DESIGNER OIL CANOLA — A REVIEW OF NEW FOOD-GRADE BRASSICA OILS WITH FOCUS ON HIGH OLEIC, LOW LINOLENIC TYPES
The development of the new technologies for trait modification has opened the possibility of engineering a wide range of new oil profiles in Brassica. Nutritional and functional considerations influence the desirable levels of the C18 mono- and poly-unsaturated fatty acids. New food-grade oils with high oleic, low linolenic profiles are being developed by Brassica breeding institutions worldwide. Brassica oils also are being developed with modified levels of the saturated fatty acids. Other modified oilseeds are competing for a share in the world vegetable oil market. The challenge facing the oilseed industry is to determine the desirable oil profile for each market application. This review will examine the current state of development of new food-grade Brassica oils.
KEYWORDS modified vegetable oil quality, mono- and poly-unsaturated fatty acids
As recently as 20 years ago, the knowledge of which crop produced the vegetable oil was sufficient to tell you the general quality of the oil. Today, one oilseed species may produce a number of new food-grade oils. What is driving the development of new food-grade oils? There are several factors. The elucidation of the biosynthetic pathways and the development of new techniques grouped under the term biotechnology have had a dramatic effect on the ability to produce new vegetable oil compositions. The time from the concept of a new oil quality to the reality of a cultivar in the field has been considerably shortened. The development of improved vegetable oils tailored for specific markets is required to maintain a favourable position in the world market in the face of new competition.
What constitutes an improved oil? The answer depends on the application or the end-use market as the performance of an oil is determined by the oil quality. Modified oils are usually described by the fatty acid which has undergone the most dramatic change – low linolenic oil for example. However, the change in one fatty acid is accompanied by changes in the other fatty acid components and in other minor components. All of these modifications contribute to the performance of the oil.
This review will describe the new food-grade Brassica oils, the nutritional or functional background to the developments and the current breeding status. The choice of categories is as follows: reduced saturated fatty acid oil (> 7% total saturates as the sum of C16:0 + C18:0 + C20:0 + C22:0), low linolenic oil (> 3.5% linolenic), mid-oleic oil (between 65-75% oleic) and high oleic oil (over 75% oleic). These categories are not mutually exclusive but they do represent separate germplasm developments which may then be combined to produce new oil profiles. The term “canola oil” is used in this review to describe the oil profile of the current B. napus and B. rapa cultivars which produce oils with very low levels of erucic acid, equivalent to the terms low erucic acid rape or rapeseed (LEAR) and colza. The typical canola oil profile can be represented as 7% saturated fat, 61% oleic acid, 21% linoleic acid and 11% linolenic acid.
Information was obtained from a number of industry sources and abstracts submitted to the 1999 GCIRC which involved fatty acid modification. However, a review of this nature cannot be definitive in the rapidly changing world of Brassica oilseed development today. Please accept the authors’ apologies in advance for any omissions. We would be happy to hear from any other contributors to this discussion of the new food-grade Brassica oils.
REDUCED SATURATED FATTY ACID OILSEEDS
Dietary recommendations in a number of countries focus attention on limiting total fat intake to 30% of energy and saturated fat intake to 10% of energy. These recommendations are based on the adverse effects of saturated fat on blood cholesterol and its implications for cardiovascular disease (CVD) (Eskin et al. 1995). Distinctions have been made between the different saturated fatty acids in their association with elevated levels of blood cholesterol and CVD risk. Lauric (C12:0), myristic (C14:0) and palmitic (C16:0) acids are cholesterol-raising saturated fatty acids. Stearic acid (C18:0) is apparently neutral in its effect on cholesterol. The labeling regulations in the United States and Canada allow oils with less than one gram of saturated fat per 14 grams of total fat or less than 7.1% saturated fatty acid content in the oil to be identified as low in saturated fatty acids. Canola oil contains a very low level (>7.1%) of saturated fatty acids, half the level of corn oil, olive oil and soybean and one-quarter of the level in cotton seed oil. Of the saturated fatty acids associated with elevated cholesterol levels, canola oil contains only 4%. Aggressive marketing of the low saturate attribute has established canola oil in the North American market. Defense of this market share requires at a minimum the maintenance of the 7% limit on saturated fat.
