Biology, Medicine, & Natural Product Chemistry ISSN 2089-6514 (paper) Volume 12, Number 1, April 2023 | Pages: 9-16 | DOI: 10.14421/biomedich.2023.121.9-16 ISSN 2540-9328 (online) Proximate Composition, Levels of Some Essential Mineral Elements and Anti-Nutritional Components of Some Yam Species Found in Minna, Niger State Eneogwe Okechukwu Godfrey1,*, Ibrahim Izihyi Esther2, Obuye Faith1 1Department of Chemistry; 2Department of Industrial Chemistry, Federal University Lokoja, P.M. B. 1154, Lokoja, Nigeria. Corresponding author* godfrey.eneogwe@fulokoja.edu.ng Manuscript received: 18 August, 2022. Revision accepted: 06 September, 2022. Published: 27 September, 2022. Abstract Samples of Dioscorea dumenturom, Dioscorea rotundata and Dioscorea cayenensis were investigated for their proximate composition, anti-nutritional and mineral contents using standard analytical methods. These varieties of Dioscorea analysed showed a significant difference (P≤0.05) amongst them. However, from the results, it was observed that Dioscorea rotundata had the highest ash (8.05±0.05 %) and crude fibre content (13.11±0.10 %) which indicates that it contains more mineral stuffing and is best for softening of stool. Dioscorea cayenensis had the highest fat content (16.31±0.30 %), indicating that it is a better source of calories than other yam species analysed. Dioscorea dumenturom had the lowest moisture content (3.51±0.01 %) as well as the highest crude protein (12.29±0.01 %) and carbohydrates (69.04±0.10 %) than other yam species analysed, indicating its longer shelf-life, high bodybuilding capacity and better source of energy than other yam species analysed. The anti-nutritional constituent of alkaloid and tannin were lowest in Dioscorea cayenensis while Dioscorea rotundata had the least cyanide, phytate and oxalate content. This implies that these particular yams are safer for consumption. The elemental analysis in mg/100g indicated that the yam species contained appreciable levels of essential minerals, with Dioscorea dumenturom having the highest sodium, calcium, iron, potassium, phosphorous and magnesium concentration of 32.05±0.07 mg/100g, 190.57±0.01 mg/100g, 5.98±0.03 mg/100g, 80.12±0.17 mg/100g, 237.10±0.48 mg/100g and 100.22±0.03 mg/100g respectively. All these mineral concentrations exist within the permissible limit of WHO and hence indicate that the yam species can serve as a good source of minerals. Keywords: proximate composition; anti-nutritional; mineral content; Dioscorea dumenturom; Dioscorea rotundata; Dioscorea cayenensis. INTRODUCTION Yam is a staple cuisine in many tropical and subtropical areas throughout the world. Nigeria in particular has the world’s largest annual output and consumption per capita (Ukom et al., 2014). There are over 600 Dioscorea species, with more than 10 species farmed for food and 6 species used in pharmaceuticals (Okigbo et al., 2015). However, white yam (Dioscorea rotundata), water yam (Dioscorea alata), aerial yam (Dioscorea bulbifera), yellow yam (Dioscorea cayenensis), trifoliate yam (Dioscorea dumentorum) and Chinese yam (Dioscorea esculenta) are the six most economically important species. Yam cultivation not only helps rural farmers survive but also provides a significant number of calories, essential micro-nutrients and phytochemical compounds such as iron, zinc, ascorbic acid and flavonoids (Ukom et al., 2014). In many regions of west Africa particularly Nigeria, yam is processed in a variety of culinary forms, such as pounded yam, fried yam, roasted yam, boiled yam, yam balls, mashed yam, yam chips and flakes (Orkwor et al., 1997), which are typically served with protein-rich soups and sources. The species has historically influenced how yams are processed. West Africa is the world’s most important yam- producing region, with Nigeria as the leading producer, accounting for more than half of global production (Modu et al., 2015). Despite these facts regarding yam, it continues to be overlooked in West African national food policy programs. This has resulted in limited Dioscorea species research and development on the continent (Sanoussi et al., 2016). This study compares the proximate composition, mineral content and anti-nutritional constituents of several yam varieties which includes Dioscorea rotundata, Dioscorea dumenturom and Dioscorea cayenensis obtained from Minna, Niger State. https://doi.org/10.14421/biomedich.2023.121.9-16 10 Biology, Medicine, & Natural Product Chemistry 12 (1), 2023: 9-16 MATERIALS AND METHOD Sample Collection Matured accessions of the three cultivated yam species were harvested randomly from rural farms in the Chanchaga, Mekunkele and Gunu areas of Niger State. The samples include cultivars of yellow yam (Dioscorea cayenensis), a variety of white yams (Dioscorea rotundata) and trifoliate yam (Dioscorea dumentorum). The samples were cleaned by brushing off soil particles and transported at tropical ambient temperature to the laboratory for analysis. Dioscorea dumenturom Dioscorea rotundata Dioscorea cayenensis Figure 1. The images of the studied plants. Sample Pre-Treatment The yam samples were washed thoroughly with water, peeled and cut using a knife. These yam species were ground separately using a laboratory mortar and pestle and then sieved using a 250 μm mesh size sieve. The three samples were stored in airtight properly labeled polythene bags and kept in a cool and dry place before analysis. Determination of Proximate Composition The proximate analysis of samples for moisture, crude fat, crude fiber and ash was determined using the method described by AOAC (2006). The protein content was determined using the micro Kjeldahl method (N x 6.25) and the carbohydrate was calculated by difference. Mineral Analysis The digestion of samples for mineral analysis was carried out according to the method described by AOAC (2006). A 250 cm3 beaker was filled with 1.00 g of the pulverized sample. The beaker was filled with an acid mixture (15.00 cm3 concentrated HNO3 and 5.00 cm 3 concentrated perchloric acid). The mixture was agitated thoroughly to ensure adequate mixing, then heated on a hot plate until a clear digest appear. The digest was allowed to cool and filtered quantitatively into a 100 cm3 volumetric flask. The filtrate was made up to the 100 cm3 mark, transferred to a plastic bottle and aspirated into the machine for trace metal analysis. Determination of Anti-Nutrients Determination of Total Alkaloids This was accomplished utilizing the method described by AOAC (2005). 0.50 g of the sample was dissolved in 5.00 cm3 of 96% ethanol and 5.00 cm3 of 20% H2SO4 (1:1) and the resulting solution was filtered. 1.00 cm3 of the filtrate was added to 5.00 cm3 of 60% H2SO4 and allowed to stand for 5 minutes. After that, 5.00cm3 of 0.5% formaldehyde was added and allowed to stand for 3 hours. The reading was taken at an absorbance length of 565 nm using an ultra-violet (UV) spectrophotometer. The extinction coefficient of vincristine (E296, ethanol {ETOH} = 15136 M¹־cm¹־) was chosen as a reference alkaloid (AOAC, 2005). Determination of Saponins This was accomplished utilizing the method described by Krishnaiah et al. (2009). 0.50 g of the sample was boiled for 4 hours in a 20.00 cm3 of 1 mol/dm-3 HCl solution. After cooling, 50.00 cm3 petroleum ether was added to the filtrate for the ether layer, which was then evaporated to dryness. 5.00 cm3 of acetone ethanol was added to the residue and 0.40 cm3 of each was divided among three test tubes. They were filled with 6.00 cm3 of ferrous sulfate reagent followed by 2.00 cm3 of concentrated H2SO4. The absorbance was measured at 490 nm after 10 minutes of complete mixing. The calibration curve was established using standard saponin. Determination of Tannin Jaffe (2003) described that 1.00 g of each sample A and B were dissolved in 10.00 cm3 distilled water and agitated, left to stand for 30 minutes at room temperature. The extract was obtained from each sample Godfrey et al. – Proximate Composition, Levels of Some Essential Mineral Elements … 11 after centrifugation. In a 50 cm3 volumetric flask, 2.50 cm3 of the supernatant was dispersed. Similarly, in a separate 50.00 cm3 flask, 2.50 cm3 of the standard tannic acid solution