fdsc - enzymes

  1. what are enzymes?
    • Enzymes are molecules that enable biological reactions to proceed at perceptible ratesmost Enzymes are proteins in nature
    • Not all enzymes are proteins, a few are nucleic acids
    • There is no transformation without binding
  2. what are enzymes comprised of?
    • Like protein molecules, most enzymes comprise of amino acid units linked together by peptide bonds
    • Peptide bonds form between an amino acid and carboxylic group with the elimination of H2O molecule
  3. what are enzymes hydrolysed by?
    • With dilute acids and alkali to produce AAs and low molecular weight peptides
    • Proteolytic enzymes cause hydrolytic cleavage of peptide bonds to form AA residueslike proteins, enzymes are also cleaved by proteolytic enzymes to form AA and ↓ molecular weight peptides
  4. what are some tests that enzymes respond to?
    • Bluret,
    • Laury ,
    • Ninhydrin
  5. enzymes absorb UV light @?
    280 nm
  6. what is an active site?
    Region that binds and transforms substrates into products
  7. what are some feature of the active site?
    • small region
    • 3D shape
    • has clefts/crevices
  8. what is catalysis?
    • Entails binding and transformation 
    • Binding of S precedes transformation
    • But there can be binding without transformation
  9. what happens when substrate bind to the active site?
    • They are brought in close proximity with each other
    • This enables collisions/interactiosn between the substrate and the molecules to be more frequent and more effective than if they were flowing around freely in the reaction mixturethus energy required to form new bonds or break existing bonds to form products is lesser vs the situation where the enzyme is also absent
  10. what is ΔG*UR?
    free energy change for uncatalysed reaction
  11. what is ΔG*CR?
    free energy change for catalysed reaction
  12. what is G*?
    ΔG* = free energy change

    Is the minimum amount of energy required to bring all of molecules in 1 of reactant to the transition state of activation complex, where the possibility is ↑ that complex would break down to form products
  13. what is Ea?
    energy of activation
  14. Formula
    • ΔG* = ΔH* - TΔS*
    • ΔH = Ea - PΔT
  15. what is glucokinase?
    Glucose → (ATP TO ADP) GLU - 6 - P

    • Enzyme displays absolute specificity for glucose
    • (Will ONLY act on glucose)
  16. what does hexokinase do?
    • it phosphorylates all hexoses to form the corresponding sugar phosphate
    •              BY hexokinase
    • Glucose → Glu-6-P
    • Fructose → Fru-6-P
    • Galactose → Gal-6-P
    • Mannose → Man-6-P

    Hexokinase exhibits group specificity because it acts on a group of closely related molecules (in this case, hexose sugars)
  17. what is a holoenzyme?
    Complete functional unit of an enzyme

    • Protein part = apoenzyme
    • ex. enzymes without cofactors like trypsin, pepsin, chymotrypsin

    • Essential non-protein part
    • Prosthetic group or cofactor
    • Usually a metal ion
    • Examples of enzymes requiring prosthetic group for activity = polyphenol oxidase and xanthine oxidase
  18. what is absolute specificity?
    When an enzyme acts on only a single substrate (catalase)
  19. what is group specificity?
    • Because it acts on a group of closely related molecules
    • ex. Hexokinase
  20. what is stererospecificity?
    • Enzymes that act on only 1 member of a set of optical isomers of the same compound
    • May act on D-amino acids and L-amino acids but not both!!!
  21. what are racemases?**
    • Catalyze inversion of stereochemistry in biological molecules with only 1 assymetric carbon
    • Ex. glyceraldehyde
  22. what are epimerases?**
    • Catalyze stereochemical inversion, but in molecules with 2 or more asymetric carbons
    • Ex. Glucose
  23. what is enzyme classification?
    • EC numbers - 4 digits (EC a.b.c.d)
    • 1st No 'a' denotes what type of reaction catalyses
    • Based on this, 6 main types of reactions are distinguished, numbered 1, 2, 3, 4, 5, 6
  24. what is EC**
    Enzyme commission
  25. what are the 6 enzyme classifications?
    • 1. Oxidoreductases (ex. PPO, GOX)
    • 2. Transferases (ex. transglutaminase)
    • 3. Hydrolases (ex. proteases, lipases)
    • 4. Lysases (ex. histidine decarboxylase)
    • 5. Isomerases (glucose isomerase)
    • 6. Ligases (ex. fatty acyl CoA synthase)
  26. what are oxidoreductases?
    • Catalyse oxidation reduction reactions
    • ex. PPO, catalase, lipoxygenase, xanthine oxidase; peroxidase
  27. what are transferases?
    • Catalyses the transfer of groups like NH2-, CH3-, acteyl, from 1 substrate to another
    • ex. peptidyl transferase, amino transferase, carbonyl CoA, transglutaminase
  28. what are hydrolases?
    use H2O molecules as co-reactant to split (or hydrolase) large molecules into smaller ones

