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Quality Traits

Brent Hinsz at the quality laboratory at NDSUColor, grain protein concentration, and gluten strength are key traits that influence end-use quality of durum wheat.  High concentration of carotenoid pigments in the endosperm is an important distinguishing characteristic of durum wheat, resulting in the yellow translucent appearance of pasta.  In durum wheat, xanthophylls are the major yellow pigment and are composed of free lutein 84.5%, lutein monoester 9.8%, lutein diester 5.3%, and carotene 4%.  Grain protein concentration and gluten strength greatly affect the mechanical strength of dried pasta and the quality of cooked pasta. Gluten is formed when gliadin and glutenin proteins are hydrated and mixed together. Gluten strength is related to the glutenin:gliadin ratio.  Gluten proteins form a network during pasta processing which gives pasta strength and directly affects pasta cooking quality, i.e., cooking loss, cooking weight, and cooked firmness. When compared to weak gluten varieties of comparable grain protein concentration, strong gluten varieties exhibit less sticky dough with better extrusion properties and superior textural characteristics in cooked spaghetti, i.e., appearance, bite, chewiness, cooking loss, flavor, resistance to overcooking, and stickiness. Variation in gluten strength is more evident in pasta dried at low than at high or ultrahigh temperatures. Because of their importance, color, protein content, and gluten strength are evaluated throughout genotype development from early generation lines to released cultivar.

Color

Frank Manthey displays spaghetti samples made from durum linesBrightness and yellowness of pasta are important color attributes. Researchers have found that for brightness, genotype was responsible for 12.6% of the variability, environment for 67.9%, and other factors 19.5%, while for yellowness, these values were 86.6%, 8.5%, and 4.9%, respectively. Thus, brightness was predominantly affected by environment, and yellowness was affected predominantly by genotype. Semolina color is a highly heritable trait and is controlled by additive gene effects. The high heritability indicates that only a few genes with several alleles control the characteristic.

Semolina color can be evaluated by quantifying pigment concentration or by using the reflectance colorimeter.  In the NDSU breeding program, semolina and spaghetti colors are evaluated using a reflectance colorimeter. Semolina color is evaluated during the F6 and subsequent generations. The color of the semolina is evaluated using the Gardener reflectance colorimeter, measuring the b-value on the Hunter color scale.  Spaghetti color is evaluated beginning at the F9 generation. Spaghetti color is evaluated using a Minolta color difference meter, measuring the L-value and b-value on the Hunter color scale.  Color is determined on spaghetti that has been neatly stacked 1 cm deep on a black background.  The Hunter L–value and b-value for each sample are converted into a single color value using a color map (AACC method 14-22, 2000).  A color score of 9.5 or higher is desired.

Grain Protein Concentration and Gluten Strength

Grain protein concentration and gluten strength are important quality traits in durum wheat.  High grain protein concentration and strong gluten durum semolina produce pasta products with better nutritive value and superior end-use quality.  In general, a minimum semolina protein concentration is required to produce acceptable quality pasta products.  This is because semolina protein concentration alone can account for 30 to 40% of the variability in pasta cooking quality.  Durum cultivars with high protein produce macaroni, spaghetti, and other pasta products with greater cooking firmness and increased tolerance to overcooking.  Similarly, pasta cooking quality improves as protein concentration in the same cultivar increases.  Thus, many pasta manufacturers require semolina suppliers to meet a minimum semolina protein content.

Breeding efforts to increase grain protein concentration in durum wheat have been marginally successful. Protein concentration is a complexly inherited trait and is strongly influenced by environmental conditions.  A negative correlation between grain yield and protein concentration hampers breeding progress.  However, the lack of progress is mostly due to the unavailability of high protein genotypes within the adapted durum wheat breeding gene pool.

Many studies have indicated that emmer wheat (T. turgidum  L. var. dicoccoides), the wild relative of cultivated durum wheat, contains a large number of accessions that have high grain protein concentrations.  Triticum dicoccoides accessions with grain protein concentrations of 200 to 240 g kg-1 have been reported.  The T. dicoccoides gene pool represents a new source of genetic variability for grain protein concentration and may provide useful sources of high protein genes for introgression into durum and bread wheat breeding germplasms.

At NDSU’s durum wheat project, the modified pedigree method is used to develop germplasm with high protein concentration. ‘Maier’ (released in 1998) and ‘Dilse’ (released in 2002) are two durum wheat cultivars that were released from the program because of their high protein concentration and gluten strength. Protein concentration is evaluated at the F5 and subsequent generations while gluten strength is evaluated, starting at the F3 generation.  Whole grain protein is evaluated using a Technicon InfraAlyzer, where the targeted whole grain protein concentration is 13.5% or higher, at 12% mb.  Visual selection for gluten strength can be practiced starting at the F2 generation.  Strong gluten is linked with the gene Rg1 for glume color in durum wheat. White glume color is associated with strong gluten, while buff or brown color is associated with weak gluten.  In the F2 population, only white glume color plants are selected.  Gluten strength at the F3 and subsequent generations is evaluated by the SDS micro-sedimentation test.  A sedimentation value below 30 mm indicates weak gluten, and a sedimentation value of 35 or higher indicates strong gluten. SDS micro-sedimentation test is effective in distinguishing weak from strong gluten, but is less effective in distinguishing strong from very strong gluten. F5 and subsequent generations are evaluated for whole grain protein and for semolina protein.  Semolina protein is evaluated using a Technicon InfraAlyzer.  The target protein concentration for semolina is 12.5% or higher, at 14% mb.

Durum lines in the F6 generation or higher are evaluated for whole grain protein and semolina protein.  Gluten strength is evaluated using SDS micro-sedimentation, mixograph, and wet gluten/gluten index tests. The mixograph procedure used is similar to AACC Method 54-40A (2000), with some modifications as follows.  Semolina (10 gm, 14% mb) was brought to constant water absorption of 58% and mixed for 8 min in the mixograph bowl (spring setting of 8).  Mixograph curves were compared to reference mixograms and scored.  Mixogram scores of 1-3 indicate a weak  gluten, 5-6 strong gluten, and 8 very strong gluten.  Wet gluten/gluten index is determined using AACC Method 38-12A (2000).   A gluten index <5% indicates weak gluten, 40-60% strong gluten, and > 80% very strong gluten.  There is a market for the three gluten strengths. Weak gluten is desirable for crimped or stamped pasta products, strong gluten is desirable for long goods, and very strong gluten is desirable for blending with lower quality semolina and may be advantageous in bread products.

Spaghetti made from durum lines in the F9 generation or higher also are evaluated for cooking quality. Spaghetti, 10 g, is cooked in 300 ml boiling water for 12 min.  Cooked weight is determined as the weight of 10 g of dry spaghetti after cooking.  Cooking loss (weight of total solids expressed as a percent) is measured by evaporating the cooking water to dryness in a 110 C oven. Firmness of cooked spaghetti is measured using a TA-XT2 texture analyzer.  Cooked firmness is measured by the work required to shear five cooked spaghetti strands.

Complete Quality Traits

quality stripsAdvanced lines are grown in quality strips at the six Research Centers in North Dakota for the following quality traits evaluations:

  • Test Weight
  • Vitreousness
  • Kernel Weight
  • Wheat Protein
  • Semolina Protein
  • Total Extraction
  • Semolina Extraction
  • Semolina Ash
  • Specks
  • Spaghetti Color
  • Mixogram
  • Cooked Weight
  • Cooking Loss
  • Spaghetti Firmness
  • Kernel Sizing
  • Falling Number

 

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