Hemp seed oil linoleic acid
Hemp seed oil:
A source of valuable
essential fatty acids
Jean-Luc Deferne 1 and David W. Pate 2
1 International College of Hospitality Administration,
Englisch-Gruss-Strasse 43, CH-3900 Brig, Switzerland .
2 HortaPharm B.V., Schinkelhavenkade 6, 1075VS
Amsterdam, The Netherlands.
Deferne, J.L. and D. W. Pate, 1996. Hemp seed oil: A source of valuable essential fatty acids. Journal of the International Hemp Association 3(1): 1, 4-7.
Interest in Cannabis has largely focused on its content of psychoactive substances (cannabinoids) or its potential industrial use as a source of cellulose fibre. While the whole seed has long been used as a source of food, its potential health contribution has never gained much attention. Hemp seed shares with no other plant resource, both a high content of easily digestible complete protein and a rich endowment of oil providing a favorable ratio of the linoleic (C18:2w6) and linolenic (C18:3w3) essential fatty acids required for proper human nutrition, in addition to a significant contribution of gamma-linolenic (C18:3w6) acid of potential therapeutic efficacy. With a recently acquired knowledge concerning the importance of these fatty acids in the human diet, it is time to both intensify research on their variable occurence among varieties of hemp seed, and investigate methods of oil extraction and storage suitable for their preservation.
Figure 1. Cannabis seed, magnified (Courtesy of VIR.)
Cannabis is probably one of the first plants to have been used (and later cultivated) by people (Schultes 1973). Throughout history and in separate parts of the world, hemp has often been an important plant revered for its psychoactivity and useful for medicine, as a source of fibre, and for the food provided by its seed. The seed oil is particularly nutritious and its properties and potentials are herein explored.
The fruit of hemp is not a true seed, but an “achene”, a tiny nut covered by a hard shell (Small 1979, Paris and Nahas 1984). These are consumed whole, used in food and folk medicinal preparations (Jones 1995) or employed as a feed for birds and fishes. Whole hemp seed contains approximately 20-25% protein, 20-30% carbohydrates and 10-15% insoluble fiber (Theimer and Mцlleken 1995, Theimer 1996), as well as a rich array of minerals, particularly phosphorous, potassium, magnesium, sulfur and calcium, along with modest amounts of iron and zinc (Jones 1995, Wirtschafter 1995), the latter of which is an important enzyme co-factor for human fatty acid metabolism (Erasmus 1993). It is also a fair source of carotene, a “Vitamin A” precursor, and is a potentially important contributor of dietary fiber. Most hemp seed also contains approximately 25-35% oil, although one variety grown in Russia called “olifera” reportedly contains 40% (Small 1979, Mathieu 1980) and a Chinese variety was claimed to slightly exceed this figure (Jones 1995).
This highly polyunsaturated oil has uses similar to that of linseed oil (e.g., fuel for lighting, printers ink, wood preservative), but also has been employed as a raw material for soaps and detergents (Olschewski 1995) and as an emollient in body-care products (Rausch 1995). However, it is the nutritional qualities of the oil that are particularly important. The crushed seed by-product is suitable for animal feed as well as a human staple (Grinspoon and Bakalar 1993, Small 1979, Paris and Nahas 1984), due to its spectrum of amino acids, including all 8 of those essential to the human diet (Jones 1995, Wirtshafter 1995), as well as carbohydrates and a small amount of residual oil. Its protein is primarily edestin (St. Angelo et al. 1968), a highly assimilable globular protein of a type similar to the albumin found in egg whites and blood. However, heat-treating whole hemp seed denatures this protein (Stockwell et al. 1964) and renders it insoluble, possibly affecting digestibility.
An ideal seed hemp variety would produce a high yield of seed (normally 0.5-1.0 t/ha) containing a high percentage of good quality oil. Highly branched varieties are usually preferred. For seed production, male plants are sometimes removed after pollination has occurred, in order to leave more space for female plants. Mathieu et al. (1980) have noted that seed yield can be doubled using monoecious varieties, although this sexual type suffers some inbreeding depression. Cultivation of a monoecious strain in Switzerland yielded up to approximately 1.5 metric tons of seed per hectare in 1995 (unpublished data), but lower yields are generally reported (Mathieu 1980, Hцppner and Menge-Hartmann 1994). Highest seed yields are obtainable with unisex female varieties, such as Uniko-B (Bуcsa 1995). The number of flowers per plant and, therefore, the quantity of seed produced, can be increased by “topping” the plants when they are 30-50 cm high. Maximum seed yield requires that hemp be sown at a much lower density than for fibre (Reichert 1994). However, weeds can prosper if planting density is too sparse (e.g., 25/m 2 ).