    • Carbohydrases → carbohydrates
    • Proteases → proteins
    • Nucleases → nucleic acids
  29. why are hydrolyses so important?
    They're the most abundantly used enzymes in the food industry (-60%)
  30. why are proteases so important?
    Constitute about 40% of all enzymes in the food industry
  31. what are lyases?
    • They remove groupes from large molecules 
    • Resulting in formation of smaller molecules and unsaturated bonds
    • ex. hydroperoxide lyases = imp. in flavor generation in food
  32. what is an aldolase?
    • A lyase
    • Breaks Fructose 1-6-diphosphate into 2 parts
    • 1. Glyceraldehyde-3-phosphate
    • 2. Dihydroxyacetone phosphate
  33. what are isomerases?
    Catalyse inter conversions between isomers
  34. what is the most common food industry isomerase?
    Glucose isomerase
  35. what does glucose isomerase do?
    It catalyses the isomeration of glucose into the much sweeter fructose isomer
  36. what are ligases?
    Catalyse the fusion of smaller molecules into smaller ones
  37. what is enzyme purification?
    Enzymes isolated using some procedures to purify proteins
  38. why do we need enzyme purification?
    • Foods
    • Plants, animal and microorganisms are complex 
    • Comprised of several other biomolecules
    • We need to isolate the enzyme before use, to be able to ascribe the transformations we see specifically to the enzyme

    • To minimize or eliminate undesirable reactions
    • To exclude harmful toxins that may be co extracted with the enzyme
    • For efficiency or better sue of other enzymes that may be present in the source material
  39. what are some factors that can affect enzyme purification?
    • Enzyme is made of amino acids
    • 1. Number of aa can very, so this can affect the size
    • 2. Ratio of hydrophobic vs hydrophilic may very to affect solubility
    • 3. Side chain of aa may be charged (+ive or -ive) or uncharged 
    • this can affect both the solubility and mobility of enzymes on protein molecule under the influence of an electric field
    • Surface interactions of enzyme molecules and their active sites may differ to affect their relative affinity for ligands
  40. what is enzyme purification based on?
    • Size difference
    • Solubilty differences
    • Charge differences
    • Selective absorption
  41. what is dialysis?
    • Separation based on size differences
    • Using a dialysis bag = semi permeable membrane
    • Concept of selective permeability
    • Exchange of small molecules thru membrane
    • Larger molecules will be left behind
    • WHY? cuz there will be equilibrium
    • Dialysis = not very effective method of separtion

                                                Image Upload 1
  42. what is ultrafiltration?
    • Separation based on size difference
    • Faster
    • Better suppression of molecule
  43. what is centrifugation?
    • Separation based on size difference
    • Larger molecules fall after than small ones
  44. what is gel filtration?
    • Separation based on size difference
    • Pack a column with this inert resin (beads)
    • Inert resin have small spores
    • Large molecules = cannot enter small pores so They come out of the column
  45. what are the 3 ways an aa can be charged?
    • Neutral
    • +ively charged
    • -ively charged
  46. what are some different ways to separate enzymes based on charge differences?
    • Ion exchange chromatography
    • Electrophoresis
    • Isoelectric focusing
  47. what is ion exchange chromatography (IEX)?
    • Separation based on charge differences
    • Uses resin (+ively and -ively charged resins)
  48. what are -ively charged resins?
    • Bind +ively charged species (cations)
    • Cation exchanger
    • Sulphonates polysystence carboxylated
    • Diethyl amino ethyl quaternary resins***
  49. what are +ively charged resins?
    • Can bind -ive charged species (anions)
    • Anion exchanger***
  50. what are strong exchangers?
    Are those whose charges do not fluctuate with changes in pH

    • Weak cation exchangers
    • Strong cation exchnagers
  51. what are weak exchangers?
    Are those whose charges fluctuate with changes in pH

