Original article Functional properties of isolated porcine blood proteins Carlos A ´ lvarez, Margarita Bances, Manuel Rendueles & Mario Dı´az* Department of Chemical Engineering and Environmental Technology, University of Oviedo, Oviedo, Spain (Received 1 September 2008; Accepted in revised form12 December 2008) Summary The isolated proteins contained in the blood from slaughterhouses could be recovered and used to improve the functional and nutritional properties of food products. In this work some functional properties, namely solubility, emulsifying capacity, gelling and foaming capacity have been tested for different protein fractions of porcine blood. The blood proteins studied were globins (a, b and c), albumin and fibrinogen and the whole plasma from the plasmatic fraction, and haemoglobin and globin obtained from the haemoglobin by a chemical method from the cellular fraction. The effect of pH and protein concentration on functional properties was determined. Results indicate that blood proteins present good functional properties specially solubility, gellation and emulsifying capacities that could make blood protein useful as food additives in the formulation of food products. Keywords Albumin, blood plasma, fibrinogen, functional properties, globulins, haemoglobin. Introduction Animal blood produced in slaughterhouses represents the most problematic by-product of the meat industries (Rendueles et al., 1997) because of the high volumes generated and its very high pollutant power. Regula- tions impede the discharge of blood to wastewater treatment plants for subsequent treatment, so different removal techniques (drying, incineration, etc.) are usu- ally used to treat this by-product. Moreover, observing that proteins constitute one of the main components of blood and that these molecules have an important economic value, it would seem obvious to consider the chance of recovering the protein contained in slaugh- terhouse blood (De Vouno et al., 1975; Wismer-Peder- sen, 1979). An alternative solution to this problem is that of processing slaughterhouse blood into marketable products (Yang & Lin, 1998). The food industry could use blood proteins as additives to dietetic or imitation products. The functional properties of these proteins are comparable with marketable products such as egg albumin or whey proteins (Crenwelge et al., 1974; Cheftel et al., 1989; Linden & Lorient, 1994). To carry out the separation and purification of blood proteins, it is first necessary to separate the plasma –the liquid fraction of the blood – from the cellular fraction. Plasma is basically constituted of proteins (7%), water (91%) and a large variety of salts and low-molecular weight compounds (1%). Nearly, all the proteins in blood are present in the plasmatic fractions, except the haemoglobin, the majority protein located in the cellular fraction (Tybor et al., 1975). A second stage of the separation of blood proteins is the fractionation of the plasma proteins, one common method developed in the 40’s (Cohn et al., 1946) is the Cohn’s method. This method is actually well-established in the industry of human blood resources, the same procedures can be applied to porcine blood. The fractionation involves successive processing steps at defined ethanol concentrations, associated with shift in pH and temperature that results the selective precipita- tion of proteins. Precipitates are separated by centrifu- gation (Burnouf, 2007). Functional properties affect the sensorial characteris- tics of food, but they can also influence its physical behaviour during preparation, transformation or stor- age (Ramos-Clamont et al., 2003; Silva & Silvestre, 2003) . It is difficult to deduce the functional properties of a protein from its structural characteristics, especially when studying a protein concentrate such as plasma, which contains different types of proteins. Solubility is highly affected by pH changes (Shahidi et al., 1984), so it is of interest to test this functional property as a function of pH. High protein solubility allows proteins to be used as ingredients in many food formulations. Under different conditions, solubility gives a good indication of the potential application of a protein. The degree of insolubility is an indirect measure of protein denaturalisation. The emulsifying *Correspondent: Fax: 34985103434; e-mail: mariodiaz@uniovi.es International Journal of Food Science and Technology 2009, 44, 807–814 807 doi:10.1111/j.1365-2621.2009.01908.x Ó 2009 Institute of Food Science and Technology