phenolic compounds 2
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what do they mean when they talk about haze formation? And how does haze formation occur?
it is about turbity one of the processes causing haze formation is the interaction between phenolics and proteins
what are the two classes of phenolics which are often associated with colour
• products from follow-up reactions of PPO-catalysed enzymatic oxidation • anthocyanins, which possess colour as such due to their inherent extended conjugated system
What are browning control methods?
• eliminate oxygen • lower the pH • cool (lower PPO activity) • add chelating agents (binds the copper ions they need for activity) • heat induced denaturation of PPO • add sulphite • remove phenolics
name a advantage and disadvantage of elimination of oxygen
highly effective expensible and reversible
name a advantage and disadvantage of lowering pH
simple and natural can affect food properties
name a advantage and disadvantage of heat-induced denaturation of PPO
simple and irreversible can affect food properties
name a advantage and disadvantage of cooling
simple and minimal impact on food properties has limited inhibiting effects
name a advantage and disadvantage of addition of chelating agent
simple and natural options available high concentration is needed (not natural)
name a advantage and disadvantage of addition of ascorbic acid
cheap consumed during reduction of o-quinones and only effective until used up
name a advantage and disadvantage of removal of phenolic compounds
can be effective íf succesfull impractical, only works for oligo- or polymeric phenolics
which phenolic compound is inherently coloured? And what influences their colour?
anthocyanins dependent on the pH from red (pH<3) to blue/violet (pH 3-6) to deep blue (pH > 6)
How do brown pigments form in enzymatic browning?
The o-quinones generated by the PPO can react with non-oxidised phenolic compounds –> enzymatic browning
what can reduce the o-quinones that are formed by PPO back to o-diphenols and thereby prevent follow up reactions?
addition of asorbic acid or other antioxidants
what can bind to o-quinones and to the active site of PPO
sulphite
how can blanching help with preventing browning
it denaturates PPO
How can adding a chelating agent help prevent enzymatic browning?
PPO has two copper ions (Cu2+) on the active site, which are essential for its catalytic activity. Chelating agents (EDTA) can bind these.