Prevention of egg-allergic reactions means avoiding eggs and egg-containing foods. People with an allergy to chicken eggs may also be allergic to other types of eggs, such as goose, duck, or turkey eggs. In cooking, eggs are multifunctional: they may act as an emulsifier to reduce oil/water separation (mayonnaise), a binder (water binding and particle adhesion, as in meatloaf), or an aerator (cakes, especially angel food). Some commercial egg substitutes can substitute for particular functions (potato starch and tapioca for water binding, whey protein for aeration or particle binding, or soy lecithin or avocado for emulsification). Food companies produce egg-free mayonnaise and other replacement foods. Alfred Bird invented egg-free Bird's Custard, the original version of what is known generically as custard powder today.