Hot Spring Enzyme Turns Milk Into Lactose-Free, Prebiotic-Rich Drink

Deep beneath the city of Ourense in northwestern Spain, the As Burgas hot spring has been releasing warm, mineral-rich water for centuries. Now, the microbial life dwelling in that geothermal environment has yielded something with the potential to reshape an entire industry: a novel, remarkably heat-tolerant enzyme capable of transforming ordinary milk into both a lactose-free product and a functional food enriched with prebiotic compounds. The discovery, published in Applied Microbiology and Biotechnology, comes from a research team at the University of A Coruña that went looking for industrial biocatalysts not in laboratory strain collections, but in the unexplored genetic material of an entire microbial community.

The enzyme, named BWbg1, belongs to a class of proteins known as beta-galactosidases, which catalyze the cleavage of lactose, the disaccharide sugar that makes up a large fraction of the solids in milk, into its two component monosaccharides, glucose and galactose. Beta-galactosidases have long occupied a central place in dairy biotechnology because they support two distinct and commercially significant applications. The first is the production of low-lactose and lactose-free milk and dairy goods for the large population of people who cannot properly digest lactose. The second is the synthesis of galacto-oligosaccharides, or GOS, through transgalactosylation reactions in which the enzyme, instead of simply splitting lactose, stitches galactose units together into short chains that humans cannot digest but that beneficial gut bacteria eagerly consume.

What makes BWbg1 stand out in a crowded field of known beta-galactosidases is its thermal profile. The purified enzyme exhibits maximum activity at 80 degrees Celsius and at a neutral pH of 7, a combination that immediately distinguishes it from the mesophilic enzymes traditionally used in dairy processing. It also demonstrates impressive resilience, retaining more than 72 percent of its activity after six hours of incubation at 55 degrees Celsius. For industrial operators, these are not merely laboratory curiosities. Elevated operating temperatures increase the initial productivity of enzymatic reactions, improve the solubility of substrates such as concentrated lactose solutions, and dramatically reduce the risk of contamination by spoilage and pathogenic microorganisms, which struggle to proliferate at temperatures that the enzyme tolerates with ease.

The path to BWbg1 illustrates the power of functional metagenomic screening, a technique that has become one of the most productive strategies in modern bioprospecting. Rather than trying to culture the microorganisms from the As Burgas hot spring, an approach that would capture only a small fraction of the community because most environmental microbes resist laboratory cultivation, the researchers extracted the collective DNA of the entire microbial ecosystem and cloned it into a metagenomic library. They then screened that library for clones exhibiting beta-galactosidase activity, allowing the function of the gene itself, rather than any prior knowledge of the organism that carried it, to guide the discovery. Sequence analysis of the protein encoded by the recovered gene revealed that BWbg1 belongs to glycoside hydrolase family 35, a well-characterized group of enzymes, yet its properties proved distinctive enough to warrant the label of novelty.

The enzyme’s performance in GOS synthesis is arguably its most commercially compelling feature. Working with a concentrated lactose solution of 40 percent weight per volume at 70 degrees Celsius, BWbg1 converted the substrate into a product mixture containing up to 48 percent galacto-oligosaccharides by weight over a four-hour reaction. That yield, achieved at a temperature at which most conventional enzymes would rapidly denature, positions BWbg1 as a serious candidate for industrial prebiotic production. GOS are among the most widely added prebiotics in infant formula and functional foods, valued for their ability to selectively stimulate the growth of beneficial bacteria such as Bifidobacteria in the gut. A thermostable enzyme that can sustain high-yield synthesis at 70 degrees Celsius offers manufacturers both faster throughput and a substantially lower microbial contamination risk during extended production runs.

