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Flour quality and pentosan prepared by polishing wheat grain on breadmaking
Food Research International 36 (2003) 603–610 www.elsevier.com/locate/foodres
Flour quality and pentosan prepared by polishing wheat grain on breadmaking T. Maeda1, N. Morita* Laboratory of Food Chemistry, Division of Applied Biochemistry, Graduate School of Agriculture and Biological Sciences, Osaka Prefecture University, 1-1, Gakuen-cho, Sakai 599-8531, Japan Received 17 August 2002; accepted 12 December 2002
Abstract Whole grains of soft-type wheat were polished from the surface layer to the center by 10% of the total weight using a modified rice-polisher. Qualities of classified flours from polishing wheat grain (PWG) and effect of pentosan in the flours of PWG (F-PWG) on breadmaking were determined. All the F-PWG contained larger amounts of dietary fiber and damaged starch, and showed higher diastatic activity than conventionally milled wheat flours of Hermes (hard-type) or Norin 61 (N61, soft-type). All kinds of FPWG made harder or less moist dough from microscopic observations than Hermes or N61 did. The gluten matrix of F-PWG dough was distinctly not continuous in the presence of large dietary fiber, and the gluten sheet was clearly more discontinuous than those of Hermes and N61. Also, the gelatinization of starch in F-PWG during baking appeared to be more incomplete than that observed with Hermes or N61. However, additions of water-soluble and-insoluble pentosans obtained from the innermost fraction of F-PWG to N61 significantly improved the bread qualities. The improvements of bread quality and maturity of dough might be caused by the large amounts of pentosans and damaged starch in F-PWG. # 2003 Elsevier Science Ltd. All rights reserved. Keywords: Polishing wheat; Dough property; Bread quality; Dietary fiber; Damaged starch; Pentosan
1. Introduction Wheat grains contain large amounts of vitamins, minerals and nutritional fibers in the pericarp and germ. However, when the grains are conventionally milled, the recovery of flour is around 70% and most of the vitamins, minerals and fibers do not remain in the flour, because the pericarp and germ are completely separated from the endosperm. The milling system of wheat flour has been developed to obtain a more white or glossy flour for a long time by the complete removal of pericarp and germ. But, recently, the traditional or conventional milling system might be refocused accompanying today’s requirement for the viewpoints of nutritional and economical values. Especially in Japan, the
* Corresponding author. Tel.: +81-72-254-9459; fax: +81-72-2549918. E-mail address: [email protected] (N. Morita). 1 Present address: Department of Life and Health Sciences, Hyogo University of Teacher Education, 942-1, Shimokume, Yashiro, Hyogo 673-1494, Japan.
production of whole grain flour containing pericarp or germ is quite small, and the processed foods using the whole grain flour are still not common. Whole grains of soft-type wheat were polished from the surface layer to the center by 10% of the total weight using a modified rice-polisher. The eight fractions of polishing wheat grain (PWG) were obtained from the surface layer. The flour of PWG (F-PWG) contains the pericarp and germ, except for the near central part, namely 30%-core of whole grain, as is possible to understand from the structure of wheat grain. Therefore, the F-PWG retains a similar nutritional value to the whole grain flour with quite easy preparation. Therefore, F-PWG is expected to apply for various processed foods with appropriate flour quality of each fraction, as compared with common whole grain flour. F-PWG is assumed to contain large amounts of pentosans or dietary fiber derived from bran. Deficiency of dietary fiber has been reported to be associated with a high incidence of serious diseases such as diverticulosis of the colon, arteriosclerosis, colon cancer and diabetes mellitus (McIntosh, 1998; McIntosh, Leu, Royle, &
0963-9969/03/$ - see front matter # 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0963-9969(03)00008-5
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Young, 1996). It is a little appreciated fact that whole grains also contain a variety of antioxidant compounds, including several of those commons to fruits and vegetables (Andlauer & Furst, 1998; Collins, 1989). But, most of these antioxidant compounds are concentrated in the bran and germ, which are lost during milling. Moreover, the whole-grain intake provides protection from serious disease compared with refined-grain intake (Jacobs, Slavin, & Marquart, 1995). The daily diet of FPWG-supplemented bread or noodles might reduce the incidence of serious diseases. In addition, a water-soluble pentosan, which is composed of total pentosans by 30–40%, improved the breadmaking qualities, having the gelling property, high viscosity and retention property of gas bubbles in the dough (Baker, Parker, & Mize, 1945; MacRitchie, 1976; Mauritzen & Stewart, 1964). Furthermore, the polishing system might increase the water absorption during mixing, and improving dough maturity during fermentation, caused by larger amounts of damaged starch, as compared with conventionally milled flour. Therefore, the F-PWG is expected to have different flour qualities from the common whole grain flour and influence the baking properties. Based on these findings, in this paper, the authors describe the flour qualities and pentosan prepared from soft-type F-PWG, comparing with those of conventionally milled flours.
2. Materials and methods 2.1. Flour and chemicals The wheat grain used for the polishing method was a soft-type wheat cultivar, ‘Norin 61’ provided by Miyake Flour Milling Co., Ltd. (Osaka, Japan). The wholewheat grain was polished from the outer layer in increments of 10% of total weight using a modified rice-polisher (Itomen Co., Ltd., Hyogo, Japan), as described Table 1 Classified flours prepared by polishing wheat grain Sample
Fraction (%)
Sample
Fraction (%)
NA-1 NA-2 NA-3 NA-4 NA-5 NA-6 NA-7 NA-8
100–90 90–80 80–70 70–60 60–50 50–40 40–30 30–0
NB-1 NB-2 NB-3 NB-4 NB-5 NB-6 NB-7 NB-8
100–90 90–80 80–70 70–60 60–50 50–40 40–30 30–0
NA and NB are soft-type flours obtained from polishing wheat grain of Norin 61, and sieved through a pore size of 125 and 600 mm, respectively. NA-1 (100–90%), 10% layer polished from outer part of whole grains; NA-2 (90–80%), 10% layer polished from outer part of NA-1; NA-3NA-7, same 10% polishing as above; NA-8 (30–0%), 30%-core of the whole grains.
