A comparative study of iron bioaccessibility and antinutrient levels in Hibiscus sabdariffa (Roselle) leaves and Calyces and Persea americana (Avocado) leaves and seeds : nutritional implications

Abstract

Objective To compare iron bioaccessibility (availability for absorption) and antinutrient levels in Roselle leaves and calyces and Avocado leaves and seeds in fresh and dry forms. Methods The iron content and nutrients linked to its metabolism such as protein, vitamin C, and betacarotene and iron absorption inhibitors such as calcium and antinutrients (total phenolic compounds, phytates, oxalates, tannins, and flavonoids) were analyzed in triplicate using standard methods. Iron and calcium inhibition was predicted using molar ratios. Data were analyzed using IBM Statistical Package for Social Scientists and means compiled. Analysis of variance and differences among means was compared by Duncan’s Post Hoc test at p < 0.05. Results The iron content in 100 grams was 15.71 ± 0.04 and 8.16 ± 0.01 mg in fresh and dry Roselle leaves respectively, 13.47 ± 0.01 mg in fresh Avocado leaves and seeds, 10.16 ± 0.01 mg in fresh Roselle calyces, 4.47 ± 0.01 mg in dry Avocado leaves and Roselle calyces and 2.47 ± 0.01 mg in dry Avocado seeds. The highest protein content of 13.82 ± 0.13% was found in fresh Avocado leaves while fresh Roselle leaves had the highest betacarotene content of 9.30 ± 0.00 mg/100 g. Vitamin C was significantly high in fresh Avocado and Roselle leaves (>30 mg/100 g). Calcium contents in all samples were low (<80 mg/100 g) and not inhibited by phytates and oxalates. In all samples, iron was not inhibited by oxalates and only in fresh Avocado seeds was iron inhibited by phytates. Tannins, phytates and oxalate concentrations were all below the maximum tolerable levels. Though fresh Roselle leaves had the highest iron content, its total phenolic compounds were above the maximum tolerable levels, depicting toxicity.