Non‐enzymic browning: The role of unsaturated carbonyl compounds as intermediates and of so 2 as an inhibitor of browning

The browning potentialities of a number of carbonyl compounds has been examined. From the results it is clear that most rapid browning with a reactive nitrogen function occurs with straight chain αβ‐unsaturated aldehydes. When the conjugated unsaturation is within a ring structure, as in the furfurals, chromophore development is slower. When the unsaturated centre is substituted, the browning rate is much reduced. Saturated carbonyl compounds are of relatively low browning potential. The retardation in the browning of carbonyl/amino systems caused by sulphites is due to combination of the sulphite both with the carbonyl group and with unsaturated centres. The latter reaction probably occurs by an ionic mechanism in the case of αβ‐unsaturated carbonyl compounds. Inactivation of sulphites as browning reaction inhibitors occurs through combination at sites of unsaturation to form sulphonates, which do not readily yield SO 2 on acid hydrolysis by the Monier‐Williams technique. This explains the loss of sulphites observed on storage of foodstuffs, and the observations that sulphite loss is not matched by concomitant equivalent sulphate development or loss of volatile sulphur, or by the formation of free sulphur.