There is a worldwide interest in the development of processes for colorants production from natural sources such as microorganism. The aim of this study was to optimize red colorants production by Penicillium purpurogenum DPUA 1275 and to evaluate the effect of pH, temperature, salts and polymers on the stability of these colorants. Under optimized conditions, a 78% increase in red colorants production was achieved. The best pH and temperature conditions were obtained at pH 8.0 and 70 degrees C, respectively. In the presence of salts NaCl and Na2SO4, both at concentrations of 0.1 and 0.5 M in Mcllvaine buffer (pH 8.0), the red colorants showed good stability. In the presence of both polymers polyethylene glycol and sodium polyacrylate, the red colorants kept their color intensity. Thus, this study presents characteristics of red colorants produced by P. purpurogenum that can be applied in different industries after toxicological examination. (c) 2013 American Institute of Chemical Engineers Biotechnol. Prog., 29:778-785, 2013