Quality Evaluation of Blended Rice bran and Mustard oil

Transcription

1 Quality Evaluation of Blended Rice bran and Mustard oil Monika Choudhary* and Kiran Grover Department of Food and Nutrition Punjab Agricultural University, Ludhiana (Punjab) ABSTRACT Rice bran oil (RBO) is nutritionally superior non-conventional vegetable oil and mustard oil (MO) is traditional oil widely used in domestic cooking in rural India. So, the present study was designed to develop a healthier and stable blend of RBO and MO. Therefore, RBO was blended with MO in two ratios i.e. 80:20 and 70:30. These blends were analyzed for fatty acid composition, physiochemical properties, oxidative stability, and antioxidant activity. Consequently, RBO+MO in the ratio of 80:20 contained 16.9 percent SFA, 32.9 percent MUFA and 50.8 percent PUFA whereas the percentage of SFA, MUFA and PUFA present in RBO+MO (70:30) was 15.2, 25.6 and 59.2 respectively. RBO+MO in the ratio of 70:30 showed adequate smoke point (188 C), frying temperature (180 C) and had low acid value (0.28 mg KOH/g) and saponification value (224.0 mg KOH/g) as well as a low percentage of free fatty acids (0.14%). In terms of oxidative stability and antioxidant activity, RBO+MO (70:30) showed least percent increase (33.9 %) in peroxide formation after 28 days of incubation period and also had highest radical scavenging activity (57.5 %) whereas the highest content of total natural antioxidants ( mg/kg) was present in RBO+MO (80:20). A significant (pd 0.05) difference was found in all the quality parameters of vegetable oils and it was concluded that RBO+MO in the ratio of 70:30 was an ideal blend in terms of overall quality parameters. Key Words: Rice bran oil, Mustard oil, Fatty acid composition, Oxidative stability, Antioxidant activity. INTRODUCTION A good quality vegetable oil must be low in saturated fat, linolenic acid, and has good flavor, high oxidative stability and should be trans fat free (Venkattakumar and Padmaiah, 2010). Rice bran oil (RBO), a non-traditional vegetable oil meets these requirements due to its unique nutritional characteristics. RBO has high levels of phytosterols, gamma-oryzanol, tocotrienols as well as tocopherols and it extends the shelf - life of snack foods (Ramesh and Murughan, 2008). As India imports considerable quantity of edible oil, use of domestic rice bran oil can help in import substitution, thus saving valuable foreign exchange. However, proper promotion of this nontraditional oil as health oil, remains the most important factor in increasing its acceptability as a cooking oil among the masses. Mustard is the second most important edible oilseed sharing 27.8 per cent in the India s oilseed economy. In India, 82 per cent of rural consumers use mustard oil (MO) as their staple edible oil, with monthly consumption varying between 2-4 liters per family. The Indian cultivars of mustard, due to high content of erucic acid and glucosinolates, have limited preference in international market. Though the nutritional advantages of mustard oil available in India outdo many other edible oils (lowest amount of harmful saturated fatty acids, and contains two essential fatty acids linoleic and linolenic), the presence of erucic acid and glucosinolates are considered to be undesirable. Hence, blending can be a feasible technique to reduce the amount of erucic acid. * Corresponding Author s moni0986@gmail.com 45

2 Both rice bran oil and mustard oil are less expensive edible oils and RBO has also been scientifically proved best for blending. Hence, the present work was designed to develop a stable and healthier blend of a non-traditional (RBO) and traditional (MO) at reduced cost. MATERIALS AND METHODS Refined rice bran oil (RBO) and mustard oil (MO) were purchased from local market. All the analytical and gas chromatography grade chemicals and solvents used were supplied by Himedia (Mumbai, India). Preparation of blends A 100 ml mixture of RBO and MO was placed in duplicate in 250-ml beakers and was mixed by using a