previously (Maeda, Okura, & Morita, 1999; Maeda & Morita, 2001). Table 1 shows the various F-PWG used for the following experiments. These F-PWG were sieved through a pore size of 125 mm (named as ‘NA’) or 600 mm (named as ‘NB’). NA-1 and NB-1 correspond to the F-PWG from 100 to 90% of the whole grain; NA-2 and NB-2, 90–80%; NA-3 and NB-3, 80–70%; NA-4 and NB-4, 70–60%; NA-5 and NB-5, 60–50%; NA-6 and NB-6, 50–40%; NA-7 and NB-7, 40–30%; NA-8 and NB-8, 30% to the core of the grain. The conventionally milled flour of soft-type wheat cultivar Norin 61 (N61) was also prepared. The control sample of conventionally milled commercial hard-type wheat flour ‘Hermes’ was donated by Okumoto milling Co., Ltd. (Osaka, Japan) and also used. For various analyses, the following enzymes were used: Kokugen G, amyloglucosidase of Aspergillus, was kindly provided by Daiwa Kasei Co., Ltd (Osaka, Japan). The activity was 104 JGU/g or more and 1 JGU was defined as the enzyme that liberates 1 m mole of glucose from 1% soluble starch solution at 40 C for 10 min (pH 4.5). Kleistase T-RC3 (Daiwa Kasei, CO.), a heat-stable aamylase of Bacillus subtilis has an activity of 3.0 104 LJ/g or more. The activity was determined according to the standard method of manufacturing amylase (JIS, K7001-1971). a- and b-amylases were obtained from Aspergillus and barley, respectively (Amano Pharmaceutical Co., Nagoya, Japan) and the activity of the former was 105 U and that of the latter was 6500 U/ml or more. Protease N (protease) of B. subtilis has an activity of 15104 U/g or more and was kindly supplied by Amano Pharmaceutical Co., Ltd. (Nagoya, Japan). All other chemicals used were purchased from Wako Pure Chemical Industries, Ltd. (Osaka, Japan) and they were of reagent grade. 2.2. Analytical methods for wheat flour 2.2.1. Dietary fiber and damaged starch of flour The contents of dietary fiber and damaged starch of flour sample were determined by AACC methods 32-05 and 76-30A (1994), respectively. 2.2.2. Mineral content of flour Mineral content of the flour sample was measured using the same fluorescent X-ray elemental analyser MESA-500 (Horiba Instrument Co., Ltd., Osaka, Japan) by the same procedure, as described previously (Maeda & Morita, 2001). 2.2.3. Pentosan content of flour Total (TP) and water-soluble pentosans (WSP) of flour were extracted by the method of Faurot et al. (1995). For the case of TP, flour (200 mg) was weighed in a pyrex glass tube fitted with a screw cap. 2N sulfuric acid (10 ml) was added to the flour sample and then the
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mixture was gently dispersed for 30 s using a homogenizer. Four grams of the sample suspension were boiled for 10 min in a water bath (100 C) and cooled in water, and then centrifuged for 10 min at 700 g. An aliquot of the clear supernatant diluted 10 times was used to determine TP content by the spectrophotometric method (Rouau & Surget, 1994). Regarding WSP, flour (1 g) was weighed into a centrifuge tube. Distilled water (8 ml) was poured into the tube, and then the flour sample was homogenized for 60 s. Two grams of the sample were shaken for 15 min at 27 C, and centrifuged for 10 min at 700 g. An aliquot of the supernatant was diluted 25 times, and the WSP was determined by the spectrophotometric method (Rouau & Surget, 1994). The content of water-insoluble pentosan (WISP) was calculated by subtracting the content of WSP from that of TP. 2.3. Measurement of enzyme activities 2.3.1. Preparation of enzyme solution from flours Water-extracts of the flour sample for the determination of enzyme were prepared by the same method, as described previously (Maeda & Morita, 2001). The enzyme solution was used in the following experiments. 2.3.2. Determination of enzyme activity in wheat flour The diastatic and proteolytic activities of flour sample were determined by the approved methods 22-15 and 22-62 (AACC, 1994), respectively. The a- and b-amylase activities of flour samples were determined by the methods of Sandstedt, Kneen, and Blish (1939), and Nikuni, Nakamura, and Suzuki (1977), respectively. These procedures are completely the same, as described previously (Maeda & Morita, 2001). 2.4. Analytical methods for dough and bread 2.4.1. Breadmaking The breadmaking formula included 280 g of flour, 5 g of sodium chloride, 17 g of sucrose, 3 g of dry baker’s yeast (Asahi Kasei Co., Ltd., Tokyo, Japan) and the same procedure was used by the automatic baker, as reported previously (Morita, Nakata, Hamauzu, & Toyosawa, 1996). In, addition, WSP and WISP obtained from F-PWG as mentioned above were added to the N61 and baked with the same method as above. Breadmaking was also carried out by the same method as described above.
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above. A portion of the dough sample mixed in the baker’s pan was cut out using scissors. For bread sample, a portion of bread baked was used by the same procedure, as described in breadmaking. 2.5.2. Scanning electron microscopy (SEM) SEM in a Hitachi apparatus (Model S-800) was done to observe the bread sample by the same method as reported previously (Morita et al., 1996). 2.5.3. Transmission electron microscopy (TEM) and light microcopy (LM) Both TEM and LM were done with a 3 3 3 mm3 portion of dough samples as described above. After these samples were frozen with liquid nitrogen, the frozen samples were fractured into a size of about 0.1 0.1 0.1 cm3, and then lyophilized. A portion of these samples was fixed with 2.5% glutaraldehyde in 0.05Mphosphate buffer (pH 6.8) for 15 h. After washing several times in the same buffer, the samples were postfixed in 2% osmium oxide for 2 h, then rinsed with the same buffer thoroughly, then dehydrated in a graded ethanol series. The samples thus prepared were embedded in an Epon mixture and sectioned with glass knives on a Porter-Blum Ultra-microtome MT1 (Sorvall Inc., USA). For TEM observation, sections from 0.01 to 0.05 mm thick were stained with saturated uranyl acetate in water and post-stained with lead citrate, and then examined with a TEM (H-600 Hitachi, Ltd., Tokyo, Japan), operated at 75 kv. For the LM observation, sections of about 1 mm thick were stained with 0.05 M-phosphate buffer containing 1% toluidine blue or 0.1% basic fuchsin at pH 6.8, then observed using an OM apparatus (Model 206065, Vanox Olympus, Co., Ltd., Tokyo, Japan). In addition, these samples were embedded in a hydrophilic resin (JB4) (Polyscience, Inc., USA), and cut in the dry resin by the same ultramicrotome. They were stained with PAS (Periodic Acid Schiff reaction) and light green SFY (Wako Pure Chemical Ind., Ltd., Osaka), and then observed using the same LM. 2.6. Analyses of pentosans from wheat flours 2.6.1. Fractionation of wheat flour by acetic acid Flour was fractionated by the method of Sollars (1958). The obtained water-extracts and tailings fractions were used for the following isolation of WSP and WISP, respectively.
