Studies on industrial polysaccharides from selected Tanzanian marine algae

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University of Dar es salaam
Studies have been conducted on the yield, characterization and gelling properties of phycooolloida from 27 speciesof Tanzanian scaweeds. The yields amongst the 23 species of red algae studied ranged from 17.5% to 74(dry weight). Amongst the phacophyta the yield ranged from 16.7%to 27.3%. Chemical analyses of the phycocolloids from the Rhodophyta species revealed galactose as the principal sugar residue. 3, 6-AG and sulphate were also detected in varying amounts. Some species contained xylose in trace quantities. Others contained methoxyl groups. From the results of chemical analyses, optical rotation, infrared spectra and physical properties, the following species were identified as falling under the category of agarophytes: Gracilaria crassa, G.fergusonii and G. millardetii. All the studied species of hypnea, eucheuma, titanophoro, Tenaciphyllum,chondrococcus, halymenia, sarconemaand corynomorpha, in Contrast, were characterised as carrageenophytes. The phycocolloids from C.hornemanii, H.venusta, C.prismatica and T.pikeana showed a resemblance to xi- and lambda carrageenans.The phycocolloids from S.filiforme, T.lobatum, R.africana were identified as deviant iota carrageenan; while those from E. okamurai, E.striatum and the four hypnea app. Behaved as kappa carrageenan. Those of E.platycladum and E. speciosum f. mauritianum showed features of both iota and koppa carrageenan. The phycocolloids from Acanthophora muscoides, laurencia papillosa, Spyridia hypomoides and Sarcodia montagneana were difficult to characterize: they were intermediate between agar and carrageenan. Gelling properties of the phycocolloids were also studied. Gelation was influenced by molecular weight, 3,6-AG and sulphate level (and its distribution)and the presence of K+ ions. Some of the phycocolloids melted and set at different temperatures and hence exhibited hysteresis loops when their their heating and cooling curves were plotted. As for the phycocolloids from the phaeophyta, it was found that guluronic and mannuronic acids were the building units and that guluronic acid occurred in greater quantities than mannuronic acid in all the species tested. Turbinaria tanzaniensis had the highest gel strength tested. The findings are discussed with reference to the M/G ratios, the molecular weights and the sequence of the mannuronic – and guluronic acids in the polymer chains.
Available in print form, Dr Wilbert Chagula Library (THS EAF QD321.S4)
Polysacharides, Algae, Tanzania
Semesi,A.K, (1979). Studies on industrial polysaccharides from selected Tanzanian marine algae, Doctor of Philosophy, University of Dar es salaam, Dar es salaam