Two major types of non-enzymatic browning reactions. • Caramelization. •
Maillard browning. Louis Camille Maillard (1878-1936) ...
Nonenzymatic Browning
w/ sugar
w/o sugar
Two major types of non-enzymatic browning reactions • Caramelization • Maillard browning
Louis Camille Maillard (1878-1936)
Reactions during caramelization • Anomeric equilibration (alpha, beta) • Pyran, furan equilibration • Sucrose inversion – Hydrolysis
• • • • •
Aldose, ketose interconversions Inter- and intramolecular condensation Dehydration Skeletal fragmentation Browning
Caramelization • Flavoring caramelization buffer Sucrose syrup heat
Inversion, fragmentation (maltol, etc.)
Caramelization • Caramel pigments Glucose syrups
Partially neutralized pH 4
heat
Caramel Colloids
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
Amadori rearrangement
Maillard reaction (slide 161)
Glycosylamine formation Glycosylamine Formation
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Amadori rearrangement Amadori Rearrangement
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Decomposition of the Amadori compound (slide 162)
Control point
Strecker degradation
Requires dicarbonyls and amino acids Nutritional loss of amino acids (especially L-lysine) Pyrazines -- flavor compounds
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
.. NH2
O CH +
Under acidic conditions
H+
.. NH2
OCH +
No reaction is possible with the nitrogen lone pair as it is already reacting with the hydrogen ion
Maillard browning reaction variables • Water 0%, min
30%, max %water
100%, min
Maillard browning reaction variables • 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).
Maillard browning reaction variables Sugar Glucose Fructose Galactose Xylose Arabinose Ribose
Open chain Melanoidin 1 1 -1.2 3.4 2.0 7.1 5.5 7.1 6.7 354 Very high
A practical example of the effect of Maillard browning in cookies
Image courtesy of Oreg. St. Univ. (www.orst.edu/food-resource/ information/maillard/nancy.html)
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
Control of browning • 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 Lactobaccilus 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 O R
O H HMF HSO 3
H m e la n o id in p ig m e n ts
R
O O
SO3
-
H sta b le -w ill n o t p ro ce e d to fo rm p ig m e n ts
Maillard overview (page 169) Control point Pigment Aromas
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
Why worry about Maillard browning? • 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 Llysine in cereals.
Reason for the reactivity of L-lysine O
Reactive epsilon amino
O
H3C OH
H2N OH
NH2 L-alanine
Alpha amino
NH2 L-lysine
Glucose and lysine
Why worry about Maillard browning? • 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.
