Selecting and Sorting Waxy Wheat Kernels Using Near‐Infrared Spectroscopy

An automated single kernel near‐infrared (NIR) sorting system was used to separate single wheat (Triticum aestivum L.) kernels with amylose‐free (waxy) starch from reduced‐amylose (partial waxy) or wild‐type wheat kernels. Waxy kernels of hexaploid wheat are null for the granule‐bound starch synthase alleles at all three Wx gene loci; partial waxy kernels have at least one null and one functional allele. Wild‐type kernels have three functional alleles. Our results demonstrate that automated single kernel NIR technology can be used to select waxy kernels from segregating breeding lines or to purify advanced breeding lines for the low‐amylose kernel trait. Calibrations based on either amylose content or the waxy trait performed similarly. Also, a calibration developed using the amylose content of waxy, partial waxy, and wild‐type durum (T. turgidum L. var durum) wheat enabled adequate sorting for hard red winter and hard red spring wheat with no modifications. Regression coefficients indicated that absorption by starch in the NIR region contributed to the classification models. Single kernel NIR technology offers significant benefits to breeding programs that are developing wheat with amylose‐free starches.     

Significance of Amylose Content of Wheat Starch on Processing and Textural Properties of Instant Noodles

The effect of amylose content of starch on processing and textural properties of instant noodles was determined using waxy, partial waxy, and regular wheat flours and reconstituted flours with starches of various amylose content (3.0–26.5). Optimum water absorption of instant noodle dough increased with the decrease of amylose content. Instant noodles prepared from waxy and reconstituted wheat flours with ≤12.4% amylose content exhibited thicker strands and higher free lipids content than wheat flours with ≥17.1% amylose content. Instant noodles of ≤12.4% amylose content of starch exhibited numerous bubbles on the surface and stuck together during frying. Lightness of instant noodles increased from 77.3 to 81.4 with the increase of amylose content of starch in reconstituted flours. Cooking time of instant noodles was 4.0–8.0 min in wheat flours and 6.0–12.0 min in reconstituted flours, and constantly increased with the increase in amylose content of starch. Hardness of cooked instant noodles positively correlated with amylose content of starch. Reconstituted flours with ≤12.4% amylose content of starch were higher in cohesiveness than those of wheat flours of wild‐type and partial waxy starches and reconstituted flours with ≥17.1% amylose content. Instant fried noodles prepared from double null partial waxy wheat flour exhibited shorter cooking time, softer texture, and higher fat absorption (1.2%) but similar color and appearance compared with noodles prepared from wheat flour of wild‐type starch.     

Functional Characteristics of Bread Wheat (Triticum aestivum L.) Near‐Isogenic Lines Differing at the Waxy (Wx) Locus

The Waxy (Wx) gene in hexaploid wheat (Triticum aestivum L.) encodes granule‐bound starch synthase (GBSS1), which is involved in the synthesis of amylose, a mostly linear glucan polymer that makes up ∼25% of wheat starch. A null mutation of the Wx gene in each of the three genomes is associated with starch almost entirely consisting of the branched glucan polymer amylopectin (waxy starch), with corresponding changes in functionality. However, the rheological behavior of partially waxy starch remains unclear. The objective of this study was to characterize flour and baking quality in 16 near‐isogenic lines, null at the Wx locus on zero, one, two, or all three genomes, grown in four different environments. Across allelic groups, significant variations in amylose concentrations, flour paste viscosity, loaf structure and texture, dough stability, and proximate variables were observed. Because waxy wheat starch has greater water absorbance and resistance to retrogradation than normal starch, its inclusion in flour blends has been suggested as a means of improving the texture and appearance of bakery products and noodles. The results indicate that wheat encoding <3 functional homeologs of GBSS1 produces starch that has potential in the production of certain food items, such as Asian noodles. However, further research is necessary to determine the optimal amylose‐to‐amylopectin ratio to improve baking quality.     

