Kneading the dough relaxes the long gliadin and glutenin molecules, breaking internal bonds
between individual atoms in each gliadin and glutenin molecule and allowing the molecules
to unfold and form new bonds between atoms in different molecules. The result is a network
structure made of a new gliadin-glutenin compound called gluten.
Gluten is very elastic. The gluten network can stretch to accommodate the gas (carbon
dioxide) formed when you add yeast to bread dough or heat a cake batter made with baking
powder or baking soda (sodium bicarbonate), trapping the gas and making the bread dough
or cake batter rise. When you bake the dough or batter, the gluten network hardens and the
bread or cake assumes its finished shape.
Starch reactions. Starch consists of molecules of the complex carbohydrates amylose and
amylopectin packed into a starch granule. When you heat flour in liquid, the starch gran-
ules absorb water molecules, swell, and soften. When the temperature of the liquid reaches
approximately 140°F the amylose and amylopectin molecules inside the granules relax and
unfold, breaking some of their internal bonds (bonds between atoms on the same molecule)
and forming new bonds between atoms on different molecules. The result is a network that
traps and holds water molecules. The starch granules then swell, thickening the liquid. If you
continue to heat the liquid (or stir it too vigorously), the network will begin to break down,
the liquid will leak out of the starch granules, and the sauce will separate.*
Combination reaction. Coating food with flour takes advantage of the starch reaction
(absorbing liquids) and the protein reaction (baking a hard, crisp protein crust).
How Other Kinds of Processing Affect This Food
Medical Uses and/or Benefits
A lower risk of some kinds of cancer. In 1998, scientists at Wayne State University in Detroit
conducted a meta-analysis of data from more than 30 well-designed animal studies mea-
suring the anti-cancer effects of wheat bran, the part of grain with highest amount of the
insoluble dietary fibers cellulose and lignin. They found a 32 percent reduction in the risk
of colon cancer among animals fed wheat bran; now they plan to conduct a similar meta-
analysis of human studies. Whole wheat flours are a good source of wheat bran. NOTE: The
amount of fiber per serving listed on a food package label shows the total amount of fiber
(insoluble and soluble).
Early in 1999, however, new data from the long-running Nurses Health Study at Brigham
Women’s Hospital/Harvard University School of Public Health showed that women who ate
a high-fiber diet had a risk of colon cancer similar to that of women who ate a low-fiber diet.
- Amylose is a long, unbranched, spiral molecule; amylopectin is a short, compact, branched molecule.
Amylose has more room for forming bonds to water. Wheat flours, which have a higher ratio of amy-
lose to amylopectin, are superior thickeners.
Flour