Foodchem Lecture 9
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What is an example of a protein acting as a regulating agent or hormone?
What is an example of a protein acting as a defense mechanism?
Antigens and antibodies
What is an example of proteins that carry oxygen and carbon dioxide?
myoglobin and hemoglobin
What does the idea of protein functionality refer to for a food scientist?
Use of physico-chemical properties of the molecule to produce a specific state of affairs or function in a food system
What are some examples of protein functionality?
- Water binding
- Gel formation
- Dough formation
- Structure formation - edible foams (meringue)
Which protein has the ability to hydrate and leaven flour in the form of dough?
Gluten - a protein with peculiar elastic properties not associated with other grain flours
Milk proteins and soybean proteins have the ability to form what?
What is an endogenous enzyme?
An enzyme contained within the source (can cause autolytic degradation)
What is an exogenous enzyme?
Introduced into the system by an outside source, such as a microorganism that will contaminate the system
What is an important use of proteases for food science?
To tenderize meat
What is an important use of lipases for food science?
To speed up flavor development
What is an important use of amylases for food science?
To manufacture corn syrup/sugar
What is an important use of glucose oxidase for food science?
To remove headspace oxygen from food packages
What are the protein breakdown products?
Amino acids and peptides
What can protein hydrolysates be used for?
To make meaty, brothy flavors
How are meat analogs made?
Can be made from soy protein using extrusion technology
What is surimi?
Proteins extracted from fish tissue to formulate analogs (avatars) of crab meat and scallop
Proteins are generally considered to be made up of how many basic amino acids?
What is the secret to the success of living systems?
Their ability to ''build'' an almost infinite variety of protein structures
What constitutes an amino acid?
To be considered an amino acid both the NH2 and COOH functional groups have to be attached to the same carbon, termed the alpha carbon
What is unusual about amino acid behavior as a function of pH?
- If one places an amino acid in a strongly acidic environment (pH<1) and titrates with a strong base the amino acid can give up 2 H+ as the pH rises toward 14
- First one from the carboxylic acid group and then one from the amino group
What is the formula for calculating the pKA1 for an amino acid?
- pKA1 occurs in COOH group
- pKA1 = -log([H+][AA+] / [AA+ or -]
- 50% positive and 50% neutral form
What is the formula for calculating the pKA2 for an amino acid?
- pKA2 occurs in the NH2 group
- pKA2 = -log([H+][AA+ or -] / [AA-])
- 50% neutral and 50% negative
What is the formula for calculating the pK1 for an amino acid?
- pK1 is the isoelectric point
- pK1 = overall charge = 0
- pK1 = (pK1 + pK2) / 2
What are amino acids like at low pH?
- Amino acid is predominantly protonated
- Predominantly positively charged (COOH/NH3+)
What happens to the amino acids as pH rises (with more OH-)?
Hydrogens are stripped away by the addition of base to become negatively charged (COO-/NH2)
In what form does the amino acid exist at the isoelectric point?
It does not have the expected standard neutral structure (form A), but exists as form B, the Zwitterion
What is the Zwitterion like?
- Individual amino acids exist as Zwitterions as they transition from an overall positive charge at low pH to negative charge at high pH
- Never exist as uncharged neutral species
- It is neutral overall in terms of charge, but the molecule is in effect ionic in nature
What does the ionic nature of the amino acid make it like?
All amino acids have more the attributes of a salt which gives ionic character to the organic molecule
What unusual physical properties to the amino acids have due to their ionic character?
- A crystalline structure
- Are soluble in water
- Are very stable
- Only decompose at relatively high temperatures
Why are amino acids said to be amphoteric?
They have both basic and acidic functional groups within the same molecule
What are the different classifications of amino acids?
- Those with aliphatic side chains
- Hydroxylic side chains
- Carboxylic side chains
- Basic side chains
- Aromatic side chains
- Sulfur containing amino acids
- Imino acids
What are two amino acids which fall into the aliphatic amino acid category?
- Glycine (R group = H)
- Alanine (R group = CH3)
What is the simplest amino acid?
Do amino acids typically have optical isomers? Why?
- Yes, all except glycine
- Because all the other amino acids have one or more asymmetric carbons with 4 different substituent groups
What does it mean that amino acids have optical isomers?
Can rotate plane polarized light
- Chiral structures are mirror images and are non superimposable, like your hands
- This is because they are 3D structures not just 2D crosses
How can you determine the configuration of a compound?
You can compare it to a reference compound (glyceraldehyde) in terms of its symmetry
What is the compound that we use to compare compounds to in order to decide if they are D or L?
Based on the reference compound, how do we know if the compound is in dextro or levo form?
- If the OH group is on the right of the n-1 carbon, then it is dextro
- If the OH group is on the left of the n-1 carbon, then it's levo
What does synthetic production of amino acids generally lead to?
Racemic mixtures of D and L isomers, of which only half can contribute to protein synthesis
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