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A new resource of nervonic acid from purpleblow maple (Acer truncatum) seed oil.

Abstract

In this study, the chemical composition of the oil extracted with petroleum ether from purpleblow maple (Acer truncatum) seeds was examined. It was found that the dried seed contained 46.6 percent oil, in which linoleic acid (33.9%), oleic acid (23.8%), and erucic acid (17.2%) were the major fatty acids. More importantly, the oil contained noticeable amounts of nervonic acid (NA) (5.8%) and vitamin E (125.23 mg/100 g), which is the most biologically active isomer. Therefore, the seed oil may be considered as a potential new source for natural NA and vitamin E. In addition, research on the application of the oil in the food, cosmetics, and medical industries was summarized.

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Purpleblow maple (Acer truncatum) is a plant belonging to the genus Acer. In ancient China, its Chinese name was Yuanbao. The tree is widely distributed in China from north of the Jilin Province to south of the Gansu Province and from south of the Anhui Province to the Kerchin Desert of Inner Mongolia. It is one of the main species of the red-leaf trees on Mount Xiangshan and in big cities such as Beijing. In the early 1970s, seeds of purpleblow maple were exploited for their edible oil; the oil content is high reaching 45 to 48 percent (Wang 2003). The cultivation technology, constituents, and medical value of purpleblow maple have been systematically studied through intensive research projects, The results showed that purpleblow maple has been developed and exploited as food and for use in medicine and chemistry. The fatty acids of purpleblow maple seed oil contain 5 to 6 percent nervonic acid (NA). Because only a few plant species contain NA, and the NA on the international market primarily comes from deep sea fish, purpleblow maple is considered to be a new sustainable resource for obtaining NA (Wang 2003),

NA, which is also called selacholeic acid, is cis-15-tetracosanoic acid, with a molecular formula of [C.sub.24][H.sub.46][0.sub.2] and a molecular weight of 366.6. Pure NA is a white solid under ambient temperature. It is a type of to-9 superlong-chain monoenic fatty acid and was first discovered in the nerve tissue of animals. The content of NA in nerve and brain tissue is relatively high and is important in the composition of biological membranes. It takes part in many special physiological functions that are connected to biological membranes (Wu 2001).

Since the physiological activity was only discovered 30 years ago and the study on NA in China began in the 1980s, many aspects of NA need further study. Many medical studies have shown that NA is essential for the development of the brain and significantly contributes to enhancing the activity of brain nerves and protecting brain nerves from aging. In a study on the biosynthetic pathway of NA formation, scientists found that NA is formed through elongation of the carbonic chain of erucic acid (docosanoic acid) (Lecerf 1980). This is confirmed by animal testing in which the content of NA in the viscera of rats rises after the injection of erucic acid (Cook et al. 1980). Today, NA is widely distributed in species of the order of Cruciferae. These plants generally contain a certain quantity of erucic acid (Ma et al. 2004). Xu and Qiu (2001) have also pointed out that some lipids, such as erucic acid, have medical effects on malnutrition and adrenal gland leucotomy. The present study examines the quantitative extraction of oils from the seeds of purpleblow maple and then determines their chemical composition. The applications of the oil in food, cosmetics, and medical industries are briefly reviewed.

Material and methods

Seeds of purpleblow maple were obtained on the farm of North-Western University of Agriculture and Forestry, Yangling, China. The seeds were ground using a Christie Laboratory mill to pass through a 5-mm screen. The ground seed was then dried in a cabinet oven with air circulation at 60[degrees]C for 16 hours before extraction. Fatty acids are abbreviated with a notation indicating the number of carbon atoms:number of double bonds. All standard compounds were purchased from Sigma (Beijing). Petroleum ether (40[degrees] to 60 [degrees]C) and other organic solvents were of analytical or regent grade.

