Food chem 12

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Morgan.liberatore
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142274
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Food chem 12
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2012-03-18 17:03:50
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Food chem 12
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Food chem 12
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  1. What is needed to produce putrefaction?
    Need presence of free amino acids- produced by proteolytic enzymes from spoilage organisms
  2. What attacks free AAs to produce putrefaction?
    Free AA produced are attacked by microbial deaminases and decarboxylases
  3. What do the microbial deaminases and decarboxylases do to the free AAs?
    These are capapble of removing amino groups and carboxl groups from free amino acids
  4. In what scenarios are decarbozylases more active and deaminases more active?
    At lower ps the decarboxylase is the most active, while at higher pHs the deaminase is the most active
  5. What results from putrefaction?
    Both reactions result in a loss of a hydrophilic group, hence reducing solubility in water and its overall molecular weight, while increasing the volatility
  6. What produces a fishy smell?
    Due to the conversion of naturally present trimethylamine oxide (TMAO) to trimethylamine (TMA)
  7. What converts TMAO to TMA?
    Trimethyl amine oxidase
  8. Why do we measure the levels of TMA in fish?
    By measuring the development of TMA in fish tissue we have an indication of its freshness and potentially its shelf-life
  9. What is hydroscopic?
    The ability to hold water
  10. Why is water holding capacity iportant?
    For example, milk proteins play an important role in absorbing moisture and retaining it in bread, giving it a soft, stretchy texture
  11. How does one make a burger juicier?
    The addition of soy protein to hamburger helps retain moisture making the burger 'juicier'
  12. What is the water binding capacity associated with?
    The water binding capacity is strongly associated with the ionic species present (NH3+ and COO-) and hydrogen bonding sites present in a protein that arer readily hydrated
  13. What does water form around polar groups?
    A hydration shell
  14. What does a moisture sorption isotherm do?
    A moisture sorption isotherm illustrates the equilibrium moisture associated with a material as a function of relative humidity at a constant temperature
  15. What are the three stages of a moisture sorption isotherm?
    Bound water, looser form, free water
  16. What is the 'bound water' stage of a moisture sorption isotherm?
    Bound water, which in essence cannot be removed- eg. hydroen bonded to theprotein or a hydrate of an ionic species- redally an integral part of the molecular structure (protein water monolayer)
  17. What is the 'looser form' of the moisture sorption isotherm?
    Water associated with the bound water, but in a looser form- more mobile and is still somewhat structured
  18. What is the 'free water' section of the moisture sorption isotherm?
    Free water- unstructured, wuite mobile and can be removed relatively easily- region where proteins show their water absorption capacity
  19. What determines a proteins ability to bind water?
    A proteins ability to bind water is a function of its amino acid composition, overall structure (including prosthetic groups) and charge
  20. How is non enzymatic browning produced in proteinaceous systems?
    Foods which contain appreciable amounts of protein generally undergo browning when they are heated under low moisture conditions
  21. What is non enzymatic browning?
    Involves the reaction of an aldehyde group of a reducing sugar and a free amino group of an amino acid or the free amino group on a peptide or protein, such as that from lysine or the amide group of asparagine
  22. How is non enzymatic browning produced in amino acids with a secondary nitrogen group?
    Other amino acids with a secondary nitrogen group (Arginine, tryptophan, hstidine, and gloutamine and asparagine) also can undergo reactions with reducing sugars at high temperatures (usually when moisture is limited)
  23. What is amadori rearrangement?
    AQfter this initial reation to form the glycosyl amino, the sugar portion undergoes a complex series of reactions termed amadori rearrangement. Involves the loss of water from within the ugar portion of the molecule
  24. What are melanoidins?
    the sugar portion undergoes scission and breaks up into low molecular weight compounds (flavor/aroma) which readily polymerize into brown pigments (color) termed melanoidins
  25. What is the end result of a maillard reaction?
    The net result is that lysine will be 'bound' thus the amino group is not available nutritionally because a sugar or a fragment thereof is attached to it
  26. How is an indigestible tripeptide formed?
    Enzymatic action will stop one AA on eiter side of the bound lysine, leaving an indigestible tripeptide, which is poorly absorbed and used by the body
  27. What is a cross linking reaction?
    If reducing sugars are mainly absent, the cross linking of proteins can occur at higher temperatures by the formation of amide bonds with free COOH and NH2 groups
