Effect of Waxy Wheat Flour Blends on the Quality of Chinese Steamed Bread

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Agricultural Sciences in China 2007, 6(10): 1275-1282

ScienceDirect

October 2007

Effect of Waxy Wheat Flour Blends on the Quality of Chinese Steamed Bread QIN P e n g 2 . 3 , CHENG Shun-he’ and MA Chum-xi2 I

Lixiahe Region Agricultural Research Institute of Jiangsu Province, Yangzhou 225007, P.R. China Agronomy College, Anhui Agricultural University, Hefei 230036, P.R.China Agronomy College, Yunnan Agricultural University, Kunming 650201, P.R. China

Abstract Steamed bread is very popular in the East and Southeast Asian regions, and its quality is affected by some physicochemical properties. Chinese steamed bread was made by adding waxy flour into normal wheat flour in the present study. The results showed that specific volume was not affected by the proportions of waxy flour, whereas, adding waxy flour decreased the appearance, color, texture, elasticity, stickiness, and the total score of Chinese steamed bread. However, there were no significant differences in all values when the proportions of waxy flour were below 10%. All evaluations but specific volume of Chinese steamed bread were positively influenced by the peak viscosity, resistance, and maximum resistance. When the waxy flour proportions were below 25%, the firmness of Chinese steamed bread stored at -18OC for 3 days gradually decreased with the increase of waxy flour. It was revealed that the qualities of Chinese steamed bread cannot.be improved by waxy flour but it can be widely used in frozen storing food in the future. Key words: waxy wheat, Chinese steamed bread, quality

INTRODUCTION Wheaten foods have a very important role in the diet and culture of Asian countries since very early times, Steamed bread is a very common food in China and the East and Southeast Asian regions. Over 1.3 billion people consume steamed bread regularly. The commercial production of frozen steamed bread has made it more convenient for consumers, and raised the popularity even further (Huang 1999). Steamed bread is a major product of wheat in East and Southeast Asian countries, and is an important item in the diet of consumers. Steamed bread produced in northern China is distinctly different from that produced in southern China in the baking formula; the northern style Chinese steamed

bread is produced from a starter “mother dough” in place of yeast while southem style ones are made with yeast. Some studies showed that dough stickiness in the Chinese wheat cultivars was a significant factor for deteriorating northern-style Chinese steamed bread quality. The significant and positive correlation was found between the farinograph stability time and the steamed bread quality in Chinese wheat, and thus, it is necessary to increase the dough strength of Chinese wheat cultivars to improve their steamed bread making quality (Zhu et al. 2001). Hard wheat flour was found to be superior to soft wheat flour in the production of good quality northem-style steamed bread, and flours with medium to strong strength were recommended for making this product (Huang et al. 1996). Flours

Received 5 January, 2007 Accepted 3 April, 2007 QIN Peng, Ph D, E-mail: qinpeng77@ 163.com; Correspondence CHENG Shun-he, Academician, E-mail: [email protected]:MA Chuan-xi, Professor, E-mail: [email protected]

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with a medium dough development time and slightly longer dough stability were most desirable with regard to the northern-style steamed bread specific volume and subjective score. Protein quantity and starch quality were important factors determining the steamed bread volume, and dough strength was the major determinant of the overall steamed bread quality (He et al. 2003). The volume, the fine-textured crumb, and the color of the surface were significantly affected by the dough water absorption, sugar-yeast combinations, and the corresponding fermentation and proof time (Rubenthaler et al. 1990). There is little or no amylose in waxy wheat, and the physicochemical properties of waxy wheat are greatly different from normal and partial-waxy wheat flours. Several studies have shown that waxy wheat behaved differently from wild-type and partial-waxy wheat in physicochemical characteristics, such as lower setback, peak viscosity, pasting and peak temperatures, higher breakdown, gelatinization temperature, protein content, water absorption, SDS-sedimentationvolume, damaged starch, swelling power and alkaline water retention capacity, a greater degree of crystallization, and an absence of an amylose-lipid complex (Graybosch et al. 2000; Park et al. 2001; Kim et al. 2003; Sharma et al. 2002; Chakraborty et al. 2004; Guo et al. 2003; Guo 2002; Morita et al. 2002; Park and Baik 2004; Sasaki et al. 2004; Abdel-Aal et al. 2002; Baik et al. 2003). Up to now, some studies on the qualities of bread and noodle of waxy wheat flour blends have been carried out. However, few studies were fulfilled on the steamed bread quality of waxy flour blends. The purpose of the present study was to show the function of waxy wheat flour blends for Chinese steamed bread making and storing.

