Gluten key to improving baking performance.

Flour fractionation and reconstitution are processes that enable scientists to bake reconstituted flours into bread that is identical to product made from the parent flour. The techniques, together with a micro bread-making test, help researchers relate flour components to functional bread-making properties and assess their impact on the bread-making process.

German scientists have used the techniques to fractionate and reconstitute wheat flour. This approach has allowed them to investigate the contribution of flour fractions to baking performance and dough rheology.

The researchers used micro-scale rheological methods and a micro-scale baking test based on 10 grams of flour. Two wheat cultivars with different baking performances were studied. Fractionation involved defatting the flour by using dichloromethane, forming a dough and isolating gluten by washing the dough with distilled water in a glutomatic unit at 15 C. The investigators then collected the aqueous suspension and separated it into a soluble fraction and two starch fractions--an upper and lower layer--using centrifugation.

Reconstituting the flour gave reproducible results. The baking volumes of the reconstituted flours decreased by a factor of 0.95, and the respective doughs and glutens had higher resistances than the native flours. Mixing the reconstituted flour in the presence of reduced glutathione led to a decrease in dough resistance. But it was not possible to establish the native values.

An increase in the total protein content of the reconstituted flour was proportional to the baking volume. Increasing the amount of the soluble fraction led to more extensible, weaker doughs. Gliadin and glutenin had a weakening and a strengthening effect on the dough, respectively. Adding reoxidized high molecular weight (HMW) subunits of glutenin caused an increase in dough extensibility and resistance. With reoxidized low molecular weight (LMW) subunits of glutenin, only the dough resistance increased.

Micro-scale baking tests showed that HMW subunits increased the loaf volume significantly. The researchers observed the opposite effect for the LMW subunits. An interchange of fractions between the two wheat cultivars showed that gluten was most important for optimizing baking performance, followed by the starch and the soluble fractions.

Further information. Peter Koehler, German Research Institute for Food Chemistry, Lichtenbergstrasse 4, 85748 Garching, Germany; phone: [phone]; fax: [phone]; email: [e-mail].