Impact of ultrasound on galactooligosaccharides and gluconic acid production throughout a multienzymatic system

Galactooligosaccharides (GOS), recognised prebiotic, can be industrially produced from lactose and commercial β-galactosidase (β-gal) from Kluyveromyces lactis. Residual lactose and glucose limit GOS applications. To handle this problem, a multienzymatic system, with β-gal and glucose oxidase (Gox), was proposed to reduce glucose content in reaction media through its oxidation to gluconic acid (GA). Besides, ultrasound (US) probe effect over the multienzymatic system to produce GOS and GA has been evaluated. A production around 40% of GOS was found in all treatments after the first hour of reaction. However, glucose consumption and GA production was significantly higher (P < 0.05) for sequential reaction assisted by US, obtaining the best production of GOS (49%) and GA (28%) after 2 h of reaction. The conformational and residual activity changes of enzymes under US conditions were also evaluated, Gox being positively affected whereas in β-gal hardly any change was found.