The possible presence of natural β-D-glucosidase inhibitors in jujube leaf extract

Abstract

Isoquercitrin is a phenolic compound well-known for having greater health benefits than quercitin, its aglycone derivative, and other related glycosides. However, isoquercitrin is rarely found in nature. Here, we optimized the conditions for the enzymatic transformation of isoquercitrin from rutin that was extracted from jujube leaf using the hesperidinase, enzyme complex containing beta-D-glucosidase and alpha-L-rhamnosidase. The maximum productivity (2.57 +/- 0.16 mg/mL) was experimentally found under the following conditions: 47.3 degrees C, 52.16 h, and pH 5.31, which agreed well with the predicted value (2.65 mg/mL). However, the achievement of this maximum yield was due to the absence of beta-D-glucosidase activity. Further investigations using a beta-D-glucosidase assay and reaction measurements under various conditions revealed that the beta-D-glucosidase activity was not blocked by denaturation or known inhibitory factors. Currently, there are no recognized beta-D-glucosidase inhibitors present in the jujube leaf; however, our observations strongly suggest that an unidentified beta-D-glucosidase inhibitor exists in jujube leaf extract. (C) 2015 Elsevier Ltd. All rights reserved.