Foodchem Lecture 9

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Foodchem Lecture 9
2012-03-15 23:16:45
Foodchem Lecture

Foodchem Lecture 9
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  1. What is an example of a protein acting as a regulating agent or hormone?
  2. What is an example of a protein acting as a defense mechanism?
    Antigens and antibodies
  3. What is an example of proteins that carry oxygen and carbon dioxide?
    myoglobin and hemoglobin
  4. 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
  5. What are some examples of protein functionality?
    • Water binding
    • Emulsification
    • Gel formation
    • Coagulation
    • Dough formation
    • Structure formation - edible foams (meringue)
  6. 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
  7. Milk proteins and soybean proteins have the ability to form what?
    A curd
  8. What is an endogenous enzyme?
    An enzyme contained within the source (can cause autolytic degradation)
  9. What is an exogenous enzyme?
    Introduced into the system by an outside source, such as a microorganism that will contaminate the system
  10. What is an important use of proteases for food science?
    To tenderize meat
  11. What is an important use of lipases for food science?
    To speed up flavor development
  12. What is an important use of amylases for food science?
    To manufacture corn syrup/sugar
  13. What is an important use of glucose oxidase for food science?
    To remove headspace oxygen from food packages
  14. What are the protein breakdown products?
    Amino acids and peptides
  15. What can protein hydrolysates be used for?
    To make meaty, brothy flavors
  16. How are meat analogs made?
    Can be made from soy protein using extrusion technology
  17. What is surimi?
    Proteins extracted from fish tissue to formulate analogs (avatars) of crab meat and scallop
  18. Proteins are generally considered to be made up of how many basic amino acids?
  19. What is the secret to the success of living systems?
    Their ability to ''build'' an almost infinite variety of protein structures
  20. 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
  21. 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
  22. 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
  23. 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
  24. 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
  25. What are amino acids like at low pH?
    • Amino acid is predominantly protonated
    • Predominantly positively charged (COOH/NH3+)
  26. 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)
  27. 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
  28. 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
  29. 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
  30. 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
  31. Why are amino acids said to be amphoteric?
    They have both basic and acidic functional groups within the same molecule
  32. 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
  33. What are two amino acids which fall into the aliphatic amino acid category?
    • Glycine (R group = H)
    • Alanine (R group = CH3)
  34. What is the simplest amino acid?
  35. 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
  36. 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
  37. How can you determine the configuration of a compound?
    You can compare it to a reference compound (glyceraldehyde) in terms of its symmetry
  38. What is the compound that we use to compare compounds to in order to decide if they are D or L?
  39. 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
  40. 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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