Combination of sulphur dioxide with concentrated orange juice. I.—Equilibrium states

Substances present in concentrated orange juice that are likely to combine with SO 2 are surveyed, and the more important are tested in pure solutions. They are shown to be, in order of importance, glucose, unidentified aldehydes or ketones, pectin, perhaps also breakdown products of pectin, e.g . arabinose. The behaviour of these substances, in equilibrium with SO 2 , is compared with that of orange juice in similar circumstances. The increased combination of SO 2 with glucose, as the concentration of glucose increases, is paralleled by a greater combination with concentrated than with dilute juices. At all concentrations, however, there is a greater combining‐power than can be accounted for by the sugar content of the juice. From comparison with heated glucose solutions, it is suggested that this is due to the presence of traces of aldehyde‐ and ketone‐like substances, some of which may have been present in the juice originally and survived processing; most, it is suggested, are formed by reaction between sugars and acids in the concentrated juice during the heat‐treatment. Because of the presence of these traces of strongly‐combining substances, the proportion of SO 2 combining is not, as in pure glucose solutions, independent of the quantity added, but is variable; this combination is almost complete with small quantities of SO 2 , but with large additions of SO 2 it decreases towards the level corresponding to the glucose content. The combining‐power of glucose and aldehydes falls if their solutions are warmed, and the same happens with heated sugar solutions. With concentrated juices, on the other hand, complicating factors apparently interfere, and the ultimate degree of combination increases with temperature. This paper deals only with equilibrium states; consideration of kinetics will follow in a second paper.