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Effects of different milling processes on whole wheat flour quality and performance in steamed bread making
LWT - Food Science and Technology 62 (2015) 310e318
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LWT - Food Science and Technology journal homepage: www.elsevier.com/locate/lwt
Effects of different milling processes on whole wheat flour quality and performance in steamed bread making Chong Liu, Lin Liu, Limin Li, Chunming Hao, Xueling Zheng*, Ke Bian**, Jie Zhang, Xiaoxi Wang College of Grain and Food, Henan University of Technology, Zhengzhou, 450001, PR China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 17 October 2013 Received in revised form 14 April 2014 Accepted 26 August 2014 Available online 16 September 2014
In recent years there has been growing interest in whole grain products. However, few studies have analyzed the influence of whole wheat flour on the quality of Chinese steamed bread. This study determined the influence of different milling processes on the physicochemical properties and steamed bread quality of whole wheat flour. A medium hard red wheat, soft white wheat and Canada hard wheat was used as raw materials. The milling processes including three entire grain grinding and four bran recombining processes. The wheat flour ground by roller mill was used as a control. Results showed that whole wheat flour made from entire grain grinding processes had higher viscosity values but lower particle size than bran recombining processes. Appropriate processes can improve the farinograph characteristics of whole wheat flour. Chinese steamed bread of whole wheat flour obtained from bran recombining had larger height/diameter ratio, specific volume than that from entire grain grinding processes. Ultrafine entire grain grinding process especially when using white wheat improved the color of steamed bread. The texture differences of steamed bread between whole wheat flour and flour were significant. Steamed bread of red wheat from heat-treated bran recombining (HTBR) process got the highest sensory score.
Keywords: Whole wheat flour Milling process Quality Steamed bread Texture
© 2015 Published by Elsevier Ltd.
1. Introduction Wheat grain is composed of three parts; the endosperm containing mostly starch and proteins, the germ composed mostly of lipids and proteins and the bran containing mainly dietary fiber (Marquart, Jacobs, McIntosh, Reicks, & Poutanen, 2007). These three components are separated at the mill during the refining process. From this process, the white wheat flour is obtained and used for wheat products making. Most often the bran and germ parts are dedicated to animal nutrition, which lead to the loss of many potentially beneficial micronutrients, antioxidants, minerals, and fiber. Therefore, considerable attentions have been paid to the production of whole wheat flour. Whole grains are defined by AACC International (1999) and U.S. Food and Drug Administration (FDA) as consisting of “the intact, ground, cracked or flaked caryopsis
* Corresponding author. Tel./fax: þ86 0371 67758016. ** Corresponding author. Tel./fax: þ86 0371 67758082. E-mail addresses: [email protected] (X. Zheng), [email protected] (K. Bian). http://dx.doi.org/10.1016/j.lwt.2014.08.030 0023-6438/© 2015 Published by Elsevier Ltd.
(fruit or kernel) of the grain, whose principal anatomical components, the starchy endosperm, germ and bran, are present in the same relative proportions as they exist in the intact grain”. Whole wheat flour contains substantially more vitamins, minerals, antioxidants and other nutrients than regular wheat flour, since these compounds are concentrated in the outer portions of the grain (Weaver, 2001). Whole grain may have beneficial effects on cardiovascular diseases, diabetes and weight management (Marquart et al., 2007). Despite the beneficial effect, the public's acceptance of whole wheat food products is limited due to their poor taste and texture (Gan, Galliard, Ellis, Angold, & Vaughan, 1992). Therefore, some technological efforts are needed in order to improve the performance of whole wheat products. Selecting the milling process that will be used is the key consideration in producing whole grain flour (Kihlberg, Johansson, Kohler, & Risvik, 2004). The four predominant techniques for grinding whole grain flours are stone mill (SM), roller mill (RM), ultra-fine mill (UM) and hammer mill (HM) (Kent and Evers, 1994). The hammer mill causes the product to be heated up and to lose moisture (Posner & Hibbs, 2005). Stone mills generate considerable
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heat due to friction, resulting in damage to starch, protein, and unsaturated fatty acids (Prabhasankar & Rao, 2001). The process of roller milling involves separation of the endosperm from the bran and germ followed by gradual size reduction of endosperm (Ziegler & Greer, 1971). Producing flour that fulfills the requirement for being whole grain is achieved by blending bran and germ back with the endosperm flour in the naturally-occurring proportions. In comparison with stone mills, roller milling is more economical and flexible (Posner & Hibbs, 2005), less heat production and thus less destruction to chemical components (Prabhasankar & Rao, 2001). A third advantage of making whole grain flours from roller mills is that wheat bran and germ can be separated from the endosperm fraction and subjected to further processing or post-milling such as heating or ultrafine grinding to affect the storage or functional properties of the flour (Posner & Hibbs, 2005). On the other hand, there are considerate studies about the post-milling processes for whole wheat flour, which including the twin-screw extrusion, the heat treatment of the bran and germ (Kock, Taylor, & Taylor, 1999) and the ultra fine grinding processes (Hemery et al., 2011). Steamed bread is a popular food in China and has a long history. It is the staple food particularly in the northern part of China (Huang, Yun, Quail, & Moss, 1996). So far, however, the application of whole wheat flour in steamed bread making especially effect of whole wheat flour processing method on the quality of whole wheat flour and steamed bread have not been thoroughly examined. The aim of this research was to determine the effect of different whole wheat flour milling processes on the technological quality of the whole wheat flour and resulting whole wheat flour steamed breads. 2. Material and methods 2.1. Material The wheat (Triticum aestivum L.) varieties Zhengmai 366 (hard red winter wheat), Yumai 57 (soft white winter wheat) and CWRS (Canada Western Red Spring) were used in this study. Wheat were purchased from Haijia Food Industry Co. Ltd (Zhengzhou, CN) and all harvested in June 2011. The chemicals used were all analytical grade. 2.2. Analysis of wheat kernel quality characteristic Weight, moisture, diameter, and hardness of 300 wheat kernels were analyzed by the Single Kernel Characterization System of SKCS-4100 (Perten, Sweden) according to Chinese national standard GB/T 21304-2007. The ash contents, test weight, protein content and 1000 kernel weight were determined according to GB/ T 5009.4e2003, GB/T 5498e85, GB/T 5009.5e2003 and GB 551985, respectively. Before determining the starch content, the samples were firstly pretreated by 1 g/100 g hydrochloric acid, and then the content of starch was determined using a WZZ-2B polarimeter (Inesa Instrument Co., Ltd., Shanghai, CN).
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2.3.2. Preparation of whole wheat flour by entire wheat grain grinding Whole wheat flours were prepared by hammer mill (HM), stone mill (SM) and ultra-fine mill (UM) processes, during which entire wheat grain was ground by a hammer mill (Penten 3100, Sweden), an electric stone mill (custom-tailor) and an FDV ultra-fine mill (Beijing Kingslh Instruments Ltd., Beijing, CN), respectively. Whole wheat flours collected from above processes were all passed though a CQ20 screen before use. 2.3.3. Preparation of whole wheat flour by pretreated bran recombining In these processes, whole wheat flours were prepared by recombining stabilized or pretreated bran back to white flour according to their original proportions. For extrudes bran recombining (EBR) process, the bran fraction was passed through a 80 mesh sieve and tempered to 40 ± 2 g/100 g moisture content, stirred, evenly blended and rest for 1 h. A co-rotating double screw extruder from Saixin (Ji'nan Saixin Machinery Co., Ltd., Shandong, CN) was used. The screw configuration was composed of conveying and mixing elements with reverse elements in the last section of the barrel. The extruder was operated at a feed rate of 25e30 kg h1, screw speed 120 r/min, mass temperature 150 C, The extruded samples were collected and dried slowly in an oven at 60 C for 16 h. After ground by a Perten LABORATORY MILL 3100, the collected bran fraction was passed through a CQ20 screen and evenly blended with white flour according to its original proportions to get whole wheat flour. For heat-treated bran recombining (HTBR) process, the bran fraction without sealing was heated in an autoclave at 121 C for 5 min. After freeze-drying and pulverizing by an FW-100 high speed grinder (Beijing Zhongxingweiye Instrument Co., Ltd., Beijing, CN), the bran fraction was sifted and blended with white flour to obtain whole wheat flour as shown in above. In a hammer-milled bran recombining (HMBR) process, the bran fraction was ground by a Perten 3100 hammer mill and the milled bran fraction was sifted and blended with white flour to obtain whole wheat flour as shown in above. For ultra-fine milled bran recombining (UMBR) process, the bran fraction was ground by an FDV ultra-mizer, then sifted and blended with white flour to obtain whole wheat flour as shown in above. 2.4. Physicochemical properties analysis of whole wheat flour Moisture content, ash content, protein content, falling number in whole wheat flours were determined according to Chinese National Standard GB/T 5009.3-2003, GB/T 5505-2008, GB/T 5009.52003 and GB/T 10361-89, respectively. Sedimentation value was measured by AACC method 76-31 (AACC, 2000). Contents of wet gluten and gluten index were determined according to GB/T 146082003.
2.3. Preparation of wheat flour and whole wheat flour
2.5. Starch pasting properties analysis
2.3.1. Preparation of wheat flour by roller mill (RM) The wheat samples from these mills were milled in a laboratory mill (Model MLU-202, Bühler) to obtain wheat flour according to AACC 26-20 (2000) method after tempering for 24 h at 16 g/100 g, 15 g/100 g and 14 g/100 g moisture contents for hard wheat, medium-hard wheat and soft wheat, respectively. The flour extraction rate was about 70 g/100 g. The remained bran fraction (30 g/100 g of wheat weight) was collected and used as raw material in post-milling processes in the following sections.