2.5. Microscopic observation 2.5.1. Preparation of dough and bread Two hundred and eighty grams of flour and 210 g of water were mixed for 15 min in the same automatic baker for the preparation of dough sample, as described
2.6.2. Isolation of pentosans WSP and WISP were isolated from the water-extracts and tailings fractions by the method of Rouau and Moreau (1993). The water-extracts (8.0 g) dissolved with 100 ml of water were boiled for 10 min, and then
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cooled at room temperature. To remove the denatured protein, the solution was centrifuged (18,000 g for 20 min at 20 C), and the supernatant was adjusted to pH 5.0 before amyloglucosidase (500 mg) was added. The solution was allowed to react at 60 C for 3 h. After cooling to 40 C, 5 ml of 1M-phosphate buffer (pH 7.5) and 30 mg of protease were added to the solution and shaken for 4 h at 50 C. The solution was heated at 100 C for 10 min to inactivate the enzyme, then it was cooled and the solution was filtered through a filter paper No. 5C (Advantec Co., Ltd., Tokyo, Japan). Thereafter, 5 vol. of 95% ethanol were added to the solution with stirring. After standing overnight at 4 C, the precipitated material was collected by centrifugation. The WSP pellets were dehydrated with ethanol, acetone, and ether, and stored in a desiccator. To isolate WISP, the tailings fractions (40.0 g) obtained above were suspended in 100 ml of distilled water, adjusted to pH 5.0 with NaOH, and incubated with heat-stable aamylase (250 mg) at 100 C for 30 min. After cooling of the solution, amyloglucosidase (50 mg) was added, and the mixture was incubated at 60 C for 3 h to complete the digestion of starch. After addition of 5 ml phosphate buffer (1M, pH 7.5) containing 30 mg of protease, the mixture was incubated for 4 h at 40 C under shaking to digest insoluble proteins. The slurry was then centrifuged (18,000 g for 20 min at 20 C). The WISP pellets were extensively washed with distilled water and dried with organic solvents as mentioned above.
3. Results and discussion 3.1. Characteristics of flour sample Table 2 summarizes the characteristics of various F-PWG. All fractions of F-PWG contained significantly larger amounts of damaged starch; these amounts were 2–2.5 times of N61. The damaged starch might be formed mechanically when the grains were grounded by the polisher. Since the polishing method does not have a refining system of the hard bran from the soft endosperm during the operation process, F-PWG contain larger amounts of minerals derived from bran. The NA-1 and -5 significantly increased total amounts of K, Ca and Fe, as compared with N61. Particularly, the outermost F-PWG, NA-1 distinctly had the highest value of all samples. 3.2. Enzyme activity of flour The amounts of various enzyme activities and pentosans in F-PWG are shown in Table 3. The values of diastatic activity in F-PWG were two times or more of N61. NA-1 had the highest value of all samples. In general, the amount of reducing sugars existed originally in the conventionally milled flour is very small and constant. During fermentation of the dough, the damaged starch granules contained are easily hydrolyzed by amylases. Therefore, these results might be
Table 2 Characteristics of various flours of polishing wheat grain Sample
S (%)
Cl (%)
K (%)
Ca (%)
Fe (ppm)
Ni (ppm)
Damaged starch (%)
Dietary fiber (%)
Hermes N61 NA-1 NA-5 NA-8
0.16c 0.13ab 0.12ab 0.11a 0.14ab
0.07b 0.12b 0.07b 0.05a 0.09c
0.14a 0.16a 0.76d 0.42c 0.26b
0.03a 0.03a 0.08c 0.05b 0.03a
5.44a 25.12b 243.3d 80.24c 40.93b
1.62a 2.01c 2.55d 1.63a 1.82b
15.29c 5.93a 14.09c 12.28b 15.03c
1.9a 2.2b 40.1e 6.2d 4.3c
Abbreviations are the same as in Table 1. The same letter in the same column is not significantly different (P <0.05).
Table 3 Enzyme activity and pentosan content of flours of polishing wheat grain Sample
Diastatic (mg/10 g flour) activity
Proteolytic activity (HUT/g flour)
a-Amylase activity (U/g flour)
b-Amylase activity (U/g flour)
WSP (%)
WISP (%)
Hermes N61 NA-1 NA-5 NA-8
273.0d 100.8a 300.4e 205.5b 244.3c
55.4e 2.3b 14.1d 2.1a 5.9c
13.74a 11.7a 11.6a 12.7a 11.4a
0.99a 1.28c 1.40e 1.38d 1.17b
0.73a 0.78b 1.08c 1.15d 1.28e
1.08b 0.89a 13.43d 2.34c 1.84b
Abbreviations are the same as in Table 1. HUT, hemoglobin units on tyrosine basis. WSP and WISP are water-soluble and -insoluble pentosans, respectively. The same letter in the same column is not significantly different (P <0.05).
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closely associated with the amount of damaged starch, as shown in Table 2. The a-amylase activity of soft-type F-PWG was in the range of 11.4–12.7 units/g flour, and NA-5 had higher activity than N61. However, these values were still lower than that of Hermes. Moreover, all F-PWG had significantly higher b-amylase activity than Hermes. Neither N61 nor the soft-type F-PWG had a significantly higher proteolytic activity than Hermes. But, for the case of proteolytic activity, no constant tendency was observed in these data among various samples, and we don’t have exact information to clarify these phenomena. Regarding the amounts of pentosans, all F-PWG significantly increased the amounts of pentosans, as compared with N61. Both amounts of WSP and WISP of NA-8 were approximately twice that of Hermes or N61. Especially, NA-1 indicated approximately 5 times Hermes or N61. During fermentation of the dough, two stages of assimilation of sugar have been proposed (Matsumoto, 1980). At the first stage, glucose in the flour is decomposed by amylolytic enzyme, a classical name of chimase in yeast. Next, when the glucose is depleted, the damaged starch is decomposed at the second stage by a- or b-amylase in the flour. In this study, there were no distinct differences in the a-amylase activity between the F-PWG and conventionally milled flours. However, the F-PWG contained significantly higher b-amylase or diastatic activities and a larger amount of damaged starch than Hermes and N61. Therefore, it was expected that F-PWG could accelerate fermentation at the second stage, caused by the decomposition of damaged starch by amylases, as compared with N61 alone.
