Lynne Wong's PhD thesis
Lynne Wong's PhD thesis Lynne Wong's PhD thesis
found that the amount of absorbed water on the fibre was dependent on the cane variety and the concentration of the solution used. They also did an experiment with pure cellulose in a 20% sucrose solution and found a value of 8%. Foster (1963) used a different method to determine Brix-free water in cane fibre. Cane (2 kg) was weighed into a wet disintegrator, and reduced to a slurry with water (6 kg). A sample of the extract was taken for Brix reading. The extract was then removed until the slurry mass was 4000 g. To this was added an exact mass of 1500 g of 67.00° Brix sucrose solution. After five minutes of further mixing in the disintegrator, the resultant Brix was measured, and the actual mass of solvent plus Brix could be calculated. Subtracting this mass from 4000 g, gave the mass of fibre plus Brix-free water. He obtained values of 25 to 40% Brix-free water on fibre. Mangion and Player (1991) ensured that all the adsorbed water was removed from a prewashed, essentially sucrose-free fibre sample, and then contacted this fibre with a sucrose solution of known concentration. They employed a method that used eight grams of fibre sample weighed into a pre-weighed jar. The fibre was vacuum dried at 80 °C, and 825 mbar for 3 hours to avoid any heat damage of the fibre prior to analysis. After which, the sample mass was determined, and 150 g of a 10° Brix sucrose solution was added and well mixed to ensure all fibre was wetted by the sucrose solution. Mixing was effected from time to time for one and a half hours. The sample was then filtered through a covered Whatman 91 filter paper prior to the Brix measurement. The Brix of the original sucrose solution was also measured. The Brix-free water of the fibre was calculated by means of the following equation: -1 % Brix-free water = [100 w 4 (1 – p 3 p 4 )]/w 3 where w 3 and w 4 are the mass of fibre sample and the mass of sucrose contact solution respectively, and p 3 and p 4 are the Brix of the sucrose solution before and after mixing with the fibre sample. Mangion and Player (1991) found from over 250 data points, an average of 20.6% Brixfree water in present day cane varieties with a standard deviation of 2.2 units. Qin and White (1991) adopted the same method and reasoned that with unit mass of fibre added to 20 times its mass of sucrose solution, if the Brix-free water was 20% and the initial sucrose solution was 10° Brix, one could only expect an increase of 0.1 unit Brix, which was a small change and very difficult to measure with any accuracy. If the contact 114
solution/fibre ratio was lowered from 20 to 3, this would give a much larger change in Brix from 10.0 to about 10.7 enhancing the accuracy of the measurement. However, with such a low contact solution/fibre ratio, the fibre would not be fully wetted. Hence, a hydraulic press (see Fig 4.1), was devised to repeatedly compress the fibre so as to ensure good mixing of the contacting solution. The press is a modification of a hydraulic press unit used to obtain pressure-filtered molasses samples from massecuites. The bottom of the cylinder was sealed, and the closefitting internal piston was replaced by a loose open-holed piston, which compressed the fibre but allowed the press juice to flow out. The piston was moved by using a hydraulic car jack. The apparatus was used in a controlled humidity cabinet. Figure 4.1. Diagram of press cell used by Qin and White (1991) for Brix-free water measurements. 115
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- Page 145 and 146: 3 57.6 126.3 23.7 97.2 31.1 53.8 11
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- Page 149 and 150: 3.5.3 Fibre/pith ratios in cane com
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- Page 157 and 158: Table 3.18. Fibre % cane results by
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- Page 161 and 162: (a). Dry leaf (b). Green leaf (c).
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- Page 191 and 192: value determined could be corrected
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solution/fibre ratio was lowered from 20 to 3, this would give a much larger change in Brix<br />
from 10.0 to about 10.7 enhancing the accuracy of the measurement. However, with such<br />
a low contact solution/fibre ratio, the fibre would not be fully wetted. Hence, a hydraulic<br />
press (see Fig 4.1), was devised to repeatedly compress the fibre so as to ensure good<br />
mixing of the contacting solution.<br />
The press is a modification of a hydraulic press unit used to obtain pressure-filtered<br />
molasses samples from massecuites. The bottom of the cylinder was sealed, and the closefitting<br />
internal piston was replaced by a loose open-holed piston, which compressed the<br />
fibre but allowed the press juice to flow out. The piston was moved by using a hydraulic<br />
car jack. The apparatus was used in a controlled humidity cabinet.<br />
Figure 4.1. Diagram of press cell used by Qin and White (1991)<br />
for Brix-free water measurements.<br />
115
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