P. W. Gras

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...

The low-molecular-weight glutenin subunit proteins of primitive wheats. IV. Functional properties of products from individual genes

Abstract Three genes encoding the low-molecular-weight glutenin subunits (LMW-GSs), LMWG-E2 and LMWG-E4, from A-genome diploid wheat species, and LMW-16/10 from a D-genome diploid wheat, were expressed in bacteria. The respective proteins were produced on a relatively large scale and compared with respect to their effects on flour-processing properties such as dough mixing, extensibility and maximum resistance; these are important features in the end-use of wheat for producing food products. The LMWG-E2 and LMWG-E4 proteins caused significant increases in peak resistance and mixing time, compared to the control, when incorporated into dough preparations. The LMWG-16/10 protein was qualitatively less effective in producing these changes. All three proteins also conferred varying degrees of decrease in dough breakdown. LMWG-E2 and LMWG-E4 caused significant increases in dough extensibility, and decreases in maximum resistance, relative to the control. LMW-16/10 did not show a significant effect on extensibility but showed a significant decrease in maximum resistance. The refinement of relating specific features of the structure of the LMW-GS genes to the functional properties of their respective proteins is discussed.

Effects of Different Salts on Mixing and Extension Parameters on a Diverse Group of Wheat Cultivars Using 2-g Mixograph and Extensigraph Methods

ABSTRACT Cations of differing chaotropic capacities (LiCl, NaCl, and KCl) were used in small-scale mixing and extensigraph studies to assess functional changes in dough behavior of wheat cultivars varying in total protein content and HMW glutenin composition. Salt addition, regardless of cationic type, caused an increase in dough strength and stability. The smaller (hydrated) and least chaotrophic cations (Li+ 12% protein). In the absence of genotypic v...

Contribution of the Chemical Structure of Wheat Starch to Japanese Noodle Quality

Wheat starch has been completely digested with bacterial α-amylase, and the pattern of oligosaccharides obtained from this digestion varies with starches from different wheat varieties. Wheat varieties of good Japanese noodle-making quality (based on sensory testing) give relatively small amounts of oligosaccharides with a degree of polymerisation (DP) of 5 or greater, while varieties of poor noodle-making quality give much greater amounts of these larger oligosaccharides. There is a significant negative correlation between the amount of DP5 oligosaccharide and noodle eating quality. The correlation between the amount of this oligosaccharide and starch paste viscosity was much smaller. The size of the HPLC peak corresponding to this oligosaccharide may be used as a rapid method of screening for noodle-making quality. Because oligosaccharides of greater than DP4 should have at least one branch point, the results suggest that the structure of the amylopectin in starch of good noodle-making wheats has relatively few branch points close together. Amylose also appeared to be important for noodle quality. The optimum amylose content seemed to be about 22% for good quality noodles, with starch of higher or lower amylose content coming from flour of lower noodle-making quality. Factors other than amylose content must contribute to noodle quality, as some flours of relatively poor noodle quality also contained close to the optimum amount of amylose.

The Contributions To Mixing Properties of 1D HMW Glutenin Subunits Expressed in a Bacterial System

Strong correlative evidence indicates that specific subunits of the glutenin proteins are at least in part responsible for differences in dough properties (Payne, 1987). In particular, HMW subunits coded by the ID chromosome have been found to be strongly associated with dough strength. The evidence for these findings is based on correlative studies. Therefore, the individual roles of these subunits in dough properties needs to be clarified by direct measurement. In the past, direct testing of the effects of specific proteins on dough structure has been possible only when large amounts of protein have been available. Conventional laboratory mixing procedures require 10–250 g flour and the isolation of purified proteins sufficient for testing on this scale is very difficult and expensive.

Application of a micro Z-arm mixer to characterize mixing properties and water absorption of wheat flour

ABSTRACT This study applied the use of a new small-scale apparatus, the micro Z-arm mixer, which has analogous mixing action to that of the traditional valorigraf and farinograph. A novel methodology has been developed for prediction of water absorption replacing the traditional titration method. The basis of this technique is a common characteristic of wheat flour samples: a reasonably constant slope (20–25.7 BU%) of the relationship between dough resistance and the amount of water present during mixing. Using an average slope value, prediction of water absorption was possible from a single measurement using a simple equation and with a standard error of 1.65%. Applications of the new mixer to cereal research are highlighted, including investigation of the effects of flour protein content and protein composition on mixing properties and water absorption. When protein content and protein composition have been systematically altered by the addition of isolated proteins into the flour, both dough developmen...

Mixing Properties, Baking Potential, and Functionality Changes in Storage Proteins During Dough Development of Triticale-Wheat Flour Blends

ABSTRACT Flours from advanced lines or cultivars of six triticales and two prime hard wheats, along with triticale-wheat blends, were investigated for mixing, extension (excluding blends), and baking properties using microscale testing. Percentage total polymeric protein (PPP) and percentage unextractable polymeric protein (UPP) of flours and doughs, including blends, mixed to optimal dough development were estimated using size-exclusion HPLC to determine the changes in protein solubility and association with blend composition (BC), mixing properties, and loaf height. Each triticale was blended with flours of each of the two wheat cultivars (Hartog and Sunco) at 0, 30, 40, 50, 60, 70, and 100% of wheat flour. Nonlinear relationships between BC and mixograph parameters (mixing time [MT], bandwidth at peak resistance [BWPR], and resistance breakdown [RBD]) were observed. A linear relationship between BC and peak resistance (PR) was predominant. PPP of triticale flours was mostly higher than PPP of wheat cul...

A quantitative study of the influences of temperature, water activity and storage atmosphere on the yellowing of milled rice

Rates of yellowing were determined for two Australian rice cultivars. The rates, k , were well described by the model k = α e β / T ( a w ) γ [ O 2 ] δ , where a w is the water activity, T is the absolute temperature and α, β, γ and δ are constants. The influences of temperature and water activity were predominant. Carbon dioxide concentration had no significant effect. The actions of temperature and oxygen concentration were independent of variety, but that of water activity showed a small varietal dependence. The results are consistent with non-enzymic browning as the mechanism of yellowing. The model predicts a discernible increase in yellowness (0·3 Hunterlab ‘b’ units) in as little as 42 days storage under typical tropical conditions (30 °C, 70% r.h. air) and may help to explain the occurrence of individually yellowed grains in poorly dried or stored rice. Rates of yellowing calculated from the model were consistent with the very limited data already published, and can be used to define the storage environment and time required to produce a particular yellowness for markets preferring aged rice.

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...

A quantitative study of the influence of temperature, water activity and storage atmosphere on the yellowing of paddy endosperm

Rates of yellowing of paddy (rough rice) stored under controlled conditions of temperature, water activity and atmospheric composition, were determined for the Australian cultivar Pelde. The influences of temperature and water activity ( a w ) on the rates of endosperm yellowing were dominant, O 2 tension had a slight effect and CO 2 concentration had no significant effect. The yellowing rates were similar to those of milled Pelde and Calrose, and were well described by the kinetic model reported previously for milled rice. Rate data for paddy were pooled with correponding data for milled rice to produce a model with common coefficients (apparent activation energy 103 MJ/kg mol). There was no need to invoke fungal growth to explain the yellowing observed. Recently presented data for various paddy cultivars stored at 60 °C were consistent with rates of yellowing calculated from this model for a w up to 0·8, but not above. The model appears to provide a general method for predicting yellowing in paddy and milled rice under conditions typical of grain storage in the humid tropics. The effects of altered O 2 and CO 2 concentrations were sufficiently small as to be unlikely to justify commercial use of controlled atmospheres specifically to retard yellowing of the type studied here.