Foodchem Lecture 12 Pics

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Morgan.liberatore
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Foodchem Lecture 12 Pics
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2012-03-19 19:17:17
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Foodchem Lecture 12 Pics
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Foodchem Lecture 12 Pics
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    • 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
    • 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
    • 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
    • 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
    • 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
    • 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'
  1. wate
    • 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)
    • 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
  2. The sugar portion undergoes scission and breaks up into low molecular weight compounds (flavor/aroma) which readily polymerize into brown pigments (color) termed melanoidins
    • Net result of Maillard reaction is that lysine will be 'bound'
    • 'Bound' lysine causes steric hindrance and limits enzymatic digestion of the protein
    • 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)
    • 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)
    • 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
    • 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)
  3. Cystine
    • 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
    • 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
    • Pallets of casein powder
    • One of the 2 categories of milk proteins
    • Comes in 2 forms, isoelectric casein (acid casein) and paracasein
    • 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
    • aS1 casein
    • Alpha fraction of casein is predomiant and can be further subdivided into alpha S1 and kappa casein
    • k Casein
    • Alpha fraction of casein is predomiant and can be further subdivided into alpha S1 and kappa casein
    • 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
    • Casein sub-micelle model
    • 10-100 casein molecules (sub-micelles)
    • 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
    • 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
  4. 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

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