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Low moisture milling of wheat for quality testing of wholegrain flour
Journal of Cereal Science 58 (2013) 420e423
Contents lists available at ScienceDirect
Journal of Cereal Science journal homepage: www.elsevier.com/locate/jcs
Low moisture milling of wheat for quality testing of wholegrain flour Andrés F. Doblado-Maldonado a, 1, Rolando A. Flores a, b, Devin J. Rose a, c, * a
Department of Food Science & Technology, University of Nebraska-Lincoln, 143 Filley Hall, Lincoln, NE 68583, USA The Food Processing Center, University of Nebraska e Lincoln, Lincoln, NE, USA c Department of Agronomy & Horticulture, University of Nebraska e Lincoln, Lincoln, NE, USA b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 15 May 2013 Received in revised form 14 August 2013 Accepted 20 August 2013
The objective of this study was to produce wholegrain wheat flour on a laboratory-scale with particle size distributions similar to commercially-milled samples without re-milling the bran. The moisture contents of four hard winter wheat cultivars were adjusted to 7.29e7.98% (by drying), 9.00e10.6% (“as is”), and 15.6% (by tempering) prior to milling into wholegrain flour. The moisture treatments appeared to affect the partitioning of wholegrain flour particles into each of three categories: fine (<600 mm), medium (600 e849 mm) and coarse (850 mm). When the distributions of particles were grouped into these categories, wholegrain flours made from dried and “as is” wheat fell within the values for commercial wholegrain flours, while that from tempered wheat contained more coarse particles than even the coarsest commercial wholegrain flour. Loaf volumes and crumb firmness were not significantly different between bread made from wholegrain flour that had been produced from dried or “as is” wheat, but loaf volume was significantly lower and bread crumb firmness was significantly higher when wholegrain flour from tempered wheat was used. These results show that wheat may be milled without tempering to produce wholegrain flour with particle size similar to some commercially-milled flours without needing to regrind the bran. Ó 2013 Elsevier Ltd. All rights reserved.
Keywords: Bread Baking Functionality Bran
1. Introduction In the literature, wholegrain wheat flour used in baking has been produced by many techniques, including: Waring blender followed by ball milling for up to 35 min (Li et al., 2012); laminated mill with 500 mm sieve (Steinfurth et al., 2012); disk mill equipped with a medium disk (Gelinas and McKinnon, 2011); a retail electric grain mill (Rose et al., 2011); among others. Most commonly, wholegrain flour has been produced by milling wheat using the standard method for producing straight-grade flour (approved methods 26-21.02 or 26-50.01; AACC International, 2013) and subsequently collecting all milling fractions. The nonflour milling fractions (bran, shorts) are then re-milled using a conical or hammer mill and then recombined with the straightgrade flour (Rose et al., 2008; Guttieri et al., 2011; Sanz-Penella et al., 2012; Sapirstein et al., 2012; Doblado-Maldonado et al., 2013). The disparity among milling methods in the literature
* Corresponding author. Department of Food Science & Technology, University of Nebraska e Lincoln, 143 Filley Hall, Lincoln, NE 68583, USA. Tel.: þ1 402 472 2802. E-mail address: [email protected] (D.J. Rose). 1 Present address: Laboratory of Food Chemistry and Biochemistry, Department of Microbial and Molecular Systems, KU Leuven, Belgium. 0733-5210/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jcs.2013.08.006
makes comparing results among studies difficult, since particle size distribution has such an important influence on flour functionality (Noort et al., 2010). In an ideal situation, wholegrain wheat flour used for laboratory baking tests would produce wholegrain flour with a particle size distribution similar to what would be produced industrially. This is indeed the idea behind standardized methods for producing white flours (approved methods 26-21.02 or 26-50.01; AACC International, 2013). Furthermore, an ideal method would not require re-milling of the bran fraction, since this doubles operator labor compared with a method that would only require one milling step. The objective of this study was to determine if omitting the tempering step from the approved methods for milling straightgrade flour (approved methods 26-21.02 or 26-50.01; AACC International, 2013) would produce wholegrain wheat flours with particle size distributions that were similar to what might be produced industrially, using a recent survey of commercially-milled whole wheat flour as a benchmark (Doblado-Maldonado and Rose, 2013), without the added step of re-milling the bran fraction as reported previously (Rose et al., 2008; Guttieri et al., 2011; Sanz-Penella et al., 2012; Sapirstein et al., 2012; DobladoMaldonado et al., 2013).
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(ASABE, 1997). After particle size separation, all fractions were recombined as described above to perform functionality tests.
2. Materials and methods 2.1. Samples
2.4. Mixograph and baking properties
Four wheat cultivars harvested in 2011: one hard white winter (i.e., Anton) and three hard red winter (i.e., McGill, Overland, and Wesley) were obtained from Husker Genetics, the University of Nebraska-Lincoln Foundation Seed Division. Moisture content was determined in triplicate using an air-oven method (approved method 44-19.01; AACC International, 2013). Protein contents in Anton, McGill, Overland, and Wesley were (% dry basis): 14.3, 14.6, 12.5, and 15.3, respectively (approved method 46-30.01; AACC International, 2013). Wheat kernel hardness (single-kernel characterization system model 4100; Perten, Springfield, IL USA) and white flour extraction rate (approved method 26-21.02; AACC International, 2013) were typical of hard wheat (range: 64.0 to 69.4 for hardness; 71.2%e72.7% for straight-grade flour yield).
