Effect of mechanically damaged starch on wheat flour, noodle and ...

International Journal of Food Science and Technology 2014, 49, 253–260

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Original article Effect of mechanically damaged starch on wheat flour, noodle and steamed bread making quality Chong Liu, Limin Li, Jing Hong, Xueling Zheng,* Ke Bian,* Yu Sun & Jie Zhang College of Grain and Food, Henan University of Technology, Zhengzhou 450001, China (Received 3 May 2013; Accepted in revised form 19 July 2013)

Summary

Wheat flour was ground in an ultrafine pulveriser to obtain different levels of damaged starch (DS). The effect of DS content on physicochemical properties of flour and quality attributes of Chinese noodles and northern-style Chinese steamed bread were investigated. Results showed that the degree of starch damage raised from 6.54% to 12.06% as grinding intensity increased from 0 to 130 Hz (P < 0.05). The falling number, sedimentation value, starch pastes’ viscosity, dough proofing stability were negatively, while water absorption, pastes thermal stability, the degree of starch pastes and dough level were positively correlated with DS content, respectively (P < 0.05). The increase in DS content from 6.54% to 8.86% did not lead to a deterioration of texture characteristic, which might be attributed to the slight declining in hardness while enhancing in springiness and cohesiveness. The flour with DS content of 6.54–9.66% was suitable for steamed bread making.

Keywords

Damaged starch, noodles, pasting properties, steamed bread, wheat flour.

Introduction

The quality of wheat flour has an important impact on the end products. DS is one of the most important factors affecting flour quality characteristics (Keskin et al., 2012). During wheat milling, some starch granules sustain mechanical damage. The level of the damage varies with both the severity of grind and the hardness of the wheat, and the extent of the damage is of technological significance (Hoseney, 1994; Barrera et al., 2007). As the amount of damaged starch increased, the amylose molecules displayed no change, while the amylopectin molecules were eventually fragmented with the smallest fractions approaching the sedimentation coefficient values of amylose (Tester et al., 2006). Starch damage can modify the surface properties of starch granules by increasing the hydrophilic bonds and thus increase the water absorption capacity of wheat flour (Tara et al., 1972; Saad et al., 2009). Furthermore, damage facilitates starch swelling and gel formation due to the destruction of the forces which prevent granules from swelling in water (Miles et al., 1991; Tester, 1997). However, as a loss of crystallinity of starch granules as DS content increase, *Correspondent: Fax: +86 0371 67758016; e-mail: [email protected] or Fax: +86 0371 67758082; e-mail: [email protected]

falling number and several pasting parameters may decrease (Devi et al., 2009; Barrera et al., 2011). While there are many studies focusing on the influences of DS content on flour quality such as physiochemical properties including pasting properties and dough mixing properties, less attention has been paid to the effect of DS content on dough fermentation characteristics. This research is important due to the fact that dough fermentation characteristic is a main factor to evaluate the baking quality of wheat flour. In recent years, numerous studies have revealed that DS content of flour is an important factor in determining baking quality. Damaged starch hydrates easily and is more susceptible to enzymatic hydrolysis. Appropriate level of damaged starch is beneficial for the increase in baking absorption, gassing power of the dough and thus the volume of bread loaves. However, excessive starch damage can accelerate enzymatic action, decline crumb grain and texture characteristics by over-hydrating the dough, and lead to inferior baking performance (Farrand, 1972; Evers & Stevens,1985; Rogers et al., 1994). Compared with baking quality, the effect of DS content on the quality of cooked or steamed wheat flour-based products attracted much less attention. Huang et al. (1996) showed that protein quantity and quality and starch quality were important factors determining northern-style Chinese steamed bread volume,

doi:10.1111/ijfs.12306 © 2013 The Authors. International Journal of Food Science and Technology © 2013 Institute of Food Science and Technology