Pasting properties were determined with a Rapid ViscoAnalyzer (Newport Science Instruments and Engineering) according to STD1 procedure of AACC methods 76-21 (2000). 2.6. Evaluation of dough quality Farinograph characteristic of dough were determined by a Farinograph equipped with a 50 g-stainless steel bowl (Brabender Farinograph) according to GB/T14614-93.
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2.7. Particle size analysis
3. Results and discussion
Particle sizes were measured by dry powder laser particle size analyzer (BT-9300H, Bettersize Instruments Ltd., Liaoning, CN).
3.1. Wheat kernel quality characteristic
2.8. Northern-style Chinese steamed bread preparation Steamed breads were prepared according to sponge dough method described by He, Liu, and Zhuo (2004) with some modification. Dry yeast, 1 g (Mauripan, Harbing Mauripan Yeast Co., Ltd., Harbing) was dispersed in water (30 C). Whole wheat flour 100 g was mixed with yeast/water (85% of Farinograph water absorption) in a flour mixer (JHMZ200, East Fude Technology Development Center, Beijing). Mixing time, water addition and proof time were adjusted based on the performance of the dough and results of a large number of experiments. The mixing time was 10 min. After pressing pieces 20 times using a rolling pin, the dough was divided into three pieces and shaped by hand to a round, long and straight dough piece with a smooth surface. Dough pieces were proofed for 50 min at 38 C and 85% RH. Flour and dough were remixed by hand until the dough became cohesive. The breads were steamed for 20 min in a steamer. 2.9. Sensory evaluation The Chinese steamed bread was evaluated according to SB/T 10139-1993. The volume and weight of Chinese steamed bread were measured by rapeseed displacement and balance (0.01 g) 60 min after cooling for 1 h. Diameter and height were also measured. Color of skin for steamed bread was determined using a Satake mini color grader (MICG1A, Satake Inc., Japan). Steamed bread used for color analysis was cut into 20 mm thin slice with bread knife. In the color difference analysis, ‘L*’, ‘a*’ and ‘b*’values were recorded. The sensory quality scoring system was based on GB/T21118-2007. The panel consisted of 7 trained tasters (three males and four females between 20 and 26 years old) from different provinces of the northern China. Specific volume, height, color, surface structure, appearance, internal structure, elasticity, toughness, stickiness and scent were scored by five experts. The best scores were 15, 5, 10, 10, 10, 15, 10, 10, 10 and 5, respectively, which give a total score of 100. Three samples were evaluated and means were given. 2.10. Texture profile analysis (TPA) of steamed breads After sensory evaluation, the steamed bread was cut into pieces of 20 mm thickness. TPA of steamed bread was tested using the TA-XT2i texture analyzer (Scarsdale, NY; Stable Micro Systems, UK) with its Pasta Firmness/Stickiness Rig probe (P35). Instrument settings were compression mode, trigger type, auto5 g; pretest speed, 2.0 mm/s; posttest speed, 1.0 mm/s; test speed, 1.0 mm/s; compression height, height of samples; strain, 50%; interval between two compressions, 5 s; compression times, 2 s. Each sample should be measured twice and the final result was the average. 2.11. Statistical analysis The data reported in all the tables are averages of triplicate observations. Analysis of variance (ANOVA) and analysis of correlation were both performed using SPSS ver. 18.0 for Windows (SPSS Institute, Cary, NC). Significance of differences was defined at p < 0.05 with Tukey's test.
Before preparation of whole wheat flour, wheat kernel quality characteristics were analyzed. Moisture content of wheat grain was in the range of 10.74e12.63 g/100 g. Ash contents ranged from 1.52 to 1.57 g/100 g. Test weight was 791.0, 791.5 and 824.5 g/L, protein content was 14.2, 13.6 and 14.6 g/100 g, crude starch content was 71.58, 72.83 and 70.41 g/100 g, and hardness was 51.68, 41.15 and 76.05 for Zhengmai 366, Yumai 57, and CWRS, respectively. CWRS had the highest level of 1000 kernel weight. 3.2. Physicochemical properties of whole wheat flour Physicochemical quality of whole wheat flour from different processes is given in Table 1. For entire grain grinding, water loss of whole wheat flours were all significantly higher than those of wheat flour. Whole wheat flour made by UM had the lowest moisture level. This might be due to greater grinding strength used by UM resulting in more heat production. There were no significant differences in the moisture content between wheat flour and whole wheat flour obtained from bran recombining processes (p < 0.05). Among different recombination processes, whole wheat flour made by EBR had lower moisture content than those made by HTBR, HMBR and UMBR (p < 0.05). The whole wheat flour had significantly higher ash content than did wheat flour (p < 0.05). Significant greater protein contents were found for whole wheat flour compared with wheat flour (p < 0.05). This was due to higher protein content present in bran (Idris, Babiker, & El Tinay, 2003). For all milling processes, samples from CWRS had the greatest protein contents, followed by red wheat (Zhengmai 366), while protein content of white wheat (Yumai 57) being the lowest. This is consistent with the results for wheat grain. In general, high sedimentation volume indicates strong gluten and vice versa (Rasper & Walker, 2000). Whole wheat flour had obvious lower sedimentation values than that of wheat flour except for UBR process, which might be attributed to denaturation of protein during entire grain grinding or the reduction of gluten strength by bran during recombining process. The values for UM were missed due to the failure in recording sedimentation values within 5 min. There were no significant differences in falling number between wheat flour and whole wheat flour (p > 0.05). Higher amounts of gluten content are desirable for steamed bread making (Day, Augustin, Batey, & Wrigley, 2006). In case of entire grain grinding processes, the gluten contents for the SM and HM processes using Zhengmai 366, the HM and UM processes using Yumai 57 and the HM process using CWRS were significantly higher than that of wheat flour. Whole wheat flour from entire grain grinding processes had higher gluten content than that from bran recombining processes. The gluten contents for all bran recombining processes were lower than that of wheat flour, with EBR getting the lowest level. This is probably due to three factors: bran is mainly consisted of albumin and globulin which had poor quality than gluten; bran can weaken gluten network; denaturation of protein caused by bran pretreatment decreased quality of gluten. Gluten indexes of whole wheat flours were higher than that of wheat flour except for UMBR using CWRS. However, there is no a trend in gluten index among different milling processes. 3.3. Pasting properties of whole wheat flour Starch pasting property recorded by RVA test reflects flour quality (Ragaee and Abdel-Aal, 2006). Different milling processes had significant influences on pasting properties of red wheat Zhengmai 366
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Table 1 Physical and chemical properties of whole wheat flour from different milling processes. Variety
Process
Moisture (g/100 g)
Ash (g/100 g)
Protein (g/100 g)
Sedimentation value (ml)
Falling number (s)
Wet gluten (g/100 g)
Gluten index
Zhengmai 366
RM HM SM UM EBR HTBR HMBR UMBR RM HM SM UM EBR HTBR HMBR UMBR RM HM SM UM EBR HTBR HMBR UMBR
12.95a 11.59c 10.75d 7.20f 9.00e 13.05a 12.35b 11.75c 13.43a 10.91d 10.40d 6.93f 9.60e 12.60b 12.15c 12.00c 14.32a 12.31c 10.75d 7.26e 10.50d 13.45b 12.4c 12.15c
0.65d 1.53a 1.18c 1.53a 1.27b 0.86d 1.19c 1.32b 0.61e 1.56a 1.13c 1.56a 1.30b 0.84d 1.19b 1.25b 0.59f 1.58a 1.14d 1.58a 1.29c 0.82e 1.28c 1.38b
11.3e 14.2b 14.8a 13.3d 13.9c 14.9a 14.3b 14.5b 10.3d 13.6ab 13.4b 13.0c 13.4b 13.7ab 14.0a 13.9a 11.8c 14.6b 14.7b 14.4b 14.8a 14.2b 15.1a 15.0a
29.4b 9.1f 15.0d e 14.2d 18.1c 11.1e 44.9a 27.8b 8.9f 14.5c e 11.1e 12.4d 11.2e 42.9a 43.4a 15.6c 9.1e e 10.9d 9.5e 15.9c 33.1b
458.5b 444.3c 401.5e 464.0a 425.5d 441.5c 438.5c 416.6d 353.5e 362.4d 378.5b 342.5f 368.1c 370.5c 402.5a 331.5f 477.5a 425.4e 441.5d 418.5e 420.8e 460.5b 414.9f 448.5c
26.9b 29.4a 29.6a 24.2c 19.1e 21.4d 24.3c 21.3d 30.8b 32.4a 22.5c 32.0a 16.4d 19.5c 21.7c 20.4c 29.9b 33.6a 24.3d 29.6b 13.9f 26.2c 21.1e 15.1f
97a 88c 69e 80d 88c 89c 81d 94b 85a 67c 78b 52d 67c 55d 66c 63cd 98a 89c 94b 71e 83d 89c 96a 98a
Yumai 57
CWRS
Different letters within a column for the same wheat variety indicate values are significantly different at the level of p < 0.05. Abbreviations: Roller mill (RM), Hammer mill (HM), Stone mill (SM), Ultra-fine mill (UM), Extrudes bran recombining (EBR), Heat-treated bran recombining (HTBR), Hammer-milled bran recombining (HMBR), Ultra-fine milled bran recombining (UMBR).
