Análises de parâmetros químicos e bioquímicos de algumas espécies de algas marinhas, para a inclusão em rações utilizadas na piscicultura, visando modificar o "flavor" de peixes de água doce

Abstract

In the present study, five species of marine algae (Gracilaria cornea Maze et Schram, Gracilaria caudata J. Agardh, Ulva fasciata Delile, Ulva lactuca Linnaeus e Vidalia obtusiloba (Mertens) J. Agardh) were used to detect the presence of bromoperoxidases that are responsible for the production of oligophenols, which are believed to confer the characteristic flavor present in marine organisms. In a view to promote flavor alterations in meet from the fresh water fish (Nile tilapia), we have used these five marine algae species as a component in the food diet. The algal samples were used to determine the chemical composition (total protein, water content, fat, ash, fiber, carbohydrate, calcium and phosphorous), amino acid and fatty acids composition. Some biological factors have been determined such as: toxicity (DL54), the presence of trypsin inhibitor and haemagglutinating activity. After these analyses we carried out a study of feeding using the fresh water fish Nile tilapia, Oreochromis niloticus, Vr "Chitralada", that was composed of five treatments. Treatment A consisted of a food diet prepared with soybean, corn, mineral and vitamin supply, and the addition of 5, 10 and 15% of algal flour from Gracilaria cornea, resulting in diets A-1, A-2 and A-3, respectively. The same procedure was used for treatment B, but with the addition of flour from the alga Gracilaria caudata, resulting in diets B-1, B-2 and B-3. The treatment C was composed of a basic diet (soybean and corn) with the addition of 135, 270 and 405 mg/bromphenol.kg4 of the diet, leading to diets C-1, C-2 and C-3, respectively. The treatment D was also composed of three diets, from the basic one, with the inclusion of 10% of marine alga, as an aqueous extract, with the D-1 diet composed of Ulva fasciata while the D-2 and D-3 diets with Ulva lactuca and Vidalia obtusiloba, respectively. The standard treatment was composed of the basic diet without the addition of marine algae. After cultivation, the fish were submitted to sensorial analysis and exhibiting the following results. The fish feed with diets from treatment A, B and C did not show alterations in the flavor in the tested animals, probably due to the inadequate manipulation during the elaboration of the diets. Fish feed with diets from treatment D exhibited a moderate alteration in flavor and color but without achieving the characteristic flavor of a marine fish. Some testers (Triangular test) classified the alterations observed as a more agreeable flavor. From these, we may conclude that the crude extracts from the algae used to humidify the ration and also the bromophenol solution could be the right way to promote the desirable alterations in the flavor. The diets A-1, B-1 and the standard one are recommended when the main aim is only the growth in weight of the cultivated animals. In regard to the treatments C and D, studies should be conducted to ascertain the percentage of inclusion and adequate handling.