    • Weak anion exchangers
    • Strong anion exchangers
  52. what happens when a a mixture of enzymes or proteins are added to a CATION EXCHANGER?
    The +ively charged enzymes/proteins will bind to the resin while the -ively charged ones do not bind
  53. what happens to the unbound molecules?
    They are washed out of the column
  54. what happens to the enzymes/protein that are bound to the resin?
    • They are diluted by changing the pH or ionic strength
    • ex. the buffer
  55. what is gel electrophoresis?
    • Separation based on charge differences
    • Charged molecules subjected to electric current 
    • Causes the molecules to migrate










    • Combined effect of charge + size will determine the migration/mobility of the proteins/enzymes
    • To result in their separation
  56. what is a special kind of gel electrophoresis?
    • SDS- polyacrylamide
    • SDS (sodium dodecyl sulfate) is used to apply a large -ive charge in all the enzyme/protein molecule in the sample
    • Because charges are equalized, separation happens by size differences only
  57. what is isolelectric focusing?
    • Separation based on charge differences
    • Amphobytes are used to generate a pH gradient in the separation material (ex. gels)
    • When samples are applied, they migrate under the influence of electric current and stay @ pH values in the medium corresponding to the PI of the enzymes
  58. what are some different ways to separate based on solubility differences?
    • Isoelectric precipitation
    • Salt fractionation
    • Solvent precipitation
  59. why do enzymes display different solubilities in aqueous systems?
    • Enzymes have different AA composition and content that influence their sizes**
    • Side chains may be charged, uncharged, hydrophobic, hydrophilic
  60. what is isoelectric precipitation?**
    Takes advantage of the PI of the enzymes at PI, net charge on protein molecule in 0 and the solubilities of the molecules is minimal

    When the molecules are present in sufficiently ↑ concentration, they would precipitate

    • thus, the pH is adjusted to the PI of the molecules of interest to cause its precipitation
  61. what is salt fractionation?***
    • The use of neutral salts
    • ex. (NH4)2SO4 and Na2SO4
  62. what is solvent precipitation?**
    • H2O miscible organic solvents
    • ex. ethanol, methanol and acetone
  63. what are some different ways to separate based on specific binding sites?
    • Affinity chromatography
    • Hydrophobic interaction chromatography (HIC)***
    • Hydrophobic interaction chromatography (HILC)**
  64. what is affinity chromatography?
    • Appropriate material that binds
    • Specifically to the enzyme
    • ex. substrate, inhibitor, cofactor
  65. what is hydrophobic interaction chromatography (HIC)***
    • You have a solution of soluble proteins in water
    • At high ionic strengths the protein will try to percipitate, so you keep it at an intermediate ionic strength
    • Use a hydrophobic surface to absorb the proteins out of solution
    • Can use for purification because different proteins have different inherent hydrophobicities
    • Use elution with lower ionic strength water to reverse the adsorption
    • HIC can be applied to the purification of most soluble proteins
  66. what is hydrophilic interaction chromatography (HILC)**
  67. what is enzyme purity?
  68. what are different ways to test enzyme purity?
    • Test for homogeneity
    • Chromatographic behaviour
    • Activity testing
    • Isoelectric focusing
  69. what are chromatographic profiles?**
    Signify less purified samples
  70. what the difference between less purified samples and highly purified samples?
    Highly purified samples tend to have symmetrical peaks
  71. how do we test for homogeneity?
    • By electrophoresis or isoelectric focusing
    • Simple bands = denote purity or homogeneity
    • Multiple bands = denote less purity
  72. how do we do activity testing?
    by using synthetic substrates that are specific for particular enzymes


    ADD
  73. what is the mechanism of enzyme catalysis?
    Conversion of reactants → products
  74. how are the reactions facilitated?
    Enzymes facilitate the reactions by ↓ the energy barrier
  75. how do enzymes enhance reactions?
    By binding with S to form complex with ↓ ΔG


