Orientador: Prof. Dr. Jesuí Vergílio Visentainer

 Data da Defesa: 21/08/2015



INTRODUCTION. Oreochromis niloticus or Nile tilapia ranks first in production of farmraised freshwater fish in Brazil, particularly due to easy adaptation and cultivation of this species. As food, tilapia fillet presents a great acceptance, excellent quality and mild flavor. Studies have shown that it is possible to improve the lipid content of the farm-raised tilapia through supplemented diets with vegetable oils as sources of interesting fatty acids. Chia oil (Salvia hispanica) presents 54-68% of alpha-linolenic acid (18:3n-3), which is an essential fatty acid and acts as precursor of long chain polyunsaturated fatty acids such as eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3). Intake of omega-3 fatty acids is associated with various benefits to human health, including the prevention of cardiovascular diseases. Evening primrose oil (Oenothera biennis) and borage oil (Borago officinalis) are sources of gamma-linolenic acid (18:3n-6). These oils are used in the treatment or prevention of some diseases such as premenstrual syndrome and diabetes. When fish are submitted to supplemented diets, it is possible to assess the acceptance of the feed, the survival of the fish, the incorporation of certain fatty acid or production of long chain fatty acids, the description of food lipids and others. Furthermore, chemometrics and multivariate analysis can be applied to the results thought assembling merit to scientific research. AIMS. The objectives of this study were: I) evaluating the influence of two factors at two levels (time of treatment, 15 and 30 days, chia oil content in the feed diet, 2.1 and 4.2%) in the lipid composition of Nile tilapia fillet, about the incorporation of alpha-linolenic acid, increase of omega-3 fatty acids and changes in the n-6/n-3 ratio; and II) investigating the incorporation of gamma-linolenic acid through supplemented diet with evening primrose and borage oils in the lipid composition of tilapia fillet. MATERIAL AND METHODS. Feed diets for tilapia were supplemented with vegetable oils such as soybean (control), chia, borage and evening primrose. The fish were adapted to the treatment, cultivated in tanks, fed with supplemented diets (for 15 and 30 days) and induced to death. All treatment process was conducted with the approval of the Ethics Committee on Animal Use in the Experimentation of State University of Maringa (CEUAUEM Opinion n. 037/2014). Samples had head, skin and viscera removed; they were washed, vacuum packed and stored at –18 °C for later analysis. Moisture, ash, protein and total lipids analyzes were performed in the diets. Total lipids, from diets and fish fillet, were extracted, esterified and subjected to analysis by gas chromatography. For fatty acid identification, retention times were compared with those of standard methyl esters. Fatty acids were quantified against tricosanoic acid methyl ester as an internal standard. Theoretical correction factors were applied to fatty acids quantification. Design-Expert and Statistica software were used in factorial design and principal component analysis, respectively. Means were statistically compared by Tukey’s test and t test, at 5% significance level. RESULTS AND DISCUSSION. The supplemented diet with chia oil (at 2.1 and 4.2% for 15 and 30 days) increased the level of polyunsaturated fatty acids in tilapia fillet. After treatments, the ratio between polyunsaturated and saturated fatty acids changed from 1.39 to 1.85, which demonstrated a significant increase, when compared to the value of the initiation of the treatment (0.97). All the fillet samples showed an enhancement of alpha-linolenic acid (17.21-84.82 mg g–1 of total lipids), eicosapentaenoic acid (0.58-2.72 mg g–1 of total lipids) and docosahexaenoic acid (9.29-25.42 mg g–1 of total lipids); thereafter, an increase in the amount of omega-3 fatty acids decreased the n-6/n-3 (omega-6/omega 3) ratio from 8.41 to 1.92. Three significant and predictive mathematical models for responses of interest, i.e., total alpha-linolenic acid incorporated into the fish, total omega-3 and n-6/n-3 ratio, were obtained from factorial design. Different sources of gamma-linolenic acid increased the amount of this fatty acid in fish fillet after 30 days of treatment. Gamma-linolenic acid was quantified in fish fillet such as 6.43, 11.43, 13.99 and 15.12 mg g–1 of total lipids, in the initiation of treatment, and after the treatments with soybean oil, borage oil and evening primrose oil, respectively. Statistically, at the level of 5% of significance, the values of gamma-linolenic acid in the fish fed with borage and evening primrose diets were not significantly different. Levels of dihomo-gamma-linolenic acid (20:3n-6) and arachidonic acid (20:4n-6) did not changed (p < 0.05). However, treatments transferred some differences to the fish fillet. Principal component analysis favored the visualization of the results, by grouping in the same graph quadrant the treatments with different sources of gamma-linolenic acid. On the other hand, the remaining points (referred to the initiation of the treatment and the conducting control treatment) were discriminated in the score plots. CONCLUSIONS. Factorial design revealed three significant mathematical models for responses of interest, through the both variables (time of treatment and chia oil content) in diets for Nile tilapia. The most desirable results for the fish lipid quality to human health were observed after 30 days of treatment with a diet containing 4.2% of chia oil. The treatments with borage and evening primrose oils increased the polyunsaturated fatty acids content, especially n-6 fatty acids, in fish fillet. Gamma-linolenic acid was increased in the lipid composition of tilapia fillet. Keywords. Omega-6, omega-3, chia, borage, evening primrose, alpha-linolenic acid, gammalinolenic acid.


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