE             

 T2: vegetable oils blend with 400 ppm OSE

T3: vegetable oils blend with 600 ppm OSE

Table 6. Acid value (mg KOH/g oil) of oil blend during incubation at 63˚C for 21 days

The same letters in the column means significant differences

 C: Control without antioxidants                

C1:  vegetable oils blend with 200 ppm BHA (positive control)

T1: vegetable oils blend with 200 ppm OSE             

T2: vegetable oils blend with 400 ppm OSE

T3: vegetable oils blend with 600 ppm OSE

Figure 1. TBA value (O.D at 532 nm) of oil blend during incubation at 63˚C for 21 days

C: control without antioxidants                

C1:  vegetable oils blend with 200 ppm BHA (positive control)

T1: vegetable oils blend with 200 ppm OSE             

 T2: vegetable oils blend with 400 ppm OSE

T3: vegetable oils blend with 600 ppm OSE  

Figure 2. Oxidative stability index (Rancimat) of oil blends

C: control without antioxidants                

C1:  vegetable oils blend with 200 ppm BHA (positive control)

T1: vegetable oils blend with 200 ppm OSE             

 T2: vegetable oils blend with 400 ppm OSE

T3: vegetable oils blend with 600 ppm OSE  

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