mechanical stirrer at 180 rpm for 15 min to prepare blends of RBO and MO. The blend was prepared in two ratios i.e., 80:20 and 70:30 (Bhatnagar et al, 2009). These blends were analyzed for physiochemical properties, fatty acid composition, oxidative stability, natural antioxidants and radical scavenging activity. Fatty acid composition by gas chromatography (GC): Oil samples were analysed for their fatty acid composition by gas chromatography using fatty acid methyl esters (FAME) preparation (Appleqvist, 1968). FAMEs were analysed on a gas chromatograph (Varian CP 3800, USA), equipped with a flame ionization detector (FID) and a fused silica capillary column (50 m x 0.25 mm i.d.), coated with CP-SIL 88 as the stationary phase. The oven temperature was programmed at 200 C for 13 min. The injector and FID were at 250 C. A reference standard FAME mix (Supelco Inc.) was analyzed under the same operating conditions to determine the peak identity. The FAMEs were expressed as relative area percentage. Physicochemical properties: Smoke point and frying temperature were determined according to the AOCS Method Cc 9a-48 (1990). Viscosity of vegetable oil was recorded with the help of viscometer (Patent no: 688/del/85). Peroxide value, iodine value, saponification value, acid value and free fatty acids of the vegetable oils were determined by using AOAC (2000) methods. Oxidative stability: Samples were placed in Choudhary and Grover beakers (50- ml) capacity and incubated at 37 C and 55 per cent RH in a lab incubator to study the oxidative stability of the blends over a period of 4 weeks (28 days). Samples were withdrawn at weekly intervals and analysed for their peroxide value (PV). The PV is a titration measure of all peroxides and lipid oxidation products that will oxidize the potassium iodide under operating conditions. Five grams of the oil sample was poured into a 250 ml flask. Thirty millilitres of glacial acetic acid/chloroform (3:2, v/v) solutions were added and stirred. A stopper was inserted and the flask was shaken for 1 min and left for 5 min in the dark at o C. Thirty millilitres of distilled water was added, and the librated iodine was titrated with 0.01 N Na 2 S 2 O 3, using starch as indicator. The PV was calculated following the AOCS (2003) method. Antioxidant activity: To analyze antioxidant activity of blend, natural antioxidants (oryzanol, á-tocopherol equivalent) and radical scavenging activity (RSA) towards DPPH radicals were determined. Natural antioxidants: The alpha tocopherol equivalent was determined by Emmerie Engel assay modified by Baker and Frank (1988). Three stoppered centrifuge tubes were taken and labelled as standard, sample, and blank. To these labelled tubes, 0.5 ml of DL-á-Tocopherol acetate (standard), 0.5 ml of blended oil (sample) and 0.5 ml of distilled water (blank) were added respectively. In each centrifuge tube, 0.5ml of ethanol and 0.5ml of xylene were added. All the three stoppered centrifuge tubes were mixed and centrifuged for 15min. In other three clean stoppered tubes, 0.5ml of each xylene layer was transferred. To this 0.5ml of dipyridyl reagent was added and 0.5 ml of this mixture was pipetted into spectrophotometer cuvettes (Systronics UV-VIS- 108, Bangalore, India) and the absorbance of sample and standard against the blank was read at 460 nm. To the blank, standard and sample, 0.33 ml of ferric chloride reagent was added and mixed for 30 seconds. After 1.5 minutes of the addition, zero setting was done at 520 nm and absorbance of the sample and standard against the blank was read. The alpha tocopherol equivalent was calculated by using this formula: 46