Effect of Amylose Content on Gelatinization,Retrogradation, and Pasting Properties of Starches from Waxy and Nonwaxy Wheat and Their F1 Seeds

We studied the effect of amylose content on the gelatinization, retrogradation, and pasting properties of starch using wheat starches differing in amylose content. Starches were isolated from waxy and nonwaxy wheat and reciprocal F1 seeds by crossing waxy and nonwaxy wheat. Mixing waxy and nonwaxy wheat starch produced a mixed starch with the same amylose content as F1 seeds for comparison. The amylose content of F1 seeds ranged between waxy and nonwaxy wheat. Nonwaxy‐waxy wheat had a higher amylose content than waxy‐nonwaxy wheat. Endothermic enthalpy and final gelatinization temperature measured by differential scanning calorimetry correlated negatively with amylose content. Gelatinization onset and peak temperature clearly differed between F1 and mixed starches with the same amylose content as F1 starches. Enthalpy for melting recrystallized starches correlated negatively with amylose content. Rapid Visco Analyser measurement showed that F1 starches had a higher peak viscosity than waxy and nonwaxy wheat starches. Mixed starches showed characteristic profiles with two low peaks. Setback and final viscosity correlated highly with amylose content. Some of gelatinization and pasting properties differed between F1 starches and mixed starches.     

Characteristics of Noodles and Bread Prepared from Double‐Null Partial Waxy Wheat

Double‐null partial waxy wheat (Triticum aestivum L.) flours were used for isolation of starch and preparation of white salted noodles and pan bread. Starch characteristics, textural properties of cooked noodles, and staling properties of bread during storage were determined and compared with those of wheat flours with regular amylose content. Starches isolated from double‐null partial waxy wheat flours contained 15.4–18.9% amylose and exhibited higher peak viscosity than starches of single‐null partial waxy and regular wheat flours, which contained 22.7–25.8% amylose. Despite higher protein content, double‐null partial waxy wheat flours, produced softer, more cohesive and less adhesive noodles than soft white wheat flours. With incorporation of partial waxy prime starches, noodles produced from reconstituted soft white wheat flours became softer, less adhesive, and more cohesive, indicating that partial waxy starches of low amylose content are responsible for the improvement of cooked white salted noodle texture. Partial waxy wheat flours with >15.1% protein produced bread of larger loaf volume and softer bread crumb even after storage than did the hard red spring wheat flour of 15.3% protein. Regardless of whether malt was used, bread baked from double‐null partial waxy wheat flours exhibited a slower firming rate during storage than bread baked from HRS wheat flour.     

Characteristics of French Bread Baked from Wheat Flours of Reduced Starch Amylose Content

Wheat genotypes of wild type, partial waxy, and waxy starch were used to determine the influence of starch amylose content on French bread making quality of wheat flour. Starch amylose content and protein content of flours were 25.0–25.4% and 14.3–16.9% for wild type; 21.2 and 14.9% for single null partial waxy; 15.4–17.1% and 13.2–17.6% for double null partial waxy; and 1.8 and 19.3% for waxy starch, respectively. Wheat flours of double null partial waxy starch produced smaller or comparable loaf volume of bread than wheat flours of wild type and single null partial waxy starch. Waxy wheat flour, despite its high protein content, generally produced smaller volume of bread with highly porous, glutinous, and weak crumb than wheat flours of wild type and partial waxy starch. French bread baked from a flour of double null partial waxy starch using the sponge-and-dough method maintained greater crumb moisture content for 24 hr and softer crumb texture for 48 hr of storage compared with bread baked from a flour of wild type starch. In French bread baked using the straight-dough method, double null partial waxy wheat flours with protein content >14.3% exhibited comparable or greater moisture content of bread crumb during 48 hr of storage than wheat flours of wild type starch. While the crumb firmness of bread stored for 48 hr was >11.4 N in wheat flours of wild type starch, it was <10.6 N in single or double null partial waxy flours. Wheat flours of reduced starch amylose content could be desirable for production of French bread with better retained crumb moisture and softness during storage.     

