Orientador: Prof.  Dr. Ricardo Pereira Ribeiro

Data da Defesa: 14/05/2014




Fish from inland waters have a great importance in the diet due to its large amounts of nutrients, high levels of protein and lipid fraction composed of polyunsaturated fatty acids (PUFA), mainly the omega-6 series (alpha-linolenic acid - LA (18:2 n -6)), but low levels of omega-3 (alpha-linolenic acid - ALA (18:3 n-3)). Cultivation systems allow the improvement of the fatty acid (FA) composition. The levels of eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3) in captivity fishes are influenced by lipid composition of feed. An alternative to improving the content of omega-3 is the addition of flaxseed in the feeds, since this grain is an excellent source of this FA. Tilapia is important specie in world aquaculture because it presents the typical requirements preferred by the consumers, such as white meat with firm texture, delicate flavor and easy filleting. In the filleting process byproducts are generated (head and carcass) and they are not used and commonly discarded in nature. The use of byproducts for the production of food depends on the quality of the raw material and technologies employed.


The aim of this study was to evaluate the effect of flaxseed addition in Nile tilapia (Oreochromis niloticus) diets, covering fatty acid composition of muscle tissue as a function of feeding time. The study also aimed at developing food mixtures with higher nutritional quality, such as greater contents of fatty acid of omega-3 series and calcium using fish byproducts.


Two diets were prepared for the feeding of tilapia for 60 days. The basic diet was formulated with soybean oil (diet T1) and 5% flaxseed for ration T2. The experimental diets were isocaloric and isoproteic, according to the nutritional requirements of the species. A total of 400 tilapia with average weight of 245 g were used in the experiment. They were distributed in eight tanks with density of 50 fishes per tank in a completely randomized design with two treatments and four replications, considering each tank as an experimental unit. The feeding was performed twice a day, at 9 am and 15 pm, the proportion was equivalent to 2% of the biomass. Three individuals were collected per experimental unit, starting at time zero (before the start of treatment) and every 15 days up to 60 days. The fish was slaughtered every collection, then they were gutted, filleted, packed in polyethylene bags and stored at -18°C for further analysis. For the preparation of fish meals from T1 and T2, 48.11% of carcasses and 48.86% of fish head were mixed with 0.31% salt and 2.72% of dried herbs. These ingredients were cooked in using 2L of water at 100°C for 2 hours. Then, the mixture was sieved through a stainless steel sieve of 14 mesh, the remainder was ground in a food processor for subsequent drying in a conventional oven at 180°C for 4 hours. After cooling (room temperature), the product was subjected to grinding and sieving again to obtain fishmeal T1 and T2. These meals were used to formulate the food mixtures in different levels with cassava flour. Five formulations with different combinations of fish meal (T1: A and D; T2: B and E) and cassava flour (C) were prepared. The moisture, ash and crude protein were determined by official methods. Total lipids were extracted cold (chloroform:methanol:water; 2:2:1,8 v/v/v). For fatty acid composition analysis, the lipids were converted to methyl esters (FAME). The FAME were separated by gas chromatography CP- 3380 (Varian, USA) equipped with flame ionization detector. In the quantification, an internal standard tricosanoato methyl (23:0) was used. Limits of detection and quantification were determined with analyses in

triplicate of serial dilutions of the standard solution of methyl arachidonic (1mg/mL). The minerals calcium, copper, iron, manganese, magnesium, sodium, zinc and potassium were determined by atomic absorption spectrophotometer AA240FS (Varian, USA) only for fish products. For quantification, analytical standard curves were used for each metal, finding the limits of detection and quantification, with the results expressed in mg of the mineral product per 100 g of product. Fish products were submitted to sensory acceptance and preference ordering. A group of 60 untrained volunteers panelists and potential consumers of products participated in the sensory analysis. Before the performance of the experiments, the proposal involving animals and humans were approved by the respective ethics committees (documents in Appendix 5). For statistical analyses, the program SAS was used and variance analysis and means comparison by t tests and Tukey were performed. The Friedman test was applied to sums test. Multivariate analysis was the application of principal component analysis (PCA). All statistical tests were evaluated at 5% of significance to reject the null hypothesis.


Total lipids of muscle tissue (fillets) ranged from 2.5 to 3.5. With respect to FA, the treatment supplemented with flaxseed presented an increase in n-3 PUFA and increase of 73% in the level of DHA (Y = 7.9040 +0.0908 * X , R ² = 0.9098). There was a decrease (p<0.05) of 15% of LA in the same experiment. Due to changes in the LA and ALA, there was an improvement in the ratio n-6:n-3. The byproducts presented the ash content increasing in proportion with the incorporation of fish meal in the formulations. The increase in protein content ranged from 509.7% (T2) to 532.6% (T1) to a mixture composed of 30% fish meal and 318.6% (T2) to 331.4% (T1) for products with 15% fish meal, compared with sample C (control cassava flour). All minerals differed (p<0.05) within the different formulations, and copper, zinc and calcium had higher concentrations in formulations A and B > D and E > C in this order. Calcium had the highest concentration compared to the others, contributing with 40-50% of the daily intake recommendations, including infant and elderly people. In multivariate analysis the decomposition of CP1 and CP2 showed that formulations containing mixtures supplemented with byproduct for both treatments contributed positively to the content of minerals. Formulation A presented the largest ratio n-6:n-3, ranging from 15:1 to 2:1. This difference in the balance of FA is due to products used in the feeds of fish, by treatment with conventional soybean oil and linseed oil, respectively rich in LA and ALA. Noteworthy is the presence of arachidonic acid (AA, 20:4n-6) and DHA in the mixtures, as they were metabolized from LA and ALA, respectively. These processes may occur in fish and humans but in the latter case the conversion can be limited by life stage and /or enzyme activity, so that the consumption of these FA becomes necessary via diet. The principal component analysis (PCA) allowed a better view of the effect of the FA incorporation, especially LA, ALA, AA and DHA, by the diet with flaxseed and to classify the samples due to these weights. Sensory analysis showed that the attribute appearance did not differ (p>0.05) for all formulations. For the attributes taste, smell and overall appearance there was no difference between the control formulation and mixtures with 15% fish meal (samples D and E). The acceptance rate ranged from 55 to 65% in formulations with fish byproducts. According to the order of preference, the samples C, D and E did not differ (p<0.05, by Friedman test) and formulations A and B were the most preferred. The highest purchase intent was presented for formulations C, B and E, respectively, 42%, 38% and 35% of the evaluators and potential consumers responded that surely/probably buy these products.


The addition of linseed was satisfactory and increased levels of fatty acids from omega-3 family occurred after 45 days, showing an improved fish. The food mixture with the highest percentage of fish byproducts had higher concentrations of protein, lipids and ash. AA and DHA were highlighted in flour mixtures and showed n-6:n-3 ratios closer to the values proposed in the literature. The minerals calcium, copper and zinc were found in significant contents. Calcium had the highest concentration and contributed with 40-50% for the daily intake requirement. The attributes of taste, smell and overall acceptability did not differ between the control formulation and the mixtures with 15% fish meal. Fishmeal added to cassava flour is a viable option in food production due to great nutrient contents. These mixtures can be used in food preparation, such as soups, meat creams, sausages, breads, pasta and nuggets. The use of byproducts contributes to reducing environmental pollution.


Oreochromis niloticus, flour, linolenic acid, minerals, sensory analysis, PCA.



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