09.12.2012 Views

Food Lipids: Chemistry, Nutrition, and Biotechnology

Food Lipids: Chemistry, Nutrition, and Biotechnology

Food Lipids: Chemistry, Nutrition, and Biotechnology

SHOW MORE
SHOW LESS

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

Figure 8 Structure of raffinose polyester.<br />

Metabolic studies in mice indicate that raffinose polyester is not hydrolyzed by<br />

intestinal lipases <strong>and</strong> is not absorbed (11). About 93–98% of the raffinose polyester<br />

fed to the mice was recovered unchanged from the feces. Thus, raffinose polyester<br />

can serve as an excellent zero-calorie fat substitute. Now that olestra has received<br />

FDA approval, more interest is expected on the possible use of raffinose polyester<br />

<strong>and</strong> others as alternative fat substitutes.<br />

5. Stachyose Polyester<br />

Stachyose, a nonreducing heterogeneous tetrasaccharide, is similar to raffinose <strong>and</strong><br />

sucrose except that stachyose contains galactose–galactose–glucose–fructose. There<br />

are 14 available OH groups for esterification with long chain fatty acids. Stachyose<br />

can be completely acetylated <strong>and</strong> used as the substrate for interesterification with<br />

FAME, catalyzed by Na metal as described for sucrose <strong>and</strong> raffinose acetates. The<br />

degree of substitution as determined by 13 C NMR spectroscopy was about 12 fatty<br />

acids per molecule of stachyose (12). The higher the degree of acetylation of the<br />

substrate, the lower the melting point, <strong>and</strong> the lower the temperature requirement for<br />

the interesterification. The only requirement is that the temperature be high enough<br />

to melt the Na catalyst (>98�C).<br />

The structure of stachyose polyester is given in Figure 9. It is conceivable that<br />

this molecule will be highly resistant to hydrolysis <strong>and</strong> absorption <strong>and</strong> able to serve<br />

as an excellent zero-calorie fat substitute. The drawback is the cost, since again<br />

sucrose is cheaper.<br />

D. Alkyl Glycoside Polyesters<br />

Alkyl glycosides are prepared by reacting the sugar (e.g., glucose) with a desired<br />

alcohol (methanol for methyl glucoside) in the presence of acid catalysts. This glycosylation<br />

is important to convert the reducing C-1 anomeric centers to nonreducing,<br />

less reactive anomeric centers. The alkyl glycosides become substrates for transesterification<br />

with FAME in the presence of potassium soap or sodium methoxide as<br />

catalysts. Alternatively, the remaining hydroxyl groups can be acetylated <strong>and</strong> used<br />

for the interesterification reaction catalyzed by Na metal as described for sucrose<br />

polyester, to produce alkyl glycoside fatty acid polyesters (12).<br />

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!