Lynne Wong's PhD thesis

ange of 0.4 to 0.6, the Halsey model up to 0.4, the Caurie I, Caurie II and Oswin models
up to 0.6, and the modified GAB model up to 0.95; whereas the GAB, Hailwood-Horrobin
and Henderson models fit for the whole range of water activity data.
In addition to the above criteria for deciding whether a model is a good fit to the
experimental data, Chen and Morey (1989) and Soysal and Öztekin (1999) showed that the
residuals (i.e. measured EMC – predicted EMC) could be plotted against the predicted
EMC as abscissa. If the residuals were uniformly scattered about the x-axis (independent
variable) and showed no systematic distribution or clear pattern in the positive or negative
directions of the y-axis (dependent variable residuals), the model showed a good fit to the
experimental values.
The residual plots for the ten candidate isotherm models were plotted for the experimental
EMC data obtained for the nine cane components aged 52 and 36 weeks. A typical plot for
stalk fibre aged 52 weeks is shown in Fig 5.11. The whole series of 18 plots is on the CD
(file: Fig 5.11.1–5.11.18 Residuals.xls). In this study, the model residual plots have the
EMC residuals (measured EMC – predicted EMC) plotted on the y-axis and the predicted
EMC on the x-axis; other workers have used measured EMC (Arslan and Toğrul, 2005) on
the x-axis, and equilibrium relative humidity (Igathinathane et al., 2005) on the y-axis.
The use of either the predicted or the measured EMC on the x-axis has been checked, and
it was established that either practice did not affect the eventual randomness or pattern of
the residual plot.
All the residual plots are examined for randomness (R) or systematic pattern (S), and the
results are compiled in Table 5.28. In general, the Halsey and the two Caurie models give
the poorest fit to the experimental data; while the residuals of the Bradley, Smith and
Oswin models exhibit two distinct regions: at low water activity up to 0.97, a pattern is
evident, at high water activity from 0.97 to 0.98, the residual distribution does not have a
pattern, but the differences between the predicted EMC and the measured EMC are large,
particularly in the case of stalk pith, rind fibre aged 52 weeks, top fibre, dry fibre, green
leaf fibre aged 36 weeks and green leaf fines. However, these large differences are no
worse than those predicted by the GAB, Hailwood-Horrobin, modified GAB and
Henderson models. The residual patterns of these last four models for all the cane
components, except dry and green leaf fibre aged 36 weeks at 60 °C, showed a random
distribution for the whole range of water activity studied.
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