Abstract
BackgroundFungal morphology and aeration play a significant role in the growth process of Mortierella alpina. The production of microbial oil rich in arachidonic acid (ARA) in M. alpina was enhanced by using a multi-stage fermentation strategy which combined fed-batch culture with precise control of aeration and agitation rates at proper times.ResultsThe fermentation period was divided into four stages according to the cultivation characteristics of M. alpina. The dissolved oxygen concentration was well suited for ARA biosynthesis. Moreover, the ultimate dry cell weight (DCW), lipid, and ARA yields obtained using this strategy reached 41.4, 22.2, 13.5 g/L, respectively. The respective values represent 14.8, 25.8, and 7.8% improvements over traditional fed-batch fermentation processes.ConclusionsThis strategy provides promising control insights for the mass production of ARA-rich oil on an industrial scale. Pellet-like fungal morphology was transformed into rice-shaped particles which were beneficial for oxygen transfer and thus highly suitable for biomass accumulation.
Highlights
Fungal morphology and aeration play a significant role in the growth process of Mortierella alpina
The C/N ratio is an important fermentation parameter which can affect mycelial morphology (Koike et al 2001; Park et al 2001), and it has been demonstrated previously that the morphology of M. alpina mycelia has a strong effect on physical properties of the broth, which in turn might lead to poor mass transfer performance
Due to the difficulty of controlling the mycelial morphology of M. alpina under constant aeration and agitation rates, the dry cell weight obtained in fed-batch fermentation (36.1 g/L) was not much higher than what was obtained in batch fermentation (31.1 g/L)
Summary
Fungal morphology and aeration play a significant role in the growth process of Mortierella alpina. The production of microbial oil rich in arachidonic acid (ARA) in M. alpina was enhanced by using a multi-stage fermenta‐ tion strategy which combined fed-batch culture with precise control of aeration and agitation rates at proper times. Egg yolk, animal liver, and adrenal glands were the main sources of ARA. Their low intrinsic ARA content (Higashiyama et al 2002) restricts their application, and it is not possible to source sufficient material for. The agitation rate in mechanically stirred bioreactors, which are normally used for the production of ARA-rich oil, has to be controlled within a very precise range.
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