Cereal Chem. 80(5):587-595The rheological properties of dough and gluten are important for enduse quality of flour but there is a lack of knowledge of the relationships between fundamental and empirical tests and how they relate to flour composition and gluten quality. Dough and gluten from six breadmaking wheat qualities were subjected to a range of rheological tests. Fundamental (small-deformation) rheological characterizations (dynamic oscillatory shear and creep recovery) were performed on gluten to avoid the nonlinear influence of the starch component, whereas large deformation tests were conducted on both dough and gluten. A number of variables from the various curves were considered and subjected to a principal component analysis (PCA) to get an overview of relationships between the various variables. The first component represented variability in protein quality, associated with elasticity and tenacity in large deformation (large positive loadings for resistance to extension and initial slope of dough and gluten extension curves recorded by the SMS/Kieffer dough and gluten extensibility rig, and the tenacity and strain hardening index of dough measured by the Dobraszczyk/Roberts dough inflation system), the elastic character of the hydrated gluten proteins (large positive loading for elastic modulus [G], large negative loadings for tan d and steady state compliance [J e 0 ]), the presence of high molecular weight glutenin subunits (HMW-GS) 5+10 vs. 2+12, and a size distribution of glutenin polymers shifted toward the high-end range. The second principal component was associated with flour protein content. Certain rheological data were influenced by protein content in addition to protein quality (area under dough extension curves and dough inflation curves [W]). The approach made it possible to bridge the gap between fundamental rheological properties, empirical measurements of physical properties, protein composition, and size distribution. The interpretation of this study gave indications of the molecular basis for differences in breadmaking performance.
The ambient oxygen ingress rate method (AOIR) is an alternative method to OxTran for measuring the oxygen transmission rates (OTR) of whole packages. The objective of the present work was (a) to compare OTR values obtained by the two methods, and (b) to evaluate the use of the AOIR method for measuring OTR at realistic food storage temperatures and humidity levels. The AOIR method gave equal OTR values compared to the Ox-Tran method for the ®ve different types of whole packages used in the experiment, with OTR values in the range 0.06±1.48 ml O 2 /day. The repeatability of the AOIR method measured on an HDPE bottle was AE2.6% of the measured value in this experiment. This is slightly higher than the general speci®cations of the Ox-Tran method (1% of reading for packages). However, the AOIR method can be considered to be a reliable, precise and cheap alternative method to the Ox-Tran method for measuring OTR of whole packages. The capacity of the method is also high. The AOIR method showed satisfactory results when comparing OTR for packages tested under realistic food storage conditions covering 23°C/50% relative humidity (RH) and at 4°C/60% RH on the outside, combined with water (100% RH) or dry air inside the packages.
The effects of protein quality, protein content, ascorbic acid, diacetyl tartaric acid ester of monoglycerides (DATEM), and their interactions on dough rheology and hearth bread properties were studied by sizeexclusion fast protein liquid chromatography, Kieffer Dough & Gluten Extensibility Rig, and small-scale baking of hearth loaves. The effect of protein content was either positive or negative on hearth loaf characteristics, form ratio, and area, depending on the amount of the largest glutenin polymers in the flour. Ascorbic acid brought out the potential in the wheat flour known as protein quality. Ascorbic acid and DATEM strengthened the doughs and improved hearth bread characteristics.
The relationships between protein content and quality and the loaf characteristics of hearth breads made from the respective flours were investigated for 20 wheat genotypes, comprising both commercially grown cultivars and advanced breeding lines, grown in 1997 and 1998. In both years the average protein content was increased by increasing the level of nitrogenous fertiliser application, this effect being more pronounced in 1997 than in 1998. Grain samples were milled and evaluated for endosperm hardness, protein content, SDS sedimentation volume, mixing properties and baking quality determined by a hearth bread baking test using optimal mixing and fixed proving time. When producing hearth bread, both the form (height/width) ratio and loaf volume are critical external characteristics. Genotype differences, mainly due to differences in protein quality, were more important for both form ratio and loaf volume than differences in protein content. The dough development time of the Farinograph, operated at high speed (126 rev min −1 ), was the best indicator of heart bread baking quality, giving high positive correlations to both the volume (r = 0.89) and form ratio of the loaf (r = 0.90). Climatic differences between the two years, in particular temperature during ripening, also affected the quality parameters studied.
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