Prolamin storage proteins of wheat and non-wheat cereals

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At 22oC and 45oC, maize and sorghum sourdough showed similar patterns in pH and

titratable acidity throughout the period of incubation (Fig. 4.1.4). At 22oC, there was an initial decrease in the pH and an increase in titratable acidity of both sourdoughs from day 1 to 5, after which an increase occurred in pH and a decrease in titratable acidity on day 6 due to backslopping. There was a slight decrease in pH and increase in titratable acidity on day 7, after which the pH started increasing gradually and titratable acidity started decreasing gradually until day 11. However, maize dough had a slightly lower pH and lower titratable acidity throughout the period of incubation.
At 45oC, the pH of both sourdoughs also initially decreased while the titratable acidity initial increased. A gradual increase in pH and decrease in titratable acidity was observed for both sourdoughs from day 2 to 5 after which an increase in pH and a sharp decrease in acidity was observed on day 6 due to backslopping. From day 7 to 11, the pH of sorghum started decreasing slightly with some fluctuations while that of maize was steady. For the titratable acidity, there was a slight increase from day 7 to 8 for both sourdoughs after which a sharp increase was observed for sorghum sourdough followed by a slight decrease on day 11.
For maize sourdough, a slight decrease was observed from day 8 to 9 after which the acidity was steady until day 11. Both sourdoughs had higher titratable acidity at 22oC than at 45oC. is believed to improve the acidification ability of the sourdough. Analyses were not done on the breads made from the traditional sourdough method. This was because steamed breads made using this method were all very soft and looked like a lump of gelatinized starch (Fig. 4.1.5). Also, baked breads using this same method had cracks and crumbled when sliced. However, bread made with the combination of sourdough and pregelatinization showed very slight expansion sideways. Using the FAO method, steamed maize breads generally had a higher loaf volume compared to the baked maize breads (Table 4.1.1, Fig. 4.1.6).
Baked or steamed maize bread made without pre-gelatinization or sourdough addition had higher loaf volume compared to the breads with sourdough or pregelatinization. Loaf volume of baked or steamed maize bread made by addition of maize sourdough and pre-gelatinization of part of the maize flour was not significantly different from the loaf volume of baked or steamed maize bread made by pre-gelatinization of part of the maize meal. Concerning the modern sourdough method, bread with sourdough had a significantly (p≤0.05) higher loaf volume (21% increase) and open crumb structure compared to the bread with no sourdough added (Table 4.1.2, Fig. 4.1.7). Comparing each wheat-free method with its control, it was only the modern sourdough method that produced bread that had a significantly better quality than its control.

Table of Contents :

• 1. INTRODUCTION
• 2. LITERATURE REVIEW
  • 2.1 Cereals
  • 2.2 Bread making
    • 2.2.1 Principles of bread making
  • 2.3 Prolamin storage proteins of wheat and non-wheat cereals
    • 2.3.1 Gluten structure and functionality
    • 2.3.2 Zein and kafirin composition and structure
    • 2.3.3 Scientific improvements of non-wheat cereal protein functionality breadmaking
  • 2.4 Sourdough Fermentation
    • 2.4.1 Types of sourdough fermentation
    • 2.4.2 Sourdough microorganisms
    • 2.4.3 Sourdough fermentation and wheat bread quality
    • 2.4.4 Sourdough and non-wheat bread quality
  • 2.5 Coeliac Disease (CD)
  • 2.7 Conclusions
• 3. HYPOTHESES AND OBJECTIVES
  • 3.1 Hypotheses
  • 3.2 Objectives
• 4. RESEARCH CHAPTER
  • 4.1 Research Chapter 1: Effect of different non-wheat bread making methods on the quality of maize bread
    • 4.1.1 Abstract
    • 4.1.2 Introduction
    • 4.1.3 Experimental
      • 4.1.3.1 Materials
      • 4.1.3.2 Methods
      • Production of sourdoughs for maize bread
      • Production of maize breads
      • Analyses
      • Statistical analyses
    • 4.1.4 Results and discussion
      • 4.1.4.1 Production of maize or sorghum sourdough
      • 4.1.4.2 Maize bread quality
    • 4.1.5 Conclusions
    • 4.1.6 References
  • 4.2 Research Chapter 2: Investigation into how sourdough fermentation improves maize bread quality
    • 4.2.1 Abstract
    • 4.2.2 Introduction
    • 4.2.3 Experimental
      • 4.2.3.1 Materials
      • 4.2.3.2 Methods
      • Selection of culture for the sourdough
      • Preparation of the sourdoughs and chemically acidified dough
      • Maize bread making
      • Maize bread quality
      • Stress relaxation of the maize dough treatments
      • Maize dough rheology under simulated baking conditions
      • Damaged starch in the maize dough
      • Thermal properties of the maize doughs
      • Structural properties of the maize dough and maize bread
      • Statistical analyses
    • 4.2.4 Results and discussion
      • 4.2.4.1 Selection of starter culture for the sourdough
      • 4.2.4.2 Maize bread quality
• Dough structural properties
• Stress relaxation of the maize dough treatments
• Dough rheology under simulated baking conditions
• Damaged starch in the maize dough
• Dough thermal properties
  • 4.2.5 Conclusions
  • 4.2.6 References
• 4.3 Research Chapter 3: Identification and characterisation of lactic acid bacteria in maize sourdoughs
  • 4.3.1 Abstract
  • 4.3.2 Introduction
  • 4.3.3 Experimental
    • 4.3.3.1 Materials
    • 4.3.3.2 Methods
• Preparation of the sourdoughs
• Selection and purification of isolates in the maize sourdoughs
• Morphological properties of the isolates
• Biochemical analyses
• Catalase test
• Gram’s test
• Amylolytic activity of isolates
• Proteolytic activity of isolates
• Identification of the isolates
  • 4.3.4 Results and discussion
• Morphology of the colonies
• Biochemical tests
• Catalase test
• Gram’s test
• Amylolytic activity of isolates
• Proteolytic activity of the isolates
• Identification of isolates from the sourdoughs
  • 4.3.5 Probable relationship of the proteolytic and amylolytic activities of LAB to starch modification
  • 4.3.6 Conclusions
  • 4.3.7 References
• 5. GENERAL DISCUSSION
  • 5.1 Methodology: critical review
  • 5.2 The role of sourdough fermentation in improving maize bread loaf volume and crumb structure
  • 5.3 Future research and development of maize bread
• 6. CONCLUSIONS
• 7. REFERENCES
• 8. PRESENTATIONS AND PUBLICATION MADE BASED ON THIS RESEARCH

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