MATERIALS AND METHODS Wheat samples Waxy wheat flour (waxy 5 ) was added to two kinds of normal wheat flour, Yangmai 158 and Yangmai 17, which were obtained from Gaoyou and Yangzhou, Jiangsu Province, China, and noted as 1 and 2 in the bracket, respectively, at levels of 0, 5 , 10, 15, 20, 25, 30, 35, and 40%, and these composites were used for

making Chinese steamed bread.

Analysis of wheat flour characteristics The moisture and protein content, Zeleny sedimentation, wheat gluten of the flours, amylose, total starch, damaged starch content, and farinograph and extensograph properties were determined using the approved method 44-15A, 46-13,56-60,38-12A, 6103, 76-13, 76-30A, 54-21, and 54-10 (AACC 2000), respectively. The flour color was measured by determining the L* (brightness or whiteness), a* (redness and greenness), and b* (yellowness and blueness) values, using a chromometer (CR-410, Minolta). Starch paste viscosity was measured using the micro-visco-amylograph (Brabender, 803201). Flour (15 g, 14% mb) was dispersed in 100 mL of water and heated in a micro-visico-amylograph bowl from 30 to 93°C at a rate of 5.5"C min-', with consistent stirring by rotating the bowl at 250 revolutions mid. The paste was held for 1 min at 93°C and cooled to 50°C at a rate of 5.5"C min-I, and was held for 1 min at 50°C.

The making procedures of Chinese steamed bread and quality evaluation Chinese steamed bread was made and evaluated according to SB/T 10139-93. All flour doughs were mixed by hand within 5 min. The 30°C water was added to form the optimum dough which was 55% of the flour weight (14% mb). The baking formula (flour basis) was flour (14% mb) 50.0 g, and vacuum-packed yeast 0.5 g. All doughs were proofed at 30°C for 45 min at 85% rh, then rolled out, molded, and placed in a steam tray for 15 min for further proofing prior to steaming. Dough pieces were steamed in a steamed rice car for 15 min, and tested after cooling for 15 min. The volume and weight of Chinese steamed bread were measured by rapeseed displacement and balance (0.01 g) 60 min after removal from the steamed rice car. The appearance, color, 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. For the frozen storing study, the Chinese steamed breads were placed

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Effect of Waxv Wheat Flour Blends on the Quality of Chinese Steamed Bread

in the Ziploc bags, stored in a refrigerator at -18°C and evaluated for firmness 3 days later. The central slices from the Chinese steamed breads were used to determine the firmness with a stable micro systems texture analyzer (TA. XT. Plus) according to the approved

performed using the statistical analysis system 9.0 (SAS 9.0). Significance was defined at P
method 74-09 (AACC 2000).

Physicochemicalproperties of flours

Statistical analysis

The physicochemical properties of waxy wheat flour blends used in the present experiment are shown in Table 1. Water absorption, dough development time, protein content, and L* (light or whiteness) of waxy

RESULTS

All experiments were performed two times for each sample. The analysis of variance and correlation was

