3.7. Comparison of cultivations in flask and fermentor
To test the effect in the fermentor, P. ergngii culture with MHP as the nitrogen source was carried out in a 5 L-fermentor. The cultivation was conducted in the fermentor containing 3-L main medium with 1.6% (w/v) MHP as nitrogen source. The results are shown in Table 5. As compared to the culture in shake flask, no significant difference on the maximal mycelial biomass production was observed. However, the mycelial growth rate (2.44 g/L/day) and specific EPS yield (28.67 mg/g-dry-weight) for MHP were significantly increased. Meanwhile, when using MHP as nitrogen source, the EPS maximal production reached 312 mg/L, a 3.39-fold increase as compared to that in flask test. To study the effect, the mass transfer coefficients for flask and fermentor were measured and compared. It was found that in the fermentor with the agitation and aeration rates of 100 rpm and 1 vvm, a mass transfer coefficient of KLa = 14.7 h 1 was obtained. This value is obviously higher than that in the shake flask (KLa = 5.1 h 1). The variation in mass transfer is expected to be the main factor contributing to the increase of mycelial growth rate and EPS production in the fermentor