(Fig. 1A and B). In case of entire grain grinding processes, the whole wheat flour made from HM process had higher while those from the UM and SM processes had much lower values in most of the viscosity parameters than did wheat flour, with whole wheat flour from SM having the lowest values (Fig. 1A). Viscosity parameters of whole wheat flour made by bran recombining processes was significantly lower than that of wheat flour (p < 0.05), except for final viscosity of whole wheat flour from UMBR (Fig. 1B). There were no differences in viscosity parameters except for final viscosity and setback values among different bran recombining processes. Viscosity parameters for bran recombining processes were much lower than those for entire grain grinding processes except for SM. The lower value of peak, troughs and final viscosities for the former might be due to their lower gluten contents but higher protein content. It was found that higher protein content would result in lower starch content, while viscosity indicators were positively correlated with starch content (Wang, Xie, & Zhang, 2013). In case of entire grain grinding processes using white wheat (Fig. 1C), viscosity parameters for whole wheat flour made from SM were much lower than those of wheat flour (p < 0.01). RVA profiles for HM and UM processes were in above that of wheat flour except for peak viscosity. Whole wheat flour produced by bran recombining procedures had lower peak viscosity than wheat flour (p < 0.01), while the differences among different bran recombining processes were relatively small (Fig. 1D). Significant differences in setback values among different bran recombining processes were found (p < 0.05), with HTBR the lowest while UMBR the highest. In comparison with white wheat Yumai 57, the impacts of different milling processes on pasting properties of CWRS (Fig.1E and F) were more similar to those for red wheat Zhengmai 366. Viscosity parameters for whole wheat flour made from SM were significantly lower than that from HM, UM and that of wheat flour. The RVA profile of whole wheat flour for HM was more similar to that of wheat flour. Whole wheat flour made from bran recombining processes had much lower peak viscosity than wheat flour (p < 0.05), but no differences were found among different bran recombining means. There were
significant differences in setback values (p < 0.05) among different bran recombining processes, with HTBR the lowest while UMBR the highest. Moreover, viscosity parameters for bran recombining processes were comparable to that of SM process. 3.4. Farinograph quality of whole wheat flour In comparison to water absorption of wheat flour (59%~64.5%), those of whole wheat flour (70.00%~80.20%) increased significantly, probably due to their higher fiber contents (Hemery et al., 2011) (Table 2). For red wheat Zhengmai 366, development time of whole wheat flour (5e8.3 min) except for those made from HMBR (11 min) and UMBR (9.2 min) were lower than that of wheat flour (9 min). However, for Yumai 57 and CWRS, development time of all whole wheat flours except for those made from HM and EBR were respectively higher than that of wheat flour. Stability time of all whole wheat flours except for those made from UM using Zhengmai 366 and Yumai 57, HMEBR and UMBR using Yumai 57 and SM using CWRS were lower than that of wheat flour. Degree of softening ranged form 5e101 FU, with HTBR for CWRS getting the lowest value and EBR for white wheat Yumai 57 getting the highest value. Farinograph quality number ranged from 56 to 212, with EBR for Yumai 57 having the lowest value and HMBR for CWRS having the highest value. The results showed that appropriate milling and post-milling processes can improve the farinograph characteristics of whole wheat flour, but this was wheat varieties-dependent. 3.5. Particle size distribution of whole wheat flour The particle size for whole wheat flour made from bran recombining processes was obviously higher than those from whole grain grinding processes (Fig. 2). Whole wheat flour made from UM had the lowest values in particle size, with the D50 of 18.61, 19.36 and 15.92 mm for red wheat (Zhengmai 366), white wheat (Yumai 57) and CWRS, respectively. Whole wheat flour made from EBR had the highest values in particle size, with the D50 of 69.13, 57.96 and
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Fig. 1. A Pasting properties of whole wheat flour made from entire grain grinding process using Zhengmai 366 (A), Yumai 57 (C) and CWRS (E), from bran recombining process using Zhengmai 366 (B), Yumai 57 (D) and CWRS (F). A: HM, UM, RM, SM (for color fig); dHM, _._UM┄RM, ━SM (for black fig); B: RM, UMBR, HMBR, HTBR (for color fig); dRM, … UMBR, ┄HMBR, ━HTBR (for black fig); C: UM, HM, RM, SM (for color fig); ┄UM, … HM, dRM, ━SM(for black fig); D: UMBR, HMBR, RM, HTBR (for color fig); … UMBR, ┄HMBR, dRM, ━HTBR (for black fig); E: HM, UM, RM, SM (for color fig); ┄HM, … UM, dRM, ━SM(for black fig); F: RM, UMBR, HMBR, HTBR (for color fig). dRM, … UMBR, ━HMBR, ┄HTBR (for black fig). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
59.22 mm for red wheat (Zhengmai 366), white wheat (Yumai 57) and CWRS, respectively. D50 was positively and significantly correlated with kernel hardness (p < 0.05). This might be due to higher hardness of grain leading to its friability. For bran recombining processes, D50 followed the order EBR > HTBR > HMBR > UMBR, indicating that the HMBR and UMBR could reduce the particle size of whole wheat to a greater degree compared to the EBR and HTBR procedures. This might be due to aggregation of bran during extrusion or heat treatment resulting in their larger particle size. 3.6. Ratio of height to diameter and specific volume of steamed bread The height/diameter and specific volume for steamed bread are given in Fig. 3A and B. Steamed breads made from bran
recombining processes had slightly lower height/diameter and specific volume than that of wheat flour except for those prepared using CWRS, whose values were higher than that of the control. This is probably due to the adverse effects of bran present in wheat flour. It was found that bran can weaken gluten network by fiberprotein interactions and dilution of gluten (Gan et al., 1992; Noort, van Haaster, Hemery, Schols, & Hamer, 2010). The dilution effects might be due to the fact that bran is mainly consisted of water soluble albumin and globulin proteins other than gliadin and glutelin (Idris et al., 2003). Moreover, steamed breads made from bran recombining processes had obvious larger height/diameter and specific volume than those made from entire grain grinding processes, while the differences among different bran recombining processes were relatively small. This might be attributed to the lower particle size of whole wheat flour for whole grain grinding
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Table 2 Farinograph characteristics of whole wheat flour from different milling processes. Variety
Process
Water absorption (%)
Development (min)
Stability (min)
Degree of softening (FU)
FQN (FU)
Zhengmai 366
RM HM SM UM EBR HTBR HMBR UMBR RM HM SM UM EBR HTBR HMBR UMBR RM HM SM UM EBR HTBR HMBR UMBR
61.5e 71.4d 77.1b 78.4a 77.2b 76.8bc 74.4c 76.7bc 59.1d 70.0c 73.5ab 72.9b 74.5a 74.5a 72.5b 72.6b 64.5g 70.4f 80.2a 79.0b 77.4c 76.9d 76.1d 74.1e
9.0b 7.7d 7.7d 8.3c 5.0e 7.2d 11.0a 9.2b 4.3d 4.2d 6.2b 6.8b 4.2d 5.5c 7.5a 7.2a 7.9b 6.2c 10.9ab 7.3bc 6.3c 11.3a 11.7a 8.3b
9.4b 5.7c 3.9e 10.8a 3.0e 3.4e 5.9c 4.8d 5.8c 3.2d 5.4c 6.4b 2.8d 2.9d 7.3a 6.1b 14.8b 8.5cd 16.4a 8.6cd 5.5e 9.8c 13.2bc 6.3d
19e 22d 35c 11f 99a 57b 9f 6f 52c 68b 34d 25e 101a 55c 17f 27d 13c 23b 17c 13c 28a 5d 9d 9d
111c 106c 96d 118b 67e 86de 147a 125b 71d 64e 97c 105b 56e 70d 123a 103b 145c 115e 115e 146c 101f 178b 212a 121d
Yumai 57
CWRS
Different letters within a column for the same wheat variety indicate values are significantly different at the level of p < 0.05.
processes than for bran recombining processes, which was similar to those results for bread reported by Noort et al. (2010). In addition, the low particle size implied high level of starch damage level leading to the production of more sugar by enzymatic hydrolysis and thus the formation of softer and stickier dough (Evers & Stevens, 1985; Rogers, Gelroth, Langemeier, & Ranhotra, 1994), which can't support the volume of streamed bread. However, this result was contradict to the fact that viscosity parameters of whole wheat flour, which was positively correlated with specific volume (Huang et al., 1996), were lower for bran recombining processes than for entire grain grinding processes, indicating that effect of bran particle size overwhelm that of flour viscosity. 3.7. Color of steamed bread Chrominance of steamed bread is listed in Table 3. Color for steamed made from whole wheat flour were significantly higher than that of wheat flour, probably due to higher bran contents
Fig. 3. Height/diameter (A), specific volume (B) and total score (C) for steamed bread. A: ￭RM, ,HM, UM, EBR, HTBR, UMBR; B: ￭RM, ,HM, UM, EBR, HTBR, UMBR; C: ￭RM, ,HM, UM, EBR, HTBR, UMBR.
