Chemical and Functional Properties of Food Saccharides

© 2004 by CRC Press LLC
acted as an emulsifier to conduct the reaction in a microemulsion system with
potassium carbonate as the catalyst. 18 Reported yield is 85% for the sucrose
monoester and 15% for the diester after purification. Feuge et al. 19 developed a
solvent-free interesterification, which carried out the reaction between molten
sucrose (melting point 185°C) and fatty acid methyl esters at 170 to 187°C, with
lithium, potassium, and sodium soaps as catalysts and solubilizers. Lithium palmitate
produced mostly sucrose polyesters with DS > 3, and lower esters were best produced
with combinations of lithium oleate with sodium or potassium oleate at a level of
25% based on sucrose weight. Vegetable oil was a solvent as well as a fatty acid
source to carry out the reaction at 110 to 140°C with potassium carbonate as a
catalyst. 20 The product can be used without further purification. In both solvent and
solvent-free processes, distillation was often needed to remove the nonreacted reactants
and by-products. As the molar ratio of sucrose to fatty acid increased, the yield
of sucrose esters was higher than that of sucrose polyesters.
Inorganic carriers commonly used in biotransformation with immobilized
enzymes, such as Celite and disodium hydrogen phosphate, catalyze the sucrose
acylation with vinyl esters of fatty acids. 2-O-Lauroylsucrose is the principal product.
21 The chemical acylation of sucrose takes place with the preference decreasing
in the order of 6-OH ≥ 6'-OH ≥ 1'-OH > secondary-OH. However, under a generalbase
catalysis, the most acid 2-hydroxyl group of sucrose was activated for a more
nucleophilic alkoxide. A simple chemical reaction in dimethyl sulfoxide at 40°C
with disodium hydrogen phosphate as the catalyst for selective synthesis of sucrose
monolaurate was reported by the same group, with 60% conversion to monoester
and 30% to diester. 22
3.6 FATTY ACID POLYESTERS
Fatty acid polyesters of saccharides are nondigestible, nonabsorbable, fat-like molecules
with physical and chemical properties of conventional fats and oils. Olestra
(generic name) or Olean ® (brand name), a sucrose polyester (DS 4 to 8) is a mixture
of sucrose esters with six to eight fatty acids. 23 This polyester was approved by the
U.S. Food and Drug Administration (FDA) in 1996 for limited uses.
Also, sucrose polyesters are available by transesterification and interesterification.
Transesterification is a two-stage process. Potassium soaps provide a homogenous
melt of sucrose and fatty acid methyl esters (FAME). Then, at 130 to 150°C,
FAME and NaH are added in excess. The interesterification is a simple ester–ester
interchange reaction involving reaction of alkyl ester of sucrose with FAME in the
presence of sodium methoxide (NaOCH 3) or sodium or potassium metal as catalyst. 24
There are preferences for the sucrose ester formation when the molar ratio of sucrose
to fatty acid increases. Sucrose polyesters are the predominant derivatives when the
molar ratio of sucrose to fatty acid decreases. 24
Sorbitol 20 and other carbohydrates, including trehalose, 25 raffinose, 26 stachyose, 27
and alkyl glycoside, 27 have been esterified. Up to six hydroxyl groups in sorbitol
can be esterified (interesterification or transesterification). Trehalose, raffinose, and
stachyose are nonreducing saccharides with 2, 3, or 4 sugar units and consist of 8,
11, or 14 available OH groups for esterification, respectively. They can be esterified