Abstract:
The nutritionists’ interest in leaf vegetables including Hibiscus sabdariffa stems from their rich contents of essential amino acids, vitamins and minerals which are needed for normal metabolic activities of the body. Vegetables are also good sources of dietary fibres that are important for bowel movement. However, the presence of some inherent anti nutrients and toxic substances in vegetables has been a major obstacle in harnessing the full nutritional benefits. It is against this background that this research was conducted to determine the effect of some processing methods on the antinutrients (soluble and total oxalates), toxic substances (cyanide and nitrate) and some micronutrients which include vitamin C, β-carotene (provitamin A) and mineral elements (Fe, Mg, Zn, Na and K) in Hibiscus sabdariffa. The processing methods include boiling (vegetable leaves were boiled in distilled water for 5 and 10 min) and sun drying. Results obtained showed that the cyanide, nitrate and soluble contents in fresh vegetable sample are within the tolerable level and they can be well tolerated in the meals. However, the total oxalate content in the vegetable is high enough to induce oxalate toxicosis. All the processing methods significantly (p<0.05) reduced the antinutrients and toxic substances in Hibiscus sabdariffa except that the reduction in soluble and total oxalate with sun drying was not significant (p>0.05). Boiling methods reduced these toxic substances significantly (p<0.05) more than sun drying. The antinutrients and toxic substances generally decreased with boiling time. These post-harvest treatments also reduced vitamin C content significantly (p<0.05) in Hibiscus sabdariffa. Boiling method retained more of the vitamin compared to sun drying. β-carotene levels increased in the boiled vegetable leaves, while its content was reduced in sundried leaves. However, boiling beyond 5 min led to significant (p<0.05) reduction of β-carotene levels in the vegetable. Mineral elements (Fe, Cu, Mg, Na and K) decreased significantly (p<0.05) with boiling in Hibiscus sabdariffa; however sun drying had no significant effect on the mineral contents. The result concludes that moderate boiling significantly reduces the levels of antinutrients and toxic substances while still conserve some micronutrients in amounts sufficient to meet our dietary requirements.
A. Musa and E.O. Ogbadoyi, 2012. Effect of Processing Methods on Some Micronutrients, Antinutrients and Toxic Substances in Hibiscus Sabdariffa. Asian Journal of Biochemistry, 7: 63-79.
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