This article will deal briefly with eggs’ nutritional value, health benefits and basic chemical composition, but the main focus will be on their role as a functional ingredient in baked goods.
Eggs contain a high amount of water, with approximate moisture levels of 73 per cent for whole eggs, 49 per cent for yolk and 86 per cent for egg whites. The typical physical composition of eggs is 10 per cent shell, 58 per cent whites and 32 per cent yolk. Eggs without the shell contain about 65 per cent whites and 35 per cent yolk. These ratios are important to know when formulating baked goods with different egg constituents, and especially dried egg products.
Yolks contain substantial amounts of lipids and protein while whites are almost completely free of lipids. Egg whites contain a high amount of protein as their major constituent, but it is diluted in a solution because of its high amount of water.
Many types of proteins are present in egg whites, and they play different roles in food formulations. The proteins in eggs are considered highly nutritious. In fact, ovalbumin, one of the major proteins in egg whites, is one of a few pure proteins that contain all the nutritionally essential amino acids.
Eggs contain other nutritional components – such as lipids, minerals and vitamins – that are essential for the human diet. But the functional properties of the proteins in egg whites are substantially different. For example, ovoglobulins have high foaming and whipping properties. On the other hand, ovomucin, with high viscosity properties, is very effective in stabilizing foams. The combination of these two properties enables us to produce angel-food cakes with large volumes.
In baking, eggs and egg ingredients are most commonly used in cake production. They are an essential ingredient in such formulations – and often the most expensive.
All egg products contribute to the texture and flavour of baked goods. Their binding and stabilization action in combination with gluten enables batters to form a complex matrix in which, at the oven stage, the proteins coagulate to form the cake’s rigid crumb structure.
This is particularly important for light foam type cakes. For heavier cakes in which the eggs are not whipped, the egg protein films are also important because of their leavening action – they trap and retain the gas generated by the baking soda.
Another important function eggs contribute to cakes is their tenderizing action. The proteins of egg whites, although very functional, result in toughening of the cake crumb. Egg yolks are responsible for counteracting this effect, resulting in more-tender cakes, and the components responsible for this action are the lipids in the yolk. Eggs are normally mild in flavour, but when used in high amounts in a formulation this flavour is transferred to the cakes. It is therefore important to select fresh eggs or ingredients made from fresh eggs for such products.
Eggs also contribute to the colour of the finished product. In particular, egg yolks are important in yellow cake formulations, while particular attention should be paid to the selection of egg whites when formulating angel-food cakes.
Eggs can be sold as whole, yolks or whites, and are available as an ingredient in three basic forms: liquid, frozen or dried.
It’s essential that eggs and egg products are safe and devoid of any pathogenic bacteria such as salmonella. For this reason, manufacturers usually pasteurize liquid eggs at temperatures between 60 and 62 C for not less than 3 1/2 minutes.
Frozen whole eggs, whites and yolks are pasteurized first and then frozen. The whole egg is mixed into a homogeneous mass and then pasteurized prior to freezing. A small amount of salt, sugar or glycerine is added to prevent coagulation.
Dried egg ingredients are a convenient and safer alternative for large manufacturers of baked goods. These ingredients are produced either by spray drying or pan drying. Although pan drying was the original method, spray drying is the preferred method because in combination with certain additives it will produce eggs that are equal in performance to the fresh ones. Freeze drying with control heat is another method of drying but is considerably slower and more expensive.
Recent advancements in research have found uses for some of the egg proteins beyond food applications. For example, the proteins lysozyme and avidin can be used as antimicrobials, while new research in the processing of eggs has led to increased performance in food applications.
Eggs, particularly egg yolks, are well known for their emulsification properties. Treatment of egg yolks with specific enzymes will result in an increase in their emulsification capacity. This is important for mayonnaise manufacturers because it allows them to reduce the amount of yolk in their formulations without compromising the quality of the finished product, while at the same time producing a lighter product. Such an enzymatic modification will also result in improved performance of egg yolks in the manufacture of baked goods.
Because of their importance and cost, many attempts have been made to develop alternatives to eggs that will perform as replacements. However, it’s proven extremely difficult to completely replace egg functionality in baked goods. Alternatives have been developed from soy and whey protein concentrates and isolates, but it is important to remember that when considering these alternatives for reformulation, a substantial amount of experimentation is required to achieve good results.
Funding for this report was provided in part by Agriculture and Agri-Food Canada through the Agricultural Adaptation Council’s CanAdvance Program.