Foodchem Lecture 12 Pics

The flashcards below were created by user Morgan.liberatore on FreezingBlue Flashcards.

  1. Image Upload
    • Decarboxylation
    • Decarboxylase is the most active at lower pH's
    • Results in loss of a hydrophilic group, hence reducing solubility in water and overall molecular weight, while increasing volatility
  2. Image Upload
    • Deamination
    • Deaminase is most active at higher pH's
    • Results in loss of a hydrophilic group, hence reducing solubility in water and overall molecular weight, while increasing volatility
  3. Image Upload
    • Fish tissue contains TMAO which has no smell but which is readily converted to volatile TMA by the enzyme trimethyl amine oxidase
    • TMA is largely responsible for the "fishy" smell associated with fish - fresh fish does not smell at all
  4. Image Upload
    • Hydrated protein
    • Water binding capacity (WBC) is strongly associated with the ionic species present (NH3+ and COO-) and hydrogen bonding sites (C=O, N-H) present in a protein that are readily hydrated
  5. Image Upload
    • Hydrated protein - in detail
    • Water binding capacity (WBC) is strongly associated with the ionic species present (NH3+ and COO-) and hydrogen bonding sites (C=O, N-H) present in a protein that are readily hydrated
  6. Image Upload
    • A moisture sorption isotherm illustrates the equilibrium moisture associated with a material as a fucntion of relative humidity at a constant temperature
    • Three stages (ideally):
    • A) Bound water
    • B) Water in looser form
    • C) 'Free water'
  7. wateImage Upload
    • Center shows a protein
    • Blue portion is the bound water (bound to the protein)
    • Green portion is transitional water (associated with the bound water, but in a looser form
    • Yellow portion is the free/bulk water (unstructured)
  8. Image Upload
    • The Maillard reaction - 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
    • The one pictured is the reaction with the free epsilon amino group of lysine
  9. Image Upload
    The sugar portion undergoes scission and breaks up into low molecular weight compounds (flavor/aroma) which readily polymerize into brown pigments (color) termed melanoidins
  10. Image Upload
    • Net result of Maillard reaction is that lysine will be 'bound'
    • 'Bound' lysine causes steric hindrance and limits enzymatic digestion of the protein
  11. Image Upload
    • Cross linking reactions: lysine and asparagine
    • (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)
  12. Image Upload
    • Cross linking reactions: lysine and glutamic acid/aspartic acid
    • (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)
  13. Image Upload
    • Hexapeptide
    • The amide bond in cross linking reactions cannot be hydrolyzed by digestive proteolytic enzymes and if such a bond is formed intra or inter protein, it will leave a hexapeptide which cannnot be utilized
  14. Image Upload
    • Loss of cystine
    • Cystine is one of the more heat sensitive amino acids and will readily hydrolyze and break down as follows
    • This reaction can be significant if the limiting amino acid of the protein is cystine - also produces a typical 'cooked' flavor (milk, meat)
  15. Image Upload
    Cystine
  16. Image Upload
    • The formation of dehydroalanine from cystine
    • Preparation of protein concentrates and isolates often calls for the treatment of proteins with alkali to solubilize them in the presence of heat to modify their properties
    • Under such harsh conditions, 'new' amino acids can be formed if free amino acids are present or produced by base hydrolysis
  17. Image Upload
    • Reaction of dehydroalanine with lysine
    • The unnatural amino acid lysinoalanine is poorly absorbed and may be toxic having been shown to cause renal failure in rats
  18. Image Upload
    • Pallets of casein powder
    • One of the 2 categories of milk proteins
    • Comes in 2 forms, isoelectric casein (acid casein) and paracasein
  19. Image Upload
    • A whey protein supplement
    • One of the 2 categories of milk proteins
    • Proteins left in solution after the casein has been precipitated out (enzymatically or via pH adjustment)
    • Again a complex mixture of proteins
  20. Image Upload
    • aS1 casein
    • Alpha fraction of casein is predomiant and can be further subdivided into alpha S1 and kappa casein
    • Image Upload
  21. Image Upload
    • k Casein
    • Alpha fraction of casein is predomiant and can be further subdivided into alpha S1 and kappa casein
    • Image Upload
  22. Image Upload
    • Milk micelle
    • Colloidal spherical protein particles
    • 80-300 nanometers in diameter
    • Made up of aS1 and k casein held together by Ca++ and inorganic phosphate
  23. Image Upload
    • Casein sub-micelle model
    • 10-100 casein molecules (sub-micelles)
  24. Image Upload
    • Rennin attacks k casein at a specific site, cleaving off a hydrophilic glycomacropeptide
    • Micelles are destabilized and the hydrophobic proteins associate to form a curd
  25. Image Upload
    • Beta lactoglobulin has been studied extensively
    • 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
  26. Image Upload
    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 by sulfhydryl interchange
Author:
Morgan.liberatore
ID:
142537
Card Set:
Foodchem Lecture 12 Pics
Updated:
2012-03-19 23:17:17
Tags:
Foodchem Lecture 12 Pics
Folders:

Description:
Foodchem Lecture 12 Pics
Show Answers: