The major pigment components in the crude Monascus pigments were yellow Monascus pigments and orange ones. The aminophilic reaction between orange Monascus pigments and MSG was carried out followed a similar procedure as reported in the literatures [18]. The crude Monascus pigments was re-dissolved in 24 ml ethanol aqueous solution (70% (V/V), pH = 7) to prepare Monascus pigments ethanol aqueous solution with 46 AU (absorbance unit, multiplication of the absorbance with its dilution ratio of a sample) at 410 nm and 39 AU at 470 nm. Then excess MSG (1.5 g) was added into the Monascus pigment ethanol aqueous solution, which was shaken at 30 C and 200 rpm. The residual orange Monascus pigments in the ethanol aqueous solution were monitored by thin layer chromatography (TLC) analysis. After the
aminophilic reaction for 10 h, 190 ml cyclohexane was added into the reaction solution. The mixture solution was separated into a cyclohexane phase and an ethanol aqueous solution phase. Yellow Monascus pigments were partitioned into the cyclohexane phase, which was recovered by air stripping off solvent.
The yellow Monascus pigments were further purified by silica gel column chromatography. The yellow Monascus pigments in the washing solution were monitored by TLC analysis. The detailed information was presented in supplementary materials of Fig. S3. The washing solution was subjected to air stripping off solvent and yellow Monascus pigments had been crystallized.