The influence of varying levels of molecular oxygen on the functionality of azodicarbonamide and ascorbic acid during wheat bread making.

Air, and thus also molecular oxygen (O2), is incorporated in wheat flour dough during mixing. O2 participates in several (enzymatic) reactions, including those resulting in the oxidation of free sulfhydryl groups, thereby increasing dough strength and bread volume. We here incorporated different O2 levels in dough by mixing dough samples for a fixed time under different modified atmospheres which led to significant changes in dough free sulfhydryl contents and bread volumes. Although altering the mixing time not only impacted how much O2 was incorporated in dough but also the mechanical input, the changes in dough and bread properties when using different mixing times, largely depended on differences in O2 uptake. When used in bread recipes, redox agents such as azodicarbonamide (ADA) and ascorbic acid (AH2) impact the dough sulfhydryl contents and bread volumes. The effect of different levels of O2 incorporation on dough samples which contained ADA or AH2 was studied by altering the mixing time or the O2 content in the mixing atmosphere. Lower ADA levels were needed when dough was mixed under an atmosphere enriched in O2. As AH2 requires O2 to be converted to dehydroascorbic acid (DHA) to exert its improver effect, it came as a surprise that when it was included in a dough which was prepared under O2 enriched conditions, no additional impact was obtained and that, even under reduced O2 conditions, its use still resulted in an increased bread volume. These findings suggest that AH2 oxidase very effectively uses O2 to form DHA.

Amylose and amylopectin functionality during storage of bread prepared from flour of wheat containing unique starches.

Bread crumb firming is largely determined by the properties of gluten and starch, and the transformations they undergo during bread making and storage. Amylose (AM) and amylopectin (AP) functionality in fresh and stored bread was investigated with NMR relaxometry. Bread was prepared from flours containing normal and atypical starches, e.g., flour from wheat line 5-5, with or without the inclusion of Bacillus stearothermophilus α-amylase. Initial crumb firmness increased with higher levels of AM or shorter AM chains. Both less extended AM and gluten networks and too rigid AM networks led to low crumb resilience. AP retrogradation during storage increased when crumb contained more AP or longer AP branch chains. Shorter AP branch chains, which were present at higher levels in 5-5 than in regular bread, were less prone to retrogradation, thereby limiting gluten network dehydration due to gluten to starch moisture migration. Correspondingly, crumb firming in 5-5 bread was restricted.

Molecular dynamics of starch and water during bread making monitored with temperature-controlled time domain 1H NMR.

Time domain proton nuclear magnetic resonance (TD 1H NMR) was applied in a temperature-controlled mode to in situ study the timing and extent of starch transitions and water redistribution during bread making. Changes in proton population areas during initial baking (≤ 60 °C) were attributed to water absorption by starch and some initial amylose leaching. During subsequent heating (60-90 °C), proton population areas changed because of amylopectin crystal melting and amylose leaching. Granule swelling and amylose leaching increased the system's viscosity and thereby decreased the proton mobility. After crumb setting at about 65 °C, proton mobility increased with a temperature dependence according to Arrhenius' law. During cooling, amylose crystallization increased the portion of rigid protons and decreased the gel network's proton mobility. The uniqueness of this study is that differential scanning calorimetry, colorimetric and gravimetric analyses underpinned NMR data interpretation and the usefulness of the online method to study molecular dynamics during bread making.