J. M. C. Dang 1 and M. L. Bason 1,2

Transcription

1 AACCI Approved Methods Technical Committee Report: Collaborative Study on a Method for Determining the Mixing Properties of Dough Using High-Energy Mixing J. M. C. Dang 1 and M. L. Bason 1,2 ABSTRACT Traditional flour mixing-quality tests were introduced during the early 20th century to suit the flours and processing conditions prevalent at the time. As a result, these tests do not emulate the high rates of mechanical energy addition now commonly used in the dough mixers that are integral in modern rapid bake systems. A new method is needed that can better emulate these higher work rates to measure the processing potential of a flour. This report summarizes the results of a collaborative study conducted by the AACC International Physical Testing Methods Committee on the repeatability and reproducibility of a new method using high-energy mixing on a doughlab to determine the mixing properties of doughs. Twelve laboratories analyzed seven wheat flour samples, including one blind duplicate, with a range of mixing properties to evaluate the performance of the method. Using a 300 g mixing bowl, repeatability relative standard deviation (RSD r ) and reproducibility (RSD R ) were <0.3 and 1.5% for water absorption, 2.2 and 6.4% for dough development time, 3.4 and 7.6% for stability, 4.0 and 10.8% for softening, and 2.4 and 7.3% for energy at peak, respectively. Four of the laboratories also tested the samples using a 50 g mixing bowl. Sample results and trends between the two mixing bowls were similar. Using a faster mixing speed, results were obtained more quickly and with improved resolution of peak consistency. Overall the method showed acceptable precision for use in determining the mixing properties of flours used in modern rapid bake systems. Traditional flour mixing-quality tests were introduced during the early 20th century to suit the flour and processing conditions prevalent at the time. One such test is AACC International (AACCI) Approved Method (1), which uses the Bra- Fig. 1. doughlab mixer (Perten Instruments Australia). Cereal processors need relevant qualitative information on flour properties to consistently produce fit-for-purpose products in an efficient manner. Bakers in particular need to know a flour s water and mixing energy requirements, as well as likely product characteristics such as loaf volume. During the dough-mixing process, flour and ingredients are hydrated, gluten is developed, and air is incorporated into the gluten matrix. Mixing continues until the dough reaches optimal consistency, providing optimal loaf volume and scores after baking (6,11,13). For the dough to be properly developed, the mixing intensity and work imparted must be greater than the minimum critical levels. Failure to meet these requirements can result in poor dough-handling properties and loaf qualities, in particular loaf volume (6). High-energy commercial dough mixers are commonly used in bakeries employing rapid bake systems, such as the Chorleywood bread process used in the United Kingdom, Canada, Australia, and New Zealand. Mix times are typically 3 min, during which the dough must reach optimum consistency through an applied mechanical energy of W hr kg 1, which equates to an average work rate of 4 W hr kg 1 min 1, with a minimum requirement of W hr kg 1 min 1 (5,12). A lower energy, straight dough process is commonly used in Europe, while bakers in the United States commonly use a higher energy, two-step sponge and dough or continuous process (10). 1 Perten Instruments of Australia Pty. Ltd., Macquarie Park, NSW, Australia. 2 Corresponding author. mbason@perten.com; Tel: ; Fax: AACC International, Inc. CEREAL FOODS WORLD / 199

2 bender farinograph to mix flour and water with a relatively gentle mixing action at 63 rpm (equivalent to 1 W hr kg 1 min 1 ) at a constant temperature of 30 C (8). The low-energy mixing rates employed in such tests have been reported to provide poor predictions of processing requirements in modern bake systems (11,13). Strong wheat flours, such as those commonly used for making pan breads, typically have long dough development times when tested using these methods. In some cases, flours produce dough consistency curves with two peaks: the first being a hydration peak and the second being the true mixing or gluten-development peak (9). For some of these flours, the second peak may not be evident until a higher mixing speed is used (7). In such cases, traditional test methods incorrectly indicate short dough development times. High-energy mixing has been reported to provide faster and more accurate mixing information (2,3,5,11,13) and a better indication of commercial baking results (11,13). Zounis and Fig. 2. Example of a doughlab curve for a wheat flour tested using the proposed method and showing commonly measured parameters: peak torque (mn m), dough development time (min), stability (min), softening at 5 min after peak (mn m), and accumulated energy at peak torque (W hr kg 1 ). Water absorption (%) is derived from the peak torque and amount of water added during the test. 200 / JULY AUGUST 2013, VOL. 58, NO. 4

3 Quail (13) found that the standard farinograph test at 60 rpm showed no correlation with bakery mix time, but when mixing speed was increased to rpm, the correlation improved dramatically. Tanaka and Tipples (11) found that mixing at low CEREAL FOODS WORLD / 201

