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I am showcasing the raw power of Industrial Hemp. Fuel for our country, safe enough to drink! Cold pressed hemp seed oil
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ALEKSANDER SIGER1, MALGORZATA NOGALA-KALUCKA and ELEONORA LAMPART-SZCZAPA
Faculty of Food Science and Nutrition Department of Food Biochemistry and Analysis August Cieszkowski University of Agriculture Poznan, Poland
Submitted for Publication May 7, 2007 Revised Received and Accepted October 1, 2007
ABSTRACT
Many nontraditional vegetable oils have been introduced to the market relatively recently, and therefore data on their antioxidant potential have not been reported. Such data are of importance for the evaluation of the nutritionalandhealthimpactoftheseoils.Antioxidantpropertiesofthemethanolic extracts of cold-pressed oils such as soybean, sunflower, rapeseed, corn, grapeseed, hemp, flax, rice bran and pumpkin were studied. The methanolic extracts were obtained by solid phase extraction and separation, and identification of phenolic acids was conducted by high-performance liquid chromatography. The obtained extracts were characterized by different scavenging activities of 2,2-diphenyl-1-picrylhydrazyl radicals. The best antioxidant properties were displayed by the extract from hemp, pumpkin and rapeseed oils. The highest content of total phenolic compounds was determined for the pumpkin and hemp oils – about 2.4 mg/100 g. Rapeseed oil was characterized by the highest content of phenolic acids, especially sinapic acid. To better understand the beneficial effects of antioxidant compounds in vegetable oils, it is important to investigate whether these bioactive compounds in oils differ in their reactions with free radicals.
PRACTICALAPPLICATIONS
Phenolic compounds have been reported to be present in all vegetable oils, which is very important for the oxidative stability of the polyunsaturated fatty acids of these oils. Additionally, edible oils rich in natural antioxidants
1 Corresponding author. TEL: +48-61-848-73-57; FAX: +48-61-848-73-52; EMAIL: aleksander.siger@op.pl
Journal of Food Lipids 15 (2008) 137–149. All Rights Reserved. © 2008, The Author(s) Journal compilation © 2008, Blackwell Publishing
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may play a role in reducing the risk of chronic diseases. Thus, the oils examined may be used in different food applications to provide nutrition and health benefits.
INTRODUCTION
The cold-pressing procedure involves neither heat nor chemical treatments, and it is becoming an interesting substitute for conventional practices because of consumers’ desire for natural and safe food products. The consumption of new and improved products such as cold-pressed oils may improve human health and may prevent certain diseases. Free radicals may causereversibleorirreversibledamagestobiologicalmoleculessuchasDNA, proteins and/or lipids (Goldberg 2003). These damages may cause cancer, heart diseases and arthritis, and could accelerate aging of organisms (Cadenas and Davies 2000). Cold-pressed edible hemp and berry fruit seed oils contain significant levels of a-linolenic acid (18:3n-3), which may be converted to the longer-chain n-3 polyunsaturated fatty acid (PUFA), eicosapentaenoic acid (EPA) (20:5n-3) and docosahexaenoic acid (DHA) (22:6n-3), in vivo through elongation and desaturation reactions (Namal Senanayake and Shahidi 2000; Shahidi and Naczk 2004; Kapoor and Nair 2005; Parry et al. 2006). Over the last few years, increased interest in cold-pressed plant oils has been observed as these oils have better nutritive properties than those after refining. Cold pressing is simple, ecological and does not require much energy. The disadvantage of this process is low productivity and difficulties in obtaining a product of constant quality (Rotkiewicz et al. 1999). Such factors as geographical location, species and processing technique may influence the final chemical composition of plant oils (Beardsell et al. 2002). Plant oils contain small amounts of such compounds as free fatty acids, phenolic compounds, tocopherols, sterols, stanols, phospholipids, waxes, squalene and other hydrocarbons (Lecker and Rodriguez-Estrada 2000). In many products of plant origin, substances having antioxidative properties have been identified. Such substances are also present in oilseeds (Kalt et al. 1999; Yu et al. 2002a,b, 2005). Phenolic compounds have much influence on the stability, sensory and nutritional characteristics of the product and may prevent deterioration through quenching of radical reactions responsible for lipid oxidation (Ruth et al. 2001; Quites et al. 2002; Koski et al. 2003). Cold-pressed oils contain phenolspresentintheseed,andtheymayhavethepotentialforapplicationsin the promotion of health and prevention of oxidative damages caused by radicals. Factors influencing the antioxidant activity of phenolic compounds include position and number of hydroxyl groups, polarity, solubility and stability of phenolic compounds during processing (Decker 1998). Cold-pressed
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oils contain more polar phenols, the concentration of which varies from 18- to 99-ppm caffeic acid equivalents (CAEs) (Koski et al. 2003). Olive oil is believed to be most stable because of its high quantity of phenols (Maniak and Targon´ski 1996). Taking into consideration the fact that plant oils are mostly used in preparing food, health benefits for the entire population could be significant, especially, among others, in the prevention of heart diseases. The goalofthisstudywastoobtainthemethanolicextractsofselectedcold-pressed oils and to determine phenolic compounds and their antiradical activity.
