Lynne Wong's PhD thesis

4.4.2 Brix measurement
As seen in Table 4.3, when the volume of the sample solution permits, three Brix values have
been recorded for each sample. This was done by pouring part of the solution into the
refractometer, three Brix readings were taken and an average was recorded. The process was
repeated two more times by pouring more sample solution into the refractometer. For the
original contact solution, six such values were recorded, three at the beginning and three more
at the end of the Brix measurement. It is understood that all Brix values were corrected for
instrument zero by using distilled water, as shown by the zero Brix before contact p 1 , in the
sample blank determination. As pointed out by Qin and White (1991) only a small difference
of about 0.1 unit Brix is expected (see Section 4.2); such a precaution is therefore essential to
ensure accuracy in the results obtained.
4.4.3 Re-generation of fibre samples
The incorporation of a blank determination does, however, imply the necessity of having
twice as much sample for the Brix-free water determination.
Since samples to be tested can sometimes be limited in quantity, the possibility of regeneration
of the sample after analysis was contemplated. Fibre samples as listed in Table 4.4
were therefore analysed and then washed free of Brix (< 0.01 Brix), dried overnight in an airoven
at 70 °C and re-analysed incorporating the blank determination. The results obtained
were much greater and highly different (p < 0.001) from the original results. This was
confirmed by analysis of further rind fibre and stalk pith samples. This concurs well with the
findings of Oguri (1932) and Stamm and Hansen (1938) who found that re-generated
cellulose adsorbed more water than the original material.
Consequently, this test showed that re-regeneration of samples for further tests is not viable
and that sufficient fibre samples must be prepared beforehand.
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