This section is from the book "Experimental Cookery From The Chemical And Physical Standpoint", by Belle Lowe. Also available from Amazon: Experimental cookery.
The percentage of fat in white flour is low, since most of the fat is found in the germ which is removed during milling. But though present in a small quantity, the lipoid content of flour is important. Some lipoid constituents improve, whereas others injure the baking quality of flour.
Working has reported that "The gluten of low grade flour increased in tenacity when the phosphatide was removed by washing. The addition of phosphatides to flour in small quantities injured the gluten as determined by the feel of the hand washed gluten, the viscosity as measured by the viscometer, and by baking tests." Working suggests that the effect of phosphatides on gluten is similar to that of oil on rope. Lubrication of the strands of the rope lessens its strength and tenacity.
In a later paper Working reported that a small amount of phosphatide, such as the normal amount present in a good patent flour, may improve the baking quality.
Sullivan, Near, and Foley report that it is well known that increasing percentages of wheat germ in flour harm the baking quality of the flour. They investigated the effect of fat from wheat germ and of each fat fraction and its hydrolytic products on normal sound patent flour as judged by gluten washing and baking tests as well as by the Farinograph and Fer-mentograph. Fat from the fresh germ was not found to be deleterious to the baking quality.
They say: "The only germ-fat constituents which were found to be injurious were the unsaturated fatty acids which develop upon aging due to hydrolysis of the triglycerides and, what is much more important, the subsequent oxidation products of these unsaturated acids.
"Higher saturated fatty acids (which may occur in small amounts in any wheat product as a result of hydrolysis of the triglycerides) have only a very slight 'shortening' effect on the flour-water curves. Unsaturated fatty acids (oleic, linolic, and linolenic) cause a decided change in the shape of the curves and produce 'short' tough glutens when added to patent flour. These unsaturated acids, however, are only slightly detrimental to the baking quality of a flour. The bake is not harmed as much as one would expect from the feeling of the gluten."
The effect of unsaturated fatty acids on flour is in direct correlation with their increasing number of double bonds. The oxidation products of these unsaturated fatty acids have a significant damaging effect on the baking quality of flour.
In addition, these investigators have shown that extracting fat from flour with ether injures the baking quality of both strong and weak flours. The addition of flour fat brought the quality of the ether-extracted flour back to normal but the addition of germ fat did not. They concluded that this indicated that flour fat contains some constituent or groups of compounds necessary for good baking quality of flour, which are absent in the germ lipoids.