[Chemical modification of proteins. 7. Effect of succinylation on some physico-chemical and functional properties of casein].

Succinylation of amino groups of the casein complex results in a spontaneous dissociation of the protein into low-molecular 1.8-S components. Succinylated samples of casein are characterized by a higher electrophoretic mobility of the components in alkaline mediums and by a lower mobility in acidic buffer systems. The anodic migration in alkaline buffer systems increases depending on the degree of modification. This effect is more pronounced for the beta-casein than for the alpha s-casein fraction. In the potentiometric acid-base titration of the modified casein a hysteresis occurs during the back-titration. Increasing with the degree of modification, this effect points to a more or less strong break-up of the structure (entropy production). The solubility minimum of casein is shifted to lower pH values by succinylation. Samples succinylated to 90 or more per cent of the amino groups are insoluble at pH less than 3.5. Succinylated casein shows at a moderate degree of substitution (approximately equal to 40%) a highly increased water adsorption capacity. The oil adsorption capacity of the protein decreases after succinylation. Amongst the modified casein samples those ones with the highest water adsorption show the highest oil adsorption, too. The emulsifying capacity of low (approximately equal to 20%) succinylated casein samples decreases below the value determined for the unmodified protein. At higher modified samples the emulsifying capacity increases as the degree of succinylation increases. The emulsifying activity and emulsion stability of modified samples are lower than that measured for the parent protein. The foaming capacity of the casein is not improved by succinylation.