MATERIALS AND METHODS
Materials Cold-pressedoilseedsfromsoya(GlycinemaxL.),sunflower(Helianthus annus L.), rapeseed (Brassica napus L.), corn (Zea mays L.), grapeseed (Vitis vinifera L.), hemp (Cannabis sativa L.), flax (Linum usitatissiumum L.), rice bran (Oryza sativa L.), pumpkin (Cucurbita pepo L.) and olive oils (Olea europaea L.) were purchased from local grocery stores in Poznan (Poland) in the years 2005–2006. Commercial samples of olive and grapeseed oils produced in Italy and rice bran produced inThailand were employed in this study. The rest of the samples were produced in Poland.
Extraction of Phenolic Compounds Chromabond System (Macherey, Nagle, Germany) with SPE column filled with diol (Discovery DSC-Diol SPE tube – 500 mg, 50 mm, 70-Å pore diameter)(Supelco,Bellefonte,PA)wasusedfortheextractionofthephenolic acid fractions.The process consisted of four stages: first, column conditioning (5 mL methanol and 5 mL n-hexane); second, sample placing (2.5 g oil in 5 mLn-hexane + 5 mLn-hexane); third, column washing (5 mL n-hexane/ ethyl acetate 90:10, v/v); fourth, leaching of phenolic acids with methanol and collection in a volumetric flask (5 mL).
Total Phenolic Compound Content The content of total phenolic compounds in methanolic extracts was determined by the Folin–Ciocalteu method.An aliquot (0.2 mL) of the methanolic extract was placed in a volumetric flask (10 mL). Diluted Folin– Ciocalteu reagent (0.5 mL) was added. After 3 min, saturated sodium carbonate (1 mL) was added. The flask was filled with water up to 10 mL. After 1 h, absorbance at lmax 725 nm against a reagent blank was measured using a UV–vis spectrophotometer SP 8001 (Metertech Inc., Taipei, Taiwan).
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Total phenolic compounds were determined after preparation of a standard curve, and on that basis, total phenolic compounds were measured as CAEs.
Phenolic Acid Composition Separation and identification of phenolic acids were carried out by highperformance liquid chromatography (Waters, Milford, MA) using a NovaPak C18 reversed phase (3.9 ¥ 150 mm, 5 mm) (Waters). SolventAwas methanol, solvent B – 2.5% acetic acid in water. The flow rate was 1 mL/min. The gradient profile was: 10% (A) (0–10 min); 10–20% (A) (10–22 min); 20–70% (A) (22–45 min).The chromatograms were recorded at 250 and 320 nm (UV– vis, Waters). The identification was carried out by retention time, and the amountofphenolicacidswasdeterminedusingexternalandinternalstandards of the individual phenolic acids.
Antioxidant Activity Determination The method consisted of spectrophotometric measurement of the intensity of the color change in solution depending on the amount of 2,2-diphenyl1-picrylhydrazyl (DPPH). The reaction was initiated by mixing 1 mL of the methanolic extract with 3 mL methanol and then by adding 1 mL of DPPH• (0.012 g/100 mL).Theabsorbanceatlmax 517 nm(UV–visspectrophotometer SP 8001, Metertech Inc.) was checked at 0, 0.5 and every 0.5 min until the reaction reached a steady state. This plateau was reached within 15 min. The activity of the extract in scavenging DPPH• was calculated as follows:
%DPPH scavenging
Absorbance of control Absorbance of sample Abs i = − o orbance of control ⎡ ⎣ ⎢
⎤ ⎦ ⎥
The amount of sample needed to decrease the initial DPPH concentration by 50%, EC50, was calculated graphically. The antiradical power (ARP) of extracts calculated as (Suja et al. 2005):
ARP
EC = () 1 50
Statistical Analysis Results are presented as means SD from three replicates of each experiment.AP value<0.05 was used to denote significant differences among mean values determined by analysis of variance with the assistance of Statistical 7.0 (StatSoft, Inc., Tulsa, OK) software.