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3.3. Microscopic results of dough and bread Fig. 1 shows light microscopic images of various doughs. In Hermes, starch granules and gluten proteins stained with pink and green, respectively are observed extensively (A). However, N61 dough does not contain a sufficient amount of gluten (B). NB-1 and NA-1 of outermost fractions contained bran of big sizes were observed, and a small amount of gluten was partly aggregated in the dough (C and D). The amount of gluten in NA-8 of the innermost fraction stained with green was not quite enough, as compared with those of Hermes and N61 (E). When viewed with the TEM, the morphological features of N61 and F-PWG doughs were almost the same as those of LM (figure not shown). In the case of Hermes, the dough matrix seemed to be quite smooth and the gluten wrapped starch granules fairly more than that of F-PWG. Fig. 2 shows SEM image of breadcrumbs. In Hermes, a fibrous structure is visible in the bread (A) and this might indicate that there was a sufficient amount of starch gelatinization. however, N61 bread contained some twisted starch granules and the morphological shape was not continuous or uniform (B). Bread baked with NA-1 and-5 breads contained some raw starch granules and a rough or discontinuous gluten substance was observed (C and D). In addition, bread made with NA-8 had twisted starch granules caused by the inferior gelatinisation (E). From microscopic observations, F-PWG could not make viscous or extensible dough structure and starch granules in the F-PWG might not be gelatinised enough during baking.
Fig. 1. Light microscopic observation of dough stained with PAS and light green. (A), Hermes; (B), N61; (C), NB-1; (D), NA-1; (E), NA-5; (F), NA-8. Abbreviations are the same as in Table 1.
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3.4. Baking results WSP and WISP obtained from NA-8 were added to the N61, and effects of pentosans on breadmaking were examined measuring specific volume and staling of breads. For the case of WSP, the loaf volume was significantly larger by additions of 0.2 1.0% of WSP, as compared with that of Hermes (Table 4). Regarding the staling of bread, the addition of WSP significantly retarded the firmness of breadcrumbs during storage for 3 days, as compared with that of N61. From these results, the WSP improved bread qualities distinctly. On the other hand, WISP had more satisfactory effects on
the increase of loaf volume and retardation of staling of bread than WSP did (Table 5). However, the addition of 1.0% or more, an amount which was obviously higher than that of WSP, had a favorable effect. As a result, a relatively larger amount of WISP than WSP is needed to obtain good baking quality. WSP in F-PWG is presumed to play a role as an improver of bread quality by the high viscous and gelling property, improving the strength of gluten and retention of gas generated in the dough (Baker et al., 1945; Mauritzen & Stewart, 1964, MacRitchie, 1976). Furthermore, WSP and damaged starch in F-PWG were confirmed to improve the dough and baking properties of the partial
Fig. 2. Scanning electron microscopic observation of bread baked in an automatic baker. (A), Hermes; (B), N61; (C), NA-1; (D), NA-5; (E), NA-8. Abbreviations are the same as in Fig. 1.
Table 4 Effect of water-soluble pentosan in flours of polishing wheat grain on baking properties Sample
Amount added of WSP (%)
Specific volume (cm3/g)
Storage days 0
1
2
3
a
Hermes N61
0 0
4.25d 2.73a
16.7 a 70.3c
28.7a 134.3c
41.3a 193.7b
43.3a 220.0c
WSP 0.2 WSP 0.5 WSP 1.0
0.2 0.5 1.0
3.79b 3.84c 4.38e
21.3b 19.3a 18.0a
52.7b 49.0b 40.0a
78.0a 69.0a 60.0a
104.3b 89.0b 80.0a
a
Firmness (102 N m 2); WSP, water-soluble pentosan. The same letter in the same column is not significantly different (P< 0.05).
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T. Maeda, N. Morita / Food Research International 36 (2003) 603–610 Table 5 Effect of water-insoluble pentosan in flours of polishing wheat grain on baking properties Sample
Hermes N61 WISP 0.5 WISP 1.0 WISP 5.0 WISP 10.0 a
Amount added of WISP (%)
Specific volume (cm3/g)
Storage days 0
1
2
3
0 0
4.25f 2.73a
16.7aa 70.3c
28.7a 148.7c
41.3a 224.3c
43.3a 266.7c
0.5 1.0 5.0 10.0
2.77b 3.84c 4.07e 3.96d
83.3d 20.7a 31.7b 15.7a
148.0c 39.7a 90.7b 45.0a
202.3c 60.3a 128.7b 67.3a
225.7bc 83.3a 174.0b 85.7a
Firmness (102 N m 2); WISP, water-insoluble pentosan. The same letter in the same column is not significantly different (P <0.05).
substitution of F-PWG (Maeda, Maeda, & Morita, 2001; Maeda, Yano, Hayashi, & Morita, 2001). In addition, this tendency coincided with the research that pentosans might have slightly positive effect on bread quality, as proposed by Shogren, Hashimoto, and Pomeranz (1987). If F-PWG are recognized to be used for breadmaking, the present polishing method would be one of the methods for the grinding of whole grain. A good baking method that uses F-PWG whose functional properties are contributed to WSP and damaged starch will be expected for further development in the near future.
4. Conclusions All fractions of the soft-type F-PWG contained larger amounts of dietary fiber and damaged starch, and showed higher diastatic activities, as compared with conventionally milled flours of Hermes and N61. Regarding the structures of dough and bread observed by microscopy, none of the fractions of F-PWG could form a good gluten network in the dough, and the structure seemed to be less extensible or moist, as compared with those of Hermes and N61. In breadcrumbs made with F-PWG, the swelling or gelatinization of starch was not complete. However, additions of WSP and WISP obtained from the innermost fraction of FPWG to N61 improved the bread qualities. The reason why the addition of F-PWG improved the bread quality and maturity of dough are still unknown in detail. This may be caused by the presence of large amounts of pentosans and damaged starch in F-PWG.
Acknowledgements The authors wish to thank the Okumoto Flour Milling Co., Ltd. (Osaka, Japan) and Miyake Flour Milling Co., Ltd. (Osaka, Japan) for supplying wheat flour; Asahi Kasei Co., Ltd. (Tokyo, Japan) for providing dry yeast; Itomen Co. Ltd. (Hyogo, Japan) for the preparation of F-PWG; Amano Pharmaceutical Co., Ltd.
(Nagoya, Japan) and Daiwa Kasei Co., Ltd. (Osaka, Japan) for donating various enzymes.
