Abstract
In this study, the nutritional composition and phytochemical composition of the rosehip seed, and the fatty acid and sterol compositions of the seed oil were investigated. The rosehip seed contained valuable phytochemicals such as phenolic compounds (2554 μg/g), carotenoids (2.92 μg/g), and ascorbic acid (1798 μg/g). Furthermore, the rosehip-seed oil was rich in polyunsaturated fatty acids, linoleic acid (54.05%), linolenic acid (19.37%), and phytosterols, mainly β-sitosterol (82.1%). The rosehip seed and seed oil were found to have antioxidant activity measured by trolox equivalent antioxidant capacity assay. It can be concluded that the rosehip seed and seed oil may be utilized as a source of phytonutrients.
INTRODUCTION
Rosa canina L., rosehip, is a wild shrub growing in Europe, northwest Africa, and western Asia. The fruits of the rosehip have been used in folk medicine for a long time. Rosehips have prophylactic and therapeutic actions against the common cold, infectious diseases, gastrointestinal disorders, urinary tract diseases, and inflammatory diseases.[Citation1,Citation2] Rosehip powder has been shown to reduce osteoarthritis symptoms in clinical trials.[Citation3,Citation4] The health benefits of rosehips are attributed to the presence of bioactive compounds such as ascorbic acid, carotenoids, and phenolic compounds. Since rosehips have the highest level of ascorbic acid among fruits and vegetables, they have been used as an herbal tea and vitamin supplement for a long time in the Europe.[Citation5] Fresh rosehips are consumed as a snack and dried rosehips are processed in products such as tea, jam, nectar, marmalade, and pestil.[Citation6] The seeds, byproducts of rosehip products, are used for animal nutrition. The lipid fraction of the rosehip seed contains more than 50% polyunsaturated fatty acids.[Citation7] Rosehip-seed oil has been used in cosmetics because of its therapeutic effect on skin disorders.[Citation8]
Research on the characterization of byproducts in the food processing industry has gained considerable attention, since the byproducts can be utilized in pharmacological, cosmetic, and food applications as potential sources of bioactive compounds. Available data on the nutritional and, phytochemical composition, and lipid characteristics of the rosehip seed are limited.[Citation9] The objective of this study was to determine the nutritional and phytochemical composition of the rosehip seed. The lipid fraction of the seed was analyzed for its fatty acid and sterol composition as well.
MATERIALS AND METHODS
Sample
Rosehip (Rosa canina L.) seeds were provided by a rosehip processing factory in Gumushane (Gumussu Food Company, Gumushane, Turkey). The air-dried seeds were ground using a laboratory mill (IKA M20). The seed powder was used for further analysis. All solvents were analytical grade or HPLC grade from Merck (Darmstad, Germany). ABTS, Folin Ciocalteu reagent, gallic acid, BSTFA-TMCS (N,O-Bis(trimethylsilyl)trifluoroacetamide-trimethylchlorosilane), and standard FAME reference mixture were supplied from Sigma (St. Louis, MO, USA).
Chemical Composition
Moisture, ash, protein, and fat contents of the seeds were determined using the AOAC methods (AOAC, 2006). The Kjedahl method was used to estimate the crude protein content (N*6.25). The crude fat was determined using the Soxhlet method.
Total Phenolic Compounds (TPC)
One gram of the seed powder was extracted with 10 ml of methanol (80%) in an orbital shaker (Daihan Scientific, Seoul, South Korea) at room temperature, 250 rpm for 2 h. After filtration, the residue was reextracted with 10 ml of methanol. The combined methanol extracts were stored at –18°C until analysis. TPC were estimated using the Folin-Ciocalteu method. 0.1 ml of the extract solution was mixed with 0.50 ml of diluted Folin-Ciocalteu reagent, 0.4 ml of sodium carbonate (1 M) and 4 ml of distilled water. The absorbance of the mixture was measured at 765 nm after 1 h. The calibration curve was prepared with standard gallic acid ranging from 0 to 50 mg/ml. Total phenolic content was expressed as mg of gallic acid equivalents (GAEs) per g of the seed.