Ground seed (10 g) was placed in a cellulose thimble and extracted using a Soxhlet extractor with 300 mL petroleum ether after boiling for 8 hours in duplicate. The solvent was evaporated at 35[degrees]C, and the flakes containing the lipids were dried in nitrogen steam to determine oil yield. The composition and content of fatty acids in oil were determined by a gas chromatography (GC) and GC-mass spectroscopy (GC-MS) after saponification (Xu and Qiu 2001) and derivation. The procedure for derivation was as follows. Bis-(trimethylsily)trifluoro-acetamide (240 [micro]l) and trimethylchlorosilane (120 [micro]l) were added to the 3 mg saponified oil. The solution was kept in an oven for 20 minutes at 75[degrees]C. When cooled, 360 [micro]l toluene was added. The solution was shaken and thereafter was ready for analysis by GC and GC-MS.

The derivatives of the fatty acids were analyzed with an ATI UN 1 CAM 610 series gas chromatograph equipped with a split-splitless injector and a flame ionization detector (FID). The capillary column was a bonded dimethyl polysiloxane Rtx-1 column (30 m by 0.25 mm i.d.) (Thames Chromatography Fairacres Industrial Center, UK) with a film thickness of 0.10 [micro]m. Helium was the carrier gas, and the initial flow rate was 1.3 mL/min. The injector and detector temperatures were set at 330[degrees] and 340[degrees]C, respectively. The oven was temperature-programmed from 80[degrees] to 336[degrees]C at 6[degrees]C/min. Triplicate samples (1 [micro]l) were injected in the splitless mode. Fatty acids were then identified by comparing their retention times with those of authentic compounds. Mass spectra were recorded with a 5970 Series instrument (Hewlett Packard, UK) equipped with the same capillary column. The spectrometry was operated with an electron energy setting of 70 eV. Fatty acids were also confirmed by comparing the mass fragmentography with standard compounds.

The content of vitamin E in the isolated oil was determined by higher performance liquid chromatography (HPLC) according to the method described by Gimeno et al. (2000). Briefly, the oil was diluted in hexane and an aliquot was mixed with ethanol containing an internal standard ([alpha]-tocopherol acetate). The chromatographic system consisted of an ODS-2 column with a methanol-water mobile phase. Tocopherols were detected at 292 nm. The methods for measuring the physiochemical properties of the seed oil from purpleblow maple were based on the procedures described by Eromosele et al. (1994).

Results and discussion

Characterization of seed oil of purpleblow maple

Extraction with petroleum ether yielded 46.6 percent oil from the air-dried seeds ofpurpleblow maple. The properties of the oil extracted by petroleum ether are the same as those of the oil obtained by mechanical pressing. Its physical and chemical properties are given in Table 1. The results obtained suggested that the physico-chemical properties of seed oil of purpleblow maple are similar to those of the high quality oils used as edible oil in daily diet.

Table 2 gives the composition and content of fatty acids in the seed oil of purpleblow maple. As can be seen, linoleic acid (33.9%), oleic acid (23.8%), and erucic acid (17.2%) were the major fatty acids in the seed oil, Gondoic acid (7.9%), palmitic acid (3.9%), linolenic acid (2.6%), and stearic acid (2.2%) appeared in small amounts. Palm-kernel oil acid (0.1%), arachic acid (0.3%), and wood tar acid (0.4%) were found in minor quantities. More importantly, the data showed that the content of NA (24: l) was 5.8 percent in the seed oil of purpleblow maple, which was much higher than that in other seed oils, suggesting that purpleblow maple seed is a new resource for natural NA.

In addition, the content of vitamin E in the seed oil of purpleblow maple was found to be much higher (125.23 mg/ 100 g) than that in the main vegetable oils (15.24 to 93.08 mg/100 g). This indicated that the oil from purpleblow maple seeds has a stronger antioxidation activity compared to the edible oil used in daily diet (Table 3).

Development and exploitation of seed oil of purpleblow maple

As early as the 1970s, the safety of eating the seed oil of purpleblow maple had been systematically studied through the combined intensive research at our university and the Pharmacy College of Xi'an Medical University. Acute toxicity and long-term toxicity tests showed that the seed oil of purpleblow maple does not cause a toxic reaction and is safe when used as a food. Antibacterial tests of the seed oil of purpleblow maple were performed at our university, and the results showed that the oil could largely inhibit several familiar putrefaction bacteria, especially Escherichia, Bacillus subtilis, and Aspergillus flavus. This indicted that the seed oil of purpleblow maple is safe when used as food and is a very good natural bacteria-inhibitor. It can be used as a natural bacteria-inhibitor and antiseptic in cake and bread, confections, and drinks (Wang 2003).

