The proportions of cornstarch, cassava starch, and rice flour were optimized for production of glutenfree bread (with 0% and 0.5% soy flour) to maximize specific volume (Y 1 ,Y 1 '), crumb-grain score (Y 2 ,Y 2 '), and bread score (Y 3 ,Y 3 '). A central composite design involving cornstarch/cassava starch ratio (X 1 ) and rice flour/cassava starch ratio (X 2 ) was used, and 2 nd -order models for Y i and Y i ' were employed to generate response surfaces. The maxima of response surfaces for crumb-grain score and bread score indicate that optimal gluten-free bread can be prepared from 74.2% cornstarch, 17.2% rice flour, and 8.6% cassava starch. Addition of soy flour at the 0.5% level also improved bread texture.

The objective of the present work was to study the effect of bread storage temperature on starch retrogradation, using water activity measurement and X-ray diffractometry technique to analyse the changes produced in the crumb firmness such as recrystallization. When storing bread with crust, the crust tends to trap moisture from the crumb, resulting in a dehydration of the crumb with faster staling. For storage temperatures of 25 and 48C, water activity decreases as a function of storage time whereas at À188C it is maintained at an almost constant level for 23 days. During storage, the starch molecules are reassociated and generate a new crystalline order which has a typical XRD pattern: the B-type structure. The peak at 17.48 is indicative of this structure and is related to bread aging. As observed with the recrystallization kinetics, at À188C only crystal growth may occur, whereas at 25 and 48C there would be not only growth but also formation of new crystals. At 48C the rate of starch retrogradation is the highest for the studied conditions.

The objective of the present work was to analyze molecular and supramolecular changes of bread starch and to relate bread firmness increase during storage with starch recrystallization and water hydration levels and migration in gluten-free bread. At the studied conditions starch was in the supercooled region of the state diagram, at a temperature between T g (glass transition temperature) and T m (melting temperature), feasible to crystallize. The crystalline degree during storage was followed by the intensity increase in the X-ray diffraction peaks. During bread storage, water migration occurred from the crumb towards the crust. Water amount and redistribution affected the kind of starch crystallites formed and firmness of aged bread. It was not the total amount of crystalline fraction that determined bread firmness, but the type of crystallites formed. These observations are a further evidence that bread firmness development and starch recrystallization, although being related phenomena, are obviously separate events.

The percentages of soy flour (X1) and dry milk (X2) were varied for the production of gluten-free bread to optimize batter softness (Y1), specific volume (Y2), crumb grain score (Y3), bread score (Y4) and bread protein content (Y5). A central composite design was used and second-order models for Y1 were employed to generate response surfaces. When bread protein content was decreased from 10 to 3%, specific volume increased from 3.2 to 4.6 cm3/g and bread score increased too. Nevertheless, the highest crumb grain score was obtained at 7.3% of bread protein content. The results demonstrated that a gluten-free bread can be prepared by adding 7.5% soy flour and 7.8% dry milk to a previously developed formulation, increasing its protein content from 1 to 7.3% and modifying in a small degree, its sensory quality.

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