H

Polyoxyethylene (20) sorbitan monostearate (Polysorbate 60)

Polyoxyethylene (20) sorbitan tristearate (Polysorbate 65)

OOC(CH2)I6CH3

Figure 4. Nonionic emulsifiers based on sorbitan esters.

coatings, in bakery icings, and in coffee creamers. The polyoxyethylene derivatives have found wider usage. Polysorbate 60 is used in a variety of applications where a high-HLB emulsifier is required, and is used in fluid oil cake shortening systems (4,5,7), generally in combination with GMS and PGMS. The various sorbitan derivatives are often used in combination to obtain a specific desired HLB; the regulations regarding the permitted levels of each emulsifier in the final product are rather complicated: details can be found in 21 CFR.

Esters of Polyhydric Compounds. Polyglycerol esters (Fig. 5) have a variety of applications as emulsifiers in the food industry (3,8). The polyglycerol portion is synthesized by heating glycerol in the presence of an alkaline catalyst; ether linkages are formed between the primary hydroxyls of glycerol. In Figure 5 n may take any value, but for food emulsifiers the most common ones are n = 1 (triglycerol), n = 4 (hexaglycerol), n = 6 (octaglycerol), and n = 8 (deca-glycerol) (in all cases n is an average value for the molecules present in the commercial preparation). The polyglycerol backbone is then esterified to varying extents, either by direct reaction with a fatty acid or by interesterification with a triglyceride fat. Again, the number of acid groups esterified to a polyglycerol molecule varies around some central value, so an octaglycerol octaoleate really should be understood as (approximately octa)glycerol (approximately octa)oleate ester. By good control of feedstocks and reaction conditions manufacturers do manage to keep the properties of their various products relatively constant from batch to batch.

The HLB of these esters depends on the length of the polyglycerol chain (the number of hydrophilic hydroxyl groups present) and the degree of esterification. As ex-

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