Effect of Single‐Pass and Multipass Milling Systems on Whole Wheat Durum Flour and Whole Wheat Pasta Quality

Single‐pass and multipass milling systems were evaluated for the quality of whole wheat durum flour (WWF) and the subsequent whole wheat (WW) spaghetti they produced. The multipass system used a roller mill with two purifiers to produce semolina and bran/germ and shorts (bran fraction). The single‐pass system used an ultracentrifugal mill with two configurations (fine grind, 15,000 rpm with 250 μm mill screen aperture; and coarse grind, 12,000 rpm with 1,000 μm mill screen aperture) to direct grind durum wheat grain into WWF or to regrind the bran fraction, which was blended with semolina to produce a reconstituted WWF. Particle size, starch damage, and pasting properties were similar for direct finely ground WWF and multipass reconstituted durum flour/fine bran blend and for direct coarsely ground WWF and multipass reconstituted semolina/coarse bran blend. The semolina/fine bran blend had low starch damage and had desirable pasting properties for pasta cooking. WW spaghetti was better when made with WWF produced using the multipass than single‐pass milling system. Mechanical strength was greatest with spaghetti made from the semolina/fine bran or durum flour/fine bran blends. The semolina/fine bran and semolina/coarse bran blends made spaghetti with high cooked firmness and low cooking loss.     

Grain Quality Characteristics and Milling Performance of Full and Partial Waxy Durum Lines

Mutation of the gene coding for the granule bound starch synthase (waxy protein) leads to reduced amylose content in cereal endosperm. Durum wheat (Triticum turgidum L. var. durum) has one waxy locus in each of its two genomes. Full waxy durum wheat is produced when both genomes carry the waxy null alleles. When only one locus is mutated, partial waxy durum wheat is obtained. Partial and full waxy near‐isogenic lines of durum wheat developed by a breeding program were analyzed as to their quality characteristics. Amylose was largely eliminated in full waxy lines; however, no reduction in amylose content was detected in partial waxy lines. The waxy mutation did not affect grain yield, kernel size, or kernel hardness. Full waxy durum lines had higher kernel ash content, α‐amylase activity, and a unique nonvitreous kernel appearance. Protein quality, as evaluated by SDS microsedimentation value, gluten index, and wet gluten was slightly lower in the full waxy lines than in the other genotypes. However, comparisons with current cultivars indicated that protein quality of all derived lines remained in the range of strong gluten cultivars. Semolina yield was lowered by the waxy mutations due to lower friability that resulted in less complete separation of the endosperm from the bran. Waxy semolina was more sensitive to mechanical damage during milling, but modified tempering and milling conditions may limit the damage. Overall, quality characteristics of waxy durum grain were satisfactory and suitable for application testing.     

Study of a Small‐Scale Laboratory Wet‐Milling Procedure for Wheat

The objectives of this research were to study the effects of slurry specific gravity, starch table slope, slurry pumping rate, and their interactions on starch recovery and purity; and to propose a small‐scale laboratory wet‐milling procedure for wheat. First‐order and second‐order response surface regression models were developed to study the effects and interactions of slurry specific gravity, starch table slope, and slurry pumping rate on starch and gluten separation for a 100‐g wheat wet‐milling procedure. The starch and starch protein content data fit the first‐order models (R² = 0.99 and 0.96) better than the second‐order models (R² = 0.98 and 0.93). Regression results from the first‐order models indicated that specific gravity, table slope, pumping rate, and their interactions all had a significant effect on starch yield and purity. However, these effects could be simplified as the effect of the resident time of starch and gluten slurry on the starch table and the specific gravity. Starch yield increased as resident time increased and specific gravity decreased. Protein content in starch decreased as the resident time decreased and the specific gravity increased. The separation condition with specific gravity of 3 Bé, table slope of 1.04 cm/m, and pumping rate of 50 mL/min was recommended. Under this condition, starch recovery was 85.6% and protein content of starch was 0.42%, which was similar to the 1.5‐kg laboratory methods in starch recovery. Total solids recovery was 98.1%, which is similar to that from 1.5‐kg laboratory methods. These results indicated that precision of the 100‐g wheat wet‐milling procedure was similar to that of the 1.5‐kg laboratory methods.     

