Applications of p-galactosidase to hydrolyze lactose in milk and cheese are greatly increasing in the last two decades, since over 70% of the global adult population have reduced lactase production, resulting in lactose sensitivity or intolerance (Curry, 2013). The enzyme can be obtained from various sources, but the major commercial preparations are isolated from GRAS (generically recognized as safe) microrganisms such as Kluyveromyces lactis and K. fragilis, Aspergillus niger and A. oryzae (Grosova et al., 2008). The source determines some technological properties: fungal p-galactosidases are more thermostable than yeast enzymes, but are more sensitive to galactose inhibition (Boon et al., 2000). Also, lactases from fungi are useful in acid whey hydrolysis due to acidic pH optimum, whereas those from yeasts give best performance in milk.
The easiest way to hydrolyze lactose in milk is discontinuous batch-process in which lactase is added to milk and activity is stopped by heating. Continuous processes based on chemical immobilization the enzyme on solid matrix or by “physical immobilization” via ultrafiltration membranes are more effective. A major problem of immobilized enzyme systems is microbial contamination and need of intermittent sanitation steps (Novalin et al., 2005).