Table 1 Physicochemical properties of waxy flour blends (14% mb) Proportion of Water absorption Development waxy flour (%) (%I Waxy-Yangmai 17(1) 0 66.9 a 5 63.5 c 10 65.2 b 15 66.5 a 20 67.3 a 25 67.4 a 30 67.7 a 35 67.1 a 40 67.8 a Waxy-Yangmai 158(1) 0 63.6 e 5 67.1 cd 10 68.0 ab 15 67.3 bcd 20 67.3 bcd 25 67.6 abc 30 68.1 a 35 68.2 a 40 66.6 d Waxy-Yangmai 158(2) 0 65.7 d 5 65.5 d 10 65.9 cd 15 66.3 c 20 67.3 ab 25 67.0 b 30 67.1 ab 35 67.4 ab 40 61.7 a Waxy-Yangmai 17(2) 0 60.5 e 5 60.8 e 10 60.5 e 15 62.5 d 20 63.6 c 25 65.0 ab 30 65.4 a 35 64.4 b 40 64.5 b

Wet gluten

Dry gluten

4.3 a 5.0 a 4.4 a 4.4 a 4.4 a 4.5 a 5.2 a 4.9 a 4.9 a

31.7 a 29.0 a 30.4 a 31.4 a 31.1 a 31.2 a 31.4 a 29.9 a 31.6 a

10.2 a 9.1 b 9.8 ab 10.0 ab 10.0 ab 10.0 ab 9.8 ab 9.4 ab 10.0 ab

2.8 b 5.8 a 5.3 a 5.6 a 5.3 a 5.7 a 5.4 a 5.2 a 5.1 a

29.4 ab 27.6 b 27.8 b 28.9 ab 30.6 a 29.9 a 25.0 c 31.0 a 29.9 a

3.7 a 3.6 a 3.9 a 3.5 a 3.5 a 3.9 a 3.9 a 4.1 a 3.9 a 4.3 a 4.6 a 4.5 a 4.2 a 4.4 a 4.5 a 4.8 a 4.6 a 4.3 a

