The invert sugar content of sugar beets is an important indicator of t
heir quality owing to the fact that its acidic degradation products (l
actic, acetic, formic, and other organic acids), formed during juice p
urification, reduce the natural alkalinity reserves of the beets. This
has adverse consequences for sugar manufacture, which makes it highly
desirable to be able to predict the alkalinity of technical juices. T
o this end, two independent proposals have recently appeared in the li
terature, which include, besides other characteristics, the invert sug
ar content of the beets as a variable in the estimate of their alkalin
ity reserves. However, the inclusion of invert sugar in the quality as
sessment of sugar beets presupposes the existence of a serial analytic
al method which meets the practical requirements of automated beet lab
oratories. The fluorimetric determination of reducing sugars in beets
(or in beet brei degirates clarified with aluminium sulfate) with benz
amidine, according to Kai et al. (1985), constitutes a method which, b
esides satisfying other conditions, is sufficiently simple and cost-ef
fective to be introduced as a serial method into routine beet analysis
. The method is selective and sensitive enough to register reducing ca
rbohydrates, which in sugar beets are represented almost exclusively b
y glucose and fructose in an average ratio of 1:0.4 (described as ''in
vert sugar)'' Interference in the fluorescence reaction by unidentifie
d constituents of the beet matrix can be overcome by the addition of E
DTA. In principle, fluorescence measurements can be carried out with t
he fluorimeters developed for beet laboratories. These must be constru
cted as two-beam devices and also be equipped with a reaction chamber
(oven unit) and a flow cuvette maintained at reaction temperature (90-
degrees-C). Comparison with the Berlin Institute method (ICUMSA standa
rd) shows that the benzamidine method registers reducing sugars in sug
ar beets with comparable accurarcy and reproducibility. With that, the
most important preconditions for the incorporation and routine applic
ation of this fluorimetric analytical method in the various automated
beet laboratory systems are satisfied.