ABSTRACT
The influence of aeration on algal growth and gamma-linolenic acid (GLA) production in a bubble column photobioreactor was investigated. Studies were performed in a 20-L reactor at different aeration rates (0.2-2.5 vvm). Static, continuous, and periodic operation of air resulted in 41.9%, 88.4%, and 108% air saturation of dissolved oxygen, for which the corresponding values of GLA were 2.3, 6.5, and 7.5 mg·g-1 dry cell weight, respectively. An increase in the aeration rate from 0.2 to 2.5 vvm enhanced both the specific growth rate and GLA content under periodic sparging in the bicarbonate medium. With a 6-fold increase in the aeration rate, the GLA content of the alga increased by 69.64% (5.6-9.5 mg· g-1 dry cell weight). In addition, the total fatty acid (TFA) content in dry biomass increased from 2.22% to 4.41%, whereas the algae maintained a constant GLA to TFA ratio within the aeration rate tested. The dependence of GLA production on the aeration rate was explained by interrelating the GLA production rate with the specific growth rate using the Luedeking and Piret mixed growth model.
ABSTRACT
Gamma-linolenic acid (GLA) production by Spirulina platensis under different stress-inducing conditions was studied. Submerged culture studies showed that low temperature (25ºC), strong light intensity (6 klux) and primrose oil supplement (0.8%w/v) induced 13.2 mg/g, 14.6 mg/g and 13.5 mg linolenic acid per gram dry cell weight respectively. A careful observation of fatty acid profile of the cyanobacteria shows that, oleic acid and linoleic acid, in experiments with varying growth temperature and oil supplements respectively, helped in accumulating excess -linolenic acid. In addition, cultures grown at increasing light regimes maintained the -linolenic acid to the total fatty acid ratio(GLA/TFA) constant, despite any change in -linolenic acid content of the cyanobacteria.
Estudou-se a produção de ácido -linolênico por Spirulina platensis em diferentes condições de estresse. Culturas submersas indicaram que temperatura baixa (25ºC), forte intensidade de luz (6 klux) e suplementação com óleo de prímula (0,8% p/v) induziram a produção de ácido linolênico de 13,2 mg/g, 14,6 mg/g e 13,5 mg/g peso seco, respectivamente. Uma observação cuidadosa do perfil de ácidos graxos da cianobacteria indica que os ácidos oléico e linoléico, em experimentos com diferentes temperaturas de crescimento e suplementos de óleo, auxiliaram no acúmulo de excesso de ácido -linolênico. Além disso, as culturas obtidas em intensidades crescentes de luz mantiveram a relação ácido -linolênico/ácidos graxos totais constante, independentemente de qualquer mudança no conteúdo de ácido -linolênico da cianobactéria.