2016 Volume 22 Issue 6 Pages 841-846
Water absorption (%) in small wheat flour samples must be determined in many flour experiments. In general, a farinograph is used to determine the water absorption, but this method requires large amounts of wheat flour (300 g). In this study, water absorption in a small amount of wheat flour (10 g) was determined using a mixograph. The water absorption measured using the mixograph was very similar to that measured using a farinograph and 300 g of wheat flour. Thus, the water absorption in a small amount of wheat flour can be accurately measured using a mixograph.
Measurement of the water absorption (%) in wheat flour is necessary to assess the nature of the wheat flour, which is related to protein quantity and quality, to damaged starch, and to wheat polysaccharides such as pentosans and β-glucans (Eliasson and Larsson 1993). Water absorption in wheat flour is also important for the process of precise breadmaking. In general, the water content in bread dough is around 65%. When the water content is lower than optimal, the mixing time will increase. The bread volume is affected more by a water content that is too low than by one that is too high. The volume of bread will be reduced when the water content is below about 45% (Eliasson and Larsson 1993).
Water absorption in wheat flour is generally measured using the Brabender farinograph test. In this test, water is added to 300 g of wheat flour (14% moisture content) until the specified consistency is brought (usually) to 500 Brabender units (BU). The water absorption of wheat flour is described as the amount of water necessary to bring the dough to a specified consistency (500 BU) at the point of optimal development. According to collaborative tests carried out in 1966-67, a value of 0.55% for the coefficient of variation for a farinograph test was indicated in water absorption (D'Appolonia and Kunerth 1990). Absorption increases linearly with the amount of protein, but the slope of the regression line depends on the variety of wheat. The level of damaged starch plays a role when the level of damaged starch increases (Holas and Tipples 1978, Tipples 1969, and Farrand 1972). The amount of pentosans and β-glucans will also affect water absorption (Lineback and Rasper 1988). When breadmaking is performed with a specific amount of water, the optimal consistency of the bread dough for good breadmaking properties (bread height (mm) and specific volume (cm3/g)) could be obtained.
However, a large amount of wheat flour (300 g) is necessary when a farinograph test is used to determine the water absorption of wheat flour. In many experiments, determination of the water absorption in a small amount of wheat flour (10 g) is necessary. Finney and Shogren (1972) measured the baking absorption and ascertained it in the mixograph profiles indicated by optimal, −2, −4, −6, +2, +4, and +6% of baking absorption, respectively, and showed that stiff doughs produce mixograms having relative wild swings, the extent of which depends on the degree of dough stiffness. In contrast, slack doughs produce unusually narrow mixograms during the hydrating and developing periods prior to reaching the peak or point of minimum mobility. However, the measurement of water absorption in wheat flour using a mixograph was not discussed in their paper. Thus, in this study, we measured the water absorption in various wheat flours using a 10-g mixograph, and compared the resulting data with data obtained from a farinograph. Mixographs are used for other measurements of wheat flour dough. The mixograph profile showed that increases in hydrophobicity of the wheat flour occurred with dry heating (Ozawa and Seguchi, 2006, and Nakamura et al. 2008), and that the viscoelasticity of wheat glutenin fraction decreases after the addition of dry-heated rice flour (Nakagawa et al. 2016).
Wheat flours Thirteen types of wheat flour were used in this experiment. Seven brands of commercial flour were used: Camellia I, II, Super Camellia, Super King (Nisshin Flour Milling, Tokyo, Japan), Kumamoto I, II (Kumamoto Flour Milling, Kumamoto, Japan), and Avalon (Nippon Flour Milling, Tokyo, Japan). In addition, six types of flour were prepared by Nippon Flour Milling (Tokyo, Japan): 1CW I, II (Canada), DNS I, II, SH I, and II (United States). The general analysis (protein, ash, and moisture content) of these wheat flours is shown in Table 1. Protein was determined by the Kjeldahl method, and protein conversion was performed using the formula N × 5.7 (Approved Method 46-10, AACC International 2000). Ash was determined by the AACC International method (08-01, 2000) at 14.0% moisture content.