Canola oil is currently the lowest saturated fat vegetable oil. However, a challenger for this position has emerged in the form of soybean germplasm with reduced saturated fat levels. The low saturated fat trait in soybean was initially developed using mutagenesis, followed by crossing and selection (Wilson, 1993). There are now soybean oils with half the normal level of palmitic acid (>5%). An additional contributing factor to the priority of lowering the level of saturated fat in canola is a major conversion in the western Canadian canola acreage from an approximately equal division between B. rapa and B. napus strains to a predominance of B. napus strains. The result has been an elevation of saturated fatty acid levels in commodity canola oil, due to the higher levels of saturated fat in the seed oil of B. napus canola cultivars currently recommended in Canada in comparison to the saturated fat levels of B. rapa canola cultivars. The environment during seed development also influences saturated fat levels in the seed oil, with higher temperatures resulting in elevated total saturated fat.
Current breeding status
Breeding institutions in Canada have focused on the reduction of saturates initially below 7%, with the long term objective of achieving reductions in palmitic and stearic levels below 4%. The reduction in saturates in B. napus candidate cultivars proposed for registration is established as a priority by the Western Canadian Canola/Rapeseed Recommending Committee Inc. (WCC/RRC Inc.). Significant reductions in saturated fatty acids are not available in current B. napus canola cultivars. Breeding approaches to reducing saturates include interspecific crosses, reconstitution of B. napus from B. rapa and B. oleracea strains with reduced saturate levels and mutagenesis in both B. rapa and B. napus. The focus for Agriculture and Agri-food Canada (AAFC ) Saskatoon is a short term reduction in saturated levels comparable to B. rapa levels with a long term objective of achieving levels below 4% total. B. napus germplasm has been developed from interspecific crosses between B. rapa and B. oleracea strains, with levels comparable to B. rapa (less than 6% of the total saturated fatty acids) ( Raney et al. 1999).
Doubled haploid B. rapa lines with reduced saturated fat levels have been developed from microspore mutagenesis conducted at the Plant Biotechnology Institute in Saskatoon. This low saturate variation will be introduced into B. napus, to produce low saturate germplasm for further cultivar development.
LOW LINOLENIC FATTY ACID OILSEEDS
Canola oil’s polyunsaturated fatty acid content with approximately 11% linolenic acid is intermediate among the vegetable oils, lower than corn oil, soybean oil and sunflower oil, and higher than olive or palm oil. Linolenic acid is recognized as an essential fatty acid and has a role in reducing plasma cholesterol levels (Eskin et al. 1996). The ratio between linolenic and linoleic acid in canola oil (1:2) is also regarded as nutritionally favorable. However, in applications which require stability, vegetable oils which are high in polyunsaturated fatty acids such as canola are stabilized using hydrogenation, with the resulting formation of trans fatty acids. Nutritionists are concerned with the trans isomers of cis-fatty acids raising the serum low-density lipoprotein cholesterol (LDL-C) levels and reducing the serum high density lipoprotein cholesterol (HDL-C). Elevated levels of LDL-C and reduced levels of HDL-C are associated with enhanced risk of CVD. The current recommendation from nutritionists is that the current levels of trans fatty acid in the diet should not be increased (Fitzpatrick and Scarth, 1998).
Low linolenic (18:3) oils were developed to increase the stability of canola oil, reducing or eliminating the requirement for hydrogenation. Low linolenic canola oil demonstrated improved stability under conditions of accelerated storage with no changes in overall odor intensity or pleasantness. There were also significantly lower levels of free fatty acids during frying with low linolenic canola oil with better flavour quality of the French fry product (Eskin et al.1996). The reduction in linolenic acid is typically accompanied by an increase in linoleic or oleic acid.