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and dough strength was the major determinant of overall steamed bread quality, whereas the influence of DS content was not examined. For noodle making, the flour with excessive damaged starch can absorb more water and reduce noodle cooking and eating quality (Oh et al., 1985; Kim & Wiesenborn, 1996; Kim et al., 1996; Wang et al., 2008). However, more work is needed to be done to examine the relationship of DS content of flour with the quality of Chinese traditional staple food such as noodles and steamed bread. Samples of wheat flour characterized by different DS content were produced by using different milling and grinding approaches. The objective was to study the effects of the DS content on physicochemical properties of flour and both noodle and Chinese steamed bread making quality. Experimental procedures

Materials

A medium hard wheat cultivar AK58 was used as the experimental material. Weight, moisture, diameter and hardness of 300 wheat kernels were analysed by the Single Kernel Characterization System of SKCS-4100 (Perten, Stockholm, Sweden). The chemicals used were all analytical grade. Preparation of flour with different mechanically damaged starch (MDS) levels

Grains were milled in a laboratory mill (Model MLU202; B€ uhler, Uzwil, Switzerland) to obtain flour according to AACC 26-20 method after tempering for 20 h at 15% moisture level. The flour extraction rate was about 70%. An ultrafine pulveriser (JiangYin Jinke Shredden Machinery Co., Jiangsu, China) with power varied from 45 to 130 Hz was used to gain different degrees of MDS from the flour milled by the laboratory mill. Analysis of wheat flour characteristics

The moisture content, ash content, protein content, damaged starch content, sedimentation value, wet gluten content, pasting properties, falling number and farinograph properties of the flour samples were determined using the approved method 44-19, 08-01, 46-10, 76-31, 56-61A, 38-12A, 76-21, 56-81B and 54-21 (AACC, 2000), respectively. Particle sizes were measured by a dry powder laser particle size analyser (Winner3001; JiNan Winner inc., Shandong, China). The fermentation behaviour of flour was measured using maturograph (Brabender oHG, Duisburg, Germany). 300 g of flour was filled into the farinograph mixer and the predissolved components (9 g yeast, 6 g NaCl and 3 g sugar) were added. Then, the mass was

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mixed for 4–15 min depending on the predetermined water absorption by farinograph with the final consistency of 500  20 FU. The obtained dough was divided into two pieces (155 g of each). One piece was put into the centre cabinet of the maturograph for proofing and another piece was used as repeat. The proofing times were 35-15-30 min for strong flours that require a mixing time of 6 min or more in the farinograph, and 25-10-20 min for medium and weak flours. Between each interval of the proofing times, the dough was punched in the dough rounder with 15 rotations. When the last proofing period elapsed, the dough piece was exactly weighed to 150 g and punched in the dough rounder with 15 rotations. Then, put the dough ball into the plastic bowl of the maturograph. After pressing, the dough was placed on the magnetic mounting block in the maturograph for testing. Four characteristics measured were final proofing time, proofing stability, elasticity and dough level. The final proofing time is the time in minutes from the start of the final proof to the first drop of the curve after the maximum, which indicates the best fermentation state by the time needed. The proofing stability is evaluated in minutes with a stencil in the range of the curve maximum and flour with higher resistance to fermentation has longer proofing stability. Dough level is the value in MU from the zero line to the maximum peak of the curve, which states the volume of the dough when dough has achieved the best fermentation state. Dough elasticity is the band width in the range of the maximum peaks expressed in maturograph units (MU). The dough proofing stability and the dough level can be used to comprehensively evaluate the fermentation characteristics of dough. Noodle making

Noodle samples were prepared according to SB/ T10137. Flour (100 g, 14% moisture basis) and tap water (33 mL, T = 30 °C) were mixed into noodle dough in a Waring 7010S mixer [(Waring 7010S, Torrington, CT, USA)] for 6 min at medium speed. The obtained stiff dough was allowed to rest 25 min in a sealed containers (covered with plastic wrap) at room temperature and then sheeted eight times in a noodlemaking machine (6YM-220-250, Chongqing, China). For the initial pass, the roll gap was 2 mm, the sheeted dough was doubled folded and passed through the same gap again, and after being doubled folded for the second time, the roll gap was adjusted to 3.5 mm for another pass. Following that, five more passes were made to reduce the gap progressively to 1 mm. Finally, part of the sheeted dough was cut off and used for colour measure, while the rest was cut into 2 mm wide noodles with a 10 or 18 mm length by a

