phenolic compounds 2

Question 1

what do they mean when they talk about haze formation?
And how does haze formation occur?

Answer 1

it is about turbity

one of the processes causing haze formation is the interaction between phenolics and proteins

Question 2

what are the two classes of phenolics which are often associated with colour

Answer 2

1. products from follow-up reactions of PPO-catalysed enzymatic oxidation
2. anthocyanins, which possess colour as such due to their inherent extended conjugated system

Question 3

What are browning control methods?

Answer 3

1. eliminate oxygen
2. lower the pH
3. cool (lower PPO activity)
4. add chelating agents (binds the copper ions they need for activity)
5. heat induced denaturation of PPO
6. add sulphite
7. remove phenolics

Question 4

name a advantage and disadvantage of elimination of oxygen

Answer 4

highly effective
expensible and reversible

Question 5

name a advantage and disadvantage of lowering pH

Answer 5

simple and natural

can affect food properties

Question 6

name a advantage and disadvantage of heat-induced denaturation of PPO

Answer 6

simple and irreversible

can affect food properties

Question 7

name a advantage and disadvantage of cooling

Answer 7

simple and minimal impact on food properties

has limited inhibiting effects

Question 8

name a advantage and disadvantage of addition of chelating agent

Answer 8

simple and natural options available

high concentration is needed (not natural)

Question 9

name a advantage and disadvantage of addition of ascorbic acid

Answer 9

cheap

consumed during reduction of o-quinones and only effective until used up

Question 10

name a advantage and disadvantage of removal of phenolic compounds

Answer 10

can be effective íf succesfull

impractical, only works for oligo- or polymeric phenolics

Question 11

which phenolic compound is inherently coloured?

And what influences their colour?

Answer 11

anthocyanins

dependent on the pH
from red (pH<3) to blue/violet (pH 3-6) to deep blue (pH > 6)

Question 12

How do brown pigments form in enzymatic browning?

Answer 12

The o-quinones generated by the PPO can react with non-oxidised phenolic compounds –> enzymatic browning

Question 13

what can reduce the o-quinones that are formed by PPO back to o-diphenols and thereby prevent follow up reactions?

Answer 13

addition of asorbic acid or other antioxidants

Question 14

what can bind to o-quinones and to the active site of PPO

Answer 14

sulphite

Question 15

how can blanching help with preventing browning

Answer 15

it denaturates PPO

Question 16

How can adding a chelating agent help prevent enzymatic browning?

Answer 16

PPO has two copper ions (Cu2+) on the active site, which are essential for its catalytic activity. Chelating agents (EDTA) can bind these.