| In this study, the influence of protein content, starch content and protein fractions on dough rheological properties were investigated using a reconstitution method. Experiments involved doughs prepared from flours derived from three weak and two strong cultivars. In addition, the changes of dough rheological properties, GMP composition, GMP particle, free SH content, and the relationships of composition and functionality during mixing and processing were researched utilizing SDS-PAGE, Texture Analyser, and protein fluorescence labeling. The results provide theoretical basis for protein functionality in dough and bread-making and for protein quality improvement in wheat breeding. The main results were as follows:1. Effect of protein and starch contents on wheat dough rheological propertiesPeak height and peak width of two kinds of dough were significantly increased (P < 0.05) compared with those of control when protein content was increased from 100% to 120%, 140% and 160%, the maximum resistances were increased from 40.7g to 49.8 g, 59.0 g and 71.6 g in Shannong 12 and from 20.6 g to 29.5 g, 32.1 g and 36.0 g in Shannong 11, respectively. However, the extensibility at maximum of these two doughs changed not obviously compared with those of control. Peak height and peak work input of two kinds of dough were significantly decreased (P < 0.05) with the increase of starch content. When the starch contents were increased from 81.11% (Shannong 12) and 83.85% (Shannong 11) to 85%, 90% and 95%, the extensibility at maximum was decreased from 110.8 mm to 68.8 mm, 59.2 mm and 36.5 mm in Shannong 12 and from 81.6 mm to 75.8 mm, 59.1 mm and 50.3 mm in Shannong 11, respectively. However, the maximum resistances of these two doughs changed not too obviously compared with those of control.2. Effect of protein fractions on wheat dough rheological propertiesAll protein fractions were added to each of the base flours at three levels (0.25%, 0.50% and 1.00% w/w) based upon protein content. Mixograph dough development time, peak width, work input to peak, resistance to extension and area under the curve were increased, but extensibility at maximum and extensibility at rupture were decreased when glutenin, insoluble glutenin, soluble glutenin or glutenin macropolymer were added to each of the base flours. However resistance to extension were decreased, but extensibility at maximum and extensibility at rupture were increased when monomeric protein, albumin-globulin, and gliadin were added to each of the base flours. These tendencies increased as addition levels were increased.3. Effect of mixing on wheat dough rheological properties and steamed bread qualityThe resistances to extension of Shannong 11 and Shannong 12 doughs were increased before peak mixing time. The resistances to extension of two kinds of dough were maximum at peak mixing time. The resistances to extension of two kinds of dough were decreased after extensive mixing, but not significant.The extensibilities at maximum of Shannong 11 and Shannong 12 doughs were maximum when mixing time was dough development time. The extensibilities at maximum of two kinds of dough were increased when mixing time was increased and decreased after extensive mixing.The area under the curve of Shannong 11 was maximum at peak mixing time and decreased after extensive mixing. However, the area under the curve of Shannong 12 was maximum when mixing time was 1 min and decreased after peak mixing time.The extensibility at rupture of Shannong 11 and Shannong 12 was maximum when mixing time was dough development time then decreased after extensive mixing.The firmnesses of Shannong 11 and Shannong 12 steamed breads were increased when mixing time was increased. The firmnesses of the two cultivar steamed breads were maximum at dough development time and decreased after extensive mixing. As to Shannong 11, mixing time showed significant positive correlations with smoothness, colour, toughness and stickiness and showed negative correlation with b* and positive correlation with cohesiveness. As to Shannong 12, mixing time showed significant negative correlations with specific volume and springiness.4. Changes of glutenin macropolymer composition and particle during mixingThe HMW-GS and B LMW-GS content in glutenin macropolymer of Shannong 11 and Shannong 12 were decreased and C LMW-GS content was increased when mixing time was increased. The bigger particles of Shannong 11 and Shannong 12 were decreased and smaller particles were increased when mixing time was increased.5. Changes of free SH contents during noodle and steamed bread makingThe free SH content of Shannong 12 and Yangmai 13 changed not significant in proofing stage during noodle making process. However, the free SH content of the two cultivar doughs decreased significantly in boiling stage. In addition, the free SH content of the two cultivar noodles increased in desiccation stage compared to boiling stage.The free SH contents of Shannong 12 and Yangmai 13 changed not significant in proofing stage during steamed bread making process. However, the free SH contents of the two cultivar steamed breads decreased in steaming stage and the base section of steamed bread showed the maximum decrease in SH content as compared to the crust and the center. In addition, the SH contents of the three sections of the steamed breads reach minimum as bread had been steamed for 10 min. The free SH contents of the two cultivar steamed breads increased when steaming time increased, but not reached original contents.6. Changes of glutenin macropolymer composition during noodle and steamed bread makingThe contents of four protein fractions in glutenin macropolymer of Shannong 12 changed not significant in proofing stage during noodle making process. However, the contents of the four kinds of proteins increased in boiling stage. The contents of the four kinds of proteins decreased significantly in desiccation stage.As to Yangmai 13, the contents of four protein fractions in glutenin macropolymer changed not significant in proofing stage during noodle making process. However, the contents of HMW-GS, LMW-GS, and B LMW-GS increased firstly and then decreased in boiling stage, but the contents of C LMW-GS increased in this stage. The contents of the four kinds of proteins decreased significantly in desiccation stage.As to Shannong 12 and Yangmai 13, the content of HMW-GS in glutenin macropolymer decreased, but the contents of LMW-GS, B LMW-GS, and C LMW-GS in GMP increased in proofing stage. The contents of all protein fractions reached maximum at 10 min in steaming stage. Also, the contents of these fractions decreased when steamed time increased. The base sections of steamed bread were maximums in the contents of all protein fractions as compared to the crust and the center sections. |
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