Combination of sulphur dioxide with concentrated orange juice. II.—The rate of the reaction

Abstract

Abstract The rate of combination of SO 2 with glucose, with acetaldehyde, with mixtures of the two and with heated glucose solutions has been compared with the rate of combination with orange juice. The velocities of combination and of breakdown of the bisulphite compounds formed can be accounted for by reactions observed in pure solutions (although the exact nature of the aldehydic compounds remains to be elucidated), at any rate as far as concerns the changes in the first few hours. Glucose and the other aldehydes behave in asimilar way towards SO 2 , the differences being merely of degree; thus they all combine more rapidly (but less completely) at higher temperatures, and more rapidly (but to about the same extent) at higher p H 's. These general trends are discernible withconcentrated orange juices, but they cannot be properly demonstrated till better methods for determining free SO 2 in such jiices are available. There remain much slower changes, extending sometimes over several days, which are characterized by high degrees of combination, variability from jiice to juice, by fluctuation, even of free SO 2 in an individual jiice and by inversion of the temperature‐effect; these changes take place even at tmperatures where breakdown of the juice seems unlikely, and their nature and duration cannot apparently be explained simply by reactions of aldehydes etc.; their cause remains to be discovered. It is noted, finally, that the nature and quantity of any active aldehydes may be greatly modified by heat‐processing of the jiice, and that combination of SO 2 with such substances might well interfere with browning reaction. The possibility of delaying combination by acidification is also envisaged.