Process for the preparation of a lactulose syrup by lactose isomerization

Process for the preparation of a lactulose syrup by isomerization of lactose comprising the following steps:

• a) reaction of an aqueous solution or suspension of lactose with sodium aluminate in order to produce the isomerization of lactose to lactulose with a conversion of lactose limited to 55-65% or with conversion of lactose of between 90 and 95%;
• b) quenching with ice of the mixture obtained in step (a);
• c) neutralization of the mixture obtained in step (b) with precipitation of the aluminum hydroxide performed by treatment with gaseous CO2 under pressure;
• d) separation of the aluminum hydroxide by filtration;
• e) deionization of the solution obtained in step (d);
• f1) concentration of the solution obtained in step (e) up to obtaining a technical syrup in the case of the conversion of lactose of between 90 and 95%;
• f2) concentration of the syrup obtained in step (e) to be treated according to the following step (i) in the case of conversion lactose limited to 55-65%
• g) treatment of the aluminum hydroxide obtain ed in step (d) with NaHCO3, Na2CO3 or with NaOH, in the quantity necessary to convert the aluminum hydroxide into sodium aluminate;
• h) calcination of the product from step (g) to obtain the sodium aluminate which is recycled to step (a);
• i) crystallization from the solution of step (f2) of the non-isomerized lactose, which is recycled to step (a).