Effect of freezing and food additives on the rheological properties of egg yolk

Egg yolk is an important food ingredient because of its nutritive value and functional properties. Egg yolk freezing is often used to extend its shelf life, however freezing induces irreversible gelation when no additives are added. This permanent loss in yolk fluidity is undesirable and has traditionally been avoided through the addition of 10% salt or sugar. Recently, prevention of frozen-thawed induced gelation by the addition of hydrolyzed egg yolk protein (HEY) was reported. Nevertheless, the properties of the resulting yolk product have not systematically been studied. In this study the rheological and thermal properties of the unfrozen and frozen thawed yolk products with and without additives were characterized. Results indicate that although gelation was prevented through different mechanisms, comparable rheological properties between the yolk treated with 5% HEY and that treated with 10% salt or sugar were observed. This whole egg product has proven to have comparable to better freeze-thaw stability than the conventional antigelation method. With the comprehensive information contained in this study, suitable parameters can be determined when designing the processing conditions for foods containing these yolk products.