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Food Chem > Quiz 5 > Flashcards

Quiz 5 Flashcards

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1
Q

Define an enzyme

A

a protein with catalytic properties due to its power of specific activation and conversion of substrates to products

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2
Q

what are enzymes used in food industry for

A
  • used as processing aids for:
    *convert a particular substance to a required product without unwanted side reactions
    *rapid action
    *can be used in small amounts
    *easily controllable by adjustment of pH, tmeperature, and enzyme concentration
    *natural origin, non-toxic
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3
Q

6 major enzyme classes

A
  1. oxidoreductases
  2. tranferases
  3. hydrolases
  4. lyases
  5. isomerases
  6. ligases (synthetases)
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4
Q

oxidoreductases

A
  • catalyze oxidations or reductions (alcohol dehydrogenase)
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5
Q

transferases

A
  • catalyze a shift of a chemical group from a donor to an acceptor substrate (methyltransferases)
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6
Q

hydrolases

A
  • catalyze hydrolytic splitting of substrates
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7
Q

lyases

A
  • catalyze removal or addition of chemical groups to substrates (excluding hydrolysis) (carbonic anhydrase)
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8
Q

isomerases

A
  • catalyze intramolecular rearrangements
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9
Q

ligases (synthetases)

A
  • catalyze combinations of substrate molecules
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10
Q

enzymes important to the food industry

A
  • hydrolases (most common): adding a water molecule for each bond split, carbohydrases, proteases, esterases, lipases
  • oxidoreductases: substrate loses hydrogen or gains oxygen
  • isomerase: intramolecular rearrangment, glucose isomerase (glucose to fructose)
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11
Q

wanted versus unwanted enzyme activity

A

*wanted: ripening of cheese, conversion of milk to cheese, conversion of corn starch to high function corn syrup
*unwanted: lipid hydrolysis producing hydrolytic rancidity in lipid containing foods, thinning of tomato paste, browning of fruits (polyphenol oxidase)

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12
Q

enzyme catalysis

A
  • enzymes increase the rate of chemical reactions by lowering the energy needed to activate the reaction
  • even reactions which release energy do not happen spontaneously because there is an energy barrier (activation energy)
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13
Q

factors that affect enzyme reaction

A
  • enzyme concentration
  • substrate concentration
  • combined effect of enzyme and substrate concentration
  • time
  • temperature
  • pH
  • coenzymes and enzymes cofactors
  • inhibitors
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14
Q

Km

A
  • Michaelis-menten constant, [S] at 1/2 Vmax
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15
Q

Vmax

A

maximum reaction velocity, attained when ES at maximum value (ES = E)

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16
Q

zero order reaction

A

rate = k
rate is independent of substrate concentration

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17
Q

first order reaction

A

rate = k [S]
rate is proportional to the first power of substrate concentration

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18
Q

second order reaction

A

rate = k [S] OR rate = k[S1][S2]
[S] = k [S]^2
#1: rate is proportional to the square of the substrate concentration
#2: rate is proportional to the first power of each of two reactants

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18
Q

effects of temperature on enzymes

A

*at low temps reaction rate increases as the temperature is raised
*over a period of time, enzymes will be deactivated at even moderate temperatures
*above optimum temp: denaturation

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19
Q

inhibitors

A
  • decrease reaction velocity
  • make some foods unavailable for our gut enzymes (ex. trypsin inhibitors in soybean)
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20
Q

effect of pH on enzymes

A

*optimum pH = where enzyme is most active
*extremely high or low pH values result in complete loss of activity for most enzymes

21
Q

enzyme cofactor

A

compound that binds to enzyme and is essential for its activity

22
Q

inhibitors

A

*decrease reaction velocity
*make some foods unavailable to our gut enzymes (trypsin inhibitors in soybean)

23
Q

competitive inhibitor

A

*it competes with substrate for binding in a dynamic equilibirum- like process (inhibition is reversible by substrate
*Vmax in unchanged
*Km is increased, as defined by [S] required for 1/2 maximal activity

24
Q

noncompetitive inhibitor

A

*binds E or ES complex other than at the catalytic site
*substrate binding unaltered, but ESI complex cannot form products
*inhibition cannot be reversed by substrate
*Km unaltered
*Vmax decreased proportionately to inhibitior concentration

25
Q

uncompetitive inhibitor

A

*binds only to ES complexes at locations other than the catalytic site
*substrate binding modifies enzyme sructure
*inhibition cannot be reversed by substrate
*Vmax decreased
*Km decreased

26
Q

substrate inhibition

A

*inhibiton of an enzyme by high concentrations of substrate is common in industrial applications
*a special case of uncompetitive inhibition - usually when parts are more active than one substrate molecule bind to the active site

