Sucrose esters

This group of substances is remarkable for the wide range of hydrophilic-lipophilic balance (HLB) that it covers.

Due to this amphipathic property, sucrose esters act as emulsifiers; i.e., they have the ability to bind both water and oil simultaneously.

A class of sucrose esters with highly substituted hydroxyl groups, olestra, is also used as a fat replacer in food.

These condensation gave low yields, and the products, which were dark in color, needed extensive purification.

The new synthesis pathway, which involved transesterification of triglycerides and sucrose in the new solvent dimethylformamide or DMF, was invented and seemed promising.

In 1950s, Foster Snell and his team conducted research on the production of several mono- and di-substituted sucrose esters.

The three primary hydroxyl groups are more reactive due to lower steric hindrance, so they react with fatty acids first, resulting in a sucrose mono-, di-, or triester.

The fewer free hydroxyl groups and the more lipophilic fatty acids, the less hydrophilic the resulting sucrose ester becomes.

The melting point of sucrose esters is between 40 °C and 60 °C depending on the type of fatty acids and the degree of substitution.

At pH higher than 8, saponification (hydrolysis of the ester bond to release the original sucrose and the salt of fatty acids) might occur.

There is no early scientific data, dating back to the 1990s or earlier, supporting experimentally the current HLB scale attributed to sucrose esters.

[5] For polyethylene oxide non ionic surfactants the HLB is defined by the Griffin's scale (Equation 1):

(Equation 2) Ryoto Sisterna 11 6 Notes: % monoesters and HLB reported in this table are the approximative values indicated by the suppliers for each blend.

The first one is that in this numerical transposition of the Griffin's scale to sucrose esters, the monoesters content is supposed to correspond the hydrophilic part of the surfactant what is a strong approximation because the monoesters fraction is not purely hydrophilic, since it also contains a high proportion of hydrophobic fatty chains in mass percent.

The second issue is that this HLB scale, established for non-ionic PEO surfactants on the basis of experimental data, is valid only for the latter.

[6] This scale has a genuine predictive value for choosing the right PEO surfactant for a given application, typically oil-in-water or water-in-oil emulsification.

It is not the case as long as experiments have not brought evidence that correspondences are possible between the scales applied to different surfactants families.

It is the case notably for their emulsifying properties, for their sensitivity to temperature and their interaction with water through hydrogen bonding.

Efforts to clarify the HLB of sucrose esters and related carbohydrate surfactants by experimental methods has been made in few works.

The results tend to show that the experimental HLB of sucrose monoesters, composed of 100% of monoesters for purified products and around 70-80% for industrial blends, would be rather around 11-12 for short fatty chains (6 to 12 carbons) and around 10-11 for long fatty chains (14 to 18 carbons).

The "wide range of HLB" currently defined for sucrose esters marketed blends, which is supposed to spread up to 16, should be considered with a critical point of view at the light of these observations.

In this case, it means that the fatty acids used for the synthesis of sucrose esters are themselves in the esterified form.

[10] The other method involves transesterification of sucrose and fatty acid methyl ester using sodium methoxide as a basic catalyst.

The by-product methanol can be removed via distillation to drive the equilibrium to favor sucrose esters.

The transesterification involves sucrose and fatty acid methyl ester in a solvent, propylene glycol.

A basic catalyst, such as anhydrous potassium carbonate, and soap, or a fatty acid salt, are added.

The solution must be heated and the pressure should be reduced to remove water and form a molten mixture.

[10] Sucrose esters of fatty acid (E 473) are used for surface treatment of some climacteric fruits such as peaches, pears, cherries, apples, bananas, etc.

European Parliament and Council Directive No 95/2/EC limited the use of sucrose esters under E 473 in each kind of food.

[18] Sucrose esters were approved and registered by European Food Safety Authority or EFSA under the E number of E 473.