Mixographs (National Manufacturing, Lincoln, NE USA) were run in triplicate using 10 g of flour each (approved method 5440.02; AACC International, 2013). Water absorption used during the experiment was determined using the regression equation based on the protein content provided in the method (water absorption ¼ 1.5*%protein þ 43.6), with a þ1.8% adjustment for wholegrain flour (Bruinsma et al., 1978). This resulted in water absorptions ranging from 62.4% to 66.3%. Data were analyzed using MixSmart software (National Manufacturing). Peak time (dough development time) and height (dough strength) were evaluated when the curve reached maximum height; mixing stability was the slope of the midline curve 1 min after Mixograph peak time; and resistance to dough extension was the total curve area at 10 min. Bread was made in triplicate using wholegrain flours milled on the Bühler mill. The 100% Whole Wheat Pan Bread Straight Dough Formula procedure was used (approved method 10-13.02; AACC International, 2013), with modifications. In particular, ingredients for a 100 g (flour weight) batch were weighed into the mixing bowl of a pin-type mixer (National Manufacturing) and water was added to match the absorption used for the Mixograph. The dough was then developed by mixing at ca. 140 rpm until the dough pulled away from the sides of the mixing bowl and appeared smooth and elastic. The remaining steps for fermentation, shaping, proofing, and baking were performed as described in the published method. Following cooling for about 1 h, loaf volume was determined by rapeseed displacement (approved method 10-05.01; AACC International, 2013). Then, loaves were sliced 12.5 mm thick per slice using an electric knife and bread slicing guide (Black & Decker Corporation, Towson, MD, USA). Bread crumb firmness was determined using a texture analyzer (TA.XT.Plus, Texture Technologies, Scardsale, NY, USA) according to approved method 74-09.01 (AACC International, 2013). Internal crumb structure was analyzed in triplicate per loaf using a C-Cell imaging system (Calibre Control International Ltd., UK). Baking tests were not performed on the Quadrumat Jr-milled samples because only 50 g of flour per replicate was available.
2.2. Wholegrain flour milling Wheat was subjected to three treatments: 1) “dried”: placed in a convection oven (GCA/Precision Scientific, Chicago, IL) at 40 C for 14 h (7.29%e7.98% moisture); 2) “as is”: no treatment (9.25%e10.6% moisture); and 3) “tempered”: moisture adjusted to 15.6% by addition of water (approved method 26-95.01; AACC International, 2013). Wheat was milled using a Bühler experimental mill (Uzwil, Switzerland; approved method 26-21.02; AACC International, 2013). Fractions (i.e., flour, bran, and shorts) were collected, weighed, and then recombined in a tumbling mixer for 3 min to obtain 100% extraction. Seven hundred fifty grams of each wheat cultivar*treatment combination were milled on the Bühler experimental mill in triplicate. Wheat was also milled using a Quadrumat Jr laboratory mill (CW Brabender, South Hackensack, NJ, USA; approved method 2650.01; AACC International, 2013). In this case, wholegrain flour was obtained by removing the sifting roller following milling. Fifty grams of each wheat cultivar*treatment combination were milled on the Quadrumat Jr laboratory mill in triplicate. 2.3. Particle size determination The three replicates of wholegrain flour (200 g for Bühler mill; 50 g for Quadrumat Jr mill) from each treatment*cultivar combination were separated on a sieve shaker (Model SS-15, Gilson Company, Lewis Center, OH) equipped with US standard sieve numbers 20, 30, 40, 50, 60 and 70, followed by a collection pan (sieve size openings: 850 mm, 600 mm, 425 mm, 297 mm, 250 mm, and 212 mm). Sample was shaken for 10 min and the weight retained on each sieve and in the pan was recorded as percent of the total. Mean particle size was calculated using equations from the American Society of Agricultural and Biological Engineers
2.5. Data analysis Data were analyzed using SAS software (version 9.2, SAS Institute, Cary, NC, USA). For the cultivars milled with different moisture treatments, a two-way ANOVA with cultivar and treatment as main effects was used. Fisher’s least significant difference test was used to determine significant differences among factors with significant F-tests. When comparing treatments with commercially-milled samples from Doblado-Maldonado and Rose (2013), a one-way
Table 1 Mean particle size (MPS) and particle size distribution (%) of wholegrain flours milled on a Bühler mill with different moisture treatments.a Factor Wheat Anton McGill Overland Wesley Treatment Dried as is Tempered a
MPS (mm) 153 159 151 148
11ab 10a 15b 17b
141 6c 149 11b 169 2a
<212 mm 73.2 71.3 74.7 74.7
1.2b 2.3c 2.5ab 2.0a
74.9 3.2a 73.6 1.7b 72.0 0.7c
212e249 mm 1.54 1.44 1.14 1.13
0.61a 0.73a 0.64b 0.59b
1.99 0.27a 1.41 0.20b 0.539 0.199c
250e296 mm 2.21 2.49 1.64 1.51
1.08ab 2.01a 0.91bc 0.76c
3.16 1.36a 2.03 0.40b 0.699 0.195c
297e424 mm 5.39 5.12 5.09 4.22
1.89a 2.13a 2.36a 1.42b
6.99 0.95a 5.25 0.67b 2.63 0.37c
425e599 mm 5.62 6.18 5.87 5.34
1.41b 1.56a 1.73b 1.24c
7.16 0.66a 6.17 0.56b 3.93 0.31c
600e849 mm 4.35 4.87 4.11 4.47
0.35bc 0.74a 0.91c 0.57b
4.03 0.69b 5.15 0.50a 4.17 0.16b
Mean standard deviation; n ¼ 9 for wheat; n ¼ 12 for treatment; values followed by the same letters within factor are not significantly different.
