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Ebook Physico-Chemical Changes Of Gluten Matrix As A Result Of Maillard Reaction With Glucose

Submitted by puput on Wed, 09/16/2009 - 04:21

The animal proteins (milk and egg) are now being replaced to plant base proteins by manufacturers of food items due to the consumers' attitude as well as the economic reasons. Gluten and soy protein are extensively being used as basic components for vegetarian food products especially in many Asian countries. Wheat gluten protein is an important raw material in the manufacture of foods for breakfast, infant, snack and pasta products. Gluten, which is a mixture of more than 100 heterogeneous polypeptides, is composed of two main storage proteins, namely, Gliadins and glutenins. Glutenins (with molecular mass of 69 to 88 kDa based on SDS-PAGE) (Anderson et al., 1988) are responsible for elastic behavior, whereas gliadins (with molecular mass of 30 to 50 kDa) (Tatham et al., 1990) are responsible for viscous flow properties of the foods.

The most significant aspect of gluten story for the food industry is the importance and the potential of gluten as a commodity, sold for a wide range of uses around the world. 'Vital Wheat Gluten' protein is now a significant ingredient in the food industry and important item of world trade (Krishnakumar & Gordon, 1995; Boland et al., 2005). Its rheological properties are the basis of the functional uses of vital gluten (Day et al., 2006). It is these properties that permit breads, cakes, biscuits and noodles to be made from wheat-flour doughs. Thus, gluten can be considered to be like a dough in which the diluting effect of starch is no longer present. In the wet state, the protein molecules form a cohesive matrix which, in dough, also holds the starch granules within it. This matrix is also elastic, allowing it to stretch and expand. In aerated doughs, this elasticity permits the expansion of gas bubbles, which produce the texture of bread and cakes (Day et al., 2006).

The nonenzymatic interaction between reducing sugars with amino groups of the lysine residue of proteins, known generally as the Maillard reaction, has proven to be extremely important in food science. Actually it is a group of complex reactions which results in the formation of both large protein aggregates and low molecular weight products that are believed to impart the various flavour, aroma, and colour characteristics of foods (Sun et al., 2004). Over the past few years there has been growing interest in the interaction of reducing sugars and protein to understand structural functionality in compositionally complex food systems (Aoki et al., 1999; Aoki et al., 1997; Morgan et al., 1999). It has been reported that the glycated proteins could improve the functional properties of food, such as thermal stability, emulsifying ability, foaming properties (Kato et al., 1993; Kato et al., 1988; Kato et al., 1995), antioxidative activity (Nakamura et al., 1992; Sun at al., 2004; Benzakul at al., 2005a, 2005b), and gelling properties (Easa et al., 1996b; Matsudomi at al., 2002; Sun at al., 2004; Yamul & Lupano, 2005).

The Maillard reaction may be desirable as in baked, fried or roasted foods or undesirable as in concentrated and dried foods. The Maillard cross-linking in protein can have a profound effect on the structure and function of proteins in food. Nevertheless, the importance of protein cross-linking in food systems is less well studied, but it is clear that such specific modifications of the properties of a protein are, potentially, of great practical importance in the food industry. The protein gels prepared in the presence of reducing sugar are shown to have changed texture, reduced solubility, and enhanced gelation, due to change in pH, charge on the protein and critical protein concentration that are responsible for gel formation.

Thus it is possible to modify the properties of wheat gluten gel through Maillard reaction in such a way that the "Maillard cross-links" are allowed to form within the gel network. The enhanced physicochemical properties of wheat gluten gel coupled with antioxidative properties will be of sufficiently high commercial values.

