Sucrose esters

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Sucrose esters or sucrose fatty acid esters are a group of surfactants chemically synthesized from esterification of sucrose and fatty acids (or glycerides). This group of substances is remarkable for the wide range of hydrophilic-lipophilic balance (HLB) that it covers. The polar sucrose moiety serves as a hydrophilic end of the molecule, while the long fatty acid chain serves as a lipophilic end of the molecule. Due to this amphipathic property, sucrose esters act as emulsifiers; i.e., they have the ability to bind both water and oil simultaneously. Depending on the HLB value, some can be used as water-in-oil emulsifiers, and some as oil-in-water emulsifiers. Sucrose esters are used in cosmetics, food preservatives, food additives, and other products. A class of sucrose esters with highly substituted hydroxyl groups, olestra, is also used as a fat replacer in food.[1]

History[edit]

Sucrose esters were first mentioned in 1880 by Herzfeld who described the preparation of sucrose octaacetate. The substance is still in use today as a food additive.[2] In 1921, Hess and Messner synthesized sucrose octapalmitate and sucrose octastearate. Both are sucrose fatty acid esters.

Rosenthal, in 1924, synthesized highly substituted sucrose fatty acid esters using the classical condensation reaction between sucrose and the acid chloride of the drying oil fatty acid; pyridine was used as a solvent. Rheineck, Rabin, and Long followed the same procedure using alternative polyhydroxyl molecules such as mannitol. These condensation gave low yields, and the products, which were dark in color, needed extensive purification. Moreover, pyridine is a toxic solvent, so the synthesis was not commercially successful.

In 1939, Cantor, who patented a production route of sucrose fatty acid esters from starch factory by-products, claimed that the products could be used as emulsifying agents or fats. The classical esterification was used with a mixture of pyridine and either chloroform or carbontetrachloride as a solvent.

Later, the concept of synthesizing sucrose ester from sucrose and fatty acids was patented in 1952. 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. Many processes are still used in commercial production today.[3]

Structure[edit]

Sucrose is a disaccharide formed from condensation of glucose and fructose to produce α-D-glucopyranosyl-(1→2)-β-D-fructofuranoside. Sucrose has 8 hydroxyl groups which can be reacted with fatty acid esters to produce sucrose esters. Among the 8 hydroxyl groups on sucrose, three (C6, C1', and C6') are primary while the others (C2, C3, C4, C3', and C4') are secondary. (The numbers 1-6 indicate the position of the carbons on glucose while the numbers 1'-6' indicate the position of the carbons on fructose.) 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. Typical saturated fatty acids that are used to produce sucrose esters are lauric acid, myristic acid, palmitic acid, stearic acid and behenic acid, and typical unsaturated fatty acids are oleic acid and erusic acid.[1]

Sucrose with labelled number.tif

Chemical properties[edit]

Emulsification[edit]

Due to the hydrophilic property of sucrose and the lipophilic property of fatty acids, the overall hydrophilicity of sucrose esters can be tuned by the number of hydroxyl groups that are reacted with fatty acids and the identity of the fatty acids. The fewer free hydroxyl groups and the more lipophilic fatty acids, the less hydrophilic the resulting sucrose ester becomes. Sucrose esters' HLB values can range from 1-16. Low HLB (3.5-6.0) sucrose esters act as a water-in-oil emulsifier while high HLB (8-18) sucrose esters act as an oil-in-water emulsifier.[1]

Physical properties[edit]

Sucrose esters are off-white powders. Though produced from sucrose, sucrose esters do not have a sweet taste, but are bland or bitter.