Fig. 2. Particle size distribution of whole wheat flour from different milling processes. ￭RM, ,HM, SM, UM, EBR, HTBR, HMBR, MBR.
resulting in greater amounts of pigment and thus increase in the color grade value (CGV), a* and b* values, decrease in L* value. Whole wheat flour made from bran recombining processes had lower CGV, a*, b* and L* values of steamed bread than that from entire grain grinding processes, except for L* values of steamed bread made from UMBR process using white wheat (Yumai 57) and
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Table 3 Color of steamed bread of whole wheat flour from different milling processes. Variety
Zhengmai 366
Yumai 57
CWRS
Process
RM HM UM EBR HTBR UMBR RM HM UM EBR HTBR UMBR RM HM UM EBR HTBR UMBR
Exterior appearance
Interior structure
CGV
L*
a*
b*
CGV
L*
a*
b*
4.84d 52.24b 55.08a 44.82c 43.44c 42.75c 7.22e 50.92b 52.39a 41.84c 42.17c 39.48d 21.3d 62.86a 61.17a 53.55b 53.85b 49.67c
91.8a 67.3b 65.8b 55.6c 56.8c 57.7c 90.6a 68.1b 67.2b 57.2c 57.0c 67.2b 83.3a 61.8c 59.6c 51.3d 51.4d 67.8b
0.5d 10.0a 8.7b 7.3c 7.3c 7.1c 0.5d 8.5a 8.8a 7.1b 7.1b 6.1c 0.1d 11.5a 12.0a 8.4c 8.4c 9.7b
18.2c 29.6a 29.5a 22.4b 22.3b 24.6b 18.7d 27.7a 29.6a 24.5b 24.6b 21.5c 16.3d 24.5a 24.8a 18.6c 18.7c 22.5b
33.26c 67.03a 68.72a 58.32b 55.64b 52.40b 34.98d 63.40a 60.18a 51.47b 52.40b 44.87c 25.89f 80.07b 87.57a 56.42e 69.49c 65.27d
77.1a 59.7b 58.8b 59.1b 52.2d 56.8c 76.3a 61.7b 63.2b 54.1c 51.8c 62.1b 80.9a 52.9b 49.1c 54.9b 43.2d 56.4b
1.0c 7.6b 8.0b 7.5b 8.9a 8.6a 1.0d 6.3b 6.4b 6.6b 8.6a 5.6c 0.5d 7.9c 8.5b 7.4c 9.9a 8.7b
16.1c 22.9a 23.7a 23.2a 21.8b 21.0b 14.9c 20.8b 22.7a 23.1a 21.0b 20.4b 15.0d 17.3c 16.8c 19.5b 18.9b 21.7a
Different letters within a column for the same wheat variety indicate values are significantly different at the level of p < 0.05.
CWRS. The UMBR process had the lowest CGV value, highest lightness and lowest redness and yellowness among all whole wheat flour milling processes, which was acceptable for consumer. Steamed bread made by UMBR process using white wheat (Yumai 57) had optimum color among all samples, while its volume and total score were lower than those for steamed bread made by the same process using other wheat. 3.8. Texture of steamed bread The effect of processing method on steamed bread quality is shown in Table 4. There were significantly higher hardness and chewiness of steamed bread for whole wheat flour than for wheat flour (p < 0.05). For different whole wheat flour milling processes, the UM process had the greatest while the UMBR process had the smallest value in both hardness and chewiness. Whole wheat flour had significantly lower level of adhesiveness, springiness, cohesiveness and resilience for steamed bread than wheat flour (p < 0.05), but the differences among different whole wheat flour milling processes were relatively small.
3.9. Sensory evaluation of steamed bread Sensory evaluation of steamed bread is given in Fig. 3C. Total scores of steamed bread for whole wheat flour were lower than those for wheat flour. Among all whole wheat flours, steamed bread made from whole wheat flour of HMBR process got the highest score, while steamed bread made from whole wheat flour of UM process got the lowest score. The taste of steamed bread made by whole wheat flour was stronger than that made by wheat flour, which might be due to volatile organic compounds produced by wheat bran. Steamed bread made from whole wheat flour for EBR and HTBR processes had lower scores in taste compared to other processes, probably due to loss of flavor matter during the bran pretreatments. Steamed bread made from UMBR process especially for red wheat (Zhengmai 366) had the best sensory quality. Fig. 4 shows the appearance of steamed bread. The results showed that steamed bread made from bran recombining processes had smoother surface than those made from entire grain grinding processes, especially those made from UMBR processes.
Table 4 Texture of steamed bread made from different milling processes. Variety
Process
Hardness/g
Adhesiveness
Springiness
Cohesiveness
Chewiness
Resilience/mm
Zhengmai 366
RM HM UM EBR HTBR UMBR RM HM UM EBR HTBR UMBR RM HM UM EBR HTBR UMBR
2222e 5596b 8562a 5650b 5118c 3842d 5449c 8158b 8895a 8948a 8037b 3576d 3146e 5797c 7618a 5552c 6513b 4358d
7.296a 90.027d 32.559b 47.120b 37.797b 57.318c 18.566a 32.858b 36.647b 29.652b 29.357b 84.436c 43.119a 94.535b 231.033d 106.357c 46.781a 47.907a
0.905a 0.786c 0.821b 0.784c 0.774c 0.847b 0.912a 0.822ab 0.757b 0.817ab 0.811ab 0.774a 0.914a 0.875b 0.732c 0.899b 0.856b 0.832b
0.805a 0.714b 0.676c 0.695c 0.738b 0.707b 0.790a 0.690b 0.691b 0.690b 0.689b 0.672b 0.813a 0.723b 0.706b 0.726b 0.701b 0.696b
1618.61e 3137.89b 4744.06a 3080.82b 2923.31c 2301.35d 3918.68c 4628.08b 4629.52b 5048.10a 4490.06b 1615.86d 2330.08c 3659.44b 3930.14a 3628.11b 3903.02a 2111.08c
0.480a 0.351b 0.321b 0.334b 0.377b 0.323b 0.470a 0.312b 0.307b 0.314b 0.310b 0.317b 0.467a 0.336b 0.328b 0.335b 0.313b 0.334b
Yumai 57
CWRS
Different letters within a column for the same wheat variety indicate values are significantly different at the level of p < 0.05.
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Fig. 4. Images of steamed bread made by Zhengmai 366 (A), Yumai 57 (B) and CWRS (C).
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4. Conclusions Steamed breads made from bran recombining processes had larger height/diameter and specific volume than those made from entire grain grinding processes, while the differences among bran recombining processes were relatively small. This might be partially attributed to their differences in particle size. The UMBR process had the lowest values of CGV, redness, yellowness, hardness and chewiness but highest lightness among all whole wheat flour milling processes, which was acceptable for consumer. Steamed bread made from UMBR process especially for red wheat (Zhengmai 366) had the best sensory quality and smooth surface. Acknowledgment This work was supported by Special Fund for the Construction of Wheat Technology System in Henan Province (No. S2010-01-G06), Special Fund for Agro-scientific Research in the Public Interest (No. 201303070), Research Foundation for Advanced Talents (No. 2011BS005), Research Foundation of HAUT (No. 2013JCYJ01) and Program for Innovative Research Team in University of Henan Province (No. 13IRTSTHN008). References AACC International. (1999). AACC International defines whole grain. Available at: http://aaccnet.org/definitions/wholegrain.asp Accessed 16.09.11. AACC. (2000). Approved methods of the American Association of Cereal Chemists American. USA. St. Paul, MN: Association of Cereal Chemists Inc. Day, L., Augustin, M. A., Batey, I. L., & Wrigley, C. W. (2006). Wheat-gluten uses and industry needs. Trends in Food Science & Technology, 17, 82e90. Evers, A. D., & Stevens, D. J. (1985). Starch damaged. In Y. Pomeranz (Ed.), Advances in cereal science and technology (pp. 321e347). St. Paul: The American Association of Cereal Chemists. Gan, Z., Galliard, T., Ellis, P. R., Angold, R. E., & Vaughan, J. G. (1992). Effect of the outer bran layers on the loaf volume of wheat bread. Journal of Cereal Science, 15, 151e163. He, S., Liu, C., & Zhuo, J. (2004). Study on the technics of one-time-fermentationmethod steamed-bread making procession. Grain Processing, 4, 47e51 (In Chinese).