    E + S ↔ ES → E+ P
  76. what does the overall reaction rate depend on?
    on <E>, <S>, T, stability of ES, <P>, pH etc
  77. how are the reaction rates measured?
    • By the disappearance of substrates from the reaction mixture
    • By the formation or appearance of products in the reaction mixture
  78. what methods are used to calculate the reaction measurement?
    • 1. Initial rate method
    • 2. End-point method
  79. what is the initial rate method?***
    As soon as u add the enzyme + substrate,
  80. what is the end point method?
    • Enzyme is added to substrate
    • Reaction is left to proceed for an interval of time 
    • Then stopped for measurements to be taken
  81. what are the advantages of the initial rate method
    • Enzymes are fully active to display its maximum potential
    • Not susceptible to substrate depletion
    • Not prone to inhibition by end product
    • takes measurements as close to time 0 as possible
    • More reliable and accurate
  82. what are the disadvantages of the initial rate method?
    • Requires more skill to do
    • Requires sophisticated equipment
    • More costly $$$
  83. what are the advantages of the end point method?
    • Simpler to do
    • Does not require much skill
    • Inexpensive and simple instruments
  84. what are the disadvantages of the end point method?
    • Enzymes that are prone to inactivation, enzyme activity may decline with time, thus we can underestimate the catalytic capacity of the enzyme
    • Susceptible to errors due to the substrate depletion
    • Susceptible for end product inhibition (when the products inhibit the enzyme)
    • Underestimates true potential if measurements are taken 10-15 minutes later
  85. why are there changes of rate in the end?
    • Substrate degradation
    • Loss of enzyme activity with time
    • Susceptibility to product inhibition

    E + S ↔ ES (portion atteins equilibrium)
  86. what are the 3 distinguished phases?
    • 1. Pre steady state
    • 2. Steady state
    • 3. Post steady state
  87. what is the pre steady state?
    • When the rate of product formation is increasing ↑ with time 
    • Very short duration
    • This occurs becasue the ES complex needs to get in equilibrium
  88. what is the steady state phase?
    • The rate of product formation is constant
    • The ES complex forms and breaks down at the same rate
    • So <ES> remains constant
  89. what is the post steady phase?
    • Rate of product formation is ↘ with time
    • Substrate = depleted and reaction slows down
  90. what is the michaelis mention equation?***
    • E + S ↔ ES → E+ P
    • Relationship between Vo and Vmax
    • When the enzyme (E) is added to the substate (S), the reaction proceeds as follows:












     chart?chf=bg,s,00000000&cht=tx&chl=Vo%3DVmax(S)%2FKm'%20%2B(s)%20&chs=414x40
  91. what is the lineweaver burk equation?
    EXPLAIN HERE
  92. what is the hanes equation?
    EXPLAIN HERE
  93. what does Km mean?
    • It measures substrate binding affinity
    • affinity E for S
  94. what does Vmax mean?
    It measures the substrate transformation capacity
  95. what does the Vmax/Km ratio mean?
    It measures catalytic efficiency of the enzyme
  96. what is enzyme inhibition?
    • Reduction in rates of enzyme catalysis caused by inhibitors
    • Inhibition may be reversible or irreversible

    ex. E + I → EI


    or E + I ↔ EI
  97. what are the 3 types of inhibition?
    • 1. Competitive
    • 2. Non-competitive
    • 3. Uncompetitive
  98. what is competitive inhibition?
    • I' binds to active site of 'E' and prevents 'S' from binding
    • 'I' resembles  'S' in structure, this competes for active site
    • eg. inhibition of succinate dehydrogenase by malonate
  99. what is non competitive inhibition?
    • 'I' binds to a site other than the active site of 'E' and prevents transformation of 'S' to 'P'
    • Reduction of reaction rate by pH is an example of non-competitive inhibition- the 'I' being the H+ on the acid side of the optimum and the OH- on the alkaline side
  100. what is uncompetitive inhibition?
    • 'I' binds to site on 'E' molecule which becomes available only after 'S' has bound to the active site; ie. to the ES-Complex.
    • ex. S inhibition which occurs at very high [S].
    • As in inhibition of invertase by high concentration of sucrose
  101. how do we overcome enzyme inhibitors?
    • Establish type of inhibition by incubating E with I and assaying for residual enzyme activity at intervals
    • For irreversible inhibitors, E loses activity progressively with time
    • Irreversible inhibition cause by heavy metals, may be relieved by IEX

    • Reversible inhibition overcome by:
    • 1. increasing [S]
    • 2. dialysis to dissociate I from E or
    • 3. dilution out eh [S] or by increasing [E]
  102. what are factors affecting catalysis?**
    1.







    if <S>  is sufficiently ↑ (i.e. for in excess of <E>), then ↑ <E> will ↑ rate of catalysis


    2.