27
Q

product inhibition

A

*results from competitive inhibition of the enzyme by the product - due to the structural similiarity of the product to the substrate (ex. inhibition of lactase by galactose)
*product inhibition often causes a serious loss in productivity of an enzyme process at high degrees of conversion

28
Q

desireable enzyme activity in foods

A

*control with enzyme type, time, temperature, pH, substrate concentration, enzyme concentration
*purpose: to optimize enzyme activity

29
Q

undesireable enzyme activity

A

*control with temperature, pH, water activity, inhibitor
*purpose: to slow down or inactivate enzyme activity

30
Q

Examples of desireable enzyme activity (6.3)

A

*amylases and syrup
*pectinases and juice
*chymosin and cheese
*beta-galactosidase and milk
*papain and beer
*papain and meat

31
Q

amylases and syrup

A

*amylases used to make dextrins from corn starch
*enzyme type: thermally stable, bacterial enzyme
*time: inc time to inc conversion of react. to prod.
*temperature: need high rxn temp bc of gelatinization
*pH: want max activity

32
Q

pectinases and juice

A

*used in apple juice to clarify product
*enzyme type: pectinase produced by aspergillus niger
*time: depends on the dosage of the enzyme and variety of apple (more enzyme = less time needed)
*temperature: optimum temp 30-40 C
*pH: want max activity

33
Q

chymosin and cheese

A

*used to produce curd by coagulating milk protein (casein)
*enzyme type: specificity toward Phe - Met
*time: about 30 min
*temp: optimum temp = 43 C, cheese manufactures use 30-37 C
*pH: optimum pH = 5.5

34
Q

beta-galactosidase and milk

A

*added to milk to hydrolyze lactose for lactose free products, ice cream production
*enzyme type: produced by aspergillus oryzae
*time: depends on enzyme conc and volume of milk
*temp: optimum temp is 55 C
*pH: optimum pH is 4.5
effective pH range = 3.5 to 7.5

35
Q

papain and beer

A

*used to prevent chill haze formation (chillproofing)
*enzyme type: isolated from papaya
*time: depends on enzyme concentration and volume of beer
*temp: optimum is 65 C
*pH: optimum is 6-7

36
Q

papain and meat

A

*plant sourced enzymes attack connective tissue
*microbial proteases preferentially hydrolyze actin and myosin

37
Q

Examples of undesireable enzyme activity (6.3)

A

*proteases in milk
*pectinases in tomato paste
*polyphenoloxidase (PPO) in fruits
*ascorbic acid oxidase
*gelatin and raw pineapples
*lipoxygenases and soybean
*transglutaminase and proteins
*enzymatic browning

38
Q

proteases in milk

A

*proteins in milk degrade proteins and significantly affect flavor and protein stability

39
Q

pectinases in tomato paste

A

*pectinases clarify tomato paste, however cloudiness is desired

40
Q

polyphenoloxidase (PPO) in fruits

A

*PPO is responsible for undesireable discoloration (brown) in fruits

41
Q

ascorbic acid oxidase

A

*widely found in plant materials
*oxidizes ascorbic acid (vit C) into dehydroascorbic acid (can cause brown melanoidin formation)

42
Q

gelatin and raw pineapples

A

*bromelain (protease) in raw pineapples will prevent gelation of gelatin

43
Q

lipoxygenases and soybean

A

*lipoxygenase in soybean produce beany flavor

44
Q

tranglutaminase and proteins

A

*“meat glue”
*enzyme catalyzed the formation of covalent bond btwn acyl group of glutamin adn free amine group of lysine
*used to form imitation crabmeat, surimi, fish balls, and some hams

45
Q

enzymatic browning

A

*copper containing enzyme that catalyzes the oxidation of phenolic compounds to o-quinones at the expense of oxygen
*occurs in almost all plants, with relatively high levels in potatoes, mushrooms, apples, peaches, bananas, avocados, tea leaves
*enzyme type: phenolase, phenoloxidase, catecholase, cresolase, tyrosinase

46
Q

when is enzymatic browning desireable

A

raisans, prunes, cocoa beans, tea, coffee and apple cider

47
Q

when is enzymatic browning undesireable

A

browning after peeling fruits like apples, potatoes, banana, peaches

48
Q

enzymatic browning process

A

monophenol (colorless) = PPO + O2 => diphenol (colorless) = PPO + O2 => o-quinone (browning pigment) = amino acids/ proteins => complex brown polymers

49
Q

how can you slow down enzymatic browning rxns (physical methods)

A

*dehydration - reduce mobility of substrate and enzymes
*freezing - more browning when temeprature rises and enzymes are active, enzyme not very active in freezer
*exclusion of molecular oxygen - vacuum package or immerse in water

50
Q

how to slow down enzymatic browning (chemical methods)

A

*inhibiting or deactivating enzyme
*complexing native substrate or cofactors
*reducing quinones back to o-diphenols or conjugating quinones

Food Chem (4 decks)

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