Phenolics Flashcards
What are phenolics (structure)?
Phenolics are a class of organic compounds in which at least one hydroxyl (-OH) group is directly attached to the aromatic ring
What are some structural features that can be added to a simple phenol?
methylation, glycosylation and alkyl groups
What is the main step in the dvp of an extraction procedure of phenolics?
selecting a suitable solvent (based on polarity and miscibility with other solvents)
What is the “Vincken rule-of-thumb”?
Extraction procedure of phenolics is considered complete when the recovery of (almost) all molecules of interest is accomplished: for this, the pellet is re-extracted multiple times
During this process, the phenolics are monitored at 280nm via UV-Vis spectrophotometry
The extraction is stopped when the absorbance of the last cycle is <5% of the sum of absorbance of all previous cycles combined
How do SPE and LLE work? Why is LLE sometimes used over SPE?
SPE is a type of chromatography in which compounds are extracted based on the differential affinity for the column material
LLE (partitioning) is used when the crude phenolic-containing extract is relatively complex and might be too “dirty” for SPE
What are the 3 most used methods for phenolics quantification?
UV-Vis spectrophotometry, Folin-Ciocalteu, RP-LC-PDA-MS
What are the 4 informations obtained from RP-LC-PDA-MS?
polarity (with the order of elution), color (UV-Vis), mass (MS) and structural features (UV-Vis and MS)
What is oxidative coupling?
two oxidative phenolics (or one oxidized and one non-oxidixed) undergo phenolic coupling resulting in the formation of a dimer
Extensive oxidation and coupling increases the size of the conjugated system leading to the formation of brown pigments
What are differences between PPO and POD in terms of substrates, hydroxylation, oxidative coupling and electron acceptor?
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What are o-quinones more likely to attack? What does this form?
O-quinones are prone to attack compounds with nucleophilic groups
a covalent interaction between protein and phenolic is formed
How can the position of sulfonation be determined by H-NMR
for o-diphenols, the coupling between 2 protons gives information on the position of sulfonation
What do larger peaks in COSY NMR spectra mean?
larger peaks suggest larger coupling of protons and therefore ortho-protons
Where is sulfite most likely to attack?
Attack by sulfite is driven by its nucleophilicity: sulfite is most likely to attack on the position on the ring that carries the most positive charge
What is the difference between inductive and resonance effects?
Inductive: more electronegative atoms “pull” electrons closer to them and become slightly more charged
Resonance: the electron is delocalized and can move between atoms this happens in double bonds, lone pairs or charged systems
What are the preferred positions of sulfonation for 4-methoxycatechol, 4-chlorocatechol and EC?
4-methoxycatechol: z
4-chlorocatechol: y
EC: y
How can sulfite act as an irreversible inhibitor?
sulfite irreversibly inactivates PPO by binding to histidine residues in the active site
What other class of compounds can react with phenolics to limit browning?
nucleophiles especially thiols (e.g. cysteine, or glutathione)
Why can’t thiols inhibit enzymatic browning?
can be explained by larger size of thiols compared to sulfite, they are sterically hindered and cannot react with copper-binding histidine residue the same way sulfite does
What is the mechanism of sulphite and ascorbic acid to inhibit enzymatic browning?
Sulphite works by binding to the histidine residue in the active site
Ascorbic acid works by reducing o-quinones back to o-diphenols
