Stability of [6]-gingerol and [6]-shogaol in simulated gastric and intestinal fluids

The degradation kinetics of [6]-gingerol and [6]-shogaol were investigated in simulated gastric (pH 1) and intestinal (pH 7.4) fluids at 37 °C. Degradation products were quantitatively determined by HPLC (Lichrospher 60 RP select B column, 5 μm, 125 mm × 4 mm; mobile phase: methanol–water–acetic acid (60:39:1 v/v); flow rate: 0.6 ml/min; detection UV: 280 nm). In simulated gastric fluid (SGF) [6]-gingerol and [6]-shogaol underwent first-order reversible dehydration and hydration reactions to form [6]-shogaol and [6]-gingerol, respectively. The degradation was catalyzed by hydrogen ions and reached equilibrium at approximately 200 h. In simulated intestinal fluid (SIF) both [6]-gingerol and [6]-shogaol showed insignificant interconversion between one another.Addition of amino acids glycine, 3-amino propionic acid (β-alanine) and γ-amino butyric acid (GABA), and ammonium acetate at a range of concentrations of 0.05–0.5 mM had no effect on the rate of degradation of [6]-shogaol in SGF and 0.1 M HCl solution. However, at exceedingly high concentration (0.5 M) of ammonium acetate and glycine, significant amounts of [6]-shogaol ammonia and glycine adducts were detected.The degradation profile of [6]-gingerol and [6]-shogaol under simulated physiological conditions reported in this study will provide insight into the stability of these compounds when administered orally.