was dispersed. In each flask, a 1.00 cm3 folin Dennis reagent was added, followed by 2.50 cm3 of saturated Na2CO3 solution. The mixture was then diluted to 50.00 cm3 and incubated for 90 minutes at room temperature. The sample’s absorbance was measured at 250 nm with the reagent blank at zero. The % tannin was calculated using the formula: 𝑇𝑎𝑛𝑛𝑖𝑛 (𝑚𝑔 𝑔) = (𝐴𝑠−𝐴𝑏 )−𝑖𝑛𝑡𝑒𝑟𝑐𝑒𝑝𝑡 𝑆𝑙𝑜𝑝𝑒×𝑑×𝑊 × 10⁄ (Eqt. 1) Where 𝐴𝑠 is the sample absorbance, 𝐴𝑏 is the blank absorbance, 𝑑 is the density of the solution (0.791g/ml), 𝑊 is the weight of the sample in grams and 10 is the aliquot. Determination of Phytic Acids Markkar et al. (1993) described the process for determining phytic acid. In a 250 cm3 conical flask, 2.00 g of each sample (A and B) were weighed. Each sample was soaked in 100.00 cm3 of 2% concentrated HCl acid for 3 hours in the conical flask before being filtered through a double layer of hardened filter papers. 50.00 cm3 of each filtrate was placed in a 250 cm3 beaker and 100 cm3 of distilled water was added to each to give proper acidity. 10.00 cm3 of 0.3% ammonium thiocyanate solution was added to each solution as an indicator. Each solution was titrated with standard iron chloride solution, which contains 0.00195 g iron per cm3. The endpoint color was slightly brownish-yellow which persisted for 5 min. The percentage of phytic acid was calculated using the formula: % 𝑃ℎ𝑦𝑡𝑖𝑐 𝑎𝑐𝑖𝑑 = 𝑦 × 1.19 × 1 (Eqt. 2) Where 𝑦 is the titre value × 0.00195 Determination of Cyanides Cyanide content was determined by the alkaline picrate method as described by Onwuka (2005). Here 5.00 g of powdered sample was dissolved in 50.00 cm3 of distilled water in a corked conical flask and the extraction was allowed to stand overnight and filtered. In a corked test tube, 1.00 cm3 of the filtered sample was mixed with 4.00 cm3 alkaline picrate and incubated in a water bath for 5 minutes. The absorbance of the blank containing 1.00 cm3 distilled water and 4 cm3 alkaline picrate solution was also measured at 490 nm after colour development (reddish-brown colour). The cyanide content was extrapolated from a cyanide standard curve prepared from a different concentration of KCN solution containing 5-50 μg cyanide in a 500 cm3 conical flask followed by 25.00 cm3 of 1 mol/dm-3 HCl. It was calculated as: 𝐶𝑦𝑎𝑛𝑖𝑑𝑒 (𝑚𝑔 100𝑔⁄ ) = 𝐴𝑏𝑠𝑜𝑟𝑏𝑎𝑛𝑐𝑒×𝐺𝐹×𝐷𝐹 𝑆𝑎𝑚𝑝𝑙𝑒 𝑤𝑒𝑖𝑔ℎ𝑡 (Eqt. 3) Where 𝐺𝐹 is the gradient factor and 𝐷𝐹 is the dilution factor. Determination of Oxalates The oxalate content of the samples was determined using the titration method described by Munro and Bassiro (2000). In a 250 cm3 volumetric flask suspended in 190.00 cm3 distilled water, 2.00 g of each sample A and B was inserted. Each sample received a 10 cm3 of 6 mol/dm-3 HCl solution, which was digested at 100ºC for 1hour. The samples were then cooled and made up to the 250 cm3 mark of the flask. The samples were filtered and a duplicate portion of 125.00 cm3 of the filtrate was measured into a beaker and 4 drops of methyl red indicator were added, followed by the addition of concentrated NH4OH solution (dropwise) until the solution changes from pink to yellow colour. Each portion was then heated to 90ºC, cooled and filtered to remove the precipitate containing ferrous ion. Each of the filtrates was again heated to 90ºC and 10.00 cm3 of 5% CaCl2 solution was added to each of the samples with consistent stirring. After cooling, the samples were left overnight. The solutions were then centrifuged for 5 minutes at 2500 rpm. The supernatant was decanted and the precipitates completely dissolved in 10.00 cm3 20% H2SO4. The total filtrate resulting from the digestion of 2.00 g of each of the samples was made up to 200 cm3. The filtrate was heated to near boiling points in aliquots of 125.00 cm3 and then titrated against 0.05 mol/dm-3 standardized KMnO4 solution to a pink colour which persisted for 30 seconds. Each sample of the oxalate contents was then calculated using the formula: 𝑂𝑥𝑎𝑙𝑎𝑡𝑒 = 𝑇 ×(𝑉𝑚𝑒)(𝐷𝑓)×105 (𝑀𝐸)×𝑀𝑓 (Eqt. 4) Where 𝑇 is the titre value of KMnO4, 𝑉𝑚𝑒 is the volume-mass equivalent, 𝐷𝑓 is the dilution factor, 𝑀𝐸 is the molar equivalent of KMnO4 in oxalate and 𝑀𝑓 is the mass of the sample. Statistical Analysis The obtained results were subjected to statistical analysis using mean standard deviation and analysis of variance (ANOVA) as described by Duncan’s multiple range test to determine the level of significance between different samples and significance was set at p ≤ 0.05. 