Estimation of Nutritional and Starch Characteristics of Dioscorea alata (Water Yam) Varieties Commonly Cultivated in the South-Eastern Nigeria

Background: Studies on the nutritional and mineral compositions of staple foods will provide evidence to regulate intake of certain common foods for optimal health condition.
Aim: To estimate the proximate, mineral and starch characteristics of five local varieties, D. purpurea, D. atropurpurea, D. liliopsida (purple yam), D. vilgaris, and D. villosa of Dioscorea alata grown in Izzi Area of Ebonyi State, Nigeria.
Methodology: Five (5) commonly cultivated varieties of D. alata were sampled, each variety in triplicates, and prepared for analysis by peeling, dicing, drying and milling into flour. The proximate, nutritional and starch characteristics were determined by standard methods. Minerals were quantified by Atomic Absorption Spectrophotometric Method.
Results: The results showed that the varieties has moisture content 9.20-10.30%, ash content 2.48-3.53%, fiber content 3.31-3.53%, fat content 1.62-2.41%, protein content 8.40-10.46%, and carbohydrate content 70.88-73.90%. There were significant differences (P<.05) in the proximate compositions within the varieties. The ranges of minerals in mg per kg (dry weight) were Na 16.38-24.84, K 97.78-141.14, Ca 79.99-269.75, Mg 18.55-31.53, P 114.65-211.63, Fe 15.18-30.86. Glycaemic index ranged from 35.56-41.31, amylose content 12.42-16.11% and gelatinization temperature 85.00-87.00°C.
Conclusion: The results indicate that the protein and fiber contents of D. alata varieties estimated in this study were high. The low glycemic index confirmed the yam varieties as low glycemic index food. It was concluded that the yam varieties are good sources of protein nutrient and suitable staple food for the diabetics. However, low mineral compositions were reported. Therefore, there is a need for intense cultivation of improved varieties for improved mineral intake from the yam by the consumers.