Effect of Soft Kernel Texture on the Milling Properties of Soft Durum Wheat

Worldwide, nearly 20 times more common wheat (Triticum aestivum) is produced than durum wheat (T. turgidum subsp. durum). Durum wheat is predominately milled into coarse semolina owing to the extreme hardness of the kernels. Semolina, lacking the versatility of traditional flour, is used primarily in the production of pasta. The puroindoline genes, responsible for kernel softness in wheat, have been introduced into durum via homoeologous recombination. The objective of this study was to determine what impact the introgression of the puroindoline genes, and subsequent expression of the soft kernel phenotype, had on the milling properties and flour characteristics of durum wheat. Three grain lots of Soft Svevo and one of Soft Alzada, two soft‐kernel back‐cross derived durum varieties, were milled into flour on the modified Quadrumat Senior laboratory mill at 13, 14, and 16% temper levels. Samples of Svevo (a durum wheat and recurrent parent of Soft Svevo), Xerpha (a soft white winter wheat), and Expresso (a hard red spring wheat) were included as comparisons. Soft Svevo and Soft Alzada exhibited dramatically lower single‐kernel characterization system kernel hardness than the other samples. Soft Svevo and Soft Alzada had high break flour yields, similar to the common wheat samples, especially the soft hexaploid wheat, and markedly greater than the durum samples. Overall, Soft Svevo and Soft Alzada exhibited milling properties and flour quality comparable, if not superior, to those of common wheat.     

Relationship Between Wheat (Triticum aestivum L.) Grain Hardness and Wet‐Milling Quality

Grain hardness variation has large effects on many different end‐use properties of wheat (Triticum aestivum). The Hardness (Ha) locus consisting of the Puroindoline a and b genes (Pina and Pinb) controls the majority of grain hardness variation. Starch production is a growing end‐use of wheat. The objective of this study was to estimate the differences in starch yield due to natural and transgenically conditioned grain hardness differences. To accomplish this goal, a small‐scale wet‐milling protocol was used to characterize the wet‐milling properties of two independent groups of isogenic materials varying in grain hardness and in Pin expression level. The first group of lines consisted of hard/soft near‐isogenic lines created in cultivars Falcon or Gamenya in which lines carried either the Pina‐D1a (functional) or the Pina‐D1b (null) alleles of Pina. The second group of lines consisted of Pina, Pinb, or Pina and Pinb overexpressing lines created in Hi‐Line, a hard red spring wheat. Soft near‐isogenic lines had higher starch extractability than the hard Pina null counterparts. This difference in starch extractability was more pronounced between Hi‐Line and its transgenic isolines, with highest levels of extractable starch observed in the transgenic isoline with intermediate grain texture. The results demonstrate that the Ha locus and puroindoline expression are both linked to wet‐milling starch yield and that selection for increased Ha function increases starch yield through the enhanced separation of starch granules and the protein matrix during wet milling.     

Effects of Salinity and Drought Stress on Grain Quality of Durum Wheat

This work aimed to assess the influences of soil salinity and drought stresses on grain quality characteristics of selected salt-tolerant genotypes differing in salinity tolerance in durum wheat. This study was conducted under control, drought, and saline field conditions in separate experiments during 2 years. A randomized complete block design with three replications was used for each experiment. The results showed significant effects of genotype and environmental conditions on all grain-quality related traits. Salt and drought stress caused the significant increment of grain protein content, wet and dry gluten contents, and sodium dodecyl sulfate (SDS) sedimentation volume. Thousand-grain weight, grain protein yield, and test weight reduced significantly under both salinity and drought stress conditions. Protein content showed positive correlation with wet gluten, dry gluten, SDS sedimentation, and volume and strong negative correlation with other traits. It is concluded that influence of salinity stress was greater than drought stress on grain protein yield and some other grain-quality-related traits.     

