Modelling of hydrolysis of the residual lactose in fermented milk

In order to utilise the residual lactose which remains unused in a fermente d milk product, lactase may be added which hydrolysis the lactose into gala ctose and glucose improving the sweetness and the digestibility for lactose -intolerant people. The aim was to calculate the required times of hydrolys is which result from the addition of a fungale lactase directly into the pa sty fermented milk matrix to reach a defined degree of hydrolysis. The kine tics of lactose hydrolysis was described for skimmed quark based on the Mic haelis-Menten equation with competitive inhibition of galactose. The tempor al evolution of lactose concentration was examined at a temperature of 4 de greesC for various additions of a fungale lactase from Aspergillus oryzae b etween 0.05 and 1.5 g/kg. The effect of different enzyme concentrations was ascertained by model parameters A and B. These parameters include the Mich aelis-Menten constant, a competitive inhibition constant and a catalytic co nstant. The model verified by experiments for the enzymatic hydrolysis of l actose in quark enables the calculation of the present lactose concentratio n depending on the time or the required enzyme addition for a desired degre e of hydrolysis. The model is valid for an initial lactose concentration wi thin the range of 92.5 and 104.4 mmol/kg.