PROTEINS OF FOOD Dr Abdur Rahman Department of
PROTEINS OF FOOD Dr. Abdur Rahman Department of Industrial Biotechnology
CONTENTS v. Recap v. Amino acids v. Types of amino acids v. Structure of proteins v. Role of proteins in different food formulations v. Baking (Breads, Cakes) v. Browning v. Pasta
RECAP • Proteins play important roles in human body • Structural role : Proteins in connective tissues, collagen and elastin • Contractile function / role in movement : Contractile proteins like actin and myosin play important role in movement of body • Regulatory Proteins • Enzymes : play v important role in different body functions from cellular level to system level, enzymes involved in digestion of food to metabolism at cellular level • Immune system : antibodies are proteins produced by immune system to fight infections • Transport proteins : haemoglobins • Hormones : regualtion of different metabolisms like insulin for glucose regulation
RECAP • What are proteins composed of? • The basic structural unit of proteins is amino acids • There are 20 different types of amino acids which contribute to the structure of different proteins
RECAP • Amino acids : acid or base? • German word for hybrid ion : Zwitterions : • A zwitterion is a compound with no overall electrical charge, but which contains separate parts which are positively and negatively charged • The amino acid residues in proteins are L Stereoisomers
PEPTIDE Peptide : Chains of amino acids, linked with a petide bond
N terminal and C terminal Amino terminal end N terminal Carboxy terminal end C terminal
Oligopeptides and Polypeptides Ø Depending on the number of amino acid residues, dipeptide, tripeptide and so on and so forth – Oligopeptide Ø Peptides can be distinguished from their ionization behavior Ø Polypeptides
Levels of Protein Structure Ø Conceptual hierarchy of structure for understanding
Protein Chemistry
Levels of Protein Structure Primary structure Secondary structure Tertiary structure Quaternary structure
Levels of Protein Structure The conceptual hierarchy of protein structure • Primary structure : Basic sequence of amino acids in a polypeptide chain • Secondary structure : refers to the local conformation of some part of a polypeptide • Tertiary structure : The overall three-dimensional arrangement of all atoms in a protein is referred to as the protein’s tertiary structure • Quaternary structure
Role of proteins in foods Role of Proteins in bread? Kneading : Addition of water causes hydration of gliadin and glutenin proteins, leads to the formation of gluten Stress inducced during kneading breaks bonds between protein chains, allowing the chains to move and become realigned. The new bonds that are formed allow relaxation of the dough.
Role in Baking Proofing (Rising) At this stage starch breakdowns and fermentation occurs. CO 2 produced and causes gluten network to expand Leaves open cellular structure with gases trapped in pockets. The effect of gluten quality and content will affect the quality of product, how?
Role in Baking During baking the temperature is high, and the gluten coagulates. As a result the gluten is no more elastic Consequently the bread is firm but open and light in texture
Role in Baking Role of Egg Proteins in Baking? Entrapment of air during beating Form the film which entraps air and increase the volume
Role in fried foods While the elastic quality of egg proteins is lost in cooked eggs, but the firmsing of proteins allows eggs to perform another important function, which is holding ingredients together. Example : Crumb coating holds more tightly when its dipped in egg
Role in Colors and flavors (baking, frying etc) The Maillard reaction is named after the French scientist Louis Camille Maillard (18781936), who studied the reactions of amino acids and carbohydrates in 1912, as part of his Ph. D thesis, which was published in 1913 Maillard reaction is not a single reaction, but a complex series of reactions between amino acids and reducing sugars, usually at increased temperatures. Likecaramelization, it is a form of non-enzymatic browning. In the process, hundreds of different flavour compounds are created. These compounds in turn break down to form yet more new flavour compounds, and so on. Each type of food has a very distinctive set of flavour compounds that are formed during the Maillard reaction.
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