12 Biology, Medicine, & Natural Product Chemistry 12 (1), 2023: 9-16 RESULTS AND DISCUSSION Table 1. proximate composition of selected yam species (%). Yam species Ash content Moisture content Crude fat Crude fibre Crude protein Carbohydrate D. cayenensis 3.09±0.19a 4.51±0.07d 16.31±0.30j 8.30±0.40b 10.14±0.40h 57.65±0.10b D. dumenturom 5.06±0.80c 3.51±0.01c 3.56±0.03a 6.54±0.01a 12.29±0.01f 69.04±0.10g D. rotundata 8.05±0.05f 5.60±0.06f 12.46±0.10h 13.11±0.10e 2.15±0.03b 58.63±0.08d Values are means ± standard deviation of triplicate analysis. Moisture Content The moisture content of the various yam species ranged from 3.51±0.01c % for Dioscorea dumenturom to 5.60±0.06f % for Dioscorea rotundata. The result indicates that the analysed yam species were significantly different (p≤0.05) with Dioscorea rotundata having the highest moisture content. However, these values are comparable to literature values as reported by Oko and Famurewa (2014) that ranged from 2.1% to 9.2% for Dioscorea dumenturom and Dioscorea alata respectively and lower than the research carried out by Anthony et al. (2014) which reported its moisture content within the range of 30.51±0.06d % to 37.90±0.08a % for Xanthosoma maff and Dioscorea cayenensis respectively. As such it could be said that Dioscorea dumenturom has a higher resistance to deterioration and longer shelf life than any of the selected yam species. Crude Fibre Content The crude fibre content ranged from 6.54±0.01a % for Dioscorea dumenturom to 13.11±0.10d % for Dioscorea rotundata. The result indicates that the analysed yam species were significantly different (p≤0.05) with Dioscorea rotundata having the highest crude fibre content. However, these results can be compared with reports by Afiukwa et al. (2013) that ranged from 6.01±0.04b % to 13.03±0.80a % for varieties of Dioscorea dumenturom and is different from reports by Oko and Famurewa (2014) that ranged from 3.31% to 3.53% for their Dioscorea alata species. Studies have shown that an increase in fiber consumption in foods reduces the incidence of obesity, cardiovascular disease, diabetes and digestive disorders (Turner, 2014). Ash Content Ash contents of the yam varieties ranged from 3.09±0.19a % for Dioscorea cayenesis to 8.05±0.05f % for Dioscorea rotundata. The result indicates that there was a significant difference (p≤0.05) in the yam species analysed with Dioscorea rotundata showing the highest ash content. However, these results were different from reports by Sorh et al. (2015) that ranged from 1.64±0.03a % to 1.78±0.03a % for varieties of Dioscorea alata. The ash content is an indication of the extent of mineral stuffing in the Dioscorea species (Akonor et al., 2017). As such, Dioscorea rotundata is stuffed with more minerals than the other yam tubers analysed. Crude Protein Content The crude protein content showed a significant difference (p≤0.05) between the yam varieties. It ranged from 2.15±0.03b % for Dioscorea rotundata to 12.29±0.01f % for Dioscorea dumenturom. However, Dioscorea dumenturom proved to be the tuber variety with the highest protein content. Nevertheless, the result can be compared with reports by Ojinnaka et al. (2017) that showed 2.43±0.11b % for Dioscorea bubilfera and in contrast with the report by Ukom et al. (2014) that showed crude protein of Dioscorea dumenturom to be 69.15±4.49b %. As such, this shows that Dioscorea dumenturom is the richest in protein among the analysed Dioscorea species. Crude Fat Content The fat content in these analysed varieties of yam tubers ranged from 3.56±0.03a % for Dioscorea dumenturom to 16.31±0.30j % for Dioscorea cayennesis. The result indicates that there was a significant difference (p≤0.05) in the yam species analysed with Dioscorea cayenensis showing the highest fat