Effects of Chicken Egg Yolk on the Ultrastructure and Loaf Volume of White Bread

Abstract

Yolk, a mixture of yolk plasma and granule, and yolk plasma did not increase the volume of fermented dough when added to dough at the level of 3% of flour weight, however, these ingredients, especially plasma, increased specific volume of breads. Egg albumen or whole egg, added to dough at the same level as above, did not affect dough fermentation, however, oven spring of these doughs was depressed. Transmission electron microscopic observation of breads, sampled at the center of loaves, showed that yolk plasma formed membraneous structure in protein matrix and also around starch and yeast and the membrane might improve extensibility and/or gas-retaining property of dough during baking and increase loaf volume. The protein matrix of bread with yolk or yolk plasma contained inclusions type II of wheat endosperm less than those of control bread. The membranes might be formed by interaction between yolk lipoproteins and flour components, and/or between proteins and lipid-rich inclusions type II. Protein matrix bread with albumen was discontinuous and was often separated away from starch granules or gelatinized starch and consequently void spaces were observed around starch. The matrix and gelatinized starch contained more electron dense particles than those in control bread. Some of the particles might be condensed proteins of albumen. The ultrastructure of the matrix might decrease extensibility of the dough with albumen and make bread of poor volume.