Published in Crop Sci. 44:173-176 (2004).
© 2004 Crop Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
CROP ECOLOGY, MANAGEMENT & QUALITY
Protein Composition and Quality of Some New Hard White Winter Wheats
P. R. Pike and
F. MacRitchie*
Department of Grain Science and Industry, Kansas State University, Manhattan, KS 66506
* Corresponding author (fim{at}wheat.ksu.edu).
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ABSTRACT
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The production of hard white winter (HWW) wheats (Triticum aestivum L.) in the USA is expected to increase in the future and to replace, at least to some extent, the traditional hard red winter (HRW) wheats that are currently grown. To monitor the effects of this change, nine HWW wheat lines including new cultivars and advanced breeding lines were evaluated for protein composition and functional quality and compared with eight corresponding HRW wheat lines. The percentages of the different classes of proteins, measured by size exclusion-HPLC, were similar in HWW lines to those of the HRW lines. Quality characteristics of the white wheat lines as measured by lactic acid solvent retention capacity, mixograph dough development times, and bake-test bread volume also equaled those for the red wheats. These data should serve as a benchmark for HWW wheats as more cultivars are released.
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INTRODUCTION
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INTERNATIONAL MARKETING of wheat is highly competitive. Requirements for high quality wheats, particularly for noodle manufacture in foreign markets have favored white wheats. This has caused exporting countries such as the USA to move toward producing more white wheats. White grain can be milled at a slightly higher extraction rate to yield more flour (1–2% higher) than red grain without altering the dry flour color (Lin and Vocke, 1998). Products such as Asian noodles processed from HWW wheat typically appear lighter in color, an important marketing characteristic. In addition, the bran, usually considered as a by-product of the milling of red wheat, could become a valuable coproduct for breakfast cereals in bran from white wheat. In Kansas, the state that produces the largest amount of HRW wheat in the USA, programs for developing HWW wheats have been in place with the objective of partially replacing the traditional HRW wheats in the near future. The primary difference between the two wheat classes (HRW and HWW) is the difference in color of the seed coat (bran) because of the presence of pigments in the HRW wheats. Bran color is determined by one, two, or three major genes. White wheats have no major genes for bran color. The first experimental Kansas HWW wheats were developed by crossing HRW wheats having only one or two genes for red grain. These crosses produce a proportion of white grain progeny from which the new cultivars were developed. The genes that determine bran color are thought not to affect other plant traits. However, white wheats are generally believed to be more susceptible to sprouting than red wheats, and this has tended to be confirmed for some of the newer white wheats grown in Kansas (Wu and Carver, 1999).
The transition from one class of wheat to another is a major step. To ensure its success, it is important to monitor the quality and composition of the new cultivars so as to anticipate any potential problems before they arise. Neglect of this precaution in the past has seen unexpected emergence of problems in the industry. For example, the production of large harvests of European wheat cultivars of poor processing quality occurred when yield was the major selection criterion (Booth and Melvin, 1979). More recently, to some extent as a reaction to this in breeding programs, cultivars with high dough strength have given problems in bakeries because of excessive dough mixing requirements (Wooding et al., 1999). Because a large proportion of the HRW wheat is used in the domestic market mainly for bread production, it is important to ensure that the newer HWW wheat cultivars match the bread-making quality of the HRW wheats. At the same time, it is important to be able to exploit the export advantages of white wheats. Preliminary results performed on flour samples from HWW cultivars grown in Kansas in the 1998 season showed that bread making quality was at least as good as that of current HRW cultivars (P. Pike, J. Gwirtz, and F. MacRitchie, unpublished results). Since then, more new HWW wheat cultivars have been released. The aim of the present work was to extend the previous study (1998) to measure the protein composition as well as the bread making quality of a number of the newer HWW wheat cultivars and advanced breeding lines grown in the 1999 season and to compare the results with those of the traditional HRW wheats from the same harvest.