Comparison of Physical Properties of Wheat Starch Gels with Different Amylose Content

The effects of amylose content and other starch properties on concentrated starch gel properties were evaluated using 10 wheat cultivars with different amylose content. Starches were isolated from grains of two waxy and eight nonwaxy wheat lines. The amylose content of waxy wheat lines was 1.4–1.7% and that of nonwaxy lines was 18.5–28.6%. Starch gels were prepared from a concentrated starch suspension (30 and 40%). Gelatinized starch was cooled and stored at 5°C for 1, 8, 16, 24, and 48 hr. The rheological properties of starch gels were studied by measuring dynamic viscoelasticity with parallel plate geometry. The low‐amylose starch showed a significantly lower storage shear modulus (G′) than starches with higher amylose content during storage. Waxy starch gel had a higher frequency dependence of G′ and properties clearly different from nonwaxy starches. In 40% starch gels, the starch with lower amylose showed a faster increase in G′ during 48 hr of storage, and waxy starch showed an extremely steep increase in G′. The amylose content and concentration of starch suspension markedly affected starch gel properties.     

Physicochemical and Thermal Characteristics of Starch Isolated from a Waxy Wheat Genotype Exhibiting Partial Expression of Wx Proteins

A unique wheat genotype carrying waxy‐type allelic composition at the Wx loci, Gunji‐1, was developed, and its starch properties were evaluated in comparison to parental waxy and wild‐type wheat varieties. Gunji‐1 was null in all three of the Wx genes but exhibited a lower level of Wx proteins than the wild‐type. Starch amylose content and cold water retention capacity were 10.1 and 70.5% for Gunji‐1, 4.2 and 76.6% for waxy, and 27.9 and 65.0% for wild‐type, respectively. No significant differences were observed in microstructure, granule size distribution, and X‐ray diffractograms of the starch granules isolated from Gunji‐1 compared with those of waxy and wild‐type wheat varieties. Starch pasting peak, breakdown, and setback viscosities and peak temperature of Gunji‐1 were intermediate between waxy and wild‐type wheat. In starch gel hardness, Gunji‐1 (1.1 N) was more similar to waxy wheat (0.5 N) than to the wild‐type variety (17.6 N). Swelling power, swelling volume, paste transmittance during storage, and gelatinization enthalpy of Gunji‐1 were lower than those of waxy wheat but greater than those of wild‐type wheat. Retrogradation of starch stored for one week at 4°C expressed with DSC endothermic enthalpy was absent in the waxy wheat variety, whereas Gunji‐1 exhibited both retrogradation of amylopectin and amylose‐lipid complex melting similar to the wild‐type parent, even though enthalpies of Gunji‐1 were much smaller than the wild‐type parent.     

Single Kernel Near‐Infrared Analysis of Tetraploid (Durum) Wheat for Classification of the Waxy Condition

Plant breeding programs are active worldwide in the development of waxy hexaploid (Triticum aestivum L.) and tetraploid (T. turgidum L. var. durum) wheats. Conventional breeding practices will produce waxy cultivars adapted to their intended geographical region that confer unique end use characteristics. Essential to waxy wheat development, a means to rapidly and, ideally, nondestructively identify the waxy condition is needed for point‐of‐sale use. The study described herein evaluated the effectiveness of near‐infrared (NIR) reflectance single‐kernel spectroscopy for classification of durum wheat into its four possible waxy alleles: wild type, waxy, and the two intermediate states in which a null allele occurs at either of the two homologous genes (Wx‐1A and Wx‐1B) that encodes for the production of the enzyme granule bound starch synthase (GBSS) that controls amylose synthesis. Two years of breeders' samples (2003 and 2004), corresponding to 47 unique lines subdivided about equally into the four GBSS genotypes, were scanned in reflectance (1,000–1,700 nm) on an individual kernel basis. Linear discriminant analysis models were developed using the best set of four wavelengths, best four wavelength differences, and best four principal components. Each model consistently demonstrated the high ability (typically >95% of the time) to classify the fully waxy genotype. However, correct classification among the three other genotypes (wild type, wx‐A1 null, and wx‐B1 null) was generally not possible.     

