Composição química de microalgas marinhas cultivadas em laboratório

Abstract

The chemical composition of the microalgae Chaetoceros gracilis, Cylindrotheca closterium, Isochrysis galbana, Tetraselmis gracilis and Thalassiosira weissflogii was determinated aiming to provido data in order to orientate aquafarmers, since the nutricional value of these microalgae, used as food for the cultivated animais, is still little known in the Northeast of Brazil. At the Federal University of Pernambuco, C. gracilis, C. closterium and T. gracilis were grown at constant temperatura of 20°C until reach the volume of 8 L, in carboys. The volume was increased and aerated from 1 L every eight days. At the Aqualider Company, C. gracilis, I. galbana and T. weissflogii were cultured at constant temperatura of 18°C imtil reach the volume of 20 L in plastic bags, with the aeration starting from 0,5 L, and the volume increased every two days. Both experiments were carried out under continuous illumination, in F2 - Guillard médium. For the cultura in plastic bags, the analyses were realized the beginning of the exponential phase and, for the culturas in carboys, at the end of the exponential phase. Regarding the culturas in plastic bags, I. galbana presented the highest cellular density (3.295 x 10® cell.L-¹), with significant difference superior to the other species, and the highest soluble carbohydrates levei (0,09 mg.L-¹), followed by C. gracilis (0,06mg.L-¹) and T. weissflogii (0,05 mg.L-¹), also presenting significant differences among the three species, and the highest values of nitrate, phosphorum and magnesium, with signiíicant differences superior, to the other species. T. weissflogii presented the highest values of sodium, potassium and sulfur. In relation to the chlorophyll a, C. gracilis presented the highest levei (3,74 mg.L-¹), followed by I. galbana (1,87 mg.L-¹) and T. weissflogii (0,96 mg.L-¹), with signiíicant differences among the three species. Conceming the cultures in carboys, C. gracilis presented the highest values for cellular density (8.447 x 10® cell.L-¹), soluble carbohydrate (0,10± 0,009 mg.L-¹) and magnesium (14,78 mg.L-¹). C. closterium presented the highest concentration of chlorophyll a (13,76 mg.L-¹), soluble protein (0,62 mg.L-¹), total free amino acids (23,82 mg.L-¹), nitrate (0,365 mg.L-¹), sodium (0,46 mg.L-¹) and phosphorus (2,80 mg.L-¹). The potassium (0,02 mg.L-¹) and sulfur (0,03 mg.L-¹) contents were the same for C. gracilis and C. closterium. The species T. gracilis presented the lowest values conceming the analyzed parameters. Due to the variation of the chemical composition among the species analyzed in both experiments, we suggest the use of multispecific diets for the animal feeding, thus promoting its hest development in a shorter period of time.