Gluten index

Protein

Starch Damaged starch

Energy

Extensibility

93.3 ab 95.0 a 90.6 c 86.7 d 89.7 f 92.9 c 82.6 ab 91.3 bc 77.8 f

10.7 h 10.8 gh 10.9 fg Il.lef 11.2 de 1 1.4 cd 11.5 bc 11.6 ab 11.8a

75.8 a 75.2 ab 74.6 bc 74.1 cd 73.5 de 72.9 ef 72.3 fg 71.8 gh 71.2 h

4.9 a 4.5 b 4.0 c 3.7 d 3.4 e 2.9 f 2.4 g 2.2 b 2.2 h

46.6 bc 60.9 a 44.8 b 42.2 cd 28.9 d 35.9 cd 39.0 bcd 39.0 bcd 32.9 bcd

174.9 a 180.6 a 191.8 a 196.5 a 177.6 a 187.0 a 192.8 a 192.8 a 175.9 a

9.9 ab 9.7 ab 9.3 b 9.6 ab 10.1 ab 9.9 ab 8.5 c 10.2 a 9.5 ab

85.8 c 94.2 a 93.9 a 89.4 b 81.7 d 88.9 b 96.4 a 77.8 e 77.9 e

11.0 g 11.1 fg 11.2efg 11.3 def 11.4 cde 11.6 bcd 11.7 abc 11.8 ab 11.9 a

71.8 a 71.3 b 71.0~ 70.6 d 70.3 e 70.0 f 69.5 g 69.2 h 68.9 i

5.8 a 5.6 b 5.3 c 4.8 d 4.4 e 4.4 e 3.4 f 3.4f 2.3 g

64.2 a 59.4 a 55.6 a 56.9 a 54.8 a 50.9 a 56.0 a 59.1 a 57.3 a

155.6 b 168.8 ab 168.8 ab 175.9 ab 168.5 ab 167.5 ab 165.4 ab 177.9 ab 185.4 a

31.1 e 34.0 a 31.8 cde 33.5 ab 31.3 de 32.6 bcd 32.5 bcd 31.6cde 32.8 bc

10.3 d 11.7 a 10.5 cd 11.3 b 11.0 bc 10.8 c 10.6 cd 10.8 cd 10.9 c

76.1 a 70.0 bc 75.2 a 67.2 c 75.3 a 72.8 ab 71.2 b 59.8 d 69.5 bc

11.3 g 11.4 Ifg 11.5 efg 11.6 def 11.7 cde 1 1.8 bcd 11.9 abc 12.0 ab 12.2 a

72.6 a 72.2 ab 71.8 bc 71.3 cd 70.9 de 70.5 ef 70.1 fg 69.7 gh 69.3 h

5.3 a 4.8 b 4.5 c 4.3 d 4.0 e 3.7f 3.2 g 2.8 h 2.3 i

39.4 a 40.0 a 35.1 a 35.6 a 34.2 a 39.0 a 34.1 a 37.5 a 34.9 a

140.1 c 137.7 c 139.7 c 140.0 c 147.2 bc 162.7 a 162.1 a 159.0 ab 153.2 abc

33.9 de 34.9 c 34.6 cd 34.7 cd 36.0 b 36.8 a 33.9 de 33.2 e 33.1 e

11.2 cde 11.8 bc 11.5cde

73.6 bcd 75.5 abc 76.9 ab 78.1 a 71.2 d 65.7 f 68.5 e 72.4 cd 74.6 bcd

73.2a 72.9 a 72.4 b 72.0 c 12.2cde 71.6 d 12.3 bcd 71.1 e 12.4 abc 70.7 f 12.5 ab 70.2 g 12.5 a 69.9 b

5.1 a 4.7 b 4.3 c 4.0 d 3.1 e 3.3 f 3.1 g 2.6 h 2.1 i

41.6 a 43.2 a 41.7 a 31.8 ab 36.6 b 35.4 b 33.7 b 29.1 b 36.1 ab

166.4 b 175.2 ab 174.5 ab 162.7 hc 175.5 ah 174.5 ab 182.0 a 154.6 c 182.7 a

-

11.6cd

12.4 a 12.3 ab 11.3 cde 11.0 de 10.8 e

12.0 g 12.0 fg 12.1 efg 12.2 def

Values followed by the same letter in the same column are not significantly different (P
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flour were higher than that of the other normal flours, whereas dry gluten content, gluten index, b" (yellowness and blueness), starch content, damaged starch, and amylose content of starch of waxy flour were lower. All properties of extensograph were lower in waxy flour except the extensibility measured at 45, 90 and 135 min. Four normal wheat flour samples were selected on their differences in rheological properties, starch paste viscosities, and ingredients. Gluten index, water absorption, and the starch content of Yangmai 17(1) were higher than the other three samples. Yangmai 158(1) possessed the highest dough stability time, damaged starch, and properties of extensograph except extensibility measured at 90 min. This indicates that the dough of Yangmai 158(1) was stronger than the other samples. The wet gluten content and a* (redness) of Yangmai 158(2) were the highest. The results showed that Yangmai 158 selected from two trial fields was better than Yangmai 17 in dough properties, predicating differences between the two wheat varieties. The properties of waxy flour blends showed that: Firstly, the rheological properties of waxy flour blends determined in this experiment were not the summation simply added by the proportion of waxy and normal flour in blends; in other words, these had no relation to the proportions of waxy flour in blends. However, most of the values of each property were in between waxy and normal flours, and few were higher or lower than any one of the two types. Secondly, most properties of Yangmai 158(1) blends such as dough stability, sedimentation,and properties of extensograph, were higher than that of the other samples; it was attributed to high quality of Yangmai 158(1) flour. Thirdly, Yangmai 17(2) and its flour blends possessed the highest protein contents. Fourthly, damaged starch decreased with the increase of waxy flour proportion, and the value of blends were not only lower than normal flour, but also lower than waxy flour, though it was dramatically lower in waxy flour than in the normal flours.

