Accordingly, a total dry weight of approximately 10 mg
was required to achieve a precision of 5%CV.
Table 1 compares the efficiency of various methods
intended to increase the precision of the moisture analyser
method when applied to samples with low biomass
concentrations (0Æ5 g l)1 of dry weight). Using the standard
method, the moisture analyser returned a zero reading at 1 ml of sample volume. Increasing the sample
volume from 1 to 5 ml enabled a biomass measurement
but the precision remained poor. Addition of a small
amount of a 100 g l)1 tartaric acid solution to the yeast
suspension samples as internal standard improved the
precision across a wide range of biomass concentrations
(Fig. 5), but for a 1-ml sample volume with 0Æ5 g l)1 of
dry weight, the precision remained comparable to a 5-ml
sample volume without internal standard (Table 1). Only
the utilisation of a 15-ml sample that was concentrated to
3 ml to reduce analysis time led to a precision below 5%
CV (Table 1).
The moisture analyser method was used to follow the
growth of yeast and bacterial cultures. The dry weight
contribution of dissolved media constituents was considered
by subtracting the dry weight of the clear supernatant
from the value obtained for samples with biomass
for every sample taken.
Figures 6 and 7 show the growth data obtained by the
dry weight method and by measuring the optical density