3 Alpha tocopherol equivalent (mg%) = [alpha tocopherol in standard (mg %) x {sample OD 520 (0.29 x sample OD 460 )}/standard OD 520 ] Oryzanol content of blended oil was determined by a spectrophotometric method (Gopal et. al. 2006) by dissolving 0.01 ml of the sample in 10 ml of hexane and reading the absorbance at 314 nm in a 1-cm cell (Systronics UV-VIS-108 spectrophotometer, Bangalore, India). The oryzanol content was calculated by using the formula: [(A/W) X (100/358.9)] Where A is the absorbance of the sample, W is the weight of the sample in gram/100 ml, is specific extinction coefficient for oryzanol. Radical Scavenging Activity (RSA) toward DPPH Radicals: DPPH radical scavenging activity was measured using the method described by Erasto et al (2007) and Miraliakbari and Shahidi (2008). This assay is based on the determination of the concentration of 2, 2-diphenyl-1-picrylhydrazyl (DPPH) methanolic solution, after adding the antioxidants. DPPH concentration is reduced by the existence of an antioxidant at 515 nm and the absorption gradually disappears with time. A 0.1 mm methanolic solution of DPPH was prepared. The oil samples (1 ml after tenfold dilution) were placed in test tubes and a 2-ml aliquot of DPPH methanolic solution was added and the mixture was vortexed for 20 s at ambient temperature. Against a blank of pure methanol without DPPH, the decrease in absorption at 515 nm was measured in 1-cm quartz cells after 1, 30, and 60 min of mixing, using a spectrophotometer (Systronics UV-VIS-108, Bangalore, India). RSA toward DPPH radicals was estimated from the differences in absorbance of methanolic DPPH solution with or without sample (control) and the inhibition percent was calculated using the following equation: % inhibition = [(absorbance of control - absorbance of test sample)/absorbance of control] X 100 Statistical analysis: All the determinations were carried out in triplicate and the results were expressed as mean ± standard error. One way analysis of variance (ANOVA) and their statistical Ealuation of blended rice bran and mustard oil significance (pd 0.05) was ascertained using a computer programme package (CPCS1). RESULTS AND DISCUSSION Fatty acid composition Fatty acid composition of RBO and its blends is given in Table 1. The total amount of SFA, MUFA and PUFA present in RBO was 15.4, 38.0 and 46.6 percent respectively. RBO+MO in the ratio of 80:20 contained 16.9 percent SFA, 32.9 percent MUFA and 50.8 percent PUFA whereas percentage of SFA, MUFA and PUFA present in RBO+MO (70:30) was 15.2, 25.6 and 59.2 respectively. Oleic content of RBO+MO (32.3 %) in the ratio of 80:20 was higher than RBO+MO (25.6%) in the ratio of 70:30. The percentage of oleic acid in both ratios was lower than RBO (38.0%). Oleic acid had been described to reduce the cardiovascular risk by reducing blood lipids, mainly cholesterol (Lopez-Huertas, 2010). The amount of linoleic acid in RBO+MO (45.2%) in the ratio of 70:30 was higher than RBO+MO (39.1%) in the ratio of 80:20 but the percentage of linoleic acid in both ratios was lower than RBO (46.6%). A significant (pd 0.05) difference was found in MUFA and PUFA content of vegetable oils. The World Health Organization (2008) has recommended the fatty acid ratio of vegetable oil to be 1:1.5:1. The results showed that blending changed the fatty acid ratio of RBO i.e. 1:2.5:3 to 1:1.9:3 (80:20) and 1:1.7:3.9 (70:30) in the blend RBO+MO. Physical properties The data on physical properties of RBO and its blends are given in Table 2. The smoke point is the temperature at which a fat or oil produces a continuous wisp of smoke when heated. Results showed that smoke point of RBO was 242 C whereas RBO+MO showed lower value of smoke point i.e. 200 C and 188 C in the ratio of 80:20 and 70:30 respectively. This does not meet the standard requirement for frying oils which should have a smoke point above 200 C (AOCS, 2003). But according to the opinion of the Working Group of Regional Food Chemistry Experts and the German Federal Public Health Department of 1991, the smoke point of a cooking oil must be at least 170 C and must not differ from the 47

