Wheat (Triticum aestivum L.) Flour Functionality in Sugar and Fat Rich Food Products

The functionalities of wheat (Triticum aestivum L.) gluten and starch vary with the food system in which flour is used. Understanding the transformations of these constituents during different production processes is necessary for improving end product quality. In the literature study of this doctoral work, a yeasted dough system rich in sugar and fat is compared with bread, cake and cookie systems based on the relative ratios of their main ingredients. This system provides a model for some sweet bread and waffle systems. When compared to the other mentioned food systems, the system studied has a relatively low volume of mobile phase consisting of water and sugar. In addition, its mobile phase is more concentrated than that of bread systems, but less concentrated than that of cake and cookie systems. The water level as well as the volume and the composition of the mobile phase are important when considering gluten and starch functionality in the abovementioned wheat based products.The general aim of the experimental part of this study was to investigate the transformations of wheat flour constituents during dough preparation, fermentation, baking and storage of the system and their impact on final product quality. First, a laboratory scale procedure for preparing waffle systems was designed. Then, the impact of gluten network development during dough making on product quality (i.e. dimensions and firmness) was studied by adding different gluten levels and altering the gluten quality by upfront flour heat treatment. Having a developed protein network allowed dough to retain gas during fermentation. During subsequent baking, dough pieces having such network expanded more and faster. However, the gluten network also contributed to shrinkage once the maximum diameter was reached during baking. The time at which shrinkage occurred probably depended on dough becoming gas continuous and/or starch gelatinization. In addition, it was shown by using redox agents that besides the formation of a developed gluten network during mixing, subsequent polymerization during baking also affects spread behavior and the diameter and firmness of the baked product. Study of the impact of the transient gluten network structure formation during dough mixing on subsequent cross-linking during baking showed that longer mixing times decrease both the rate and extent of gliadin incorporation in the glutenin polymer network. More in particular, the effects observed during baking could mostly be explained by a slower and therefore smaller loss of gliadins extractable in sodium dodecyl sulfate containing medium when longer mixing times were applied. In samples containing the dough strengthener sodium stearoyl lactylate (SSL) both the rate and extent of gluten polymerization during heating were lower than for control samples, regardless of the mixing time. We hypothesized that SSL interacts with gliadin proteins, limits participation of the latter in cross-linking reactions and thereby yields softer products. In addition, during baking, part of the SSL formed amylose inclusion complexes. Thus, besides changing the behavior of gluten proteins, SSL also affected starch characteristics. When combining SSL with maltogenic Bacillus stearothermophilus alfa-amylase (BStA) in a water-starch model system, SSL (partly) hindered and/or delayed starch hydrolysis by the amylase. In contrast, monoacylglycerols (MAG) did not affect the enzyme's activity. We here hypothesized that SSL covers the starch granule surface more effectively than MAG. This then would retard water uptake and delay starch gelatinization. As a consequence, starch hydrolysis by BStA was postponed. Combining BStA with either SSL or MAG yielded softer gels than when adding the enzyme alone. This indicated that the effect of the surfactants is more important than that of the amylase. Adding BStA or SSL to a wheat based model system containing fat but no invert syrup showed that retrogradation influences the evolution of product firmness during storage. Remarkably, when combining BStA with SSL, the enzyme did not impact the evolution of firmness during storage to the same extent than adding it alone did. This indicated that, much as in the starch model system, the effect of surfactants outweighs that of the enzyme. However, further investigation of the impact of structural differences in the network on product firmness seems necessary. Finally, when including invert syrup in the system s recipe, the (high) levels of SSL and/or BStA used had little if any impact on its dough and baking properties. The high sugar concentrations limited the effects of the improving agents.In conclusion, both gluten and starch impacted spread behavior during mixing and baking, and influenced the firmness (during storage) of yeasted dough systems containing high levels of sugar and fat. Altering molecular scale characteristics of the main constituents of wheat flour affected the macroscale dough making, dough, baking and final product properties. Evidently, the present results may provide a basis for reducing sugar and fat content in these systems. Furthermore, they also contribute to understanding flour functionality in similar wheat based food products.status: publishe