850 mm 7.68 8.56 7.49 8.61
5.84b 6.15a 7.32b 6.02a
1.77 0.64c 6.43 1.27b 16.1 0.8a
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A.F. Doblado-Maldonado et al. / Journal of Cereal Science 58 (2013) 420e423
ANOVA was used with brands 1e4 and treatments (dried, “as is”, and tempered) as the factor. Tukey’s multiple comparison test was used to determine significant differences among factors. For bread slice image analysis, 25 variables related to crumb structure were analyzed. Only variables that showed a significant treatment effect were reported. In all cases, statistical significance was defined as P < 0.05. 3. Results and discussion 3.1. Particle size distribution The particle size distributions of wholegrain flours milled on the Bühler mill are shown in Table 1. The same trends were observed when wheat was milled on the Quadrumat Jr mill (though numerical values were slightly different; data not shown). In particular, although there were significant differences in mean particle size and particle size distribution among wheat cultivars, the differences were relatively minor. More substantial differences were noted as a result of the moisture treatments prior to milling. As expected, higher mean particle sizes were obtained when wheat was tempered prior to milling due to less bran fracturing. For particle size distribution, a consistent decreasing trend was observed as moisture content of the wheat increased from dried to tempered in each of the five fractions below 600 mm. Conversely, the opposite was true for particles 850 mm. Between these two particle size categories (600e849 mm) appeared to be a transitional group with no clear trends as a result of the treatments. Thus the moisture treatments appeared to affect the partitioning of wholegrain flour particles into each of three categories: fine (<600 mm), medium (600e849 mm) and coarse (850 mm). The wholegrain flours were grouped into these three categories and compared with a set of commercial samples reported previously (Fig. 1; Doblado-Maldonado and Rose, 2013). The distribution of particles for wholegrain flours made from dried and “as is” wheat fell within the values for commercial samples for each of the three categories. Notably, the wholegrain flour made from dried wheat was not significantly different from commercial brand 1 for any of the particle size categories. In contrast, wholegrain flour from tempered wheat contained much more coarse particles than even the coarsest commercial wholegrain flour. These data support previous studies where tempered wheat produced wholegrain flour with a very coarse bran fraction that needed to be re-milled (Rose et al., 2008; Guttieri et al., 2011; SanzPenella et al., 2012; Sapirstein et al., 2012; Doblado-Maldonado et al., 2013). On the other hand, drying the wheat or milling the wheat “as is” resulted in wholegrain flours with particle sizes that were in the range of the wholegrain flours on the market without re-grinding the bran fraction. This offers a substantial advantage over the current practice, since only one milling operation is required rather than two. 3.2. Mixograph and baking properties Treatments did not result in substantial differences in Mixograph properties, but there were a few significant differences among them. In particular, peak height was higher in the flours from dried wheat compared with the flours from “as is” or tempered wheat [47.9% torque (TQ) compared with 47.0% TQ and 46.5% TQ, respectively; p < 0.01]. Peak height is a measure of dough strength; therefore, doughs became stronger as wheat decreased in moisture content during milling. Total Mixograph area decreased progressively from the dried flour to the tempered flours (160% TQ*min, 146% TQ*min, 133% TQ*min, respectively, p < 0.01), indicating reduced resistance to dough extension.
Fig. 1. Distribution of commercially milled wholegrain flours (brands 1e4) and wholegrain flours milled with different moisture treatments on a Bühler mill into fine (<600 mm), medium (600e849 mm), and coarse (850 mm) fractions; error bars show standard deviation; n ¼ 9 for brands 1e4; n ¼ 12 for dried, as is, and tempered; bars labeled with different letters are significantly different within particle size fraction; data for commercially milled wholegrain flours taken from Doblado-Maldonado and Rose (2013).
Milling moisture treatments influenced bread quality parameters much more so than Mixograph properties. The greatest loaf volumes were achieved when dried or “as is” wheat was used for milling (Table 2). Bread firmness was also lower when flour from
A.F. Doblado-Maldonado et al. / Journal of Cereal Science 58 (2013) 420e423 Table 2 Properties of wholegrain breads produced from flours milled on a Bühler mill with different moisture treatments.a Bread analysis parameter
Dried
Volume (cm3) Firmness (N) Slice brightness Cell contrast Number of cells Area of cells (%) Wall thickness (mm) Cell volume Cell elongation Curvature
522 3.34 85.5 0.604 1630 52.4 0.489 9.26 1.55 1430
As is
24a 0.86b 8.7c 0.021a 170a 0.8a 0.014a 1.03ab 0.05a 280a
514 3.47 86.9 0.597 1570 52.6 0.492 9.64 1.54 1370
Tempered
36a 0.94b 9.0b 0.021b 130b 0.8a 0.014a 1.03a 0.03a 210a
460 4.17 88.5 0.606 1530 52.1 0.482 9.09 1.52 1220
29b 1.01a 7.0a 0.019a 100b 0.9b 0.014b 1.06b 0.03b 160b
a Mean standard deviation; n ¼ 12; values followed by the same letters within row are not significantly different.
dried or “as is” wheat was used compared with tempered. Bread from wholegrain flour from tempered wheat was brighter than dried or “as is”, which suggested a lower occurrence of air cells (air cells appear black on the image). This was also evident in the number of cells, where wholegrain flour from tempered wheat produced bread with fewer cells than dried. Cell wall thickness, elongation, and curvature were also improved when wholegrain flour from dried wheat kernels was used as opposed to tempered. Since the major effect of the moisture treatments was on the size of the coarse (or bran) particles, these results can be likened to literature describing the effects of wheat bran of different particle sizes on flour functionality. These studies, unfortunately, report conflicting results (Lai et al., 1989; Moder et al., 1984; de Kock et al., 1999; Zhang and Moore, 1997, 1999; Noort et al., 2010). Noort et al. (2010) conducted the most comprehensive and recent of these studies and found that wheat bran particle size had minimal effects on mixing properties and substantial effects on bread properties, which is consistent with data from this study. However, Noort et al. (2010) reported that loaf volume decreased as bran particle size decreased, which is in opposition to that reported here (Table 2). In Noort et al. (2010), the negative effects of bran were mostly evident with very small mean particle sizes (129 mm); when wheat bran with larger mean particle sizes was used (374 mm) no substantial differences in loaf volume were evident. The Codex Alimentarius Commission (1995) suggests that a screen size with 212 mm opening be used to separate white flour from bran. If this criterion is used, the bran in the present study contained mean particle sizes of 440 5 mm, 504 29 mm, and 705 7 mm for dried, “as is”, and tempered, respectively. Thus, all wholegrain flours produced in this study had coarse mean particle sizes 374 mm, and therefore likely would not have the negative effects of fine bran reported in Noort et al. (2010). In support of the present results, Zhang and Moore (1999) reported higher loaf volume in bread made with bran of moderate mean particle size (415 mm) compared with very coarse (609 mm) and very fine (278 mm). Zhang and Moore (1999) also conducted a sensory panel on these breads and found that breads containing very coarse wheat bran scored significantly lower than bread that contained moderate or very fine bran particles. 4. Conclusion Wholegrain flour produced by collecting all millstreams from a pilot-scale Bühler mill or a laboratory scale Quadrumant Jr mill contained very coarse bran particles when milled from tempered wheat (15.6% moisture) and produced poor quality bread. Studies on wholegrain flour baking have subsequently re-milled the bran fraction to obtain wholegrain flour with typical particle sizes and acceptable functionalities (Rose et al., 2008; Guttieri et al., 2011;
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Sanz-Penella et al., 2012; Sapirstein et al., 2012; DobladoMaldonado et al., 2013). However, this research has shown that wheat may be milled without tempering to obtain whole wheat flour with a particle distribution in the range of commercially milled flour without the need to regrind the bran fraction. Furthermore, the wholegrain flours milled from wheat that had not been tempered had mixing and breadmaking properties that were superior to wholegrain flour from tempered wheat that had not undergone a separate milling step for the coarse bran fraction. This procedure may be useful for laboratory milling of wheat for quality testing in order to provide whole wheat flour that is appropriate for functionality tests with one milling step.