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MATERIALS AND METHODS
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Wheat Samples and Milling
The study was performed with eight HRW and nine HWW wheats grown at the Kansas State University Agricultural Research Center, Hays, KS, in 1999 and supplied by Dr. T.J. Martin. These included released cultivars and advanced breeding lines, shown in Table 1. The 17 genotypes were grown in a randomized complete block design in 3.7-m2 plots with 30-cm row spacing between plots on previous summer fallow land. The plots were treated preplant with ammonia at a rate of 67.2 kg ha–1 (60 lb acre–1). The growing season is described as typical with little winterkill and a total of 419 mm rainfall from October 1998 through June 1999. The mean yields of all plots was 5039 kg ha–1 (75 bushels acre–1). The grain was harvested with few weather delays and little shattering. Grain was milled to 75% extraction on a Buhler mill.
Protein Characterization
High-molecular weight glutenin subunits (HMW-GS) were identified by SDS-PAGE. This was performed with 12% (w/v) separating and 4% (w/v) stacking gels on a Nu-Page mini-gel system (Novex, San Diego, CA). The protein was reduced by adding ß-mercaptoethanol to the sample buffer followed by vortexing for 1 h and holding at 80°C in a water bath. Gels were electrophoresed at 200 V for 2 h in a tris/glycine buffer, washed with deionized water, stained with Gelcode Blue Stain Reagent (Pierce, Rockford, IL) and dried between cellophane. Identification of HMW-GS was made by comparison to known standards. Calculation of Glu-1 scores was made according to Payne (1987).
Size exclusion-HPLC (SE-HPLC) was performed as described by Batey et al. (1991) with a HP 1100 system (Hewlett Packard) with automatic injection. For total protein characterization, flour samples (10 mg) were sonicated in 1 mL of SDS-phosphate buffer [0.5% (w/v) SDS, pH 6.9] for 15 s at 6 W output. Unextractable polymeric protein (UPP) was measured according to Gupta et al. (1993) by sonication for 25 s after removing the extractable protein by stirring in a vortex mixer. Means of duplicates were calculated for total protein and means of triplicate determinations for the UPP.
Solvent Retention Capacity Test
The lactic acid solvent retention capacity test (AACC method 56-10, AACC, 2000) was modified to a smaller scale. A suspension of flour [0.2 g in 1.0 mL 5% (v/v) lactic acid solution] was vortexed five times at 5-min intervals. The samples were centrifuged at 1020 x g for 15 min, inverted and drained for 5 min, and the tube and residue weighed. Flour samples were analyzed in triplicate and showed a 4.0% coefficient of variation. Specific SRC was calculated by dividing the SRC by the flour protein percentage.
Mixograph
Mixographs were obtained with a swinging-arm 10-g mixograph equipped with an analog digital data processor (National Manufacturing Co., Lincoln, NE). Mixing characteristics were determined using a constant water absorption of 60.0% based on a 14% moisture basis (140 g kg–1). Precautions were taken to keep temperature conditions constant and the final dough temperature after mixing was consistently 28 ± 1.0°C.
Baking Test
The baking test was based on the optimized straight-dough AACC method 10-10B (AACC, 2000) adapted for a 35-g flour scale and use of a fixed water absorption (60.0%) as for the mixograph. The formula included 35 g flour (14% moisture basis), 2.1 g sucrose, 1.1 g all-purpose shortening (ADM, Decatur, IL), 0.7 g dry yeast (Universal Food Corp., Milwaukee, WI), 0.53 g NaCl, and 0.7 g malted barley flour (Malt Products, Saddle Brook, NJ). Dough oxidant was omitted to assess the natural breadmaking potential of each flour. Doughs were mixed to peak development time with a 35-g mixograph. Doughs were molded with a manual 35-g running board molder based on the 10-g molder described by Shogren and Finney (1984). Doughs were proofed to 2.3 cm above the pan and baked for 15 min at 230°C. The bake test was conducted according to a randomized incomplete block design and each flour was baked in triplicate. Baked loaves were waterproofed by immersing in a 85/15 mixture of paraffin wax/petrolatum jelly. Loaf volume was measured by water displacement by an apparatus similar to the one described by Gras and MacRitchie (1973).
Statistical Analysis
Covariance estimates of day x cultivar interactions affecting at least triplicate estimates of loaf volume and significant differences between loaf volume values were analyzed by the pairwise t test (5% error rate) by statistical software (SAS, Cary, NC). A covariance estimate of loaf volume differences between days was conducted for the control flour loaf volume data. A zero root mean square analysis (determined by SAS) showed that variation in loaf volume observations between days for the same flour was not significant. ANOVA of triplicate replications between and within measurements of protein composition by SE-HPLC was obtained with the same statistical software. Lactic acid solvent retention capacity (SRC) determinations are the means of triplicate runs.