Hemery, Y., Chaurand, M., Holopainen, U., Lampi, A. M., Lehtinen, P., Puronen, V., et al. (2011). Potential of dry fractionation of wheat bran for the development of food ingredients, part I: Influence of ultra-fine grinding. Journal of Cereal Science, 53, 1e8. Huang, S., Yun, S. H., Quail, K., & Moss, R. (1996). Establishment of flour quality guidelines for northern style Chinese steamed bread. Journal of Cereal Science, 24, 179e185. Idris, W. H., Babiker, E. E., & El Tinay, A. H. (2003). Fractionation, solubility and functional properties of wheat bran proteins as influenced by pH and/or salt concentration. Nahrung, 47, 425e429. Kent, N. L., & Evers, A. D. (1994). Kent's Technology of Cereals (4th ed.). Oxford: Pergamon Press. p. Oxford. Kihlberg, I., Johansson, L., Kohler, A., & Risvik, E. (2004). Sensory qualities of whole wheat pan bread e influence of farming system, milling, and baking technique. Journal of Cereal Science, 39, 67e84. Kock, S. D., 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 eTechnologie, 32, 349e356. Marquart, L., Jacobs, D., McIntosh, G., Reicks, M., & Poutanen, K. (Eds.). (2007). Whole grains and health. Ames, IA, USA: Blackwell Publishers. 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-Evidence for fibre-protein interactions. Journal of Cereal Science, 52, 59e64. Posner, E. S., & Hibbs, A. N. (2005). Wheat flour milling. St. Paul, MN: American Association of Cereal Chemists. Prabhasankar, P., & Rao, P. H. (2001). Effect of different milling methods on chemical composition of whole wheat flour. European Journal of Food Research and Technology, 213, 465e469. Ragaee, S., & Abdel-Aal, E. M. (2006). Pasting properties of starch and protein in selected cereals and quality of their food products. Food Chemistry, 95, 9e18. Rasper, V. F., & Walker, C. E. (2000). Quality evaluation of cereals and cereal products. Revised and Expanded. In K. Kulp, & J. G. Ponte (Eds.), Handbook of Cereal science and technology (2nd ed.). (pp. 505e538). New York, USA: Marcel Dekker. Rogers, D. E., Gelroth, J. A., Langemeier, J. M., & Ranhotra, G. S. (1994). Evaluation of starch damage value determined enzymatically or amperometrically. Cereal Chemistry, 71, 578e581. Wang, J., Xie, A., & Zhang, C. (2013). Feature of air classification product in wheat milling: physicochemical, rheological properties of filter flour. Journal of Cereal Science, 57, 537e542. Weaver, G. L. (2001). A miller's perspective on the impact of health claims. Nutrition Today, 36, 115e118. Ziegler, E., & Greer, E. N. (1971). Wheat flour milling. In Y. Pomeranz (Ed.), Wheat chemistry and technology (pp. 134e143). St. Paul, MN: American Association of Cereal Chemists.
Contents lists available at ScienceDirect
LWT - Food Science and Technology journal homepage: www.elsevier.com/locate/lwt
Effects of different milling processes on whole wheat flour quality and performance in steamed bread making Chong Liu, Lin Liu, Limin Li, Chunming Hao, Xueling Zheng*, Ke Bian**, Jie Zhang, Xiaoxi Wang College of Grain and Food, Henan University of Technology, Zhengzhou, 450001, PR China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 17 October 2013 Received in revised form 14 April 2014 Accepted 26 August 2014 Available online 16 September 2014
In recent years there has been growing interest in whole grain products. However, few studies have analyzed the influence of whole wheat flour on the quality of Chinese steamed bread. This study determined the influence of different milling processes on the physicochemical properties and steamed bread quality of whole wheat flour. A medium hard red wheat, soft white wheat and Canada hard wheat was used as raw materials. The milling processes including three entire grain grinding and four bran recombining processes. The wheat flour ground by roller mill was used as a control. Results showed that whole wheat flour made from entire grain grinding processes had higher viscosity values but lower particle size than bran recombining processes. Appropriate processes can improve the farinograph characteristics of whole wheat flour. Chinese steamed bread of whole wheat flour obtained from bran recombining had larger height/diameter ratio, specific volume than that from entire grain grinding processes. Ultrafine entire grain grinding process especially when using white wheat improved the color of steamed bread. The texture differences of steamed bread between whole wheat flour and flour were significant. Steamed bread of red wheat from heat-treated bran recombining (HTBR) process got the highest sensory score.
Keywords: Whole wheat flour Milling process Quality Steamed bread Texture
© 2015 Published by Elsevier Ltd.
1. Introduction Wheat grain is composed of three parts; the endosperm containing mostly starch and proteins, the germ composed mostly of lipids and proteins and the bran containing mainly dietary fiber (Marquart, Jacobs, McIntosh, Reicks, & Poutanen, 2007). These three components are separated at the mill during the refining process. From this process, the white wheat flour is obtained and used for wheat products making. Most often the bran and germ parts are dedicated to animal nutrition, which lead to the loss of many potentially beneficial micronutrients, antioxidants, minerals, and fiber. Therefore, considerable attentions have been paid to the production of whole wheat flour. Whole grains are defined by AACC International (1999) and U.S. Food and Drug Administration (FDA) as consisting of “the intact, ground, cracked or flaked caryopsis
* Corresponding author. Tel./fax: þ86 0371 67758016. ** Corresponding author. Tel./fax: þ86 0371 67758082. E-mail addresses: [email protected] (X. Zheng), [email protected] (K. Bian). http://dx.doi.org/10.1016/j.lwt.2014.08.030 0023-6438/© 2015 Published by Elsevier Ltd.
(fruit or kernel) of the grain, whose principal anatomical components, the starchy endosperm, germ and bran, are present in the same relative proportions as they exist in the intact grain”. Whole wheat flour contains substantially more vitamins, minerals, antioxidants and other nutrients than regular wheat flour, since these compounds are concentrated in the outer portions of the grain (Weaver, 2001). Whole grain may have beneficial effects on cardiovascular diseases, diabetes and weight management (Marquart et al., 2007). Despite the beneficial effect, the public's acceptance of whole wheat food products is limited due to their poor taste and texture (Gan, Galliard, Ellis, Angold, & Vaughan, 1992). Therefore, some technological efforts are needed in order to improve the performance of whole wheat products. Selecting the milling process that will be used is the key consideration in producing whole grain flour (Kihlberg, Johansson, Kohler, & Risvik, 2004). The four predominant techniques for grinding whole grain flours are stone mill (SM), roller mill (RM), ultra-fine mill (UM) and hammer mill (HM) (Kent and Evers, 1994). The hammer mill causes the product to be heated up and to lose moisture (Posner & Hibbs, 2005). Stone mills generate considerable
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heat due to friction, resulting in damage to starch, protein, and unsaturated fatty acids (Prabhasankar & Rao, 2001). The process of roller milling involves separation of the endosperm from the bran and germ followed by gradual size reduction of endosperm (Ziegler & Greer, 1971). Producing flour that fulfills the requirement for being whole grain is achieved by blending bran and germ back with the endosperm flour in the naturally-occurring proportions. In comparison with stone mills, roller milling is more economical and flexible (Posner & Hibbs, 2005), less heat production and thus less destruction to chemical components (Prabhasankar & Rao, 2001). A third advantage of making whole grain flours from roller mills is that wheat bran and germ can be separated from the endosperm fraction and subjected to further processing or post-milling such as heating or ultrafine grinding to affect the storage or functional properties of the flour (Posner & Hibbs, 2005). On the other hand, there are considerate studies about the post-milling processes for whole wheat flour, which including the twin-screw extrusion, the heat treatment of the bran and germ (Kock, Taylor, & Taylor, 1999) and the ultra fine grinding processes (Hemery et al., 2011). Steamed bread is a popular food in China and has a long history. It is the staple food particularly in the northern part of China (Huang, Yun, Quail, & Moss, 1996). So far, however, the application of whole wheat flour in steamed bread making especially effect of whole wheat flour processing method on the quality of whole wheat flour and steamed bread have not been thoroughly examined. The aim of this research was to determine the effect of different whole wheat flour milling processes on the technological quality of the whole wheat flour and resulting whole wheat flour steamed breads. 2. Material and methods 2.1. Material The wheat (Triticum aestivum L.) varieties Zhengmai 366 (hard red winter wheat), Yumai 57 (soft white winter wheat) and CWRS (Canada Western Red Spring) were used in this study. Wheat were purchased from Haijia Food Industry Co. Ltd (Zhengzhou, CN) and all harvested in June 2011. The chemicals used were all analytical grade. 2.2. Analysis of wheat kernel quality characteristic Weight, moisture, diameter, and hardness of 300 wheat kernels were analyzed by the Single Kernel Characterization System of SKCS-4100 (Perten, Sweden) according to Chinese national standard GB/T 21304-2007. The ash contents, test weight, protein content and 1000 kernel weight were determined according to GB/ T 5009.4e2003, GB/T 5498e85, GB/T 5009.5e2003 and GB 551985, respectively. Before determining the starch content, the samples were firstly pretreated by 1 g/100 g hydrochloric acid, and then the content of starch was determined using a WZZ-2B polarimeter (Inesa Instrument Co., Ltd., Shanghai, CN).
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2.3.2. Preparation of whole wheat flour by entire wheat grain grinding Whole wheat flours were prepared by hammer mill (HM), stone mill (SM) and ultra-fine mill (UM) processes, during which entire wheat grain was ground by a hammer mill (Penten 3100, Sweden), an electric stone mill (custom-tailor) and an FDV ultra-fine mill (Beijing Kingslh Instruments Ltd., Beijing, CN), respectively. Whole wheat flours collected from above processes were all passed though a CQ20 screen before use. 2.3.3. Preparation of whole wheat flour by pretreated bran recombining In these processes, whole wheat flours were prepared by recombining stabilized or pretreated bran back to white flour according to their original proportions. For extrudes bran recombining (EBR) process, the bran fraction was passed through a 80 mesh sieve and tempered to 40 ± 2 g/100 g moisture content, stirred, evenly blended and rest for 1 h. A co-rotating double screw extruder from Saixin (Ji'nan Saixin Machinery Co., Ltd., Shandong, CN) was used. The screw configuration was composed of conveying and mixing elements with reverse elements in the last section of the barrel. The extruder was operated at a feed rate of 25e30 kg h1, screw speed 120 r/min, mass temperature 150 C, The extruded samples were collected and dried slowly in an oven at 60 C for 16 h. After ground by a Perten LABORATORY MILL 3100, the collected bran fraction was passed through a CQ20 screen and evenly blended with white flour according to its original proportions to get whole wheat flour. For heat-treated bran recombining (HTBR) process, the bran fraction without sealing was heated in an autoclave at 121 C for 5 min. After freeze-drying and pulverizing by an FW-100 high speed grinder (Beijing Zhongxingweiye Instrument Co., Ltd., Beijing, CN), the bran fraction was sifted and blended with white flour to obtain whole wheat flour as shown in above. In a hammer-milled bran recombining (HMBR) process, the bran fraction was ground by a Perten 3100 hammer mill and the milled bran fraction was sifted and blended with white flour to obtain whole wheat flour as shown in above. For ultra-fine milled bran recombining (UMBR) process, the bran fraction was ground by an FDV ultra-mizer, then sifted and blended with white flour to obtain whole wheat flour as shown in above. 2.4. Physicochemical properties analysis of whole wheat flour Moisture content, ash content, protein content, falling number in whole wheat flours were determined according to Chinese National Standard GB/T 5009.3-2003, GB/T 5505-2008, GB/T 5009.52003 and GB/T 10361-89, respectively. Sedimentation value was measured by AACC method 76-31 (AACC, 2000). Contents of wet gluten and gluten index were determined according to GB/T 146082003.
