Decolorization of slaughterhouse thick blood for the recovery of a colourless protein preparation and an iron-containing heme fraction

Blood is the most important by-product of slaughtering. It consists predominantly of protein and water and is a valuable protein resource. The protein content in blood from domestic meat animals is equivalent to 6-7 % of the lean meat content in the carcass. Regarding the nutritionally valuable composition of blood and the large amounts of slaughterhouse blood, utilization of blood seems to be reasonable. A requirement for blood utilized in human consumption is its hygienic collection. Coagulation of freshly drawn blood is prevented by the addition of sodium citrate. Centrifugation of the treated blood yields a thickblood fraction (red cell fraction) and a light coloured plasma fraction. Blood plasma is used as food additive in meat industry. Thickblood which contains the major portion of the protein content (60-70 wt%) cannot be used for human nutrition because of its dark red colour. The intense red colour caused by the hemoglobin content of blood is aesthetically objectionable to a majority of the world's population when considering this product as a potential foodstuff. Therefore a decolorization treatment must be performed in order to remove the heme pigment from the globin moiety. If the protein preparation is used as food additive, heme should be removed almost completely because of its catalytic activity which leads to autoxidation processes of lipids.