Abstract
Geniposide is an iridoid glycoside, which is abundant in Gardeniae Fructus. Despite the various pharmaceutical effects of geniposide on a human body, its hydrolysis into a smaller molecule, genipin, by β-glucosidase produced by bacteria in the intestines is particularly important to improve geniposide uptake into the body. Since geniposide is much more abundant in Gardeniae Fructus than its aglycone genipin, we herein transformed geniposide into genipin using purified recombinant β-glucosidase from Lactobacillus antri (rBGLa), which was expressed in Escherichia coli to enhance the genipin content. Purified rBGLa was characterized using p-nitrophenyl β-D-glucopyranoside, and the optimal temperature and pH for its β-glucosidase activity were found to be 45 °C and 6.0. When the enzyme was immobilized, rBGLa was active at higher temperatures than the free enzyme, and we confirmed that its stability upon changes in pH and temperature was highly improved. Using 0.5 μg/mL free rBGLa, single compound of 0.4 mM geniposide was efficiently converted into genipin within 2 h, and the immobilized rBGLa also successfully transformed geniposide in a hot-water extract of Gardeniae Fructus into the aglycone, which makes it applicable to the food and pharmaceutical industries.