Sources of Variation for Starch Gelatinization,Pasting, and Gelation Properties in Wheat

The starch of wheat (Triticum aestivum L.) flour affects food product quality due to the temperature-dependent interactions of starch with water during gelatinization, pasting, and gelation. The objective of this study was to determine the fundamental basis of variation in gelatinization, pasting, and gelation of prime starch derived from seven different wheat cultivars: Kanto 107, which is a partial waxy mutant line, and six near-isogenic lines (NILs) differing in hardness. Complete pasting curves with extended 16-min hold at 93°C were obtained using the Rapid Visco Analyser (RVA). Apparent amylose content ranged from 17.5 to 23.5%; total amylose content ranged from 22.8 to 28.2%. Starches exhibited significant variation in onset of gelatinization. However, none of the parameters measured consistently correlated with onset or other RVA curve parameters that preceded peak paste viscosity. Peak paste viscosity varied from 190 to 323 RVA units (RVU). Higher peak, greater breakdown, lower final viscosity, negative setback, and less total setback were associated with lower apparent and total amylose contents. Each 1% reduction in apparent or total amylose content corresponded to an increase in peak viscosity of about 22 and 25 RVU, respectively, at 12% starch concentration. Of the seven U.S. cultivars, the lower amylose cultivars Penawawa and Klasic were missing the granule-bound starch synthase (GBSS; ADPglucose starch glycosyl transferase, EC 2.4.4.21) protein associated with the Waxy gene locus on chromosome 4A (Wx-B1 locus). Kanto 107 was confirmed as missing both the 7A and 4A waxy proteins (Wx-A1 and Wx-B1 loci). The hardness NIL also were shown to be null at the 4A locus. Apparent and total amylose contents of prime starch generally corresponded well to the number of GBSS proteins; although the hardness NIL tended to have somewhat higher amylose contents than did the other GBSS 4A nulls. We concluded that reduced quantity of starch amylose due to decreased GBSS profoundly affects starch gelatinization, pasting, and gelation properties.     

Quality of Spaghetti Made from Full and Partial Waxy Durum Wheat

The waxy character is achieved in durum wheat (Triticum turgidum L. var. durum) when the granule‐bound starch synthase activity is eliminated. The result is a crop that produces kernels with no amylose in the starch. The presence of two Waxy loci in tetraploid wheat permits the production of two partial waxy wheat genotypes. Advanced full and partial waxy durum wheat genotypes were used to study the effect of waxy null alleles on pasta quality. Semolina from full and partial waxy durum wheats was processed into spaghetti with a semicommercial‐scale extruder, and pasta quality was evaluated. Cooked waxy pasta was softer and exhibited more cooking loss than pasta made from traditional durum cultivars. These features were attributed to lower setback of waxy starch as measured with the Rapid Visco Analyser. High cooking loss may be due to the lack of amylose‐protein interaction, preventing the formation of a strong protein network and permitting exudates to escape. Waxy pasta cooked faster but was less resistant to overcooking than normal pasta. Partial waxy pasta properties were similar to results obtained from wild‐type pasta. This indicates that the presence of a single pair of functional waxy genes in durum wheat was sufficient to generate durum grain with normal properties for pasta production. Waxy durum wheat is not suitable for pasta production because of its softening effect. However, this property may offer an advantage in other applications.     

