Non-enzymatic browning
The Maiilard Reaction

First reported by Louis Camille Maillard in 1911.
Not a single reaction. Complex series in all foods containing carbonyl groups and free amino groups.
Reaction products contribute colors, flavors and odors to foods (both desirable and underisrable).
May reduce availability of essential amino acids such as lysine
May reduce absorption of zinc.

Reaction steps.

Formation of glucosamines
Amadori reaarangement - ketosamine formation
Diketose amine formation
Degradation
Polymerization.

Step 1

The same reaction can be drawn with the sugar in the ring structure as:

Step 2

The next step results in the rearrangement of the aldose to form a ketose and is known as an Amadori Rearrangement.

Drawn in the ring form:

Step 3

Step 4

2,3 enol Deoxyhexosone Fructose Glycine

Results of non enzymatic Browning

Loss of essential amino acids (lysine, agrinine, histidine)
Formation of possibly mutagenic products.

Little browning at 100% RH
Maximum browning at 30% RH
Less browning at pH below 6.0
Greatest reation rate between pH 7.8 - 9.2

Effect of sugar D-xylose> L arabinose> hexoses> dissacharides
Proportional to open chain form of sugar.

Prevention

Decrease pH to belwo 6.0
Decrease temperature
Lower water activity
Remove reducing sugars
Remove Cu++ and Fe +++
Chemical inhibition, sulfites and bisulfites

Types of products:

Oxole		Furan (Oxozole)		Thiazole
Imidazole		Pyrrolidine		Thiophene (Thiole)
Trithiolane		Pyrimidine		Pyrazine