4 speed (65 rpm) provided distinctly misleading results for weak to strong flours, especially when salt was included in the formulation and that the development times obtained when flour was tested at higher mixing speeds (90 and 120 rpm) were more in line with actual work input in the baking process. Allen et al. (2, 3), while studying the mixing properties of very strong hard wheats, found that high-energy mixing helped to discriminate samples that appeared similar when mixed at 63 rpm. High-energy mixing not only reduced test times, but also resulted in better peak resolution and gave a better indication of dough stability. Because traditional low-energy mixing protocols have limited relevance for the strong flours and rapid processes now commonly used for breadmaking (11), there is a need for a new method that can better emulate these higher work rates in order to measure the processing potential of a flour and achieve faster, more accurate and relevant results that are easier to interpret. The doughlab (Fig. 1) was introduced in 2004 as a highintensity dough mixer designed to emulate the high work rates of modern dough mixers. Its user base is now expanding in the industry, where it is being used to measure the quality of wheat flour for making bread and many other products. It measures the resistance of a dough to mixing, including dough properties such as water absorption, dough development time, stability, and other dough-mixing characteristics. 202 / JULY AUGUST 2013, VOL. 58, NO. 4

5 For this study, a mixer speed of 120 rpm, corresponding to a work rate of 3 W hr kg 1 min 1, was selected. This report summarizes the results of a collaborative study conducted by the AACCI Physical Testing Methods Committee on the repeatability and reproducibility of the proposed method using highenergy mixing on a doughlab to determine the mixing properties of doughs. Collaborative Study Collaborators. Collaborators from various countries in Oceania, Europe, and North America were invited to participate in the study. Of the 14 collaborators who submitted results, 12 laboratories returned valid, duplicate 300 g bowl data, 4 of these laboratories also returned valid, duplicate 50 g bowl data. Of the two remaining laboratories, one failed to follow the method by not optimizing added water to bring the peak torque within tolerance of the target value, and the other only returned data for one sample after using a faulty method for moisture determination. Results from these laboratories were excluded from analysis. Materials. Collaborators were supplied with seven wheat flour samples with a range of mixing characteristics. The samples were designated using three-digit random numbers: biscuit flour (sample 416), soft biscuit flour (sample 521), plain flour (sample 104), baker s flour (sample 209), protein-enriched flour (sample 756), protein-enriched baker s flour (sample 961), and a blind duplicate of the plain flour (sample 459). The samples were purchased in bulk from a local supplier. Each sample was thoroughly mixed, packaged in 1.5 kg vacuum bags, coded, and distributed to collaborators by national and international couriers. Method. Collaborators were instructed to perform the following tests, in duplicate, on each of the samples: 1) Moisture content (% as is) determined by AACCI Approved Method (1). 2) doughlab Standard Method (proposed method) to determine peak torque (mn m); water absorption as a percentage of flour weight (%, ml/g) corrected to target torque and 14% moisture basis; dough development time (min); stability (min); softening at 5 min after peak torque (mn m); and accumulated energy at peak torque (W hr kg 1 ). The testing profile for the proposed doughlab method is shown in Table I. An example of a doughlab curve for a wheat flour tested using the proposed method and the measured parameters is shown in Figure 2. Statistical Analysis. Collaborative trial data for the measured parameters are provided in Tables II VIII. Data for the 300 g mixing bowl were analyzed according to the AOAC guidelines for collaborative study procedures (4) using templates provided by AACCI (Microsoft Excel worksheet). The following analyses were performed: Fig. 3. Sample bowl interaction plots. Error bars show ± 1 SD. Softening is shown as the percentage of target peak torque for comparison purposes. 1) Cochran Test To remove laboratories with poor repeatability or replication within the laboratory 2) Single and Double Grubbs Tests To remove laboratories with a mean value substantially different from the bulk of the laboratories 3) Precision Statistics Analysis of variance (ANOVA) performed on the remaining data to give precision values, including CEREAL FOODS WORLD / 203

