Optimized enzymatic synthesis of digestive resistant anomalous isoquercitrin glucosides using amylosucrase and response surface methodology.

Abstract

Diverse flavonoid glycosides are present in the plant kingdom. Advanced technologies have been utilized to synthesize glycosyl flavonoids which exhibit good physicochemical characteristics. Previously, novel isoquercitrin (IQ) mono-, di-, and tri-glucosides (IQ-G1', IQ-G2', and IQ-G3'; atypical IQ-Gs (IQ-Gap)) were synthesized through the reaction of amylosucrase. Here, the regio-selective transglycosylation yields were predicted using response surface methodology for three variables (glucose donor (sucrose; 100-1500mM), glucose acceptor (IQ; 100-400µM), and pH (5.0-8.8)) using 1 unit/mL of enzyme at 45°C; then, the optima were verified according to the experimental responses. Acidity (pH 5.0) was a major contributor for IQ-G1' production (> 50%), and high sucrose concentration (1500mM) limited IQ-G3' production (< 15%). Low sucrose concentration (100mM) at pH 7.0 promoted higher glycosyl IQ production (> 30%). Time-course production of IQ-Gap showed an exponential growth with different rates. IQ-Gap was stable under the simulated intestinal conditions compared with typical IQ-Gs. Digestive stable IQ-Gap can be effectively synthesized by modulating reaction conditions; thereby, atypical glycosyl products may contribute to the elucidation of nutraceutical potential of flavonoid glycosides. KEY POINTS: •Predictions of RSM were validated for the regio-selective IQ-Gap production. • Time course changes of IQ-Gap indicate non-processive glycosylation of DGAS. • IQ-Gap exceed typical IQ-G in digestive stability at simulated intestinal condition.