Identification of Bioactive Substances Derived from the Probiotic-Induced Bioconversion of Lagerstroemia speciosa Pers. Leaf Extract That Have Beneficial Effects on Diabetes and Obesity

<i>Lagerstroemia speciosa</i> L. (Banaba) has been used as a functional food because of its diuretic, decongestant, antipyretic, anti-hyperglycemic, and anti-adipogenic activities. Triterpene acids, including corosolic acid, oleanolic acid, and asiatic acid, are the principal phytochemicals in Banaba and are potentially anti-diabetic substances, owing to their effect on blood glucose concentration. Bioconversion of Banaba leaf extract (BLE) by <i>Lactobacillus plantarum</i> CBT-LP3 improved the glucose uptake, insulin secretion, and fat browning of this functional food. Furthermore, we identified asiatic acid, which was found to be increased by 3.8-fold during the <i>L. plantarum</i> CBT-LP3-mediated bioconversion process using metabolite profiling. Most previous studies have focused on corosolic acid, another triterpene acid that is a known anti-diabetic compound and is used to standardize BLE preparations. However, asiatic acid is the second most common of the triterpene acids and is also well known to have anti-diabetic properties. The present study has provided strong evidence that asiatic acid represents an alternative to corosolic acid as the most important active compound. These results suggest that the probiotic-mediated bioconversion of BLE may improve the anti-diabetic effects of this functional food. This implies that the consumption of a probiotic should be encouraged for people undergoing BLE treatment to improve its anti-diabetic effects.