Page 483 - Biosystems Engineering

Super critical Fluid Extraction Applications 455

(Ratledge 1992). In cultures of Mortierella for ARA production, glu-
cose and starch are most frequently used as the primary carbon
source. In terms of nitrogen sources, yeast extract (YE) and soybean
meal (SM) are widely used. Bajpai et al. (1991) studied the effect of
carbon sources in the medium on the growth of fungi, M. alpina ATCC
32222. This medium was prepared according to the procedure of
Hansson and Dostalek (1988). Glycerol, glucose, fructose, xylose,
maltose, sucrose, starch, olive oil, and linseed oil were compared.
Fungal growth was poor in the medium containing xylose or sucrose.
With other carbon sources, biomass production ranged from 16.9 g/L
for dextrin to 28.2 g/L for linseed oil. However, ARA content of bio-
mass and content of lipids in biomass was very low when linseed oil
was the carbon source. ARA content of biomass produced with fruc-
tose, maltose, glycerol, and glucose ranged from 9.6 to 10.8 percent
(w/w) with ARA accounting for 44.7 to 54.1 percent of the total fatty
acids. Jang et al. (2005) also investigated various carbon sources,
including soluble starch, glucose, glycerol, galactose, and maltose,
as well as nitrogen sources including KNO , NaNO , NH NO ,
3 3 4 3
(NH ) SO , urea, YE, and their combinations, and found that soluble
4 2 4
starch at 10 percent and the mixture of KNO and yeast extract 2:1
3
(w/w) was the best carbon and nitrogen combination for ARA and
total PUFA production. Totani et al. (1992) reported the effect of glu-
cose concentration on ARA production, and showed that more than
20 percent glucose inhibited the growth of M. alpina. Totani et al.
(2000) also reported that when peptone and wheat bran were used as
nitrogen sources, a high ARA productivity of 11 g/L was obtained.
Only a small amount of biomass was obtained in the medium com-
prising NH NO , NaNO , KNO , or (NH ) SO as nitrogen sources,
4 3 3 3 4 2 4
suggesting that Mortierella fungi hardly assimilate inorganic nitrogen
source, and require an amino acid or a protein to obtain a certain
amount of biomass. Singh and Ward (1997) also reported when
NaNO was replaced with corn steep liquor, ARA yield was signifi-
3
cantly improved.
Lipid production was one of a few biotechnological processes that
proceeded quite well in a simple batch culture. In this system, the
carbon-to-nitrogen (C/N) ratio was an important parameter (Streekstra
2005). Jang et al. (2005) conducted an elemental analysis of M. alpina
ATCC 32222, with a C/N ratio of 4.9, and reported that a C/N ratio
of 9.0 gave a high cell yield, whereas a C/N ratio of 5.2 gave maximal
ARA and total PUFAs production. However, an optimal C/N ratio of
15 to 20 for ARA production was reported by Koike et al. (2001).
Sajbidor et al. (1990) reported that Mortierella sp. had high ARA
production at a C/N ratio of 20. The difference might result from dif-
ferent strains or culture conditions.
The ratio of C/N also affects the morphology of fungi, which
affects the whole fermentation process, including the productivity of
targeted metabolites and product recovery/purification in downstream