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RESULTS AND DISCUSSION
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Protein Composition
Protein analyses of the eight HRW and nine HWW wheats are summarized in Table 1 (HMW-GS composition and Glu-1 Quality Scores) and Table 2 (flour protein content, percentages of polymeric protein, gliadin and albumin/globulin and unextractable polymeric protein, UPP). Polymeric protein includes all the multiple-chain proteins but it is mainly glutenin. The main variation of HMW-GS occurs at the Glu-B1 locus (Table 1). Trego differs in having HMW-GS 13+16 and Jagger has 17+18. The other lines have either 7+8 or 7+9. At Glu-A1, the lines have either subunit 1 or 2*. All the lines have HMW-GS 5+10 expressed at Glu-D1 except the HWW advanced breeding line KS92709 which has subunits 2+12 and therefore has a relatively low HMW-GS Score. Mean values of all protein composition parameters are closely similar for the two wheat classes (Table 2). The HRW line KS97180B has an unusually low percentage of polymeric protein (33.8%), explained by it being a wheat/rye (1B/1R) translocation line, the only 1B/1R line in the sets of wheats used. The HWW line KS92946 also has a very low polymeric protein content but the reason for this is not apparent. The HWW line KS92709 is low in polymeric protein. This is the line having subunits 2+12. This is not reflected in the UPP which is not particularly low, possibly because the Glu-D1 subunits do not exert a large effect when strength-contributing subunits are present at Glu-A1 and Glu-B1 (MacRitchie et al., 1990).
Flour Functionality
Data for solvent retention capacity, mixograph dough development time and loaf volume in a bread-making test are summarized in Table 3. Although differences in solvent retention capacity are evident between individual lines, the mean values for the two classes are closely similar. This test using lactic acid is considered to be a good predictor of bread-making quality (Slade and Levine, 1994). Generally, a value above 100% is considered to be an indicator of good breadmaking quality. Mixograph peak dough development time is an important quality parameter as it is important for flours to have dough development times above a certain value to be good for bread-making (Pomeranz, 1968). On the other hand, excessively long mixing times are not desirable as this puts strains on bakery production schedules (Wooding et al., 1999). The development times are generally within the optimum limits for both wheat classes. The only HWW line showing an excessive mixing time is the HWW advanced breeding line KS96HW94, which has a time of 9.8 min. Its overstrong dough properties can be rationalized by its percentage of polymeric protein and UPP, which are both the highest among the HWW lines. The bake-test loaf volumes are also comparable between the two classes. The mean value for loaf volumes of HWW cultivars is close to that for the HRW cultivars.
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CONCLUSIONS
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Both protein composition and quality of the newer HWW lines being developed for the Great Plains area compared favorably with those of the HRW lines, some of which are the main cultivars currently being grown. Since it is anticipated that the HWW wheat class will progressively replace the HRW wheats, it will be important to continue to monitor the HWW lines to ensure that the quality is maintained. The protein composition and quality data for the HWW wheat cultivars in this study may serve as a benchmark in future evaluation of this wheat class.
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ACKNOWLEDGMENTS
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The authors gratefully acknowledge financial support from the Kansas Wheat Commission for this project. We thank Dr. T.J. Martin for supplying all the grain samples. Dr. J.A. Gwirtz is thanked for contributing to the initial phase of the study by carrying out milling of grain from the 1998 harvest.
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NOTES
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Contribution No. 03-78-J from the Kansas Agricultural Experiment Station, Manhattan, KS 66506.
Received for publication November 4, 2002.
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REFERENCES
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- AACC. 2000. Approved Methods of the AACC, 10th ed. Methods 56–10 and 10–10B. American Association of Cereal Chemists, St. Paul, MN.
- Batey, I.L., R.B. Gupta, and F. MacRitchie. 1991. Use of size-exclusion high-performance liquid chromatography in the study of wheat flour proteins: An improved chromatographic procedure. Cereal Chem. 68:207–209.
- Booth, M.R., and M.A. Melvin. 1979. Factors responsible for the poor breadmaking quality of high yielding European wheat. J. Sci. Food Agric. 30:1057–1064.
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INTRODUCTION
