Studies on chemical elements and anti-nutrients compositions of three traditional vegetable oils in Nigeria

Melon (Citrullus vulgaris), groundnut (Arachis hypogea) and shea butter (Vitellaria paradoxa) seeds have been established as major sources of edible oils, but scientific data is scanty on their minerals, heavy metals and anti-nutrient contents. Manually extracted vegetable oils from melon, groundnut and shea butter were analyzed in triplicates for some minerals (sodium, potassium, magnesium and calcium), heavy metals (copper, iron, lead and zinc) and anti-nutrients (tannin, saponin, oxalate and gossypol) using Buck Scientific Atomic Absorption Spectrophotometer Model 210 VGP standard procedures. Data were analyzed by ANOVA and results expressed as means and standard deviation accepted at p≤0.05. Sodium (40.50 to 41.10 mg/100g), potassium (702.00 to 704.36 mg/100g); magnesium (3.51 mg/100g) and calcium (2.56 mg/100g) were in the oils and they did not differ from one another at p≤0.05. The heavy metals in the oils were not significantly different from each other. They ranged from 0.0002 to 0.0004 mg/kg for lead (Pb); 0.00 to 0.0002 mg/kg for copper (Cu); 0.0005 to 0.0006 mg/kg for iron (Fe) and 0.0012 to 0.0015 mg/kg for zinc (Zn). Anti-nutrient, tannin from melon differed significantly from those of groundnut and shea butter oils at p≤0.05. Melon oil had the least saponin (0.05 mg/100g) and the three oils had the same oxalate content (0.33 mg/100g). Their gossypol content differed significantly from one another. Shea butter and groundnut oil had the lowest (0.44 µg/100g) and highest (1.07µg/100g) gossypol contents respectively. The evaluated heavy metals in all the tested oils were lower than the maximum permissible values by FAO/WHO. Further studies on phytates content and other heavy metals such as cadmium, arsenic and mercury are recommended before the oils are certified safe for human consumption.