Acknowledgments This project was partially supported by US Department of Agriculture-National Institute of Food and Agriculture, NC-213: Marketing and Delivery of Quality Grains and Bioprocess Coproducts (#NEB-31-131). References AACC International, 2013. Approved Methods of Analysis, eleventh ed. AACC International, St. Paul, MN USA. Methods 10-05.01, 10-13.02, 26-21.02, 26-50.01, 26-95.01, 44-19.01, 46-30.01, 54-40.02, and 74-09.01 http://methods.aaccnet. org/default.aspx. ASABE, 1997. Method of Determining and Expressing Fineness of Feed Materials by Sieving. ASABE, St. Joseph, MI USA. Method S319.3. Bruinsma, B.L., Anderson, P.D., Rubenthaler, G.L., 1978. Rapid method to determine quality of wheat with the mixograph. Cereal Chem. 55, 732e735. Codex Alimentarius Commission, 1995. Codex Standard for Wheat Flour. Codex Standard 152-1985 http://www.codexalimentarius.org/download/standards/ 50/CXS_152e.pdf. de Kock, S., Taylor, J., Taylor, J.R.N., 1999. Effect of heat treatment and particle size of different brans on loaf volume of brown bread. Lebensmittel Wissenschaft und Technologie 32, 349e356. Doblado-Maldonado, A.F., Arndt, E.A., Rose, D.J., 2013. Effect of salt solutions applied during wheat conditioning on lipase activity and lipid stability of whole wheat flour. Food Chem. 140, 1e15. Doblado-Maldonado, A.F., Rose, D.J., 2013. Particle distribution and composition of retail whole wheat flours separated by sieving. Cereal Chem. 90, 127e131. Gelinas, P., McKinnon, C., 2011. A finer screening of wheat cultivars based on comparison of the baking potential of whole-grain flour and white flour. Int. J. Food Sci. Tech. 46, 1137e1148. Guttieri, M.J., Souza, E.J., Sneller, C., 2011. Laboratory milling method for whole grain soft wheat flour evaluation. Cereal Chem. 88, 1e5. Lai, C.S., Davis, A.B., Hoseney, R.C., 1989. Production of whole wheat bread with good loaf volume. Cereal Chem. 66, 224e227. Li, J., Kang, J., Wang, L., Li, Z., Wang, R., Chen, Z.X., Hou, G.G., 2012. Effect of water migration between arabinoxylans and gluten on baking quality of whole wheat bread detected by magnetic resonance imaging (MRI). J. Agric. Food. Chem. 60, 6507e6514. Moder, G.J., Finney, K.F., Bruinsma, B.L., Ponte, J.G., Bolte, L.C., 1984. Bread-making potential of straight-grade and whole-wheat flours of Triumph and Eagleplainsman V hard red winter wheats. Cereal Chem. 6, 269e273. Noort, M.W.J., van Haaster, D., Hemery, Y., Schols, H.A., Hamer, R.J., 2010. The effect of particle size of wheat bran fractions on bread quality e evidence for fibreprotein interactions. J. Cereal Sci. 52, 59e64. Rose, D.J., Ogden, L.V., Dunn, M.L., Pike, O.A., 2008. Enhanced lipid stability in whole wheat flour by lipase inactivation and antioxidant retention. Cereal Chem. 85, 218e223. Rose, D.J., Ogden, L.V., Dunn, M.L., Jamison, R.G., Lloyd, M.A., Pike, O.A., 2011. Quality and sensory characteristics of hard red wheat after residential storage for up to 32 y. J. Food. Sci. 76, S8eS13. Sanz-Penella, J.M., Laparra, J.M., Sanz, Y., Haros, M., 2012. Influence of added enzymes and bran particle size on bread quality and iron availability. Cereal Chem. 89, 223e229. Sapirstein, H.D., Siddhu, S., Aliani, M., 2012. Discrimination of volatiles of refined and whole wheat bread containing red and white wheat bran using an electronic nose. J. Food. Sci. 77, S399eS406. Steinfurth, D., Koehler, P., Seling, S., Muhling, K.H., 2012. Comparison of baking tests using wholemeal and white wheat flour. Europ. Food Res. Tech. 234, 845e851. Zhang, D., Moore, W.R., 1997. Effect of wheat bran particle size on dough rheological properties. J. Sci. Food. Agric. 74, 490e496. Zhang, D., Moore, W.R., 1999. Wheat bran particle size effects on bread baking performance and quality. J. Sci. Food. Agric. 79, 805e809.
