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Maillard (Non-Enzymatic) Browning
Beneficial Development of crust and flavor
when baking bread
Deleterious Discolorization of milk when
cooking
Series of reactions that begin with a
carbonyl group (e.g., sugar) and an
amino group (e.g., protein)
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Steps in Maillard Browning
Formation of an N-substituted glycosylamine
aldose or a ketose sugar reacts with aminogroup (requires open
chain structure of sugar)
rate is high at low moisture content
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Amadori and Heyns Rearrangement Reactions
(aldoseamine ketoseamine, vise versa)
Amadori involves protonation of N at carbon 1 Heynes involes
protonation of O at carbon 6
1,2-Enolization reactions
Formation of hydroxymethylfurfural (HMF), which takespart in a
series of degradation and condensation reactions
that result in melanoidins
Formation of osulose compounds that take part in the
Strecker Degradation reactions
Steps in Maillard Browning
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Strecker Degradation Reactions
Reaction between an osulose (dicarbonyl)compound with an amino
acid, gives rise to:
Aldehydes produced with 1 carbon less than
the parent amino acid (aroma of breads,peanuts, cocoa)
Carbon dioxide
Nitrogen containing cyclic compounds, which
condense and polymerize to form melanoidins
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A
scorbicA
cid Browning
Takes part in Strecker degradation,
leads to brown pigments
Used to inhibit enzymatic
browning
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Aldols andN-free polymers
Aldosesugar
+ Aminocompound
N-substituedglycosylamine
- H2O
Amadori rearrangement
1-amino-1-deoxy-2-ketose(Amadori products)
Schiff baseof HMF or furfural
+amino cpds
HMF or furfural
+ aminocpd
-2H +2H
Dehydroreductones
Fission products(acetol, diacetyl,
pyruvaldehyde, etc)
CO2+
aldehydes
Heterocyclic nitrogen compounds and brown color
+ aminocpds
withor withoutamino cpd
aldimines orketimines
+ aminocpd
+ H2O
+ aminocpd
+ -aminoacid
Streckerdegradation
aldiminesaldimines
reductones
Maillard Browning
Reactions
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Maillard Browning Stages
Initial stages
Reactions: Condensation, enolization,
Amadori rearrangement. With proteins,glucose and free amino
groups combine in
1:1 ratio
Properties: Reducing power in alkaline
solution increases. Storage of colorless 1:1glucose-protein
product produces browning
and insolubility
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Intermediate stages
Reactions: Sugar dehydration to 3-deoxyglucosone and its -
3, 4-ene, HMF, and 2-(hydroxyacetyl)furan; sugarfragmentation;
formation of alpha-dicarbonyl compounds,
reductones, pigments.
Properties: Addition of sulfite decolorizes; reducing power
in
acidic solution develops; pH decreases; sugars disappearfaster
than amino acids. With proteins, acid hydrolysis fails to
regenerate the sugar(D-glucose). Positive Elson-Morgan test
for amino sugars (Amadori compounds)
(buff yellow; strong absorption in near-ultraviolet range)
Maillard Browning Stages
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Final stages(red-brown and dark brown color)
Reactions: Aldol condesnations; polymerization; Strecker
degradation of alpha amino acids to aldehydes and
N-heterocyclics at elevated temperatures. Carbon dioxide
evolves
Properties: Acidity; caramel-like and roasted aromas
develop; colloidal and insoluble melanoidins form;fluorescence;
reductone reducing power in acid solution;
addition of sulfite does not decolorize
Maillard Browning Stages
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Factors Affecting the Maillard Reactions
Water content and water activity Formation of glycosylamine
favored at low
moisture content and low Aw
(e.g., dehydrated products)
Later reactions favored at high moisturecontent and Aw
Type of sugars and amino acids
pentoses > hexoses > reducing dissacharides,mannose >
galactose > glucose
short chain amino acids > long chain amino
acids, glycine is most reactive > lysine (free
amino groups)
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Factors Affecting the Maillard Reactions
Temperature
High temperature favors browning Low temperature retards
browning
Buffering Capacity Alkaline pH favors browning (recall
freezing
and dehydration and buffer precipitation)
Acidic pH prevents browning
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Methods to Control the Maillard Reactions
Keep temperature low
Keep moisture content low
Try to reduce pHRemove reactive compounds
remove sugars (glucose oxidase)
remove carbonyl groups
(NaHSO3)
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Effects of the Maillard Reactions in Food
Color
Pigments are produced
Flavor
Sweetness affected by loss of sugarTexture
Reaction of sugars with amino acids givetough texture in
dehydrated meat,
modification of protein interactionsNutrition
Loss of essential amino acids, loss ofcalories, loss of vitamin
C
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Inversion of sucrose to D-glucose and D-fructose
Equilibration of anomeric and ring forms
Condensation, intermolecular, i.e., acid-catalyzed
reversion of starch sugars to di-, tri-, and higher
oligosaccharides. Condensation, intramolecular, i.e., formation
of
glycosans and difructose dianhydrides.
Isomerization of aldoses to ketoses
Dehydration reactions
Fragmentation reactions
Browning (formation of unsaturated polymers)
Carmelization Reactions
