phenolic compounds 4
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flavour is the combination of taste & aroma? True or false
taste (non volatile) aroma (volatile)
effects of phenolics on food flavour
• bitterness • astingency • inherent aroma • participation in aroma formation reactions
which of these names are bitter? naringerin, naringin, narirutin, neohesperidin, hesperidin, hesperitin
naringin & neohesperidin
What linkages taste bitter? (1-2) or (1-6) linkages
1 –> 2 linkages
how do aroma compounds form via o-quinone reactivity?
• (free!) nucleophilic groups in amino acid side chains of proteins, can react with o-quinones • followed up by a stecker degradation • leads to the formation of an aldehyde from the amino acid
is the fermentation of black tea enzymatic?
yes
how can phenolics improve the stability and shelf -life of food
by radical scavenging and metal chelation
The aglycons (naringenin and hesperitin) and rutinosides (narirutin and hesperidin) are not perceived as bitter.. True or false
true
whereas flavanone glycosides with neohesperidose (naringin and neohesperidin), are perceived as intensely bitter
True
When is the astringency of condensed tannins highest? In which range of degree of polymeratisation?
between 5 and 7
What are the odours phenolic aroma compounds are assiciated with?
smoky, woody, spice and or sweet
only starts after disruption of plant tissue to enable phenolics, PPO, O2 to get into contact with each other
browning
happens when di- and oligomeric phenolics interact with salivary proteins and precipitate in the mouth
Astringent taste
can be caused by specific structures, e.g. the flavanone glycosides naringin and hesperidin
bitter taste
one of the underlying mechanism is via the formation of resonance-stabilised phenolic radicals
antioxidant activity
can be either covalent and irreversible, or non-covalent and reversible
protein phenolic interactions
can be influenced by food processing, e.g. by treatment of fruit juice with enzymes that hydrolyse flavonoids’ glycosidic linkages
bitter taste
occurs when o-quinones react with non-oxidised phenols
browning
can be prevented by removal of phenolics via complexation and precipitation with gelatin or PVPP
protein phenolic interactions
one of the underlying mechanisms is via binding of metal ions, also referred to as metal chelation
antioxidant
Strecker degradation to form amino acid-derived aromas can take place when an o-quinone reacts with a free amino acid, because the carboxylic acid and amino group have to be available to participate in the reaction.
true