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Protein summary food chemistry (FCH20806)
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Complete summary of the information needed to understand proteins during this course.
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Introduction to proteinsSources of proteins
1. Animal proteins
- Milk proteins
- Egg (white) proteins
- Animal by-products (blood/gelatin)
2. Plant proteins (legumins)
- Soy proteins
- lupine proteins
- sunflower proteins
3. Novel (plant) proteins
- Potato proteins
- Algae proteins
- “leafy” proteins, from leaf materials of plants
Function of proteins in nature
- Provide nutrition
o Source of nitrogen (N) and essential amino acids for the young plant or growing
animal
- Provide structure
o Muscle tissue/collagen provides structure in animals
- Metabolism
o Homeostasis, enzymes and antibodies
- Peptides: dipeptides in meat products and glutathione in flour
o Glutathione helps to form the structure of bread for example and incorporates
air into the products
- Free amino acids & small peptides also found in plant materials because they have a
hormone function
Functions of proteins in food products
- Provide consumers with essential nutrients
- Give texture to food products (gluten in bread)
- Used to provide taste (Maillard reaction)
Formed during production
- Amino acids and peptides formed during fermentation processed (example: cheese)
Added as ingredients to food products
- Proteins: whey proteins in ice-cream provide better structure
- Peptides: hydrolysates in sport nutrition due to improved digestibility
- Amino acids: non-allergenic infant formula to reduce allergenic potential of the food
- All proteins are built up of amino acids
, - Amino acids are characterized as having a central carbon bound to an amino group,
carboxylic acid group, Hydrogen atom and a side chain
- Difference between amino acids comes from the properties of the different side
residues/chain (R.)
- Free amino acids can react with each other by linking the carboxylic group of one amino
acid to the amino group of another, losing a water molecule in the process
- Linking of amino acids forms peptides
- Oligopeptides: 2-100 amino acids bound together
- Proteins: 100-300 amino acids (polypeptide)
- Properties and function of the protein depend on;
o the amino acid residues in the amino acid chain
o The final structure/orientation of the polypeptide
Q: How is the function of meat (muscle) proteins in the body related to the solubility of these
proteins?
A: The function of the muscle tissue is to provide structure in the body, therefore these proteins are
NOT soluble
Q: How is the function of milk proteins related to the solubility of these proteins
A: The functions of milk proteins is to give nutrition to the calf and therefore these proteins should
be soluble
Amino acids
- Building blocks of proteins
Structure
- Central carbon is a α-carbon atom and because 4 different molecules are bound to it the
central carbon is chiral
- In nature >200 types of amino acids are present
- In proteins only ±20 amino acids occur (α-L-amino acids)
Stereoisomers of amino acids
in nature (and in proteins)(α-)L amino acids
after processing (α-)D amino acids (non-digestible)
, Difference between alpha and beta amino groups?
α: amino group is attached to the α-carbon atom
β: amino group is attached to the β-carbon atom (Carbon next to the anomeric α-carbon)
Different amino acid side chains
Examples
Aromatic and aliphatic amino acids do not have any
polar groups and therefore do not dissolve very well
in water
- Based on the side chains of amino acids they can be classified into 3 groups;
o Non-polar, non-charged
o Polar, non-charged
o Polar, charged
Amino acid classification
1. Essential: amino acids that are NOT produced by the body and need to be consumed in our
diet
2. Conditionally essential: amino acids that are essential for a certain part of the population for
a certain part of their life and should be included in their diets at a higher dosage
3. Non-essential amino acids which ARE produced by the body and don’t need to be included in
our diet
Example: lysine is an important amino acid in the Maillard reaction which means that once it has
reacted it is no longer available for the body and is therefore an essential amino acid
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