Nonenzymatic Browning

Transcription

1 Nonenzymatic 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 Inter- and intramolecular condensation Dehydration Skeletal fragmentation Browning 1

2 Caramelization Flavoring caramelization buffer Sucrose syrup Inversion, fragmentation ti heat (maltol, etc.) Caramelization Caramel pigments Glucose Partially heat Caramel syrups neutralized Colloids ph 4 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 Pepsi A disaster-see the marketing section of the Wikipedia entry 2

3 Maillard reaction (slide 158) nt Amadori rearrangemen Decomposition of the Amadori compound (slide 159) Control point Strecker degradation Requires dicarbonyls and amino acids Nutritional loss of amino acids (especially L-lysine) Pyrazines -- flavor compounds 3

4 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.. NH 2 - CH + Under acidic conditions H NH 2 CH + No reaction is possible with the nitrogen lone pair as it is already reacting with the hydrogen ion 4

5 Maillard browning reaction variables Water 0%, min 30%, max 100%, min %water Maillard browning reaction variables xygen Seems to have little effect Metal ions Cu(I), Cu(II) and Fe(II), Fe(III) speed up the reaction. ther metals seems to have little effect. Can control the with metal chelators (e.g., EDTA). Maillard browning reaction variables Sugar pen chain Melanoidin Glucose 1 1 Fructose Galactose Xylose Arabinose Ribose 354 Very high 5

6 A practical example of the effect of Maillard browning in cookies Image courtesy of reg. St. Univ. ( 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. 6

7 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 R H HMF - HS 3 melanoidin pigments R H - S 3 H stable-- will not proceed to form pigments Maillard overview (page 166) Control point Pigment Aromas 7

8 Why worry about Maillard browning? Aesthetics verly 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 L- lysine in cereals. Reason for the reactivity of L-lysine H 3C H Reactive epsilon amino N H 2 H NH 2 L-alanine Alpha amino L-lysine NH 2 8

9 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. 9