Ascorbic Acid and Total Carotenoids
Ascorbic acid content was determined according to the method of Klein and Perry,[Citation10] with some modification. The seed powder (300 mg) was extracted with metaphosphoric acid (5 ml, 2%). The pH of the extract was adjusted to 3.6 with the addition of a citrate-phosphate buffer (3 g of meta-phosphoric acid, 2.85 g of citric acid, and 1.1 g of sodium hydroxide in 100 ml; pH = 3.6 ± 0.1). The filtrate (2 ml) was mixed with a citrate-phosphate buffer (2 ml) and 2,6-dichloroindophenol(125 mg/L, 2 ml). The absorbance was measured at 520 nm. The calibration curve was prepared with ascorbic acid ranging from 0.001 to 0.05 mg/ml. Total carotenoid content was determined according to the method of Szentmihalyi et al.[Citation7] The seed powder (150 mg) was extracted with 10 ml of hexane. The absorbance of the filtrate was measured at 450 nm. The extinction coefficient was taken as 2505 (100 ml g−1 cm−Citation1).
Fatty Acid Composition
The fatty acid composition was determined according to the analytical methods described in the AOAC methods (AOAC, 2006). The determination of fatty acid composition was carried out by gas chromatography with flame ionization detection (GC-FID). Fatty acid methyl ester was injected into a Shimadzu GC-2010 Plus gas chromatograph equipped with a flame ionization detector, a split/splitless injector, and a long capillary column (0.25 mm × 0.20 μm × 60 m, Teknokroma TR-CN100). The oven temperature program was as follows: the initial temperature of the column was 90°C, held for 5 min, then a 10°C/min ramp to 240°C, and held for 20 min. The carrier gas was helium at a flow rate of 1 ml/min, the split ratio was 100:1, and the injection quantity was 1 μl. The identification of FAMEs was performed by using a standard FAME reference mixture. The peak areas were computed by the integration software and fatty acids were given in percentages relative to total fatty acid contents.
Sterol Composition
Total sterol content was determined according to a modified DGF official method.[Citation11] A total of 1 g of oil was weighed in a flask and 1 ml of internal standard (0.1 g/100 ml cholesterol in chloroform) was added to the flask. After the chloroform evaporated under nitrogen stream, the sample was saponified with 6 ml aqueous 10 mol/L KOH in 10 ml of ethanol. Saponification took at least 90 min. The unsaponifiable fraction was extracted twice with diethyl ether. The combined fractions were washed twice with 0.5 mol/L KOH (7 ml) and 2–4 times with a saturated sodium chloride solution (7 ml) until the washing water had a neutral pH, and then the organic phase was dried with anhydrous sodium sulfate. The residue obtained after evaporation was re-dissolved in 0.3 ml pyridine and 0.3 ml BSTFA + TMCS, and derivatized for 30 min at 80°C. The samples were injected in a Shimadzu GC-2010 Plus gas chromatograph equipped with a flame ionization detector, a split/splitless injector and a capillary column (0.22 mm × 0.22 μm × 30 m, Teknokroma TRB-Sterol). Detection was done by flame ionization detector (325°C). Oven temperature was isothermal at 280°C for 40 min. The carrier gas was helium at a flow rate of 0.5 ml/min. The identification of sterols was performed according to the relative retention time (the ratio of the retention time of each sterol to the retention time of β-sitosterol). The internal standard (cholesterol) method was used for the quantification.