Influence of waxy flour on Chinese steamed bread qualities Chinese steamed bread scores made from different waxy

OIN Peng et al.

flour proportions are shown in Table 2. Specific volumes of Chinese steamed bread did not significantly decrease with the proportions of waxy flour increasing. It was shown that the specific volume was not affected by the proportions of waxy flour, and the decrease of Yangmai 158(1) with 0 and 5% proportion of waxy flour should attribute to its high dough stability and sedimentation volume. There was no significant difference on scent score among all waxy flour blends, which indicates that scent was not affected by adding waxy flour. Addition of waxy flour decreased the appearance, color, texture, elasticity, stickiness, and total score. However, all values were not significantly different when the proportions of waxy flour were below 10%. The results showed that the waxy flour was not appropriate to make Chinese steamed bread when the proportions were 15%. In other words, waxy flour proportions below 10% could be used to make Chinese steamed bread without decreasing their qualities significantly. Correlations among the Chinese steamed bread scores and the physicochemical properties are shown in Table 3. The results indicated that Chinese steamed bread scores were greatly affected by the physicochemical properties. All scores of Chinese steamed bread except specific volume were positively influenced by peak viscosity, resistance, and maximum resistance. Specific volume was positively influenced by wet gluten and dry gluten contents, however, it was negatively or was not affected by most of the other physicochemical properties. Farinograph properties were not very important for Chinese steamed bread made from waxy flour blends, whereas extensograph properties affected the quality of Chinese steamed bread to a certain extent. Flour color had no significant effect on each score of Chinese steamed bread, but the increase of amylose and starch content should promote the total score and monomial scores but the specific volume and scent. Damaged starch was highly positively correlated to its appearance, color, texture, elasticity, stickiness, and total score of Chinese steamed bread. With the increase of waxy flour proportion, the appearance, color, texture, elasticity, stickiness, and total score decreased significantly, and the protein content was negatively correlated to all scores of

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Table 2 Eating quality of Chinese steamed bread made from waxy wheat flour blends Proportion of waxy flour (%) Waxy-Yangmai 17(1) 0 5 10 15 20 25 30 35 40 Waxy-Yangmai 158(1) 0

5 10 15

20 25 30 35 40 Waxy-Yangmai 158(2) 0 5 10 15 20 25 30 35 40 Waxy-Yangmai 17(2) 0 5 10 15 20 25 30 35 41) .-

Specific volume (20) Amearance (15) Color (10) Texture (15) Elasticitv (20) Stickiness (15)

Scent ( 5 ) Total score (100)