Extraction of oil from hemp seed is not being carried out on a large scale at the present time. That being processed, is sometimes relatively unhomogenous, mature seeds mixed with green ones. This is due to the difficulty of finding the optimal time for harvesting, since not all seeds reach maturity simultaneously, especially in hemp undeveloped for seed production. The presence of unripe seeds not only increases seed crop moisture content, it also lowers oil yield and modifies its taste.
After harvest, hemp seed undergoes a drying process that reduces its moisture content to 10% or less, so as to prevent sprouting during storage. Batches of this material are then fed into a hydraulic screw press and a pressure of 500 bars is progressively applied, resulting in only a minor elevation in temperature. Best quality oil is obtained from the first fractions recovered. Approximately 35% of the available oil remains in the seed cake (Jones 1995). The pressing process is sometimes repeated with this crushed residue to obtain a small additional amount of oil, although quality is decreased.
This “cold pressing” does not allow an extraction yield equal to that of techniques employing solvents or high temperatures, but it has the advantage of minimizing degradative changes in the oil. A small amount of oil is also unrecovered during the subsequent filtration process. Further refining procedures should be avoided in order to preserve the native qualities of this product. Bottling must occur quickly and filling under nitrogen into opaque bottles, then refrigerating, offers significant protection against oil degradation due to oxidation and the action of light, although freezing is necessary for long-term storage. Addition of anti-oxidants extends shelf life of the product at room temperature (McEvoy et al. 1996).
Oil composition and properties
Non-refined hemp seed oil extracted by cold-pressing methods varies from off-yellow to dark green and has a pleasant nutty taste, sometimes accompanied by a touch of bitterness. The seed (and therefore the extracted oil) normally does not contain significant amounts of psychoactive substances (Paris and Nahas 1984, Vieira et al. 1967). Trace amounts of THC, sometimes found upon analysis, are probably due to contamination of the seed by adherent resin or other plant residues (Matsunaga et al. 1990, Mathй and Bуcsa 1995), although reports to the contrary exist (e.g., Patwardhan et al. 1978).
Analytical data reported for the fatty acid composition of hemp seed oil (Weil 1993, Kralovansky and Marthй-Schill 1994, Hцppner and Menge-Hartmann 1994, Theimer and Mцlleken 1995, Wirtshafter 1995), together with an analysis performed on an oil produced in Switzerland from a monoecious variety (unpublished data), reveals that it is unusually high in polyunsaturated fatty acids (70-80%), while its content in saturated fatty acids (below 10%) compares favorably with the least saturated commonly consumed vegetable oils (Table 1). This high degree of unsaturation explains its extreme sensitivity to oxidative rancidity, as the chemical “double-bonds” that provide such unsaturation are vulnerable to attack by atmospheric oxygen. This degradation is accelerated by heat or light. For this reason, the oil is unsatisfactory for frying or baking, although moderate heat for short periods is probably tolerable. It is best consumed as a table oil, on salads or as a butter/margarine substitute for dipping bread, similar in use to olive oil. Proper steam sterilization of the seed probably does not cause significant damage to the oil, but does destroy the integrity of the seed, allowing penetration by air and molds. If this procedure is required, it should be done at a legally bonded facility immediately before release of the seed for further processing. By the same reasoning, one should avoid eating whole hemp seed that has been subjected to any cooking process, unless reasonably fresh.
