Chemistry of Non-Enzymic Browning. XI. The Reactions of Bisulphite with Reducing Sugars

Abstract

The reactions of reducing sugars with bisulphite have been studied at 100 °C and lower temperatures. Reducing sugars promoted the autoxidation of bisulphite to sulphur and sulphate, the ketoses being more effective than the aldoses. During the autoxidation the aldoses were oxidized, in part, to the corresponding aldonic acids. The ketose sugars reacted more rapidly and extensively than the aldoses, only 32 per cent. of unchanged fructose being recovered after 8 hr at 100 °C. Oxidation of the ketoses probably occurred via the osone and gave a complex mixture of keto acids. Ascorbic acid was converted to dehydroascorbic acid and an unidentified acid. The reactions offer possible explanations for the formation of sulphate and the loss of bisulphite observed during storage of foods treated with sulphur dioxide. An oxidative mechanism has been suggested for the inhibition of non-enzymic browning by sulphur dioxide.