Water‐Extractable Nonstarch Polysaccharide Distribution in Pilot Milling Analysis of Soft Winter Wheat

Commercial wheat (Triticum aestivum em. Thell) flour milling produces flour streams that differ in water absorption levels because of variability in protein concentration, starch damaged by milling, and nonstarch polysaccharides. This study characterized the distribution of water‐extractable (WE) nonstarch polysaccharides (NSP) in long‐flow pilot‐milling streams of soft wheat to model flour quality and genetic differences among cultivars. Existing reports of millstream analysis focus on hard wheat, which breaks and reduces differently from soft wheat. Seven soft winter wheat genotypes were milled on a pilot‐scale mill that yields three break flour streams, five reduction streams, and two resifted streams. Protein concentration increased linearly through the break streams. WENSP concentration was low and similar in the first two break streams, which are the largest break streams. Flour recovery decreased exponentially through the reduction streams; flour ash and water‐extractable glucose and galactose polymers increased exponentially through the reduction streams. Protein concentration and WE xylan concentration increased linearly through the reduction streams. The ratio of arabinose to xylose in WE arabinoxylan (WEAX) decreased through the reduction streams, and response varied among the genotypes. Flour ash was not predictive of stream composition among genotypes, although within genotypes, ash and other flour components were correlated when measured across streams. The second reduction flour stream was the largest contributor to straight‐grade flour WEAX because of both the size of the stream and the concentration of WEAX in the stream.     

Distribution of Peroxidases in Durum Wheat (Triticum durum)

A biochemical study of the main durum wheat milling fractions (bran, embryo, and semolina) showed that peroxidases (POD) were present in multiple forms in the kernel and appeared to be tissue specific: one form for the embryo, one for the endosperm, one for the subaleuronic layer, and one for the outer layers. Large varietal differences were found regarding both the composition and the POD activity. POD activity, detected by diaminobenzidine, was found mainly in the cell wall of the subaleurone layer and inside some specific, differentiated cells of the embryo. Immuno‐localization with antibodies of durum wheat POD showed the presence of POD in several layers of the pericarp (epidermis) and the seed coat (testa), in the embryo, and also in the endosperm. In this latter tissue, the staining intensity decreased gradually from the outer layers toward the center of the kernel. The localization of POD in durum wheat kernel suggests specific functions for different forms.     

Using Rheological Phenotype Phases to Predict Rheological Features of Wheat Hardness and Milling Potential of Durum Wheat

Predictions about milling, dough making, and baking properties can be made by measuring properties of the wheat grain with different small‐ and medium‐scale equipment. In this study, rheological hardness index (RHI) was shown to separate hexaploid wheats and durums into clearly distinct hardness classes. Earlier work demonstrated the utility of RHI to give new insight about the classification of wheat types, and in this study further use of the rheological phenotype phases (RPPs) to construct combinations of RPPs (cRPPs) is explored. In particular, it is shown how different cRPPs can be used to compare, for various wheat varieties, the elastic, fragmentation, equilibrium, and viscoelastic phases of an average crush response profile. In addition, relationships were obtained, based on selected RPPs from the single‐kernel characterization system, that gave good predictions of the laboratory milling potential of durum wheats. This information could be used as an early generation test to predict milling yield in breeding programs without having to mill the sample. Further validation of these relationships is required by evaluating the prediction across multiple environments.     

Bran Size Distribution at Milling and Mechanical and Biochemical Characterization of Common Wheat Grain Outer Layers: A Relationship Assessment

Mechanical properties of wheat grain outer layers from common wheat (Triticum aestivum L.) cultivars known to display distinct milling behavior were analyzed using uniaxial tension tests. Tensile modulus and strain to rupture of the tissues distinguished between the wheat cultivars. Values of strain to rupture were related to coarse bran size generated by grain milling, a characteristic that distinguishes the two hardness classes. As content of an aleurone marker in total or first break flour was also related to coarse bran size, extensibility of wheat grain outer layers' could be a key parameter to explain the observed tissue mechanical behavior and thus distribution of the aleurone layer content in flours. As tissue mechanical properties are generally linked to the cell wall biochemical composition and structure, analysis of the main wheat outer layers' cell wall compounds was undertaken to establish relationships with the differences observed in mechanical properties. No clear correlation could be found with one of the wheat outer layers' component but involvement of the outer layers' cell wall structure in the tissues behavior at milling was confirmed.     

