Dynamic Rheological Properties of Wheat Starch-Gluten Doughs1 K. A. Miller2,3 and R. C. Hoseney2,4 ABSTRACT
Cereal Chem. 76(1):105-109
Flour-water doughs made from strong and weak flours were tested using a dynamic rheometer with cone-and-plate geometry. Flour was fractionated to determine what component or components were responsible for the dynamic rheological properties (elastic modulus [G′], viscous modulus [G′′], and tan δ [G′/G′′]) values. Doughs made from strong flour had lower tan δ values than medium or weak flours. The isolated starch or gluten fraction was combined with vital wheat gluten or commercial wheat starch. Only
Larned starch gave doughs that were significantly different in dynamic rheological properties from dough made with other starches. The gluten isolated from strong flours gave doughs that were significantly different from doughs made with gluten isolated from weak flours. Reconstituted flours containing starch, gluten, and various amounts of lyophilized water-solubles were tested. Addition of water solubles decreased the elastic modulus and dramatically shortened optimum mixing time of the reconstituted flour.
The interactions between starch and gluten play a role in dough rheology (Sipes 1993, Petrofsky and Hoseney 1995). Petrofsky and Hoseney (1995) showed that starch from different sources (i.e., soft wheat, hard wheat, durum wheat, potato, rice, rye, oat, and corn) when mixed with a constant gluten source, gave doughs with different dynamic rheological properties. Sipes (1993) found that doughs produced from blends of corn starch and wheat gluten had higher elastic modulus than that of doughs made from blends of wheat starch and gluten. The water-soluble fraction of flour is known to affect its rheological and baking qualities. Removal of water solubles from flour increased the mixing time (Mattern and Sandstedt 1957). The watersoluble constituent responsible for that effect appeared to be the gliadin. Smith and Mullen (1965) reported that flours with shorter mixing times had more water solubles than flours with longer mixing times. Hoseney et al (1969) found that omission of the water-soluble fraction from reconstituted flour resulted in bread with decreased loaf volume. Sipes (1993) showed that surface lipids of starch granules were important to dough rheology. Surface lipids of corn starch increased the interaction between corn starch and gluten, whereas surface lipids of wheat starch decreased the interaction between wheat starch and gluten. Several authors have studied the rheological properties (elastic modulus [G′], viscous modulus [G′′], and tan δ [G′/G′′]) of good and poor breadmaking flours and their glutens (He and Hoseney 1991, Janssen et al 1996). Flours with good baking quality gave doughs that had good gas retention, relatively low amounts of protein soluble in 1% SDS and made bread with high loaf volume (He and Hoseney 1991). When tested in a dynamic rheometer, doughs made from good quality flour had lower tan δ (G′′/G′) values than those made from poor quality flour (He and Hoseney 1991, Janssen et al 1996). He and Hoseney (1991) suggested that the higher tan δ of the doughs made from poor quality flours resulted either from fewer entanglements or entanglements that were easily dissociated, possibly because of less hydrophilic interaction between the gluten proteins. Abdelrahman and Spies (1986) compared the dynamic rheological properties of two hard red winter wheat flours that had similar characteristics, except that one had good breadmaking qualities and the other had poor breadmaking qualities. The flour with good breadmaking qualities had lower G′, G′′, and tan δ values.
