NON ENZYMATIC
BROWNING
Two Major Types Of
Non-Enzymatic Browning Reactions
• Caramelization
• Maillard browning
Reactions During Caramelization
• Anomeric equilibration (alpha, beta)
• Pyran, furan equilibration
• Sucrose inversion – Hydrolysis
• Aldose, ketose interconversions
pyran furan
• Inter- and intramolecular condensation
• Dehydration
• Skeletal fragmentation
• Browning
CARAMELIZATION
Flavoring Caramelization
buffer
sucrose syrup inversion, fragmentation
heat
(maltol, etc)
CARAMELIZATION
Caramel pigments
• Glucose Partially Heat Caramel
syrup neutralized colloid
pH
• Used to color colas. They are not naturally brown but have these
pigments added to color them.
CLEAR COLAS
• See the Wikipedia entry on Pepsi Crystal here
http://en.wikipedia.org/wiki/Crystal_Pepsi
• A disaster-see the marketing section
of the Wikipedia entry
MAILLARD REACTION
Amadori compounds
• Partial stability in comparison with imines (the cyclic molecular structures)
• Amadori rearrangement leads to furanose (hemiacetal) - has stability to mutarotation
• React further with second sugar molecule → glycosylamine formation + conversion to di-D-
ketosylamino acids (“diketose amino acids”) by an Amadori rearrangement
• Amadori products: intermediates formed in the course of the Maillard reaction. Eg.
Deoxyosones
• As an analytical indicator of the extent of the heat treatment of food.
• Amadori compounds are degraded to (1-, 3-, and 4-deoxydicarbonyl compounds /deoxyosones)
in the pH range 4–7
• - Vary concentration - depends on the reaction conditions (pH value, temperature, time, type
and concentration of the educts) → change in the product spectrum (Eg. color, taste, odor)
Degradation of Amadori compounds
Strecker Reaction
α-dicarbonyl compounds (Eg. Deoxyosones) + amino acids
↓
Strecker aldehydes (aroma potential) + CO2 + α-aminoketones
• Occurs in foods at higher concentrations of free amino acids or drastic reaction
conditions (Eg. higher temperatures, under pressure)
• Strecker aldehydes: methional, phenylacetaldehyde, 3- and 2-methylbutanal and
methylpropanal
• Other compounds formed via the Strecker degradation and influence the aroma of
food: H2S, NH3, 1-pyrroline and cysteamine
MAILLARD BROWNING REACTION VARIABLES
Temperature
• Generally, the higher the temperature, the greater the browning
pH
• As pH goes down, so does browning. Due to protonation of the
reactive amino group, making it unreactive.
UNDER NEAR NEUTRAL CONDITIONS
UNDER ACIDIC CONDITIONS
CONT..
• Water
CONT..
Oxygen
• Seems to have little effect
Metal ions
• Cu(I), Cu(II) and Fe(II), Fe(III) speed up the reaction.
• Other metals seems to have little effect.
• Can control the with metal chelators (e.g., EDTA).
Sugar Open chain Melanoidin
Glucose 1 1
Fructose - 1.2
Galactose 3.4 2.0
Xylose 7.1 5.5
Arabinose 7.1 6.7
Ribose 354 Very high
A PRACTICAL EXAMPLE OF THE EFFECT OF
MAILLARD BROWNING IN COOKIES
CONTROL OF BROWNING
• Create unfavorable conditions for the reactions to
take place
Water → low or high
pH → lower, decreases browning
Temperature→ the lower the temperature, the less
the browning
CONT..
Removal of substrates
• Glucose oxidase→ removes the open chain form by converting it to
gluconic acid.This technology is used in preserving dried egg whites.
• Ribose oxidase→ this enzyme activity occurs in Lactobacillus
pentoaceticum and is used to prevent fish from browning.
SULFITE BROWNING INHIBITORS
• Principally sulfur dioxide or bisulfite.
• These sulfur compounds react with HMF near the end of
the decomposition of the Amadori compound and divert
it to a non-reactive product, that is one that cannot be
converted into melanoidin pigments.
SULFITE INHIBITOR REACTION
WHY WORRY ABOUT MAILLARD BROWNING
Aesthetics
• Overly browned foods are not aesthetically attractive and may
not be accepted
• Also, due to the pyrazines produced by the Strecker
degradation, these highly browned foods may have odd, off
flavors and also not be accepted
CONT..
Nutritional effects
• Amino acids that participate in the Maillard reactions are lost from a
nutritional point of view.
• This may be especially important where the amino acid is very
reactive and in foods where it is already in very low concentration.
• This would be the case for L- lysine in cereals.
REASON FOR THE REACTIVITY OF L-LYSINE
CONT..
Mutagenicity
• This is not yet settled in the literature. Some researchers find
mutagenic products in browned model systems, others do not.
• But there is still the possibility that highly browned food may
contain potential mutagens.
