Six Main Ways to Inhibit Nonenzymic Browning

There are six main ways in which nonenzymic browning can be reduced or prevented  

Sulfur dioxide (see ref. 553) is frequently used, concentrations of up to 12,000 ppm (1.2%) being encountered, since it is more effective as the concentration is increased. Increased concentrations increase the time lag before browning starts, but, once it does, it proceeds at the normal rate. High concentrations should not be present in food products to be consumed, since even 30 ppm can at times be detected by taste. Dried fruits may contain up to 2000 ppm however, much would be expected to be lost in subsequent cooking. 

There are legal limits to the concentrations of sulfur dioxide that are permissible in consumables. Thus the EU stipulates limits for sulfur dioxide (E220),569 available from all sources (sulfites of various types, E221-224, 226-228), as illustrated by the following (mg kg-1 or mg L 1)  

Chemically, the obvious explanation for the use of sulfur dioxide is its reversible combinations with carbonyl intermediates of the browning reaction, but the substances that have been identified show that the situation is considerably more complex (see below). 

Lowering the pH is useful up to a point. It may favour the initiation of alternative mechanisms, but these tend to be less rapid. If the system contains ascorbic acid, then any measures taken to conserve vitamin C will help to prevent initiation of nonenzymic browning by its oxidation. Even the addition of extra ascorbic acid will prove useful for some time, but, once oxidised, browning will be worse than without it. 

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