Perhaps the most surprising finding, however, concerns what happens when the enzyme is exposed to heat before it is asked to work. The researchers observed a remarkable heat activation effect: after two hours of incubation at 65 degrees Celsius, BWbg1’s ability both to hydrolyze lactose and to produce GOS was enhanced rather than diminished. This behavior has direct implications for how the enzyme could be deployed in real dairy plants. Milk destined for the market is routinely pasteurized, and the two dominant methods are HTST, high-temperature short-time pasteurization, and VAT, the older vat pasteurization approach that uses lower temperatures over longer holding periods. The study demonstrated that BWbg1 retains its activity after both HTST and VAT pasteurization of commercial milk, and that the heat activation it experiences during these treatments actually improves its subsequent performance on the lactose in the milk.

This compatibility with pasteurization regimes is a genuinely practical advantage. In current industrial practice, lactose hydrolysis is typically performed as a separate step after pasteurization, requiring additional equipment, time, and careful hygiene controls. An enzyme that can be added to milk, survive the pasteurization step itself, and then go on to work more effectively afterward could allow manufacturers to merge two processing stages into one streamlined operation. The enzyme’s tolerance of the exact thermal conditions used to make milk safe for consumers means that the same heat treatment that protects public health simultaneously primes the biocatalyst for action, a coincidence of process requirements that enzyme engineers usually struggle to achieve by design.

Equally noteworthy is the enzyme’s behavior at the opposite end of the temperature scale. The study reports that BWbg1 remains capable of hydrolyzing lactose from commercial milk and producing GOS even at 8 degrees Celsius, a temperature within the range of standard refrigerated storage. This cold activity opens the door to applications in which milk is treated during chilled logistics or storage, extending the enzyme’s usefulness well beyond the hot processing floor. A single biocatalyst that functions productively from refrigeration temperatures up to 80 degrees Celsius spans a thermal range that few, if any, commercially established beta-galactosidases can match, and it gives process designers an unusual degree of freedom in choosing where and when in the production chain to deploy it.

The broader significance of the work lies in what it says about the untapped enzymatic wealth of extreme environments. Hot springs have long been recognized as reservoirs of thermostable proteins, because the microorganisms adapted to life at elevated temperatures must maintain enzymes that keep their structure and function under conditions that would destroy the proteins of ordinary organisms. Yet the vast majority of these thermophilic communities remain genetically uncharacterized, and functional metagenomics offers a way to access their catalytic repertoire without ever growing a single cell in the laboratory. The As Burgas spring, flowing through a geologically active region of Galicia, proved to be a productive hunting ground, and the researchers suggest that BWbg1’s versatility, spanning lactose hydrolysis, GOS synthesis, pasteurization compatibility, and cold-temperature activity, makes it a strong candidate for industrial application.

For consumers, the practical outcome of such research is tangible. Lactose intolerance affects a substantial share of the global population, and demand for lactose-free dairy continues to climb, while the market for prebiotic ingredients that support gut health grows in parallel. An enzyme that can serve both markets, converting milk into a digestible product for one consumer group and into a GOS-enriched functional food for another, addresses two major trends in food science with a single biocatalyst. As the team’s results demonstrate, the answer to some of the dairy industry’s most persistent processing challenges may have been waiting all along in the steaming waters of a Spanish hot spring, encoded in the genomes of microbes no one has ever cultured.

Subject of Research: A thermostable GH35 beta-galactosidase from a hot spring metagenome for lactose hydrolysis and galacto-oligosaccharide production in milk

Article Title: A novel thermostable beta-galactosidase for low-lactose and galacto-oligosaccharide-rich milk

Article References: DeCastro, M.-E., Becerra-Fernández, M., Rodríguez-Belmonte, E., & González-Siso, M.-I. (2026). A novel thermostable beta-galactosidase for low-lactose and galacto-oligosaccharide-rich milk. Applied Microbiology and Biotechnology. https://doi.org/10.1007/s00253-026-14045-z

Image Credits: AI Generated

DOI: 10.1007/s00253-026-14045-z

Keywords: beta-galactosidase, metagenomics, thermostable enzyme, galacto-oligosaccharides, lactose-free milk, hot spring, bioprospecting, dairy biotechnology, prebiotics, pasteurization, GH35, transgalactosylation