Photo-stability of coloring constituents in paprika color

Capsanthin (CP) and esterified capsanthins are the main coloring constituents in paprika color. Several reports have suggested that esterified capsanthins are more stable to light than CP itself in paprika powder and paprika extract. To clarify whether this is so, the photo-stability of lauroylmyristoylcapsanthin (LM-CP) and CP was investigated in paprika powder, commercial paprika solution and isolated individual solutions. After irradiation of the samples with visible light (4,000 lux) at 25 degrees C, HPLC analyses were performed to quantify both compounds. 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 of paprika powder and commercial paprika solution after photo-irradiation. A peak, which appears at 68.3 min, about 2 min after the peak of LM-CP in the chromatograms, decreased quickly during an early stage of photo-irradiation and the peak of LM-CP significantly increased concomitantly. HPLC analyses revealed that the isolated fraction corresponding to the peak at 68.3 min was transformed to LM-CP by photo-irradiation. The LC-APCI-MS analysis of the peak (68.3 min) showed a quiasi molecularion 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 occurred along with the photo-degradation of LM-CP. We conclude that LM-CP and CP do not differ significantly from each other in photo-stability. When 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 with that of CP. It was considered that these phenomena led erroneous interpretation of the stability of esterified capsanthins.