2.3. Preparation of wheat flour and whole wheat flour
2.5. Starch pasting properties analysis
2.3.1. Preparation of wheat flour by roller mill (RM) The wheat samples from these mills were milled in a laboratory mill (Model MLU-202, Bühler) to obtain wheat flour according to AACC 26-20 (2000) method after tempering for 24 h at 16 g/100 g, 15 g/100 g and 14 g/100 g moisture contents for hard wheat, medium-hard wheat and soft wheat, respectively. The flour extraction rate was about 70 g/100 g. The remained bran fraction (30 g/100 g of wheat weight) was collected and used as raw material in post-milling processes in the following sections.
Pasting properties were determined with a Rapid ViscoAnalyzer (Newport Science Instruments and Engineering) according to STD1 procedure of AACC methods 76-21 (2000). 2.6. Evaluation of dough quality Farinograph characteristic of dough were determined by a Farinograph equipped with a 50 g-stainless steel bowl (Brabender Farinograph) according to GB/T14614-93.
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2.7. Particle size analysis
3. Results and discussion
Particle sizes were measured by dry powder laser particle size analyzer (BT-9300H, Bettersize Instruments Ltd., Liaoning, CN).
3.1. Wheat kernel quality characteristic
2.8. Northern-style Chinese steamed bread preparation Steamed breads were prepared according to sponge dough method described by He, Liu, and Zhuo (2004) with some modification. Dry yeast, 1 g (Mauripan, Harbing Mauripan Yeast Co., Ltd., Harbing) was dispersed in water (30 C). Whole wheat flour 100 g was mixed with yeast/water (85% of Farinograph water absorption) in a flour mixer (JHMZ200, East Fude Technology Development Center, Beijing). Mixing time, water addition and proof time were adjusted based on the performance of the dough and results of a large number of experiments. The mixing time was 10 min. After pressing pieces 20 times using a rolling pin, the dough was divided into three pieces and shaped by hand to a round, long and straight dough piece with a smooth surface. Dough pieces were proofed for 50 min at 38 C and 85% RH. Flour and dough were remixed by hand until the dough became cohesive. The breads were steamed for 20 min in a steamer. 2.9. Sensory evaluation The Chinese steamed bread was evaluated according to SB/T 10139-1993. The volume and weight of Chinese steamed bread were measured by rapeseed displacement and balance (0.01 g) 60 min after cooling for 1 h. Diameter and height were also measured. Color of skin for steamed bread was determined using a Satake mini color grader (MICG1A, Satake Inc., Japan). Steamed bread used for color analysis was cut into 20 mm thin slice with bread knife. In the color difference analysis, ‘L*’, ‘a*’ and ‘b*’values were recorded. The sensory quality scoring system was based on GB/T21118-2007. The panel consisted of 7 trained tasters (three males and four females between 20 and 26 years old) from different provinces of the northern China. Specific volume, height, color, surface structure, appearance, internal structure, elasticity, toughness, stickiness and scent were scored by five experts. The best scores were 15, 5, 10, 10, 10, 15, 10, 10, 10 and 5, respectively, which give a total score of 100. Three samples were evaluated and means were given. 2.10. Texture profile analysis (TPA) of steamed breads After sensory evaluation, the steamed bread was cut into pieces of 20 mm thickness. TPA of steamed bread was tested using the TA-XT2i texture analyzer (Scarsdale, NY; Stable Micro Systems, UK) with its Pasta Firmness/Stickiness Rig probe (P35). Instrument settings were compression mode, trigger type, auto5 g; pretest speed, 2.0 mm/s; posttest speed, 1.0 mm/s; test speed, 1.0 mm/s; compression height, height of samples; strain, 50%; interval between two compressions, 5 s; compression times, 2 s. Each sample should be measured twice and the final result was the average. 2.11. Statistical analysis The data reported in all the tables are averages of triplicate observations. Analysis of variance (ANOVA) and analysis of correlation were both performed using SPSS ver. 18.0 for Windows (SPSS Institute, Cary, NC). Significance of differences was defined at p < 0.05 with Tukey's test.
Before preparation of whole wheat flour, wheat kernel quality characteristics were analyzed. Moisture content of wheat grain was in the range of 10.74e12.63 g/100 g. Ash contents ranged from 1.52 to 1.57 g/100 g. Test weight was 791.0, 791.5 and 824.5 g/L, protein content was 14.2, 13.6 and 14.6 g/100 g, crude starch content was 71.58, 72.83 and 70.41 g/100 g, and hardness was 51.68, 41.15 and 76.05 for Zhengmai 366, Yumai 57, and CWRS, respectively. CWRS had the highest level of 1000 kernel weight. 3.2. Physicochemical properties of whole wheat flour Physicochemical quality of whole wheat flour from different processes is given in Table 1. For entire grain grinding, water loss of whole wheat flours were all significantly higher than those of wheat flour. Whole wheat flour made by UM had the lowest moisture level. This might be due to greater grinding strength used by UM resulting in more heat production. There were no significant differences in the moisture content between wheat flour and whole wheat flour obtained from bran recombining processes (p < 0.05). Among different recombination processes, whole wheat flour made by EBR had lower moisture content than those made by HTBR, HMBR and UMBR (p < 0.05). The whole wheat flour had significantly higher ash content than did wheat flour (p < 0.05). Significant greater protein contents were found for whole wheat flour compared with wheat flour (p < 0.05). This was due to higher protein content present in bran (Idris, Babiker, & El Tinay, 2003). For all milling processes, samples from CWRS had the greatest protein contents, followed by red wheat (Zhengmai 366), while protein content of white wheat (Yumai 57) being the lowest. This is consistent with the results for wheat grain. In general, high sedimentation volume indicates strong gluten and vice versa (Rasper & Walker, 2000). Whole wheat flour had obvious lower sedimentation values than that of wheat flour except for UBR process, which might be attributed to denaturation of protein during entire grain grinding or the reduction of gluten strength by bran during recombining process. The values for UM were missed due to the failure in recording sedimentation values within 5 min. There were no significant differences in falling number between wheat flour and whole wheat flour (p > 0.05). Higher amounts of gluten content are desirable for steamed bread making (Day, Augustin, Batey, & Wrigley, 2006). In case of entire grain grinding processes, the gluten contents for the SM and HM processes using Zhengmai 366, the HM and UM processes using Yumai 57 and the HM process using CWRS were significantly higher than that of wheat flour. Whole wheat flour from entire grain grinding processes had higher gluten content than that from bran recombining processes. The gluten contents for all bran recombining processes were lower than that of wheat flour, with EBR getting the lowest level. This is probably due to three factors: bran is mainly consisted of albumin and globulin which had poor quality than gluten; bran can weaken gluten network; denaturation of protein caused by bran pretreatment decreased quality of gluten. Gluten indexes of whole wheat flours were higher than that of wheat flour except for UMBR using CWRS. However, there is no a trend in gluten index among different milling processes. 3.3. Pasting properties of whole wheat flour Starch pasting property recorded by RVA test reflects flour quality (Ragaee and Abdel-Aal, 2006). Different milling processes had significant influences on pasting properties of red wheat Zhengmai 366
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Table 1 Physical and chemical properties of whole wheat flour from different milling processes. Variety
Process
Moisture (g/100 g)
Ash (g/100 g)
Protein (g/100 g)
Sedimentation value (ml)
Falling number (s)
Wet gluten (g/100 g)
Gluten index
Zhengmai 366
RM HM SM UM EBR HTBR HMBR UMBR RM HM SM UM EBR HTBR HMBR UMBR RM HM SM UM EBR HTBR HMBR UMBR
12.95a 11.59c 10.75d 7.20f 9.00e 13.05a 12.35b 11.75c 13.43a 10.91d 10.40d 6.93f 9.60e 12.60b 12.15c 12.00c 14.32a 12.31c 10.75d 7.26e 10.50d 13.45b 12.4c 12.15c
0.65d 1.53a 1.18c 1.53a 1.27b 0.86d 1.19c 1.32b 0.61e 1.56a 1.13c 1.56a 1.30b 0.84d 1.19b 1.25b 0.59f 1.58a 1.14d 1.58a 1.29c 0.82e 1.28c 1.38b
11.3e 14.2b 14.8a 13.3d 13.9c 14.9a 14.3b 14.5b 10.3d 13.6ab 13.4b 13.0c 13.4b 13.7ab 14.0a 13.9a 11.8c 14.6b 14.7b 14.4b 14.8a 14.2b 15.1a 15.0a
29.4b 9.1f 15.0d e 14.2d 18.1c 11.1e 44.9a 27.8b 8.9f 14.5c e 11.1e 12.4d 11.2e 42.9a 43.4a 15.6c 9.1e e 10.9d 9.5e 15.9c 33.1b
458.5b 444.3c 401.5e 464.0a 425.5d 441.5c 438.5c 416.6d 353.5e 362.4d 378.5b 342.5f 368.1c 370.5c 402.5a 331.5f 477.5a 425.4e 441.5d 418.5e 420.8e 460.5b 414.9f 448.5c
26.9b 29.4a 29.6a 24.2c 19.1e 21.4d 24.3c 21.3d 30.8b 32.4a 22.5c 32.0a 16.4d 19.5c 21.7c 20.4c 29.9b 33.6a 24.3d 29.6b 13.9f 26.2c 21.1e 15.1f
97a 88c 69e 80d 88c 89c 81d 94b 85a 67c 78b 52d 67c 55d 66c 63cd 98a 89c 94b 71e 83d 89c 96a 98a
Yumai 57
CWRS
Different letters within a column for the same wheat variety indicate values are significantly different at the level of p < 0.05. Abbreviations: Roller mill (RM), Hammer mill (HM), Stone mill (SM), Ultra-fine mill (UM), Extrudes bran recombining (EBR), Heat-treated bran recombining (HTBR), Hammer-milled bran recombining (HMBR), Ultra-fine milled bran recombining (UMBR).
