Lynne Wong's PhD thesis

parts. Hence, the Brix-free water values determined by this method must have 1.12 units
added to correct for the residual moisture.
The nine cane components (dry leaf fibre and fines, green leaf fibre and fines, top fibre,
rind fibre and fines, and stalk fibre and pith) of triplicate cane samples of four cane
varieties (R 579, R 570, M 1557/70 and M 1400/86) aged 52, 44 and 36 weeks were
analysed in duplicate by the Brix-free water determination method devised. The Brix-free
water results obtained were analysed statistically.
The Brix-free water values (corrected for residual moisture) of the reconstituted cane stalk
of the four cane varieties aged 52 weeks were calculated, the average value is 16.03%,
which is much lower than the traditionally accepted value of 25% for Brix-free water of
cane stalk. For reconstituted dry leaf, green leaf and cane stalk, the Brix-free water values
do not vary much with age nor with variety. The reconstituted dry leaf, green leaf and
cane stalk of the four cane varieties each has an average of Brix-free water value of 15-
16%. If these values are taken together with the corresponding 15-16% Brix-free water
value of intact cane tops, it would mean that Brix-free water values of the different parts of
the sugar cane plant, i.e. dry leaf, green leaf, cane tops and cane stalk, are all about 15-
16%. Only those of fibres differ from those of fines or pith.
Equilibrium moisture content of the cane components of R 570 aged 52 and 36 weeks were
determined by a static method at 30, 45, 55 and 60 °C at water activity from 0.1 – 0.9. The
isotherms exhibit a type II sigmoid pattern. Of the 17 isotherm models fitted, the
Hailwood-Horrobin and GAB models describe best the sorption behaviour of the sugar
cane components.
Most authors divide the type II isotherm into three regions. The first low water activity
region (0 – 0.3) is indicative of strongly bound water, at the intermediate water activity
region (0.3 to 0.6 – 0.8), water molecules which are less firmly bound, and in the region of
high water activity (a w ≥ 0.6), excess water is present in larger voids and capillaries, and
essentially acts as bulk water.
Calculations were carried out to provide an insight in some properties of the sorbed water
and the sorbent. The number of monolayers varies from about 7 to 4, which is similar to
the number of hydration layers (5 or 6) estimated at the fibre saturation point in wood.
The heats of sorption of monolayer and multilayer have been calculated for the nine cane
components of R 570 aged 52 and 36 weeks. The heat of sorption of multilayer for each
27