    when <E> is constant, ↑ <S> will ↑ catalysis up till point where the E
  103. how does ↓ temperature affect catalysis?
    Low temperatures slow down enzyme catalysis (used in foods to retard undesirable effects like texture softening, off-flavors, ripening)
  104. how does ↑ temperature affect catalysis?
    Higher tempertures enhance enzyme catalysis but may also deactivate enzymes
  105. what is the Q10 or the temperature coefficient?
    Q10 = rate of (T+10)°C / rate (T)°C
  106. what are some factors affected by temperature?
    • Enzyme stability
    • Affinity to enzyme for substrte; inhibitors or activators
    • Rate of conversion of substrate to products
    • Changes in solubility of gases
    • pH of buffer
    • Competing reactions
    • Ionization of prototropic groups
  107. what does a graph of enzyme activity vs temperature look like?
    The graphical representation of ENZYME ACTIVITY VS TEMPERATURE is a bell shaped curve









    • Activation = ≤ Topt
    • Inhibition = ≥Topt
  108. what is the Arrhenius equation?
    • chart?chf=bg,s,00000000&cht=tx&chl=k%3DAe%5E-%5EE%5Ea%5E%2F%5ER%5ET&chs=212x38
    • chart?chf=bg,s,00000000&cht=tx&chl=Ln%20k%20%3D%20LnA-E_a%2FRT&chs=342x40









    Graphical representation of Ln k vs 1/T
  109. how does pH influence catalysis?
    E's active within narrow pH range

    • pH optimum of enzymes:
    • Duration of reaction,
    • Nature of S and [S],
    • Ionic strength of medium,
    • Purity of E,
    • Presence/absence of an inhibitor or activator
  110. effect of pH - SUMMARY
    • At extreme pH values, there is irreversible denaturation of the enzyme
    • Temperature activity profiles of enzymes to verify Topt
    • Substrate is incubated at various temperature prior to addition by enzymes to monitor catalysis
    • Temparture stability profiles of enzymes are verified by incubating the enzyme of different temperatures prior to their addition to the [S]
  111. how do we determine the pH stability of an enzyme?
    • Incubate enzyme at various pH values
    • Apply enzyme to the substrate
    • Measure relative activity
  112. how do we determine the pH activity of an enzyme?
    • Prepare substrate in buffer solutions at various pH values
    • Apply enzyme to substrate
  113. how do we determing the pH optimum for an enzyme? (REVIEW)**
    • Prepare substrates at different pHs
    • Add enzyme, and then measure activity
  114. what are some effects that enzymes can have in food processing?
    • Enzymes can have:
    • Beneficial effects
    • Undesirable effects
    • and can control undesirable effects of enzymes in food
  115. what are the beneficial effects of enzymes?
    • Natural, non toxic substances
    • Specificity
    • Activity under mild conditions
    • Ease of control after desired process
  116. what are 3 sources of industrial enzymes?
    • Plant
    • Animal
    • Microbial
  117. what are some examples of enzymes from plants?
    • Papain = papaya
    • Bromelain = pineapple
    • Ficin = fig trees
    • Lipoxygenase = used to bleach wheat flower to make white flower
  118. what are some examples of enzymes from animals?
    • Rennet
    • Trypsin = digestive enzyme
    • Pepsin = digestive enzyme
    • Chymotrypsin
    • Gastricin
    • Catalase
  119. what are some examples of enzymes from microorganisms?
    • Glucose isomerase
    • Glucose oxidase
    • Invertase
    • Microbial rennet
    • Pullanases
    • Lipases
    • Amylases, Proteases
  120. what are 2 groups of enzymes?
    • Exo Enzymes
    • act on substrate at their end

    • Endo Enzymes
    • act on bonds within or inside enzyme molecules
  121. what are 4 changes by endo and exo enzymes that result in food products?**
    • 1. Textural changes
    • 2. Flavor changes
    • 3. Color changes
    • 4. Yield

