F. L. Stoddard

Survey of Starch Particle-Size Distribution in Wheat and Related Species

ABSTRACT The existence of a population of small (B-type) starch granules (<10 μm diameter) in addition to the major (A-type) granules presents a problem for starch-gluten manufacture and certain other wheat processes. A survey of starches in 761 accessions of cultivated wheats, ryes, and wild relatives was conducted. Starch was extracted from grains and analyzed for particle-size distribution by laser diffraction. Australian hexaploid wheat cultivars showed 23–50% of starch in B granules. Landraces from Asia extended this range down to 17%. Tetraploid wheats (Triticum turgidum) showed a similar range of 17–47%, and einkorn wheat (T. monococcum) ranges were 23–62%. The range for B-granule content in rye was only 20–40%, while that in triticale and T. tauschii went down to 15%. The results show that there are clear prospects for manipulating the starch particle-size distribution of cultivated wheats.

Basic Rheology of Bread Dough with Modified Protein Content and Glutenin-to-Gliadin Ratios

ABSTRACT The uniaxial elongational and shear rheology of doughs varying in either the protein content or glutenin-to-gliadin ratio were investigated. Increasing the protein content at constant glutenin-to-gliadin ratio increased the strain-hardening properties of the dough, as shown by increasing elongational rupture viscosity and rupture stress. Glutenin and gliadin had a more complex effect on the elongational properties of the dough. Increased levels of glutenin increased the rupture viscosity but lowered the rupture strain, while elevated gliadin levels lowered the rupture viscosity but increased the rupture strain. These observations provide rheological support for the widely inferred role of gliadin and glutenin in shaping bread dough rheology, namely that gliadin contributes the flow properties, and glutenin contributes the elastic or strength properties. The shear and elongational properties of the doughs were quite different, reflecting the dissimilar natures of these two types of flow. Increasin...

Effects of Incorporated Glutenins on Functional Properties of Wheat Dough

ABSTRACT The development of reduction-oxidation methods to open the native gluten polymer, incorporate monomers, and repolymerize the modified polymer, has allowed new types of investigation of the effects of glutenin subunits on dough characters. These methods were used to incorporate bulk high molecular weight glutenin subunits (HMW-GS) and bulk low molecular weight glutenin subunits (LMW-GS) from four cultivars into the parent flours to modify the HMW-GS-to-LMW-GS ratio. In addition, the glutenins from the four cultivars were added to a single base flour of differing glutenin subunit composition. Finally, HMW-GS 7, 8, 5, and 10 were incorporated singly and in pairs into two base flours. The mixing time, peak resistance, maximum resistance to extension, and loaf height increased with increases in HMW-GS-to-LMW-GS ratio. There was a decrease in resistance breakdown observed with increase in HMW-GS-to-LMW-GS ratio. The maximum resistance to extension slightly increased with increases in HMW-GS-to-LMW-GS r...

Effects of Gliadin Fractions on Functional Properties of Wheat Dough Depending on Molecular Size and Hydrophobicity

ABSTRACT The effects of α- + β-, γ-, ω- and total gliadins on mixing, extension baking, and techno-functional properties of doughs from hard and soft flours were measured using small-scale techniques. The addition of all gliadin fractions resulted in decreased mixing time, peak resistance, maximum resistance to extension, and loaf height, and in increased resistance breakdown and extensibility. The various gliadin fractions showed differences in functional properties, with γ-gliadin reducing the mixing time and maximum resistance to extension to the greatest extent, ω-gliadin contributing to the greatest reduction in loaf height, and α- + β-gliadins having the least effect on reducing loaf height. The effects of gliadin fractions on loaf height were correlated with molecular mass, and effects on mixing time, maximum resistance to extension, and extensibility were correlated with hydrophobicity.

Lupin Flours as Additives: Dough Mixing, Breadmaking, Emulsifying, and Foaming

ABSTRACT The nutritional quality of various food products could be improved by supplementation with grain legumes to increase protein content and to improve the balance of essential amino acids. The lupin grain is a good candidate for this role, given its yield potential in a range of climatic environments and soil types. To establish the practicality of extending the use of lupins as food additives, the functional properties of various species and cultivars of lupin were studied for their effect as additives to baked products and their ability to provide foaming and emulsifying properties. Of the two lupin species that are commonly cultivated commercially, Lupinus albus showed the greater potential as a bread additive; loaf height and structure were maintained when lupin flour was substituted for wheat flour at levels up to 5%. This level of substitution offered the advantage of reducing mixing time. The detrimental effects at higher substitution levels appeared to be associated with the nonprotein compo...