Effect of Fusarium Head Blight on Semolina Milling and Pasta-Making Quality of Durum Wheat

Ten durum wheat cultivars harvested in Manitoba in 1995, which were downgraded primarily because of fusarium-damaged (FD) kernels, were subjected to mycological tests and evaluated for semolina milling and pasta-making quality. Fusarium graminearum was the primary fungus infecting kernels. The ratio of FD to deoxynivlaenol (DON) level varied slightly among cultivars but was generally near unity. Retention of DON in semolina was about 50%. FD had a negative impact on kernel weight and test weight, resulting in lower semolina yield. Semolina ash content and bran specks were not affected by FD, but semolina became duller and redder. FD had no effect on protein content, but gluten strength was weaker probably due to a lower proportion of glutenins as shown by reversed-phase high-performance liquid chromatographic analysis of sequentially extracted gluten proteins. The influence of FD on gluten strength was not sufficient to alter pasta texture. FD had a strong adverse effect on pasta color. Even for the least damaged cultivars, which had FD levels near the limit of 2% established for the No. 3 and No. 4 Canadian Western Amber Durum (CWAD) grades, the deterioration in pasta color was readily discernible by eye, confirming that the strict FD tolerances for premium No. 1 CWAD (0.25%) and No. 2 CWAD (0.5%) grades are warranted.     

Impacts of SSIIa‐A Null Allele on Durum Wheat Noodle Quality

A small increase in amylose content may impact end‐product quality of wheat. The effect of elevated amylose content in durum wheat is not known. We surveyed 255 durum wheat accessions and found two genotypes that lacked the SGP‐A1 protein. These genotypes were crossed to Mountrail, an adapted durum genotype, to create populations segregating for the SSIIa‐Ab null allele. Our goal was to determine the influence of allelic variation at the SSIIa‐A locus on semolina properties and end‐product quality with noodles as a test product. Amylose content increased 3% and cooked noodle firmness increased 2.8 g·cm for the SSIIa‐Ab class compared with the SSIIa‐Aa class for the PI 330546 source, but no change in either trait was detected between classes for the IG 86304 source. The SSIIa‐Ab class had a 10% reduction in flour swelling compared with the SSIIa‐Aa class for both crosses. Grain protein and semolina yield did not differ between SSIIa‐A classes. The relationship between flour swelling power and noodle firmness did not differ between SSIIa‐A allelic classes within a cross. The different results for amylose content and noodle firmness between these sources may be because the two sources of the SSIIa‐Ab null mutation contributed different linkages to the segregating populations. Results show that the SSIIa‐Ab allele could be used to produce durum‐based products that are slightly more firm in texture. However, the effect of the SSIIa‐Ab allele may depend on the source.     

Investigation of Wheat Milling Yield Based on Grain Hardness Parameters

The objectives of this study were to investigate the relationship between milling yield and grain hardness. A preliminary study was carried out with 20 samples (both hard and soft wheats) using the Brabender hardness tester (BHT) with two grind settings: one‐step grind (0‐10) and two‐step grind (2‐12: coarse; 0‐8: fine). The two‐step grind was correlated with particle size index, single‐kernel characterization system (SKCS) hardness, break yield, and reduction yield (P < 0.05), whereas there was no correlation with the one‐step grind method. An additional 64 samples were ground with the two‐step grind setting to further validate this method. In terms of the BHT crush profile, no discernible differences were observed between varieties for the coarse grind, whereas for the fine grind, hard wheat gave a higher BHT maximum peak height and shorter grinding time compared with soft wheat. The break and reduction yields were significantly correlated with both BHT and SKCS hardness (P < 0.05). The findings indicated that the BHT method could be used to differentiate for milling yield among the different varieties. Based on the results, two milling yield models were developed, and both gave highly significant correlations between the predicted and Buhler mill break (R² = 0.791, P < 0.05) and reduction yield (R² = 0.896, P < 0.05).     