Trolox Equivalent Antioxidant Capacity (TEAC)
Extraction was carried out according to the method of Adnan et al.,[Citation12] with some modifications. One gram of the seed was extracted with 10 ml of extraction solvent in an orbital shaker (Daihan Scientific, Seoul, South Korea) at room temperature, 250 rpm for 2 h. The extract was filtered through Whatman No. 4 paper. The extraction procedure was repeated and two filtrates were combined. 0.5 g of the seed oil was dissolved in hexane (5 ml). The antioxidant compounds were extracted two times with the extraction solvents (5 ml) in the separation funnel. The extraction solvents used in this study were methanol (80%), acetone (70%), and ethanol (60%). The methanol, acetone, and ethanol extracts of the seed and seed oil were stored at –18°C until analysis. For the ABTS assay, first, ABTS stock solution was prepared by reacting 7 mM ABTS with 2.45 mM potassium persulfate solution (2:1). The stock solution was left in the dark at room temperature for 16 h. The stock solution was diluted with ethanol to reach an absorbance of 0.70 (± 0.02) AU at 734 nm. Fifty μL of the extract was mixed with 1000 μL of ABTS•+ solution, and the absorbance was measured at 734 nm after 10 min. The results were expressed as micromoles of trolox per g of seed.
RESULTS AND DISCUSSION
Nutritional Composition
The results of the proximate analysis and estimated energy value of the rosehip seed are presented in . Carbohydrate was found to be the most abundant macronutrient in the seed, whereas protein was the less abundant macronutrient. The nutritional composition of the rosehip fruit was studied by Barros et al.[Citation13] The rosehip seed contained a slightly lower amount of carbohydrate and a slightly higher amount of protein compared to the rosehip fruit (93.16 g/100 g; 2.72 g/100 g). The seed was rich in lipids. The seed showed a higher lipid content than the whole fruit (0.65 g/100 g). However, the seed revealed a lower ash content than the whole fruit (3.47 g/100 g). The nutritional composition and high energy value of the seed indicated that rosehip seed may be consumed as a dietary supplement to provide carbohydrate and energy after the toxicity index is determined.
Table 1 Nutritional composition and energy value of the rosehip seed
Phytochemical Composition
shows total phenolic, total carotenoids, and ascorbic acid contents of the seed and seed oil. The seed had a lower content of TPC compared to the rosehip fruit (143.2 mg/g),[Citation13] whereas the content of TPC in the seed was similar to the rosehip leaves (2.57 mg/g).[Citation14] The rosehip seed revealed a lower content of TPC than the white and red grape seed studied by Bozan et al.[Citation15] and Makris et al.[Citation16] However, the rosehip seed had a higher content of TPC than the pomegranate seed.[Citation17] The ascorbic acid content of the studied seed was higher than the value (1060 μg/g) reported by Barros et al.[Citation9] The rosehip seed revealed a lower ascorbic acid content than the rosehip fruit.[Citation5] The ascorbic acid content of the seed was higher compared to citrus fruits (<0.5 mg/g),[Citation18,Citation19] which have been considered the main dietary sources of ascorbic acid. The rosehip seed oil contained a higher amount of phenolic compounds (215.4 μg/g), indicating that the rosehip-seed oil is a good source of phenolic compounds similar to grape-seed oil[Citation20] and pomegranate-seed oil,[Citation21] which have gained much attention recently. The total carotenoid content of the studied seed oil was found to be lower than the seed studied by Szentmihalyi et al. (137.5 μg/g).[Citation7]
Table 2 Total phenolics, total carotenoids, ascorbic acid contents, and antioxidant activity of the rosehip seed (fresh weight basis) and seed oil
TEAC
shows the TEAC of the rosehip seed and seed oil. Methanol and acetone extracts exhibited higher values than the ethanol extract. It can be interpreted that methanol and acetone may be the most suitable solvents for the extraction of antioxidant compounds from the rosehip seed. No comparable data on the antioxidant activity of the rosehip seed was found in the literature. The TEAC values of the rosehip fruits were found to range from 457.2 to 626.2 μmol/g.[Citation22] The TEAC value of the rosehip leaves was reported as 190 μmol/g.[Citation14] It can be interpreted that the rosehip seed had a lower antioxidant capacity compared to the whole fruit and leaves. Moreover, the rosehip seed had a lower antioxidant capacity than the grape seed.[Citation23]
The seed oil had a lower antioxidant activity than the seed (), which may be related to a higher TPC of the seed compared to the seed oil. The TEAC value of the rosehip-seed oil was found to be higher than the grape-seed oils.[Citation20] The TEAC values of vegetable oils (corn, olive, and sunflower) were reported to vary from 0.61 to 1.79 μmol/g.[Citation24] The rosehip-seed oil had a higher antioxidant capacity compared to the vegetable oils. Antioxidant compounds are known to have protective effects against chronic diseases. Antioxidant compounds were found in the rosehip seed and seed oil, which have been found to possess antioxidant activity. It can be interpreted that the rosehip seeds may be utilized as sources of dietary antioxidants.