6 a) Mean b) Repeatability standard deviation (S r ) c) Repeatability relative standard deviation (RSD r ) within laboratory repeatability d) Reproducibility standard deviation (S R ) e) Reproducibility relative standard deviation (RSD R ) between laboratory reproducibility 4) Interaction Test Two-factor ANOVA (Minitab, version 16, general linear model) to determine two-way interactions for sample bowl, laboratory bowl, and sample laboratory Analysis of Precision Data. Data for a maximum of 2 of 12 laboratories were removed as outliers for the 300 g bowl data (Table IX), which was within the acceptable limit of 2 of 9 laboratories (4). The values in Table IX indicate the precision of the method was generally acceptable. Water absorption precision RSD r and RSD R values were <0.3 and 1.5%, respectively (derived from values in Table IX). Dough development time RSD r was <2.2%, and RSD R was <6.4%. Similar observations were made for stability, with an average RSD r of <3.4% and an average RSD R for all samples of 7.6%, and for energy at peak torque, with an average RSD r and RSD R of 2.4 and 7.3%, respectively. The method also showed reasonable precision for softening data, with an average RSD r and RSD R of 4.0 and 10.8%, respectively. The 50 g bowl data set did not meet the AOAC requirement for a minimum of eight laboratories (4), so it is included here for comparison rather than as part of the method evaluation. Data for the 50 g bowl (Table X) were compared to corresponding 300 g bowl results using two-way interaction ANOVAs and showed that sample bowl interaction terms were small but significant (P < 0.01), with sample trends generally similar between bowls for the quality parameters measured (Fig. 3). Method users should note bowl size when reporting test results. Conclusions The collaborative study conducted by the AACCI Physical Testing Methods Committee provides a new method that better emulates the higher work rates required for determining the flour quality of strong wheats in a modern dough process. The proposed method shows acceptable within laboratory repeatability and between laboratory reproducibility for measuring dough mixing properties. Acknowledgments We thank Elaine Sopiwnyk, Physical Testing Methods Technical Committee chair; Roy Robertson, AACCI statistician; and the participating laboratories for their assistance in this study: Perten Instruments Australia, Australia; NSW Department of Primary Industries, Wagga Wagga Agricultural Institute, Australia; CSIRO Plant Industry, Australia; Department of Agriculture and Food, WA, Australia; GrainCorp, Australia; Perten Instruments AB, Sweden; Nofima AS, Norway; Kornax ltd., Iceland; München Technical University, Germany; and Grupo Gamesa, Mexico. References 1. AACC International. Method , Moisture Air-Oven Methods; Method , Rheological Behavior of Flour by Farinograph: Constant Flour Weight. Approved Methods of Analysis, 11th ed. Published online at AACC International, St. Paul, MN. 2. Allen, H. M., Pleming, D. K., and Pumpa, J. K. The development of a rapid dough bread baking method using a doughlab. Page 293 in: Cereals 2005: Proceedings of the 55th Australian Cereal Chemistry Conference and AACC International Pacific Rim Symposium. The Regional Institute Ltd., Sydney, Australia, Allen, H. M., Pumpa, J. K., and Blakeney, A. B. Dough mixing using a high speed dough mixer The doughlab. Page 256 in: Proceedings of the 54th Australian Cereal Chemistry Conference and 11th Wheat Breeders Assembly. C. K. Black, J. F. Panozzo, and G. J. Rebetzke, eds. Royal Australian Chemical Institute, North Melbourne, Australia, AOAC International. Appendix D: Guidelines for collaborative study procedures to validate characteristics of a method of analysis. In: Official Methods of Analysis of AOAC International, 18th ed. The Association, Gaithersburg, MD, Frazier, P. J., Daniels, N. W. R., and Russell Eggitt, P. W. Rheology and the continuous breadmaking process. Cereal Chem. 52(Suppl.): 106r, Kilborn, R. H., and Tipples, K. H. Factors affecting mechanical dough development. I. Effect of mixing intensity and work input. Cereal Chem. 49:34, Preston, K. R., and Kilborn, R. H. Dough rheology and the farinograph. Page 38 in: The Farinograph Handbook, 3rd ed. B. L. D Appolonia and W. H. Kunerth, eds. AACC International, St. Paul, MN, Shuey, W. C. The farinograph. Page 1 in: The Farinograph Handbook, 3rd ed. B. L. D Appolonia and W. H. Kunerth, eds. AACC International, St. Paul, MN, Shuey, W. C. Interpretation of the farinogram. Page 31 in: The Farinograph Handbook, 3rd ed. B. L. D Appolonia and W. H. Kunerth, eds. AACC International, St. Paul, MN, Sluimer, P. Mixing. Page 81 in: Principles of Breadmaking: Functionality of Raw Materials and Process Steps. AACC International, St. Paul, MN, Tanaka, K., and Tipples, K. H. Relation between farinograph mixing curve and mixing requirements. Cereal Sci. Today 14:296, Wilson, A. J., Wooding, A. R., and Morgenstern, M. P. Comparison of work input requirement on laboratory-scale and industrialscale mechanical dough development mixers. Cereal Chem. 74:715, Zounis, S., and Quail, K. J. Predicting test bakery requirements from laboratory mixing tests. J. Cereal Sci. 25:185, / JULY AUGUST 2013, VOL. 58, NO. 4