(Fig. 1A and B). In case of entire grain grinding processes, the whole wheat flour made from HM process had higher while those from the UM and SM processes had much lower values in most of the viscosity parameters than did wheat flour, with whole wheat flour from SM having the lowest values (Fig. 1A). Viscosity parameters of whole wheat flour made by bran recombining processes was significantly lower than that of wheat flour (p < 0.05), except for final viscosity of whole wheat flour from UMBR (Fig. 1B). There were no differences in viscosity parameters except for final viscosity and setback values among different bran recombining processes. Viscosity parameters for bran recombining processes were much lower than those for entire grain grinding processes except for SM. The lower value of peak, troughs and final viscosities for the former might be due to their lower gluten contents but higher protein content. It was found that higher protein content would result in lower starch content, while viscosity indicators were positively correlated with starch content (Wang, Xie, & Zhang, 2013). In case of entire grain grinding processes using white wheat (Fig. 1C), viscosity parameters for whole wheat flour made from SM were much lower than those of wheat flour (p < 0.01). RVA profiles for HM and UM processes were in above that of wheat flour except for peak viscosity. Whole wheat flour produced by bran recombining procedures had lower peak viscosity than wheat flour (p < 0.01), while the differences among different bran recombining processes were relatively small (Fig. 1D). Significant differences in setback values among different bran recombining processes were found (p < 0.05), with HTBR the lowest while UMBR the highest. In comparison with white wheat Yumai 57, the impacts of different milling processes on pasting properties of CWRS (Fig.1E and F) were more similar to those for red wheat Zhengmai 366. Viscosity parameters for whole wheat flour made from SM were significantly lower than that from HM, UM and that of wheat flour. The RVA profile of whole wheat flour for HM was more similar to that of wheat flour. Whole wheat flour made from bran recombining processes had much lower peak viscosity than wheat flour (p < 0.05), but no differences were found among different bran recombining means. There were
significant differences in setback values (p < 0.05) among different bran recombining processes, with HTBR the lowest while UMBR the highest. Moreover, viscosity parameters for bran recombining processes were comparable to that of SM process. 3.4. Farinograph quality of whole wheat flour In comparison to water absorption of wheat flour (59%~64.5%), those of whole wheat flour (70.00%~80.20%) increased significantly, probably due to their higher fiber contents (Hemery et al., 2011) (Table 2). For red wheat Zhengmai 366, development time of whole wheat flour (5e8.3 min) except for those made from HMBR (11 min) and UMBR (9.2 min) were lower than that of wheat flour (9 min). However, for Yumai 57 and CWRS, development time of all whole wheat flours except for those made from HM and EBR were respectively higher than that of wheat flour. Stability time of all whole wheat flours except for those made from UM using Zhengmai 366 and Yumai 57, HMEBR and UMBR using Yumai 57 and SM using CWRS were lower than that of wheat flour. Degree of softening ranged form 5e101 FU, with HTBR for CWRS getting the lowest value and EBR for white wheat Yumai 57 getting the highest value. Farinograph quality number ranged from 56 to 212, with EBR for Yumai 57 having the lowest value and HMBR for CWRS having the highest value. The results showed that appropriate milling and post-milling processes can improve the farinograph characteristics of whole wheat flour, but this was wheat varieties-dependent. 3.5. Particle size distribution of whole wheat flour The particle size for whole wheat flour made from bran recombining processes was obviously higher than those from whole grain grinding processes (Fig. 2). Whole wheat flour made from UM had the lowest values in particle size, with the D50 of 18.61, 19.36 and 15.92 mm for red wheat (Zhengmai 366), white wheat (Yumai 57) and CWRS, respectively. Whole wheat flour made from EBR had the highest values in particle size, with the D50 of 69.13, 57.96 and
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Fig. 1. A Pasting properties of whole wheat flour made from entire grain grinding process using Zhengmai 366 (A), Yumai 57 (C) and CWRS (E), from bran recombining process using Zhengmai 366 (B), Yumai 57 (D) and CWRS (F). A: HM, UM, RM, SM (for color fig); dHM, _._UM┄RM, ━SM (for black fig); B: RM, UMBR, HMBR, HTBR (for color fig); dRM, … UMBR, ┄HMBR, ━HTBR (for black fig); C: UM, HM, RM, SM (for color fig); ┄UM, … HM, dRM, ━SM(for black fig); D: UMBR, HMBR, RM, HTBR (for color fig); … UMBR, ┄HMBR, dRM, ━HTBR (for black fig); E: HM, UM, RM, SM (for color fig); ┄HM, … UM, dRM, ━SM(for black fig); F: RM, UMBR, HMBR, HTBR (for color fig). dRM, … UMBR, ━HMBR, ┄HTBR (for black fig). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
59.22 mm for red wheat (Zhengmai 366), white wheat (Yumai 57) and CWRS, respectively. D50 was positively and significantly correlated with kernel hardness (p < 0.05). This might be due to higher hardness of grain leading to its friability. For bran recombining processes, D50 followed the order EBR > HTBR > HMBR > UMBR, indicating that the HMBR and UMBR could reduce the particle size of whole wheat to a greater degree compared to the EBR and HTBR procedures. This might be due to aggregation of bran during extrusion or heat treatment resulting in their larger particle size. 3.6. Ratio of height to diameter and specific volume of steamed bread The height/diameter and specific volume for steamed bread are given in Fig. 3A and B. Steamed breads made from bran
recombining processes had slightly lower height/diameter and specific volume than that of wheat flour except for those prepared using CWRS, whose values were higher than that of the control. This is probably due to the adverse effects of bran present in wheat flour. It was found that bran can weaken gluten network by fiberprotein interactions and dilution of gluten (Gan et al., 1992; Noort, van Haaster, Hemery, Schols, & Hamer, 2010). The dilution effects might be due to the fact that bran is mainly consisted of water soluble albumin and globulin proteins other than gliadin and glutelin (Idris et al., 2003). Moreover, steamed breads made from bran recombining processes had obvious larger height/diameter and specific volume than those made from entire grain grinding processes, while the differences among different bran recombining processes were relatively small. This might be attributed to the lower particle size of whole wheat flour for whole grain grinding
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315
Table 2 Farinograph characteristics of whole wheat flour from different milling processes. Variety
Process
Water absorption (%)
Development (min)
Stability (min)
Degree of softening (FU)
FQN (FU)
Zhengmai 366
RM HM SM UM EBR HTBR HMBR UMBR RM HM SM UM EBR HTBR HMBR UMBR RM HM SM UM EBR HTBR HMBR UMBR
61.5e 71.4d 77.1b 78.4a 77.2b 76.8bc 74.4c 76.7bc 59.1d 70.0c 73.5ab 72.9b 74.5a 74.5a 72.5b 72.6b 64.5g 70.4f 80.2a 79.0b 77.4c 76.9d 76.1d 74.1e
9.0b 7.7d 7.7d 8.3c 5.0e 7.2d 11.0a 9.2b 4.3d 4.2d 6.2b 6.8b 4.2d 5.5c 7.5a 7.2a 7.9b 6.2c 10.9ab 7.3bc 6.3c 11.3a 11.7a 8.3b
9.4b 5.7c 3.9e 10.8a 3.0e 3.4e 5.9c 4.8d 5.8c 3.2d 5.4c 6.4b 2.8d 2.9d 7.3a 6.1b 14.8b 8.5cd 16.4a 8.6cd 5.5e 9.8c 13.2bc 6.3d
19e 22d 35c 11f 99a 57b 9f 6f 52c 68b 34d 25e 101a 55c 17f 27d 13c 23b 17c 13c 28a 5d 9d 9d
111c 106c 96d 118b 67e 86de 147a 125b 71d 64e 97c 105b 56e 70d 123a 103b 145c 115e 115e 146c 101f 178b 212a 121d
Yumai 57
CWRS
Different letters within a column for the same wheat variety indicate values are significantly different at the level of p < 0.05.
processes than for bran recombining processes, which was similar to those results for bread reported by Noort et al. (2010). In addition, the low particle size implied high level of starch damage level leading to the production of more sugar by enzymatic hydrolysis and thus the formation of softer and stickier dough (Evers & Stevens, 1985; Rogers, Gelroth, Langemeier, & Ranhotra, 1994), which can't support the volume of streamed bread. However, this result was contradict to the fact that viscosity parameters of whole wheat flour, which was positively correlated with specific volume (Huang et al., 1996), were lower for bran recombining processes than for entire grain grinding processes, indicating that effect of bran particle size overwhelm that of flour viscosity. 3.7. Color of steamed bread Chrominance of steamed bread is listed in Table 3. Color for steamed made from whole wheat flour were significantly higher than that of wheat flour, probably due to higher bran contents
Fig. 3. Height/diameter (A), specific volume (B) and total score (C) for steamed bread. A: ￭RM, ,HM, UM, EBR, HTBR, UMBR; B: ￭RM, ,HM, UM, EBR, HTBR, UMBR; C: ￭RM, ,HM, UM, EBR, HTBR, UMBR.