Contents lists available at ScienceDirect
Journal of Cereal Science journal homepage: www.elsevier.com/locate/jcs
Low moisture milling of wheat for quality testing of wholegrain flour Andrés F. Doblado-Maldonado a, 1, Rolando A. Flores a, b, Devin J. Rose a, c, * a
Department of Food Science & Technology, University of Nebraska-Lincoln, 143 Filley Hall, Lincoln, NE 68583, USA The Food Processing Center, University of Nebraska e Lincoln, Lincoln, NE, USA c Department of Agronomy & Horticulture, University of Nebraska e Lincoln, Lincoln, NE, USA b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 15 May 2013 Received in revised form 14 August 2013 Accepted 20 August 2013
The objective of this study was to produce wholegrain wheat flour on a laboratory-scale with particle size distributions similar to commercially-milled samples without re-milling the bran. The moisture contents of four hard winter wheat cultivars were adjusted to 7.29e7.98% (by drying), 9.00e10.6% (“as is”), and 15.6% (by tempering) prior to milling into wholegrain flour. The moisture treatments appeared to affect the partitioning of wholegrain flour particles into each of three categories: fine (<600 mm), medium (600 e849 mm) and coarse (850 mm). When the distributions of particles were grouped into these categories, wholegrain flours made from dried and “as is” wheat fell within the values for commercial wholegrain flours, while that from tempered wheat contained more coarse particles than even the coarsest commercial wholegrain flour. Loaf volumes and crumb firmness were not significantly different between bread made from wholegrain flour that had been produced from dried or “as is” wheat, but loaf volume was significantly lower and bread crumb firmness was significantly higher when wholegrain flour from tempered wheat was used. These results show that wheat may be milled without tempering to produce wholegrain flour with particle size similar to some commercially-milled flours without needing to regrind the bran. Ó 2013 Elsevier Ltd. All rights reserved.
Keywords: Bread Baking Functionality Bran
1. Introduction In the literature, wholegrain wheat flour used in baking has been produced by many techniques, including: Waring blender followed by ball milling for up to 35 min (Li et al., 2012); laminated mill with 500 mm sieve (Steinfurth et al., 2012); disk mill equipped with a medium disk (Gelinas and McKinnon, 2011); a retail electric grain mill (Rose et al., 2011); among others. Most commonly, wholegrain flour has been produced by milling wheat using the standard method for producing straight-grade flour (approved methods 26-21.02 or 26-50.01; AACC International, 2013) and subsequently collecting all milling fractions. The nonflour milling fractions (bran, shorts) are then re-milled using a conical or hammer mill and then recombined with the straightgrade flour (Rose et al., 2008; Guttieri et al., 2011; Sanz-Penella et al., 2012; Sapirstein et al., 2012; Doblado-Maldonado et al., 2013). The disparity among milling methods in the literature
* Corresponding author. Department of Food Science & Technology, University of Nebraska e Lincoln, 143 Filley Hall, Lincoln, NE 68583, USA. Tel.: þ1 402 472 2802. E-mail address: [email protected] (D.J. Rose). 1 Present address: Laboratory of Food Chemistry and Biochemistry, Department of Microbial and Molecular Systems, KU Leuven, Belgium. 0733-5210/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jcs.2013.08.006
makes comparing results among studies difficult, since particle size distribution has such an important influence on flour functionality (Noort et al., 2010). In an ideal situation, wholegrain wheat flour used for laboratory baking tests would produce wholegrain flour with a particle size distribution similar to what would be produced industrially. This is indeed the idea behind standardized methods for producing white flours (approved methods 26-21.02 or 26-50.01; AACC International, 2013). Furthermore, an ideal method would not require re-milling of the bran fraction, since this doubles operator labor compared with a method that would only require one milling step. The objective of this study was to determine if omitting the tempering step from the approved methods for milling straightgrade flour (approved methods 26-21.02 or 26-50.01; AACC International, 2013) would produce wholegrain wheat flours with particle size distributions that were similar to what might be produced industrially, using a recent survey of commercially-milled whole wheat flour as a benchmark (Doblado-Maldonado and Rose, 2013), without the added step of re-milling the bran fraction as reported previously (Rose et al., 2008; Guttieri et al., 2011; Sanz-Penella et al., 2012; Sapirstein et al., 2012; DobladoMaldonado et al., 2013).
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421
(ASABE, 1997). After particle size separation, all fractions were recombined as described above to perform functionality tests.
2. Materials and methods 2.1. Samples
2.4. Mixograph and baking properties
Four wheat cultivars harvested in 2011: one hard white winter (i.e., Anton) and three hard red winter (i.e., McGill, Overland, and Wesley) were obtained from Husker Genetics, the University of Nebraska-Lincoln Foundation Seed Division. Moisture content was determined in triplicate using an air-oven method (approved method 44-19.01; AACC International, 2013). Protein contents in Anton, McGill, Overland, and Wesley were (% dry basis): 14.3, 14.6, 12.5, and 15.3, respectively (approved method 46-30.01; AACC International, 2013). Wheat kernel hardness (single-kernel characterization system model 4100; Perten, Springfield, IL USA) and white flour extraction rate (approved method 26-21.02; AACC International, 2013) were typical of hard wheat (range: 64.0 to 69.4 for hardness; 71.2%e72.7% for straight-grade flour yield).
