Erucic acid control

Producers normally rely on only a few source oils indigenous to their geographic area or that can be imported economically. Soybean is the primary oil used in the United States while very little palm is consumed and none is produced. Canada s major oil is canola (low-erucic-acid rapeseed). Malaysia, Indonesia, and Central America are the largest producers and users of palm oil. Eastern Europe, like Canada, relies on low-erucic-acid rapeseed (LEAR), sunflower, and soybean oils. It is apparent from Table 3 that it is virtually impossible to formulate products with controlled melting and crystalline properties using only one of these oils. Even in areas where conditions and economics justify a variety of types, modification methods other than blending are essential to adequately control rheologic properties. 

Until recently the fatty acid composition of rapeseed oil was quite different from that of other edible vegetable oils from 40 to 60% of the fatty acid components of rapeseed oil consisted of the long chain fatty acids, erucic and eicosenoic. This unusual fatty acid composition has been the subject of numerous nutritional studies. Detrimental effects attributed to the long chain fatty acid components of rapeseed oil stimulated plant breeders to search for genetically controlled variation in these components. Rape plants which produce seed oil essentially without erucic acid were isolated (Ste-fansson et al., 1961) and this characteristic was incorporated into cultivars suitable for commercial production. The new "low erucic acid" rapeseed oils contain only the fatty acid components found in other edible vegetable oils traditionally used as food in the Western World. 

The erucic acid content is largely controlled by the genotype of the developing seed rather than by the genotype of the maternal plant (Downey and Harvey, 1963 Harvey and Downey, 1964 Stefansson and Hougen, 1964 Kondra and Stefansson, 1965). For this reason, a technique could be developed whereby one cotyledon or a part of one cotyledon could be used as a sample for fatty acid analysis, while the remainder of the seed could be used to produce a plant (Downey and Harvey, 1963). This technique is useful in breeding and can also be used to facilitate genetic studies, since the seeds on an Fi plant represent the F2 population. 

Screening procedures, the analyses and selection of large numbers of cultivars, strains, individual plants and half-seeds carried out in several countries, have been relatively ineffective in establishing genetically controlled low levels of linolenic acid in rape and turnip rape. For this reason, large-scale mutation experiments were initiated in Germany (Robbelen and Ra-kow, 1970) and in France (Morice, 1975). Levels of 3.5% linolenic acid in low erucic acid summer rape selections from the mutation experiments have been reported (Robbelen and Thies, 1980a). 

Due to the large variation in erucic acid content (0.1-60%) in the seed oils from rape and turnip rape, the separation of genetically controlled variation of erucic acid from environmental variation was relatively easy. The invariable association of substantial amounts of eicosenoic acid (e.g. 6%) with an allele for the presence of erucic acid which might condition the production of a low level of erucic acid (e.g., less than 2%) ensured selection of the genetically lowest level of erucic acid. 

The elimination of erucic acid from rapeseed oil resulted in an increase in the linoleic acid content of the oil from approximately 13 to 21%. Further increases appear to be possible since the values as high as 50% have been reported. However, such values do not appear to be stable and were not recovered in progeny tests (Jonsson, 1977a). Values up to at least 30% linoleic are stable, that is, are under genetic control. Some variation in linoleic acid content seems to occur in many populations of low erucic acid rape-seed. Since a reduction in component fatty acids other than oleic and linoleic provide greater opportunity for variation in these components, it may be desirable to select for increased linoleic acid content in populations low in both erucic and linolenic acids and thus to add this characteristic after reduced levels of linolenic have been achieved. 

The production of HEAR has been controlled by the Canadian Crushing Industry through contracts to meet expected demands for oil. Up to the present time only one company has been involved in this market and there has been no evidence of high erucic acid seed appearing in the edible oil export market. The Canadian Crushing Industry will continue to control this market as it is in their own best interests for the erucic acid content of Canadian rapeseed to remain low. 

Myocardial Necrosis Reported in Male Rats Fed High Erucic Acid Rapeseed (HEAR) and Control Oils... 

It appears there are two main reasons for the accumulation of cholesterol esters in rats that are fed HEAR oil or erucic acid containing diets. First, the cholesterol ester hydrolase fails to increase in activity when these rats are stressed, while in control rats, when stressed, the enzyme doubles its activity (Beckett and Boyd, 1975). Second, cholesteryl erucate, which accumulates in the adrenals of rats fed HEAR oil, is only slowly hydrolyzed by the enzyme, i.e., at 25-30% of the rate of cholesteryl oleate. This may be very significant, since there is considerable cholesteryl erucate accumulation in the adrenal glands of rats fed diets high in erucic acid, i.e., this ester may constitute 29-35% of the total (Carroll, 1962 Walker and Carney, 1971). In addition, in these rats there was an accumulation of 8% cholesteryl eicose-noate. In agreement with this evidence of impaired adrenal function, the results indicate that plasma levels of one of the adrenal hormones, corticosterone, are lower in these rats than in control rats when exposed to an environmental stress (Walker and Carney, 1971 Budzynska-Topolowska eta/., 1975). 