Fig. 2. Particle size distribution of whole wheat flour from different milling processes. ￭RM, ,HM, SM, UM, EBR, HTBR, HMBR, MBR.
resulting in greater amounts of pigment and thus increase in the color grade value (CGV), a* and b* values, decrease in L* value. Whole wheat flour made from bran recombining processes had lower CGV, a*, b* and L* values of steamed bread than that from entire grain grinding processes, except for L* values of steamed bread made from UMBR process using white wheat (Yumai 57) and
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Table 3 Color of steamed bread of whole wheat flour from different milling processes. Variety
Zhengmai 366
Yumai 57
CWRS
Process
RM HM UM EBR HTBR UMBR RM HM UM EBR HTBR UMBR RM HM UM EBR HTBR UMBR
Exterior appearance
Interior structure
CGV
L*
a*
b*
CGV
L*
a*
b*
4.84d 52.24b 55.08a 44.82c 43.44c 42.75c 7.22e 50.92b 52.39a 41.84c 42.17c 39.48d 21.3d 62.86a 61.17a 53.55b 53.85b 49.67c
91.8a 67.3b 65.8b 55.6c 56.8c 57.7c 90.6a 68.1b 67.2b 57.2c 57.0c 67.2b 83.3a 61.8c 59.6c 51.3d 51.4d 67.8b
0.5d 10.0a 8.7b 7.3c 7.3c 7.1c 0.5d 8.5a 8.8a 7.1b 7.1b 6.1c 0.1d 11.5a 12.0a 8.4c 8.4c 9.7b
18.2c 29.6a 29.5a 22.4b 22.3b 24.6b 18.7d 27.7a 29.6a 24.5b 24.6b 21.5c 16.3d 24.5a 24.8a 18.6c 18.7c 22.5b
33.26c 67.03a 68.72a 58.32b 55.64b 52.40b 34.98d 63.40a 60.18a 51.47b 52.40b 44.87c 25.89f 80.07b 87.57a 56.42e 69.49c 65.27d
77.1a 59.7b 58.8b 59.1b 52.2d 56.8c 76.3a 61.7b 63.2b 54.1c 51.8c 62.1b 80.9a 52.9b 49.1c 54.9b 43.2d 56.4b
1.0c 7.6b 8.0b 7.5b 8.9a 8.6a 1.0d 6.3b 6.4b 6.6b 8.6a 5.6c 0.5d 7.9c 8.5b 7.4c 9.9a 8.7b
16.1c 22.9a 23.7a 23.2a 21.8b 21.0b 14.9c 20.8b 22.7a 23.1a 21.0b 20.4b 15.0d 17.3c 16.8c 19.5b 18.9b 21.7a
Different letters within a column for the same wheat variety indicate values are significantly different at the level of p < 0.05.
CWRS. The UMBR process had the lowest CGV value, highest lightness and lowest redness and yellowness among all whole wheat flour milling processes, which was acceptable for consumer. Steamed bread made by UMBR process using white wheat (Yumai 57) had optimum color among all samples, while its volume and total score were lower than those for steamed bread made by the same process using other wheat. 3.8. Texture of steamed bread The effect of processing method on steamed bread quality is shown in Table 4. There were significantly higher hardness and chewiness of steamed bread for whole wheat flour than for wheat flour (p < 0.05). For different whole wheat flour milling processes, the UM process had the greatest while the UMBR process had the smallest value in both hardness and chewiness. Whole wheat flour had significantly lower level of adhesiveness, springiness, cohesiveness and resilience for steamed bread than wheat flour (p < 0.05), but the differences among different whole wheat flour milling processes were relatively small.
3.9. Sensory evaluation of steamed bread Sensory evaluation of steamed bread is given in Fig. 3C. Total scores of steamed bread for whole wheat flour were lower than those for wheat flour. Among all whole wheat flours, steamed bread made from whole wheat flour of HMBR process got the highest score, while steamed bread made from whole wheat flour of UM process got the lowest score. The taste of steamed bread made by whole wheat flour was stronger than that made by wheat flour, which might be due to volatile organic compounds produced by wheat bran. Steamed bread made from whole wheat flour for EBR and HTBR processes had lower scores in taste compared to other processes, probably due to loss of flavor matter during the bran pretreatments. Steamed bread made from UMBR process especially for red wheat (Zhengmai 366) had the best sensory quality. Fig. 4 shows the appearance of steamed bread. The results showed that steamed bread made from bran recombining processes had smoother surface than those made from entire grain grinding processes, especially those made from UMBR processes.
Table 4 Texture of steamed bread made from different milling processes. Variety
Process
Hardness/g
Adhesiveness
Springiness
Cohesiveness
Chewiness
Resilience/mm
Zhengmai 366
RM HM UM EBR HTBR UMBR RM HM UM EBR HTBR UMBR RM HM UM EBR HTBR UMBR
2222e 5596b 8562a 5650b 5118c 3842d 5449c 8158b 8895a 8948a 8037b 3576d 3146e 5797c 7618a 5552c 6513b 4358d
7.296a 90.027d 32.559b 47.120b 37.797b 57.318c 18.566a 32.858b 36.647b 29.652b 29.357b 84.436c 43.119a 94.535b 231.033d 106.357c 46.781a 47.907a
0.905a 0.786c 0.821b 0.784c 0.774c 0.847b 0.912a 0.822ab 0.757b 0.817ab 0.811ab 0.774a 0.914a 0.875b 0.732c 0.899b 0.856b 0.832b
0.805a 0.714b 0.676c 0.695c 0.738b 0.707b 0.790a 0.690b 0.691b 0.690b 0.689b 0.672b 0.813a 0.723b 0.706b 0.726b 0.701b 0.696b
1618.61e 3137.89b 4744.06a 3080.82b 2923.31c 2301.35d 3918.68c 4628.08b 4629.52b 5048.10a 4490.06b 1615.86d 2330.08c 3659.44b 3930.14a 3628.11b 3903.02a 2111.08c
0.480a 0.351b 0.321b 0.334b 0.377b 0.323b 0.470a 0.312b 0.307b 0.314b 0.310b 0.317b 0.467a 0.336b 0.328b 0.335b 0.313b 0.334b
Yumai 57
CWRS
Different letters within a column for the same wheat variety indicate values are significantly different at the level of p < 0.05.
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Fig. 4. Images of steamed bread made by Zhengmai 366 (A), Yumai 57 (B) and CWRS (C).
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4. Conclusions Steamed breads made from bran recombining processes had larger height/diameter and specific volume than those made from entire grain grinding processes, while the differences among bran recombining processes were relatively small. This might be partially attributed to their differences in particle size. The UMBR process had the lowest values of CGV, redness, yellowness, hardness and chewiness but highest lightness among all whole wheat flour milling processes, which was acceptable for consumer. Steamed bread made from UMBR process especially for red wheat (Zhengmai 366) had the best sensory quality and smooth surface. Acknowledgment This work was supported by Special Fund for the Construction of Wheat Technology System in Henan Province (No. S2010-01-G06), Special Fund for Agro-scientific Research in the Public Interest (No. 201303070), Research Foundation for Advanced Talents (No. 2011BS005), Research Foundation of HAUT (No. 2013JCYJ01) and Program for Innovative Research Team in University of Henan Province (No. 13IRTSTHN008). References AACC International. (1999). AACC International defines whole grain. Available at: http://aaccnet.org/definitions/wholegrain.asp Accessed 16.09.11. AACC. (2000). Approved methods of the American Association of Cereal Chemists American. USA. St. Paul, MN: Association of Cereal Chemists Inc. Day, L., Augustin, M. A., Batey, I. L., & Wrigley, C. W. (2006). Wheat-gluten uses and industry needs. Trends in Food Science & Technology, 17, 82e90. Evers, A. D., & Stevens, D. J. (1985). Starch damaged. In Y. Pomeranz (Ed.), Advances in cereal science and technology (pp. 321e347). St. Paul: The American Association of Cereal Chemists. Gan, Z., Galliard, T., Ellis, P. R., Angold, R. E., & Vaughan, J. G. (1992). Effect of the outer bran layers on the loaf volume of wheat bread. Journal of Cereal Science, 15, 151e163. He, S., Liu, C., & Zhuo, J. (2004). Study on the technics of one-time-fermentationmethod steamed-bread making procession. Grain Processing, 4, 47e51 (In Chinese).
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