18.0 c 19.0 b 18.0 c 20.0 a 0.0 a 19.5 ab 19.0 b 19.0 b 18.0 c

13.3 a 13.0 a 12.3 ab 12.0 ab 11.5 ab 11.0 bc 10.5 bc 10.3 bc 9.5 c

8.3 a 7.5 ab 7.8 ab 7.3 ab 6.8 ab 6.5 ab 6.0 ab 5.5 ab 5.0 b

13.5 a 13.3 a 12.5 a 12.8 a 12.0 a 12.0 a 11.5 a 11.0 a 10.5 a

18.0 a 17.5 ab 17.8 a 17.0 ab 16.3 ab 15.8 b 12.8 c 11.3 d 9.5 e

13.8 a 13.3 a 13.0 a 12.3 ab 12.5 ab 11.5 abc 10.5 bcd 10.0 cd 9.0 d

4.3 a 4.5 a 4.3 a 4.0 a 4.3 a 4.0 a 4.0 a 4.0 a 4.0 a

89.0 a 88.0 a 85.5 a 85.3 a 83.3 a 80.3 a 74.3 b 71.0 bc 65.5 c

16.5 a 15.5 a 18.0 a 17.0 a 17.0 a 18.0 a 18.5 a 17.5 a 17.5 a

13.3 a 13.0 ab 12.8 ab 12.3 abc 11.5 bcd 11.8 abcd 10.5 cd

8.5 a 7.5 a 8.3 a 7.8 a 8.0 a 8.0 a 7.5 a 8.3 a 8.0 a

13.3 a 13.8 a 13.8 a 12.8 a 12.5 a 11.5 ab 10.5 bc 9.0 cd 8.5 d

17.8 a 17.3 ab 16.5 ab 16.8 ab 15.3 b 13.5 c 12.0 cd 10.5 de 9.0 e

13.5 a 13.3 a 12.5 a 11.5 ab 11.0 ab 11.0 ab 10.5 ab 9.0 b 8.5 b

4.3 a 4.0 a 4.0 a 4.0 a 4.0 a 4.3 a 4.5 a 4.3 a 4.0 a

87.0 a 84.3 ab 85.8 a 82.0 abc 79.3 bc 78.0 cd 74.0 d 69.5 e 65.0 f

11.0de

9.5 e

18.5 a 18.5 a 18.5 a 20.0 a 20.0 a 20.0 a 20.0 a 18.5 a 18.0 a

13.3 a 12.3 ab 12.8 a 11.5 ab 11.5 ab 10.5 bc 9.5 cd 8.5 d 8.5 d

8.3 a 8.3 a 7.5 a 7.3 ab 7.3 ab 6.3 b 5.3 c 5.0 c 4.8 c

13.8 a 13.5 a 12.5 ab 12.5 ab 12.8 ab 12.5 ab 11.5 ab 10.5 bc 9.0 c

18.3 a 17.5 ab 16.3 bc 15.3 c 13.5 d 12.5 d 10.5 e 9.5 e 9.3 e

13.5 a 13.3 a 12.3 ab 11.3 bc 10.5 bc 11.0 bc 10.5 bc 9.5 cd 8.5 d

4.3 a 4.5 a 4.3 a 4.0 a 4.3 a 4.0 a 4.3 a 4.5 a 4.0 a

89.8 a 87.8 ab 84.0 abc 81.8 bcd 79.8 cd 76.8 d 71.5 e 66.0 f 62.0 f

17.0 b 18.5 ab 18.5 ab 20.0 a 20.0 a 20.0 a 19.5 a 18.5 ab 18.5 ab

12.8 a 12.3 a 11.3 ab 10.8 ab 9.8 bc 8.8 cd 8.5 cd 7.5 de 6.5 e

8.3 a 7.8 ab 7.5 abc 7.3 abc 7.3 abc 6.5 bcd 6.0 cd 5.5 d 5.3 d

13.3 a 13.3 a 12.5 a 12.5 a 11.5 a 11.5 a 11.0 a 8.5 b 8.5 b

17.8 a 18.3 a 17.5 a 17.0 ab 15.5 bc 15.3 bc 13.8 cd 12.5 d 10.5 e

13.3 a 12.8 ab 12.3 ab 11.5 abc 11.3 abc 10.3 bcd 9.5 cd 8.3 d 8.0 d

4.3 a 4.0 a 4.3 a 4.0 a 3.8 a 4.0 a 4.0 a 4.0 a 4.0 a

86.5 a 86.8 a 83.8 a 83.0 a 79.0 b 76.3 b 72.3 c 64.8 d 61.3 e

Chinese steamed bread except the specific volume. These results showed that the waxy flour was not suitable for steamed bread making, and the use of waxy wheat on steamed bread in the future should be limited to lower proportion.

Influence of waxy flour on Chinese steamed bread under frozen storing conditions The firmness of Chinese steamed bread was measured after storing at -18°C for three days, and the results are shown in Table 4. The firmness of Chinese steamed bread measured in 15 min after being removed from the steamed car showed that adding waxy flour at lower

levels (proportionslower than 20%) resulted in softening of Chinese steamed bread, and the firmness increased when the proportions of waxy flour were more than 25%. After storing at -18°C for three days, the firmness of Chinese steamed bread increased slightly when compared with fresh ones on the same waxy flour proportions; however, the trend of firming influenced by waxy flour did not change. These results indicated that the low proportions of waxy flour had the function of decreasing the firmness of Chinese steamed bread, but excessive waxy flour resulted in compacting the internal structure of it. Moreover, frozen storing conditions increased the f m e s s of re-steamed Chinese steamed bread, and thus, it is worth using lower

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Table 3 Correlation coefficients of Chinese steamed bread scores and flour blends uroQerties Physicochemical properties Proportion of waxy flour Water absorption Stability Peak viscosity Setback Sedimentation Wet gluten Gluten index Protein Starch Amylose Damaged starch Energy (45 min) Resistance (45 min) Extensibility (45 min) Maximum resistance (45 min) Maximum ratio number (45 min) Extensibility (90 min) Maximum resistance (90 min) Maximum ratio number (90 min) Maximum ratio number (135 min)

