PHOTOSTABILITY OF COLORING CONSTITUENTS I N PAPRIKA COLOR

Capsanthin (CP) and esterified capsanthins are the main coloring const ituents in paprika color. Several reports have suggested that esterifi ed capsanthins are more stable to light than CP itself in paprika powd er and paprika extract. To clarify whether this is so, the photo-stabi lity of lauroylmyristoylcapsanthin (LM-CP) and CP was investigated in paprika powder, commercial paprika solution and isolated individual so lutions. After irradiation of the samples with visible light (4,000 lu x) at 25 degrees C, HPLC analyses were performed to quantify both comp ounds. The degradation curves of these compounds in paprika powder and commercial paprika solution were different. Namely, the amount of LM- CP began to decrease after photo-irradiation for several weeks, while that of CP decreased with time. On the other hand, the curves for both isolated compounds were quite similar in the same solvent. To resolve the discrepant observations, we precisely checked the chromatograms o f paprika powder and commercial paprika solution after photo-irradiati on. A peak, which appears at 68.3 min, about 2 min after the peak of L M-CP in the chromatograms, decreased quickly during an early stage of photo-irradiation and the peak of LM-CP significantly increased concom itantly. HPLC analyses revealed that the isolated fraction correspondi ng to the peak at 68.3 min was transformed to LM-CP by photo-irradiati on. The LC-APCI-MS analysis of the peak (68.3 min) showed a quiasi mol ecularion peak (m/z 978), which was also observed in LM-CP. These data suggested that the peak at 68.3 min is due to a geometrical isomer of LM-CP and that the photo-isomerization of the isomer to LM-CP occurre d along with the photo-degradation of LM-CP. We conclude that LM-CP an d CP do not differ significantly from each other in photo-stability. W hen samples contained a significant amount of geometrical isomer of LM -CP, an additional amount of LM-CP was generated by photo-irradiation. Consequently, degradation of LM-CP was apparently delayed, compared w ith that of CP. It was considered that these phenomena led erroneous i nterpretation of the stability of esterified capsanthins.