Effect of Variation in Amylose Content and Puroindoline Composition on Bread Quality in a Hard Spring Wheat Population

Milling and breadbaking quality of hard‐textured wheat may be influenced by alternative alleles at the Wx loci controlling percent amylose in the endosperm, and the puroindoline (pin) loci controlling grain hardness. For this experiment, we developed recombinant inbred lines (RIL) from a cross between Choteau spring wheat cultivar and experimental line MTHW9904. Choteau has the PinB‐D1b mutation conferring grain hardness and the Wx‐B1a allele at the Wx‐B1 locus conferring wild‐type amylose content. MTHW9904 has the PinA‐D1b allele conferring grain hardness and the Wx‐B1b allele conferring lower amylose content, causing a partial waxy phenotype. RIL with the PinB‐D1b mutation (n = 49) had significantly softer kernels, higher break flour yield, and higher loaf volume than lines with the PinA‐D1b mutation (n = 38). Lines with partial waxy phenotype due to Wx‐B1b (n = 43) had significantly lower kernel weight, lower amylose content, and higher flour swelling power than lines with wild‐type starch due to Wx‐B1a (n = 51). These results provide additional evidence for the positive effect of PinB‐D1b on bread quality in hard wheats, while genotype at Wx‐B1 was generally neutral for bread quality in this population. Interactions between the Pin and Wx loci were minimal.     

Association of Starch Granule Proteins with Starch Ghosts and Remnants Revealed by Confocal Laser Scanning Microscopy

Starch suspensions (0.25%) were gelatinized to 70 and 100°C, and starch ghosts (defined as gelatinized starch granule envelopes after the majority of internal starch polymers have been released) and remnants were collected by centrifugation and washed with water. Protein was revealed in isolated gelatinized normal starch ghosts using confocal laser scanning microscopy and a protein‐specific dye that fluoresces only after reaction with primary amines in protein. This technique eliminates background interference from residual dye. Observation of fluorescent‐labeled protein in the starch ghosts at different optical depths of field revealed that protein was concentrated in the envelopes of swollen, gelatinized potato, maize, and wheat starch ghosts. Only traces of protein were found in gelatinized starch granule remnants of waxy maize and amylose‐free potato starches after they were heated to 100°C, indicating that the proteins observed in gelatinized normal maize starch were largely granule‐bound starch synthase (GBSS). Moreover, fragility of the gelatinized waxy and amylose‐free starch granule remnants might be caused in part by the lack of GBSS. Gel electrophoresis of proteins in starch ghosts confirmed that GBSS in potato and maize was tightly associated with the starch ghosts. The study provides a structural explanation for a role of granule‐associated proteins in maintaining the integrity of starch ghosts and remnant structures, and their consequent effect on paste rheology.     

Observations on the Quality Characteristics of Waxy (Amylose‐Free) Winter Wheats

Previous investigations have suggested waxy (amylose‐free) wheats (Triticum aestivum L.) possess weak gluten properties and may not be suitable for commercial gluten extraction. This limitation could prevent the use of waxy wheat as a source of unique starch, because gluten is a by‐product of the wheat starch purification process. Fifty waxy wheat lines were used to determine the extent to which gluten protein and other grain quality related traits might vary and, consequently, allow the development of waxy wheat with acceptable gluten properties. Among the waxy lines, significant variation was observed for all measured quality traits with the exception of flour protein concentration. No waxy entries statistically equaled the highest ranking nonwaxy entry for grain volume weight, falling number, flour yield, or mixograph mix time. No waxy lines numerically exceeded or equaled the mean of the nonwaxy controls for falling number, flour yield, or mixograph mix time. For grain and flour protein related variables, however, many waxy lines were identified well within the range of acceptability, relative to the nonwaxy controls used in this study. Approximately 50% of the waxy lines did not differ from the highest ranking nonwaxy cultivar for grain and flour protein concentrations. Forty‐three (86%) of the tested waxy lines were not sig‐nificantly different from the nonwaxy line with the highest mixograph mixing tolerance, 22/50 (44%) of the waxy wheat lines did not differ from the highest ranking nonwaxy line in gluten index scores, and 17/50 (34%) did not differ from the highest ranking nonwaxy line in extracted wet gluten. All waxy experimental lines produced gluten via Glutomatic washing. The quality of the gluten, as measured both by mixograph and gluten index, varied widely among the waxy lines tested. These observations suggest that weak gluten is not a natural consequence of the waxy trait, and waxy cultivars with acceptable gluten properties can be developed.     