Specific volume

Appearance

Color

Texture

Elasticity

Stickiness

Scent

Total score

0.21 0.02 -0.48" -0.36'

-0.86" -0.27 0.46" 0.81" 0.64" -0.02 -0.42" 0.55" -0.82" 0.62" 0.85' 0.86"

-0.73" -0.37' 0.45" 0.70" 0.48" 0.15 -0.32' 0.42" -0.56" 0.43" 0.78" 0.82" 0.67" 0.66" -0.27 0.70" 0.64" -0.39' 0.59" 0.53" 0.49"

-0.90" -0.28

-0.94" -0.54" 0.24 0.73" 0.64" -0.07 -0.02 0.37' -0.55" 0.71" 0.82" 0.83" 0.28 0.35' -0.20 0.35' 0.36' -0.27 0.32' 0.33' 0.33'

-0.96" -0.40' 0.27 0.82" 0.73" -0.08 -0.19 0.44" -0.72" 0.71" 0.85" 0.85" 0.36' 0.41" -0.22 0.42" 0.42" -0.37' 0.33'

-0.27 -0.07

-0.96"

-0.04 -0.40' 0.46" -0.3 1 0.29 0.08

-0.28 -0.38' -0.63" -0.49" 0.05 -0.55" -0.43" 0.16 -0.42" -0.34

0.56" 0.57" -0.27 0.61 *' 0.58" -0.44" 0.49" 0.47"

-0.33'

0.44"

0.25 0.79" 0.63" -0.06 -0.12 0.33' -0.63" 0.60" 0.81" 0.82" 0.25 0.33' -0.24 0.32' 0.33' -0.40' 0.22 0.26 0.25

0.16 0.40' 0.29 -0.17 -0.35' 0.14 -0.36'

-0.43" 0.28 0.80" 0.69" -0.09 -0.15 0.42" -0.68" 0.72"

0.26 0.33' 0.28 0.26 0.44" -0.39' 0.40' 0.44" -0.33'

0.34'

0.38' 0.39'

0.32.'

0.38'

0.87" 0.87" 0.35' 0.42" -0.26 0.43" 0.44' -0.38' 0.36' 0.37' 0.36'

* and ** indicate significance at 0.05 and 0.01 probability levels, respectively. The same as below.

Table 4 Effect of blending waxy wheat flour on the firmness of Chinese steamed bread after frozen storing Proportion of waxy wheat flour (%) Yangmai 17(1) 0 5 10

4.48 b 4.26 b 3.67 c

15 20

3.40 c 3.43 c

25 30 35 40

4.36 b 4.59 b 5.79 a 6.13 a

Fresh Chinese steamed bread Yangmai 158(1) Yangmai 158(2) 5.35 a 4.36 b 4.45 b 3.78 c 3.37 c 4.71 b 4.94 ah 5.47 a 5.43 a

Firmness of Chinese steamed bread (g) Frozen storing Chinese steamed bread Yangmai 17(2) Yangmai 17(1) Yangmai 158(1) Yangmai 158(2) Yangmai 17(2)

4.83 h 4.17 h 4.45 bc 4.18 c 3.99 c 5.41 a 5.39 a 5.49 a 5.82 a

proportion of waxy flour blends (maybe 20%) in frozen steamed bread making. Correlations among the firmness of Chinese steamed bread and the physicochemical properties are shown in Table 5. The peak viscosity, breakdown, setback, gluten index, starch, amylose, and damaged starch contents were negatively correlated to fresh Chinese steamed bread firmness significantly. The effects of peak viscosity, setback, starch, amylose, and damaged starch contents on the firmness of frozen Chinese steamed bread were negative, and the other physicochemical properties such as farinograph and extensograph had no correlations to it. Waxy wheat flour has no amylose in its endosperm, and possesses lower peak viscosity