The two polyunsaturated essential fatty acids, linoleic acid (C18:2w6) or “LA” and linolenic acid (C18:3w3) or “LNA”, usually account for approximately 50-70% and 15-25% respectively, of the total seed fatty acid content (Theimer and Mцlleken 1995, Rumyantseva and Lemeshev 1994). Such a 3:1 balance has been claimed optimal for human nutrition (Erasmus 1993) and is apparently unique among the common plant oils (Table 1), although black currant seed oil approaches this figure (Table 2). Cannabis seed from tropical environments seems to lack significant quantities of LNA (ElSohly 1996, Theimer and Mцlleken 1995). Temperate variety oils are less saturated, perhaps due to a natural selection in northern latitudes for oils with a higher energy storage capacity or which remain liquid at a lower temperature. It will be interesting to see if this trend continues for Nordic hemp varieties. The range of results found in some analyses may be attributable to differences in crop ripeness, since formation of polyunsaturated fatty acids is incomplete in immature Cannabis seed (ElSohly 1996). This suggests that a maximum ripening of the seed and the culling of immature seed are important considerations for the production of a quality oil. Likewise, proper seed sampling criteria are also crucial for representative analyses.
GLA sources and importance
Gamma-linolenic acid (C18:3w6) or “GLA” is found in minute quantities in most fats of animal origin (Horrobin 1990a, 1990b). Oats and barley also contain small amounts. Human milk contains some GLA (Carter 1988), but any significance is probably overshadowed (Erasmus 1993) by the greater presence of its metabolic derivative dihomo-gamma-linolenic acid or “DGLA” (C20:3w6).
GLA is available exclusively in health food shops or pharmacies, mostly as soft gelatine capsules, and is not found in oils usually consumed by most people. Good sources of GLA include the blue-green alga Spirulina (
Hemp seed oil linoleic acid Hemp seed oil: A source of valuable essential fatty acids Jean-Luc Deferne 1 and David W. Pate 2 1 International College of Hospitality Administration,
Hempseed oil in a nutshell
In This Section
Industrial hemp is as a class of non-drug Cannabis sativa varieties, and hempseed is technically an achene, or nut. Both the seed and hemp’s tall stalk provide significant carbohydrate feedstocks for a wide variety of industrial purposes in several countries. The oil pressed from hempseed, in particular, is a rich source of polyunsaturated omega-3 and omega-6 fatty acids, which are essential for human health. These same fatty acids in hempseed oil make it a fine drying oil that is used in the production of paints, varnishes, and other coating materials. Plastic flooring such as linoleum and similar materials have been made from hempseed oil, and other non-food uses of hempseed oil are similar to those of linseed oil (flaxseed oil). Flax, of course, also has a long history as a companion species that parallels hemp in the founding of our civilizations.
Unfortunately, when one reads the Latin words Cannabis sativa these days, the first thoughts that come to mind may not be of hemp, or its nutritious seed, or useful oil products, or even the durable outer bast (stem) fiber or the cellulose core from the stalk of this old-world plant. These lesser-known features of Cannabis were certainly well known to Carl Linneaus when he assigned its name in 1753. The words “canvas” and “cannabis,” for example, both derive from similar-sounding words in Greek, Latin, and Arabic for the fabric and the plant from which it is made. The second part of the Linnean binomial, sativa, comes from the Latin word sativus, which means “sown” or “cultivated.” Cannabis sativa is one of the oldest cultivated crops, and no other plants can provide such easily available food, oil, fiber, and even medicine. The largest obstacle that currently prevents hemp from fully participating in modern industrial agriculture is its botanical association with the drug cannabis. In fact, the production of THC (tetrahydrocannabinol) and other cannabinoids is under genetic control, so it would take an ambitious breeding project to convert a hemp variety into a drug variety, much like converting a dachshund into a Doberman pinscher. In other words, it would be much easier just to start with drug Cannabis seeds, if that were the objective.
Our historic foundations were built on the fibers of hemp
Ancient Asian mariners and more recent trans-Atlantic voyagers made good use of sturdy canvas sails made from hemp fiber. Fine linens were once made from both flax and hemp, as the fibers from the male hemp plants were well known to produce the finest linens. The oldest known paper from China was made from hemp, and many historical documents have been written and printed on paper made from hemp fibers. Even today, hemp fibers are found in such common products as tea bags, cigarette papers, and other specialty papers as well as paper currency.
