Quiz 5

Question 1

Define an enzyme

Answer 1

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

Question 2

what are enzymes used in food industry for

Answer 2

• 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

Question 3

6 major enzyme classes

Answer 3

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

Question 4

oxidoreductases

Answer 4

• catalyze oxidations or reductions (alcohol dehydrogenase)

Question 5

transferases

Answer 5

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

Question 6

hydrolases

Answer 6

• catalyze hydrolytic splitting of substrates

Question 7

lyases

Answer 7

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

Question 8

isomerases

Answer 8

• catalyze intramolecular rearrangements

Question 9

ligases (synthetases)

Answer 9

• catalyze combinations of substrate molecules

Question 10

enzymes important to the food industry

Answer 10

• 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)

Question 11

wanted versus unwanted enzyme activity

Answer 11

*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)

Question 12

enzyme catalysis

Answer 12

• 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)

Question 13

factors that affect enzyme reaction

Answer 13

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

Question 14

Km

Answer 14

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

Question 15

Vmax

Answer 15

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

Question 16

zero order reaction

Answer 16

rate = k
rate is independent of substrate concentration

Question 17

first order reaction

Answer 17

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

Question 18

second order reaction

Answer 18

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

Question 18

effects of temperature on enzymes

Answer 18

*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

Question 19

inhibitors

Answer 19

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

Question 20

effect of pH on enzymes

Answer 20

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

Question 21

enzyme cofactor

Answer 21

compound that binds to enzyme and is essential for its activity

Question 22

inhibitors

Answer 22

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

Question 23

competitive inhibitor

Answer 23

*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

Question 24

noncompetitive inhibitor

Answer 24

*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

Question 25

uncompetitive inhibitor

Answer 25

*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

Question 26

substrate inhibition

Answer 26

*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

Question 27

product inhibition

Answer 27

*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

Question 28

desireable enzyme activity in foods

Answer 28

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

Question 29

undesireable enzyme activity

Answer 29

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

Question 30

Examples of desireable enzyme activity (6.3)

Answer 30

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

Question 31

amylases and syrup

Answer 31

*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

Question 32

pectinases and juice

Answer 32

*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

Question 33

chymosin and cheese

Answer 33

*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

Question 34

beta-galactosidase and milk

Answer 34

*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

Question 35

papain and beer

Answer 35

*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

Question 36

papain and meat

Answer 36

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

Question 37

Examples of undesireable enzyme activity (6.3)

Answer 37

*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

Question 38

proteases in milk

Answer 38

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

Question 39

pectinases in tomato paste

Answer 39

*pectinases clarify tomato paste, however cloudiness is desired

Question 40

polyphenoloxidase (PPO) in fruits

Answer 40

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

Question 41

ascorbic acid oxidase

Answer 41

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

Question 42

gelatin and raw pineapples

Answer 42

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

Question 43

lipoxygenases and soybean

Answer 43

*lipoxygenase in soybean produce beany flavor

Question 44

tranglutaminase and proteins

Answer 44

*"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

Question 45

enzymatic browning

Answer 45

*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

Question 46

when is enzymatic browning desireable

Answer 46

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

Question 47

when is enzymatic browning undesireable

Answer 47

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

Question 48

enzymatic browning process

Answer 48

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

Question 49

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

Answer 49

*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

Question 50

how to slow down enzymatic browning (chemical methods)

Answer 50

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