CONTENTS

TITLE
DEDICATION
ACKNOWLEDGEMENTS
TABLE OF CONTENTS
LIST OF TABLES
LIST OF FIGURES
LIST OF SYMBOLS AND ABBREVIATIONS
LIST OF PLATES
ABSTRAK
ABSTRACT
CHAPTER 1: INTRODUCTION
1.1 Background and significant implication of study
1.2 Hypothesis
1.3 Objectives
CHAPTER 2: LITERATURE REVIEW
2.1 Introduction
2.2 Definition of terms
2.3 Classification of gels
2.4 Gelling systems in this thesis
2.5 Factors affecting the gelation of globular proteins
2.6 Study of the Maillard reaction

    2.6.1 Maillard reaction in wheat gluten

2.7 Chemistry of the Maillard reaction
2.8 Factors influence the Maillard reaction products on food properties 26
2.9 Chemical basis of browning

    2.9.1 Colour measurement
    2.9.2 Nonenzymatic browning produced as a consequence of the Maillard reaction

2.10 Alteration to charge and amino acid contents
2.11 Binding of sugars to protein
2.12 Decrease in pH
2.13 Wheat gluten protein
2.13.1 Classification of wheat gluten protein

    2.13.2 Structural properties of gluten
    2.13.3 The basis of gluten viscoelasticity
    2.13.4 Denaturation
    2.13.5 Protein- protein cross-linking in foods
    2.13.6 The types of cross-linking found in foods
    2.13.7 Cross-linking derived from Maillard reaction
    2.14 The implication of the Maillard reactions in food processing

CHAPTER 3: MATERIALS AND METHODS
3.1 Materials
3.2 Preparation of gels and gel particles
3.3 Methods of assessment

    3.3.1 Solubility of gluten in water
    3.3.2 Measurement of pH
    3.3.3. Measurement of colours

3.3.3.1 Measurement of absorbance or optical density
3.3.4 Syneresis

    3.3.4.1 Water holding capacity (WHC)

3.3.5 Determination of unreacted glucose and sucrose
3.3.6 Determination of unreacted lysine
3.3.7 Solubility estimation

    3.3.7.1 Dispersibility index of gluten
    3.3.7.2 Estimation of protein solubility in disrupting solvents 104

3.3.8 Rheological properties

    3.3.8.1 Preparation of cross-linked wheat gluten protein gels 105
    3.3.8.2 Gel breakstrength
    3.3.8.3 Stress relaxation (SR) experiments

3.3.9 Determination of disulfide (SS) and sulfhydryl (SH) groups 107
3.3.10 Thermo analytical assessment by differential scanning calorimetry (DSC)
3.3.11 Statistical analysis.
CHAPTER 4: RESULTS AND DISCUSSION
4.1 Formation of Maillard gels
4.2 Visual assessment of different gels

    4.2.1 Visual assessment of different gels at different pH
    4.2.2 Visual assessment of different gels at different heating time 117

4.3 Characterizations of glucose-WG reactions at high temperature

    4.3.1 Decrease in pH
    4.3.2 L-values and Optical density of the gels matrices
    4.3.3 Syneresis values and Water holding capacity of the gels matrices
    4.3.4 Estimation of unreacted glucose and sucrose
    4.3.5 Estimation of unreacted lysine

4.4 The occurrence of "Maillard Cross-links" during heating of glucose-WG
4.4.1 Solubility estimation

    4.4.1.1 Solubility of wheat gluten in Water
    4.4.1.2 Gel solubility

4.4.2 Rheological assessment
4.4.3 Sulfhydryl (SH) & disulfide (SS) estimation

    4.4.3.1 Estimation of sulfhydryl groups
    4.4.3.2 Estimation of disulfide content

4.4.4 Thermo analytical assessment by differential scanning calorimetry
CHAPTER 5: CONCLUSION
REFERENCES
APENDICES
APPENDIX A: Standard curve for glucose estimation.
APPENDIX B: Standard curve for sucrose estimation.
APPENDIX C: Standard curve for protein estimation.
APPENDIX D: Thermogram of only wheat gluten dispersion
APPENDIX E: Thermogram of wheat gluten dispersion with sucrose

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