Mixographs (National Manufacturing, Lincoln, NE USA) were run in triplicate using 10 g of flour each (approved method 5440.02; AACC International, 2013). Water absorption used during the experiment was determined using the regression equation based on the protein content provided in the method (water absorption ¼ 1.5*%protein þ 43.6), with a þ1.8% adjustment for wholegrain flour (Bruinsma et al., 1978). This resulted in water absorptions ranging from 62.4% to 66.3%. Data were analyzed using MixSmart software (National Manufacturing). Peak time (dough development time) and height (dough strength) were evaluated when the curve reached maximum height; mixing stability was the slope of the midline curve 1 min after Mixograph peak time; and resistance to dough extension was the total curve area at 10 min. Bread was made in triplicate using wholegrain flours milled on the Bühler mill. The 100% Whole Wheat Pan Bread Straight Dough Formula procedure was used (approved method 10-13.02; AACC International, 2013), with modifications. In particular, ingredients for a 100 g (flour weight) batch were weighed into the mixing bowl of a pin-type mixer (National Manufacturing) and water was added to match the absorption used for the Mixograph. The dough was then developed by mixing at ca. 140 rpm until the dough pulled away from the sides of the mixing bowl and appeared smooth and elastic. The remaining steps for fermentation, shaping, proofing, and baking were performed as described in the published method. Following cooling for about 1 h, loaf volume was determined by rapeseed displacement (approved method 10-05.01; AACC International, 2013). Then, loaves were sliced 12.5 mm thick per slice using an electric knife and bread slicing guide (Black & Decker Corporation, Towson, MD, USA). Bread crumb firmness was determined using a texture analyzer (TA.XT.Plus, Texture Technologies, Scardsale, NY, USA) according to approved method 74-09.01 (AACC International, 2013). Internal crumb structure was analyzed in triplicate per loaf using a C-Cell imaging system (Calibre Control International Ltd., UK). Baking tests were not performed on the Quadrumat Jr-milled samples because only 50 g of flour per replicate was available.
2.2. Wholegrain flour milling Wheat was subjected to three treatments: 1) “dried”: placed in a convection oven (GCA/Precision Scientific, Chicago, IL) at 40 C for 14 h (7.29%e7.98% moisture); 2) “as is”: no treatment (9.25%e10.6% moisture); and 3) “tempered”: moisture adjusted to 15.6% by addition of water (approved method 26-95.01; AACC International, 2013). Wheat was milled using a Bühler experimental mill (Uzwil, Switzerland; approved method 26-21.02; AACC International, 2013). Fractions (i.e., flour, bran, and shorts) were collected, weighed, and then recombined in a tumbling mixer for 3 min to obtain 100% extraction. Seven hundred fifty grams of each wheat cultivar*treatment combination were milled on the Bühler experimental mill in triplicate. Wheat was also milled using a Quadrumat Jr laboratory mill (CW Brabender, South Hackensack, NJ, USA; approved method 2650.01; AACC International, 2013). In this case, wholegrain flour was obtained by removing the sifting roller following milling. Fifty grams of each wheat cultivar*treatment combination were milled on the Quadrumat Jr laboratory mill in triplicate. 2.3. Particle size determination The three replicates of wholegrain flour (200 g for Bühler mill; 50 g for Quadrumat Jr mill) from each treatment*cultivar combination were separated on a sieve shaker (Model SS-15, Gilson Company, Lewis Center, OH) equipped with US standard sieve numbers 20, 30, 40, 50, 60 and 70, followed by a collection pan (sieve size openings: 850 mm, 600 mm, 425 mm, 297 mm, 250 mm, and 212 mm). Sample was shaken for 10 min and the weight retained on each sieve and in the pan was recorded as percent of the total. Mean particle size was calculated using equations from the American Society of Agricultural and Biological Engineers
2.5. Data analysis Data were analyzed using SAS software (version 9.2, SAS Institute, Cary, NC, USA). For the cultivars milled with different moisture treatments, a two-way ANOVA with cultivar and treatment as main effects was used. Fisher’s least significant difference test was used to determine significant differences among factors with significant F-tests. When comparing treatments with commercially-milled samples from Doblado-Maldonado and Rose (2013), a one-way
Table 1 Mean particle size (MPS) and particle size distribution (%) of wholegrain flours milled on a Bühler mill with different moisture treatments.a Factor Wheat Anton McGill Overland Wesley Treatment Dried as is Tempered a
MPS (mm) 153 159 151 148
11ab 10a 15b 17b
141 6c 149 11b 169 2a
<212 mm 73.2 71.3 74.7 74.7
1.2b 2.3c 2.5ab 2.0a
74.9 3.2a 73.6 1.7b 72.0 0.7c
212e249 mm 1.54 1.44 1.14 1.13
0.61a 0.73a 0.64b 0.59b
1.99 0.27a 1.41 0.20b 0.539 0.199c
250e296 mm 2.21 2.49 1.64 1.51
1.08ab 2.01a 0.91bc 0.76c
3.16 1.36a 2.03 0.40b 0.699 0.195c
297e424 mm 5.39 5.12 5.09 4.22
1.89a 2.13a 2.36a 1.42b
6.99 0.95a 5.25 0.67b 2.63 0.37c
425e599 mm 5.62 6.18 5.87 5.34
1.41b 1.56a 1.73b 1.24c
7.16 0.66a 6.17 0.56b 3.93 0.31c
600e849 mm 4.35 4.87 4.11 4.47
0.35bc 0.74a 0.91c 0.57b
4.03 0.69b 5.15 0.50a 4.17 0.16b
Mean standard deviation; n ¼ 9 for wheat; n ¼ 12 for treatment; values followed by the same letters within factor are not significantly different.
