Effect of Heat and Oxygen on Proteins

Introduction

Proteins are essential components of many foods, and their behaviour during cooking, exposure to heat, and interaction with oxygen can significantly impact food quality and texture.

Solubility of Proteins

• Fibrous proteins are generally insoluble in water, while globular proteins tend to be soluble. These characteristics affect how proteins interact with other food components.

Hydrolysis Reactions

• When proteins in food are heated in the presence of water, hydrolysis reactions can occur, leading to the cleavage of amide or peptide links within proteins.
• Hydrolysis of proteins results in the formation of individual amino acids.

Catalysts for Hydrolysis

• Some foods may contain acids or alkalis that act as catalysts for hydrolysis reactions, facilitating the breakdown of proteins.

Denaturation of Proteins

• Proteins are complex molecules made up of long chains of amino acids, often with branching.
• These chains are held together by intermolecular bonding, including hydrogen bonds between amide links and other groups in the molecule.
• The presence of hydrogen bonds gives proteins their three-dimensional structures, which can include sheets, spirals, or coils.
• Heating proteins during cooking can disrupt these intermolecular bonds, leading to denaturation, or a change in the protein's shape.
• The changes in protein shape can alter the texture and properties of foods during cooking.

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Effect of Heat and Oxygen on Proteins

Example: Denaturation of Egg White

• Egg white contains a globular protein called albumen.
• When an egg is boiled or fried, the protein structure in the albumen is irreversibly changed, resulting in the formation of a solid.
• During cooking, the protein in egg white is denatured, causing the protein chains to unfold.
• The unfolded protein chains can form intermolecular bonds with neighbouring albumen molecules, creating a network of interconnected proteins.
• This network solidifies the egg white, altering its texture.

Conclusion

• The effect of cooking, heat, and oxygen on proteins can lead to various changes, including hydrolysis reactions, denaturation, and alterations in food texture. Understanding these processes is essential for achieving desired cooking results and maintaining food quality.