When Xi'an Pharmacy Plant manufactured tetracycline in the 1970s, high-quality vegetable oil was added as a component of the substrate during the bacterium culture. The plant used refined soybean oil, and we compared the seed oil of purpleblow maple to refined soybean oil in the bacterium culture. The results of the six mini-type experiments are listed in Table 4. The results showed that seed oil of purpleblow maple does not cause a toxicity reaction in the growth and metabolism of tetracycline. This is similar to the effect of refined soybean oil.

Research on the antitumor action of the seed oil of purpleblow maple, using a mouse model of sarcoma S 180 conducted by Pharmacy College of Xi'an Transportation University, showed that the average inhibiting rate to sarcoma S 180 was 82.94 percent, which meant that the inhibiting action of the seed oil of purpleblow maple on sarcoma S180 is similar to that of cyclophosphamide (an anticancer drug), while the toxicity of the former was much lower than that of the latter. In addition, the research on antitumor action of the seed oil of purpleblow maple using a model of ascitic tumor showed that the average inhibiting rate of small and large dosage of it to ascitic cancer in mice was 81.9 percent and 57.7 percent, respectively, both of which were higher than the standard life-prolonging rate of non-cavum-abdominis medicine supply (5%). The statistical processing of the result showed that the difference between the treatment team and the control team was significant, and the effect of a small dose of the oil (equivalent to 8 mL/day) was the best. These tests indicated that the seed oil of purpleblow maple certainly has the inhibiting action to the growth of tumors and is a promising vegetable oil (Wang 2003),

Besides its use in medication as a basic ingredient of bacteriophage substrate or as an antitumor drug, the seed oil of purpleblow maple has also been used widely in the cosmetics industry. In the last 10 years, significant attention has been paid to the application of seed oil of purpleblow maple in cosmetics manufacture, since it is safe, without toxicity, stable to oxygen, and contains a high content of vitamin E and essential fatty acids. Development and utilization tests in recent years also showed that cosmetics made with the seed oil of purpleblow maple has beneficial physiological actions on skin. It infiltrates the skin rapidly without feeling greasy or tacky, causing no irritation or hypersusceptibility. It also maintains skin moisture well, slowing the evaporation of water from the surface of skin and making skin soft, smooth, and elastic.

Conclusions

The results show that the seed oil of purpleblow maple contains 5.8 percent NA (24:1) and 125.23 (mg/100 g) vitamin E, suggesting that it is a new resource of NA and edible oil. Research on purpleblow maple oil application in the food, cosmetics, and medical industries indicate that the utilization of purpleblow maple seed oil will be promising in the near future.

Literature cited

Cook, C., J. Barnett, K. Coupland, and J. Sargent. 1980. Effects of feeding Lunaria oil rich in nervonic and erucic acids on the fatty acid compositions of sphingomyelins from erythrocytes, liver, and brain of the guaking mouse mutant. Lipids 33(10):993-1000.

Eromosele, I.C., C.O. Eromosele, A.O. Akintoye, and T.O. Komolafe. 1994. Characterization of oils and chemical analyses of the seeds of wild plants. Plant Foods Hum. Nutr. 46:361-365.

Gimeno, E., A.I. Castellote, R.M. Lamuela-Raventns, M.C. de la Torre, and M.C. Lopez-Sabater. 2000. Rapid determination of vitamin E in vegetable oils by reversed phase high-performance liquid chromatography. J. Chromatogr. A881:251-254.

Lecerf, J. 1980. Evidence of accumulation of ceramides containing [14C] nervonic acid in the rat lung following injection of [14C] erucic acid. Biochim. Biophys. Acta 617(3):398-409.