850 mm 7.68 8.56 7.49 8.61
5.84b 6.15a 7.32b 6.02a
1.77 0.64c 6.43 1.27b 16.1 0.8a
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ANOVA was used with brands 1e4 and treatments (dried, “as is”, and tempered) as the factor. Tukey’s multiple comparison test was used to determine significant differences among factors. For bread slice image analysis, 25 variables related to crumb structure were analyzed. Only variables that showed a significant treatment effect were reported. In all cases, statistical significance was defined as P < 0.05. 3. Results and discussion 3.1. Particle size distribution The particle size distributions of wholegrain flours milled on the Bühler mill are shown in Table 1. The same trends were observed when wheat was milled on the Quadrumat Jr mill (though numerical values were slightly different; data not shown). In particular, although there were significant differences in mean particle size and particle size distribution among wheat cultivars, the differences were relatively minor. More substantial differences were noted as a result of the moisture treatments prior to milling. As expected, higher mean particle sizes were obtained when wheat was tempered prior to milling due to less bran fracturing. For particle size distribution, a consistent decreasing trend was observed as moisture content of the wheat increased from dried to tempered in each of the five fractions below 600 mm. Conversely, the opposite was true for particles 850 mm. Between these two particle size categories (600e849 mm) appeared to be a transitional group with no clear trends as a result of the treatments. Thus the moisture treatments appeared to affect the partitioning of wholegrain flour particles into each of three categories: fine (<600 mm), medium (600e849 mm) and coarse (850 mm). The wholegrain flours were grouped into these three categories and compared with a set of commercial samples reported previously (Fig. 1; Doblado-Maldonado and Rose, 2013). The distribution of particles for wholegrain flours made from dried and “as is” wheat fell within the values for commercial samples for each of the three categories. Notably, the wholegrain flour made from dried wheat was not significantly different from commercial brand 1 for any of the particle size categories. In contrast, wholegrain flour from tempered wheat contained much more coarse particles than even the coarsest commercial wholegrain flour. These data support previous studies where tempered wheat produced wholegrain flour with a very coarse bran fraction that needed to be re-milled (Rose et al., 2008; Guttieri et al., 2011; SanzPenella et al., 2012; Sapirstein et al., 2012; Doblado-Maldonado et al., 2013). On the other hand, drying the wheat or milling the wheat “as is” resulted in wholegrain flours with particle sizes that were in the range of the wholegrain flours on the market without re-grinding the bran fraction. This offers a substantial advantage over the current practice, since only one milling operation is required rather than two. 3.2. Mixograph and baking properties Treatments did not result in substantial differences in Mixograph properties, but there were a few significant differences among them. In particular, peak height was higher in the flours from dried wheat compared with the flours from “as is” or tempered wheat [47.9% torque (TQ) compared with 47.0% TQ and 46.5% TQ, respectively; p < 0.01]. Peak height is a measure of dough strength; therefore, doughs became stronger as wheat decreased in moisture content during milling. Total Mixograph area decreased progressively from the dried flour to the tempered flours (160% TQ*min, 146% TQ*min, 133% TQ*min, respectively, p < 0.01), indicating reduced resistance to dough extension.
Fig. 1. Distribution of commercially milled wholegrain flours (brands 1e4) and wholegrain flours milled with different moisture treatments on a Bühler mill into fine (<600 mm), medium (600e849 mm), and coarse (850 mm) fractions; error bars show standard deviation; n ¼ 9 for brands 1e4; n ¼ 12 for dried, as is, and tempered; bars labeled with different letters are significantly different within particle size fraction; data for commercially milled wholegrain flours taken from Doblado-Maldonado and Rose (2013).
Milling moisture treatments influenced bread quality parameters much more so than Mixograph properties. The greatest loaf volumes were achieved when dried or “as is” wheat was used for milling (Table 2). Bread firmness was also lower when flour from
A.F. Doblado-Maldonado et al. / Journal of Cereal Science 58 (2013) 420e423 Table 2 Properties of wholegrain breads produced from flours milled on a Bühler mill with different moisture treatments.a Bread analysis parameter
Dried
Volume (cm3) Firmness (N) Slice brightness Cell contrast Number of cells Area of cells (%) Wall thickness (mm) Cell volume Cell elongation Curvature
522 3.34 85.5 0.604 1630 52.4 0.489 9.26 1.55 1430
As is
24a 0.86b 8.7c 0.021a 170a 0.8a 0.014a 1.03ab 0.05a 280a
514 3.47 86.9 0.597 1570 52.6 0.492 9.64 1.54 1370
Tempered
36a 0.94b 9.0b 0.021b 130b 0.8a 0.014a 1.03a 0.03a 210a
460 4.17 88.5 0.606 1530 52.1 0.482 9.09 1.52 1220
29b 1.01a 7.0a 0.019a 100b 0.9b 0.014b 1.06b 0.03b 160b
a Mean standard deviation; n ¼ 12; values followed by the same letters within row are not significantly different.
dried or “as is” wheat was used compared with tempered. Bread from wholegrain flour from tempered wheat was brighter than dried or “as is”, which suggested a lower occurrence of air cells (air cells appear black on the image). This was also evident in the number of cells, where wholegrain flour from tempered wheat produced bread with fewer cells than dried. Cell wall thickness, elongation, and curvature were also improved when wholegrain flour from dried wheat kernels was used as opposed to tempered. Since the major effect of the moisture treatments was on the size of the coarse (or bran) particles, these results can be likened to literature describing the effects of wheat bran of different particle sizes on flour functionality. These studies, unfortunately, report conflicting results (Lai et al., 1989; Moder et al., 1984; de Kock et al., 1999; Zhang and Moore, 1997, 1999; Noort et al., 2010). Noort et al. (2010) conducted the most comprehensive and recent of these studies and found that wheat bran particle size had minimal effects on mixing properties and substantial effects on bread properties, which is consistent with data from this study. However, Noort et al. (2010) reported that loaf volume decreased as bran particle size decreased, which is in opposition to that reported here (Table 2). In Noort et al. (2010), the negative effects of bran were mostly evident with very small mean particle sizes (129 mm); when wheat bran with larger mean particle sizes was used (374 mm) no substantial differences in loaf volume were evident. The Codex Alimentarius Commission (1995) suggests that a screen size with 212 mm opening be used to separate white flour from bran. If this criterion is used, the bran in the present study contained mean particle sizes of 440 5 mm, 504 29 mm, and 705 7 mm for dried, “as is”, and tempered, respectively. Thus, all wholegrain flours produced in this study had coarse mean particle sizes 374 mm, and therefore likely would not have the negative effects of fine bran reported in Noort et al. (2010). In support of the present results, Zhang and Moore (1999) reported higher loaf volume in bread made with bran of moderate mean particle size (415 mm) compared with very coarse (609 mm) and very fine (278 mm). Zhang and Moore (1999) also conducted a sensory panel on these breads and found that breads containing very coarse wheat bran scored significantly lower than bread that contained moderate or very fine bran particles. 4. Conclusion Wholegrain flour produced by collecting all millstreams from a pilot-scale Bühler mill or a laboratory scale Quadrumant Jr mill contained very coarse bran particles when milled from tempered wheat (15.6% moisture) and produced poor quality bread. Studies on wholegrain flour baking have subsequently re-milled the bran fraction to obtain wholegrain flour with typical particle sizes and acceptable functionalities (Rose et al., 2008; Guttieri et al., 2011;
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Sanz-Penella et al., 2012; Sapirstein et al., 2012; DobladoMaldonado et al., 2013). However, this research has shown that wheat may be milled without tempering to obtain whole wheat flour with a particle distribution in the range of commercially milled flour without the need to regrind the bran fraction. Furthermore, the wholegrain flours milled from wheat that had not been tempered had mixing and breadmaking properties that were superior to wholegrain flour from tempered wheat that had not undergone a separate milling step for the coarse bran fraction. This procedure may be useful for laboratory milling of wheat for quality testing in order to provide whole wheat flour that is appropriate for functionality tests with one milling step.