4 temperature of the fresh oil by more than 50 C so that the oil can still be classified as usable. Frying temperature of RBO was observed to be 174 C whereas this value was higher for RBO+MO (70:30) i.e. 180 C. Frying temperature of RBO+MO in the ratio of 80:20 was 177 C. A significant (pd 0.05) difference was observed in frying temperature of vegetable oils but still the frying temperature was within the range ( C) suggested by Choe and Min (2007). With respect to viscosity, RBO had the highest (40 CST) value followed by RBO+MO (38 CST) in the ratio of 80:20 and RBO+MO (37 CST) in the ratio of 70:30 respectively. Chemical properties The data on chemical properties of RBO and its blends are given in Table 2. Peroxide value is a useful indicator of the early stages of rancidity occurring under mild condition and it is a measure of the primary lipid oxidation products. So, greater the peroxide value, the more will be the rate of oxidation in the oil (Atinafu and Bedemo, 2011). It was found that RBO had lowest peroxide value i.e., 0.62 meq /Kg whereas RBO+MO in the ratio of 80:20 and 70:30 had higher peroxide values i.e., 1.33 and 1.73 meq /Kg respectively. Still the peroxide values of blended oils were in agreement with the maximum Codex standard peroxide value (10 meq O 2 /Kg) for vegetable oil deterioration. Iodine value is an index of the unsaturation, which is the most important analytical characteristic of oil (Otunola et al, 2009). Iodine value of RBO+MO in the ratio of 80:20 and 70:30 was recorded to be g and g respectively which were higher than the iodine value of single oil i.e g (RBO). The greater the degree of unsaturation (or high IV), the more rapid the oil tends to be oxidized, particularly during deep-fat frying (Alireza et al, 2010). Although the highest iodine value was observed in RBO+MO, the protective role of the natural antioxidants induced by the presence of rice bran oil (i.e., oryzanol, alpha-tocopherol equivalent) resulted in a lower value of iodine value (Gopal et al, 2005). Acid value is a measure of the free fatty acids in oil. Acceptable levels for all oil samples should be below 0.6 mg KOH/g (measured in potassium hydroxide per gram) (AOCS, 2003). Acid value Choudhary and Grover of RBO+MO in the ratio of 80:20 and 70:30 was recorded to be 0.37 and 0.28 mg KOH/g respectively whereas the acid value of RBO was 0.42 mg KOH/g. Free fatty acids occur in fats as a result of enzymatic hydrolysis by lipases, metal ions acting as free radicals or at an elevation of temperature (Gulla and Waghray, 2011). The percentage of free fatty acids was found to be highest in RBO+MO (80:20) i.e The percentage of free fatty acids in the RBO was lower than percentage of free fatty acids present in RBO+MO (80:20) and RBO+MO (70:30). Saponification value is an indication of the molecular weights of triglycerides in oil (Muhammad et al, 2011). The highest saponification value was found in RBO+MO (80:20) i.e mg KOH/g as compared to the other oils. Similar findings were reported by Nasirullah et al, (2012). There was significant difference (p<0.05) among the vegetable oils in terms of chemical properties. Oxidative stability Oxidative stability of oil can be improved by modification of fatty acid composition and addition of antioxidants to the oil. The oxidative stability of single and blended oils is given in Table - 3. A significant (pd 0.05) difference was found in peroxide value of all vegetable oils after 28 days. It was observed that peroxide formation in RBO increased by 52.2 percent whereas RBO+MO in the ratio of 80:20 and 70:30 showed increase in peroxide formation by 39.3 and 33.9 percent respectively after 28 days. So, blends in both ratios showed least percent increase in peroxide formation as compared to single oil. Highest percent increase in peroxide formation in RBO could be due to presence of PUFA as given in Table 1. Recent studies reported that oxidative stability was inversely proportional to PUFA content of vegetable oil (Bhatnagar et al, 2009). There was a significant (pd 0.05) steady increase in PV of rice bran oil blends, but this increase was seen to be the least. The nutritional contribution of the three minor components of tocopherol, tocotrienols and ã-oryzanol in rice bran oil blends may have conferred this greater oxidative stability (Gulla and Waghray, 2011). 48

