The microstructure and gas retention of bread dough

Molecular structure and baking performance of individual glycolipid classes from lecithins

The potential of individual glycolipid classes from lecithins (soybean, rapeseed, and sunflower) in breadmaking was determined in comparison to classical surfactants such as diacetyltartaric acid esters of mono- and diacylglycerides (DATEM), monoacylglycerides, sodium stearoyl-2-lactylate (SSL), and two synthetic glycolipids by means of rheological and baking tests on a microscale. A highly glycolipid-enriched sample containing the entire glycolipid moiety of the lecithin was obtained using an optimized batch procedure with silica gel. This sample was subsequently used to gain individual glycolipid classes through column chromatography on silica gel. The major glycolipid classes in the lecithins, digalactosyl diacylglycerides (1), sterol glucosides (2), acylated sterol glucosides (3), and cerebrosides (4), were identified and characterized. All isolated glycolipid classes displayed excellent baking performance. A better baking activity than that of the classical surfactants was displayed by 1, 3, and 4 and an equivalent baking activity by 2. The same glycolipid classes, except 3, of different lecithin origin showed only slight differences in their baking activities, due to different fatty acid compositions. Furthermore, the glycolipid classes influenced the crumb structure significantly by improving the crumb softness and grain. Interestingly, none of the glycolipid classes showed significant antistaling effect. A direct effect on the overall rheological behavior of the dough was only found for the commercial surfactants. However, the rheological effect seen on gluten isolated from surfactant-containing dough revealed that the surfactants could be divided into two main groups, one of them directly forming and stabilizing liquid film lamellae through adsorption to interfaces and the other indirectly increasing the surface activity of the endogenous lipids in the flour. The results suggest that in wheat dough, glycolipids seem to have an impact on the dough liquor rather than on the gluten-starch matrix.

The identification of foam-forming soluble proteins from wheat (Triticum aestivum) dough

Proteomic methods have been used to identify foam-forming soluble proteins from dough that may play an important role in stabilising gas bubbles in dough, and hence influence the crumb structure of bread. Proteins from a soluble fraction of dough (dough liquor) or dough liquor foam have been separated by two-dimensional gel electrophoresis, and 42 identified using a combination of matrix-assisted laser desorption/ionization-time of flight and quadrupole-time of flight analyses. Major polypeptide components included beta-amylase, tritin and serpins, with members of the alpha-amylase/trypsin inhibitor family being particularly abundant. Neither prolamin seed storage proteins nor the surface-active protein puroindoline were found. Commonly used dough ingredients (NaCl, Na L-ascorbate) had only a minor effect on the 2-DE protein profiles of dough liquor, of which one of the more significant was the loss of 9 kDa nonspecific lipid transfer protein. Many proteins were lost in dough liquor foam, particularly tritin, whilst a number of alpha-amylase inhibitors were more dominant, suggesting that these are amongst the most strongly surface-active proteins in dough liquor. Such proteins may play a role determining the ability of the aqueous phase of doughs, as represented by dough liquor, to form an elastic interface lining the bubbles, and hence maintain their integrity during dough proving.

Australian wheat for the sponge and dough bread making process

This work investigates the suitability of Australian wheats for the sponge and dough bread market, and determines the wheat quality attributes most important for large loaf volume. A group of 30 genotypes was selected for quality testing and baking using a purpose-developed sponge and dough test baking method. Genotypes were grown at 2 sites in Queensland during winter of 2001 and 2002, and then grain from the field trials was tested in the laboratory. The traits measured included grain, flour, and dough quality, along with loaf volume as the main trait of interest. Glutenin alleles and Wx-B1 allele status of the genotypes were also determined. Genetic correlations were calculated between loaf volume and all the quality traits. The quality trait with the strongest relationship to loaf volume was flour swelling volume. Glutenin alleles and Wx-B1 alleles may also be important for sponge and dough bread quality but the data presented here were insufficient to draw strong conclusions. Consistent, large sponge and dough loaf volumes (>850 cm3) were achieved by the Batavia/Pelsart double haploids QT8753, QT10793, and QT10778. The wheat varieties Hartog and Kennedy also performed well. The work demonstrated that Australia can produce wheat suitable for this market.

Interaction of maize zein with wheat gluten in composite dough and bread as determined by confocal laser scanning microscopy

Protein body-free maize zein, when mixed at 35 degrees C (above its glass transition temperature range), significantly (p < 0.01) improved the rheological and leavening properties of sorghum-wheat composite flour dough, resulting in improved loaf volume. Confocal laser scanning microscopy was used to observe the structure of zein fibrils and the interaction between zein and gluten proteins in the composite dough and bread systems. Autofluorescence and immunolocalization techniques were used to locate gluten and zein, respectively. Optical sections were collected every 0.4 microm through the samples and digitally processed to produce reconstructed three-dimensional images. Results showed that zein fibrils form an outer layer that intermittently coats the gluten networks, thereby strengthening them. This type of microstructure is able to withstand the pressure exerted by gas cell expansion during yeast fermentation to increase loaf volume.

Lipid interactions in breadmaking

Both the natural lipids of flour and added fats are known to play an important role during the production of bread. In this review, the chemical and physical interactions of fat have been assessed in an attempt to explain these technological functions. Particular emphasis has been placed on the "binding" or complexing of lipid by flour proteins during the development of dough. While publications in this field have frequently been contradictory, evidence now indicates that observed lipid binding may involve lipid mesophase transformation and the nonspecific occlusion of lipid phases within the gluten network. The significance of these suggested events has been compared with current theories of lipid function in the breadmaking process.