Acknowledgments This project was partially supported by US Department of Agriculture-National Institute of Food and Agriculture, NC-213: Marketing and Delivery of Quality Grains and Bioprocess Coproducts (#NEB-31-131). References AACC International, 2013. Approved Methods of Analysis, eleventh ed. AACC International, St. Paul, MN USA. Methods 10-05.01, 10-13.02, 26-21.02, 26-50.01, 26-95.01, 44-19.01, 46-30.01, 54-40.02, and 74-09.01 http://methods.aaccnet. org/default.aspx. ASABE, 1997. Method of Determining and Expressing Fineness of Feed Materials by Sieving. ASABE, St. Joseph, MI USA. Method S319.3. Bruinsma, B.L., Anderson, P.D., Rubenthaler, G.L., 1978. Rapid method to determine quality of wheat with the mixograph. Cereal Chem. 55, 732e735. Codex Alimentarius Commission, 1995. Codex Standard for Wheat Flour. Codex Standard 152-1985 http://www.codexalimentarius.org/download/standards/ 50/CXS_152e.pdf. de Kock, S., Taylor, J., Taylor, J.R.N., 1999. Effect of heat treatment and particle size of different brans on loaf volume of brown bread. Lebensmittel Wissenschaft und Technologie 32, 349e356. Doblado-Maldonado, A.F., Arndt, E.A., Rose, D.J., 2013. Effect of salt solutions applied during wheat conditioning on lipase activity and lipid stability of whole wheat flour. Food Chem. 140, 1e15. Doblado-Maldonado, A.F., Rose, D.J., 2013. Particle distribution and composition of retail whole wheat flours separated by sieving. Cereal Chem. 90, 127e131. Gelinas, P., McKinnon, C., 2011. A finer screening of wheat cultivars based on comparison of the baking potential of whole-grain flour and white flour. Int. J. Food Sci. Tech. 46, 1137e1148. Guttieri, M.J., Souza, E.J., Sneller, C., 2011. Laboratory milling method for whole grain soft wheat flour evaluation. Cereal Chem. 88, 1e5. Lai, C.S., Davis, A.B., Hoseney, R.C., 1989. Production of whole wheat bread with good loaf volume. Cereal Chem. 66, 224e227. Li, J., Kang, J., Wang, L., Li, Z., Wang, R., Chen, Z.X., Hou, G.G., 2012. Effect of water migration between arabinoxylans and gluten on baking quality of whole wheat bread detected by magnetic resonance imaging (MRI). J. Agric. Food. Chem. 60, 6507e6514. Moder, G.J., Finney, K.F., Bruinsma, B.L., Ponte, J.G., Bolte, L.C., 1984. Bread-making potential of straight-grade and whole-wheat flours of Triumph and Eagleplainsman V hard red winter wheats. Cereal Chem. 6, 269e273. Noort, M.W.J., van Haaster, D., Hemery, Y., Schols, H.A., Hamer, R.J., 2010. The effect of particle size of wheat bran fractions on bread quality e evidence for fibreprotein interactions. J. Cereal Sci. 52, 59e64. Rose, D.J., Ogden, L.V., Dunn, M.L., Pike, O.A., 2008. Enhanced lipid stability in whole wheat flour by lipase inactivation and antioxidant retention. Cereal Chem. 85, 218e223. Rose, D.J., Ogden, L.V., Dunn, M.L., Jamison, R.G., Lloyd, M.A., Pike, O.A., 2011. Quality and sensory characteristics of hard red wheat after residential storage for up to 32 y. J. Food. Sci. 76, S8eS13. Sanz-Penella, J.M., Laparra, J.M., Sanz, Y., Haros, M., 2012. Influence of added enzymes and bran particle size on bread quality and iron availability. Cereal Chem. 89, 223e229. Sapirstein, H.D., Siddhu, S., Aliani, M., 2012. Discrimination of volatiles of refined and whole wheat bread containing red and white wheat bran using an electronic nose. J. Food. Sci. 77, S399eS406. Steinfurth, D., Koehler, P., Seling, S., Muhling, K.H., 2012. Comparison of baking tests using wholemeal and white wheat flour. Europ. Food Res. Tech. 234, 845e851. Zhang, D., Moore, W.R., 1997. Effect of wheat bran particle size on dough rheological properties. J. Sci. Food. Agric. 74, 490e496. Zhang, D., Moore, W.R., 1999. Wheat bran particle size effects on bread baking performance and quality. J. Sci. Food. Agric. 79, 805e809.