Lynne Wong's PhD thesis

In order to test for homogeneity of samples, fibres of various components of cane were
extracted from 15 kg of cane. After removing and discarding the nodes, the rind was
separated from the stalk. Fibres were extracted from the rind and the stalk, washed free of
sucrose and dried as per the method described in Chapter 3 (Sections 3.4.3.1 and 3.4.3.2).
Fibres were separated from the fines/pith as much as possible to obtain four well-separated
fractions: stalk fibre (620 g), pith (1175 g), rind fibre (1240 g) and rind fines (830 g).
There were also two mixtures: stalk with pith weighing 250 g and rind fibre with fines
weighing 915 g. No effort was made to further separate these two mixtures as they would
serve to see to what extent reproducible results could be obtained from them.
Each of these six fractions was tested in five replicates and one blank determination was
effected. Drying was effected in a vacuum oven at 80 °C for 3 hours. To 6 g of sample
when cool were added 110 g of 10° Brix sucrose solution. A contact time of one and a half
hours was allowed during which period, the sample was shaken every ten minutes.
The Brix-free water results are shown in Table 4.6, which indicate that the fractions of
stalk fibre, rind fibre, rind fibre + fines, and rind fines were homogeneous, despite such a
small sample (6 g) taken from a large sample, e.g. 1240 g, in the case of rind fibres. For
the stalk fibre + pith mixture and stalk pith sample, results were not reproducible, probably
because of the difficulty associated with drying the pith. Hence the drying condition prior
to analysis needed investigation.
4.4.5 Drying conditions prior to analysis
When more of the samples which had been examined previously (results shown in Table
4.3) were analysed again two days later for their Brix-free water content under the same
analytical conditions and incorporating the blank value, significantly higher results (P <
0.05) were obtained (see Table 4.7). This would indicate that the samples were drier on
the second occasion than when first examined, and took up more water to satisfy their
Brix-free water capacity. Thus, the overnight vacuum drying at 65 °C so far adopted
needed to be re-examined.
One green leaf fibre sample was well mixed, and sub-samples of 6 g were weighed into
separate bottles. Samples were dried at 65 °C under vacuum of 875 mbar for 2, 4, 6 and 16
hours. The Brix-free water results (Table 4.8) show increasing values from 2, 4, 6 hours
reaching the highest value at 16 hours, implying that drying under these conditions for less
than 16 hours is insufficient to drive off the moisture originally present in the sample.
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