The enzyme b-galactosidase, also known as lactase, is widely used in the dairy industry to
produce lactose-free milk. This enzyme is able to hydrolyse lactose from milk into galactose and
glucose, thus enabling the consumption of milk by lactose-intolerant people. Under suitable
conditions, some b-galactosidases can also catalyze transgalactosylation reactions and produce
interesting compounds with recognized prebiotic effect, namely galactooligosaccharides (GOS) or
lactulose. The enzyme can be obtained from different biological sources such as microorganisms,
plants and animals. Nevertheless, the most interesting b-galactosidases for technological
applications are those obtained through microbial routes since higher production yields can be
achieved. In this study, the fungus Aspergillus lacticoffeatus is described as a new and promising
source of b-galactosidase. Preliminary chromogenic tests performed in agar plates suggested that
this strain was able to produce the enzyme and additional studies carried out under submerged
fermentation conditions confirmed the presence of b-galactosidase in the fermentation broth, as
well as in the cell extract obtained after ultrasonic cell disruption. The enzyme production was
evaluated in different fermentation media: synthetic medium composed by lactose (20 g/L),
yeast extract (4g/L), peptone (4g/L) and salts; and fermentation media with some industrial byproducts
as cheese whey and/or corn steep liquor. However, the higher values of enzymatic
activity (444 U/L) were obtained using the synthetic medium. The enzyme presented a molecular
weight around 130 kDa and optimal pH and temperature in the range 3.5-4.5 and 50-55 ºC,
respectively. The effect of some metal ions (Na+, K+, Li+, Ba2+, Fe2+, Mg2+, Zn2+, Mn2+, Co2+
and Cu2+), detergents (Triton, SDS and Tween), additives (EDTA, PMSF and ascorbic acid) and
sugars (glucose, fructose and galactose) on the enzymatic activity was also evaluated.
Afterwards, the potential of the enzyme for the synthesis of prebiotics was studied and it was
demonstrated that b-galactosidase from A. lacticoffeatus is able to catalyze the transfer
reactions involved in the formation of lactulose and GOS