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Rouau, X., & Moreau, D. (1993). Modification of some physicochemical properties of wheat flour pentosans by an enzyme complex recommended for baking. Cereal Chemistry, 70, 626– 632. Rouau, X., & Surget, A. (1994). A rapid semi-automated method for the determination of total and water-extractable pentosnas in wheat flours. Carbohydrate Polymers, 24, 123–132. Sandstedt, R. M., Kneen, E., & Blish, M. J. (1939). A standardized wohlgemuth procedure for alpha-amylase activity. Cereal Chemistry, 16, 712–723. Shogren, M. D., Hashimoto, S., & Pomeranz, Y. (1987). Cereal pentosans: their estimation and significance. II. Pentosans and breadmaking characteristics of hard red winter wheat flours. Cereal Chemistry, 64, 35–38. Sollars, W. F. (1958). Fractionation and reconstitution procedures for cake flours. Cereal Chemistry, 35, 85–99.
Flour quality and pentosan prepared by polishing wheat grain on breadmaking T. Maeda1, N. Morita* Laboratory of Food Chemistry, Division of Applied Biochemistry, Graduate School of Agriculture and Biological Sciences, Osaka Prefecture University, 1-1, Gakuen-cho, Sakai 599-8531, Japan Received 17 August 2002; accepted 12 December 2002
Abstract Whole grains of soft-type wheat were polished from the surface layer to the center by 10% of the total weight using a modified rice-polisher. Qualities of classified flours from polishing wheat grain (PWG) and effect of pentosan in the flours of PWG (F-PWG) on breadmaking were determined. All the F-PWG contained larger amounts of dietary fiber and damaged starch, and showed higher diastatic activity than conventionally milled wheat flours of Hermes (hard-type) or Norin 61 (N61, soft-type). All kinds of FPWG made harder or less moist dough from microscopic observations than Hermes or N61 did. The gluten matrix of F-PWG dough was distinctly not continuous in the presence of large dietary fiber, and the gluten sheet was clearly more discontinuous than those of Hermes and N61. Also, the gelatinization of starch in F-PWG during baking appeared to be more incomplete than that observed with Hermes or N61. However, additions of water-soluble and-insoluble pentosans obtained from the innermost fraction of F-PWG to N61 significantly improved the bread qualities. The improvements of bread quality and maturity of dough might be caused by the large amounts of pentosans and damaged starch in F-PWG. # 2003 Elsevier Science Ltd. All rights reserved. Keywords: Polishing wheat; Dough property; Bread quality; Dietary fiber; Damaged starch; Pentosan
1. Introduction Wheat grains contain large amounts of vitamins, minerals and nutritional fibers in the pericarp and germ. However, when the grains are conventionally milled, the recovery of flour is around 70% and most of the vitamins, minerals and fibers do not remain in the flour, because the pericarp and germ are completely separated from the endosperm. The milling system of wheat flour has been developed to obtain a more white or glossy flour for a long time by the complete removal of pericarp and germ. But, recently, the traditional or conventional milling system might be refocused accompanying today’s requirement for the viewpoints of nutritional and economical values. Especially in Japan, the
* Corresponding author. Tel.: +81-72-254-9459; fax: +81-72-2549918. E-mail address: [email protected] (N. Morita). 1 Present address: Department of Life and Health Sciences, Hyogo University of Teacher Education, 942-1, Shimokume, Yashiro, Hyogo 673-1494, Japan.
production of whole grain flour containing pericarp or germ is quite small, and the processed foods using the whole grain flour are still not common. Whole grains of soft-type wheat were polished from the surface layer to the center by 10% of the total weight using a modified rice-polisher. The eight fractions of polishing wheat grain (PWG) were obtained from the surface layer. The flour of PWG (F-PWG) contains the pericarp and germ, except for the near central part, namely 30%-core of whole grain, as is possible to understand from the structure of wheat grain. Therefore, the F-PWG retains a similar nutritional value to the whole grain flour with quite easy preparation. Therefore, F-PWG is expected to apply for various processed foods with appropriate flour quality of each fraction, as compared with common whole grain flour. F-PWG is assumed to contain large amounts of pentosans or dietary fiber derived from bran. Deficiency of dietary fiber has been reported to be associated with a high incidence of serious diseases such as diverticulosis of the colon, arteriosclerosis, colon cancer and diabetes mellitus (McIntosh, 1998; McIntosh, Leu, Royle, &
0963-9969/03/$ - see front matter # 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0963-9969(03)00008-5
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Young, 1996). It is a little appreciated fact that whole grains also contain a variety of antioxidant compounds, including several of those commons to fruits and vegetables (Andlauer & Furst, 1998; Collins, 1989). But, most of these antioxidant compounds are concentrated in the bran and germ, which are lost during milling. Moreover, the whole-grain intake provides protection from serious disease compared with refined-grain intake (Jacobs, Slavin, & Marquart, 1995). The daily diet of FPWG-supplemented bread or noodles might reduce the incidence of serious diseases. In addition, a water-soluble pentosan, which is composed of total pentosans by 30–40%, improved the breadmaking qualities, having the gelling property, high viscosity and retention property of gas bubbles in the dough (Baker, Parker, & Mize, 1945; MacRitchie, 1976; Mauritzen & Stewart, 1964). Furthermore, the polishing system might increase the water absorption during mixing, and improving dough maturity during fermentation, caused by larger amounts of damaged starch, as compared with conventionally milled flour. Therefore, the F-PWG is expected to have different flour qualities from the common whole grain flour and influence the baking properties. Based on these findings, in this paper, the authors describe the flour qualities and pentosan prepared from soft-type F-PWG, comparing with those of conventionally milled flours.
2. Materials and methods 2.1. Flour and chemicals The wheat grain used for the polishing method was a soft-type wheat cultivar, ‘Norin 61’ provided by Miyake Flour Milling Co., Ltd. (Osaka, Japan). The wholewheat grain was polished from the outer layer in increments of 10% of total weight using a modified rice-polisher (Itomen Co., Ltd., Hyogo, Japan), as described Table 1 Classified flours prepared by polishing wheat grain Sample
Fraction (%)
Sample
Fraction (%)
NA-1 NA-2 NA-3 NA-4 NA-5 NA-6 NA-7 NA-8
100–90 90–80 80–70 70–60 60–50 50–40 40–30 30–0
NB-1 NB-2 NB-3 NB-4 NB-5 NB-6 NB-7 NB-8
100–90 90–80 80–70 70–60 60–50 50–40 40–30 30–0
NA and NB are soft-type flours obtained from polishing wheat grain of Norin 61, and sieved through a pore size of 125 and 600 mm, respectively. NA-1 (100–90%), 10% layer polished from outer part of whole grains; NA-2 (90–80%), 10% layer polished from outer part of NA-1; NA-3NA-7, same 10% polishing as above; NA-8 (30–0%), 30%-core of the whole grains.