Average ± standard deviation (n=3)
Brabender farinograph and mixograph tests Water absorption of the wheat flour was measured using a farinograph (AACC International method 54-21, 2000) test, in which 300 g of wheat flour (14% moisture content) was mixed with water added by burette-titration to attain 500 BU. Water absorption of the wheat flour was then obtained from reading the graduated burette. A mixograph test was performed as reported by Nakamura et al. (2008). Wheat flour (10 g) (14% moisture content) and water were mixed in a 10-g mixograph (National MFG Company, Lincoln NE) bowl at 21°C. The mixing speed of the mixograph was 86 rpm. Water absorption was determined from a mixogram of wheat flour as follows: maximum peak height in the mixograph profile was measured (mm) with a dial and digital calipers.
Bread making test Bread making was performed in accordance with the method of Seguchi et al. (1997). Flour (290 g), compressed yeast (8.7 g), sugar (14.5 g), salt (2.9 g), and water (estimated from a farinograph at 500 BU) were mixed in a computer-controlled National Automatic Bread Maker (SD-BT6; Panasonic Corp., Osaka, Japan) with the 1st proof of 2 h 20 min at 30°C. The timing was 15 min for the 1st mixing, 50 min to allow the mixture to rest, 5 min for the 2nd mixing, and 70 min for fermentation. Mixing conditions (time and temperature) were carefully computer-controlled in the bread maker. The bread dough was then removed from the bread maker and divided into 120-g pieces, rounded, molded, and placed into baking pans (AACC Intl. 2000 (method 10-10B)). Bread dough was further proofed for 22 min at 38°C, and then baked at 210°C for 30 min in a model DN-63 deck-style oven (Yamato Scientific Co., Ltd., Tokyo, Japan). After baking, bread was removed from the pan and cooled for 1 h at a room temperature of 26°C and a relative humidity of 43%. Bread height (mm), weight (g), and volume (cm3) were measured, and the crumb (porous structures) grain was evaluated visually. Loaf volume was measured by the rapeseed displacement method.
Determination of water absorption by farinograph Figure 1 shows the typical farinograph profile of wheat flour (for example, DNS II), in which the vertical axis indicates the consistency (BU) of the wheat flour and the horizontal axis indicates running time (min) of an experiment. Wheat flour (300 g) containing 14% moisture content was mixed with water added from a graduated burette in a farinograph, and the water absorption (mL) in the wheat flour could be obtained when the consistency of the dough reached 500 BU. It is generally known that the amount of added water to bread dough calculated from the water absorption gives optimal breadmaking properties (bread height (mm) and specific volume (cm3/g)). To indicate clear differences in breadmaking properties with different water contents, SH I wheat flour having lower water absorption (5.83 mL/10 g in Table 3) was selected for the breadmaking test. It is known that the water absorption in SH I wheat flour was 58.3%, and excellent breadmaking properties were obtained at 58.3% (bread height; 79.02 mm and specific volume; 3.38 cm3/g) (Fig. 2B and Table 2). In the case of 40.3% and 71.3%, the resulting values of 72.33 mm and 2.91 cm3/g (Fig. 2A), and 63.90 mm and 2.85 cm3/g, respectively (Fig. 2C), were obtained. Large differences in breadmaking properties were obtained when 40.3% (−18%) and 71.3% (+13%) were selected.
