Lynne Wong's PhD thesis

dissolved and hydrated waters, and which is normally greater than the Brix-free water
value as determined in this work.
The water sorption characteristics of the various cane component parts were further
investigated by making measurements to determine the equilibrium moisture contents at
various water activity values. These data were used to construct adsorption isotherms.
These were fitted to 17 existing isotherm models, of which two, namely, the Hailwood-
Horrobin and Guggenheim-Anderson-de Boer models, gave the best fit.
The sorbed water was subsequently characterised in terms of various parameters, namely,
the monolayer moisture content, the number of adsorbed monolayers, the percentage of
bound water, the total surface area for hydrophilic binding, the heats of sorption of the
monolayer and multilayers, the net and total isosteric heats of sorption and the entropy of
sorption.
From the monolayer moisture content and the amount of “hydrated water” as calculated
from the Hailwood-Horrobin model, it is clear that at EMC values between 0 and 5% (a w =
0 – 0.3), the non-freezable water is tightly bound to the surface of the fibre. The second
region starts at EMC values from 5% to 10 – 15% (a w = 0.3 to 0.6 – 0.8) depending on the
cane components, and the bound water in this region is termed the freezable water. The
third type of water is essentially free water, it exists after the second region and ends at
EMC values of about 25%. From this study, it is apparent that the Brix-free water as
measured in this work measures the amount of water bound in the first two regions.
(iii)