previously (Maeda, Okura, & Morita, 1999; Maeda & Morita, 2001). Table 1 shows the various F-PWG used for the following experiments. These F-PWG were sieved through a pore size of 125 mm (named as ‘NA’) or 600 mm (named as ‘NB’). NA-1 and NB-1 correspond to the F-PWG from 100 to 90% of the whole grain; NA-2 and NB-2, 90–80%; NA-3 and NB-3, 80–70%; NA-4 and NB-4, 70–60%; NA-5 and NB-5, 60–50%; NA-6 and NB-6, 50–40%; NA-7 and NB-7, 40–30%; NA-8 and NB-8, 30% to the core of the grain. The conventionally milled flour of soft-type wheat cultivar Norin 61 (N61) was also prepared. The control sample of conventionally milled commercial hard-type wheat flour ‘Hermes’ was donated by Okumoto milling Co., Ltd. (Osaka, Japan) and also used. For various analyses, the following enzymes were used: Kokugen G, amyloglucosidase of Aspergillus, was kindly provided by Daiwa Kasei Co., Ltd (Osaka, Japan). The activity was 104 JGU/g or more and 1 JGU was defined as the enzyme that liberates 1 m mole of glucose from 1% soluble starch solution at 40 C for 10 min (pH 4.5). Kleistase T-RC3 (Daiwa Kasei, CO.), a heat-stable aamylase of Bacillus subtilis has an activity of 3.0 104 LJ/g or more. The activity was determined according to the standard method of manufacturing amylase (JIS, K7001-1971). a- and b-amylases were obtained from Aspergillus and barley, respectively (Amano Pharmaceutical Co., Nagoya, Japan) and the activity of the former was 105 U and that of the latter was 6500 U/ml or more. Protease N (protease) of B. subtilis has an activity of 15104 U/g or more and was kindly supplied by Amano Pharmaceutical Co., Ltd. (Nagoya, Japan). All other chemicals used were purchased from Wako Pure Chemical Industries, Ltd. (Osaka, Japan) and they were of reagent grade. 2.2. Analytical methods for wheat flour 2.2.1. Dietary fiber and damaged starch of flour The contents of dietary fiber and damaged starch of flour sample were determined by AACC methods 32-05 and 76-30A (1994), respectively. 2.2.2. Mineral content of flour Mineral content of the flour sample was measured using the same fluorescent X-ray elemental analyser MESA-500 (Horiba Instrument Co., Ltd., Osaka, Japan) by the same procedure, as described previously (Maeda & Morita, 2001). 2.2.3. Pentosan content of flour Total (TP) and water-soluble pentosans (WSP) of flour were extracted by the method of Faurot et al. (1995). For the case of TP, flour (200 mg) was weighed in a pyrex glass tube fitted with a screw cap. 2N sulfuric acid (10 ml) was added to the flour sample and then the
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mixture was gently dispersed for 30 s using a homogenizer. Four grams of the sample suspension were boiled for 10 min in a water bath (100 C) and cooled in water, and then centrifuged for 10 min at 700 g. An aliquot of the clear supernatant diluted 10 times was used to determine TP content by the spectrophotometric method (Rouau & Surget, 1994). Regarding WSP, flour (1 g) was weighed into a centrifuge tube. Distilled water (8 ml) was poured into the tube, and then the flour sample was homogenized for 60 s. Two grams of the sample were shaken for 15 min at 27 C, and centrifuged for 10 min at 700 g. An aliquot of the supernatant was diluted 25 times, and the WSP was determined by the spectrophotometric method (Rouau & Surget, 1994). The content of water-insoluble pentosan (WISP) was calculated by subtracting the content of WSP from that of TP. 2.3. Measurement of enzyme activities 2.3.1. Preparation of enzyme solution from flours Water-extracts of the flour sample for the determination of enzyme were prepared by the same method, as described previously (Maeda & Morita, 2001). The enzyme solution was used in the following experiments. 2.3.2. Determination of enzyme activity in wheat flour The diastatic and proteolytic activities of flour sample were determined by the approved methods 22-15 and 22-62 (AACC, 1994), respectively. The a- and b-amylase activities of flour samples were determined by the methods of Sandstedt, Kneen, and Blish (1939), and Nikuni, Nakamura, and Suzuki (1977), respectively. These procedures are completely the same, as described previously (Maeda & Morita, 2001). 2.4. Analytical methods for dough and bread 2.4.1. Breadmaking The breadmaking formula included 280 g of flour, 5 g of sodium chloride, 17 g of sucrose, 3 g of dry baker’s yeast (Asahi Kasei Co., Ltd., Tokyo, Japan) and the same procedure was used by the automatic baker, as reported previously (Morita, Nakata, Hamauzu, & Toyosawa, 1996). In, addition, WSP and WISP obtained from F-PWG as mentioned above were added to the N61 and baked with the same method as above. Breadmaking was also carried out by the same method as described above.
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above. A portion of the dough sample mixed in the baker’s pan was cut out using scissors. For bread sample, a portion of bread baked was used by the same procedure, as described in breadmaking. 2.5.2. Scanning electron microscopy (SEM) SEM in a Hitachi apparatus (Model S-800) was done to observe the bread sample by the same method as reported previously (Morita et al., 1996). 2.5.3. Transmission electron microscopy (TEM) and light microcopy (LM) Both TEM and LM were done with a 3 3 3 mm3 portion of dough samples as described above. After these samples were frozen with liquid nitrogen, the frozen samples were fractured into a size of about 0.1 0.1 0.1 cm3, and then lyophilized. A portion of these samples was fixed with 2.5% glutaraldehyde in 0.05Mphosphate buffer (pH 6.8) for 15 h. After washing several times in the same buffer, the samples were postfixed in 2% osmium oxide for 2 h, then rinsed with the same buffer thoroughly, then dehydrated in a graded ethanol series. The samples thus prepared were embedded in an Epon mixture and sectioned with glass knives on a Porter-Blum Ultra-microtome MT1 (Sorvall Inc., USA). For TEM observation, sections from 0.01 to 0.05 mm thick were stained with saturated uranyl acetate in water and post-stained with lead citrate, and then examined with a TEM (H-600 Hitachi, Ltd., Tokyo, Japan), operated at 75 kv. For the LM observation, sections of about 1 mm thick were stained with 0.05 M-phosphate buffer containing 1% toluidine blue or 0.1% basic fuchsin at pH 6.8, then observed using an OM apparatus (Model 206065, Vanox Olympus, Co., Ltd., Tokyo, Japan). In addition, these samples were embedded in a hydrophilic resin (JB4) (Polyscience, Inc., USA), and cut in the dry resin by the same ultramicrotome. They were stained with PAS (Periodic Acid Schiff reaction) and light green SFY (Wako Pure Chemical Ind., Ltd., Osaka), and then observed using the same LM. 2.6. Analyses of pentosans from wheat flours 2.6.1. Fractionation of wheat flour by acetic acid Flour was fractionated by the method of Sollars (1958). The obtained water-extracts and tailings fractions were used for the following isolation of WSP and WISP, respectively.