B. farinograph profile of DNS II wheat flour.
Appearance of bread baked with SH I wheat flour at various water levels. A; 40.3%, B; 58.3%, C; 71.3%
Average ± standard deviation (n=3)
Determination of water absorption by mixograph It was found that water absorption at 500 BU showed the most suitable amount of water in the bread dough. Although 300 g of wheat flour is needed to measure the water absorption with a farinograph, in many cases it is necessary to determine the water absorption in a smaller amount of wheat flour, such as 10 g. Thus, we designed a small-scale method to assess water absorption in wheat flour using a mixograph instrument. A mixograph instrument is generally used for many dough rheological studies in this field. First, various wheat flours (12 samples) (Table 1) were subjected to the farinograph test, and water absorption in the wheat flours was determined (Table 3). Although the values of water absorption (mL/10 g wheat flour) obtained from the farinograph varied, they were in the range of 5.83 – 6.93 mL (average 6.45 ± 0.33 mL) per 10 g of wheat flour (Fig. 3 and Table 3). Next, mixograph tests with the same wheat flours were performed according to the data of water absorption (mL/10 g wheat flour) obtained from the farinograph. Figure 4 shows a mixograph profile of wheat flour (1CW I), in which the vertical axis indicates consistency (mm) of the dough and the horizontal axis indicates the running time (min) of the experiment. The height of the maximum peak in the mixograph profile (arrow in Fig. 4) was measured (mm) with a dial and digital calipers, and was calculated from the difference between highest swing (65.4 mm) and lowest swing (50.0 mm) as follows: (65.4 – 50.0)/2+50.0 = 57.7 mm. According to the water absorption obtained from the farinograph test in 1CW I wheat flour (Table 3), 6.35 mL of water was added to 10 g of 1CW I wheat flour in a mixograph bowl and tested, and the height of the maximum peak of 57.7 mm of 1CW I wheat flour was obtained from the mixograph profile. Other wheat flours yielded various data; however, all of the highest maximum peaks were within the range of 53.6 – 57.7 mm (average = 55.7 ± 1.1 mm) (Table 3 and Fig. 5). As mentioned in the Introduction section, the coefficient of variation for the farinograph test was rather small (0.55%); however, the maximum peak height on the mixographs indicated higher variation (1.1/55.7×100 = 1.97%), probably due to the imprecise temperature control of the room in which the mixograph was used. It is known that 500 BU of water absorption (mL/g), as determined by the farinograph test, was equivalent to 55.7 mm obtained from the mixograph test. Figure 5 indicates the relationship between the maximum peak height (mm) in the mixograph profile and the water (mL) in 10 g of wheat flour at 500 BU in the farinograph.
Water absorption in wheat flour at 500 BU in farinograph.
Mixograph profile of 10 g of 1CW I wheat flour and maximum peak height. Upper dotted line indicated 65.4 mm, and lower dotted line indicated 50.0 mm of consistency.
Relation between maximum peak height in mixograph profile and water absorption in wheat flour at 500 BU in farinograph.
In order to ascertain the relationship between the maximum peak height (mm) in mixograph test and 500 BU in farinograph test, Avalon wheat flour, which is generally used in breadmaking was examined by both farinograph and mixograph tests. First, to determine the water absorption in Avalon wheat flour, 10 g of wheat flour was examined in a mixograph test (Fig. 6). Various amounts of water (7.00, 7.05, 7.10, 7.16, 7.18, 7.20, 7.25, and 7.30 mL) were added to 10 g of the wheat flour, and the height of each maximum peak (61.00, 59.20, 58.20, 55.20, 56.40, 57.75, 54.70, and 53.40 mm, respectively) was determined from each mixograph profile. Plots of each height (mm) of the maximum peaks in the mixograph profiles were plotted linearly above the 55.7 mm line (Fig. 6), and the water absorption of 7.20 mL/10 g of Avalon wheat flour could be determined. To determine whether the water absorption (mL/10 g) obtained from the mixograph test was related to the water absorption obtained from the farinograph test, a farinograph test of wheat flour was performed with 216.0 (7.20 × 300/10 = 216.0) mL of water in 300 g of the wheat flour. Figure 7 shows the farinograph profile (500 BU) in which water (216.0 mL) was added to 300 g Avalon wheat flour. It was demonstrated that the water absorption (%) obtained using the mixograph coincided with that obtained using the farinograph test. Thus, we conclude that water absorption (%) in a small amount of wheat flour (10 g) can be measured using a mixograph.
Determination of water absorption (mL/10 g) from mixograph profile of Avalon wheat flour.
Confirmation of water absorptions of Avalon wheat flour (7.20 mL/10 g) by mixograph and farinograph tests.
Water absorption values of 12 types of wheat flour measured using a farinograph were compared with those measured using a mixograph. It was found that the water absorption in a small amount of wheat flour (10 g) can be measured using a mixograph.