The connection between Cannabis and its misuse as a drug gained official traction when the US Congress passed the Marihuana Tax Act on June 14, 1937; the Act included no practical exemption for hemp production. By that time, the United States was already importing most of its hempseed and fiber from countries with cheaper labor, and the timber and paper industries in the United States were completely invested in the Kraft process for making newsprint. In 1937, commercial wild bird feed was primarily made from hempseed, and hempseed was also pressed for oil used in the manufacture of paints, varnishes, and other coatings. Industrial-scale hemp production mostly continued in the USSR (Union of Soviet Socialist Republics) and China until modern petroleum products slowly began to replace products previously made from hempseed oil and hemp fiber. At least in the days of the USSR, hempseed oil for human consumption was called “black oil,” because of its high chlorophyll content, which was especially used by those who were too poor to afford butter. Hempseed appears as an ingredient in many spices and ethnic foods from Eastern Europe, India, and most parts of Asia. A fine tofu can be easily made from just hempseed, water, and heat.
The Marihuana Tax Act of 1937 had very little impact on the use of marijuana as a narcotic in the United States, if for no other reason than the Act did not penalize the possession or use of hemp, cannabis, or marijuana. It did, though, penalize persons dealing commercially in these products. Thus, the Act effectively brought all industrial hemp production in the United States to a grinding halt by the next year. Subsequently, the United States re-introduced hemp production in 1942 for the war effort, after the Japanese had cut off hemp supplies from the Philippines and East India. (After the war, US hemp production was shut down yet again.) Petroleum-based polymers quickly replaced hemp and other natural fibers in many common products such as sacks, tarps, and ropes. In just a short time, a carbohydrate culture based on agriculture quickly shifted into a culture dependent on petroleum-derived hydrocarbons. Since then, hempseed and hemp fiber production have been excluded from the technological developments enjoyed by other industrial crops. Nor have there been any advances in nutritional research pertaining to hempseed oil. This prohibition on hemp cultivation continues to this day in the United States, even as remarkable advances are being made with medical marijuana. The irony deepens when one realizes that the main psychoactive component of drug Cannabis, THC, has been available as a synthetic pharmaceutical in the United States as Marinol® (dronabinol) since 1972.
In Canada marijuana is already available to registered patients for medical purposes. After years of prohibition, hemp cultivation was cautiously restarted there under heavy licensing in 1998. With eager markets in both Canada and the United States, hempseed oil and other hempseed food products remain in high demand, and the area devoted to oilseed hemp cultivation in Canada has continued to expand accordingly during this time. The Finola oilseed variety of hemp continues to form the cornerstone of the Canadian hempseed production because of its short stature (average plant height: 1.5 m), which allows for mechanical harvesting by a grain combine, and because of its exceptionally high seed yield (over 2000 kg per hectare, under irrigation).
Hempseed as an exceptional food and oil SOURCE
Hempseed is a rich source of easily digestible protein (ca. 20-25%) and highly unsaturated food oil (ca. 30-35%). The remainder consists of dietary fiber, mostly from the hull, various phytosterols, oil-soluble vitamins, and trace minerals (Table 1).
Aside from being extremely low in saturated fats, hempseed oil is interesting in other ways. For example, hempseed oil has a higher content of polyunsaturated fatty acids (PUFA) than most other industrial food oils (Table 2). This has been known for quite a long time, as the essential omega-6 linoleic acid (18:2n-6) was first identified in hempseed oil as “sativic acid” by German chemists in 1887. More recently, presence of omega-3 stearidonic acid (SDA, 18:4n-3) has been detected in hempseed oil (Callaway et al., 1997).
Good amounts of the other essential fatty acid (EFA), α-linolenic acid (18:3n-3), and omega-6 γ-linolenic acid (GLA, 18:4n-6) are also found in this oil. Not only are both of the essential fatty acids (EFA) well represented in hempseed oil, but their direct human metabolic products, GLA and SDA, are too; the latter are not found in any other industrial oilseed crop. This is significant because both dietary EFA must compete for the enzymatic activity of ∆6 desaturase to produce GLA and SDA. As these two fatty acids are already in the oil, this enzymatic step can be bypassed, so they contribute more directly to the downstream production of other omega-6 and omega-3 metabolites.