Thermal stability[edit]

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. Sucrose esters can be heated to 185 °C without losing their functionality. However, the color of the product might change due to caramelization of sucrose.[1]

pH stability[edit]

Sucrose esters are stable in the pH range of 4 to 8, so they can be used as an additive in most foods. At pH higher than 8, saponification (hydrolysis of the ester bond to release the original sucrose and the salt of fatty acids) might occur. Hydrolysis could also occur at pH lower than 4.[1]

Production[edit]

Sucrose esters are mainly manufactured by using interesterification, the transfer of fatty acid from one ester to another. In this case, it means that the fatty acids used for the synthesis of sucrose esters are themselves in the esterified form. There are three processes that have been developed.[1]

Solvent process[edit]

The process involves transesterification of sucrose and triglycerides under a basic condition at 90 °C. DMF was used as a solvent at first, but was later substituted with dimethyl sulfoxide or DMSO, which is less hazardous and cheaper. This process produces a mixture of sucrose monoesters and more substituted esters at about a 5:1 ratio.[4]

Sucrose ester synthesis using triglycerides.tif

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.

Sucrose ester synthesis.tif

The process does not work for food industry because DMF is poisonous and may not be used in food production.

Emulsion process[edit]

The concept of microemulsion is applied in this process. 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 reaction is carried out at 130-135 °C. Propylene glycol is removed through distillation under vacuum at above 120 °C. The purified product is achieved by filtration. The yield of the reaction is 96%. 85% of sucrose esters is monosubstituted and 15% is disubstituted.[5]

Melt process[edit]

Molten sucrose is used instead of solvent. The reaction involves molten sucrose and fatty acid ester (methyl ester or triglyceride) with a basic catalyst, potassium carbonate or potassium soap. The high temperature (170-190 °C) is required for this process.[6] Since the process is carried out at a high temperature, sucrose can be degraded.

Later, a new synthesis pathway was introduced. First, sucrose and fatty acid soap are dissolved in water. Then, fatty acid ester and a basic catalyst are added to the solution. The solution must be heated and the pressure should be reduced to remove water and form a molten mixture. The transesterification is carried in the temperature range of 110-175 °C.[7]

Uses[edit]

Cosmetics[edit]

Some sucrose esters, such as sucrose distearate, sucrose dilaurate, sucrose palmitate, etc. are added in cosmetics products as an emulsifier. Some have a function in skin conditioning and emollient.[8] Cosmetics products that might have sucrose esters as an ingredient includes eyelash products, hair treatments, oil gels, skin products and deodorants.[4]

Fruit preservation[edit]

Sucrose of fatty acid esters (E 473) is used for surface treatment of some climacteric fruits such as peaches, pears, cherries, apples, bananas, etc. The coating preserves the fruits by blocking respiratory gases.[9]

Pharmaceuticals[edit]

Due to its surface property, sucrose esters are used in pharmaceutical research as a stabilizer or a surfactant on vesicles for drug delivery systems.[10]

Foods[edit]

Sucrose esters are used as food additives in a variety of food. European Parliament and Council Directive No 95/2/EC limited the use of sucrose esters under E 473 in each kind of food.[11]

Foodstuff Maximum level
Canned liquid coffee 1 g/L
Heat-treated meat products 5 g/kg (on fat)
Fat emulsions for baking purposes 10 g/kg
Fine bakery wares 10 g/kg
Beverage whiteners 20 g/kg
Edible ice 5 g/kg
Sugar confectionery 5 g/kg
Desserts 5 g/kg
Sauces 10 g/l
Soups and broths 2 g/l
Fresh fruits, surface treatment quantum satis
Non-alcoholic aniseed-based drinks 5 g/l
Non-alcoholic coconut and almond drinks 5 g/l
Spirituous beverages (excluding wine and beer) 5 g/l
Powders for the preparation of hot beverages 10 g/l
Dairy-based drinks 5 g/l
Dietary food supplements quantum satis
Dietetic foods intended for special medical purposes;

Dietetic formulae for weight con- trol intended to replace

total daily food intake or an individual meal

5 g/kg
Chewing gum 10 g/kg
Cream analogues 5 g/kg
Sterilised cream and sterilised cream with reduced fat content 5 g/kg