Fatty Acid Composition
The fatty acid composition of the seed oil is presented in . The main fatty acids detected in the seed oil were linoleic acid (54.05%), linolenic acid (19.37%), and oleic acid (19.50%). The linoleic acid percentage of the studied seed oil was found to be higher than the value reported by Barros et al.,[Citation9] whereas the linolenic acid percentage of the studied seed oil was lower than the value determined by Barros et al. Differences in the fatty acid composition between the Turkish and Portuguese samples may be related to environmental conditions (climate and altitude etc.), which are known to have an impact on fatty acid composition. The rosehip-seed oil contained a higher percentage of linolenic acid compared to the grape-seed oils[Citation25] and pomegranate-seed oils.[Citation17] Moreover, the rosehip seed revealed a higher level of linolenic acid than vegetable oils such as canola and soybean oils, the main dietary sources of linolenic acid. High levels of linoleic acid and linolenic acid of the rosehip-seed oil can make it susceptible to lipid oxidation. However, its antioxidant content may enhance oxidative stability. Linolenic acid has a protective effect against heart disease and is important in the development of the brain and retina.[Citation26] Linoleic and linolenic acids−essential fatty acids−are precursors of omega-3 and omega-6 fatty acids. A balanced omega-6 fatty acid and omega-3 fatty acid intake is important in the prevention of chronic diseases such as coronary heart disease and cancers. The recommended ratio of omega-6 fatty acids to omega-3 fatty acid ranges from 1:1 to 4:1[Citation27] The higher percentage of polyunsaturated fatty acids and the ratio of linolenic acid to linoleic acid may make rosehip-seed oil a valuable source for omega fatty acids.
Table 3 Fatty acid and sterol composition of the rosehip seed oil
Sterol Composition
The sterol composition of the rosehip-seed oil is presented in . The major detected sterols in the rosehip-seed oil were β-sitosterol, Δ7-stigmastenol, Δ5-avenasterol, campesterol, and stigmasterol. Δ7-Avenasterol and clerosterol were the minor sterols found in the seed oil. The total sterol content of the studied seed oil was found to be higher than the value reported by Zlatanov.[Citation28] Moreover, the total sterol content of the rosehip-seed oil was higher than the grape-seed oils.[Citation25] However, it was lower than those of the pomegranate-seed oils.[Citation29] The rosehip-seed oil had a higher amount of sterols compared to the most economically available vegetable oils such as sunflower, soybean, and olive oils (<500 mg/100 g).[Citation30] The results of the sterol analysis revealed that the rosehip-seed oil was a good source of phytosterols. Phytosterols are known to have a lowering effect on the cholesterol absorbed in the intestine. The consumption of sterol-enriched foods providing 2 g of phytosterols per day is recommended to reduce total serum and LDL cholesterol. Moreover, phytosterols may provide protection against several types of cancers.[Citation30]
CONCLUSION
The findings of this study showed that rosehip seed and seed oil were good sources of phytonutrients. Consumption of foods rich in phytonutrients is recommended to reduce the risk of chronic diseases. The nutritional composition and the presence of bioactive compounds make the rosehip seed a valuable source of phytonutrients. The rosehip seed was highly rich in carbohydrates and ascorbic acid, and the rosehip-seed oil was highly rich in polyunsaturated fatty acids and phytosterols. The rosehip seed and seed oil proved to have antioxidant activity. The findings of the study indicated that the rosehip seed and seed oil may be proposed as ingredients in functional food formulations and dietary supplements.
ACKNOWLEDGMENTS
The author would like to express thanks to Professor Dr. Beraat Ozcelik and Msc. Mine Gultekin-Ozguven for their support.
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