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)

Isolation of branched chain alpha-keto acid dehydrogenase from rabbit liver

An enzyme catalysing a series of reactions resulting in the oxidative decarboxylation of branched chain alpha-keto acids and production of NADH, was extracted from rabbit liver mitochondria with the aid of NaClO4. Purification yielded a product which appeared homogeneous on alpha-ketoisocaproate, alpha-keto-beta-methyl valerate, and alpha-ketoisovalerate. (AU)