Current breeding status
In general, the definition of a low linolenic canola oil is >3.5% linolenic acid. Both the mutagenic source and transgenic modification is being used in Brassica breeding programs to reduce linolenic acid content. The low linolenic trait was produced by seed mutagenesis of the B. napus cultivar Oro, which led to the isolation of a mutation line, M11 with an altered C18:2/C18:3 ratio (Rakow, 1973). A program of backcrossing to the adapted cultivar Regent, combined with selection, led to the release of the cultivar Stellar with approximately 3% C18:3 in the seed oil ( Scarth et al. 1988). The low linolenic trait of the cultivar Stellar was relatively stable over environments (Deng and Scarth, 1998).Genetic studies conducted using Stellar demonstrated that low linolenic acid content is controlled by two major genes L1 and L2. A desaturase gene fad3 was shown to be linked to L1 (Jourdren et al 1996). A second gene has been shown to be linked to the second locus L2 (Barret et al. 1999).
The following breeding organizations reported having low linolenic cultivars in production: Ag Seeds (Australia), Cargill (France and Canada), Danisco Seeds (Denmark), Limagrain (Canada) and the University of Manitoba (Canada). There is one low linolenic variety under Plant Variety Protection from Norddutsche Pflanzenzucht (NPZ, Germany). AAFC Saskatoon (Canada) has the objective of combining the low linolenic trait with meal containing zero aliphatic glucosinolates (Raney et al. 1999). The University of Guelph (Canada) is developing low linolenic cultivars using doubled haploidy. The low linolenic profile is being developed in zero-erucic acid spring turnip rape B. rapa at the University of Helsinki and Boreal Plant Breeding in Finland. Current levels of linolenic acid are 7% with a ratio of linoleic/linolenic acid levels of four, achieved through selection (Laakso et al. 1999).
MID and HIGH OLEIC FATTY ACID OILSEEDS
Oils with increased levels of oleic acid in combination with reduced linoleic and linolenic acid show a higher oxidative stability, lower oxidation products and provide stability without extensive hydrogenation. The rate of oxidation of oils is influenced by the degree of unsaturation of fatty acids, light, temperature, the level and type of antioxidants and pro-oxidants present. Secondary oxidation products such as carbonyl compounds, aldehydes, ketones and alcohols produce unpleasant flavours and odors associated with oil rancidity (Fitzpatrick and Scarth, 1998). Mid-oleic oils are marketed for those food applications which require high cooking and frying temperature stability and for snack foods requiring long shelf-life. Comparative studies of genetically modified oils identified the optimum oil profile for frying performance or life of the oil, shelf-life, dietary benefits and sensory properties of end products. The optimum profile is composed of 5 to 7% saturates (C16:0+C18:0+C20:0), 67 to75% oleic, 15 to 22% linoleic and <=3% linolenic acid. The role of linoleic acid in enhanced sensory properties was noted as oleic acid levels over 75% results in a reduction in sensory properties (flavour and taste) and an increase in off-odours (Warner and Mounts, 1993). Research at Institute of Food Science Technology in Australia compared mid-oleic canola oil with palm olein, refined bleached and deodourized (RBD) canola oil, hydrogenated canola oil, sunflower oil and high oleic sunflower oil and showed similar trends. High oleic oils (over 75%) are targeted for industrial end-use in the oleate market or can be blended with conventional oils to lower oleic levels. The oil profile with oleic acid levels over 80% has been protected through patent. The competing oils in this market are the mid- and high oleic sunflower oils.
Current breeding status
Enhanced oleic acid levels have been produced through mutagenesis, applied both to seed and to microspore derived embryos and through transgenic modification. Seed mutagenesis followed by crossing and selection resulted in Brassica genotypes with >85% oleic and reduced levels of linoleic and linolenic acid (Wong et al. 1991).
The University of Göttingen Institute fur Pflanzenbau und Pflanzenzuchtung has a project to establish high oleic (over 90%) quality in winter rapeseed developed from mutagenic lines from cv. Wotan and other high oleic lines. The mutagenic line from Wotan had one seed specific mutation which enhanced oleic acid levels; two other mutation lines had a second non-seed specific mutation which is epistatic over the first mutation. Lines with over 84% oleic acid have been selected. The yield of the best line with more than 80% oleic was 10% less than the check cultivars. A study of the influence of the environment on the high oleic trait showed a high genetic heritability, but with a significant environment and GXE component (Schierholt and Becker 1999).
High oleic canola (>86% oleic,< 7% linoleic, <2.5% linolenic) has been produced using seed specific inhibition of microsomal oleate desaturase and microsomal linoleate desaturase gene expression, either through co-suppression or antisense technology. Co-suppression has been used in combination with mutation treatments to produce modified fatty acid profiles (Debonte and Hitz, 1996).