Morphological Changes of Granules of Different Starches by Surface Gelatinization with Calcium Chloride

Native starch granules of 11 selected cultivars (potato, waxy potato, sweet potato, normal maize, high‐amylose maize, waxy maize, wheat, normal barley, high‐amylose barley, waxy barley, and rice) were treated with a calcium chloride solution (4M) for surface gelatinization. The surface‐gelatinized starch granules were investigated using light microscopy and scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). In general, those starches with larger granule sizes required longer treatment time to complete the gelatinization. The salt solution treatment of starch was monitored by light microscopy and stopped when the outer layer of the granule was gelatinized. The surface gelatinized starch granules were studied using scanning electron microscopy. On the basis of the gelatinization pattern from calcium chloride treatments, the starches could be divided into three groups: 1) starches with evenly gelatinized granule surface, such as normal potato, waxy potato, sweet potato, maize, and high‐amylose maize; 2) starches with salt gelatinization concentrated on specific sites of the granule (i.e., equatorial groove), such as wheat, barley, and high‐amylose barley; and 3) starches that, after surface gelatinization, can no longer be separated to individual granules for SEM studies, such as waxy barley, waxy maize, and normal rice. The morphology of the surface gelatinized starch resembled that of enzyme‐hydrolyzed starch granules.     

Identification and Characterization of U.S. Wheats Carrying Null Alleles at the wx Loci

Granule-bound starch synthase (GBSS) is the primary enzyme responsible for the synthesis of amylose in amyloplasts of cereal endosperm cells. Bread wheats, due to their hexaploid genetic system, carry three genes (wx loci) encoding GBSS. Purification and separation of GBSS from more than 200 North American hexaploid wheats allowed the identification of genotypes that carry null alleles at either the wx-A1 and wx-B1 loci. In addition, the cultivar Ike carried both wx-A1 and wx-B1 null alleles. No wx-D1 nulls were detected. Null alleles were found in 10% of the hard winter wheats tested, but in only 2% of the sampled soft winter wheats. Amylose contents of wheats carrying single null alleles at either the wx-A1 or wx-B1 loci often were lower than those of wild type wheats, but greater reduction in amylose content was observed in Ike. Monoclonal antibodies were used to quantify water-extractable GBSS in both wild-type and null genotypes. Gene dosage compensation was evident, although GBSS content, as measured by ELISA, was significantly lower in Ike than in all other wheats. The identification of null alleles in adapted genotypes suggests the development of wheats with a wide range of amylose contents will be possible by simple genetic crossing and selection.     

Interactions Among Wx Genes and Effects of a Mutated Wx‐D1e Allele on Starch Properties in Wheat

The waxy mutant wheat Tanikei A6599‐4 contains little amylose and exhibits a stable hot paste viscosity. It has null alleles at the Wx‐A1 and Wx‐B1 loci and a mutated allele at the Wx‐D1 locus (Wx‐D1e). From the cross‐combination of Kanto 123 (normal amylose line) and Tanikei A6599‐4, 51 DH (doubled haploid) lines were produced and their genotypes were determined by SDS‐PAGE and a derived cleaved amplified polymorphic sequence (dCAPS) analysis. Eight genotypes were obtained at the expected ratio. Using a Rapid Visco Analyser (RVA), all the lines with the same genotype as Tanikei A6599‐4 showed a stable hot paste viscosity. The other lines did not show a stable hot paste viscosity regardless of the presence of the Wx‐D1e allele. When two genotypes with the same Wx‐A1 and Wx‐B1 alleles were compared, the one with Wx‐D1e contained less amylose and exhibited a lower final viscosity and a lower setback with RVA. Although the Wx‐D1e allele produces an almost inactive Wx protein, these findings suggest that this allele contributes at some level to starch synthesis.     

