Alpha-amylases typically act on starch and oligosaccharides that contain α-1,4 glycosidic linkages, while ginsenosides primarily consist of β-1,2 and β-1,6 glycosidic bonds, which cannot be hydrolyzed by α-amylases. However, for the first time, we have successfully isolated Streptococcus thermophilus 17140 (St17140), capable of converting ginsenoside Rb1 into rare ginsenosides. St17140 expresses a novel α-amylase (StAMY), which hydrolyzes ginsenoside Rb1 to produce Rd, gypenoside XVII, F