Abstract:
Dry biomass of algae is a good source of nutrients and biologically active substances, which in the recent years
attracted the interest of the specialists in their search for natural, ecologically and healthy sound foods for the
animals. The aim of the present study was to determine the mineral composition, the antioxidant and
antimicrobial activities of the dry biomass of freshwater algae (spirogyra genus). The freshwater algae were
collected in February and March 2010 at the pond of Jomo Kenyatta University of Agriculture and Technology
(JKUAT). The Mineral content by acid digestion (HNO3:HClO4) in mg / 100g was as high as 387.22 ± 38.72 for Ca and
as low as 2.53 ± 0.48 for Cu. Phytochemical screening of methanolic and water extract showed the presence of
alkaloids steroids, flavonoids, tannins, terpenoids, but only the water extract showed the presence of total
reducing sugars. The content of phenolic compounds and tannins was respectively 10.63 ± 0.05g gallic acid/100g of
extract and 0.399 ± 0.02g tannic acid/100g of dried sample and the level of flavonoids was 6.86 ± 0.14g
Quercetin/100g of extract. The algal antioxidant activity expressed in a dose able to decrease the initial DPPH
concentration by 50% was 0.078 mg/ml. The antimicrobial activity was found only for methanolic extract against
Escherichia coli and Candida albicans but no antimicrobial activity for aqueous extract. The freshwater algae used
in this study were identified as Spirogyra nitida associated Spirogyra weberi both filamentous green algae. The
mineral composition showed that they contain minerals which give the possibility of using them as food for fish
and also by human as food supplement. The levels of Ca, Mg and Fe were very high as the Spirulina and Chlorella
are used as food supplement. The strains showed a relative antioxidant and antimicrobial activities.
