Lynne Wong's PhD thesis
Lynne Wong's PhD thesis Lynne Wong's PhD thesis
In this work the model which best described the experimental data was determined in order to extract thermodynamic parameters that provide information on the bound water content. 5.3.4 Fitting of sorption data to adsorption isotherm models The criteria adopted to evaluate whether the isotherm model used was a good fit of the experimental data were: 1) the coefficient of determination, R 2 , 2) the mean relative deviation modulus P, and 3) the standard error of the estimate, E s . n 100 The mean relative deviation modulus P is defined as: P = ∑ N n = 1 m − mˆ m and E s is given by: E s = ∑ ( m − df mˆ ) 2 where m and mˆ are the measured and predicted EMC (on a dry basis), N is the number of data points and df is the number of degrees of freedom which equals N minus the number of parameters. The criteria for accepting the fit of a model to the experimental data are that R 2 should approach 1 and that the value of E s should be as small as possible. In addition if P is ≤ 5, the fit is considered to be excellent. If 5 ≤ P ≤ 10, the fit is considered reasonably good, but if P > 10, the fit is deemed poor (Lomauro et al., 1985). In addition, Chen and Morey (1989) showed that the residuals (i.e. measured EMC – predicted EMC) can be plotted against the predicted moisture content, and the plots evaluated visually for randomness or pattern. If the plots have a clear pattern, the model is not accepted. In the present study, the above criteria were adopted to decide whether a model is a good fit of the experimental data. 5.4 PREVIOUS RESEARCH PERFORMED TO MEASURE MOISTURE SORPTION ISOTHERMS ON SUGAR CANE FIBRE AND SOME WOODY FIBRES While work on the determination of adsorption isotherms of cane fibre is relatively rare, the literature abounds with adsorption studies on fruits such as apple (Prothon and Ahrné, 2004) and pineapple (Hossain et al., 2001); on foodstuff, e.g. macaroni (Arslan and Toğrul, 2005), semolina (Erbas et al., 2005) and alligator meat (Lopes Filho et al., 2002); 179
and on agricultural products such as potatoes (McMinn and Magee, 2003; McLaughlin and Magee, 1998), starch (Al-Muhtaseb et al., 2004a) and cowpea (Ayranci and Duman, 2005). Fibres from eucalyptus (Moreira et al., 2001) and fibres from flax, hemp and reed canary grass (Nilsson et al., 2005) have also been the subjects of study. The above list is by no means exhaustive; many more publications exist on other materials. 5.4.1 Sugar cane fibre One of the few works on the determination of adsorption isotherms involving cane fibre dates back to the late 1950s, when Kelly (1957) studied the water adsorption of sugar cane fibre in an atmosphere of constant water vapour pressure provided by sulfuric acid solutions of appropriate concentrations at two temperatures. Sugar cane fibre samples after fibration were washed free of sucrose and other water-soluble materials. The dry samples were then exposed to an atmosphere of constant water vapour pressure in a desiccator placed in a thermostatically-controlled oven for at least 40 hours. After which period, it was assumed that the condition of equilibrium had been reached. The tests were carried out at 27.2 °C and 51.0 °C. Approximately one gram of fibre was spread as a thin layer on a flat silica dish and allowed to remain in the prepared atmosphere for the required time. To determine the equilibrium moisture content, the sample was quickly transferred to a stoppered weighing bottle and weighed after cooling before and after drying to constant mass at 105 °C. The technique was found to operate satisfactorily even when the samples were in an atmosphere of 100% humidity, when water was the air-conditioning reagent. He estimated a value of 35% Brix-free water at 100% relative humidity. When the log of adsorbed water per 100 g dry fibre was plotted as ordinate against the log of water vapour pressure as abscissa, for each temperature, there exist two equilibrium conditions for which straight lines obeying a Freundlich type of equation were shown above and below a transition point occurring at an EMC value of 14.5% of fibre (Fig 5.2). 180
- Page 181 and 182: Table 4.7. Results of the repeat de
- Page 183 and 184: The experiment was repeated with th
- Page 185 and 186: e any residual moisture in the samp
- Page 187 and 188: By means of the same technique, Won
- Page 189 and 190: was still hot. Since the filter was
- Page 191 and 192: value determined could be corrected
- Page 193 and 194: Qin and White’s finding was confi
- Page 195 and 196: A sample size of 3.5 g with 75 g co
