A thermostable β-glucosidase from Thermus sp. Z-1 that not only hydrolyzes β-glucosides but also β-galactosides was shown to efficiently produce oligosaccharides during hydrolysis of lactose. The yield of oligosaccharides was more than 40% for 0.88 M lactose solution at 70°C at pH 7.0. The major product was a trisaccharide, 3'-galactosyllactose, formed by a galactosyltransfer reaction.
