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promoting aeration of the batter. They are usually added in hydrated paste or gel form (25-50% solids) to aid in dispersion. Naturally occurring surfactants such as phospholipids from egg also contribute to emulsification of the batter.

As early as 1925, it had been confirmed that the addition of eggs improved the whipping quality of ice cream mixes (18). It was assumed that the albumin protein fraction of egg was the principal aerating agent. In 1928 it was demonstrated that egg albumin had no beneficial effect on the ice cream mix and that the improved aerating quality was being contributed by the yolk (19). It was later determined that the improvement was due to the emulsification imparted by phospholipids and lipoprotein in the yolk (20,21). Inclusion of yolk in the mix was also shown to increase the electrical charge (anionic) carried by the fat globule (22).

In 1936 a patent was granted on the use of glyceryl monostearate as an emulsifier and whipping aid for ice cream (23). It was found that the monoester was as effective at 0.1 to 0.2% as egg yolk was at 0.5%. It was also found that the use of the monoester provided an ice cream that was drier and stiffer on freezing and thus extruded and packaged with greater facility.

Surfactants based on saturated fatty acids were found to be more effective as aerating agents when used as ice cream emulsifiers, as compared with those based on unsaturated fatty acids (Figs. 7 and 8). The more hydrophilic ethoxylated surfactants are more effective than those of lower HLB value. Those approved for use in food contain an average of 20 mol of ethylene oxide and have an HLB in the 14 to 16 range.

In the production of whippable emulsions, such as ice cream or whipped toppings, it is desirable to obtain good volume and stiffness. Contrary to published hypothesis, it was demonstrated that a partial breakdown of the emulsion during whipping to produce agglomerated (but not coalesced) fat globules provides maximum product stiffness (24,25). It was found that the more hydrophilic ethoxylated surfactants based on saturated fatty acids such as stearic provided maximum whippability, whereas those based on unsaturated fatty acids such as oleic provided maximum dryness and stiffness to the aerated product. A turbidi-metic procedure was used to prove that surfactants actually accelerated the breakdown of the ice cream mix emulsion to provide agglomerated fat globules (Fig. 9) (24).

Combining a lipophilic saturated surfactant such as glyceryl monostearate with a hydrophilic unsaturated sur-

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