VARIABILITY OF PROCESSING PROPERTIES OF A LBUMIN AND YOLK BETWEEN ANDWITHIN PURE LINES OF BROWN-EGG LAYERS

Eggs of three different pure Lines of a brown-egg breeding program wer e used to evaluate the variation in processing properties as potential selection criteria. In some 4200 eggs obtained in the 24th and in the 32th week of laying, height and width of albumen and yolk were obtain ed. Out of the members of each line, 2 x 30 hens showing extremely low or high albumen height were selected according to the result of the f irst measurement. In four eggs of these hens obtained in intervals of three weeks, albumen and yolk pH as well as foaming ability and the st ability of foam and of yolk-oil-water emulsions mere determined. All e ggs mere stored for a variable time before analyses, however the resul ts were unbiased with respect to storage length due to the particular design of the analysis. Within and between the breeding lines, a consi derable variation was found in albumen proportions and in the stabilit y of foam and emulsion. Variation was low in yolk proportions and in p H values. Foam stability was 82.2%, 88.3% and 89.9% in the three lines , the corresponding values for emulsion stability were 21.5%, 33.9% an d 31.5% with mostly significant differences among means. Direct select ion for foam or emulsion stability seems promising according to the fa vourable repeatabilities of about 0.4 to 0.6, however the determinatio n is quite time-consuming. Foaming ability had a poor repeatability an d behaved contrary to foam stability. The possibilities to improve fun ctional egg properties by indirect selection for albumen or yolk propo rtions were calculated. A relatively close relation existed between al bumen height and foam stability. The phenotypic correlation between bo th criteria as obtained in different eggs of the same hens was 0.4, an d hens with low or high albumen height significantly differed in the f oaming properties. Yolk proportion had little predictive value for the emulsifying properties.