Lynne Wong's PhD thesis

where m is the equilibrium moisture content (% dry solid), m o is the monolayer moisture
content (% dry solid), a w is the water activity, b in the Caurie I equation is the density of
the bound water, and b in the modified BET equation is a constant.
The monolayer moisture content, m o , of each of these models was determined by fitting the
experimental EMC data to these sorption equations (see Section 5.6.4.4). Tables 5.19 –
5.27 show the m o values for the nine cane component parts of R 570 aged 52 and 36 weeks.
For stalk fibre aged 52 weeks, the m o values at 30, 45, 55 and 60 °C calculated from the
GAB model decrease from 5.43, 5.18, 3.68 to 3.22 g/100 g dry fibre, and with stalk fibre
aged 36 weeks, the respective values were 4.17, 3.99, 3.54 and 4.00 g/100 g dry fibre. In
general, the m o values determined from the GAB equation range from 3 – 5, whereas those
from the Caurie I are less than one, and those from the modified BET model were between
2 and 3.
The change of m o values with temperature is best illustrated in Figs 6.1 to 6.3 for the GAB,
Caurie I and modified BET models respectively. In general, the m o values of the GAB and
Caurie I models tend to decrease with increased temperature while that of the modified
BET tend to do the opposite. The decrease in monolayer moisture content with increase in
temperature at a given water activity can be explained by considering the structural
changes in the fibres of the sugar cane components at increased temperatures. The degree
of hydrogen bonding in such materials is reduced with increased temperature, thereby
decreasing the availability of active sites for water binding and thus, the monolayer
moisture content (Westgate et al., 1992).
As described in Section 5.6.4.5, the calculated EMC for reconstituted R 570 cane stalk, dry
leaf and green leaf aged 52 weeks and 36 weeks (Tables 5.29 to 5.32), were fitted to the
Caurie I sorption model by linear regression with Microsoft Excel software, and to the
modified BET model by the non-linear regression procedure of SigmaPlot (SPSS Inc.).
The values of the isotherm parameters, together with the calculated regression coefficient
of determination R 2 , the mean deviation modulus P, and the standard error of the estimate
E s , are shown in Table 6.1.
The magnitudes of R 2 , P and E s for reconstituted cane stalk, dry leaf and green leaf were
similar to those for the nine cane component parts, therefore, the previous conclusion that
the Caurie I and modified BET models do not fit the data adequately also applies to
reconstituted cane stalk, dry leaf and green leaf.
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