Treatment of cheese whey by immobilized enzyme membrane bioreactor

REGENHARDT, SILVINA; TORRES, AGUSTÍN; MAMMARELLA, ENRIQUE; RUBIOLO, AMELIA

Porto, Portugal

Conferencia; Internacional Functional Foods Conference; 2008

Universidad Católica Portuguesa de Porto - CyTED

Cheese whey contains more than 25% of the proteins of the milk, near 8% of the fatty matter and of 95% of the original lactose. Some industries recover this proteins using ultrafiltration process and sell them as whey protein concentrate (WPC), but the effluent still has a problem to be disposed because of the great quantities of lactose. It is totally forbidden to dump milk whey into the rivers, so there are two ways to follow: purification or recovery of valued nutrients. The recovery of valued nutrients seems to be the best way to treat this effluent. Using membrane processes enable to recover all the nutrients that we are interested in. In those processes with the protein fraction, it is been retained big quantities of lactose; a little attractive sugar because of its low solubility and its insufficient sweetener power. One way to solve this problem is the enzymatic hydrolysis of lactose into glucose and galactose during the concentration process. Enzyme immobilization onto highly activated supports allows working continuously and re-using the catalyst so that the global yield is improved if compared to batch procedure. Continuous reaction and simultaneous separation of products from the reaction mixture can be achieved with a continuous membrane recycle reactor. The membrane reactor avoids the main difficulties related to the enzymatic immobilization: soluble enzymes can be used, high substrate conversion is achieved due to the elimination of inhibitors and the molecular size of the product is controlled by an ultrafiltration module with the appropriate molecular weight cut-off (MWCO). Low molecular weight species permeate through the membrane. It was studied the behavior of the b-galactosidase from Kluyveromyces fragilis immobilized with covalent multipoint attachment on a polyethersulphone ultrafiltration membrane which has 10 kDa of molecular weight cut-off. This was carried out under different operational conditions; next to the residence time and transmembrane fluxs they were been adjusted. All of this to have an efficient process with the minimum enzyme deactivation possible. In order to improve the stability of immobilization, we used glutaraldehyde to make the multipoint covalent attachment. The immobilization conditions that show best results were: 5% (w/v) of glutaraldehyde adding galactose 0.03 M with the enzyme solution to do the immobilization. It was found that increasing the concentration of the linking agent the quantity of joined enzyme onto the membrane also increase but actually reduce its activity. The experimental results showed that using an inhibitor (galactose) during the immobilization process preserve the enzyme activity. Under those operational conditions we could immobilize 12.49 mg of enzyme, with a total activity of 86.3 LAU at 37°C using as a reagent 5% (w/v) lactose solution in phosphate buffer 100 mM pH 6.9, corresponding at 44.2% of equal quantity of free enzyme. The stability of the enzyme increased about 44.1 times from the free enzyme. The stabilization factor can be improved making a controlled reduction of the double bonds in the Schiff bases, or making a post treatment to the membrane with the immobilized enzyme.