Differentiating Vitreous and Nonvitreous Durum Wheat Kernels by Using Near‐Infrared Spectroscopy

The vitreousnss of durum wheat is used by the wheat industry as an indicator of milling and cooking quality. The current visual method of determining vitreousness is subjective, and classification results between inspectors and countries vary widely. Thus, the use of near‐infrared (NIR) spectroscopy to objectively classify vitreous and nonvitreous single kernels was investigated. Results showed that classification of obviously vitreous or nonvitreous kernels by the NIR procedure agreed almost perfectly with inspector classifications. However, when difficult‐to‐classify vitreous and nonvitreous kernels were included in the analysis, the NIR procedure agreed with inspectors on only 75% of kernels. While the classification of difficult kernels by NIR spectroscopy did not match well with inspector classifications, this NIR procedure quantifies vitreousness and thus may provide an objective classification means that could reduce inspector‐to‐inspector variability. Classifications appear to be due, at least in part, to scattering effects and to starch and protein differences between vitreous and nonvitreous kernels.     

Laboratory Milling Method for Whole Grain Soft Wheat Flour Evaluation

Whole grain wheat products are a growing portion of the foods marketed in North America, yet few standard methods exist to evaluate whole grain wheat flour. This study evaluated two flour milling systems to produce whole grain soft wheat flour for a wire‐cut cookie, a standard soft wheat product. A short‐flow experimental milling system combined with bran grinding in a Quadro Comil produced a whole grain soft wheat flour that made larger diameter wire‐cut cookies than whole grain flour from a long‐flow experimental milling system. Average cookie diameter of samples milled on the short‐flow mill was greater than samples milled on the long‐flow system by 1 cm/two cookies (standard error 0.09 cm). The long‐flow milling system resulted in more starch damage in the flour milling than did the short‐flow system. The short‐flow milling system produced flours that were useful for discriminating among wheat cultivars and is an accessible tool for evaluating whole grain soft wheat quality.     

Characterization of Durum Wheat Semolina by Means of a Rapid Shear‐Based Method

A rapid shear‐based test (the GlutoPeak test, recently proposed by Brabender) was used to investigate gluten aggregation properties of durum wheat semolina and to relate them to pasta cooking behavior. Thirty semolina samples were characterized by means of the conventional approaches used for pasta‐quality prediction (protein content, gluten index, and alveographic indices). All samples were also analyzed by the GlutoPeak test, obtaining three parameters: maximum peak torque, maximum peak time, and area under the peak. The GlutoPeak indices were significantly correlated with protein content, gluten index, and W alveographic parameter. The cooking quality of pasta obtained from the 30 semolina samples was evaluated by sensory analysis in terms of stickiness, bulkiness, firmness, and overall quality. The GlutoPeak indices were significantly correlated with the sensorial parameters. In comparison with the alveographic test, which is presently the most used rheological approach for semolina characterization, GlutoPeak analysis presents some advantages represented by a smaller amount of sample (9 g), a shorter time (less than 5 min), and the possibility that untrained analysts can carry it out. In addition, following testing with larger sample numbers, the GlutoPeak test has the potential to be used instead of the gluten index as a rapid and reliable approach for medium‐quality semolina characterization.     

Nutritional Profile of Whole‐Grain Soft Wheat Flour

Whole‐grain wheat flour is used in baking to increase fiber content and to provide vitamins from the bran layers of the kernel. We surveyed whole‐grain soft flour samples from North America to determine the nutritional profile using recently revised fiber quantification protocols, Codex 2009.1. Standard compositional and vitamin analyses were also included in the survey. Three separate studies were included in the survey: sampling of commercial whole‐grain soft wheat flour, a controlled study of two cultivars across three years and two locations, and a regional study of soft white and soft red grain from commercial grain production. The Codex method for fiber measurement estimated total fiber concentration in the commercial sampling at 15.1 g/100 g, dry weight basis (dwb). In the controlled research trial, the largest source of variation in total fiber concentration was attributed to year effects, followed by genotype effects. For the two locations used in this study, location effects on fiber concentration were significant but an order of magnitude less important than the year and genotype effects. The third study of regional variation within North America found limited variation for total fiber, with the resistant oligosaccharide fraction having the greatest variation in concentration. When all three studies were combined into a meta‐analysis, the average total fiber concentration was 14.8 g/100 g dwb. In the meta‐analysis, concentrations of folate, thiamin, riboflavin, niacin, and pyridoxine were lower than in previous summary reports. Vitamin E and pantothenic acid were the exceptions, with concentrations that were nearly identical to previous standard reports. Several other recent studies also point to current cultivars and production systems as producing lower concentrations of the essential vitamins than previously reported. The results suggest that vitamin concentrations in diets of populations using grain‐based diets from modern cereal‐production systems may require review to determine if previous assumptions of vitamin consumption are accurate.     