Composition and Reactivity of A‐ and B‐type Starch Granules of Normal,Partial Waxy,and Waxy Wheat

Wheat has great potential to make inroads into starch markets with the advent of partial waxy and waxy starches of diverse composition and properties. The majority of isolated starch utilized in food applications is chemically modified to improve starch properties according to the intended use. Therefore, it is critical to understand factors that affect wheat starch reactivity. This work investigated the relative reactivities of normal, partial waxy, and waxy wheat starches and their respective A‐ and B‐type starch granule fractions. Native starch isolated from four closely related soft wheat lines (normal, partial waxy, and full waxy) was modified through 1) substitution (propylene oxide analog) and 2) cross‐linking (phosphorus oxychloride) reactions to generate both types of modified starch products for each wheat line. Characterization of the unmodified starch fractions confirmed compositional differences among the cultivars and their respective granule types. In cross‐linking reactions, B‐type granules were slightly more reacted than A‐type granules for all cultivars, while the waxy starch generally exhibited higher reactivity compared with normal and partial waxy starches. For the substituted starches, no differences in reactivity were observed among the cultivars or between the two granule types.     

Significance of Starch Properties and Quantity on Sponge Cake Volume

We evaluated the qualitative and quantitative effects of wheat starch on sponge cake (SC) baking quality. Twenty wheat flours, including soft white and club wheat of normal, partial waxy, and waxy endosperm, as well as hard wheat, were tested for amylose content, pasting properties, and SC baking quality. Starches isolated from wheat flours of normal, single‐null partial waxy, double‐null partial waxy, and waxy endosperm were also tested for pasting properties and baked into SC. Double‐null partial waxy and waxy wheat flours produced SC with volume of 828–895 mL, whereas volume of SC baked from normal and single‐null partial waxy wheat flours ranged from 1,093 to 1,335 mL. The amylose content of soft white and club wheat flour was positively related to the volume of SC (r = 0.790, P < 0.001). Pasting temperature, peak viscosity, final viscosity, breakdown, and setback also showed significant relationships with SC volume. Normal and waxy starch blends having amylose contents of 25, 20, 15, and 10% produced SCs with volume of 1,570, 1,435, 1,385, and 1,185 mL, respectively. At least 70 g of starch or at least 75% starch in 100 g of starch–gluten blend in replacement of 100 g of wheat flour in the SC baking formula was needed to produce SC having the maximum volume potential. Starch properties including amylose content and pasting properties as well as proportion of starch evidently play significant roles in SC baking quality of wheat flour.     

Physicochemical and Structural Characteristics of Flours and Starches from Waxy and Nonwaxy Wheats

A waxy spring wheat (Triticum aestivum L.) genotype was fractionated into flour and starch by roller and wet‐milling, respectively. The resultant flour and starch were evaluated for end‐use properties and compared with their counterparts from hard and soft wheats and with commercial waxy and nonwaxy corn (Zea mays L.) starches. The waxy wheat flour had exceptionally high levels of water absorption and peak viscosity compared with hard or soft wheat flour. The flour formed an intermediate‐strength dough that developed rapidly and was relatively susceptible to mixing. Analysis by differential scanning calorimetry and X‐ray diffractometry showed waxy wheat starch had higher gelatinization temperatures, a greater degree of crystallization, and an absence of an amylose‐lipid complex compared with nonwaxy wheat. Waxy wheat and corn starches showed greater refrigeration and freeze‐thaw stabilities than did nonwaxy starches as demonstrated by syneresis tests. They were also similar in pasting properties, but waxy wheat starch required lower temperature and enthalpy to gelatinize. The results show analogies between waxy wheat and waxy corn starches, but waxy wheat flour was distinct from hard or soft wheat flour in pasting and mixing properties.