13-12-2014, 02:40
Cyanogenic Glycosides
Flaxseed is increasingly being used in some food products because of its high content of alpha-linolenic acid and dietary fibre. However, flaxseed contains cyanogenic glycosides, which release toxic hydrogen cyanide in the presence of water (autohydrolysis).
(Chadha R, et al (Food Research Division, Bureau of Chemical Safety, Ottawa, Ontario, Canada), Food Addit Contam, 12: 527, 1995) Cyanogenic glycosides (linamarin, linustatin, neolinustatin) were highest in extracted flaxseed mucilage.
We conclude that up to 50 g high-alpha-linolenic acid flaxseed is palatable, safe and may be nutritionally beneficial in humans by raising n-3 fatty acids in plasma and erythrocytes and by decreasing post-prandial glucose responses. Cunnane S, et al, (University of Toronto, Toronto, Canada) Br J Nutr, 69:443, 1993)
The presence of cyanogenic glycosides and diglucosides in flaxseeds is a concern, as they may release cyanide upon hydrolysis. In addition, the polyunsaturated fatty acids may undergo thermal or auto-oxidation (rancidity) when exposed to air or high temperatures that are used in food preparation (& needed to detoxify the cyanogenic glycosides in the mucilage).
Cyanide levels produced as a result of autolysis, are below the harmful limits to humans (remember however that �??the dose maketh the poison�??). (Wanasundara P & Shahidi F, Adv Exp Med Biol, 434: 307, 1998)
Cyanogenic Glycosides in Flaxseed
By Robin J. Marles, Ph.D.
The presence of cyanogenic glycosides in the diet is significant only in relation to dose and the nutritional status of the consumer. Flax seed meal contains two cyanogenic glycosides, linustatin and neolinustatin.
Many foods are slightly cyanogenic (e.g. wheat and barley!), probably as an evolutionary adaptation to discourage herbivory, and our body has a limited capacity to detoxify low concentrations of cyanide through addition of sulphur (from amino acids) to form thiocyanate or reaction with cysteine directly to form beta-cyanoalanine.
Thus if the dietary levels of sulphur-containing amino acids are high the body can resist a low intake of cyanide, but if the diet is low in protein overall or due to imbalances in vegetable protein amino acid composition it is low in the sulphur-containing amino acids, then we see toxicity.
The two most common symptoms of chronic cyanide intoxication are goitre, probably caused by high levels of thiocyanate formation where dietary protein levels are adequate and the detoxification mechanism is operating in high gear but the body can't clear the thiocyanate product quickly enough,
And fibrocalculous pancreatic diabetes associated with protein malnutrition, where toxicity is probably directly due to cyanide because of the lack of adequate detoxification. Few of us are likely to consume significant quantities of flax seed, nor are those people consuming flax seed likely to have protein malnutrition.
Robin J. Marles, Ph.D.
Associate Professor, Botany Department
Brandon University, Brandon, MB R7A 6A9 CANADA
Flaxseed is increasingly being used in some food products because of its high content of alpha-linolenic acid and dietary fibre. However, flaxseed contains cyanogenic glycosides, which release toxic hydrogen cyanide in the presence of water (autohydrolysis).
(Chadha R, et al (Food Research Division, Bureau of Chemical Safety, Ottawa, Ontario, Canada), Food Addit Contam, 12: 527, 1995) Cyanogenic glycosides (linamarin, linustatin, neolinustatin) were highest in extracted flaxseed mucilage.
We conclude that up to 50 g high-alpha-linolenic acid flaxseed is palatable, safe and may be nutritionally beneficial in humans by raising n-3 fatty acids in plasma and erythrocytes and by decreasing post-prandial glucose responses. Cunnane S, et al, (University of Toronto, Toronto, Canada) Br J Nutr, 69:443, 1993)
The presence of cyanogenic glycosides and diglucosides in flaxseeds is a concern, as they may release cyanide upon hydrolysis. In addition, the polyunsaturated fatty acids may undergo thermal or auto-oxidation (rancidity) when exposed to air or high temperatures that are used in food preparation (& needed to detoxify the cyanogenic glycosides in the mucilage).
Cyanide levels produced as a result of autolysis, are below the harmful limits to humans (remember however that �??the dose maketh the poison�??). (Wanasundara P & Shahidi F, Adv Exp Med Biol, 434: 307, 1998)
Cyanogenic Glycosides in Flaxseed
By Robin J. Marles, Ph.D.
The presence of cyanogenic glycosides in the diet is significant only in relation to dose and the nutritional status of the consumer. Flax seed meal contains two cyanogenic glycosides, linustatin and neolinustatin.
Many foods are slightly cyanogenic (e.g. wheat and barley!), probably as an evolutionary adaptation to discourage herbivory, and our body has a limited capacity to detoxify low concentrations of cyanide through addition of sulphur (from amino acids) to form thiocyanate or reaction with cysteine directly to form beta-cyanoalanine.
Thus if the dietary levels of sulphur-containing amino acids are high the body can resist a low intake of cyanide, but if the diet is low in protein overall or due to imbalances in vegetable protein amino acid composition it is low in the sulphur-containing amino acids, then we see toxicity.
The two most common symptoms of chronic cyanide intoxication are goitre, probably caused by high levels of thiocyanate formation where dietary protein levels are adequate and the detoxification mechanism is operating in high gear but the body can't clear the thiocyanate product quickly enough,
And fibrocalculous pancreatic diabetes associated with protein malnutrition, where toxicity is probably directly due to cyanide because of the lack of adequate detoxification. Few of us are likely to consume significant quantities of flax seed, nor are those people consuming flax seed likely to have protein malnutrition.
Robin J. Marles, Ph.D.
Associate Professor, Botany Department
Brandon University, Brandon, MB R7A 6A9 CANADA