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RESULTS AND DISCUSSION
The total phenolic content of cold-pressed oils is shown in Table 1. The highest total phenolic content was obtained in the pumpkin and hemp oils (2.5 and2.4 mg/100 g,respectively).Grapeseedoilwascharacterizedbythelowest total phenolic compound content (0.51 mg/100 g). The content of those compoundsintheremainingoils(soy,sunflower,rapeseed,corn,flax,ricebran)was at the level above 1 mg/100 g and did not exceed 2 mg/100 g (Table 1). Koski et al. (2003) reported a higher level of total phenolic content in the refined rapeseed oil, 16 ppm as CAEs, than that found here. On the other hand, Koski et al. (2002) also found that the cold-pressed olive and rapeseed oils contained a total phenolic content of 4 ppm. Yu et al. (2005) determined the content of total phenolic compounds at a level of 0.44 mg/g as gallic equivalents in hemp oil. Haiyan et al. (2007) determined 15.9 mg/g of total phenolic content in pumpkin oil as CAEs and 22.7 mg/g in soybean oil. Abuzaytoun and Shahidi (2006) reported nearly the same ability to reduce Folin–Ciocalteu’s reagent in extracts of flax and hemp oils. Parry et al. (2006) determined that the total phenoliccontentsrangedfrom0.98-to3.35-mggallicacidequivalentspergram of cold-pressed oils (onion, parsley, cardamom, mullein, roasted pumpkin and milk thistle). Folin–Ciocalteu reagent measures the ability of any mixture to reduce phosphomolybdic and phosphotungstic acids to a blue complex (Swain and Hillis 1959). The presence of ascorbic acid or other very easily oxidized substances, not considered as phenolic compounds, may also result in the
TABLE 1. TOTAL PHENOLIC COMPOUND CONTENT IN PLANT OIL EXTRACTS
Oil Total phenolic compound content (mg CAE/100 g)*
Soybean 1.48 0.05e† Sunflower 1.20 0.03b,c Rapeseed 1.31 0.04d Corn 1.26 0.04c,d Grapeseed 0.51 0.04a Hemp 2.45 0.05f Flax 1.14 0.03b Rice bran 1.44 0.03e Pumpkin 2.46 0.03f
* Total phenolic contents are expressed as milligrams of CAEs/100 gram samples. † Values (means SD) with different index letters are statistically significantly different (P < 0.05). CAE, caffeic acid equivalent.
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formation of blue color with Folin–Ciocalteu reagent, causing an overestimation of total phenolic content (Singleton et al. 1999; Shahidi and Naczk 2004). It has been argued that Folin reagents may be inappropriate for plant extracts with high levels of other easily oxidizable substances (Padda and Picha 2007). The content of phenolic acids in oils is shown in Table 2.The application of SPE columns with diol allowed the extraction of polar substances from nonpolar matrix oils. The highest level of phenolic acids was determined in rapeseed oil at 256.6 mg/100 g. The remaining oils were characterized by a substantially lower level of phenolic acids, from 0.4 (rice bran oil) to 22.1 mg/100 g (pumpkin oil). Similarly, rapeseed oil contained the highest level of sinapic acid 236 mg/100 g. Corn and rapeseed oils contained the highest level of ferulic acid: 5.8 and 5.6 mg/100 g, respectively. Pumpkin