5 Antioxidant activity The term total natural antioxidants collectively refers to total alpha tocopherol equivalent and oryzanol content in vegetable oils. Results showed that the amount of total natural antioxidants present in RBO, RBO+MO (80:20) and RBO+MO (70:30) was , and mg/kg respectively (Table 4). By comparing both ratios, it was found that RBO+MO in the ratio of 70:30 had highest (57.5%) RSA towards DPPH radicals (Fig. 1). This could be due to the presence of natural antioxidants i.e. oryzanol ( mg/kg) and alpha tocopherol equivalent (176.6 mg/kg). In vegetable oils alpha-tocopherol inhibits the effects of singlet oxygen during sensitized photoxidation (Min and Boff, 2002). Scientific studies reported that higher the alpha tocopherol and oryzanol content, the higher the DPPH scavenging activity would be (Malik et al, 2011; Vorarat et al, 2010). Interestingly, RSA towards DPPH radicals was found on the higher side in the ratio of 70:30 whereas the amount of total natural antioxidants was more in the ratio of 80:20. A significant (pd 0.05) difference was found in RSA of all vegetable oils. CONCLUSION By comparing both ratios, it was found that fatty acid ratio of RBO+MO (70:30) i.e. 1:1.7:3.9 were close to the recommendations given by WHO. In terms of physicochemical properties RBO+MO in the ratio of 70:30 showed adequate smoke point (188 C), frying temperature (180 C) and had low acid value (0.28 mg KOH/g) and saponification value (224.0 mg KOH/g) as well as low percentage of free fatty acids (0.14%). In terms of oxidative stability and antioxidant activity, RBO+MO (70:30) showed least percent increase (33.9 %) in peroxide formation after 28 days of incubation period and also had highest radical scavenging activity (57.5 %) whereas the highest content of total natural antioxidants ( mg/ kg) was present in RBO+MO (80:20). Hence, the present study revealed that blending of nontraditional oil (RBO) with traditional oil (MO) in the ratio of 70:30 to obtain stable and healthier blended oil can be done as it also reduces the demand and cost of traditional oils. Ealuation of blended rice bran and mustard oil REFERENCES Alireza S, Tan C P, Hamed M and Che Man Y B (2010). Effect of frying process on fatty acid composition and iodine value of selected vegetable oils and their blends. Int Food Res J 17: AOAC (2000). Oils and Fats. In Official Methods of Analysis of AOAC International. (Ed. William, H), AOAC International, Maryland, USA. Pp: AOCS (1990). Official Methods and Recommended Practices of the American Oil Chemists Society. AOCS Press, Champaign, Illinois. AOCS (2003). Sampling and Analysis of Commercial Fats and Oils. AOCS Official Method Cd 8-53 Surplus Peroxide Value Acetic Acid Chloroform Method Definition, New York, USA, AOCS Cold Spring Harbour. Appleqvist L Å (1968). Rapid methods of lipid extraction and fatty acid ester preparation for seed and leaf tissue with special remarks on preventing the accumulation of lipid contaminants. Ark. Kenci. 28: Atinafu D G and Bedemo B (2011). Estimation of total free fatty acid and cholesterol content in some commercial edible oils in Ethiopia, Bahir DAR. J Cereals Oilseeds 2: Baker H and Frank O (1988). Determination of serum hysicrol. In: Varley s Practical clinical Biochemistry. (Ed. Gowenlock, AH), 902. Bhatnagar S A, Kumar K P, Hemavathy J and Krishna G A (2009). Fatty acid composition, oxidative stability and radical scavenging activity of vegetable oil blends with coconut oil. J Amer Oil Chem Soc 86: Choe E and Min D B (2007). Chemistry of deep-fat frying oils. J Food Sci 72: Erasto P, Grierson D S and Afolayan A J (2007). Evaluation of antioxidant activity and the fatty acid profile of the leaves of Vernonia amygdalina growing in South Africa. Food Chem 104: Gopal K A G, Hemakumar K H and Khatoon S (2006). Study on the composition of rice bran oil and its higher free fatty acis value. J Amer Oil Chem Soc 83: Gopal K A G, Khatoon S and Babylatha R (2005). Frying performance of