Belay, Amha (Ass.prof.)Assaye, Hirut2022-04-062023-11-092022-04-062023-11-092014-12http://10.90.10.223:4000/handle/123456789/31162The cyanobacterium Arlhrospira (Spirulina) is known for its high protein content and having various bioactive phytochemicals with potential health benefits. It is, therefore, produced worldwide either artificially or directly from natural lakes to be used as a dietary and/or protein supplement. Spirulina grows abundantly almost as a uni -algal population in an Ethiopian soda lake, Lake Chitu throughout the year. The objective of this study was to evaluate the nutrient profile and safety of Lake Chitu's Spirulina for possible applications in human nutrition. A one year study (March 2012-January 2013) was undertaken where sampling was done at two months interval. Variations were observed in the nutrient profile of the biomass on seasonal basis and in general wet season samples had relatively higher protein (47.9-55.7%) and low carbohydrates contents (30.9-36.4%) compared to dry season samples. Higher amino acids content was recorded for a wet season sample (86.4g/100g protein) compared to a dry season sample (62. l g/I00g protein). Variations were also observed in the fatty acid composition of Lake Chitu 's Spirulina as relatively higher proportion of unsaturated fatty acids were recorded for a sample harvested in wet season (61.8%) compared to a dry season sample (58.2%). Similarly, higher contents of phylonutrients (pigments) (mg g.I): chlorophyll a (8.2-10.3), phycobiliproteins (104.1-120.7), total carotenoids (3.17-4.31) and ~-carotene (1.24-1.61) were recorded for wet season samples. The mineral content of the biomass also varied according to season. While Na and K were found to be higher in the dry season sample, other major (Ca, P, Mg) and trace (Mn, Fe, Cu, Zn and Se) minerals were found in higher concentrations in the wet season sample. The safety of Lake Chitu's Spirulina was evaluated in terms of its microbial profile, heavy metals, pheophorbides, microcystin and nucleic acids content. Aerobic mesophilic count of the biomass ranged from 0.4 xl03 to 130 xl03 CFU/g for wet season and from 0.37 xlO3 to 15 xlO3 CFU/g for dry season samples. Counts of total coliforms, fecal coliforms, Ecoli, S. aureus, yeasts and molds were < 102CFU/g for both wet and dry season samples. Heavy metal contents of the biomass (mg kg-I) were: Pb (0.18), Cd (0.03), Hg (0.04) and As (18 .8). Pheophorbides content of the biomass were 16.2mg/100g and 22.3mg/J OOg for wet and dry season samplesrespectively. The nucleic acids content of the samples were 0.18 and 0.13% for wet and dry season samples respectively. Microcystins were not detected in both wet and dry season samples and short term feeding offreeze dried biomass (10 g/kg body weight) to mice didn't result any signs of toxicity or mortality. Phycobiliprotein-rich crude extract (PBE) was prepared from Spirulina and was evaluated for its chemical composition, amino acid profile, in vitro protein digestibility and functional properties for possible food applications. Phycobiliprotein-rich crude extract had higher contents of proteins (60.1 vs 45.2%) and amino acids (45.6 vs 39.0g/100gsample) than the crude Spirulina powder. Simi larly, in vitro protein digestibility value of PBE was higher (86%) than the crude Spirulina powder (59%) in a single enzyme assay. The extract had 50.5% protein solubility at pH 7 and 62.2% solubility at pH 12 although at this pH discoloration of the pigment was noted . PBE showed good emulsifying activity at neutral and basic pH regions and at higher protein concentrations the extract showed comparable emulsifYing activity with bovine serum albumin. Similarly, the foaming capacity and stability of PBE were high and comparable with the commonly used foaming agent, egg albumin. In conclusion, the nutrient profile of Lake Chitu's Spil'ulina is comparable with that reported for commercial Spirulina. Except arsenic which was found in higher concentrations, the biomass is safe in terms of other safety evaluation parameters and thus can potentially be used in human nutrition. In addition to using the whole biomass as a food supplement, high value products such as phycobiliproteins can be extracted from the crude biomass which can serve as a component in functional foods. Key words: Arthrospira, biomass quality, functional property, Lake Chitu, safety, season, phycobiliproteins, SpirulinaenArthrospirabiomass qualityfunctional propertyLake ChitusafetyseasonphycobiliproteinsThesis