Variation in Grain Mass, Grain Nitrogen, and Starch B-Granule Content Within Wheat Heads

ABSTRACT Grain mass (mg) and grain nitrogen concentration (%) were determined in 3,278 individual grains from eight cultivars with reference to the position of the grain on the head (spikelet number and floret number). Selected grains were removed from certain heads at anthesis. Grain nitrogen content (mg) was determined as the product of grain nitrogen concentration and grain mass. Grain mass and starch B-granule content were determined in 3,030 grains from a further 12 cultivars with reference to grain position, and selected grains were removed from certain heads at anthesis. Grains from distal florets were always smaller and had lower B-granule contents, nitrogen contents, and nitrogen concentrations than those from the two proximal florets on each spikelet, which were not significantly different from each other. Grains in the basal two spikelets of the head were smaller with lower nitrogen contents and higher B-granule contents than those in most of the head. Their nitrogen concentration, however, did...

Effects of Nitrogen and Sulfur Fertilizer on Protein Composition, Mixing Requirements, and Dough Strength of Four Wheat Cultivars

ABSTRACT Two field trials using four New Zealand wheat cultivars were undertaken to observe the effects of nitrogen and sulfur fertilization on protein composition, mixing requirements, and dough strength and to compare the results with that observed with a single cultivar, Otane. The results confirmed that adequate sulfur fertilization was necessary to ensure lower dough mixing requirements. The existence of a nexus between mixing requirements and dough strength was confirmed and genotype has significant effects on it. Variation in the content of HMW-GS in the protein corresponded to changes in dough mixing requirement of Otane. Across the four cultivars, dough mixing requirements (mechanical dough development work input and mixograph development time) and dough strength (Extensigraph resistance to extension) depended on different aspects of protein composition. As the content of polymeric proteins increased, MDD work input increased, but mixograph development time decreased, while the effect on Rmax was...

Link Between Mixing Requirements and Dough Strength

ABSTRACT Industrial bakeries in Australia and New Zealand using the mechanical dough development (MDD) process have experienced undesirable increases in dough mixing requirements. This problem is an unwanted outcome of breeding programs that have endeavored to increase dough strength as a desirable characteristic. Research was undertaken to determine the nature of the link between dough strength and mixing requirements and its relevance to the MDD process across a wide range of wheat lines. Data from three similar trials of 20 wheat lines confirmed the existence of an apparently tight, positive correlation between mixing requirements and dough strength. Although a wide range in genotypes and environments was used, no significant outliers were found, despite the belief that the link between these quality attributes was breakable or at least flexible. This creates a dilemma, as it would be desirable to reduce work input (WI) for economic reasons but not at the expense of loaf quality, which could have a del...

Characterization of Starch in Aegilops Species

ABSTRACT Starch was extracted and cleaned from 99 accessions of 20 species of Aegilops and also from 200 accessions of hexaploid wheat. Amylose content was determined by iodine staining and absorbance at 535 and 620 nm. Particle-size distribution was determined by laser scattering. The amylose content of the Aegilops accessions did not exceed the extremes found in domesticated wheat. Aegilops species, on the whole, had a lower content of small particles than the hexaploid wheats. There was no correlation between amylose content and particle-size distribution. Some species of Aegilops may be useful sources of low-starch B-type granules for hexaploid wheat, if the trait can be transferred, but they are unlikely to contribute to further variation in amylose content.

Optimized Methods for Incorporating Glutenin Subunits into Wheat Dough for Extension and Baking Studies

ABSTRACT In order to study the functional properties of glutenin subunits added to a dough, they must be incorporated into the glutenin polymer. This requires partial reduction to open up the polymer, followed by oxidation to incorporate the added monomer into the polymer. Existing methods for incorporating glutenin subunits were suitable only for studies on mixing properties and needed to be modified for use in studies on extension and baking. A range of concentrations and of reaction times was therefore tested for both the reductant and the oxidant. In addition, mixing time as well as relaxation time before extension were varied. Extension curves and loaf heights were used to evaluate the treatments. Optimum conditions were developed that provided extension curves of normal dimensions but with altered shape. The conditions were reduction with 0.2 mg/mL of dithiothreitol (DTT) solution for 1 min followed by oxidation with 5 mg/mL of KIO3 solution, then mixing the dough to 70% of the peak dough developmen...