4.75 ab 4.36 bc 4.19 bc 3.941 cd 3.46 d 5.23 a 5.18 a 5.35 a 5.55 a

5.50 c 5.58 c 4.45 de 4.03 e 4.43 de 4.71 d 5.88 bc 6.48 a 6.23 ab

5.52 b 5.13 bc 5.84 b 5.47 b 4.71 hc 5.14 5.22 5.65 6.68

5.15 5.33 5.12 4.93 4.49

ab ab ab ab ab 5.88 ab 5.70 ab 4.36 b 6.12 a

bc c b a

4.92 b 5.07 h 4.76 hc 4.58 bc 4.30 c 6.16 a 5.76 a 5.92 a 6.19 a

and setback; thus, adding waxy wheat flour into normal ones can decrease the firmness of frozen Chinese steamed bread.

Table 5 Correlation coefficients of Chinese steamed bread firmness and flour blends Qrouerties ~~

Physicochemical properties Peak viscosity Breakdown Setback Gluten index Protein content Starch content Amylose content Damaeed starch content

Firmness of fresh Chinese steamed bread

Firmness of frozen Chinese steamed bread

-0.34' 0.45" -0.48"

-0.32' 0.15 -0.47"

-0.35'

-0.09

0.41' -0.46" -0.44" -0.46"

0.27 -0.41" -0.43" -0.42"

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Effect of Waxy Wheat Flour Blends on the Quality of Chinese Steamed Bread

DISCUSSION Most studies of waxy wheat focused on making and staling quality of bread and noodle, and the results showed that adding waxy wheat flour in appropriate proportions will improve the eating quality of white salted noodle and delay the staling of bread (Bhattacharya et ad. 2002; Baik and Lee 2003). There have been no reports on Chinese steamed bread made from waxy wheat flour blends. The present study was carried out in order to determine the effect of waxy wheat flour blends on fresh and frozen storing Chinese steamed bread qualities. Adding waxy flour into normal ones decreased the scores of Chinese steamed bread except specific volume, and the total score was highly negatively correlated to waxy wheat flour proportion, though there was no significant difference among blends with 015% waxy wheat flour proportions. Farinograph properties were not as important as extensograph ones for Chinese steamed bread made from waxy flour blends. The peak viscosity, starch content and amlose content (of starch) were positively correlated to the scores of Chinese steamed bread. Waxy wheat possessed lower peak viscosity and no amylose, and therefore, waxy wheat flour was not suitable for fresh Chinese steamed bread making. The shelf life of Chinese steamed bread was 1-3 d (storing at room temperature); and it is shorter with the increase of temperature and decrease of relative humidity. Chinese steamed bread became firmer when stored at room temperature or at -18°C with consequent decrease in the qualities. Adding an appropriate proportion (< 20%) of waxy flour into normal ones decreased the firmness of re-steamed Chinese steamed bread stored at - 18°C. Gelatification was performed mainly by amylose, and amylose was easier to form regular structure than amylopectin. Chinese steamed bread made from blends with excessive amylopectin could not hold sufficient air during steaming, and its internal structure was compacted; therefore, the firmness of fresh and frozen Chinese steamed bread will be increased when the proportions are increased by more than 25%. Waxy flour was not suitable for steamed bread making, however, it was capable of improving the

qualities of frozen steamed bread with lower proportions. Flour blends with 10-15% waxy wheat flour were the best proportions to decrease the firmness of frozen Chinese steamed bread without decreasing its eating qualities. These results showed that the use of waxy flour on frozen steamed bread was feasible.

Acknowledgements This work was supported by the National High Technology Research and Development Program of China (863 Program, 2001AA241033). We wish to thank Prof. Liu Feihu, Yunnan University, China, and Prof. Qiu Zhihua, Baoshan Teachers’ College, China, for assistance in writing. We also thank Prof. Zhang Boqiao, Dr. Gao Derong, and Zhang Yong, Lu Guofeng, Wu Hongya, Wu Ronglin, Lu Chengbin, Lixiahe Region Agricultural Research Institute of Jiangsu Province, China, and Prof. Tian Jichun, Shandong Agricultural University, China, for their assistancein experimentation.

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