The principal components of meat are water, protein and fat, with a significant level of vitamins and minerals with a high bioavailability (Fernandez-Gines et al., 2005). Blood accounts for ~3-5% of an animal's live weight and contains —18—19% protein, similar to that found in lean meat, with the protein contents of plasma and red blood cells (RBCs) being —7-8% and 34-38%, respectively. Blood is the first co-product obtained while processing animals for meat. Blood should be collected in a hygienic manner for food use with or without anticoagulants, and serum can be separated from RBCs with the help of a cream separator and can be preserved under refrigeration. From serum and RBCs, protein isolates can be prepared separately by spray drying, freeze drying, solvent precipitation or by chro-matographic techniques (Mandal et al., 1999).
Blood proteins make up the largest part of the meat proteins market by volume. Blood products typically contain —70% protein, and blood components such as plasma, haemoglobin, immunoglobin and globin are used in a number of food applications. Plasma is often used in sausages to help bind and emulsify meat, haemoglobin is used in pet food and to colour black pudding, immunoglobin can be used as an emulsifier in meat products, while globin is used in mincemeat and hamburgers, where it improves textural properties and to some extent helps bind ingredients together. Blood proteins such as immunoglobulin are also used in the pharmaceutical industry in the preparation of antibodies and other immunoassay products (Frost & Sullivan, 2005a). The pharmaceutical industry also creates isolates such as creatine from blood proteins, to be used in nutraceutical applications. Although the demand from the pharmaceutical industry is increasing, it only constitutes a small fraction of the blood protein market.
A meat product formulated with mechanically deboned poultry meat and bovine blood has been used as an iron supplement to evaluate its effect on the haematological parameters of school children with ferropenic anaemia. Children with subnormal haematological parameters with a diagnosis of ferropenic anaemia received the meat product over 30 days. The results indicated that the consumption of the meat product increased the haematological parameters in children with ferropenic anaemia, with the authors suggesting that the product could be used in social programmes for school children with this deficiency in order to prevent and recover from ferropenic states (Rangel et al., 2003).
Cooked hams have been formulated with bovine plasma and/or red cells with the objective of evaluating the effect on yield, moisture, protein and palatability. The results indicated that products with plasma at 3.6% and 5.4% protein gave a higher yield. Addition of plasma, red cells or a mix of both at 1.8% protein did not affect yield. Final moisture and protein content were unaffected, but sensory evaluation indicated that only products with added red cells were unacceptable. The study concluded that plasma proteins are more suitable than red cell proteins for addition to these products and that it is necessary to add more than 1.8% of plasma proteins to increase yield (Rodas et al., 1998).
The blood plasma of calves and cattle has been reported to be a good nutritional supplement to meat products due to the essential amino acids it contains (Belkot, 2001). The pet food industry also uses blood proteins as a protein source as they contribute all the amino acids needed for a carnivorous pet diet. The pet food industry is a fast-growing market in Europe, and demand from the pet food industry for blood proteins is expected to increase in coming years.
Dehydrated blood plasma is also used as a protein ingredient for its gelation properties, especially in meat derivative products. Generally, blood is concentrated by either ultrafiltration or evaporation under reduced pressure. The resulting pH and ash concentration (mineral salts and sodium citrate) allow modification of the gelation properties of the products (Dailloux et al., 2002).
Bovine blood has been fractionated into blood plasma protein concentrate, red blood cell concentrate, globin isolate and a carboxymethylcellulose-heme-iron (CMC-heme) complex. The amino acid content in plasma protein concentrate has been shown to be well balanced and produced net protein utilization and a net protein ratio equivalent to 95% that of casein. Globin isolate (similar to 91% protein) is deficient in isoleucine and S-containing amino acids and was unable to support rat growth at a 10% concentration in the diet. Red blood cell concentrate and the isolated CMC-heme complex were good sources of bioavailable iron. Iron availabilities for CMC-heme and whole blood cell concentrates were 64 and 70% of ferrous sulphate, respectively (Duarte et al., 1999).
Globin is an edible protein that is obtained in large quantity from animal blood and can be used as an ingredient in a variety of meat products. However, globin has been reported to have a low solubility at neutral pH and little advantage compared with other proteins used in the food industry. However, globin's functional properties can be improved via hydrolysis with citric acid. These aggregates of globin hydrolysates were composed of the beta-chain, originating from the native globin and beta-1, originating from the beta-chain by cleavage between 99 (Asp) and 100 (Pro) of the beta-chain (Liu et al., 1996).
For the preparation of globin protein isolates, decolourization is one of the important steps. These protein isolates have excellent functional properties and nutritive value, which make them suitable for use in meat and bakery products. Furthermore, they can replace the use of chicken egg to some extent in food products without affecting acceptability (Mandal et al., 1999).
Response surface methodology has been used to investigate the effects and interactions of blood plasma (0-2%), microbial transglutaminase (0-0.6%) and kappa-carrageenan (0-0.8%) on water binding, textural and colour characteristics of pork gels. An increased addition of both kappa-carrageenan and plasma protein favourably affected thermal stability of pork batters, but the effects were attenuated by increased blood plasma and kappa-carrageenan addition, respectively. The combination of kappa-carrageenan with blood plasma was unable to improve springiness or cohe-siveness and led to the formation of less cohesive and more brittle gels. Microbial transglutaminase had little effect on colour and water binding properties although it was found that its addition improved cohesiveness and elastic properties of meat gels processed with blood plasma. Addition of blood plasma produced an increase in lightness and a decrease in redness of pork gels, while the presence of kappa-carrageenan resulted in lower chromametric values (Jarmoluk and Pietrasik, 2003).
Animal blood is a by-product from meat processing and contains a variety of proteins that can be reclaimed. The efficiency of protein precipitation from blood by the use of hydroxyethyl cellulose (HEC) has been reported to be similar to that precipitated by the use of CMC with both methods being superior to precipitatation by trichloroacetic acid. The plasma protein-HEC complex was reported to contain a large amount of essential amino acids and electrophoretic separation of plasma protein resulted in complex albumin forming the major fraction (El-Sayed et al., 1998).
The recovery of protein from red cells of bovine blood has been achieved by hydrolysis of red cells with papain and up to 32% of the heme group being released by this process was separated by ultrafiltration. Treating the retentate with sodium hypochlorite produced a white product that was 75% protein, nearly 1% ash and almost tasteless. The results indicated that the protein contained in this fraction had a good amino acid profile for use as an ingredient in formulated foods for human consumption (Gomez-Juarez et al., 1999).
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