Heterogeneity can appear due to the presence of lipophilic and hydrophilic components. A similar situation is when one wants to change an oily extract into a water- soluble or water-dispersible emulsion. In some cases, emulsifiers can help solve the problem.

Emulsifiers are surfactants that are useful as detergents, wetting agents, antifoaming agents, and so on. Such molecules will have a hydrophilic end (e.g., sodium in a soap) and a lipophilic end (e.g., the aliphatic end of a fatty acid). The hydrophilic/ lipophilic balance based on the structure of the molecule determines its efficiency to function as an emulsifier. In an oil-in-water dispersion, the lipophilic end will be attached to the oil droplet. Micelles are formed with oil droplets where the surrounding molecules of the emulsifier have the hydrophilic ends outside in the water. Such a system can form a stable dispersion.

Emulsifiers are either the oil-in-water or water-in-oil type. Based on the molecular mass of the hydrophilic end and the mass of the whole molecule, the hydrophile/lipo- phile balance (HLB) value of an emulsifier is fixed on an arbitrary scale of 0-20, with 0 corresponding to a completely hydrophobic molecule and 20 corresponding to a completely hydrophilic molecule. A good emulsifier for a water-in-oil type of emulsion will have an HLB value of 4-6, while an oil-in-water type will have an HLB value of 8-18.

Some commonly used emulsifiers are as follows:

Polysorbates are excellent emulsifiers, which can be used to bring about water solubility for spice oleoresins. Polyethylene glycol sorbitan monooleate is supplied as polysorbate 80. While the polysorbates can also be supplied as derivatives of saturated fatty acids for use in liquid spice extracts, the oleic acid derivative is the most satisfactory. With unsaturated fatty acids, the HLB will be 10-16. The oleic acid derivative is a yellowish viscous liquid. In recent years, some countries in Europe, as well as Japan and Korea, have raised doubts about its safety, although it is still legal to use it (polysorbate 80: FEMA: 2917; CAS: 9005-65-6; US/CFR: 172.515; E-No. 432).

DATEM, or diacetyl tartaric acid esters of mono- and diglycerides of the fatty acid, are partially soluble emulsifiers, which make oleoresins water dispersible. The HLB for DATEM will be 7-8.

Fatty acid esters of many polyhydric compounds are also emulsifiers. Of these, sucrose esters of fatty acids are good emulsifiers with a high HLB value (7-16) and polarity (FEMA: 4092; US/CFR: 182.1101; E-No. 472e).

Glyceryl monooleate is a good emulsifier, especially for making lipid products more dispersible in oil. During the esterification of glycerol with a calculated quantity of fatty acids, not all 100% will come as monoglyceride; generally about 20% will come as diglycerides and the rest as monoglycerides. Therefore, these are sometimes referred to as mono- and diglycerides. For oleoresins that are liquids, oleic esters are more suitable than esters of saturated acids. The HLB for glyceryl monounsaturated fatty acid will be 3-4 (FEMA: 2526; CAS: 111-03-5; US/CFR: 172.515; E-No. 471 [unsaturated]).

Glycerol-polyethylene glycol oxystearate (macrogol-glycerol hydroxyl stearate) produced from hydrogenated castor oil is a new class of emulsifier, which is very effective in making oily extracts water-soluble. However, the food laws of major countries have not allowed this to be used as yet. It is manufactured by BASF under the name Cremophor and by ICI/Uniqema (now by Croda) under the name Cresmer.

Lecithins are a complex mixture of phosphatides and glycolipids. They are obtained from soy, corn, sunflower, and rapeseed, and come as a cream-to-brown-colored viscous liquid and increase miscibility in oil. The HLB will be around 3-4 (US/CFR: 184.1400; E-No. 322).

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