The Stability of Yellow and Orange Monascus Pigments

In order to understand the difference in stability of different MPs components,a yellow fraction F1 which mainly contained monascin and ankaflavin,and a orange fraction F2 which mainly contained monascorubrin and rubropunctatin,were separated from crude MPs extract by macroporous resin column chromatography. The yellow fraction F1 and orange fraction F2 were then used to analyze to the stability of yellow MPs(YMPs)and orange MPs(OMPs)under varying pH,temperature and light conditions based on UV-Vis spectra and residual values. Results showed that YMPs were stable in the pH range of 2~9,while OMPs were stable in the pH range of 2~4. When pH≥ 5,the λ_max of OMPs shifted obviously. Both of the YMPs and OMPs exhibited good UV-light stability. After 270 min UV-light exposure,no shift of λ_max was observed in UV-Vis spectra of YMPs and OMPs,and the residual percentages of YMPs and OMPs were 70.4%±0.2% and 64.4%±0.9%,respectively,which were significantly higher than that of curcumin(7.9%±0.7%). The thermal stability of YMPs was better than that of OMPs. After heated at 80 ℃ for 120 min,there was an obvious change in the shape of the UV-Vis spectrum of OMP,but not in that of YMPs. Additionally,residual percentage of OMPs after heating was 40.8%±1.9%,which was significantly lower than that of YMPs(87.4%±3.2%)and curcumin(90.9%±4.5%). These results suggested that YMPs was the stable components of MPs and could be used to develop MPs products with high stability.