Structural changes of sinapic acid and sinapine bisulfate during autoclaving with respect to the development of colored substances

Structural changes in sinapic acid during autoclaving were studied using sp ectral analysis, thin-layer chromatography, high-performance liquid chromat ography, nuclear magnetic resonance (NMR), and mass spectroscopy. Color pro perties of sinapic acid and its derivatives were studied by determining the transmittance spectrum, calculating the Commission Internationale de I'Ecl airage 1931 tristimulus values and converting to Hunter L a b values. It wa s found that the colorless sinapic acid aqueous solution (100 mu g/mL) turn ed yellow after 15 min in an autoclave at 121 degrees C and 0.1 MPa. Filter ing the yellow aqueous solution through a 0.45-mu m filter removed a brown solid consisting of at least three undetermined colored substances and left a yellow liquid. A newly developed yellow substance, syringaldehyde, was i dentified in the liquid phase by comparing the NMR and mass spectra of the unknown with those of authentic syringaldehyde. Thomasidioic acid was also found in the liquid phase. Under the same autoclaving conditions, sinapine bisulfate showed no evidence of any structural or color changes.