The objectives of this study were to determine the dynamic rheological properties of strong and weak flours and to determine the contributions of starch, gluten, water-soluble, and lipid fractions on the dynamic rheological properties of doughs. MATERIALS AND METHODS Sources of Flours Pure samples of wheat cultivars were obtained from Kansas seed producers (Triumph 64, Ponderosa, and Larned). A sample of a strong Canadian wheat (Glenlea) was obtained from Walter Bushuk, Department of Food Science, University of Manitoba. All wheats were tempered for 18 hr to 15.5% moisture and milled into straightgrade flours using a Buhler experimental mill. The milling room environment was 70% rh and 27°C. The wheats gave flours that varied widely in strength. Commercial flour was obtained from Cargill, Inc. (Wichita, KS). Optimum mixing times and water absorptions of the flours determined with the mixograph are shown in Table I. Flour Fractionation and Rehydration Flour was fractionated into starch, gluten, and water-soluble fractions (Miller and Hoseney 1997). Flour (500 g) and distilled water (320 g) were mixed to optimum using a pin mixer (National Manufacturing Division-TMCO, Lincoln, NE). The dough was washed by hand with 500-mL aliquots of distilled water until the wash water was clear. The wet gluten was frozen, lyophilized, and ground with a Krups household coffee mill to pass through a U.S. standard testing sieve No. 40 with an opening size of 425 µm. The gluten fraction consists mostly of protein with smaller amounts of starch, nonstarch polysaccharide (pentosans), lipid, and water. The liquid fraction was centrifuged for 30 min at 500 × g to separate the water solubles. The water-soluble fraction was frozen, lyophilized, and ground. The water-soluble fraction contains soluble proteins, starch, pentosans, and many low molecular weight materials. The starch fraction was frozen, lyophilized, and ground with a mortar and pestle until it passed through a U.S. standard testing sieve No. 40 with an opening size of 425 µm. The starch fraction was rehydraTABLE I Relative Strength, Protein Content, and Moisture Content of Flours
1 Contribution
No. 98-436-J. Kansas Agricultural Experimental Station, Manhattan, KS 66506. 2 Graduate research assistant and professor, respectively, Department of Grain Science and Industry, Kansas State University, Manhattan, KS 66506. 3 Present address: The Pillsbury Company, 330 University Avenue, S.E., Minneapolis, MN 55414. 4 Corresponding author. E-mail:
[email protected] Present address: R&R Research Services, Inc., 8831 Quail Lane, Manhattan, KS 66502. Publication no. C-1999-0107-01R. © 1999 American Association of Cereal Chemists, Inc.
Flour Triumph 64 Larned Ponderosa Glenlea Commercial a
Protein Relative Content Strength (14% mb) Weaka Weak Stronga Strong Average
11.22 10.03 12.44 13.20 11.27
Moisture Optimum Optimum Content Mixing Time Absorption (%, wb) (min) (%) 13.74 11.27 12.75 12.08 12.42
2.50 2.50 6.00 6.50 4.50
60 48 62 64 61
Characterization in the Fall 1995 Certified Seed Directory, Kansas Crop Improvement Association, Manhattan, KS. Vol. 76, No. 1, 1999
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ted to 11–14% moisture under 90–95% rh in a fermentation cabinet. The starch fraction consists mostly of prime starch with smaller amounts of damaged starch, small-granule starch, water-insoluble pentosans, protein, and ash. Protein and moisture contents of the starch, gluten, and water-soluble fractions are given in Table II. To determine the effect of the water-soluble fraction on the rheological properties of reconstituted flour, commercial flour was fractionated into gluten, starch, and water-soluble fractions. Isolated starch, gluten, and water solubles were reconstituted in the proportions in which they were isolated from flour: 81.6, 11.6, and 6.8, respectively. Other reconstituted flours were made with 0, 50, and 200% of the quantity of water solubles used above. As the amount of water solubles increased, the quantity of starch was reduced an equal amount. To determine the contribution of lipids to the rheological properties of flour-water doughs, the commercial flour was defatted with petroleum ether using a Soxhlet extractor. The amount of lipids extracted was 0.86% (wb). Lipids were reconstituted in the proportions found in the original flour. The lipid fraction was mixed with a small amount of flour by mulling with a mortar and pestle and then combined with the remainder of the flour and ground in a laboratory TABLE II Moisture and Protein Contents of Gluten, Starch, and Water-Soluble Fractions Component
Moisture Content (%, wb) Protein Content (14% mb)
Glutena
4.31 12.66 6.29 4.25 11.82 6.90 13.66 6.20 11.99 7.41 12.32
Starcha Water solubles a Glenlea gluten Glenlea starch Larned gluten Larned starch Ponderosa gluten Ponderosa starch Triumph 64 gluten Triumph 64 starch a
76.74 0.90 21.10 68.44 0.59 77.33 0.60 78.57 0.64 75.87 0.44
Fig. 1. Rheological properties of flour-water doughs made from strong and weak flours tested at 200% strain. l = Larned, n = Triumph 64, = Glenlea, = Ponderosa.
