Edith Wilderjans

Wheat Gluten Functionality as a Quality Determinant in Cereal-Based Food Products

The unique properties of wheat reside primarily in its gluten-forming storage proteins. Their intrinsic viscoelastic behavior is responsible for the characteristics of different wheat-based foods and for the use of wheat gluten proteins in different food products. Wheat-based food processing generally develops and sets the gluten protein network. Heat-induced gluten aggregation proceeds through cross-linking within and between its protein fractions. Prominent reactions include sulfhydryl (SH) oxidation and SH-disulfide (SS) interchange, which lead to SS cross-links. Other covalent bonds are also formed. Gluten functionality can be (bio-) chemically impacted. We focus on bread making, in which gluten proteins contribute to dough properties, bread loaf volume, and structure, and on pasta production, in which gluten proteins generate the desired cooking quality. Furthermore, it is speculated that the structure and texture of soft wheat products are also, at least to some degree, shaped by the heat-induced changes in the gluten protein fraction.

The role of gluten in a pound cake system: A model approach based on gluten-starch blends.

In order to evaluate the role of gluten in cake-making, gluten-starch (GS) blends with different ratios of gluten to starch were tested in a research pound cake formula. The viscosities of batters made from commercial GS blends in the otherwise standardised formula increased with their gluten content. High viscosities during heating provide the batters with the capacity to retain expanding air nuclei, and thereby led to desired product volumes. In line with the above, increasing gluten levels in the cake recipes led to a more extended oven spring period. Cakes with a starch content exceeding 92.5% in the GS blend suffered from substantial collapse during cooling. They had a coarse crumb with a solid gummy layer at the bottom. Image analysis showed statistical differences in numbers of cells per cm(2), cell to total area ratio and mean cell area (p<0.05). Both density and mean cell area were related to gluten level. Moreover, mean cell area and cell to total area ratio were the highest for cakes with the lowest density and highest gluten levels. Relative sodium dodecyl sulfate (SDS, 2.0%) buffer (pH 6.8) extractabilities of protein from cakes baked with the different GS blends decreased with gluten content and were strongly correlated with the intensity of collapse. Taken together, the results teach that protein gives the cakes resistance to collapse, resulting in desirable volumes and an optimal grain structure with uniform cell distribution.

Fate of Starch in Food Processing: From Raw Materials to Final Food Products

Starch, an essential component of an equilibrated diet, is present in cereals such as common and durum wheat, maize, rice, and rye, in roots and tubers such as potato and cassava, and in legumes such as peas. During food processing, starch mainly undergoes nonchemical transformations. Here, we focus on the occurrence of starch in food raw materials, its composition and properties, and its transformations from raw material to final products. We therefore describe a number of predominant food processes and identify research needs. Nonchemical transformations that are dealt with include physical damage to starch, gelatinization, amylose-lipid complex formation, amylose crystallization, and amylopectin retrogradation. A main focus is on wheat-based processes. (Bio)chemical modifications of starch by amylolytic enzymes are dealt with only in the context of understanding the starch component in bread making.

Importance of Gluten and Starch for Structural and Textural Properties of Crumb from Fresh and Stored Bread

Bread crumb cellular structure and elasticity were monitored during aging and their relation to the main flour constituents, gluten and starch, was studied. The linear relation between the time-dependent slope of the linear part of the force-deformation curve, obtained in a static compressive test, and the shear modulus, obtained in quasi-static shear wave measurements, allowed calculating the Poisson’s ratio of bread crumb. This ratio and, thus, cell geometry remain unaffected during bread storage. While the elastic modulus of bread crumb strongly increased upon storage, image analysis and ultrasonic inspection, interpreted in the framework of the Biot-Allard model for porous structures, further confirmed that its cellular structure parameters did not change. Changing gluten properties in dough by means of redox agents had a profound impact on bread crumb density and its foam structure without affecting the rheological properties of the crumb cell walls. In agreement with the theory for cellular solids with open cells, bread with a lower density and a uniform crumb structure initially had a lower elastic modulus, which was maintained during aging, while bread with a higher density showed the opposite. Inclusion of an antifirming maltogenic exo-amylase in the recipe altered neither bread density, nor its macroscopic cellular structure parameters, but strongly affected the impact of storage on crumb texture. It was concluded that, without affecting starch properties or moisture content, the bread density, which is inter alia related to gluten properties, is a major determinant of bread crumb structure and texture during storage. In breads with a similar density and crumb foam structure, the evolution of crumb modulus during storage is determined by the changes in starch.

Low resolution 1H NMR assignment of proton populations in pound cake and its polymeric ingredients.

Based on a model system approach, five different proton populations were distinguished in pound cake crumb using one dimensional low resolution (1)H NMR spectroscopy. In free induction decay (FID) measurements, proton populations were assigned to (i) non-exchanging CH protons of crystalline starch, proteins and crystalline fat and (ii) non-exchanging CH protons of amorphous starch and gluten, which are in little contact with water. In Carr-Purcell-Meiboom-Gill (CPMG) measurements, three proton populations were distinguished. The CPMG population with the lowest mobility and the FID population with the highest mobility represent the same proton population. The two CPMG proton populations with the highest mobility were assigned to exchanging protons (i.e., protons of water, starch, gluten, egg proteins and sugar) and protons of lipids (i.e., protons of egg yolk lipids and amorphous lipid fraction of margarine) respectively. Based on their spin-lattice relaxation times (T1), two dimensional (1)H NMR spectroscopy further resolved the two proton populations with the highest mobility into three and two proton populations, respectively.

Relative importance of moisture migration and amylopectin retrogradation for pound cake crumb firming

Moisture migration largely impacts cake crumb firmness during storage at ambient temperature. To study the importance of phenomena other than crumb to crust moisture migration and to exclude moisture and temperature gradients during baking, crustless cakes were baked using an electrical resistance oven (ERO). Cake crumb firming was evaluated by texture analysis. First, ERO cakes with properties similar to those baked conventionally were produced. Cake batter moisture content (MC) was adjusted to ensure complete starch gelatinisation in the baking process. In cakes baked conventionally, most of the increase in crumb firmness during storage was caused by moisture migration. Proton nuclear magnetic resonance ((1)H NMR) showed that the population containing protons of crystalline starch grew during cake storage. These and differential scanning calorimetry (DSC) data pointed to only limited amylopectin retrogradation. The limited increase in amylopectin retrogradation during cake storage cannot solely account for the significant firming of ERO cakes and, hence, other phenomena are involved in cake firming.

A 1H Nucear Magnetic Resonance Study of the Changes Occurring During Pound Cake Storage

During storage at ambient temperatures, cake crumb gradually firms. This can partly be ascribed to water migration from crumb to crust. Such moisture migration and water incorporation in starch crystals can be monitored with 1 dimensional 1H NMR. In previous work using model systems, we successfully assigned 1H NMR peaks to different components present in cake batter and produced a complex fingerprint with four different peaks. In this study, cake crumb samples were withdrawn at different time intervals during storage and water migration was monitored with 2 dimensional 1H NMR. This enabled us to further differentiate the two most mobile peaks from the 1 dimensional profile into respectively two and three different peaks. During cake storage, spin spin as well as spin lattice relaxation times decreased for peaks containing exchangeing protons (i.e. protons of water, starch, gluten, egg proteins and sugar). Strong negative correlations were found between the relaxation times (measured with 2 dimensional 1H NMR) and crumb firmness (measured with texture analysis) and amylopectin melting enthalpy (measured with differential scanning calorimetry). We found 2 dimensional 1H NMR to be useful for studying cake ageing.