FC Browning reactions 2013

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FC Browning reactions
Ulf Svanberg
Food Chemistry 2013
MSc Program in Food Technology
Faculty of Chemical Engineering, UEM
 Browning reactions
 Non-enzymatic browning
 Maillard reaction
• reactants
• mechanism
• low molecular products
• melanoids
 Ascorbic acid oxidation
 Inhibition
Ulf Svanberg
Enzymatic
Phenolase-browning
Non-enzymatic
Maillard reaction
Caramelization
Ascorbic acid oxidation
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Desirable
Undesirable
Aroma
Anti-oxidants
Colour Anti-microbial
Taste
Burned taste
Nutrient loss
Toxicity
Miscolouring
Mechanisms for browning reactions
Ulf Svanberg
Mechanism Requires 
oxygen 
Requires 
amino group 
PH optimum 
Maillard - + Neutral to alkaline 
Caramelization - - Acid and alkaline 
Asc. oxidation + - Slightly acid 
Phenolase + - Slightly acid 
 
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What affects the Maillard reaction?
Ulf Svanberg
Maillard products
Time (storage) Temperature 
Fe/Cu pH 
aw Reactants 
The Maillard reaction
Ulf Svanberg
 Reactants:
Reducing sugars + amino acids/proteins
glucose, (fructose), maltose, lactose;
Lys, Arg (with NH2 in the side chain)
 Reaction conditions:
high temperature
water activity 0.5 - 0.8
pH - optimal between 6 - 8
prolonged storage
 Similar to the reaction with monosaccharides in weak
acid/basic environment. Amino acids (N-) catalyses the reaction
faster at lower temp.
Initial formation of N-glycoside
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The Maillard reaction
Ulf Svanberg
 Condensation – amine/carbonyl
 Rearrangement – enolization
 Fragmentation
 Strecker degradation
 Polymerization – brown color
Steps in the Maillard reaction
First reaction steps in the Maillard reaction
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Amadori
compound
Formation of Amadori compound
 Present in e.g. dried fruit and dried milk 
(reaction with lysine and lactose)
Source: Coultate p. 34, Figure 2.13
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…cont.
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Formation of an Amadori compound during storage 
of skim-milk powder
 Lysin no longer available for absorption in humans
 70% of lysin reacted in a mixture of
glucose and casein during storage for 5 days
at 37oC; cp. storage of milk in the tropics
Source: Coultate p. 39, Figure 2.17
N-containing polymers Brown colour
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Simplified scheme of the Maillard reaction
pH<7.0 pH>7.0
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Reactions with Amadori compounds,
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Hydroxymethyl furfural
…isomaltol


-dicarbonyl
…maltol
Diacetyl and acetol
(aroma compounds) 
 Flavour and aroma compounds in bread
Source: Coultate p. 35, Figure 2.14
…and -dicarbonyl – The Strecker degradation
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Strecker aldehyde -
derived from valine
…and condensation into a pyrazine (aroma compound)
e.g. chocolate and roast meat
Source: Coultate p. 37, Figure 2.15
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Amadori products in dried carrots
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Increase of Amadori compounds in two stage air drying of carrots as 
influenced by carrot moisture content. 
(— 10, 20, 30 min at 110°C; and then at --- 60°C; 
Sensory assessment: 1) detection threshold, 2) quality limit.
Source: Belitz et al. p. 289, Figure 4.10 (adopted from Waller 
and Feather (1983) in “Maillard reaction in foods and nutrition”)
Strecker degradation of Ascorbic acid
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 Formed in e.g. fruit juices
Brown
pigments
Red 
colour
Sorbamic acid
See Belitz et al. p. 425.
Cp. Ascorbic acid
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Formation of Acrylamide
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Where Z is,
-CH2CONH2 (side chain in Asn)
-CH2CH2SCH3 (side chain in Met)
Acrylamide formation at temp. of
140 - 180oC.
Cp. potato – high content of
free Asn + free glucose.
with Asn
with Met
z
Source: Mottram et al. (2002) Nature vol. 419:448 and 
Stadler et al. (2002) Nature vol. 419:449.
See Coultate pp. 44-47.
Acrylamide formation from Asn and Glucose
Ulf SvanbergSource: Coultate p. 47, Figure 2.18
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Formation of mutagenic compounds
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 Formation at rel. low temp. in grilled beef- and fish meat
Mutagenic compounds
IQ – Imidoazo-Quinoline
MeIQ – MethylImidoazo-
Quinoline
MeIQx - MethylImidoazo-
Quinoxaline
Reactants: 
Intermediate products in the Maillard reaction, 
creatinine and amino acids (see also Proteins in foods)
pyrazine
pyridine
creatinine
See: Fennema, pp. 774-776 and Belitz, pp. 24-29
How to control the Maillard reaction?
Ulf Svanberg
Maillard products
Dilution with waterLower temp 
Sulfite
Lower pH 
Lower aw 
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Inhibition of the Maillard reaction with sulfite
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 Sulfite reacts with carbonyl groups to colourless compounds
and inhibits further reactions with carbonyl groups in the 
Maillard reaction
Colourless
Colourless