The fatty acid profile of Cargill’s Clear Valley 75 shows 75% oleic, 10% linoleic and 5% linoleic acid. Ag-Seed Research program in Australia has the trademark MONOLA registered for a canola oil profile of 70% oleic, <3% linoleic and also for >70% oleic with normal levels of linolenic acid, from non-transgenic sources. Field contract production was at 1,000 ha in 1998 with an estimated production of 1,500 MT.
HIGH SATURATED FATTY ACID OILSEEDS
Oils with high levels of saturated fat offer alternatives to the use of hydrogenated liquid oils modified through hydrogenation in applications such as shortenings and margarines where unmodified liquid oils cannot be used. Canola and soybean oils with high saturated fatty acid levels can replace animal fats and tropical oils. Support for this breeding objective includes the benefits of supply stability through domestic production with reduced dependence on imports of tropical high saturate oils.
Current breeding status
Transgenic modification has been used to increase the total saturated fatty acid content of canola. High laurate (C12:0) oil canola was the world’s first transgenic oilseed crop in commercial production. The high laurate trait was the result of the insertion of the acyl-ACP thioesterase isolated from California Bay Laurel (Umbellularia californica). The typical analytical value of Monsanto’s Laurical TM oil profile is 38% lauric acid, 4% myristic, 3% palmitic, 31% oleic, 11% linoleic, 7% linolenic acid and 6% other fatty acids. (LC2- 3/96 Monsanto). The Laurical TM product is suitable for use in the confectionery industry, simulated dairy products, icings and frostings.
Overexpression of the oleate preferring acyl-ACP thioesterase from soybean (Phaseolin vulgaris) increased the palmitate and stearate content to approximately 20% of the total in transgenic lines of the canola cultivar Westar (Hitz et al. 1995). Transgenic lines with the thioesterase gene C1FatB4 from Cuphea lanceolata have been characterized with 16% C14:0 myristic acid content and 43 % C14:0 and C16:0 (Rudloff et al. 1999). No yield depression was noted in the transgenics and there were no differences in oil processing of the transgenics compared to the non-transgenic parent cultivar.
NEW CANOLA OIL PROFILES IN OTHER BRASSICA AND RELATED SPECIES
Current breeding status
The Oilseeds Group at AAFC Saskatoon (Canada) has the objective of developing Brassica juncea with seed oil containing 60% (from 45%) oleic, 20% (from 32%) linoleic and 10% (from 14%) linolenic (current levels in low erucic low glucosinolate B. juncea are in brackets). Low saturate and low linolenic oil quality are longer term objectives. The Saskatchewan Wheat Pool (Canada) has several low erucic, low glucosinolate B. juncea lines in demonstration plots in 1999. Low erucic acid content has been established in Brassica carinata at AAFC Saskatoon and in Sinapis alba at two breeding organizations: AAFC Saskatoon and the University of Idaho, USA.
CURRENT PRODUCTION OVERVIEW
Current contract production of new food-grade oil Brassica species includes low linolenic and mid and high oleic canola, and high saturate canola. Typical premiums for contract production in Canada range from $10 - $50 a tonne depending on the value of the new food-grade oil and the agronomic performance of the cultivars. There is general agreement in the industry that the current limitation to the production of the new food-grade oils is the lack of sufficient premium value to encourage economic contract production, and the reluctance to change the current commodity profile without an assurance of acceptance. Once the new food-grade oil profile has been established in adapted cultivars, breeding objectives focus on improved agronomic performance and other quality characters such as seed oil and protein content. There will always be a trade-off between nutrition, functionality and the economics of oilseed production, particularly in the introductory period of a new oil quality. We are entering the next millennium with an exciting choice of new food grade oil qualities available in Brassica species.
The authors wish to thank the following individuals for their contributions to this review: Allison Ferrie, Jo Bowman, Jack Brown, Dave Charne, William Hitz, Phillippe Guerche, Laima Kott, Zenon Lisieczko, William Loh, Denis Murphy, Morten Poulsen, Gerhard Rakow, Habibur Rahman, Michael Renard, Antje Schierholt and Keith White.
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