content. However, these results contradict Ukom which showed 4.4±1.91a % for Dioscorea cayenensis. That dietary fat supplies most of the energy required by man suggests that Dioscorea cayenensis is a better source of calories than other Dioscorea species analysed. Carbohydrate Content The carbohydrate content of the analysed yam varieties was significantly different (p≤0.05) and ranged from 57.65±0.10b % for Dioscorea cayenensis to 69.04±0.10g % for Dioscorea dumenturom. Despite the huge carbohydrate content contained by the Dioscorea species, Dioscorea dumenturom appeared to be more than Dioscorea cayenensis and Dioscorea rotundata. However, these values are comparable to literature by Ukpabi and Akobundu (2014), which had 78.32±0.29 % for Dioscorea dumenturom and in contrast with Frank and Kingsley (2014) that ranged from 24.25±0.62b % for Dioscorea alata to 32.03±0.89c % Dioscorea rotundata. Carbohydrates are considered as the primary source of energy for all organisms, playing a nutritional as well as structural role (Ojinnaka et al., 2017). Godfrey et al. – Proximate Composition, Levels of Some Essential Mineral Elements … 13 Table 2. Mineral concentration of selected yam species (mg/100g). Yam samples Ca Fe Mg Na K P D. cayenensis 67.12±0.11b 3.09±0.01a 74.38±0.03d 24.10±0.14b 50.06±0.09d 131.51±0.05b D. dumenturom 190.57±0.01i 7.37±0.04i 100.22±0.03i 32.05±0.07e 72.23±0.37g 193.11±0.01b D. rotundata 60.60±0.17a 3.18±0.03a 60.85±0.21b 31.10±0.14g 42.08±0.11b 117.20±0.01b Values are means ± standard deviation of triplicate analysis. Iron Concentration Minerals are an important component of diet because of their physiological and metabolic function in the body. Table 2 shows iron concentrations that ranged from 3.09±0.01a mg/100g for Dioscorea cayenensis to 7.37±0.04i mg/100g for Dioscorea dumenturom samples. The result indicates that the analysed yam species were significantly different (p≤0.05) with Dioscorea dumenturom having the highest iron concentration. However, this result was low when compared to results reported by Mergedus et al. (2015) which ranged from 10.10±0.01a mg/100g to 11.60±0.01a mg/100g for cultivars of Colocasia esculenta (Cocoyam). Iron is a major component of hemoglobin, a type of protein in red blood cells that carries oxygen from the lungs to all parts of the body (Mergedus et al., 2015). The recommended dietary allowance for iron is 13.7–15.1 mg/day for children and 17.0–18.9 mg/day for adults (WHO, 2014). Sodium Concentration The sodium concentration in this study ranged from 24.10±0.14b mg/100g for Dioscorea cayenensis to 32.05±0.07e mg/100g for Dioscorea dumenturom. The result indicates that there was a significant difference (p≤0.05) in the yam species analysed with Dioscorea dumenturom showing the highest sodium concentration. However, the sodium concentration was comparable to the report by Oko and Famurewa (2015) which had 24.84±0.37a mg/100g and 21.06±0.77b mg/100g for Dioscorea vilgaris and Dioscorea villosa respectively. Sodium as a macronutrient plays an important role in various metabolic processes including excitation and transmission of nerve impulses during action (Olajumoke et al., 2014). The recommended daily dietary intake for sodium is 10 mg/day for adult males and below 15 mg/day for females (WHO, 2014). Potassium Concentration Potassium is a macro-nutrient required by both plants and animals and is involved in various metabolisms. In this study, the concentration of potassium ranged from 42.08±0.11b mg/100g for Dioscorea rotundata to 72.23±0.37g mg/100g for Dioscorea dumenturom. The result indicates that the analysed yam species were significantly different (p≤0.05) with Dioscorea dumenturom having the highest potassium concentration. However, these values were lower when compared with reports by Ellong et al. (2014) that ranged from 338.00±59.29 mg/100g to 407.04±168.36 mg/100g for varieties of sweet potato (Ipomoea batatas). Potassium is important in the regulation of heartbeat, neurotransmission, signal and immune response and water balance in the body (Olajumoke et al., 2014). The recommended dietary intake of