    These can be desirable or undesirable
  122. what are some desirable textural changes in food by enzymes?
    • Meats/fish = tenderization, texture firming, ↑ in water binding capacity
    • Dairy = milk coagulation, TGase can cause thickening of yogurt and hardening of cheeses
    • Baked goods = modification of texture by proteases/TGases
    • Vegetables/fruits = formation of hydrolysates using proteases and carbohydrates (ex. fish sauce, soy sauce etc)
  123. what are some desirable flavour changes in foods by enzymes?
    • Lipases can produce ↓ molecules weight alcohols and carbonyl compounds that import flavours we associate with certain products
    • ex. cheeses; hydrolysates
    • Enzymes like glucose isomerase, invertases, amylases produce sweeteners in food products
  124. what are some desirable color changes in foods by enzymes ?
    • Browining in tea, cocoa and chocolates via enzymatic browning reactions catalyses by PPO
    • Bleaching of flower using lipoxygenases
    • Classification of beverages using carbohydrases (ex. pectic enzymes) and proteases (as in chill proofing in beer)
  125. what is the desirable yield?
    • As in the manufacture of vegetable oils
    • Enzymes like proteases and carbohydrases breakdown the proteins and carbohydrates that may be complexed with the vegetable oils to release the oil and ↑ yield
    • Enhance yield of pigments as in the recovery of carotenoid pigments from coruscates
    • Use of TGases to cause aggregation of smaller molecules to ↑ yields of cheeses, yogurts, breads etc..

  126. what are some undesirable textural changes in food by enzymes?
    Excessive breakdown of larger molecules can result in undesirable softening, even liquefaction

    •                                          TMAO
    •                                              ↓
    •                                           TMA
    •                                          ↙   ↘
    •                                  DMA          FA (can cause undesirable texture softening in fish during storage)
  127. what are some undesirable flavour changes in foods by enzymes?
    • Both oxidative and hydrolytic rancidity can cause off flavours in foods (particularly in fatty foods)
    • Bitterness in products (such as cheeses) caused by excessive proteolysis
    • Bitterness usually due to hydrophobic amino acid residues (ex. proline) at the termini of ↓ molecular weight peptides
    • They can be removed by "debittering" enzyme (ex. proteases that remove the AA residues from the termini of the peptide)
  128. what are 2 proteases used as debittering peptides?
    • 1. Aminopeptidases
    • 2. Carboxy-peptidase
  129. what are some undesirable color changes in foods by enzymes ?
    • Dark discolouration caused by enzymatic browning in fruits, vegetables and crustacea
    • Action of LOX on salmonids flesh during storage
    • LOX breaks down the carotenoid pigments to go from orange colors to lighter shades of yellow
  130. what is the undesirable yield?
    Use of proteases in cheese making to produce small curds that are lost during the cheese making process
  131. what are other lesser known uses of enzymes in the industry?
    • Use of enzymes tannases to break down tannins in cold tea for both clarification and desirable flavours
    • In protein "re-synthesis" to link amino acids and ↓ molecular weight peptides together to form bland gel-like protenaceous products
    • Dextranase in toothpaste
    • Keratinase in hair removal creams
    • Macerating enzymes used in fish processing to de-scale fish
    • Production of caviar : ex. sturgeon fish roe macerating enzymes may be used to remove membraneous material that holds the egg-breakscape and ↑ the yield
  132. what are different methods of controlling enzymatic reactions in food?
    • 1/2. Based on ↑ or ↓ temperature
    • 3. By reducing the H20 content in the milieu
    • 4. Addition of chemicals
    • 5. Antioxidants
    • 6. Chelating agents
    • 7. High pressure treatment
    • 8  Enzyme treatments
    • 9. Use of enzyme inhibitors
  133. how do we control enzymatic reactions in foods by ↑ the temperature?
    • ex. Cooking, pasteurization, sterilization
    • This causes denaturation/inactivation of the enzyme (protein)
  134. how do we control enzymatic reactions in foods by ↓ the temperature?
    • ex. Refrigeration, freezing
    • Molecules = sluggish and don't react as effectively
    • causes a reaction in the thermal energy of the milieu
    • Catalysis = slowed in the reduced environment but does NOT stop catalysis
    • Freezing can actually enhance activity in some cases (oxygenase)
    • Frozen storage may actually cause activation of enzymes like lipoxygenases + lipase
    • The freezing process strips H20 from the enzymes, therefore exposing the hydrophobic residues on the surface to enhance interactions w/hydrophobic molecules (such as fats)
  135. how do we control enzymatic reactions in foods by reducing the H2O activity of the milieu?
    • When substances such as salts or organic solvents are added to the enzyme, they:
    • 1. Strip the H2O from the surface of the enzyme
    • 2. Disturbs the film of its integrity
    • 3. Causes the enzyme to lose activity
  136. how do we control enzymatic reactions in foods by the addition of chemicals?
    • Acids/Alkali
    • Extreme pH can cause irreversible denaturation of enzymes = loss of activity
  137. how do we control enzymatic reactions in foods by antioxidants?
    • May remove essential co-substrates from the reaction medium 
    • Cause reaction in catalysis
  138. how do we control enzymatic reactions in foods by chelating agents?
    • May remove essential non-protein parts (or cofactors) from enzymes
    • Cause loss of activity
  139. how do we control enzymatic reactions in foods by ↑ high pressure temperature?
    • Can cause compaction + reduction in volume of the enzymes
    • Which can disrupt the conformation of the molecules + result in loss of activity
  140. how do we control enzymatic reactions in foods by enzyme treatment?
    • Advantage is taken of the fact that most enzymes are proteins to use proteases to break down/inactivate the other enzymes (ex. inactivation of PPO in apple juices to control the browning)
    • ex. Inactivation of PME to control destabilization of citrus juices
  141. what happens to the animals that are w/out distinct stomaches?
    • Since digestion in the stomach precedes + prepares molecules for subsequent vitalization by intestinal enzymes, it is to be wondered how intestinal enzymes in stomach utilize undermanned molecules
    • These animals seem to have solved the problem by developing more potent proteases that can hydrolyze native protein molecules
    • Crayfish + Cunner fish = Stomach less fishes
    • Alaskan Pollack = flesh softens due to proteases
  142. what is the use of enzyme inhibitors?
    • ex. Fish flesh from some species = very soft due to enzymatic action (like the Alaskan Pollock)
    • they are not preferred because of their softness
  143. what are some food industry uses of enzymes?
    • Cheese making: with rennin or rennet, pepsins or chymosins
    • Winemaking and Brewing: with proteases and amylases
    • Baking: with amylases, proteases, (lipases), lipoxidases
    • Meat industry: proteases (tenderization, solubilization), TGases (texturization), Lipases (flavor)
  144. what are different chemical reactions in foods that are catalyzed by enzymes?
    • 1. Chemical reactions of Proteases
    • 2. Chemical reactions of Carbohydrases
    • 3. Chemical reactions of Lipases
    • 4. Chemical reactions of Oxidoreductases
  145. what are the chemical reactions of Proteases?
    • Different proteases hydrolyze proteins in different ways:
    • Exoproteases vs Endoproteases
  146. what are endoproteases?
    • Act randomly on peptide within the protein molecules to form peptides
    • Useful in preparation of hydrolysates
  147. what are exoproteases?
    • Remove amino acids stepwise from the termini of the proteins
    • Useful in flavor modifications
    • 2 kinds - aminopeptidases/another one
  148. what are chemical reactions of Carbohydrases?
    • Starch + Cellulose = 2 major carbohydrates found in foods
    • Starch (alpha-1,4 linkage)
    • Cellulose (beta-1,4 linkage)
  149. Which is more resistant to enzymatic hydrolysis, cellulose or starch?
    Cellulose
  150. what are the chemical reactions of Lipases?
    • Lipases = cause degradation or modification of fats and oils
    • Involved in several complex reactions
    • In food processing = interested in hydrolysis of acylglycerides 