2.5. Microscopic observation 2.5.1. Preparation of dough and bread Two hundred and eighty grams of flour and 210 g of water were mixed for 15 min in the same automatic baker for the preparation of dough sample, as described
2.6.2. Isolation of pentosans WSP and WISP were isolated from the water-extracts and tailings fractions by the method of Rouau and Moreau (1993). The water-extracts (8.0 g) dissolved with 100 ml of water were boiled for 10 min, and then
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cooled at room temperature. To remove the denatured protein, the solution was centrifuged (18,000 g for 20 min at 20 C), and the supernatant was adjusted to pH 5.0 before amyloglucosidase (500 mg) was added. The solution was allowed to react at 60 C for 3 h. After cooling to 40 C, 5 ml of 1M-phosphate buffer (pH 7.5) and 30 mg of protease were added to the solution and shaken for 4 h at 50 C. The solution was heated at 100 C for 10 min to inactivate the enzyme, then it was cooled and the solution was filtered through a filter paper No. 5C (Advantec Co., Ltd., Tokyo, Japan). Thereafter, 5 vol. of 95% ethanol were added to the solution with stirring. After standing overnight at 4 C, the precipitated material was collected by centrifugation. The WSP pellets were dehydrated with ethanol, acetone, and ether, and stored in a desiccator. To isolate WISP, the tailings fractions (40.0 g) obtained above were suspended in 100 ml of distilled water, adjusted to pH 5.0 with NaOH, and incubated with heat-stable aamylase (250 mg) at 100 C for 30 min. After cooling of the solution, amyloglucosidase (50 mg) was added, and the mixture was incubated at 60 C for 3 h to complete the digestion of starch. After addition of 5 ml phosphate buffer (1M, pH 7.5) containing 30 mg of protease, the mixture was incubated for 4 h at 40 C under shaking to digest insoluble proteins. The slurry was then centrifuged (18,000 g for 20 min at 20 C). The WISP pellets were extensively washed with distilled water and dried with organic solvents as mentioned above.
3. Results and discussion 3.1. Characteristics of flour sample Table 2 summarizes the characteristics of various F-PWG. All fractions of F-PWG contained significantly larger amounts of damaged starch; these amounts were 2–2.5 times of N61. The damaged starch might be formed mechanically when the grains were grounded by the polisher. Since the polishing method does not have a refining system of the hard bran from the soft endosperm during the operation process, F-PWG contain larger amounts of minerals derived from bran. The NA-1 and -5 significantly increased total amounts of K, Ca and Fe, as compared with N61. Particularly, the outermost F-PWG, NA-1 distinctly had the highest value of all samples. 3.2. Enzyme activity of flour The amounts of various enzyme activities and pentosans in F-PWG are shown in Table 3. The values of diastatic activity in F-PWG were two times or more of N61. NA-1 had the highest value of all samples. In general, the amount of reducing sugars existed originally in the conventionally milled flour is very small and constant. During fermentation of the dough, the damaged starch granules contained are easily hydrolyzed by amylases. Therefore, these results might be
Table 2 Characteristics of various flours of polishing wheat grain Sample
S (%)
Cl (%)
K (%)
Ca (%)
Fe (ppm)
Ni (ppm)
Damaged starch (%)
Dietary fiber (%)
Hermes N61 NA-1 NA-5 NA-8
0.16c 0.13ab 0.12ab 0.11a 0.14ab
0.07b 0.12b 0.07b 0.05a 0.09c
0.14a 0.16a 0.76d 0.42c 0.26b
0.03a 0.03a 0.08c 0.05b 0.03a
5.44a 25.12b 243.3d 80.24c 40.93b
1.62a 2.01c 2.55d 1.63a 1.82b
15.29c 5.93a 14.09c 12.28b 15.03c
1.9a 2.2b 40.1e 6.2d 4.3c
Abbreviations are the same as in Table 1. The same letter in the same column is not significantly different (P <0.05).
Table 3 Enzyme activity and pentosan content of flours of polishing wheat grain Sample
Diastatic (mg/10 g flour) activity
Proteolytic activity (HUT/g flour)
a-Amylase activity (U/g flour)
b-Amylase activity (U/g flour)
WSP (%)
WISP (%)
Hermes N61 NA-1 NA-5 NA-8
273.0d 100.8a 300.4e 205.5b 244.3c
55.4e 2.3b 14.1d 2.1a 5.9c
13.74a 11.7a 11.6a 12.7a 11.4a
0.99a 1.28c 1.40e 1.38d 1.17b
0.73a 0.78b 1.08c 1.15d 1.28e
1.08b 0.89a 13.43d 2.34c 1.84b
Abbreviations are the same as in Table 1. HUT, hemoglobin units on tyrosine basis. WSP and WISP are water-soluble and -insoluble pentosans, respectively. The same letter in the same column is not significantly different (P <0.05).
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closely associated with the amount of damaged starch, as shown in Table 2. The a-amylase activity of soft-type F-PWG was in the range of 11.4–12.7 units/g flour, and NA-5 had higher activity than N61. However, these values were still lower than that of Hermes. Moreover, all F-PWG had significantly higher b-amylase activity than Hermes. Neither N61 nor the soft-type F-PWG had a significantly higher proteolytic activity than Hermes. But, for the case of proteolytic activity, no constant tendency was observed in these data among various samples, and we don’t have exact information to clarify these phenomena. Regarding the amounts of pentosans, all F-PWG significantly increased the amounts of pentosans, as compared with N61. Both amounts of WSP and WISP of NA-8 were approximately twice that of Hermes or N61. Especially, NA-1 indicated approximately 5 times Hermes or N61. During fermentation of the dough, two stages of assimilation of sugar have been proposed (Matsumoto, 1980). At the first stage, glucose in the flour is decomposed by amylolytic enzyme, a classical name of chimase in yeast. Next, when the glucose is depleted, the damaged starch is decomposed at the second stage by a- or b-amylase in the flour. In this study, there were no distinct differences in the a-amylase activity between the F-PWG and conventionally milled flours. However, the F-PWG contained significantly higher b-amylase or diastatic activities and a larger amount of damaged starch than Hermes and N61. Therefore, it was expected that F-PWG could accelerate fermentation at the second stage, caused by the decomposition of damaged starch by amylases, as compared with N61 alone.
