Abstract:In this study，orange Monascus pigments，along with tryptophan or threonine，were used as precursors for the in vitro synthesis of tryptophan-derivatized red Monascus pigmensts （Trp-RMPs）and threoninederivatized red Monascus pigments （Thr-RMPs）based on the aminophilic reaction.The stability of Trp-RMPs and Thr-RMPs at different pH and temperature was then investigated.The synthesized Trp-RMPs and Thr-RMPs were bright red in color，and their color was stable in the pH range of 3-7，with no significant shifts in the maximum absorption wavelength.Trp-RMPs and Thr-RMPs were sensitive to heat，and their thermal degradation reactions were in accordance with the first-order kinetics.In the range of 40℃-80℃，the half-life of Trp-RMPs and Thr-RMPs decreased significantly with an increase in temperature.In addition，pH had a remarkable effect on the thermal stability of Trp-RMPs and Thr-RMPs.In the pH range of 3-7，the higher the pH，the longer the half-life and the better the stability.At pH 3，the thermal stability of Trp-RMPs was better than that of Thr-RMPs as the half-life of Trp-RMPs was significantly longer than that of Thr-RMPs；however，in the pH range of 5-7，Trp-RMPs and Thr-RMPs showed similar thermal stability as their half-life did not differ significantly.