The influence of extraction methods on composition and antioxidant properties of rice bran oil

The seed of Oryza species is commonly known as rice, which are the foremost cereal food crop in most of the developing countries. Approximately 95% of the rice production is documented in Asian countries, and about half of the world population consumes rice as their primary source of carbohydrate (Muthayya et al., 2014). Rice grains, known as endosperm, are surrounded by nutrient rich (almost 60% of total nutritional value) outer layer called rice bran (RB) and it accounts for 8% of total weight of the rice. The color of the rice coat differs with respect to the degree of deposition of anthocyanin pigment. Consequently, the rice cultivars also varied with respect to the color of the rice, which can be black, brown, or red (Chaudhary, 2003).


Introduction
The seed of Oryza species is commonly known as rice, which are the foremost cereal food crop in most of the developing countries.Approximately 95% of the rice production is documented in Asian countries, and about half of the world population consumes rice as their primary source of carbohydrate (Muthayya et al., 2014).Rice grains, known as endosperm, are surrounded by nutrient rich (almost 60% of total nutritional value) outer layer called rice bran (RB) and it accounts for 8% of total weight of the rice.The color of the rice coat differs with respect to the degree of deposition of anthocyanin pigment.Consequently, the rice cultivars also varied with respect to the color of the rice, which can be black, brown, or red (Chaudhary, 2003).
Oryza sativa L. indica, commonly known as black rice (BlR), is routinely cultivated in Southeast Asian countries.BlR is reported to have an abundant amount of protein, vitamins, minerals and bioactive compounds with slight quantity variations which depends on land cultivation and diversity (Suzuki et al., 2004).BlR has been reported as one of the potential sources of antioxidants and health promoting compounds (Hu et al., 2003;Yawadio et al., 2007;Fardet et al., 2008;Goufo & Trindade, 2014;Pengkumsri et al., 2015).BlR has the ability to prevent and can be useful to treat oxidative stress related diseases and cancer (Salgado et al., 2010).The outer layer of BlR is enriched with phytochemicals and these bioactive were broadly divided into polar (phenolic acids, flavonoids, anthocyanins) and non-polar components (tocopherols, tocotrienols, γ-oryzanol, and sterols) (Patel & Naik. 2004;Zhou et al., 2004;Holtekjølen, et al., 2006).Studies have proven that the active components of RB improve the human health because of the high content of antioxidants (Laokuldilok et al., 2011).Jun et al. (2012) reported that black and red rice brans exhibited high content of phenolic compounds and antioxidant activity.
Rice bran oil (RBD) is one of the best sources of tocols and oryzanol.Tocols (tocopherols and tocotrienols), a family of vitamin E-active substances, are wildly used plant-based ingredients in the food, cosmetics and pharmaceutical industries (Bramley et al., 2000;Abidi, 2003).Studies suggested that tocotrienols are more efficient antioxidant, anti-cancer agent and inhibitor of cholesterol synthesis than the tocopherols (Singh et al., 2013).Gamma-oryzanol is one of the major components of RBD, and it is a mixture of several ferulate esters of triterpene alcohols and plant sterols (Friedman, 2013).Dryzanol is a well known antioxidant compound and is linked with decreasing serum and plasma cholesterol, decreasing platelet aggregation, and cholesterol absorption.Moreover oryzanol has been used in the treatment of hyperlipidemia, and disorders of menopause (Patel & Naik, 2004).The extraction and refining of RBD and the content of γ-oryzanol, along with its health benefits have been reviewed in detail (Patel & Naik, 2004;Lerma-García et al., 2009).The quality and concentration of the tocols and γ-oryzanol content depend on the extraction processes and refining steps.Therefore, the current study was conceived to compare the non-polar extracts of CBlR, SBrR and MRR bran oil of Thai rice variety with respect to its tocols content, oryzanol content as well as its antioxidant properties.

Collection of rice bran and extraction
Chiang Mai black rice (CBlR), Suphanburi-1 brown rice (SBrR) and Mali red rice (MRR) were collected from the farm at Maerim district, Chiang Mai, Thailand and dried at 60 °C for 48 h.Then it was milled and the rice bran was separated through 60-mesh strainer.Lipase in RB was destroyed through 100 °C for 5 min thereafter RB was then stored at -20 °C until the time of processing.RBD was extracted with hexane (1:10 ratios of RB and hexane was incubated at 40 °C with shaking at 150 rpm for 30 min and thereafter filtrated through 0.45 µm membrane and the solvent was evaporated to obtain crude RBD), hot press (screw pressing at 80-100 °C), cold press (screw pressing at 40-60 °C), and supercritical fluid (40 °C, 200 bar, CD 2 rate 15 g/min, 1 h) extraction.The collected oil samples were membrane filtered (0.45 μm) and the percentage of yield was calculated (Equation 1).
Percentage of Yield = (RBO (g) / Initial weight of RB (g)) x 100 (1) Filtered RBDs were stored at -20 °C under nitrogen gas (N 2 ) to prevent the degradation of active compounds until analysis.

