Lactulose has several usages in food applications and it is the first commercially available prebiotic. It is used as laxative and for the treatment of portal systemic encephalopathy.Lactulose is chemically obtained by isomerization of lactose in basic media, which is first transformed into lactulose to be subsequently degraded to galactose, epilactose and isosaccharinic acids.
On the other hand, power ultrasound (US) has emerged not only as an alternative to conventional food processing, but also as a tool to accelerate different chemical reactions. Moreover, it is environmentally friendly and offers advantages in terms of productivity and selectivity with better processing time and enhanced quality and functionalities. The effect of US on carbohydrate reactions has been investigated during the oxidation of sucrose, and the enzymatic isomerization of glucose to fructose. However, no studies have been carried out on the influence of this treatment on the isomerization of lactose. Thus, the aim of this work is to investigate the impact of US on the lactulose formation and degradation in alkaline media. Lactose solutions (10%) in 8 mM sodium hydroxide or 0.2 M bicarbonate buffer were subjected to treatments at 60°C for 15-60 min in a system by USwith a probe of 13 mm diameter, 20 kHz frequency and 400 W full power. Equivalent heat treatments were also carried out in a conventional bath. In general, US gave rise to an acceleration of lactose isomerization with higher concentrations of lactulose, galactose and epilactose, as compared to the control conventional ones. This was particularly evident in the buffer system due to the fact that, insodium hydroxide,a higher formation of acids could slow down the reaction. These results point out the usefulness of US as complement of heating to efficiently obtain lactulose.
Acknowledgments
Projects ALIBIRD S2009/AGR-1469 (CAM), AGL2011-27884 and FUN-c-FOOD CSD2007-00063 (MINECO).