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cutter and placed in a zip-lock bag and stored at 4 °C for no longer than 24 h before cooking. Noodle quality evaluation

The colour uncooked of noodle samples was measured using a chromameter (MICG1A; Satake Inc., Hiroshima, Japan). The chromameter uses the Commission Internationale de l’Eclairage (CIE) colour system to measure L* (brightness) a* (red-green) b* (yellow blue). More positive values of L*, a* and b* indicate increasing white, red and yellow, respectively. Each sample was measured three times. Five-hundred milli litre tap water was transformed into a small aluminium pan (diameter 20 cm), and the water was boiled in a 2000W electric stove. Then, 50 g dry noodle samples was added into the pot. After cooking until the core white flour disappeared, the noodles were immediately took out, washing with flowing tap water for about 10s and put in the bowl for testing. Cooked noodles was evaluated according to SB/T10137-93 and scored by a taste panel consisted of five experts. The best scores were 10, 10, 20, 25, 25, 5 and 5 for colour, appearance, palatability, toughness, stickiness, smoothness and taste, respectively. Noodles (20 strips, 10 cm in length for compressive test; 12 strips, 18 cm in length for tensile test) were cooked for 4 min in 500 mL tap water maintained at a rolling boil. Then, the cooked noodles were placed in 200 mL water (20 °C) for 1 min and drained for 30 s, immediately followed by compressive (texture profile analysis, TPA) tests using the TA-XT2i texture analyser (Scarsdale, NY, USA; Stable Micro Systems, Surrey, UK). Texture profile analysis of cooked noodles was performed with the Pasta Firmness/Stickiness Rig probe. Instrument settings were the following: compression mode, trigger type, auto, 20 g; pretest speed, 2.0 mm/ s; post-test speed, 0.8 mm/s; test speed, 0.8 mm/s; strain, 70%; interval between two compressions, 2 s. From the force–distance curves, five texture parameters can be obtained: hardness (g), springiness, cohesiveness, adhesiveness (g.sec) and resilience. In addition, chewiness (g) is the product of gumminess and springiness. For each sample, six determinations were carried out, with the high and low values discarded, so that data were the means for four strands (Toyokawa et al., 1989; Hou et al., 1997; Lu et al., 2009). Preparation of northern-style Chinese steamed bread

Steamed breads were prepared according to the method of Huang et al. (1993) with modification. Dry yeast (1.3 g, Mauripan; Harbing Mauripan Yeast Co., Ltd., Harbing, China) was dispersed in water (38 °C, 75% of farinograph water absorption). Flour 130 g

was mixed with yeast/water in a mixer (JHMZ200, Shengxuan mechanical Inc., Hebei, China). The mixing time was 7 min. Dough was fermented for 45 min at 38 °C and 85% RH (Huang et al., 1995). After fermentation, the dough was divided into two pieces, pressing pieces twenty times using a rolling pin and then shaped by hand to a round dough piece with a smooth surface. The dough pieces were proofed for 15 min, respectively. The breads were steamed for 20 min in a steamer and took out and cooled to room temperature. Quality evaluation of steamed bread

The Chinese steamed bread was evaluated according to SB/T10139-93.The volume and weight of Chinese steamed bread were measured by rapeseed displacement and balance (0.01 g) 60 min after removal from the steamer. The appearance, colour, texture, elasticity, stickiness and scent were scored by five experts. The best scores were 15, 10 15, 20, 15 and 5, respectively, and the best score of specific volume was 20. 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 analyser (Scarsdale, NY; Stable Micro Systems, UK) with its Pasta Firmness/Stickiness Rig probe. Instrument settings were the following: compression mode, trigger type, auto- 20 g; pretest speed, 3.0 mm/s; post-test speed, 5 mm/s; test speed, 1 mm/s; compression height, 5.0 mm; interval between two compressions, 10 s; compression times, 2. Each sample should be measured twice, and the final result was the average (Kim et al., 2009). Statistical analysis