Determination of tocols content
The tocols content (both tocotrienols and tocopherols) of RBD samples were evaluated by reversed-phase HPLC which is equipped with LC-10AV VP pumps, SPD-10AV VP (Shimadzu, Japan) and fluorescent detector (Bruscatto et al., 2009).The KINETEX PFP column (150 mm × 4.6 mm; 100 A), was used (Phenomenex, USA) and 90% methanol in deionized water acts as mobile phase.The flow rate was set at 0.5 mL/min.The excitation and emission wavelength was set at 296 and 325 nm, respectively.All the samples were measured in triplicate.

•-
) radical scavenging assay and inhibition of lipid peroxidation (LPD) assay as described in our previous publications.ABTS •+ radical scavenging activity was measured by ABTS assay according to Chalermpong et al. (2012).DPPH • radical scavenging activity was assessed by DPPH assay according to Rattanachitthawat et al. (2010) and Wahid et al. (2014).FRAP assay was performed according to the method of Suwannalert et al. (2010) and inhibition of lipid peroxidation was assessed according to Chalermpong et al. (2012).Nitric oxide (ND • ) radical scavenging activity was measured according to Francis & Andrew (2010) and Pengkumsri et al. (2015).Superoxide (D 2

Statistical analysis
The quantification of γ-oryzanol, tocols (tocotrienols and tocopherols) content and determination of antioxidant activity of RBD were performed in triplicates to confirm the reproducibility of the results.The report of the data was given as mean ± SD. Analysis of variance (ANDVA) was performed using statistical SPSS software version 17 (Chicago, SPSS Inc, U.S.A).The Least Significant Difference (LSD) post hoc test was performed in order to analyze the significant differences in antioxidant activities and p< 0.05 was considered to be significant.
The γ-oryzanol content of RBD has been assessed by HPLC with respect to different extraction methods.About 17.54 ± 0.75, 17.54 ± 0.88, and 18.49 ± 1.52 mg/g of γ-oryzanol content in CBlR, MRR, and SBrR bran oil, respectively were recorded in hexane extracts, whereas a very low amount (1.75 ± 0.09 and 2.71 ± 0.14 mg/g in CBlR and SBrR, respectively) of γ-oryzanol were observed in RBD obtained by SFe.Hot press extraction yielded 5.62 ± 0.28, 5.66 ± 0.25, and 6.23 ± 0.31 mg/g of γ-oryzanol content in CBlR, MRR, and SBrR bran oil extract, respectively.Cold press extraction represented 6.08 ± 0.34, 6.75 ± 0.3, and 6.48 ± 0.37 mg/g of γ-oryzanol content in CBlR, MRR, and SBrR bran oil, respectively (Figure 1).Previous studies have been reported on the recovery of γ-oryzanol from different RB varieties by methanol, hexane, and ethyl acetate mediated extraction techniques (Iqbal et al., 2005;Chotimarkorn et al., 2008;Lin & Lai, 2011).Varying quantity of γ-oryzanol have been reported based on the extraction methods and rice cultivars.In the present study, highest γ-oryzanol yield was obtained by He followed by CPe, HPe and SFe methods (Figure 1).This data suggested that variation in the amount of γ-oryzanol in RBD depends on the extraction methods.
Total tocols and subgroups of tocopherol and tocotrienol were measured.The total tocopherol (included α, β, γ, and δ) content of about 0.40 ± 0.02, 0.15 ± 0.01, 0.16 ± 0.01, and 0.08 ± 0.00 mg/g in CBlR bran oil samples were obtained from He, HPe, CPe, and SFe methods, respectively.The total tocopherol content of about 0.22 ± 0.01, 0.19 ± 0.01, 0.21 ± 0.01, and 0.05 ± 0.00 mg/g in MRR bran oil samples were obtained from He, HPe, CPe, and SFe methods, respectively.The total tocopherol content of about 0.43 ± 0.02, 0.12 ± 0.01, 0.13 ± 0.01, and 0.06 ± 0.00 mg/g in SBrR bran oil samples were obtained from He, HPe, CPe, and SFe methods, respectively.In all the preparations, γ-tocopherol was found to be a major subgroup of tocopherol followed by α, δ and β types that were recorded for their abundance, respectively.The total tocopherol concentration also suggested that hexane extraction is significantly (p<0.05)better than the other mining methods employed in the present study.The total tocotrienol (included α, β, γ, and δ) content of about 0.67 ± 0.03, 0.28 ± 0.01, 0.34 ± 0.02, and 0.18 ± 0.01 mg/g in CBlR bran oil samples were obtained from He, HPe, CPe, and SFe methods, respectively.The total tocotrienol content of about 0.84 ± 0.04, 0.62 ± 0.03, 0.74 ± 0.04, and 0.26 ± 0.01 mg/g in MRR bran oil were obtained from He, HPe, CPe, and SFe methods, respectively.The total tocotrienol content of about 1.11 ± 0.06, 0.52 ± 0.03, 0.62 ± 0.03, and 0.31 ± 0.02 mg/g in SBrR bran oil samples were obtained from He, HPe, CPe, and SFe methods, respectively.The quantification of sub-groups revealed that the abundance of γ-tocotrienol was higher and followed by α-tocotrienol, δ-tocotrienol, and β-tocotrienol (Figure 2).The quantity of δ and β type of tocopherol and tocotrienol have no significant variation in both cold and hot press extraction.The quantity of δ and β type tocopherol and tocotrienol were not significantly affected by the cold press and hot press extraction when compared to the yield of hexane extracts.Similar to tocopherol, the abundance of tocotrienol was also recorded in hexane extracted oil (Figure 2).Chotimarkorn et al. ( 2008)   has reported the richness of α-tocopherol and the absence of γ -tocotrienol in the methanolic extraction of RB than in those of the other types.Basically, concentration of total tocopherol and tocotrienol content variation depends on the cultivars and the extraction method used.Moreover, few studies have reported that the extractions of all the subgroups of tocols are not entirely succeeded in an efficient manner (Iqbal et al., 2005;Aguilar-Garcia et al., 2007).In the present study, all subgroups of tocols were reported in all the preparations with varying concentration.
Therefore, all in vitro antioxidant assay results indicated that He based RBD preparations are enriched with antioxidant properties significantly (p<0.05)than other tested HPe, CPe, and SFe based RBD preparations.Even though, hexane extraction yields efficient and enriched RBD, the presence of hexane residues that are not completely eliminated is the disadvantage of the solvent based extraction process.The present study also investigated the efficiency of RBD yielded by the solvent independent extraction process.Dverall results indicated that the efficiency of HPe, CPe, and SFe which are solvent independent extraction process is less compared to the He of RBD.The second high yield of RBD was obtained by SFe (Table 1), but the quality of the oil was slightly compromised in its antioxidant property compared to HPe and CPe samples (Figures 3 and 5).The oil extraction temperature greatly influenced the yield and quality of the oil.Hot pressed method produced a slightly enhanced yield of RBD compared to cold pressed, but the quality of cold pressed oil in terms of antioxidant properties was superior to the hot pressed one (Figures 3 and 5).
Considerable differences in antioxidant capacity of RBD extracts of different cultivars suggested that the content of the phytochemicals had a vast impact on their antioxidant properties (Iqbal et al., 2005;Chotimarkorn et al., 2008).The chemical composition (tocols, γ-oryzanol), and antioxidant    properties of white, red, and brown rice bran were compared with the unique extraction method (Aguilar-Garcia et al., 2007;Finocchiaro et al., 2007).However, all previous studies have shown that the phytochemical composition and the ability of the antioxidant of rice varieties depend on many factors, majorly, cultivars, and extraction methods.The results of the current investigation suggested that hexane extraction yielded prosperous RBD with respect to the content of active phytochemicals and antioxidants.Development of new or modified extraction method independent of solvent usage that provides an efficient yield of RBD will eliminate the health hazards that might occur when used in food, cosmetic and pharmaceutical industries.