Perhaps the really good news for consumers is that good-quality cold-pressed hempseed oil has an excellent taste that resembles walnuts and sunflower seeds. When the seeds are toasted, a savory umami flavor develops somewhere between that of bacon and fried prawns.Moreover, the balance of EFA in hempseed is considerably more nearly optimal than in most other industrial food oils, in terms of having a relatively low omega-6 to omega-3 ratio. In this regard, hempseed oil is more like rapeseed oil (also known as canola oil), yet it is still much higher in polyunsaturates. Taken together, these factors at least partly explain a remarkable number of anecdotal benefits from consuming daily hempseed oil, for example, especially marked improvements in skin, hair, and nail quality, as these fatty acids are integral in cell membrane formation and functions at the molecular level. Studies at the University of Kuopio, Finland, have investigated some of the properties, and particularly the improvements in skin quality for patients that suffer from atopic dermatitis (i.e., eczema). Improvements in strength of both hair and nail thickness are also attributed to daily use of dietary hempseed oil.
The high level of PUFA in hempseed oil is certainly a plus for health, but a considerable drawback for deep frying, not only because there is an increased risk of peroxide and trans fat formation, but also because hempseed oil has a relatively low flash point and will burn well once it is ignited. Also, the shelf life of hempseed oil tends to be rather short, because this high level of unsaturation provides more opportunity for oxidation with atmospheric oxygen. Ideally, as a food, hempseed oil is cold pressed from fresh, clean, good-quality seed and then stored in a cool, dark place before, during, and after processing. Unfortunately, much of the hempseed oil that is currently available in North America is distributed in plastic containers to reduce the costs of both production and shipping of this niche crop. Oil purchased in plastic is more susceptible to degradation with time. With a small amount of effort, the interested buyer will typically find hempseed oil in glass bottles on the European markets.
To this day, the US government continues to define hemp as the stalks and fiber of the marijuana plant, and has decided not to recognize any of the varieties that are extremely low in drug content. An analogous situation exists for poppy seed, which is legal in the United States; the seed always contains some measurable amount of morphine, but these amounts are not of sufficient concentration for drug purposes.
Due to the burden of Cannabis prohibition, there has been very little development or innovation in hemp or hempseed production during the last 70 years, and almost no research on hempseed nutrition since its incorporation into Chinese medicine thousands of years ago. It is, in essence, an orphan crop when we consider the present situation of food production in Europe and North America. While this situation began to change with the reintroduction of hemp to Canadian agriculture in 1998, the subsidy scheme for hemp in the European Union continues to favor the production of hemp fiber and not hempseed. What few results we now have from hempseed research tend to contradict the politically narrow horizon that the United States has offered the world. Fortunately, hempseed oil and other hempseed food products are legally available in the United States, either from the shelves of some natural food stores or when ordered directly online from Canada. Viable hempseed, however, remains illegal in the United States.
Leaving political rhetoric aside, there is plenty of convincing scientific evidence to show that hempseed is one of the most nutritious products that can be produced by modern industrial agriculture. As a grain, it fits into the mechanized infrastructure without retooling. Apparently, the only remaining change that needs to be made is to convince US policymakers that hemp is not dangerous.
J.C. Callaway is chief executive officer of Finola ky (Kuopio, Finland; http://www.finola.com/ ). Contact him via email at [email protected] .
For further reading:
Callaway, J.C., T. Tennilä, and D.W. Pate, Occurrence of “omega-3” stearidonic acid (cis-6,9,12,15-octadecatetraenoic acid) in hemp (Cannabis sativa L.) seed, Journal of the International Hemp Association 3:61-63 (1997).
Callaway, J.C., U. Schwab, I. Harvimaa, P. Halonen, O. Mykkänen, P. Hyvönen, and T. Järvinen, Efficacy of dietary hempseed oil in patients with atopic dermatitis, Journal of Dermatological Treatment 16:87-94 (2005).
Callaway, J.C., Hempseed as a nutritional resource: An overview, Euphytica 140:65-72 (2004).
For more information about hempseed oil, see the “Hempseed Oil” chapter by J.C. Callaway and David W. Pate in the Gourmet and Health-Promoting Specialty Oils monograph, published by AOCS Press. Edited by Robert A. Moreau and Afaf Kamal-Eldin, Gourmet and Health-Promoting Specialty Oils is the third volume in the AOCS Monograph Series on Oilseeds. Learn more at http://tinyurl.com/gourmet-oils-aocs . See a review of the book on page 164.
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