Ma, B.L., S.F. Liang, and D.W. Zhao. 2004. A study on plants containing nervonic acid. Acta. Bot. Boreal-Occident 24(12):2362-2365.

Wang, X.Y. 2003. Purpleblow Maple in China. Minority Nationality Press of Sichuan, Chengdu, China.

Wu, S.M. 2001. Functional Lipids. Light Industry Press of China, Beijing, China.

Xu, S.G. and A.Y. Qiu. 2001. Lipid Chemistry and Technology. Vol. 5. Light Industry Press of China, Beijing, China. pp. 378-388.

The authors are, respectively, Professors, College of Forestry, North-Western Univ. of Agriculture and Forestry, Yangling, China (xywang@nwuaf.edu.cn; jsfan@nwuaf.edu.cn; sywang@nwuaf. edu.cn; ynsun@scut.edu.cn). This paper was received for publication in December 2005. Article No. 10140.

[c] Forest Products Society 2006. Forest Prod. J. 56(11/12): 147-150.
Table 1.--Physiochemical properties of the seed oil
extracted from purpleblow maple.

Property

Transparency Transparent
Smell Of peanuts
Specific gravity 0.9162
Refractive index (n20D) 1.4733
Viscosity (Angelas 20[degrees]C) 9'24" centipoises
Acidity value 1.52
Free fatty acid (oleic acid) 0.76
Iodine value (g/100 g) 100-110
Saponification value (mgKOH) 185-190
Nonsaponification value 1.06

Table 2.--Content of fatty acids in the seed oil of
purpleblow maple.

Composition of fatty acids Content

Linoleic acid (18:2) 33.9
Oleic acid (18:1) 23.8
Erucic acid (22:1) 17.2
Gondoic acid (20:1) 7.9
Nervonic acid (24:1) 5.8
Palmitic acid (16:0) 3.9
Linolenic acid (18:3) 2.6
Stearic acid (18:0) 2.2
Behenic acid (22:0) 0.9
Wood tar acid (24:0) 0.4
Arachic acid (20:0) 0.3
Palm-kernel oil acid (16:1) 0.1

Table 3.--Content of vitamin E in the seed oil of
purpleblow maple and vegetable oils. (a)

Oil Total E [alpha] E [beta] + r E [delta] E

 (mg/100 g)

Rape seed oil 60.89 10.81 38.21 11.87
Soybean oil 93.08 ND (b) 57.55 35.53
Peanut oil 42.06 17.45 19.31 5.30
Cotton seed oil 86.45 19.31 67.14 ND
Sesame oil 68.53 1.77 64.65 2.11
Tea-sea oil 27.90 1.45 10.30 16.15
Palm-kernel oil 15.24 12.62 2.62 ND
Purpleblow maple 125.23 14.79 72.86 37.88

(a) Adopted from constituents table for food (nationwide
representative values) compiled by the China Academy of
Prevention Medicine and Research Institute of Food Hygiene.

(b) ND = not detectable.

Table 4.--Experiments of tetracycline growth using the
seed oil of purpleblow maple and refined soya bean oil.

Experiment Substrate Tetracycline
 no. Oil (a) formula unit

 (% oil) (r/ml)

1 A 2 13000
 B 0.5 11800
 B 1 12180
 B 2 12250
 B 3 14760
2 A 2 14053
 B 2 13800
 B 3 12800
 B 4 14025
3 A 2 14500
 B 1 13600
 B 2 13700
 B 3 14500
 B 4 16100
4 A 2 14400
 B 1 14200
 B 2 13920
 B 3 14220
 B 4 14440
5 A 2 11500
 B 1 13000
 B 2 12300
 B 3 12800
 B 4 13000
6 A 2 14400
 B 2 14200
 B 3 15000
 B 4 16100

(a) A = refined soybean oil and B = seed oil of
purpleblow maple.
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Author:Wang, Xing-Yan; Fan, Jin-Shuan; Wang, Shu-Ying; Sun, Run-Cang
Publication:Forest Products Journal
Geographic Code:9CHIN
Date:Nov 1, 2006
Words:2742
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