The investigation and modelling of enzymatic hydrolysis of lactose recovered from whey

Lactose is the dominant carbohyrate in milk and dairy products (such as whey). Lactose is a sugar with low sweetness and low solubility when compared to the products of its hydrolysis (glucose and galactose) and being a hygroscopic sugar has a strong tendency to adsorb flavours and odours. Moreover, due to a lack or inactivity of the intestinal beta-galactosidase enzyme, a large number of people do not digest lactose properly. Therefore, they suffer from intestinal dysfunctions such as; gas, abdominal pain and diarrhea if their diet contains lactose. These people should consume products without lactose ingredient. The hydrolysis of this sugar is very attractive towards the improvement of processes for the production of refrigerated dairy products (such as, ice cream). It would also be very interesting for the development of additives for animal and human alimentation, reducing costs in energy and avoidance of the sandy texture due to the crystals of lactose. Hydrolysis of lactose can be performed either by acids or by enzymatic treatment. The enzymatic hydrolysis of lactose is carried out by beta-galactosidases, enzymes that are widely distributed in nature; appearing in micro-organisms, plants and animal tissues. In the present study, lactose recovered from whey is hydrolyzed with beta-galactosidase enzyme which is produced from Kluyveromyces marxianus. Both the Gallenkamp Modular Bioreactor System and Bandelin Sonopuls Sonicator were used for the lactose hydrolysis experiments. The hydrolysis reactions were carried out in 250 ml of 25 mM phosphate buffer solution. In the modular bioreactor system, the amount of lactose concentration (g/L), the degrees of lactose hydrolysis (%) and enzyme activity (%) against time were investigated versus initial lactose concentration, enzyme concentration, temperature, pH, impeller speed, viscosity, amount of hydrolysate added, glucose concentration, galactose concentration and different ion (Mg2+, Mn2+ and Ca2+) concentration;in the sonicator those values were investigated versus acoustic power, duty cycle and reaction volume. Beside of this; the mathematical models, which represent the residual lactose concentration and residual enzyme activity, depending on the operating conditions were also derived by using the experimental data. An evaluation of the experimental data showed that hydrolysis degree of lactose and residual beta-galactosidase activity were different for each set of the conditions applied. Keywords: Lactose hydrolysis, beta-galactosidase, bioreactor, sonicator, modelling, process variables