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3.3. Microscopic results of dough and bread Fig. 1 shows light microscopic images of various doughs. In Hermes, starch granules and gluten proteins stained with pink and green, respectively are observed extensively (A). However, N61 dough does not contain a sufficient amount of gluten (B). NB-1 and NA-1 of outermost fractions contained bran of big sizes were observed, and a small amount of gluten was partly aggregated in the dough (C and D). The amount of gluten in NA-8 of the innermost fraction stained with green was not quite enough, as compared with those of Hermes and N61 (E). When viewed with the TEM, the morphological features of N61 and F-PWG doughs were almost the same as those of LM (figure not shown). In the case of Hermes, the dough matrix seemed to be quite smooth and the gluten wrapped starch granules fairly more than that of F-PWG. Fig. 2 shows SEM image of breadcrumbs. In Hermes, a fibrous structure is visible in the bread (A) and this might indicate that there was a sufficient amount of starch gelatinization. however, N61 bread contained some twisted starch granules and the morphological shape was not continuous or uniform (B). Bread baked with NA-1 and-5 breads contained some raw starch granules and a rough or discontinuous gluten substance was observed (C and D). In addition, bread made with NA-8 had twisted starch granules caused by the inferior gelatinisation (E). From microscopic observations, F-PWG could not make viscous or extensible dough structure and starch granules in the F-PWG might not be gelatinised enough during baking.
Fig. 1. Light microscopic observation of dough stained with PAS and light green. (A), Hermes; (B), N61; (C), NB-1; (D), NA-1; (E), NA-5; (F), NA-8. Abbreviations are the same as in Table 1.
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3.4. Baking results WSP and WISP obtained from NA-8 were added to the N61, and effects of pentosans on breadmaking were examined measuring specific volume and staling of breads. For the case of WSP, the loaf volume was significantly larger by additions of 0.2 1.0% of WSP, as compared with that of Hermes (Table 4). Regarding the staling of bread, the addition of WSP significantly retarded the firmness of breadcrumbs during storage for 3 days, as compared with that of N61. From these results, the WSP improved bread qualities distinctly. On the other hand, WISP had more satisfactory effects on
the increase of loaf volume and retardation of staling of bread than WSP did (Table 5). However, the addition of 1.0% or more, an amount which was obviously higher than that of WSP, had a favorable effect. As a result, a relatively larger amount of WISP than WSP is needed to obtain good baking quality. WSP in F-PWG is presumed to play a role as an improver of bread quality by the high viscous and gelling property, improving the strength of gluten and retention of gas generated in the dough (Baker et al., 1945; Mauritzen & Stewart, 1964, MacRitchie, 1976). Furthermore, WSP and damaged starch in F-PWG were confirmed to improve the dough and baking properties of the partial
Fig. 2. Scanning electron microscopic observation of bread baked in an automatic baker. (A), Hermes; (B), N61; (C), NA-1; (D), NA-5; (E), NA-8. Abbreviations are the same as in Fig. 1.
Table 4 Effect of water-soluble pentosan in flours of polishing wheat grain on baking properties Sample
Amount added of WSP (%)
Specific volume (cm3/g)
Storage days 0
1
2
3
a
Hermes N61
0 0
4.25d 2.73a
16.7 a 70.3c
28.7a 134.3c
41.3a 193.7b
43.3a 220.0c
WSP 0.2 WSP 0.5 WSP 1.0
0.2 0.5 1.0
3.79b 3.84c 4.38e
21.3b 19.3a 18.0a
52.7b 49.0b 40.0a
78.0a 69.0a 60.0a
104.3b 89.0b 80.0a
a
Firmness (102 N m 2); WSP, water-soluble pentosan. The same letter in the same column is not significantly different (P< 0.05).
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Hermes N61 WISP 0.5 WISP 1.0 WISP 5.0 WISP 10.0 a
Amount added of WISP (%)
Specific volume (cm3/g)
Storage days 0
1
2
3
0 0
4.25f 2.73a
16.7aa 70.3c
28.7a 148.7c
41.3a 224.3c
43.3a 266.7c
0.5 1.0 5.0 10.0
2.77b 3.84c 4.07e 3.96d
83.3d 20.7a 31.7b 15.7a
148.0c 39.7a 90.7b 45.0a
202.3c 60.3a 128.7b 67.3a
225.7bc 83.3a 174.0b 85.7a
Firmness (102 N m 2); WISP, water-insoluble pentosan. The same letter in the same column is not significantly different (P <0.05).
substitution of F-PWG (Maeda, Maeda, & Morita, 2001; Maeda, Yano, Hayashi, & Morita, 2001). In addition, this tendency coincided with the research that pentosans might have slightly positive effect on bread quality, as proposed by Shogren, Hashimoto, and Pomeranz (1987). If F-PWG are recognized to be used for breadmaking, the present polishing method would be one of the methods for the grinding of whole grain. A good baking method that uses F-PWG whose functional properties are contributed to WSP and damaged starch will be expected for further development in the near future.
4. Conclusions All fractions of the soft-type F-PWG contained larger amounts of dietary fiber and damaged starch, and showed higher diastatic activities, as compared with conventionally milled flours of Hermes and N61. Regarding the structures of dough and bread observed by microscopy, none of the fractions of F-PWG could form a good gluten network in the dough, and the structure seemed to be less extensible or moist, as compared with those of Hermes and N61. In breadcrumbs made with F-PWG, the swelling or gelatinization of starch was not complete. However, additions of WSP and WISP obtained from the innermost fraction of FPWG to N61 improved the bread qualities. The reason why the addition of F-PWG improved the bread quality and maturity of dough are still unknown in detail. This may be caused by the presence of large amounts of pentosans and damaged starch in F-PWG.
Acknowledgements The authors wish to thank the Okumoto Flour Milling Co., Ltd. (Osaka, Japan) and Miyake Flour Milling Co., Ltd. (Osaka, Japan) for supplying wheat flour; Asahi Kasei Co., Ltd. (Tokyo, Japan) for providing dry yeast; Itomen Co. Ltd. (Hyogo, Japan) for the preparation of F-PWG; Amano Pharmaceutical Co., Ltd.
(Nagoya, Japan) and Daiwa Kasei Co., Ltd. (Osaka, Japan) for donating various enzymes.
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