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Isolated from commercial flour. TABLE III Optimum Mixing Times and Water Absorptions of Starch-Gluten Doughsa
Gluten
Starch
Commercial Glenlea Glenlea Commercial Larned Larned Commercial Commercial Triumph 64 Triumph 64 Commercial
Commercial Glenlea Commercial Glenlea Larned Commercial Larned Ponderosa Triumph 64 Commercial Triumph 64
a
Optimum Mixing Time (min)
Optimum Water Absorption (%)
3.8 25.5 23.0 7.8 3.0 3.0 4.5 5.8 4.5 6.5 3.8
64 80 76 68 62 66 62 66 74 72 66
All samples labeled commercial were isolated from commercial flour. TABLE IV Optimum Mixing Times and Water Absorptions of Reconstituted Commercial Flour Containing Various Levels of Water Solubles
Combination Flour Reconstituted flour Reconstituted flour Reconstituted flour Reconstituted flour a
Water Solublesa ... 0 0.5 1.0 2.0
Optimum Mixing Time (min)
Optimum Water Absorption (%)
4.50 9.25 4.50 4.25 3.25
61 71 64 58 54
Multiplied by the normal level of water solubles.
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Fig. 2. Rheological properties of gluten-starch (1:4 ratio) doughs made from starch and gluten isolated from the same wheat cultivar and tested at 1% strain. l = Larned, n = Triumph 64, = Glenlea.
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Fig. 3. Rheological properties of gluten-starch (1:4 ratio) doughs made from starch and gluten isolated from the same wheat cultivar and tested at 200% strain. l = Larned, n = Triumph 64, = Glenlea.
Fig. 5. Rheological properties at 1% strain of gluten-starch (1:4 ratio) doughs made from glutens isolated from different flours and combined with wheat starch isolated from commercial flour. l = Larned gluten, n = Triumph 64 gluten, = Glenlea gluten.
Fig. 4. Rheological properties at 1% strain of gluten-starch (1:4 ratio) doughs made from starches isolated from different flours and wheat gluten isolated from commercial flour. l = Larned starch, n = Triumph 64 starch, = Glenlea starch, = Ponderosa starch.
Fig. 6. Rheological properties at 50% strain of gluten-starch (1:4 ratio) doughs made from glutens isolated from different flours and combined with commercial wheat starch. l = Larned gluten, n = Triumph 64 gluten, = Glenlea gluten.
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mill (Fred Stein Laboratories, Inc., Atchison, KS) for 10 sec to evenly distribute the lipids. Dough Preparation Starch-gluten doughs were made from a mixture of 80% starch and 20% gluten (wb). Doughs made from starch, gluten, and watersoluble fractions were reconstituted based on the proportions given previously. Optimum mixing times and optimum water absorptions were estimated (Tables III and IV) with a 10-g mixograph (National) using Approved Method 54-40A (AACC 1995). Doughs were mixed to optimum using a 10-g pin mixer (National). A sample of dough (2–4 g) was placed in a lightly greased, covered container and allowed to rest for 30 min at room temperature before testing in the dynamic rheometer. Dynamic Rheological Testing Dynamic rheological analysis was performed with a rheometer (RDS-7700, Rheometric Scientific, Piscataway, NJ) using a 25-mm cone-and-plate geometry. The cone had an angle of 0.1 radians. After placing the dough between the cone and plate, the minimum gap was adjusted to 0.05 mm. The excess dough was trimmed with an samll knife, and the edges were coated with automotive lubricant (Blue Guard 500+, high-temperature lithium complex grease, Farmland Industries, Kansas City, MO) to reduce water loss from the dough. After loading, the dough was allowed to rest for 5 min before testing. Wheat flour dough is a nonlinear material and often studied at very low strains where it approaches linear behavior. However, during processing and baking doughs are subjected to large strains. Therefore, we examined doughs at several strains. Statistical Analysis Each sample was measured in at least duplicate. Data were analyzed for statistical differences between treatments (α = 0.05) using the Statistical Analysis System (SAS Institute, Inc., Cary, NC).