- Page 197 and 198: Figure 4.4. Fibre samples drying in
- Page 199 and 200: - One large fibre sample (rind) of
- Page 201 and 202: Table 4.18. Brix-free water values/
- Page 203 and 204: Table 4.20. Brix-free water values/
- Page 205 and 206: 4.7.3 Statistical analysis It is es
- Page 207 and 208: Table 4.23. Analysis of variance (B
- Page 209 and 210: pointing out that at 52 weeks old,
- Page 211 and 212: The crop of R 570 sampled in 2001 w
- Page 213 and 214: 4.7.4. Estimated Brix-free water co
- Page 215 and 216: The main difference in the two sets
- Page 217 and 218: Table 4.27. Predicted Brix-free wat
- Page 219 and 220: 4.8 SUMMARY AND CONCLUSIONS An anal
- Page 221 and 222: component parts, and verify the Bri
- Page 223 and 224: 3) Thermodynamic, water in equilibr
- Page 225 and 226: Langmuir (1916, 1917, 1918) propose
- Page 227 and 228: to determine the moisture sorption
- Page 229 and 230: Table 5.1. Some commonly used isoth
- Page 231: Lomauro et al. (1985) found that wi
- Page 235 and 236: Bruijn (1963) studied the mass incr
- Page 237 and 238: After measuring the EMC of dry corn
- Page 239 and 240: approached, that is, either by adso
- Page 241 and 242: Table 5.4. Water activity (a w ) of
- Page 243 and 244: 5.6.3 Procedure to determine equili
- Page 245 and 246: 5.6.4 Results and discussion An exa
- Page 247 and 248: Table 5.8. Equilibrium moisture con
- Page 249 and 250: Table 5.10. Equilibrium moisture co
- Page 251 and 252: Table 5.12. Equilibrium moisture co
- Page 253 and 254: 30 o C 45 o C 55 o C 60 o C Water w
- Page 255 and 256: m/m of 96% activity, a w (g/100g dr
- Page 257 and 258: vaporisation generally decreases fr
- Page 259 and 260: 30 o C isotherm 45 o C isotherm 55
- Page 261 and 262: 4 0 Stalk fibre 5 0 Stalk pith 5 0
- Page 263 and 264: 5.6.4.4 Fitting of sorption models
- Page 265 and 266: Table 5.19. Parameters of the sorpt
- Page 267 and 268: Table 5.21. Parameters of the sorpt
- Page 269 and 270: Table 5.23. Parameters of the sorpt
- Page 271 and 272: Table 5.25. Parameters of the sorpt
- Page 273 and 274: Table 5.27. Parameters of the sorpt
- Page 275 and 276: Modified GAB Kuhn Iglesias - Chirif
- Page 277 and 278: Table 5.28. Classification of resid
- Page 279 and 280: Stalk fibre Stalk pith Rind fibre 4
- Page 281 and 282: 5.6.4.5 Calculated EMC values of re
and on agricultural products such as potatoes (McMinn and Magee, 2003; McLaughlin and<br />
Magee, 1998), starch (Al-Muhtaseb et al., 2004a) and cowpea (Ayranci and Duman, 2005).<br />
Fibres from eucalyptus (Moreira et al., 2001) and fibres from flax, hemp and reed canary<br />
grass (Nilsson et al., 2005) have also been the subjects of study. The above list is by no<br />
means exhaustive; many more publications exist on other materials.<br />
5.4.1 Sugar cane fibre<br />
One of the few works on the determination of adsorption isotherms involving cane fibre<br />
dates back to the late 1950s, when Kelly (1957) studied the water adsorption of sugar cane<br />
fibre in an atmosphere of constant water vapour pressure provided by sulfuric acid<br />
solutions of appropriate concentrations at two temperatures. Sugar cane fibre samples after<br />
fibration were washed free of sucrose and other water-soluble materials. The dry samples<br />
were then exposed to an atmosphere of constant water vapour pressure in a desiccator<br />
placed in a thermostatically-controlled oven for at least 40 hours. After which period, it<br />
was assumed that the condition of equilibrium had been reached. The tests were carried<br />
out at 27.2 °C and 51.0 °C. Approximately one gram of fibre was spread as a thin layer on<br />
a flat silica dish and allowed to remain in the prepared atmosphere for the required time.<br />
To determine the equilibrium moisture content, the sample was quickly transferred to a<br />
stoppered weighing bottle and weighed after cooling before and after drying to constant<br />
mass at 105 °C. The technique was found to operate satisfactorily even when the samples<br />
were in an atmosphere of 100% humidity, when water was the air-conditioning reagent.<br />
He estimated a value of 35% Brix-free water at 100% relative humidity.<br />
When the log of adsorbed water per 100 g dry fibre was plotted as ordinate against the log<br />
of water vapour pressure as abscissa, for each temperature, there exist two equilibrium<br />
conditions for which straight lines obeying a Freundlich type of equation were shown<br />
above and below a transition point occurring at an EMC value of 14.5% of fibre (Fig 5.2).<br />
180
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