Influence of UV Exposure on Phenolic Acid Content,Mechanical Properties of Bran,and Milling Behavior of Durum Wheat (Triticum Durum Desf.)

Durum wheat bran was exposed to UV radiation up to 48 hr and the changes in ferulic acid (FA) content in the peripheral part s of grain were measured. The treatment resulted in a 25% decrease in FA monomer and a 44% decrease in dehydrodiferulic acid (DHD) ester‐linked to the cell‐wall arabinoxylans. This reduction was partly explained by a significant increase of FA (30%) and DHD (36%) engaged in hot alkali‐labile linkages. The results suggest that UV irradiation induced the formation of new cross‐links between feruloylated arabinoxylan and lignin in the pericarp. The effects of UV treatment on bran mechanical properties and wheat milling behavior were investigated. UV irradiation for 15 hr increased the stress to rupture by 30% and decreased the extensibility of bran tissues by 54%. This stiffening was associated with an increase in bran friability during grinding. Although this effect was due in part to the hydrothermal history of the grain, chemical modification induced by UV significantly influenced the size reduction of bran particles, which can be explained by the modification of the mechanical properties of bran. Relationships between the organization of cell‐wall polymers, the mechanical properties of tissues, and the behavior of wheat grain during milling were investigated.     

Influence of High‐Temperature Drying on Structural and Textural Properties of Durum Wheat Pasta

Starch and protein are the main polymeric ingredients of pasta and they determine the structural and textural properties of cooked pasta. The present investigation sought better understanding of the impact of high‐temperature (HT) drying on the starch and the protein fraction, and their role in structure and texture of pasta. Durum wheat spaghetti was prepared in a pilot‐plant installation. The drying conditions were selected for the HT phase at 80 or 100°C applied at high, intermediate, or low product moisture content. Spaghetti dried at 55°C served as a reference sample. The color of dry pasta was measured and the changes in the starch and protein fractions were determined by protein solubility, light microscopy, confocal scanning laser microscopy (CSLM), cooking tests, and texture measurements. HT drying at 100°C and low product moisture promoted browning of pasta. At the molecular level, HT drying promoted protein denaturation. At the microscopic level, HT drying contributed to a better preservation of the protein network and reduced swelling of starch and disintegration of granules. At the macroscopic level, HT drying enhanced the firmness of cooked pasta and reduced surface stickiness. In general, the changes were more pronounced by increasing the drying temperature from 80 to 100°C and by shifting the HT phase from an early to a late stage of the drying process. The drying conditions are determinant for the phase morphology of protein and starch in cooked pasta which, in turn, govern the textural properties of pasta.     

Application of the Single‐Kernel Characterization System to Durum Wheat Testing and Quality Prediction

The Single Kernel Characterization System (SKCS 4100) measures single kernel weight, width, moisture content, and hardness in wheat grain with greater speed than existing methods and can be calibrated to predict flour starch damage and milling yield. The SKCS 4100 is potentially useful for testing applications in a durum improvement program. The mean SKCS 4100 kernel weight and moisture values from the analysis of 300 individual kernels gave good correlations with 1,000 kernel weight (r² = 0.956) and oven moisture (r² = 0.987), respectively. Although significant correlations were obtained between semolina mill yield and SKCS 4100 weight, diameter, and peak force, they were all very low and would be of little use for prediction purposes. Similarly, although there were significant correlations between some SKCS 4100 parameters and test weight and farinograph parameters, they too were small. The SKCS 4100 has been calibrated using either the single kernel hardness index or crush force profile to objectively measure the percentage vitreous grains in a sample with reasonable accuracy, and it correlates well with visual determination. The speed and accuracy of the test would be of interest to grain traders. An imprecise but potentially useful calibration was obtained for the prediction of semolina mill yield using the SKCS 4100 measurements on durum wheat. The SKCS 4100 is useful for some traits such as hardness, grain size and moisture for early‐generation (F3) selection in a durum improvement program.