J. A. Bietz

High-performance capillary electrophoresis of cereal proteins

Cereal grains are widely used of human foods and animal feed throughout the world. Cereals provide dietary protein, which also often has a functional role, as wheat gluten does in bread. Cereal proteins are unique in many ways: they are highly complex and heterogeneous, are often difficult to extract, and aggregate readily, making them difficult to characterize. Because of the economic importance and widespread use of cereal proteins, however, many techniques have been used for their analysis. High-performance capillary electrophoresis (HPCE) is one of the newest techniques to be so used. This review describes the development of charge- and size-based HPCE methods for analysis of cereal grain proteins, and the use of these methods for cultivar identification, classification, and prediction of quality. HPCE is versatile, rapid, easily automated, readily quantified, and provides high-resolution separations. Clearly, HPCE is a valuable addition to other methods of cereal protein analysis and should, in time, be applicable to all protein classes from all cereals.

Protein Distributions Among Hard Red Winter Wheat Varieties as Related to Environment and Baking Quality

ABSTRACT Previous size-exclusion high-performance liquid chromatography (SEHPLC) studies of hard red spring (HRS) wheat proteins reported correlations of amounts of certain gliadin and glutenin fractions with general score, a quality descriptor based on loaf volume, mixing time, and other parameters. We now extended these studies to 12 hard red winter (HRW) wheats, each grown at six Midwestern locations. Gliadin and reduced glutenin fractions were isolated and fractionated by SE-HPLC. Amounts of fractions corresponding to specific molecular weight (MW) ranges, determined by integrating peaks from SE-HPLC elution profiles, were statistically correlated with various baking quality parameters. Amounts of one fraction rich in γ-gliadins correlated well with loaf volume; correlations were better than found previously for HRS wheats. Correlations adjusted for overall protein (partial correlations) were >0.5 for 10 of the 12 samples, and >0.84 for six samples when estimated among samples, among locations, among ...

Rheological Properties of Vital Wheat Gluten Suspensions

ABSTRACT Flour and doughs represent rheologically complex materials whose properties are dependent on many factors including processing conditions. To avoid some of the problems associated with the rheological characterization of dough, we have initiated a study focused on the rheological properties of one of the major components of dough, vital wheat gluten. Suspensions of vital wheat gluten were prepared with concentrations of 225–325 mg/mL.The moduli of the gluten suspensions was 0.2 Pa at 225 mg/mL to 37 Pa at 325 mg/mL. At 300 mg/mL, the gluten suspensions exhibited solidlike behavior. The crossover frequencies were independent of concentration and equal to 100 rad/sec. At 300 mg/mL, the high-frequency...

Electrophoresis and chromatography of wheat proteins: available methods, and procedures for statistical evaluation of the data

Analysis of gluten proteins from the wheat grain endosperm has long challenged the analytical chemist. Several hundred unique polypeptides are present, many in large polymers. This complexity, plus useful relationships of composition to genotype and quality, encouraged development and application of electrophoresis and chromatography for gluten analysis. We review the methods of polyacrylamide gel electrophoresis, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, isoelectric focusing and high-performance liquid chromatography available for study of wheat proteins. Singly and in combination, they provide rapid, reproducible, high-resolution separations based on size, charge, or surface hydrophobicity. As challenging and important as the analyses themselves, however, is interpretation of data. Subjective evaluation is sometimes possible, but statistical methods such as similarity scores, clustering, principal components, multiple linear regression, and partial least squares now are increasingly used for data analysis. We review the use of these procedures, and precautions necessary to avoid misinterpretation of data. Optimal evaluation of protein analytical data will enhance the value of such analyses in wheat breeding, marketing, and processing.

Soft wheat quality as related to protein composition

ABSTRACT Soft red and white winter wheats from the eastern United States, used primarily to produce cookies, cakes, and biscuits, have quality requirements very different from those of bread wheats. In general, soft wheats have been bred to have low protein content, and conventional wisdom has been that protein composition of soft wheat is relatively unimportant. To test this hypothesis, relationships between soft wheat protein composition and end-use functional quality characteristics were examined. Quantitative protein compositions of eight cultivars of soft wheats grown in a wide area of the eastern United States during seven years (53 samples total) were analyzed by size-exclusion HPLC. Results were statistically correlated with numerous chemical and physical characteristics and quality factors of these wheats, their flours, and of cookies baked from the flours. For the entire sample set, wheats containing high molecular weight glutenin subunits 2+12 showed significantly different properties and cooki...

Grouping and identification of Argentine Maize races by principal component analysis of zein reversed-phase HPLC data

ABSTRACT Racial classification of maize has important taxonomic and phylogenetic implications. It may also serve to organize germ plasm inventory, thus helping breeders choose their stocks. Maize racial classification is usually based on phenotypic descriptors, which may not always accurately express genetic characteristics. In contrast, synthesis and expression of zeins is directly associated with genotype. This study was conducted to determine whether racial grouping and identification of maize can be done by applying principal component analysis to zein reversed-phase high-performance liquid chromatography (RP-HPLC) data. Zeins from samples of 97 landraces (primitive varieties) of the Argentine races Cristalino Colorado, Dentado Blanco, Avati Moroti, Capia, and Pisingallo, stored at the Pergamino Active Maize Germplasm Bank, were analyzed by RP-HPLC. Data from the ≈21- to 53-min chromatogram region (total zeins [ZT]), the ≈21- to-30 min region (zeins 2 [Z2]), or the ≈38- to 52- min region (zeins 1 [Z1]...

Quantitation and reproducibility problems in reversed-phase and size-exclusion HPLC analyses of wheat proteins

ABSTRACT Reversed-phase (RP-) and size-exclusion (SE-) high-performance liquid chromatography have become important methods for rapid identification of wheat and other cereal cultivars and for revealing quality differences. Accuracy and reproducibility are essential for good results. Due to recent changes in these methods, however, such as using smaller columns, lower flow rates, and smaller samples, small procedural errors become more critical for final results. We therefore further studied the causes and magnitude of problems involving quantitation and reproducibility in RP- and SE-HPLC analyses of wheat proteins. Because of potential problems with protein adsorption to stainless steel system components, we modified systems to contain, insofar as possible, all plastic-type components. Other potentially major problems included weighing flour samples, achieving accurate solvent composition, and interpretation of data. Recognizing and dealing with these problems will enhance the accuracy, reproducibility, ...