3.2. Effect of incubation temperature
Significant variation (p < 0.05) of citric acid production was observed at different temperature levels. Maximum production was observed at 28 C (Fig. 2). Beyond 28 C, the production was significantly reduced. Temperature above 28 C also reduces the biomass production indicating the optimum level of temperature for citric acid and biomass production for A. niger was 28 C. Similar findings were reported earlier (Roukas, 2000). However, it was also reported that 31.5 C was the optimum temperature for citric acid production by A. niger (Walid et al., 2007). Citric acid production and biomass was highly correlated (R2 = 0.92) at different incubation temperatures