oil contained the highest level of vanillic acid – 11.4 mg/100 g (Table 2). Only this oil contained protocatechuic acid (3.1 mg/100 g). The lowest content of phenolic acid was determined in rice bran oil, which contained ferulic acid (0.4 mg/100 g). In rapeseed, phenolic acids consist mostly of sinapic acid (Kozlowska et al. 1983; Zadernowski and Kozlowska 1983; Shahidi and Naczk 1992; Cai and Arntfield 2001; Siger et al. 2004). Niwa et al. (2001) also determined the presence of p-coumaric, ferulic and sinapic acids in corn oil. They also noted that sinapic acid and its methyl and ethyl esters better inhibited the formation of lipid peroxides than ferulic and p-coumaric acids. The total phenolic acid content of flaxseed meal on a dry-weight basis, as reported by Wanasundara and Shahidi (1994), ranged from about 130 to 220 mg/100 g, as ferulic acid equivalents. Choo et al. (2007) showed a total phenolic acid content of 76.8–307.3 mg/100 g in cold-pressed flaxseed oils. The total flavonoid contents in seven samples of cold-pressed flaxseed oils as reported by Choo et al. (2007) ranged from 12.7 to 25.6 mg/100 g, as luteolin equivalents.According to Tuberoso et al. (2007), olives and extra virgin olive oil are rich in minor compounds like phenols. What is interesting, most of the phenolic compounds found in olive oil are not present in oilseeds (rapeseed, sunflower, flaxseed, maize, soybean, grapeseed, pumpkin). Maize seed oil contained vanillin, trans-cinnamic acid and ferulic scid (2.8, 0.9 and 0.5 mg/ kg, respectively). Rapeseed oil had a high amount of syringic acid (6.8 mg/kg) (Tuberoso et al. 2007). Crude rice bran oil is reported to contain desmethylsterols (3,225 mg/100 g, reduced to 1,055 mg/100 g in refined oil), monomethylsterols (420 mg/100 g), and dimethylsterols or triterpene alcohols (1,176 mg/100 g), making a total of 4.8 g/100 g. Kochhar (2002) has collated information about the major members of each class. Many of these sterols are present as esters of ferulic acid (3-methoxy-4-hydroxycinnamic acid) and are known collectively as oryzanols (115–787 mg/100 g) (Gunstone and Harwood 2007). These are powerful antioxidants and show physiological properties. Oryzanols were not determined in this work.
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TABLE2. PHENOLICACIDCONTENTINPLANTOILEXTRACTS
OilPhenolicacidcontent(mg/100goil)*
Protocatechuicp-hydroxybenzoicVanillicCaffeicp-coumaricFerulicSinapicSum
Soybeannd0.8 0.03a1.1 0.06b0.8 0.07b1.5 0.06a1.2 0.08c,d0.9 0.03b6.3 0.33d Sunflowernd1.5 0.05b6.9 0.15e4.9 0.10c1.8 0.06b1.3 0.08d1.4 0.03c17.8 0.47g Rapeseednd1.6 0.05b,cnd0.3 0.05a13.1 0.12f5.6 0.10f236.0 0.50e256.6 0.73i Cornnd1.7 0.02cndnd1.9 0.08b,c5.8 0.10f0.6 0.03a,b10.0 0.23e Grapeseedndnd0.8 0.05andndnd0.2 0.08a1.0 0.13b Hempnd6.0 0.06e2.0 0.10dnd2.0 0.15c1.0 0.08b,c3.0 0.05d14.0 0.44f Flaxnd3.1 0.07d1.0 0.15bndnd1.0 0.05bnd5.1 0.27c Ricebranndndndndnd0.4 0.03and0.4 0.03a Pumpkin3.1 0.15nd11.4 0.10fnd3.8 0.06e3.8 0.06end22.1 0.37h
*Values(mean SD)withdifferentindexlettersarestatisticallysignificantlydifferent(P<0.05). nd,notdetected.
