Linamarin levels in economically important yam varieties and implications for health

There are over 600 species of Dioscorea of which some 50 are eaten worldwide. World production is estimated at some 20 million tonnes annually. In tropical and subtropical countries such as West and East Africa, the Caribbean, South America, India, and South East Asia, yam tubers constitute an economically important food crop. In some of these countries yam constitutes an important part of the daily staple, serving as an ideal source of calories and contributing vitamins and minerals vital to health. Antinutritional components are however also a part of the total compostion, one class among these being the cyanoglucosides. This study centers on the extraction, quantification and identification of the cyanoglucosides in economically important yam varieties. High Performance Liquid Chromatography Studies on purified extracts of cyanoglucosides in different varieties of four Dioscorea species - namely D alata, D cayenensis, D esculenta and D rotundata - have confirmed linamarin as the main cyanoglucoside in yams. Among the twelve cultivars studied, linamarin levels varied from 573.7 ñ 193.6 ppm for D cayenensis cv. roundleaf to 165.7 ñ 17.5 ppm for D rotundata cv lucea. This result could be of revelance in appropriate selectively in the promotion of desirable cultivars of yam for the food and health industries, since cyanide from linamarin, apart from interfering with oxidative processes of metabolism, also produces pancreatic damage by free radical mechanisms reactions and is therefore thought to be a factor in malnutrition related diabetes. This effect is most likely when there is ingestion of cyanide containing food coupled with low protein intake. There is a definite coincidence of malnutrition related diabetes and the consumption of staples containing cyanide yielding substances. Against their background, cultivars with low enough levels of cyanoglucoside should be favoured, since there are safe limits for cyanide ingestion.(AU)

Diabetes and cassava in Dominica

A study of 110 non-insulin dependent diabetics and 110 controls failed to find evidence that chronic consumption of cassava flour containing significant amounts of cyanide, predisposes to diabetes mellitus. (AU)

Plasma thiocyanate and free radicals in Jamaican neuropathy (tropical paraparesis

Tropical spastic paraparesis (TSP) in West African countries is caused by a combination of excess cyanide from the ingestion of cassava and a deficiency of the sulphur-containing amino-acids required to detoxify the cyanide. Free radical damage to long axons has also been reported to result in damage similar to that seen in Jamaican TSP. To investigate the possibility that these mechanisms may be responsible for Jamaican TSP, venous blood from non-smoking blood donors and 22 patients with TSP were analysed for thiocyanate, superoxide dismutase and glutathione. Serum thiocyanate is an index of cyanide exposure. Superoxide damage is an important sulphur-containing peptiae. Levels of thiocyanate in the patients with TSP were similar to those in control patients. Glutathione was elevated in all the patients, and a superoxide dismutase activity was normal. The low levels of thiocyanate suggest that cyanide toxicity is not the primary cause of Jamaican TSP and, in any event, sufficient amounts of sulphur-containing amino-acids are present to detoxify cyanide. Free radical mechanisms are also unlikely to be responsible for damage to the neurons in these patients (AU)

Is Jamaican neuropathy (TSP) caused by cyanide intoxication? - abstract

Jamaican neuropathy, one of the earliest forms of tropical Spastic Paraparesis (TSP) to be described, is a major cause of neurological disability in Jamaica. Its cause has not been satisfactorily established, but chronic treponemal and, more recently, retroviral infections (HTLV-I) have been considered likely aetiological agents. Cyanide toxicity is regarded as the cause of TSP in certain West African countries. Free radicals have also been reported to cause damage to long axons. Although cassava and other cyanogenic items are used as staple items of diet in Jamaica, levels of this toxin have not been measured in Jamaican patients with TSP. The present study was therefore undertaken to determine whether (a) cyanide toxicity was associated with Jamaican TSP and (b) the levels of substances which protect against free radical damage were altered in these patients. Venous blood, obtained from twenty-two (22) patients with TSP, was analysed for thiocyanate (SCN). The levels of Cu/Zn superoxide dismutase, glutathione peroxidase and total glutathione, agents which protect against free radical damage, were also measured. Control samples were obtained from non-smoking blood donors matched for age. All patients and controls were questioned about their dietary habits. The levels of thiocyanate found in patients with the Jamaican form of TSP were similar to those found in control patients. Glutathione levels were elevated in all the patients. Superoxide dismutase activity was normal in all patients. The results obtained suggest that: (a) cyanide toxicity is not the primary cause of Jamaican TSP; (b) sufficient amounts of sulphur containing amino-acids are present to detoxify cyanide, even when present in high concentrations, and (c) free radical mechanisms are unlikely to be responsible for damage to the neurones in these TSP subjects (AU)

West Indian amblyopia

The visual fields of ten patients with West Indian amblyopia, but with no other sign of neurological disease, have been carefully charted. The scotomata found varied considerably in size, shape and density between the individuals in the group. They were scattered, and quite large with irregular margins, sometimes with small dense defects in their central areas and usually with very shelving edges; a connexion with the blind spot was often present and/or break-through to the periphery. The causative lesions are likely to be subchiasmal. There is a slight resemblance to the field defects in tobacco amblyopia, but as tobbaco does not seem to be a factor in our cases, cyanide poisoning may be the common factor.(Summary)

Observations on the cyanide content and toxicity of tropical pulses

The content of cyanogenetic glucosides in West Indian and other pulses was estimated by the release of hydrocyanic acid on hydrolysis. In the varieties of phaseolus lunatus (lima bean) examined, the CN content was under 20mg. per cent, and not of the order previously known to cause acute poisoning. Trace amounts were found in 5 other species, and a high content was found in a variety of vicia sativa seeds (common vetch). A comparison of hydrolytic procedures in ph. lunatus showed that whereas the cyanogenetic glucoside is stable on cooking the intact bean, neither human saliva nor dilute hydrochloric acid at 37oC was effective in releasing free HCN from beans crushed after cooking. Animal feeding tests of crushed uncooked beans showed that the toxicity of these varieties was unrelated to their CN content. Severe 'toxicity' of ph. vulgaris (kidney bean, red pea) in rats and guinea pigs was mainly, if not entirely, due to unpalatability, causing starvation. Palatability was much improved by cooking. Absorption and utilisation of other species were good when fed to rats, even at 50 per cent level. There was some evidence of pancreatic hypertrophy and of impaired absorption or utilization of vigna sp. (black-eye pea) and cajanus cajan (gungo pea) in guinea pigs. No neurological lesions were detected in rats in feeding tests of up to 6 month's duration (AU)