Protein Flashcards
Protein in cheese
Caseinogen
Protein in milk
Lactalbumin, caseinogen
Protein in eggs
Ovalbumin, livetin, vitellin, albumin
Protein in fish
Myosin, collagen, actin
Protein in meat fibres
Myosin, actin, globulin
Protein in meat connective tissue
Collagen, elastin
Protein in wheat
Gluten
Protein in soya beans
Glycinin
Protein in rice
Oryzenin
Protein in corn/maize
Zein
Structural function of protein
Growth and repair of body cells. Deficiency can result in retarded growth and delayed healing
Physiological function of protein
Making hormones, enzymes, antibodies, blood proteins and nucleoprotein. Deficiency can result in malfunction of body organs and prone to infection
Nutritive function of protein
Provides essential amino acids to the body. Excess is used for heat and energy. Deficiency can result in kwashiorkor, marasmus and a lack of energy
Two classifications of protein
Simple, conjugated
Conjugated protein
A protein molecule and non-protein molecule joined together
Two examples of conjugated proteins
Lipoproteins eg lecithin (egg), phosphoproteins eg caseinogen (milk)
Two subgroups of simple animal proteins
Fibrous, globular
Two subgroups of simple plant proteins
Glutenins, prolamines
Example of simple fibrous and globular animal proteins
Fibrous - elastin (meat connective tissue)
Globular - ovalbumin (egg whites)
Example of simple glutenin and prolamine plant proteins
Glutenins - glutenin (wheat)
Prolamines - zein (maize)
6 properties of protein
Denaturation, solubility, Maillard reaction, elasticity, foam formation, gel formation
denaturation
Change in the nature of the protein. Protein chain unfolds causing a permanent change to the structure. Caused by heat, chemicals, agitation
Heat denaturation
Most proteins coagulate when heated eg egg white at 60°, egg yolk at 68°
Chemical denaturation
Acids, alkali, alcohol and enzymes cause protein structure to change. Eg lemon juice in milk causes milk protein caseinogen to curdle
Agitation denaturation
Involves whipping or whisking the protein. Causes protein chains to unfold and partial coagulation
Solubility (property of protein)
Proteins are generally insoluble in water. Two exceptions are - egg white in cold water, connective tissue (converts to gelatine) in hot water
Maillard reaction (property of protein)
Also known as non-enzymic browning. Occurs when food is roasted, baked or grilled.
Amino acid + carbohydrates + dry heat = brown colour
Elasticity (property of protein)
Certain proteins have an elastic property eg gluten in flour enabling bread to rise during cooking
Foam formation (property of protein)
Eggs whites are whisked causing air bubbles to form as protein chains unravel, whisking produces heat which slightly sets egg whites (this foam will collapse after a while unless subjected to heat).
Baking causes permanent coagulation of the protein, trapping air bubbles
Gel formation (property of protein)
Collagen, when heated, forms gelatine. Gelatin can absorb large amounts of water. On cooling this becomes solid and a gel is formed.
A gel is a semi-solid viscous solution. All gels have a 3 dimensional network whereby water becomes trapped
Effects of heat on protein
Coagulation, colour change (myoglobin in meat changed red to brown), Maillards reaction (dry heat), tenderizing (moist heat)(collagen in meat changes to gelatine and fibres fall apart), becomes digestible
Protein deamination
Left over amino acids are brought to the liver. The NH2 group is broken off, changed to ammonia, then to urea, and then excreted. The rest of the molecule is converted to glucose and used for releasing energy
RDA of protein
1g per kg of body weight
Energy value of protein
1g of protein gives 4kcal of 17kj
What happens to proteins in the stomach
Proteins are churned.
Gastric juice contains enzymes rennin and pepsin
Rennin changed caseinogen to casein
Pepsin changes proteins to peptones
What happens to proteins in the pancreas
Pancreatic juice contains enzyme trypsin
Trypsin changes protones to peptides
What happens to proteins in small intestine
Intestinal juice contains enzyme peptidase
Peptidase changes peptides to amino acids
