Biochemical composition and storage of Jamaican yams (Dioscorea sp)

Dioscorea yam tubers of 11 cultivars from five common species grown in Jamaica were analysed for the following: protein content, total phenolics, vitamin C, total lipids, fatty acid composition and activity of the polyphenol oxidase enzyme. The results show that the yams grown in Jamaica are of good nutritional value with considerable amounts of protein, vitamin C, low lipids with only one cultivar ‘renta yam’ (D alata) possessing high levels of phenolic compounds. The fatty acids present in the total lipid extracts show that yam tubers generally possess high levels of saturated fatty acids mainly palmitic acid. However, the species D alata (cv white yam) and the species D trifida (cv yampie) have high levels of the unsaturated fatty acid, linolenic. All the polyphenol oxidases from the 11 cultivars show activities towards the diphenol substrates, catechol and DL‐DOPA (DL‐3,4‐dihydroxyphenylalanine). However, no oxidation was observed with L‐tyrosine, a monophenol substrate. All cultivars studied were found to have different lengths of dormancy which varied with storage conditions. When the harvested tubers were washed, sunned and stored at 20†C in a dark cupboard, it was possible to extend their lengths of dormancy by a further 11 weeks.