Modifizierung der funktionellen Eigenschaften von Ackerbohnenprotein durch Acetylierung

[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.

Actual problems of research in food science

Starting from the necessary trend towards development in the field of food production, the author outlines, on the basis of current knowledge, the problems to be solved in food science. A general research conception is deduced for the essential nutrient "protein" (as an example) which is illustrated by results from studies on protein fibre and protein gel formation.

[Nutritional-physiological studies on acetylated fractions of protein from Vicia faba]

The nutritional-physiological value of an easily soluble and of a difficulty soluble fraction of protein from Vicia faba (showing a degree of acetylation of 0%, 43% and 94%, respectively) was characterized by determining the amino-acid content, the enzymatic amino-acid availability and the nitrogen balance in the rat. The results from both the amino-acid analysis and the animal experiments on the biological value evidenced that the nutritional-physiological value of the easily soluble fraction of protein from Vicia faba is significantly lower, which is in particular attributable to its lower content of sulphur-containing amino acids. Acetylation did not reduce the nutritional-physiological value of the easily soluble fraction of protein from Vicia faba, and impaired that of the difficulty soluble fraction but slightly. From the viewpoint of nutritional physiology, there are no objections against the use of these protein fractions as food additives.

[Use of the combined Kjeldahl-wet digestion/Berthelot-reaction for determining nitrogen in biological materials. 2. Design and testing of a partially automated apparatus for routine determination of nitrogen]

The authors describe the design and the mode of operation of a partially automated analyzer system, based on the combination of the Kjeldahl wet digestion with the Berthelot reaction, for the determination of nitrogen in biological materials. The results from three years of operation are discussed from the view-points of variability of the materials to be tested, of accuracy and of precision. This analytical technique (with an accuracy of 98% and a precision of 4%) is suited for determining amino and amido nitrogen as well as non-aromatically bound ring nitrogen. The statistical evaluation of the analytical results revealed that the deviation of the measured values is mainly caused by the high-temperature digestion.