Effect of pH
The results from flask cultures performed using optimized medium at various pH are presented in Fig. 6. The initial pH value of the medium markedly influenced red pigment formation. A pH range of 5.5 to 8.5 favored red pigment production. At pH higher than 8.5 and lower than 5.5 red pigment production decreased noticeably. Maximum biomass and red pigment production were obtained at pH 4.0 and 7.0, respectively. On the other hand, Carels and Shepherd [17] reported that reducing the pH inhibits the formation of conidia and increases pigment production, suggesting that pH of the medium might affect the transport of certain media constituents such as glucose and nitrogen sources. Growth and activity of fungus was better at pH 4.0 than at pH 7.0. This was evidenced by markedly higher maximum specific rates of glucose consumption and faster specific growth rate at pH 5.5 (data not shown). Regardless of the initial pH, the final pH of the cultures showed a similar value. This pH change during cultivation depends on the nitrogen source [17] and, to lesser extend, on the carbon source [20].