1.1. Theory
The Gordon Taylor equation [1] (4) is primarily used to predict the effect of moisture content on the glass
transition point of a substance. In order to use this equation the moisture content of the material must also be known.
In most cases when a new juice is going to be produced, the moisture adsorption isotherm for the mixture, and often
even for the individual components, is not known. Thus, in order to proceed some gross approximations must be made. The approach taken here was to use known adsorption isotherms where they exist to predict the moisture
content associated with a particular component. If no adsorption isotherm could be found, then the adsorption
isotherm for amorphous lactose was used as a first approximation. The total moisture content was found by
summing all the moisture contents associated with each component, including those components thought not to have
a glass transition temperature, such as soluble fibre. In some cases equations relating the glass transition temperature
directly to the water activity of the component were found and in these cases these equations were used directly in