Fig. 7. Effect of water solubles on the rheological properties of reconstituted flour-water doughs tested at 1% strain. Multiplied by the normal level of water solubles: l = 0, n = 0.5, = 1, = 2.
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RESULTS AND DISCUSSION Contributions of Starch and Gluten to the Rheological Properties of Flour-Water Doughs Two weak flours (Triumph 64 and Larned) and two strong flours (Ponderosa and Glenlea) were fractionated into gluten and crude starch fractions. Optimum mixing times and water absorptions for all combinations were estimated using a mixograph and then optimized at the dough mixer. Mixtures containing Ponderosa gluten were not developed into continuous doughs after 30 min of mixing. Therefore, gluten from Ponderosa was not studied. The dynamic rheological properties of the strong and weak flours are shown in Fig 1. The G′ and G′′ of the flour-water doughs increased with the frequency of oscillation. At strains ranging from 1 to 200%, G′ and G′′ were higher for strong flours. The strong flours tested had significantly lower tan δ values than weak flours. In other words, the strong flours were relatively more elastic than the weak flours. The lower tan δ value agrees with the report of Abdelrahman and Spies (1986). Gluten and starch fractions from those flours were recombined at a 1:4 ratio, mixed to optimum, and tested in the dynamic rheometer (Figs. 2 and 3). At 1% strain, the rheological properties (G′, G′′, and tan δ) were similar for Larned gluten-starch doughs and Larned flour-water doughs, indicating that the deletion of the watersoluble fractions had little effect on the rheological properties of those doughs. At 1% strain, Glenlea gluten-starch doughs had lower tan δ values than doughs made with Glenlea flour. However, at 200% strain, the gluten-starch doughs had higher tan δ values. At 1, 100, and 200% strains, Triumph 64 gluten-starch doughs had lower tan δ values than doughs made with Triumph 64 flour. In other words, Triumph 64 flour behaved more like a strong flour after fractionation and deletion of the water-soluble fraction. Thus, with Triumph and Glenlea, at low strains, the water-soluble fraction had a reducing action. This is consistent with the water solubles containing a low molecular weight thiol compound (i.e., cystiene, glutathione, or a similar compound). It would appear that Larned water solubles does not have this entity. The starches isolated from wheat cultivars were combined with a gluten isolated from commercial flour to determine whether they affected the dough’s rheological properties (Fig. 4). At all strain levels, reconstituted doughs containing starch isolated from Larned had lower G′ and G′′ than doughs made with any of the other starches. At 1% strain, doughs containing Larned starch had significantly higher tan δ than doughs made with other starches. The rheological properties of doughs made with starch from Triumph 64, Glenlea, and Ponderosa flours were not significantly different from each other. The starch from Larned flour appears to not interact as strongly with the gluten as the other starches. The factors responsible for the interaction of starch and gluten are not known. However, it has been reported that the starch can affect the interaction (Petrofsky and Hoseney 1995). The glutens isolated from the wheat cultivars were combined individually with a starch isolated from the commercial flour at the 1:4 ratio to determine whether the glutens controlled the dough’s rheological properties (Figs. 5 and 6). Doughs containing Glenlea gluten gave lower G′ and G′′ values than the other gluten doughs; however, the tan δ values were not significantly different. At 1% strain, the dough made with Triumph 64 gluten had a lower tan δ than doughs made with the other glutens. At 50% strain, the gluten from Larned flour had a much higher tan δ, indicating that it was relatively more viscous than the other samples. Effect of Water Solubles on the Rheological Properties of Reconstituted Flour-Water Doughs When the flour was fractionated and reconstituted, the optimum water absorption and the optimum mixing time decreased slightly (Table IV). The rheological properties of reconstituted flour and the original flour were similar but not identical.