potassium is 2000 mg/day for adults and 1000 mg/day for children (WHO, 2014). Calcium Concentration The calcium content in this study ranged from 60.60±0.17a mg/100g for Dioscorea rotundata to 190.57±0.01i mg/100g for Dioscorea dumenturom. The result indicates that there was a significant difference (p≤0.05) in the yam species analysed with Dioscorea dumenturom showing the highest calcium concentration. However, this concentration was low when compared to reports by Sorh et al. (2015) which ranged from 150±14.50ab mg/100g to 185±18.14d mg/100g for varieties of Dioscorea alata. Calcium is necessary for blood clotting, muscle contraction, neurological function, bone and teeth formation (Trailokya et al., 2017). The recommended dietary intake of calcium is 500–800 mg/day for children and 1000 mg for adults (WHO, 2014). Magnesium Concentration Magnesium was also present in small quantities in the range of 60.85±0.21b mg/100g for Dioscorea rotundata to 100.22±0.03i mg/100g for Dioscorea dumenturom. The result indicates that the analysed yam species were significantly different (p≤0.05) with Dioscorea dumenturom having the highest magnesium concentration. However, its results were comparable to reports by Cyrile et al. (2014) that showed 53.70±0.32b mg/100g for its Dioscorea dumenturom species. Magnesium is involved in muscle degeneration, growth retardation, alopecia, dermatitis, immunologic dysfunction, poor spermato-genesis, congenital abnormalities and bleeding disorders among other things (Mergedus et al., 2015). The recommended dietary intake of magnesium is 80–320 mg/day (WHO, 2014). Phosphorous Concentration Phosphorus, together with calcium, helps to strengthen bones and teeth, particularly in children and breastfeeding mothers. The phosphorus content of the samples analysed ranged from 117.20±0.01b mg/100g for Dioscorea rotundata to 193.11±0.01c mg/100g for 14 Biology, Medicine, & Natural Product Chemistry 12 (1), 2023: 9-16 Dioscorea dumenturom. The result indicates that the analysed yam species were significantly different (p≤0.05) with Dioscorea dumenturom having the highest phosphorous concentration. However, these values are low when compared to those of 410 mg/100g of sweet potato reported by Sorh et al. (2015). Furthermore, phosphorous appeared to be the most abundant mineral in all the yam samples analysed. The recommended dietary allowance for both children and adults is 800 mg/day (WHO, 2014). Table 3. Anti-nutritional contents of the selected yam species (mg/100g). Yam species Tannin Phytate Cyanide Alkaloids Oxalate D. cayenensis 30.06±0.30d 49.44±0.30h 1.70±0.06d 8.35±0.10b 4.86±0.08d D. dumenturom 72.99±0.50j 30.00±0.20f 3.38±0.06e 24.17±2.70g 3.67±0.30c D. rotundata 62.00±0.50h 15.06±0.30d 1.54±0.06c 11.58±0.20d 3.19±0.90bc Values are means ± standard deviation of triplicate analysis. Tannin Content Tannins have been reported to form complexes with proteins and impair their digestibility and palatability. However, cooking is known to diminish the contents in foods (Lewu et al., 2010). Tannin concentration in the yam samples studied ranged from 30.06±0.30d mg/100g for Dioscorea cayenensis to 72.99±0.50j mg/100g for Dioscorea dumenturom. The result indicates that the analysed yam species were significantly different (p≤0.05) with Dioscorea cayenensis having the least tannin concentration. However, these values are relatively lower than those of 20-255 mg/100g reported on various under-utilized Dioscorea tubers (Arinathan et al., 2009) and higher than reports by Polycarp et al. (2012) that ranged from 4.56±0.01a to 19.23±0.03b mg/100g for different Dioscorea species. Tannin has been shown to decrease the activity of several enzymes including trypsin, amylase and lipase as well as interfere with the absorption of dietary iron (Rao and Desothe, 2008). The total acceptable tannin intake for a man is 560 mg/kg (Stephene, 2004). As such the tannin contents in these yam species are low and within permissible limits and thus, cannot be harmful to consumers (Stephene, 2004). Phytate Content The phytate contents of the yam tuber ranged from 15.06±0.30d mg/100g