Conclusion
The influence of the different extraction methods on the recovery of the principal compounds like total tocols and γ-oryzanol from RBD has been demonstrated.The effect of extraction methods on antioxidant activities of the same cultivar was also studied.This study revealed that hexane extraction yielded precious RBD, with respect to both quantity and quality wise.The SFE affects the desired qualities of RBD though it gives better yield in terms of quantity.The role of the temperature in RBD recovery and property was also explained.To the best of our knowledge, this is the primary study about the influence of extraction methods on phytochemical content and antioxidant properties of CBlR, MRR, and SBrR bran oil.Further, in-depth study on factors affecting the recovery of phytonutrients and its properties is required for the development of enhanced functional foods and other related products.

Figure 2 .
Figure 2. Total (a) and subgroups of tocopherol (b) and tocotrienol (c) content in CBlR, SBrR and MRR bran oil extracted by He, HPe, CPe, and SFe.The values were represented as mean ± SD.

Figure 3 .
Figure 3. ABTS (a), DPPH (b) and Lipid peroxidation (c) inhibition activity of RBD extracts in comparison with its standard.The values were represented as mean ± SD.

Figure 4 .
Figure 4. Reducing power of RBD extracts assessed by FRAP assay.The values were represented as mean ± SD.

Figure 5 .
Figure 5. Superoxide (D 2 •-) radical (a) and nitric oxide (ND • ) radical (b) scavenging activity of RBD extracts in comparison with its standard.The values were represented as mean ± SD.

Table 1 .
Recovery of Rice bran oil from different rice cultivars with different extraction methods and sample codes used in the current study.
*% of yield is significant (p<0.05)compared to respective RBD extract of other extraction methods (HPe, CPe and SFe).

Table 2 .
Antioxidant activity (IC 50 ) of different Rice bran oil extracts with different evaluation method.
All the values are represented as mean ± SD of triplicate experiments.*IC 50 value is significant (p<0.05)compared to respective RB oil extract of other extraction methods (HPe, CPe and SFe).