A blog maintained by Tevita Kete, PGR Officer
Secretariat of the Pacific Community (SPC), Suva, Fiji Islands
This weblog documents the activities of Pacific Agricultural Genetic Resources Network (PAPGREN), along with other information on plant genetic resources (PGR) in the Pacific.
The myriad varieties found within cultivated plants are fundamental to the present and future productivity of agriculture. PAPGREN, which is coordinated by the Land Resources Division of the Secretariat of the Pacific Community (SPC), helps Pacific countries and territories to conserve their crop genetic diversity sustainably, with technical assistance from the Bioversity International (BI) and support from NZAID and ACIAR.
SPC also hosts the Centre of Pacific Crops and Trees (CEPaCT). The CEPaCT maintains regional in vitro collections of crops important to the Pacific and carries out research on tissue culture technology. The CEPaCT Adviser is Dr Mary Taylor (MaryT@spc.int), the CEPaCT Curator is Ms Valerie Tuia (ValerieT@spc.int).
PAPGREN coordination and support
Mr William Wigmore
Mr Adelino S. Lorens
Dr Lois Englberger
Mr Apisai Ucuboi
Dr Maurice Wong
Mr Tianeti Beenna Ioane
Mr Frederick Muller
Mr Herman Francisco
Ms Rosa Kambuou
Ms Laisene Samuelu
Mr Jimi Saelea
Mr Tony Jansen
Mr Finao Pole
Mr Frazer Bule Lehi
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Sunday, May 08, 2005
Posted 7:43 PM by Luigi
Cyanide in Cassava
Following the recent spate of articles about cyanide in cassava, here's a contribution from Prof. Bill Aalbersberg of USP's Institute of Applied Science which tries to summarize our knowledge and set the record straight.
Cyanide occurs naturally in cassava (and other crops) as a glucoside. This is thought to be related to natural defence against pests. Cyanide, of course, is a potent poison and its presence in food crops has caused concern. Cassava has often been classed as “sweet,” or low in cyanide, or “bitter,” high in cyanide, though these correlations do not always hold. Concentrations in cassava range from roughly 10-1000 mg/kg of raw root. Pacific cultivars are usually classed as “sweet,” though during droughts Tonga reports they might taste bitter.
Health effects are not simple to predict based on cyanide content of the cassava. First of all, total cyanide removal by processing is variable. Simple boiling, which removes 50-60% of the cyanide, is sufficient in the Pacific for low cyanide cultivars, whereas in Africa, with higher average levels of cyanide, traditional processing involves a complex process of grating, fermentation and frying. The fate of the remaining cyanogenic glycoside during digestion - that is, how much is released as cyanide in the body - is not well known.
Cyanide in the body is mainly detoxified by reaction of sulphur-containing amino acids. The thiocyanide produced blocks iodine uptake by the thyroid gland. Thus, neurological disorders and lack of mental and physical development are the hallmarks of chronic intake of high cyanide varieties. More acute effects, even death, can occur if this is combined with improper food processing and malnourishment (lack of the sulphur containing amino acids).
In this somewhat murky scientific situation, New Zealand regulators decided to “protect” their consumers from cassava poisoning by calculating a worse-case scenario that all cyanide in the cyanogenic glycoside of raw cassava ended up as cyanide in the body. With some safety factor, this yielded a figure of 50 mg/kg as the safe limit for cyanide in cassava. Using the data of Bradbury from the 1980s that all Pacific cassava cultivars fell below this level, it was felt that this regulatory level would create no barrier to the considerable trade of cassava from Pacific island countries to New Zealand.
Unfortunately, the published research by Aalbersberg showing that most cultivars in Fiji contained more than 50 mg/kg and suggesting that the Bradbury samples were likely compromised during their journeys to his laboratory in Australia seems not have been consulted.
Since then, Tonga samples have also been analysed and all mature cultivars are above 50 mg/kg. The absence of goitre in Tonga, which would be an early sign of possible health effects from cassava consumption, suggests that Pacific islanders can consume large amounts of cassava that have moderate levels of cyanide without apparent health effects. This suggest that regulators need to relook at this issue.
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