Analysis of variance (ANOVA) and analysis of correlation were both performed using SPSS ver. 13.0 for Windows (SPSS Institute, Cary, NC, USA). Significance of differences was defined at P < 0.05 with Tukey’s test. Results and discussion

Effect of grinding strength on DS levels

We can obtain four indicators by Perten SKCS-4100, that is, hardness index (67.73  3.2), moisture content (12.09  0.23%, wb), the single-particle grain weight (41.63  2.1 mg) and grain diameter (3.06  0.23 mm). As shown in Fig. 1, the DS content of flour was 6.54%, 7.30%, 8.86%, 9.66% and 12.06% at grinding strength of 0, 45, 70, 100 and 130 Hz, respectively. Results exhibited that the DS content increased as grinding strength increased. During milling, the rapid

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particle size decreased with the grinding power increasing. The flour without grinding had a particle size of 145.08 lm for D90 and 59.57 lm for D50, respectively, wherein D50 and D90 represent particle diameters corresponding to cumulative particle size frequencies of 50 and 90, in the order of increasing particle diameter. When grinding at 45 Hz, the flour achieved more DS content and D90 and D50 decreased to 81.63 lm and 32.43 lm, respectively. The D50 of flour decreased to 25.07 lm for grinding strength of 70 Hz. When grinding strength increased to 100 Hz and 130 Hz, the D50 of flour further decreased to 19.67 lm and 12.57 lm, respectively, although the trend of decreasing became slowly at higher power. Results also confirmed that DS content increased with the decreased particle size of flour. This can be contributed to the fact that the amylopectin molecule is progressively depolymerised by damage (Tester et al., 2006).

Figure 1 Damaged starch levels of flour at different grinding strength.

Flour quality

increase in mechanical strength might lead to instantaneously generation of huge stress on the flour particles surface and thus the fracture of flour particles. In this process, the surface properties of flour particle may change and DS content increased (Saad et al., 2009). At the same time, the granular lattice distorts and then the crystal or semi-crystal region converts to amorphous region (Tester et al., 2006). Particle size of flour

The influence of different grinding strength on wheat flour particle size is shown in Fig. 2. As expected, the

Table 1 showed that the moisture content of flour decreased with increasing grinding time, which might be attributed to more thermal energy produced by the pulveriser as grinding time increased. DS content has negative and significant correlation with falling number, in consistent with those results of Devi et al. (2009) and Barrera et al. (2011). This may be caused by the great improvement in the enzyme reaction sensitivity of damaged starch. Generally, damaged starch can be more easily hydrolysed into oligosaccharides, which lead to the decrease in system viscosity and falling number. The sedimentation value of flour grew rapidly from 35.30 mL to 81.60 mL with the DS content enhancing from 6.54% to 12.06%. Different observation was found by Keskin et al. (2012) who showed that the effect of milling treatment on sedimentation value was insignificant, which might be due to weaker milling strength used in their study resulting in moderate starch damage. Results also showed that wet gluten content remained constant as DS content increased. While gluten index exhibited an initial slight increased and then decreased as grinding intensity or DS content enhanced, which might be attributed to the moderate denaturation of gluten with increasing temperature during grinding steps, despite of the grinding process being gradually conducted by the present study. Pasting properties

Figure 2 Particle size of flour at different grinding strength. Different letters among columns for the same particle indicator are significantly different (P < 0.05).

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It was indicated in Table 2 that peak viscosity, breakdown, setback and pasting temperature decreased when DS content increased. This result exhibited that even though the increase in DS content caused the decrease in starch viscosity, the retrogradation

© 2013 The Authors International Journal of Food Science and Technology © 2013 Institute of Food Science and Technology

Mechanically damaged starch of wheat flour C. Liu et al.

