Based on the results of Table 1, extraction of Monascus pigments
from the excess IL phase by IL–tert-butanol two-phase system was to carry out aminophilic reaction. After complete aminophilic reaction,addition of cyclohexane into the reaction solution separated into two phases, where the upper one (cyclohexane) was yellow while the lower one (ethanol aqueous solution) was red (Fig. 4A). The visible spectrum of reaction solution, the cyclohexane phase, and the ethanol solution phase was determined, respectively (Fig. 4B), in which pigment absorbance of the cyclohexane phase was normalized to 24 ml. The pigment spectrum of the cyclohexane
phase exhibited the character of yellow Monascus pigments with an apex at 395 nm while that of the ethanol solution phase exhibited the characteristic apex at 510 nm of red Monascus pigments [26]. Those results were further confirmed by TLC analysis (Fig. 4C). Thus, yellow Monascus pigments was achieved in the cyclohexane phase by conversion of hydrophobic orange Monascus pigments into hydrophilic red ones via aminophilic reaction. Further purification of
the yellow Monascus pigments was carried out using silica gel column chromatography (detailed in Fig. S3) and yellow Monascus pigments could be crystallized in ethanol aqueous solution.