Ratanasethkul et al. (1976) fed chickens, ducks, and turkeys high and low erucic acid rapeseed oil, soybean oil, and a lard/corn oil control diet. All the ducks and some of the chickens fed the HEAR oil diet (36% erucic acid) died with hydropericardium and ascites. Myocardial lipidosis was present in all species fed the HEAR oil and the severity of the lipidosis (as judged by oil red O staining) decreased with time on diet. In ducks, they found thickening of the epicardium and myocardial fibrosis. Granulomas characterized by giant cells and histiocytic infiltration were present in some of the hearts of turkeys fed the HEAR oil. 

The lipid content in pig hearts normally is approximately 2%, which is similar to that observed in rat hearts. Little is known about the cardiac lipid content of monkeys fed a low fat control diet. These species respond differently to experimental diets which contain high levels of fat and are rich in docosenoic acid. In the rat and pig studies (Fig. 1) HEAR oils were fed which contained erucic acid (22 1 n-9). In some of the monkey studies fish oils were fed which contained cetoleic acid (22 1 n-11) as the main docosenoic acid isomer. The results from both 22 1 isomers are combined because of their similarity in response. 

Fig. 1. The concentration (mg/g wet weight) of the total cardiac lipids and the cardiac triglycerides of rats, pigs, and monkeys fed a low fat control diet (time 0) and diets to which a control oil (first bar) or a docosenoic acid containing oil (second bar) was added. The portion of triglycerides in the total lipids are indicated by a hatched bar wherever this information is available. Source of data rat (Kramer and Hulan, 1978 Kramer et al., 1979) pig, 1.4 weeks (Opstvedt et al., 1979), all other values (Kramer et a/., 1975) and monkey, 1 and 10 weeks (Beare-Rogers and Nera, 1972), all other values (Ackman, 1980). Erucic acid was the docosenoic acid in all studies except the monkey data from Ackman (1980) who fed partially hydrogenated fish oil containing mainly cetoleic acid.

When rats are fed a diet rich in erucic acid, a rapid accumulation of cardiac TG occurs within the first week. The concentration of heart TG then declines, but even after 16 weeks the level still remains about twice that found in the controls (Fig. 1). Similar results were obtained by other investigators (Table III). The amount of cardiac TG which accumulate during peak lipidosis is proportional to the erucic acid content in the diet (Table III). 

Figure 3 shows the probability of accepting samples containing different concentrations of erucic acid. Two levels of variation are represented, both plausible in view of the Firestone and Horwitz (1979) results. The two curves, referred to as operational characteristic curves in quality control the-... 

The characteristic fatty acid patterns of plant triacylglycerols are to some extent under genetic control (see Section VI). In addition, environmental factors may modify the basic patterns, the extent of modification depending on the species. Thus the seed oils of plants grown in cool climates tend to be more unsaturated than those grown in warm climates (Hitchcock and Nichols, 1971). The chief influence seems to be on the characteristic fatty acid of the seed, so that for example in flaxseed oil there is a marked decline in the proportion of linolenic acid between 10° and 30°C and a corresponding increase in the proportion of its precursor, oleic acid (Canvin, 1965). Similarly, the proportion of linoleic acid in sunflower seed oil steadily declines between 10° and 30°C, to be replaced by oleic acid. Yet the linoleic content of safflower and the ricinoleic acid of castor are unaffected by the same variation in temperature (Canvin, 1965). All rules have exceptions, and the experiments of Appelqvist (1975) showed that different lines of zero-erucic acid rape could respond differently to the same climatic variations. 

In an attempt to engineer trierucin and increased erucic acid levels into HEAR, constructs have been made for expression of either the full length or a truncated open reading frame (ORE) from pLAT2 under the control of a napin promoter. Both constructs were introduced into a HEAR line and seeds from transgenic plants were analysed. 

The absence of erucate in rapeseed oil is conditioned by two genes in B. napus and one in B. campestris (Stefansson, 1983). The level of erucic acid in crosses of high- and low-erucate lines is complex and controlled by several genes. Eicosenoate is controlled separately from erucate, and the inheritance of high eicosenoate is dominant. 

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