Legal status[edit]

Japan was the first country that allowed the use of sucrose esters as food additives. The Japanese Ministry of Health and Welfare approved sucrose esters in 1959. Then, in 1969, FAO/WHO approved the use of sucrose esters.[12]

Sucrose esters were approved and registered by European Food Safety Authority or EFSA under the E number of E 473.[13]

In the US, sucrose esters were approved by the FDA (Food and Drug Administration).[14][15]

References[edit]

  1. ^ a b c d e f Nelen, Bianca A. P.; Cooper, Julian M. (2004). Whitehurst, Robert J., ed. Emulsifiers in Food Technology. Blackwell Publishing Ltd. pp. 131–161. doi:10.1002/9780470995747.ch6. ISBN 9780470995747.
  2. ^ Pubchem. "SUCROSE OCTAACETATE". pubchem.ncbi.nlm.nih.gov. Retrieved 2017-10-19.
  3. ^ Akoh, Casimir C. (1994-04-19). Carbohydrate Polyesters as Fat Substitutes. CRC Press. ISBN 9780824790622.
  4. ^ a b Plat, Tülay; Linhardt, Robert J. (2001-10-01). "Syntheses and applications of sucrose-based esters". Journal of Surfactants and Detergents. 4 (4): 415–421. doi:10.1007/s11743-001-0196-y. ISSN 1097-3958.
  5. ^ Osipow, Lloyd I.; Rosenblatt, William (1967-05-01). "Micro-emulsion process for the preparation of sucrose esters". Journal of the American Oil Chemists' Society. 44 (5): 307–309. doi:10.1007/BF02635621. ISSN 0003-021X.
  6. ^ Holmberg, Krister (2003-07-03). Novel Surfactants: Preparation Applications And Biodegradability, Second Edition, Revised And Expanded. CRC Press. ISBN 9780203911730.
  7. ^ Yamagishi, F. (Feb 12, 1974). "PROCESS FOR SYNTHESIZING SUCROSE ESTERS OF FATTY ACIDS". United States Patent Office.
  8. ^ "amending Decision 96/335/EC establishing an inventory and a common nomenclature of ingredients employed in cosmetic products". Official Journal of the European Union. Feb 9, 2006.
  9. ^ EFSA Panel on Food additives and Nutrient Sources added to Food (ANS) (2012-05-01). "Scientific Opinion on the exposure assessment of sucrose esters of fatty acids (E 473) from its use as food additive". EFSA Journal. 10 (5): n/a. doi:10.2903/j.efsa.2012.2658. ISSN 1831-4732.
  10. ^ Szűts, Angéla; Szabó-Révész, Piroska (2012-08-20). "Sucrose esters as natural surfactants in drug delivery systems—A mini-review". International Journal of Pharmaceutics. 433 (1): 1–9. doi:10.1016/j.ijpharm.2012.04.076. PMID 22575672.
  11. ^ "EUROPEAN PARLIAMENT AND COUNCIL DIRECTIVE No 95/2/EC of 20 February 1995 on food additives other than colours and sweeteners" (PDF). European Parliament and Council Directive. Feb 20, 1995.
  12. ^ Shurtleff, William; Aoyagi, Akiko (2014-02-19). History of Soybeans and Soyfoods in Japan, and in Japanese Cookbooks and Restaurants outside Japan (701 CE to 2014). Soyinfo Center. ISBN 9781928914655.
  13. ^ Agency, Food Standards. "Current EU approved additives and their E Numbers | Food Standards Agency". www.food.gov.uk. Retrieved 2017-10-26.
  14. ^ "CFR - Code of Federal Regulations Title 21". www.accessdata.fda.gov. Retrieved 2017-10-26.
  15. ^ Nutrition, Center for Food Safety and Applied. "Food Additives & Ingredients - Food Additive Status List". www.fda.gov. Retrieved 2017-10-26.