Depending on the composition of food products, there are oil-in-water emulsions and water-in-oil emulsions. For food products, oil-in-water emulsions are more common than water-in-oil emulsions. For example, mayonnaise, homogenized milk and ice-cream, are typical oil-in-water emulsions. An oil-in-water emulsifier is required to create an oil-in-water emulsion. In a stable emulsion, the attractions between the emulsifier and the water phase and oil phase have to be balanced. To choose a suitable emulsifier or a combination of emulsifiers, we need to know the hydrophilic-lipophilic balance of the emulsifier. The hydrophilic-lipophilic balance (HLB) scale ranges from 0 to 20, where the midpoint 10 indicates that an emulsifier is equally attracted to oil and water. HLB values less than 10 are more hydrophobic, meaning more suitable for water-in-oil (w/o) emulsions; whereas HLB values greater than 10 are more hydrophilic, therefore better suited for oil-in-water (o/w) emulsions.
Emulsifiers can be used alone or in a combination to formulate a blend of emulsifiers that suits a particular food matrix the best. For example, polysorbate 80 is commonly used in ice-cream formulation to stabilize the o/w emulsion. Polysorbate 80 reduces the surface tension of particles and promotes the accumulation fat globules. It can also facilities in the distribution of small air bubbles in ice-cream, thus resulting in silky texture. Depending on the formulation and nature of the food matrix, polysorbate 80 can be used in combination with sorbitan ester 80, which is a w/o emulsifier.