Lynne Wong's PhD thesis

Table 5.28. Classification of residual plots for various isotherm models applied to the nine cane
components of R 570 aged 52 and 36 weeks.
Stalk
fibre
Stalk pith
Rind
fibre
Rind
fines
Top fibre Dry leaf fibre
Dry leaf
fines
Green leaf
fibre
Green leaf fines
Isotherm model 52 36 52 36 52 36 52 36 52 36 52 36 52 36 52 36 52 36
GAB R R R R R R R R R R R R R R R R R R
Hailwood Horrobin R R R R R R R R R R R R R R R R R R
Henderson R R S S R R R R S S S R S S S R S S
Bradley R R R R R R R R R R S R R R R R S R
Caurie I S S S S S S S S S S S R S S S S S S
Smith R R R R R R R R R R R R R R R R R R
Oswin R R R R S R S R S R R R S R S R S R
Halsey S S S S S S S S S S S R S S S S S R
Caurie II S S S S S S S S S S S S S S S S S S
Modified GAB R R R R R R R R R R R R R R R R R R
R = random, S = systematic
For the four remaining models, a comparison of the performance parameters R 2 , P and E s
listed in Tables 5.19 – 5.27 showed that, in general, the GAB, Hailwood-Horrobin and
modified GAB models all yield comparable R 2 values, however, the modified GAB model
gave a slightly lower value of P and E s than the Hailwood-Horrobin, GAB and Henderson
models, in that order. Hence, it has been shown that the modified GAB model provides an
acceptable description of the isotherms of sugar cane component parts in the range of water
activity and temperature studied, with only the exception mentioned above, with GAB and
Hailwood-Horrobin models rank a close second followed by Henderson models. It is to be
noted that none of the models studied gave a satisfactory fit to the data obtained at 60 °C
for dry leaf fibre and green leaf fibre, both aged 36 weeks. This is due to the data obtained
as seen in Fig 5.9, both components gave isotherms which were in general less steep than
those of the other cane components.
The experimental EMC data of the nine cane components aged 52 weeks were compared
with the data predicted by the modified GAB, Hailwood-Horrobin and GAB models (see
Figs 5.12 – 5.14). Although the modified GAB model was found best to describe the
isotherms of the sugar cane component parts at temperatures of 30, 45, 55 and 60 °C, it did
not extend beyond water activity of 0.95, whereas the other two did, up to a water activity
of one. So, in conclusion, the models which best describe the sorption characteristics of
the sugar cane component parts are the Hailwood-Horrobin and the GAB isotherms.
In contrast, as mentioned in Section 5.4.1, Han and Wu (2004) found that Nelson’s
sorption isotherm model was a good fit for their experimental adsorption data of sugar cane
rind. As Nelson’s model involves desorption which was not performed on samples
investigated, comparison could not be made.
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