BROWNING IN THERMALLY
PROCESSED FOODS: THE
MAILLARD REACTION
Food modifications during
thermal treatment (1)
• Protein denaturation
• Physical changes (starch
gelatinization, structural alterations
of cell wall, depolymerization of
dietary fibre)
• Lipid oxidation
• Degradation of some bioactive
components
Food modifications during
thermal treatment (2)
• Reaction between different
components generate new compounds.
• Proteins-sugar: Maillard reaction
formation of Advanced Glycosilation
End-products (AGEs)
• Lipid-protein: Advanced lipoxidation
end products (ALEs)
The same chemistry
The reaction is in both cases (sugars or
oxidised lipids) between a carbonyl
moiety and an amino group
The same products
The final product of both reaction
patways (AGEs and ALEs) are polymeric
brown macromolecules
The Maillard Reaction in Foods
 Produces aromas in heated
foods
 Responsible for colour
formation
(non-enzymatic browning)
 Maillard products have
antioxidant properties
•
•
Can cause loss of nutrients
Some products may be toxic
Temperatura e tempo di trattamento termico
Stadi iniziali
LATTE STERILIZZATO
BIRRA CHIARA
Stadi intermedi
PASTA
PRODOTTI DA FORNO
BIRRA SCURA
CACAO
CARNE ARROSTITA
CAFFE’
Stadi avanzati
Diminuzione dell’attività dell’acqua
LATTE UHT
Louis-Camille
Maillard
(1878 - 1936)
Photographed in
his laboratory
ca 1915
1912 – 1916:
He published 8 papers
on his observations of
colour changes on
mixing amino acids and
sugars.
No one else took much
interest in the
reaction until 1950s
John Hodge: 1914 -1996
• Chemist at USDA in Illinois (1941 – 1980)
• His proposed mechanism for the chemistry of
non-enzymic browning is largely unchanged
after 60 years.
Citations since 1970
Paper
Citations
Hodge, J. E.
Chemistry of browning reactions in model
systems.
J. Agric. Food Chem. 1953, 1: 928-943.
890
Maillard, L. C.
Action des acides amines sur les sucres:
formation des melanoidines par voie
methodique.
Compt. Rend. 1912, 154: 66-68.
634
Maillard-Hodge Reaction?
Hodge Scheme
Hodge J E. Dehydrated foods: chemistry of browning reactions in model systems.
J. Agric. Food Chem. 1:928-43, 1953.
First step: formation of Amadori
product
RNH
RNH
HC
+
CH
+H+
(HCOH)n
O
HC
CH2OH
Glicosilammina
N-sostituita
RNH
RNH
CH
CH2
COH
CO
-H+
(HCOH)n
HCOH
CH2OH
Catione della
base di Schiff
(HCOH)n
CH2OH
Forma enolica
del PA
(HCOH)n
CH2OH
1-ammino-1-deossi2-chetoso (PRA)
PRODOTTO DI
AMADORI
slow
fast
Formation of Carbonyl through Maillard Reaction
O
OH
OH
O
OH
H2O
 RNH2
fast
R N
H
2,3-enolisation
OH
OH
O
R N
H
O
O
OH
O
OH
OH
O
O
OH
1-deoxyosone
O
O
O
OH
OH
Amadori compound
OH
H+
1,2-enolisation
slow
OH
OH
OH
OH
R
OH
H2O
 RNH2
- H2O
R N
H
O
H2O
N+
H
OH
O
OH
3-deoxyosone
O
CHO
Strecker Degradation
Free amino acids with dicarbonyl compounds
R-CHO
Aldeide di Strecker
Flavour and Colour in the
Maillard Reaction
OH
OH
O
H
OH
OH
+
R NH2
OH
H 2O
H
OH OH
amino
compound
O
Amadori intermediate
 H 2O
 RNH2
O
O
FLAVOUR
COMPOUNDS
NHR
rearrangement
OH
reducing sugar
OH
O
H
O
O
MELANOIDIN
PIGMENTS
O
O
O
CHO
OH
HO
amino
Aminoacids
acid
or
proteins
OH
O
O
OH
O
O
carbonyl compounds
CHO
General scheme of MR browning
Amine
Melanoidins
Brown colour
Ammonia
Phospholipids
Amino acids
Proteins
HEAT
Carbonyl
Aldehydes
Ketones
Reducing sugars
Polysaccharides
Oxidised lipids
Amides
Acrylamide
Amino Carbonyl
Interaction
(Amadori product)
Furans, Pyrroles,
Thiopenes, Thiazoles,
Oxazoles, Imidazoles,
Pyridines, Pyrazines
Food “melanoproteins”
R
O
HO
CHO
O
O
OH
R
N
R
Lysine
O
H
N
N
H
R
O
R'
R'
N
H
N
O
H
N
O
R'
O
H
N
N
H
HO
R'
O
H2N
O
N
O
N
H
R'
O
H
N
H
N
N
H
O
N
CH3
OH
O
CH3
Protein A
R'
+
N
N
H
N
R
N
O
R
R
O
O
N
N
R'
O
R'
R'
O
N
N
O
R'
N
N
O
O
N
N
O
R'
N
N
O
O
R'
R'
N
O
R'
O
R'
Protein B
Pronyl-lysine
This compound is formed on the lateral chain
of Lysine residues
Pronyl-lysine has a high antioxidant activity
Possible toxicants
•
•
•
•
•
Acrylamide
Furan
Heterocyclic amines
3-MPCD (Mono Chloro Propan Diol)
3-Methyl Imidazolone
Development of mitigation strategies to
reduce their concentration
A network of many reactions
giving thousands of products
Products formed depends on:
• Chemical nature of the reactants
• Time and temperature of heating
• Technological conditions
• Water activity, pH
Practice
Effects of reactants:
Sodium Carbonate (pH effects)
Protein and carbohydrates
Water activity (fibre addition)
Butter clarification
Control
Added with sodium bicarbonate