Avaliação nutricional, em tilápias-do-nilo, de farinhas de sangue bovino obtidas por três métodos de processamento

Avaliaram-se farinhas de sangue obtidas pelos métodos de processamento em tambor, convencional e atomização. As farinhas foram submetidas ao processo de extração e fracionamento da proteína para determinação do perfil do tamanho molecular, que foi comparado ao do sangue bovino in natura. Nas amostras, submetidas ou não ao processo de desengorduramento, foram realizadas análises da digestibilidade in vitro da proteína. Para determinação dos coeficientes de digestibilidade dos nutrientes in vivo, foram confeccionadas quatros rações, sendo uma sem farinha de sangue, denominada ração-referência purificada. Para essa etapa, juvenis de tilápia-do-nilo com peso médio inicial de 100,0±5,0 g foram estocados em aquários de 250 L, em delineamento de blocos casualizados, com quatro repetições e dez peixes/unidade experimental. As rações-teste foram obtidas com a introdução de 30% das farinhas de sangue em estudo. O processamento afetou a estrutura proteica original do sangue in natura em condições de alta temperatura e tempo prolongado, efeito traduzido pela alta proporção de peptídeos de baixo peso molecular e aminoácidos livres, correspondendo a baixos valores de digestibilidade da proteína da farinha de sangue nos testes in vivo e in vitro. A farinha de sangue atomizada e a de tambor são eficientemente utilizadas por tilápias-do-nilo. Na farinha de sangue convencional, a proteína teve valor biológico inferior ao das outras duas farinhas. Na formulação de rações contendo farinha de sangue para tilápias-do-nilo, a isoleucina deve ser considerada o primeiro aminoácido limitante, seguida pela metionina+cistina, arginina e treonina, que foram encontradas em níveis críticos para essa espécie, principalmente na farinha de sangue convencional.Three kinds of blood meal coming from different processing conditions (spray-dried, drum-dried and vat-dried blood meals) were evaluated. Protein extraction and fractionation were performed in each blood meal type to determine the molecular weight profile, which was compared with standard bovine blood in natura. In vitro digestibility analyses of the protein in the diets were carried out in samples, which underwent defattening process or not. The apparent digestibility coefficients of the blood meal in vivo nutrients was determined with the creation of four diets; one of them did not have blood meal, called purified reference diet. For this stage, Nile-tilapia juveniles, with 100.00±5.0 g/fish of average weight were stocked in tanks of 250 liters in a completely randomized blocks design with four replicates and 10 fish per experimental unit. The test diets were obtained with the introduction of 30% of the blood meals in the study. The protein structure of the blood in natura is affected by high temperature and length of time of processing, resulting in an increase in the amount of low molecular weight peptides, and free amino acids, corresponding to low values of blood meal protein digestibility, both in- vivo and in-vitro tests. Spray-dried blood meal and drum-dried blood meal are efficiently used by the Nile-tilapia. In the regular blood meal, protein has lower value than the two other blood meal types. At the development of diets containing blood meal for Nile-tilapia, isoleucine must be the first limiting amino acid, followed by methionine + cystine, arginine, and threonine, which were found in critical levels for this specie, mainly in the conventional blood meal

Nutritional aspects of food extrusion: a review

Extrusion cooking, as a multi-step, multi-functional and thermal/mechanical process, has permitted a large number of food applications. Effects of extrusion cooking on nutritional quality are ambiguous. Beneficial effects include destruction of antinutritional factors, gelatinisation of starch, increased soluble dietary fibre and reduction of lipid oxidation. On the other hand, Maillard reactions between protein and sugars reduce the nutritional value of the protein, depending on the raw material types, their composition and process conditions. Heat-labile vitamins may be lost to varying extents. Changes in proteins and amino acid profile, carbohydrates, dietary fibre, vitamins, mineral content and some non-nutrient healthful components of food may be either beneficial or deleterious. The present paper reviews the mechanisms underlying these changes, as well as the influence of process variables and feed characteristics. Mild extrusion conditions (high moisture content, low residence time, low temperature) improve the nutritional quality, while high extrusion temperatures (200 &deg;C), low moisture contents (&lt;15%) and/or improper formulation (e.g. presence of high-reactive sugars) can impair nutritional quality adversely. To obtain a nutritionally balanced extruded product, careful control of process parameters is essential.<br /