Table 1 Basic characteristics of flour obtained with different grinding strength NO. of samples

Moisture/% a

F-0 F-45 F-70 F-100 F-130

12.56 10.45b 8.81c 7.58d 6.66e

Ash/% a

0.40 0.43a 0.42a 0.40a 0.44a

Protein/% a

11.98 12.03a 11.99a 12.00a 12.01a

Sedimentation value/mL e

Falling number/s a

35.30 41.90d 49.10c 65.00b 81.60a

Wet gluten content/% a

387 373b 332c 302d 265e

Gluten index 62b 68a 67a 65a,b 63b

31.18 31.07a 31.22a 31.78a 31.54a

Different letters in the same column are significantly different (P < 0.05).

Table 2 Pasting properties of flour with different grinding strength NO. of samples F-0 F-45 F-70 F-100 F-130

Peak viscosity/cp a

Trough viscosity/cp b

3187 3090b 2886c 2773d 2232e

Breakdown/cp a

2027 2163a 1993c 1905d 1542e

1160 927b 893c 868c 690d

Final viscosity/cp a

3488 3536a 3307b 3240b 2761c

Setback/cp a

1461 1373b 1314c 1335b 1219d

Peak time/min b

6.38 6.52a 6.45a 6.52a 6.38b

Pasting temperature/℃ 88.00a 86.95b 84.75c 70.70d 67.45e

Different letters in the same column are significantly different (P < 0.05).

Table 3 Farinograph parameters of dough NO. of samples

Water Absorption/%

Development time/min

Stability/min

Degree of softening (12 min, FU)

Farinograph index

F-0 F-45 F-70 F-100 F-130

62.6e 64.5d 66.0c 67.8b 74.6a

4.5b 7.2a 7.7a 7.3a 7.5a

6.6c 7.7a 6.4c 7.1b 4.7d

42a 29b 27b 22d 25c

89b 100a 102a 107a 103a

Different letters in the same column are significantly different (P < 0.05).

(setback) of starch was restrained. What’s more, the damaged starch was easily hydrolysed by enzyme and thus might reduce the pasting temperature of starch. This study also confirmed that the falling number had an obviously positive correlation with the peak viscosity (P < 0.05), in agreement with the result of Tara et al.(1972) and Tester (1997). Dough quality characteristics

The farinograph characteristics of the flour contained different DS content were determined (Table 3). The data proved that there was a significant positive correlation between the DS content and water absorption (P < 0.05). These results were in agreement with other authors who demonstrated that increased damaged starch enhances water absorption (Tara et al., 1972). This may be due to the fact that increase in DS content lead to the crystal region broken and the water molecules entering into the starch granules more easily. Table 3 also showed that both the dough development time and the farinograph index were the lowest

for the control among all the samples. Once the flour treated with ultrafine pulveriser, both the dough development time and the farinograph index increased dramatically, but the difference between various samples ground with different strength was not significant (P > 0.05). There were no significant differences in flour stability time among the four samples contained DS content of 6.54–9.66%, while the stable time decreased as the DS content further increased to 12.06%. This might be caused by the increase in DS in wheat flour, which led to an increase in water absorption of flour and thus a decrease in dough mixing stability (Fu, 2008). Generally, a correct range of protein content is important for textural characteristics of noodle (Ross et al., 1997; Park & Baik, 2004; Zhao & Seib, 2005), adequate gluten strength and extensibility are required in all noodle flours and noodle dough must be strong enough to withstand sheeting, but not so strong as to cause tearing or breakage of the sheet or the noodles (Fu, 2008). In case of steamed bread, Huang et al. (1996) showed that protein quantity and quality and

