1.2. Maillard Reaction Flashcards
What’s the particularity of reducing sugars?
They have a carbonyl end (aldehyde or ketone)
What’s the reactivity order of reducing sugars?
ribose > xylose > fructose > glucose and galactose
What’s the initial step in Maillard?
Starts with condensation reaction between an amino group and a reducing sugar which leads to the formation of N-glycosylamine that rearranges into an Amadori product (for aldoses) or a Heyns products (for ketoses)
What is formed during the intermediate phase of Maillard?
diketones
What are 2 main pathways diketones undergo?
- Formation of cyclic compounds
- Further fission into (dehydro) reductones
What is the particularity of a diketone molecule?
Presence of 2 carbonyl groups
How are HMF, furfural and furanone formed?
HMF and furfural: formed from 3-deoxyosones (formed from 1,2-enolization at LOW pH) when nitrogen content is low
furanone: formed from 1-deoxyosone (formed from 2,3-enolization at HIGH pH)
What is the retro-aldol reaction? How is the pH changed?
- Breaking of beta-hydroxyl-carbonyl bond leading to formation of carbonyl compound + enolate fragments
- The pH drops
Give the equation of the Strecker degradation.
diketones + free a.a. -> Strecker aldehydes (aroma) + CO2 + amino ketones
What products are formed when cysteine oxidizes?
- cyclization to form acetylthiazole precursors
- splitting into mercapto-acetaldehyde + amino sugar
- full cleavage into acetaldehyde + H2S + ammonia + amino sugar
What is the particularity of H2S?
Can undergo further reactions influenced by pH
Forms meaty flavors with Strecker aldehyde of cysteine
Give some example of aroma compounds formed during Maillard?
2-methyl-3-furanthiol (MFT)
pyrazines
HMF
furfural
furanone
Strecker aldehydes
furanoids (maltol during caramelization)
What compounds give meaty flavor?
2-methyl-3-furanthiol (MFT)
Which sugar and which a.a. make 2-methyl-3-furanthiol (MFT)?
Xylose + cysteine
What pH leads to more pyrazine formation?
Higher pH leads to more retro-aldol reaction and more pyrazine formation
Why should you add ammonia during caramelization?
Ammonia catalyses the rearrangement of diketones
How do melanoidins contribute to taste and aroma?
They don’t!
How can the activation energy be lowered?
By using a catalyst
What pH results in increased color formation?
Higher pH
Why isn’t low pH leading to high colour formation? What can you do to help reaction?
- A.a are protonated (NH3+) which makes it harder for them to react with reducing sugars
- Add HCl
What is the role of Lipid Oxidation during Maillard?
Unsaturated lipids undergo autoxidation accelerated with the presence of iron > formation of aldehydes
What reaction forms pentyl-pyridines?
Reaction between aldehydes and H2S
What do pentyl pyridines do?
They are reactive and remove other aroma molecules