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The percentage of DPPH• scavenged by antioxidants contained in oil extractsisshowninTable 3.AlloilextractsscavengedDPPH•.Themethanolic extracts of the oils were characterized by statistically significant differences in their antioxidant activity measured by the DPPH• method. The highest antioxidantactivitywasdisplayedbytheextractobtainedfromhempandpumpkin oils (70%), then rapeseed oil (over 50% of DPPH• scavenged). Other extracts of oils deactivated about 20% of DPPH•. Soybean oil methanolic extract possessed the lowest ARP calculated from the amount of sample needed to decrease the initial DPPH• concentration by 50% (2.94 ¥ 10-2) (Table 3). Rapeseed oil methanolic extract (10.31 ¥ 10-2) possessed an ARP similar to that of rice bran oil (9.37 ¥ 10-2). The best ARP was exhibited by the extract obtained from pumpkin (11.36 ¥ 10-2) and hemp oils (11.49 ¥ 10-2). The molecular structure of phenols is important for their antioxidant activity, as this activity is enhanced by the presence of a second hydroxyl or a methoxy group in the ortho- orpara-position (Laranijinha 2002). De Leonardis et al. (2003) examined the antioxidant properties and oxidative stability of coldpressed sunflower oil. They claimed that phenols extracted from sunflower seeds protect sunflower oil from autoxidation more effectively than butylated hydroxyanisole. Vuorela et al. (2004) confirmed strong antioxidant properties ofphenoliccompoundsextractedfromrapeseedwhichscavengedover60%of DPPH radicals and inhibited the formation of hexanal (over 90%) and hydroperoxides(over80%).Matthäus(2002)alsoconfirmedtheantioxidantactivity of oilseed extracts such as those of rapeseed and sunflower, which inhibited the formation of conjugated dienes of linoleic acid. It should be noted that the results so obtained may be influenced by other substances contained in the methanolicextractsthatwerenotdeterminedinourstudies,e.g.,vinylsyringol
TABLE 3. ANTIOXIDANT ACTIVITY IN PLANT OIL EXTRACTS
Oil DPPH• scavenging (%)* EC50 (mg) ARP
Soybean 17.4 3.2b 34.0 2.94 ¥ 10-2 Sunflower 23.8 2.1c 16.9 5.92 ¥ 10-2 Rapeseed 51.2 4.1d 9.7 10.31 ¥ 10-2 Corn 11.1 1.3a 14.8 6.76 ¥ 10-2 Grapeseed 13.4 2.0a 15.9 6.28 ¥ 10-2 Hemp 76.2 4.5f 8.7 11.49 ¥ 10-2 Flax 19.3 2.1b,c 24.6 4.06 ¥ 10-2 Rice bran 23.7 2.6c 10.7 9.37 ¥ 10-2 Pumpkin 65.3 3.1e 8.8 11.36 ¥ 10-2
* Values (means SD) with different index letters are statistically significantly different (P < 0.05). ARP, antiradical power; EC50, the amount of sample needed to decrease the initial DPPH* concentration by 50%.
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(canolol) present in rapeseed oil.This compound is the product of sinapic acid decarboxylation, which has strong antioxidant activity (Koski et al. 2003) and which protects DNA, fats and proteins from oxidation (Kuwahara et al. 2004). Grapeseeds are a rich source of monomeric phenols such as (+) catechin, (–) epicatechin, di-, ti- and tetrameric procyanidin (Saito et al. 1998; Kim et al. 2006). Espin et al. (2000) examined the ARP of plant oils, e.g., soybean, sunflower and corn oils, in both lipid and methanolic fractions, and reported that free radical scavenging capacity on DPPH• in polar fraction was not significant. The ARP to scavenge DPPH• by phenolic compounds extracted from rapeseeds also depended on the number of hydroxyl groups in the aromatic ring of the studied compounds (Sroka and Cisowski 2003). Papadopoulos et al. (2003) found that methanol-soluble phases from maize and sunflower oils have an antioxidant activity much lower than methanol-soluble phase of olive oils. Data presented by Tuberoso et al. (2007) showed that differences were not so distinct, especially for maize oil. Ramadan and Moersel (2006) compared, using the same per-weight basis, the antiradical performance of oils with respect to DPPH radical. The order of effectiveness of oils in inhibiting free radicals was as follows: coriander > black cumin > cottonseed > peanut > sunflower > walnut > hemp seed > linseed > olive > niger seed. We found a correlation between the total phenolic content and the scavenging of DPPH• (r = 0.87, P < 0.05). The best antioxidant activities were displayed by the extracts obtained from hemp and pumpkin oils.These oils contained the highest amount of total phenolic compounds. In the case of the above-mentioned oils, the total phenolic compound content did not differ statistically, whereas the rapeseed oil extract contained the highest level of phenolic acids, especially sinapic acid. Cold-pressed oils may retain higher levels of natural antioxidants that may be removed during the refining steps of a conventional oil processing procedure, and exhibit acceptable shelf stability and improved safety without added synthetic antioxidants. In addition, cold pressing involves no organic solvent, which results in a product that is chemically contaminant free.
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