Using Corn Zein to Improve the Quality of Gluten-Free Bread
Cereals are the most highly produced crops in the world and their storage proteins account for up to 50% of the total protein necessary for the nutrition of humans. As the number of people with celiac disease grows and diagnosis of the disease is improved, the development of high quality gluten-free foods is very important. Zein, the prolamin of maize (Zea mays L.) is used in this study in combination with starches to replace some of the functionality of wheat gluten. Zein can be made viscoelastic when it is freed and separated from protein bodies, and when it is moistened above its glass transition temperature and shear is applied. This is due to the fact that, during the mixing of the dough, zein fibers are produced that have some similarity in appearance to wheat glutenin fibers. The objective of this study was to use corn zein, as a viscoelastic protein, to make better quality gluten-free bread; i.e., to add chewiness and cohesiveness to the bread crumb, and to maintain integrity when sliced and used in a sandwich containing high moisture components. The general study design centered around variations of three different types of breads made each in four replicates: wheat as the control, gluten-free without zein, and gluten-free with zein. The ingredients, except yeast, were weighed and moistened, and placed in closed containers and kept overnight in a 35 °C temperature-controlled room, which is above the glass transition temperature of the zein (28°C). Different percentages of corn zein were used (4%, 6%, 8% and 10%). Also, different formulations were used by removing the sodium caseinate or by using whey protein and water instead of milk and eggs to understand how zein acts related to the quality of the breads (Tables 4 and 5). A Texture Analyzer was used to determine textural parameters of the bread crumb structure (hardness, gumminess, springiness and chewiness) after baking and cooling of the breads and also after exposure to moisture (by placing a moistened cotton round between two slices of bread). Overall, the addition of zein to gluten-free bread formulations trended to a firmer bread, though was not matched to the control wheat bread. The addition of 4% and 6% zein to the dough formulation gave breads with hardness close to the hardness of wheat bread. Gluten-free bread without zein, as well as gluten-free with 8% and 10% zein, were less hard than wheat bread. Gluten-free breads were less chewy than wheat bread. Among the gluten-free breads (with or without zein), the ones with 4% and 6% zein were chewier but the difference was not significant. When a moistened cotton round (15 ml of water added) was placed between two slices of bread and kept there for 10 minutes, the wheat bread was firmer than the gluten-free bread with zein which was firmer than the gluten-free without zein. The study findings suggest that corn zein somewhat ameliorates the quality of gluten-free bread when the conditions are met to make the zeins participate to form a viscoelastic network in the dough and bread structure.
Hamaker, Purdue University.
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