Efeito do estresse na composição química de microalgas e do extrato na germinação de sementes de alface

Abstract

Microalgae are a group of aquatic organisms that might have great potential for cultivation due to the high growth rate. Many species are grown commercially in several countries and the produced biomass has been used as a source in the food industry, in the production of natural dyes, as a source of lipids in the production of biofuels (bioethanol and biodiesel) and in the production of bioproducts for using in plant cultivation. An economically viable way of producing microalgae can be using wastewater as culture medium. The present work aimed to evaluate the effect of stress on biochemical variation of microalgal biomass grown in wastewater and, study the potential of extracts produced by microalgal biomass in the lettuce seed germination. Three microalgae, Chlorella vulgaris (Cv), Scenedesmus obliquus (Sc) and a Consortium (Cons C) of isolated microalgae extracted of urban effluent of Figueira da Foz / Portugal, were used. The microalgae were grown under normal conditions. Thereafter, to stress the microalgae, they were placed in solution without nutrients. The biochemical characterization of biomass was made through analysis of the volatile solids, total solids, moisture, ash, protein, sugar, oil and total pigments. Later, aqueous and methanolic extracts in three concentrations (2, 10 and 20 g L-1) of microalgae Cv, Sc and Cons. C were prepared. The extracts were applied in lettuce seeds. The germination on the third day, total germination, the speed of germination index (SGI), root size, hypocotyl size, dry matter per plant and total dry matter (DM) were measured. The biomass showed variation in biochemical characterization, when the biomass is subjected to stress conditions in cultivation. The profile of fatty acids from microalgae has higher levels of unsaturated fatty acids, except for Sc that has a higher saturated fatty acid content. The application of aqueous extracts of Cv, Sc, CvSt, SCST and Cons C St exhibit inhibitory effect when the SGI was evaluated. A stimulating effect on radicle growth of microalgae extracts for Cons C and C Cons St was observed. All the methanolic extracts have inhibitory effect on germination on the third day, total germination and SGI. Increasing the concentration of the methanol extract decreases the final germination values. Increasing the concentration of the methanol extract Cv decreases the content of dry matter per plant.