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starch quality were important factors determining northern-style Chinese steamed bread volume, and dough strength was the major determinant of overall steamed bread quality. Chinese noodle and steamed bread are generally made from flours in the range 8– 13% protein (Fu, 2008; Huang et al., 1995). However, there is still no standard defined optimum protein range for each type of noodle and steamed bread in China. The stability time for all flour in present study is in accordance with the standard of wheat flour used for noodles (SB/T10137-93) and steamed bread (SB/ T10139-93), respectively, which state that wheat flour used for Chinese noodle and steamed bread making should had stability time of >3.0 min. The fermentation characteristics of dough have very important influence on the quality of baking products. Table 4 showed that the dough fermentation characteristics varied significantly with the change in DS content. When DS content was in the range of 6.54– 7.30%, the dough was resistant to proof, whereas the final proofing time decreased dramatically as DS content increased beyond 7.30%. Although the dough with DS content of 12.06% was easy to proof, its proofing stability was poor. Results showed that dough proofing stability decreased as DS content increased to more than 7.30% and dough level had an opposite trend. Noodles quality

L value of noodle increased from 89.53 to 95.57 when DS content of the flour increased from 6.54% to 7.30% (with grinding power increased from 0 to 45 Hz) and decreased gradually as DS content further rose (Table 5). This might be due to the fact that smaller flour particle resulted from higher DS content had larger surface area and thus higher reflectance and L value (brightness). However, increasing DS content of flour will cause the irregular of starch granule and thus the formation of diffuse reflection on the particle surface, which result in the reduction of noodle brightness (Oh et al., 1985; Fu, 2008). It was found that both a* and b* values of noodle declined as DS content Table 4 Proofing characteristics of dough NO. of samples

Final proofing time/min

Proofing stability/min

Dough level/MU

Dough elasticity/MU

F-0 F-45 F-70 F-100 F-130

31.5b 35.5a 14.5d 16.5c 12.5e

10a 10a 8b 5c 4d

350c 291e 330d 388b 403a

120c 108e 115d 135b 155a

Different letters in the same column are significantly different (P < 0.05).

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Table 5 Quality evaluation of noodles No. of samples

L*value

a*value

b*value

Optimal cooking time/s

Total score (100)

F-0 F-45 F-70 F-100 F-130

89.53e 95.57a 93.47b 92.70c 91.03d

1.30a 0.80b 0.57c 0.53c 0.83b

20.13a 16.30b 14.93c 16.57b 15.10c

171c 161d 191b 211a 205a

91.2b 93.5a 89.9c 85.1d 84.9d

Different letters in the same column are significantly different (P < 0.05).

increased, except those at DS content of 9.66% and 12.06%, respectively. More negative values of a* and b* indicate increasing green and blue, respectively. The noodles prepared with the flour that contained 7.30% of DS had the shortest cooking time, while the noodles produced with the flour that contained 9.66% of DS had the longest time. The most excellent quality of noodles with the highest total score had DS content of 7.30%, which followed by DS content of 6.54% and 8.86%, respectively. Although noodles made from flour contained 6.54% DS had higher score than noodles made from flour contained 8.86% DS, brightness of the former was much lower than that of the latter. Although the mechanisms for the effect of DS levels on sensory quality of cooked noodles are not very clear, we consider that the slight increase in DS content may be the main influencing factors. The slight increase in DS content gave moderate hardness, higher springiness and cohesiveness for the noodles contained DS content of 7.30% compared to 6.54% (Table 6). Cooked starch noodles should be neither too firm nor too soft (Galvez & Resurreccion, 1992), and higher springiness and cohesiveness is consumer desirable. The result also displayed that the peak viscosity of starch paste as well as the noodles making quality of the flour reduced with increasing DS level of flour, except at DS level of 7.30%. This was in agreement with other (Oda et al., 1980; Huang et al., 1995; Zeng et al., 1997) who stated that the peak viscosity of starch pasting was significant and positive correlated with noodle quality. Textural qualities are important concerns to consumers of noodle products. The instrumental parameters of hardness, springiness, resilience, adhesiveness, cohesiveness and chewiness are closely correlated with sensory texture characters of cooked noodles (Li et al., 2012). After cooking, the texture of noodles was determined by TPA analyser and the results are shown in Table 6. Results showed that noodles prepared with flour contained 7.30% DS exhibited the minimum hardness, thereby the noodles were more easy to bite (Galvez & Resurreccion, 1992). There were no significant differences in springiness and resilience

