Coagulants of Moringa Oleifera Lam. seeds: purification & characterisation
Water has been declared a human right by the United Nations, thus urging countries who have ratified the International Covenant on Economic, Social and Cultural Rights to ensure supply with drinking water for their populations1. However, supply of drinking water in developing countries underlies different constraints than those met in industrialized countries. An example is the dependency on treatment chemicals that may pose problems in these countries regarding importation and distribution2. In pioneering work in the Darfur region (Sudan) S.A.A. Jahn has instructed rural people how to use local natural coagulants, that had been used traditionally by parts of the population, for the preparation of water for household use with special emphasis on the seeds of the Moringa oleifera tree3. The implementation of water supply for the population on the other hand demands centralized water treatment for villages and cities and thus traditional techniques will reach their limitations. The present work tries to identify and characterise the coagulating principle present in the seeds and press-cake of M.oleifera, in order to produce quantities of a standardized coagulant that could be used in small treatment works. Therefore, different extraction methods, reported in the literature, are compared regarding extraction efficiency and composition. All extracts contained a large proteinaceous moiety, which differed from proteins described before as Mo 2.1 (flocculating proteins4) in the way that two proteins were detected under reducing conditions, both not co-migrating with a synthetic protein having the amino acid sequence of Mo 2.1. Moreover a different group of proteins with higher molecular weight was only present during the first two days of storage of the liquid extract. An optimized extraction procedure is presented, resulting in a total protein yield of 40g/L. Separation of proteinaceous components present in the seed and press-cake extracts lead to the determination of relative molecular masses of two protein components present (4 and 8 kDa) which form a 12 kDa heterodimer under non-reducing conditions, such as those found in the raw extracts. Further evidence is presented that the number of different proteins present in the extracts using the reported techniques may be an artifact due to sample degradation, oxidation and reaction with non-proteinaceous substances present in the extracts. The presence of glucosinolates and of their derivatives that belong to the reactive group of isothiocyanates was show in the extracts of M.oleifera seeds and press-cake, thus increasing the risk of protein stability problems during storage of the potential product. Furthermore, a method for protein isolation which reduces interference of isothiocyanates has been developed for extraction from M.oleifera. In order to compare the coagulating activities of different components present in fractions after separation of the seed extracts a miniaturized assay has been developed. Highest coagulating activities were found for the 8 kDa protein chain. Partial sequencing of different preparations of the 8 kDa chain indicated the presence of several forms of the protein having slight sequence differences. The protein chain is very similar to the published Mo 2.1 protein, but appears to contain 70 amino acid residues instead of the 60 residues reported for Mo 2.1. These results clearly indicate that the original protein Mo 2.1 is only a fragment of the proteins present in extracts from M.oleifera seeds. Experiments for pilot scale production were conducted involving extraction of the coagulant from M.oleifera press cake. Different possible technologies for the preparation of coagulant from M.oleifera press-cake are compared. Difficulties were encountered in solid-liquid separation after initial extraction, due to high solid loads and very slow settling, and during concentration of extracts by ultrafiltration. Alternatively tests for percolation of press-cake were carried out, which resulted in high extraction efficiencies. Finally an extraction process using sequential percolation with two different solvents, in order to separate glucosinolates and proteins is proposed, followed by a precipitating concentration step of the product. ------------------------------ UN, Substantive issues arising in the implementation of the international covenant on economic, social and cultural rights. 2002, United Nations, Economic and Social Council, Committee on Economic, Social and Cultural Rights. Folkard, G. and J. Sutherland, Development of a naturally derived coagulant for water and wastewater treatment. Water Science and Technology: Water Supply, 2002. 2(5-6): p. 89-94. Jahn, S.A.A., Proper use of African natural coagulants for rural water supplies research in the Sudan and a guide for new projects. 1986, Eschborn: Deutsche Gesellschaft für Technische Zusammenarbeit. 541 S. Gassenschmidt, U., et al., Isolation and Characterization of a Flocculating Protein from Moringa- Oleifera Lam. Biochimica Et Biophysica Acta-General Subjects, 1995. 1243(3): p. 477-481.
Section de chimie et génie chimique
Faculté des sciences de base
Institut des sciences et ingénierie chimiques
Jury: Geoff Folkard, Claude Friedli, Catherine Servis, Urs von Stockar, Christine Wandrey
Public defense: 2005-5-27
Record created on 2005-04-06, modified on 2016-08-08