Assessment of Phytochemical and Nutrient Compositions of Edible Yam Species in Southeastern Nigeria
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This study assessed the phytochemical and nutrient compositions of edible yam species Dioscorea rotundata 1, Dioscorea rotundata 2, Dioscorea rotundata 3, Dioscorea rotundata 4, Dioscorea Cayenensis, Dioscorea alata, Dioscorea dumentorum and Dioscorea bulbifera in Southeastern Nigeria. The phytochemical and nutrient (proximate, minerals, vitamins, fatty acids and amino acids) compositions of the yam tubers were investigated using standard analytical methods. Result of the proximate analyses show variation (p <0.05) among the cultivars with the tubers containing carbohydrate (71.31±0.03-81.01±0.02), and moisture (11.86±0.02-13.14±0.02), crude protein (2.91±0.05-5.81±0.07), crude fat (0.73±0.02-2.33±0.02) and ash (1.24±0.02-2.44±0.02) g/100g. Presence of phytochemicals was found in the samples, while the antinutrient phytochemicals (tannin, phytate and oxalate) were very low. Hydrogen cyanide was the most abundant phytochemical present (3.79±0.02–8.80±0.01 g/100g). The mineral analysis show that potassium (0.48 ± 0.35 – 0.95±0.00 g/100g) was the most abundant mineral in the tubers with trace amount of minor minerals (Zn and Fe) also present. The calculated mineral safety index showed no trace of Na overload (2.14±0.06-3.78±0.03). The Na/K, Ca/P and Ca/Mg ratios were within the recommended limits, respectively. The [Phy]/[Zn] and [Ca]/[Phy] ratios were also within their reference values respectively. The vitamin content also showed significant variation (p <0.05) with high level of total carotene (46.917±0.025-89.283±0.021µg/100g) and vitamin C (3.143±0.02110.320±0.017 µg/100g) present in the tubers. The results also reveal the presence of essential fatty and amino acids. Linoleic acid and valine were the most abundant essential fatty and amino acids present respectively. The protein quality assessment indicate that the protein is probably basic. The predicted protein efficiency ratio (P-PER) values were lower than that of the reference whole hen’s egg. The essential amino acid index (EAAI) was low, while the Leu/Ile ratio indicate leucine bioavailability. Tryptophan (0.84±0.01-1.32±0.02 g/100g) was the highest and lysine (0.12±0.000.21±0.00 g/100g) was the lowest from the amino acid scores. To obtain the maximum nutritional composition of this crop, the use of a particular cultivar should be considered based on the result of the study since the nutritional composition of each cultivar vary in several ways.