Microbial transformation of lactose: potencial of β-galactosidases for probiotic and prebiotic purposes

Abstract

In the last decades, the interest of food industry has focused in the development of functional foods because of the high demand of healthy foods by consumers around the world. In this sense, foods containing probiotic microorganisms have received particular attention. One of the firsts beneficial properties ascribed to probiotics is their ability to contribute to the intestinal metabolism of lactose from the diet and the amelioration of intolerance symptoms. This effect is mediated by the enzyme β-D-galactosidase of the microorganisms included in the product that can hydrolyze the disaccharide into the food before consumption, as well as to contribute to the intraintestinal digestion of lactose. However, β-galactosidases have more biotechnological potentialities with a wider spectrum of application. This enzyme possess, depending on the reaction conditions (substrate concentration, aw, pH, reaction temperature), hydrolase or transferase activities, owing the last one to the production of oligosaccharides containing 2 to 10 monomers obtained by transgalactosylation reactions that transfer galactose hydroxyl groups to the disaccharide lactose and/or the different oligomers that are being generated. Galactooligosaccharides (GOS) are well known prebiotics that modulate the colonic microflora in a healthy manner and also have other promising industrial applications such as their addition to foods as no-cariogenic, low-calories sweeteners. The raw material used for GOS production could be the lactose from milk as well as the whey discarded by dairy industries from cheeses manufactures. Since whey is considered an environmental contaminant its utilization in this regard seems to be an attractive option. In the present chapter, the potential of well-known probiotics (such as lactic acid bacteria, bifidobacteria, propionibacteria and yeasts) to contribute to the intestinal metabolism of lactose and/or to produce prebiotic galactooligosaccharides (GOS) by their β-galactosidase activities is reviewed. In many cases the main biochemical properties of the enzyme of the microorganisms with the higher hydrolytic activities have been determined as well as their abilities to improve lactose digestion in animal models and clinical trials. In this regard, multiple therapeutic strategies have been assessed with different results. On the other side, the production of galactooligosaccharides (GOS) by transgalactosylation using β-galactosidases from GRAS microorganisms has also been studied. Depending on the enzyme source and the reaction conditions, the extent of oligosaccharide formation could be as high as 40% of the total sugar content in the solution and three to eleven types of oligosaccharides could be found, including disaccharides other than lactose, trisaccharides and various tetrasaccharides. Although some suitable sources of â-galactosidases that can be used to synthesize novel GOS have been characterized, further studies on the prebiotic effects of these GOS in pure cultures of bifidobacteria, and colonic microbiota of animals and human volunteers are still missing. Besides, the selection of probiotic microorganisms with appropriate β-galactosidase activities should be complemented with in vivo assays (survival and activity in the intestinal conditions) and certain technological parameters in order to be included in the formulation of novel functional foods, particularly fermented products enriched in GOS and β-galactosidase.