processed rice bran oils. J Food Lipids 12: Gulla S and Waghray K (2011). Effect of storage on physicchemical characteristics and fatty acid composition of selected oil blends. J Life Sci 3: Lopez-Huertas E (2010. Health effects of oleic acid and long chain omega-3 fatty acids (EPA and DHA) enriched milks. A review of intervention studies. Pharmacol Res 61: Malik A, Kushnoor A and Saini V (2011). In vitro antioxidant properties of Scopoletin. J. Chem Pharma Res 3: Min D B and Boff J M (2002). Chemistry and Reaction of Singlet Oxygen in Foods. Compr Rev Food Sci F 1: Miraliakbari H and Shahidi F (2008). Antioxidant activity of minor components of tree nut oils. Food Chem. 111:

6 Choudhary and Grover Muhammad N, Bamishaiye E, Bamishaiye O, Usman L, Salawu M, Nafiu M. and Oloyede O (2011). Physicochemical properties and fatty acid composition of cyperus esculentus (Tiger Nut) Tuber Oil. Biores Bull 5: Nasirullah Ankaiah K N, Krishnamurthy M N, Nagaraja K V (2011). Quality characteristics of edible vegetable oil blends. J Amer Oil Chem Soc 68: Otunola A G, Adebayo G B and Olufemi O G (2009). Evaluation of some physicochemical parameters of selected brands of vegetable oils sold in Ilorin metropolis. Intl J Phys Sci 4: Table 1. Fatty acid composition of vegetable oils. Ramesh P and Murughan M (2008). Edible oil consumption in India. Asia and Middle East Food Trade J 3: 8-9. Venkattakumar R and Padmaiah M (2010). Adoption Behaviour of Oilseed Growers in India. Indian Res J Ext Edu 10: Vorarat S, Managit C, Iamthanakul L, Soparat W and Kamkaen N (2010). Examination of antioxidant activity and development of rice bran oil and gamma- Oryzanol microemulsion. J Health Res 24: WHO (2008). Interim Summary of Conclusions and Dietary Recommendations on Total Fat & Fatty Acids. The Joint FAO/ WHO Expert Consultation on Fats and Fatty Acids in Human Nutrition, WHO, Geneva. Pp: Fatty acid (%) RBO(100%) RBO+MO(80:20) RBO+MO(70:30) CD Ï% Palmitic acid (C16:0) 14.5± ± ±0.9 NS Stearic acid (C18:0) 0.9± ± ±0.1 NS Oleic acid (C18:1) 38.0± ± ± Linoleic acid (C18:2) 46.6± ± ± Linolenic acid (C18:3) ND 8.6± ±0.9 - Arachidic acid (C20:0) ND 3.1± ±0.9 - SFA % 15.4± ± ±0.8 NS MUFA % 38.0± ± ± PUFA % 46.6± ± ± SFA:MUFA:PUFA 1:2.5:3.0 1:1.9:3.0 1:1.7:3.9 - Values are expressed as mean ±SE, Ï% = Significant 5%, ND- Not detected, NS-Non significant, RBO rice bran oil, MO Mustard oil Table 2. Physicochemical properties of vegetable oils. Physical Properties RBO(100%) RBO+MO(80:20) RBO+MO(70:30) CD Ï% Smoke point ( C) 242± ± ± Frying temperature ( C) 174± ± ± Viscosity (CST) 40±0.1 38±0.3 37±0.3 NS Chemical Properties RBO(100%) RBO+MO(80:20) RBO+MO(70:30) CD Ï% Peroxide value (meq/kg) 0.62± ± ± Iodine value (g) 102± ± ± Acid value (mg KOH/g) 0.24± ± ± Free fatty acids (%) 0.12± ± ± Saponification value (mg KOH/g) 199.7± ± ± Values are expressed as mean ±SE, Ï% = Significant 5%, NS-Non significant, RBO rice bran oil, MO Mustard oil Table 3. Peroxide values (meq/kg) of vegetable oils for oxidative stability after weekly interval. Peroxide value Sample 0 7 days 14 days 21 days 28 days RBO (100%) 0.62± ± ± ± ±0.22 RBO+MO (80:20) 1.33± ± ± ± ±0.47 RBO+MO (70:30) 1.73± ± ± ± ±0.33 CD Ï% 2.8 NS NS Percent increase in peroxide value Sample 7 days 14 days 21 days 28 days RBO (100%) RBO+MO (80:20) RBO+MO (70:30) Values are expressed as mean ±SE, Ï% = Significant 5%, NS-Non significant, RBO rice bran oil, MO Mustard oil 50

7 Ealuation of blended rice bran and mustard oil Table 4. Total natural antioxidants and DPPH radical scavenging activity of vegetable oils. Sample Oryzanol (mg/kg) Alpha tocopherol Total natural equivalent (mg/kg) antioxidants (mg/kg) RBO (100%) ± ± ±1.9 RBO+MO (80:20) ± ± ±1.4 RBO+MO (70:30) ± ± ±1.3 CD Ï% Values are expressed as mean ±SE, Ï% = Significant 5%, NS-Non significant, RBO rice bran oil, MO Mustard oil Fig. 1. DPPH radical scavenging activity of vegetable oils. CD value between time intervals (0, 30, 60 minutes) (pde0.05), CD value between vegetable oils- 0.3 (pde0.05) Received on Accepted on