for Dioscorea rotundata to 49.44±0.30h mg/100g for Dioscorea cayenensis samples. The result indicates that the analysed yam species were significantly different (p≤0.05) with Dioscorea rotundata having the least phytate concentration. However, these values were higher when compared to the report by Otoo et al. (2008) that showed 2.60±0.20a mg/100g for its Dioscorea rotundata cultivars and lower than sweet potato which contained 119.98±0.01a mg/100g (Akaninwor, 2004). The issue with phytate in diets is that it can bind some essential mineral nutrients in the digestive tract, leading to mineral deficiencies. There is no particular recommended daily allowance for phytic acid as it differs from country to country (Bello et al., 2008). Oxalate Content Comparatively, the oxalate content of the various yam species analyzed ranged from 3.19±0.90bc mg/100g for Dioscorea rotundata to 4.86±0.08d mg/100g for Dioscorea cayenensis samples. The result indicates that the analysed yam species were significantly different (p≤0.05) with Dioscorea rotundata having the least oxalate concentration. However, these values are lower than reports according to Princewill and Ibeji (2012) that had 12.60a mg/100g for their Dioscorea bubilfera specie and higher than 0.48±0.01a, 0.50±0.03a mg/100g for Dioscorea rotundata and Dioscorea alata respectively according to reports by Afoakwa et al. (2012). Oxalic acid and oxalate are found naturally in plants but they have little or no benefit for human health. Though high levels in diet irritate tissues and the digestive system notably the stomach and kidney (Ogbuagu, 2008). Soluble oxalate is known to be poisonous at high concentrations, particularly above 3mg/kg (Norwood and Fox, 1994). The oxalates levels found in this study indicate that while the analysed yam tubers were slightly above the maximum permitted limit, they lose most of their toxicity when treated (boiled) and so cannot be consumed raw. Cyanide Content The cyanide contents ranged from 1.54±0.06c mg/100g for Dioscorea rotundata to 3.97±0.06e mg/100g for Dioscorea dumenturom. The result indicates that the analysed yam species were significantly different (p≤0.05) with Dioscorea rotundata having the least cyanide concentration. However, these values are low when compared to reports by Afiukwa et al. (2013) that showed 26.687±0.081a and 21.827±0.058b mg/100g for Dioscorea villosa species (okpura and ighobe) respectively. It is also higher than reports by Umoh (2013) that had 0.22±0.02a to 0.53±0.01b mg/100g for raw and processed false yam flour. The permissible limits for cyanide are 0.5-3.5 mg/kg which indicates that the level of the cyanide in the samples is above the acceptable range for human consumption and as such must not be consumed in their raw state (Mohammed et al., 2013). Godfrey et al. – Proximate Composition, Levels of Some Essential Mineral Elements … 15 Alkaloid Content The observed values for the alkaloid samples ranged between 8.35±0.10b mg/100g for Dioscorea cayenensis to 24.17±2.70g mg/100g for Dioscorea dumenturom. The result indicates that the analysed yam species were significantly different (p≤0.05) with Dioscorea cayenensis having the least alkaloid concentration. However, the values obtained for the alkaloids contents of these yam species were higher when compared to some varieties of Dioscorea cayenensis that ranged from 0.38±0.12 mg/100g to 0.68±0.02 mg/100g and 1.68±0.01 mg/100g for Dioscorea rotundata (Okwu and Ndu, 2006) and lower than reports by Ogbuagu (2008) that contained 30.62±0.03a and 32.46±0.01b mg/100g for different species of Dioscorea dumenturom. Because of their effect on the nervous system, electrochemical transmission and disruption of the cell membrane in the gastrointestinal tract, alkaloids are considered to be anti- nutrients (Friedman, 2001). However, human lethal dosages range between 3-6 mg/kg body weight and a dose above 3 mg/kg is usually considered toxic (Habtamu and ratta, 2014). The good news is that it loses most of its toxicity when treated or processed (cooked or boiled). 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