Comparison of the traditional oven method and the
new moisture analyser method for yeast cell suspensions
adjusted to 1–40 mg l)1 of dry weight with a sample volume
of 2 ml revealed a very good linear relationship of
the data with a slope of 1Æ024 ± 0Æ005 and a correlation
coefficient of r2 > 0Æ99 for the two methods (Fig. 3). In
addition, there was no statistically significant difference of
the measurement averages for the comparison made at
any given biomass concentration (n = 3, P = 0Æ05). The coefficients of variation (n = 5) ranged from 9 to 0Æ7 and
5Æ3 to 1Æ2%CV for biomass concentrations between 1 and
40 g l)1 dry weight for the oven and the moisture analysis
method, respectively.
A further evaluation of the accuracy and precision of
the moisture analyser method was carried out by adding
known quantities of dried diatomaceous earth as a nonorganic
internal standard to a yeast suspension with
10 g l)1 of dry weight. Using this method, accuracy
expressed as recovery ranged from 94Æ2 to 106Æ4%, and
the precision expressed as %CV ranged from 4Æ53 to
1Æ39% for 5–20 g of diatomaceous earth added (Table 2).
Figure 4 shows the effect of the sample volume and the
biomass concentration on the precision of the moisture analyser method. Higher sample volumes and biomass
concentrations led to higher precision. The method precision
was well correlated with the total dry weight contained
in the sample calculated from sample volume and
biomass concentrations (insert in Fig. 4). A simple nonlinear
regression with good correlation to the experimentally
acquired data could be generated (Eqn 2), allowing
to estimate the amount of total dry weight needed to
achieve a certain level of precision.