  28. What is the end result of the amide bond?
    The amide bond cannot be hydrolyzed by digestive proteolytic enzymes and if such a bond is formed intra or inter-protein it will leave a hexa-peptide which cnanot be utilized
  29. What produces a typical 'cooked' flavor (milk, meat)?
    Cystine is one of the more heat sensitie amino acids and will readily hydrolyze and break down- this reaction can be significant if the limiting amino acid of the protein is cystine
  30. How are new amino acids formed?
    The preparation of protein concentrates and isolates often calls or the treament of proteins with alkali to solubilize them in the presence of heat to modify their properties- under such ahrsh conditions, 'new' amino acids can be forme if free amino acids are present or produced by base hydrolysis
  31. How is lysinoalanine produced?
    Lysinoalanine is produced from the reaction of alanine and cystine
  32. What are the properties of lysinoalanine?
    the unnatural amino acids lyrinoalanine is poorly absorbed and may be toxic, having been shown to cause renal failure in rates
  33. What is another consequence of the strong alkaline conditions?
    Another consequence of strong alkaline conditions is the recemization of free amino acids from L- to D-L mixtures
  34. What are some common protein sources?
    Milk, meat, eggs, fish, cereals and seed proteins such as the soubean
  35. How much protein does milk contain?
    Fluid milk contains ~12% solids, of which ~3.5% is protein
  36. What is milk protein a good source of?
    Lysine
  37. What are the two categories of milk proteins?
    Caseins and whey
  38. What are the two forms of casein protein?
    Isoelectric casein (also known as acid casein) and paracasein
  39. How is isoelectric casein isolated?
    Isolated by adjusting the pH of milk to 4.5, its isoelectric point, using acid
  40. What happens to acidic milk?
    At the isoelectric point they are at minimum solubility, precipitate and associate to form a curd
  41. What is left once caseins are curded out?
    Proteins left behind in the solution are termed the whey proteins
  42. What types of proteins are caseins predominantly?
    Caseins are predominantly phosphoproteins, with phosphate being attached to the amino acid serine
  43. How are caseins separated?
    Can separate caseins electrophoretically (on the basis of charge) into three major fractions, alpha, beta and gamma casein
  44. What is the predominant fraction of caseins?
    Alpha fraction
  45. What are the subdivisions of alpha casein?
    Alpha S1 and kappa casein
  46. How are alpha S1 and kappa casein differentiated?
    Differentiated from each other by their sensitivity to the presence of Ca++ ions
  47. What do milk micelles look like>
    Milk micelles are colloidal spherical protein particles, 80-300 nanometers in diameter made up of alpha S1 and kappa casein held ogether by Ca++ and inorganic posphate
  48. What are micelles responsible for?
    Micelles are responeible for the opaque whiteness of milk, an optical effect produced due to light scattering
  49. What is the core coate model for micelle formation?
    Core coat model for micelle formation envisages the calcium sensitie alpha S1 casein to be surrounded by kappa casein
  50. How is paracasein obtained?
    Obtained by the action of rennin
  51. What is rennin?
    A proteolytic enzyme obtained from the fourth stomach of the calf
  52. What does rennin do?
    • Rennin attacks kappa casein at a specific site, cleaving off a hydrophilic glycomacropeptide
    • The micelles are destabilized and the hydrophobic proteins associated to form a curd
  53. How are acid casein and paracasein similar?
    They are not temperature sensitive- can boil them without denaturing them
  54. How is casein used as a functional ingredient?
    Casein is used extensively used as a functional ingredient in food systems to increase the protein content of food products
  55. What are the major proteins present in whey?
    Beta lactoglobulin and alpha lactalbumin
  56. What is beta lactoglobulin?
    It is a heat labile protein and contains 2 disulfide bonds (cystine) and one cysteine, which provides the protein with a reactive free SH group
  57. Does Beta-lactoglobulin denature?
    Beta-lactoglobulin is a globular protein which denatures readily, exposing the SH which is reactive
  58. How is the skin on boiled milk formed?
    When beta-lactoglobulin boils it denatures and polymerizes to form a 'skin' on the surface of milk
  59. What is NFDMS?
    Non fat dried milk solids, used extensively in bread for added nutrition and as a water binding agent (retain moisture)
  60. What happens when whey proteins are denatured?
    Their SH groups are exposed and are capable of interacting with the SH and S-S bonds in gluten, to strengthen the dough matrix y sulfhydryl interchange
  61. What happens if NFDMS are used in bread baking?
    They have to be given a harsher heat tretment to ensure they are denatured to activate SH reactivity

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