The influence of the initial substrate concentration on citric acid an
d polyols production by means of free and immobilized A. niger was stu
died in this work. The immobilization increases yield and concentratio
n of citric acid. With both free and immobilized cultures, citric acid
concentration increases with substrate, pass a maximum value and decl
ines at high substrate concentration, although the obtained profiles a
re different for the several cultures. Polyols are only detected at re
latively high substrate concentrations; when these latter are small, p
olyols are consumed by the microorganisms, disappearing continously of
the medium. More abundant polyol is glicerol, which reaches its maxim
um value for free A. niger experiment, with a 30% sacarose. Erythritol
and arabitol are always with low concentration values.