Modified Bio-Sorbents For Pre-Concentration Of Essential Trace Elements From Raw And Fermented Selected Foods

 ABSTRACT

This study reports a new method of pre-concentrating Zn2+, Fe2+, Mn2+, Mo6+ and I- ions present in food stuffs using modified bio-sorbents. These elements are in low levels in many food stuffs commonly consumed and some are way below the recommended daily intake (RDI). Examples of mitigating such situations include the addition of iodine to table salt in minute portions. However, table salt in foods increases sodium levels causing problems to consumers with high blood pressure. Dietary iron supplements have been used by people with iron deficiency in their bodies. Stomach upsets and pain, constipation, nausea and vomiting have been reported as some of the side effects of taking iron supplements. There is need therefore to find a way of increasing their levels in food intake. A possible route for this is to pre-concentrate these elements from common foodstuffs using readily available bio-sorbents. Maize cobs (Zea mays L.), common beans husks (Phaseolus vulgaris L.) and millet tassels (Eleusine coracana L.) which have traditionally been used either to make animal feeds or manure were used as pre-concentrating agents through adsorption. Another route is through fermentation followed by pre-concentration. The bio-sorbents were separately chemically modified and characterized to confirm the presence of the anchored functional groups using Fourier Transform Infrared (FT-IR) spectroscopy. Sorption capacities of essential trace elements by chemically modified and unmodified biomaterials were investigated separately using batch sorption experiments. Sorption parameters such as pH, concentration, contact time and dosage of both modified and unmodified forms of adsorbent were investigated. Essential trace elements present in black nightshade (Solanum nigrum L.) leaves, spinach (Spinacia oleracia L.) leaves and pumpkin (Cucurbita maxima L.) flesh aqueous extracts were determined without pre-concentration, after pre-concentration, and in fermented samples followed by pre-concentration. Best adsorption pH values ranged between 5.0 to 6.0 for Zn2+, 4.0 to 4.5 for Fe2+, 6.0 to 6.5 for Mn2+, 4.0 to 6.0 for Mo6+ and 5.0 to 5.5 for I-. The optimum concentration for all ions was found to be best below 50.0 mg/L while adsorption dose was best below 60.0 mg. The results show adsorption fitted more to the Langmuir model which had R2 values in the range 0.9957 to 0.9999 than Freundlich model with R2 values in the range 0.6710 to 0.9632 for all adsorbents. Sorption kinetics indicates pseudo second order model can be used to explain the rate determining step. The results show that fermentation increased the concentration of the essential trace elements in the solution. The elements were then pre-concentrated with pre-concentration ratios of up to 5.0 being achieved. The bio-sorbents are re-generable up to ten times. The results from this study have a potential application in the preparation of dietary supplements for human consumption. The study therefore recommends that this new method of preconcentration be adopted in large scale production of dietary supplements.