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Table 6 Texture analyses of cooked noodles and steamed bread Type/No. of samples Noodles F-0 F-45 F-70 F-100 F-130 Steamed bread F-0 F-45 F-70 F-100 F-130

Hardness/g

Adhesiveness

6585d 5582e 7291c 7898b 8159a

245a 283b 400c 569d 423c

2057a 977c 1147b 706e 866d

2.141b 1.341a 2.716c 3.646d 5.785e

Springiness

Cohesiveness

Chewiness

Resilience/mm

0.789c 0.867a 0.792c 0.812b 0.821b

0.622d 0.675a 0.635c 0.676a 0.659b

3230d 3272d 3672c 4361b 4437a

0.322c 0.372a 0.313e 0.338b 0.341b

0.936a 0.952a 0.943a 0.927a 0.960a

0.921c 0.928b 0.914d 0.919c 0.936a

1772a 862c 988b 601e 779d

0.631b 0.617c 0.581d 0.596d 0.652a

Different letters in the same column are significantly different (P < 0.05).

Table 7 Steamed bread quality External chromaticity NO. of samples

L value

a* value

F-0 F-45 F-70 F-100 F-130

84.10a 83.70b 83.55b 81.90c 82.45c

0.15a 0.10b 0.15b 0.40d 0.20c

Internal chromaticity b* value

L value

a*value

16.15c 16.75b 17.05a 14.75d 14.05e

82.65a 81.40b 81.55b 80.60c 80.85c

0.35a 0.05b 0.05b 0.60d 0.20c

b* value

Diameter/mm

Height/mm

Total sensory (100)

14.85b 14.85b 15.15a 15.20a 14.90b

71.74e 80.50b 76.70d 82.34a 77.48c

53.02e 56.91c 55.02d 57.50b 59.57a

87.60d 93.25a 92.45b 92.95a 89.15c

Different letters in the same column are significantly different (P < 0.05).

among all of noodles (P > 0.05). For the taste of noodles, chewiness was first decreased and then increased, while cohesiveness remained relatively constant. Steamed bread quality

The effect of DS content on steamed bread quality is shown in Table 7. The results indicated that there were no significant differences in both the external and internal colour among five types of streamed bread prepared from flour with different DS content. The sensory score of streamed bread made from flour of 7.30% DS content was the highest, followed by that of streamed bread made from flour of 8.86% and 9.66% DS content. From the texture analysis (Table 6), it was found that the increase in DS levels caused a significant decrease in hardness, adhesiveness and chewiness of streamed bread, while the springiness, cohesiveness and resilience changed little. The texture analysis data was inconsistent with the result of dough proofing characteristics which stated that the dough level and dough elasticity obtained the minimum values at 7.30% DS content among all samples. This might be contributed to the use of different sampling stages of steamed bead for Maturograph and texture analysis. Results showed that the DS content of flour

greater than 9.66% would reduce streamed bread quality. This might be due to the fact that higher levels of starch damage would lead to the production of more sugar by enzymatic hydrolysis and thus the formation of softer and stickier dough (Evers & Stevens,1985; Rogers et al., 1994), which can’t support the volume of streamed bread. Conclusions

By changing the mechanical grinding intensity, we can control the damage levels of starch granules. The starch damage levels rose from 6.54% to 12.06% as grinding intensity increased, which caused the D50 of particle size dropped from 59.57 lm to 12.57 lm. The falling number, sedimentation value, starch pastes viscosity and dough fermentation stability were negatively correlated with DS content, while water absorption, pastes thermal stability, the ageing degree of starch pastes and dough level were positively correlated with DS content (P < 0.05), respectively. However, there was no significant relationship between quantity and quality of gluten and DS content (P > 0.05). When DS content in the range of 6.54– 9.66% the stability time of flour changed little. The increase in mechanical DS content could make starch

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pasting easier. DS content was not significantly correlated with both the external and internal colour of streamed bread. Acknowledgments

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