    Triglyceride +nH2O → Glycerol + nFA


  151. Why is the action of lipases usually undesirable in food processing?
    FFAs formed are less stable than the acyl glycerols, and are responsible for undesirable rancid odors
  152. in what foods rancidity is a great economic concern?
    • Dairy
    • Fish
    • Other foods containing fats
  153. in what products lipolysis is desirable?
    • Buttermilk
    • Roquefort cheese
    • Milk chocolate
    • Margerines
    • Baked goods
    • Imitation dairy
  154. what are the chemical reactions of Oxidoreductases (OR)?
    • Ascorbic acid oxidase
    • Polyphenol oxidase
    • Glucose oxidase
    • Catalase
    • Lipoxygenase (lipoxidase)
    • Xanthine oxidase
    • Peroxidase
  155. what are enzymatic modifications of foodstuffs?
    • Changes in solubility (in production of cheese and beer)
    • Changes in functional properties (important in meat tenderization and protein concentrates)
    • Flavour changes (in soups and sauces)
  156. What are some industrial applications of proteases?
    • Removal of bitterness
    • Modification of milk an whey proteins for incorporation into dietetic products
    • Hydrolysis of wheat gluten for use as flavorants
    • Modification of colagen and gelatin
    • Alcoholic beverages
    • Baking
    • Recovery of scrap protein from offal, bones, and blood
Author
K.A
ID
324941
Card Set
fdsc - enzymes
Description
fdsc
Updated