Harness lactose using enzymatic conversion.

The goal of research across the European Union has been to find new enzymatic processes for converting and using lactose and its derivatives. The motivation behind this research effort is the low degree and not-very-profitable utilization of the 1.2 million tons of lactose produced annually worldwide, primarily as byproducts of cheese manufacture or whey processing.

Lactose is one of the largest biomasses available today and has been mostly used as a fermentation substrate, as a filler or sweetener, and in small amounts in infant and dietetic foods, coffee whiteners and feeds. Lactose itself has limited application in foods, mainly due to intolerance problems on the part of consumers.

Scientists identified a thermostable hydrolizing enzyme, b-glycosidase, from genetically modified hyperthermophilic Archea Sulfolobus solfataricus and Pyrococcus furiosus that grew in continuous fermentors. These included a continuously stirred tank reactor with an external ultrafiltration unit, an immobilized enzyme reactor and a diffusional hollow-fiber reactor. The last reactor was scaled up to a demonstration plant. The unit was successful in terms of product quality and stability.

Because there is a lack of natural enzymes that can reduce or oxidize lactose, the scientists engineered existing enzymes to develop a novel process that converts galactose from hydrolyzed lactose into D-tagatose, a ketohexose which is a low-calorie sweetener and well-suited for diabetics.

The process is based on a two-step conversion of D-galactose. The first step involves a reduction into galactitol by using NADH-dependent aldose reductase from yeast and continuously regenerates the NADH. In the second step, the C-2 in galactitol is oxidized by a polyol dehydrogenase from Burkholderia cepacia.

Investigators developed an efficient enzymatic bioprocess that converts lactose into lactobionic acid using cellobiose dehydrogenase and lactase. Both enzymes are very stable and excreted abundantly by fungal organisms. Lactobionic acid may be used in foods because of its sweet-sour mildly acidic taste, its presumed prebiotic function and its metal-chelating properties that are harnessed to fortify drinks with minerals. The scientists have begun to document the prebiotic effect--the stimulation of specific microorganisms in the colon--of several lactose derivatives.

Further information. Klaus Kulbe, University of Agriculture, Institute of Food Technology, Biochemical Engineering Division, Muthgasse 18, 1190 Vienna, Austria; phone: [phone]; email: [e-mail].