Flour that was reconstituted without water solubles had a higher optimum water absorption and a much longer optimum mixing time than the original unfractionated flour (Table IV). The higher water absorption presumably results from the need to compensate for the reducing effect of the water solubles. As the amount of water solubles was increased, the optimum water absorbance and the optimum mixing time both decreased. Both the flour reconstituted in the original proportions and the reconstituted flour with 50% of the water solubles had approximately the same optimum mixing time and water absorption as the original flour. At 1% strain, the water-soluble content of dough influenced the dynamic rheological properties. The dough made from reconstituted flours containing 200% of the water solubles had significantly higher tan δ than the treatment with no water solubles (Fig. 7). At 50% strain, no significant differences occurred between the G′ values of the doughs made from reconstituted flours with different water-soluble contents. Lipids Contribution to Rheological Properties of Flour-Water Doughs Doughs made from defatted flours and tested at 1% strain were not significantly different from doughs made from the original flour. In addition, the doughs made from reconstituted flour was not significantly different from doughs made from either the defatted or the original flour. CONCLUSIONS Doughs made from strong flours had lower tan δ values than doughs made with medium or weak flours. Both gluten and watersoluble fractions affected the dough’s dynamic rheological properties. Only the starch isolated from Larned flour significantly affected the rheological properties of doughs. Less force was needed to
deform the glutens isolated from strong flours. Both G′ and G′′ generally increased as the water-soluble content was increased. The tan δ values increased with increased water solubles, thus, the dough became relatively more viscous. Water solubles dramatically shortened mixing times. Absence of the lipids normally present in the flour did not alter the rheological properties of the dough. LITERATURE CITED American Association of Cereal Chemists. 1995. Approved Methods of the AACC, 9th ed. Method 54-40A. The Association: St. Paul, MN. Abdelrahman, A., and Spies, R. 1986. Dynamic rheological studies of dough systems. Pages 87-103 in Fundamentals of Dough Rheology. H. Faridi and J. Faubion, eds. Am. Assoc. Cereal Chem.: St. Paul, MN. He, H., and Hoseney, R. C. 1991. Differences in gas retention, protein solubility, and rheological properties between flours of different baking quality. Cereal Chem. 68:526-530. Hoseney, R. C., Finney, K. F., Shogren, M. D., and Pomeranz, Y. 1969. Functional (breadmaking) and biochemical properties of wheat flour components. II. Role of water-solubles. Cereal Chem. 46:117-125. Janssen, A. M., van Vliet, T., and Vereijken, J. M. 1996. Fundamental and empirical rheological behaviour of wheat flour doughs and comparison with bread making performance. J. Cereal Sci. 23:43-54. Mattern, P. J., and Sandstedt, R. M. 1957. The influence of the water-soluble constituents of wheat flour on its mixing and baking characteristics. Cereal Chem. 34:252-267. Miller, R. A., and Hoseney, R. A. 1997. Factors in hard wheat flour responsible for reduced cookie spread. Cereal Chem. 74:330-336. Petrofsky, K. E., and Hoseney, R. C. 1995. Rheological properties of dough made with starch and gluten from several sources. Cereal Chem. 72:53-58. Sipes, K. K. 1993. Factors affecting protein and starch interaction. MS thesis. Kansas State University: Manhattan, KS. Smith, D. E., and Mullen, J. D. 1965. Studies on short- and long-mixing flours. II. Relationship of solubility and electrophoretic composition of flour proteins to mixing properties. Cereal Chem. 42:275-287.
[Received June 1, 1998. Accepted September 23, 1998.]
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