Abstract
The study was conducted to investigate the effect of spatial variation, alkali treatment and the volume of extractant on yield and gel strength of agar for three Gracilaria species (G. salicornia, G. edulis and G. corticata) collected from the Tanzanian coast (Dar es Salaam, Tanga and Zanzibar). Treated and untreated G. corticata showed the highest yield (27 ± 0.7 % and 26.2 ± 1.3 % for treated and untreated, respectively), followed by G. salicornia then G. edulis. G. salicornia collected from Zanzibar showed the highest mass yield (22.9 ± 4.3 % for treated) followed by those collected from Tanga. Varying the volume for extraction showed no significant difference in mass yield where the p-value was >0.05. The highest gel strength was recorded from treated G. salicornia collected from Tanga (495 ± 29.5 gcm−2). Gel strength varied significantly between species. Spatial variability showed a significant difference in gel strength; the sample collected from Tanga showed the highest gel strength, followed by Zanzibar then Dar es Salaam. The variation due to the volume of distilled water used for extraction showed no significant difference in gel strength at a p-value >0.05. The highest gel strength was recorded at the volume of 1500 mL (467.5 ± 98.4 gcm−2), and the smallest gel strength was recorded at 500 mL. In all cases, there was a significant difference in mass yield and gel strength between treated and untreated samples. G. salicornia showed promising results as a local source of agar as it showed the highest gel strength though it produced an intermediate amount of agar. Based on the finding of this study, the volume of extraction of agar should be maintained as 1000 mL because by increasing the volume of extraction from 1000 mL to 1500 mL, the agar yield and gel strength don't change significantly. Agar yield and gel strength of Gracilaria species (G. salicornia, G. edulis and G. corticata) can be improved by alkali treatment, but further study is needed to determine the optimum amount and concentration of alkali to be used that will produce maximum yield and gel strength.
Highlights
The demand for agar in Africa, including Tanzania, is growing rapidly due to the increasing number of biotechnology and microbiology laboratories
It is well established that, agar yield of Gracilaria species varied among each other (Arminsen, 1995)
The agar yield for G. salicornia recorded in this study is closely similar to that recorded by Buriyo and Kivaisi in 2003 where the agar yield ranged from 13.7 to 30.2 %
Summary
The demand for agar in Africa, including Tanzania, is growing rapidly due to the increasing number of biotechnology and microbiology laboratories. The genus Gracilaria is of considerable economic importance as an agarophyte, and it is the most abundant and promising resource of agar production. It has more than 150 species, distributed mainly in the temperate and subtropical zones (Radiah et al, 2011). The value of Gracilaria has increased with demand because of the high production cost of the agar from the genus Gelidium and insufficient wild stock of this genus. Different species of Gracilaria include G. edulis, G. corticata, G. millardetii, G. debilis (formally G. fergusonii) and G. salicornia have been reported to be potential sources of agar along the Indian Ocean water, including Tanzania (Jaasund, 1976; Kappanna and Rao 1963; Guiry and Guiry, 2021)
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