close relationship between the foaminess of the cultivation medium and the
excreted proteins was observed. The foam stability increased in the sequence
C-, N- and P-limited growth cultures.
In cultures with C- and N-growth limitation, the foaminess was influenced
by the dilution rate. At low dilution rate, the foaminess was low, and the
foam consisted of large foam lamellae that were unstable. This phenomenon
was not caused by the change in the proteins, because the dilution rate did not
influence the protein pattern, but by extracellular lipids that were excreted by
the yeast at low dilution rates. The main proteins (75 kD) excreted at P-limitation had a significantly different electrophoretic behavior than those excreted
during C- and N-limitation. They were quantitatively enriched in the foam.
With increasing dilution rate the amount of excreted lipids diminished. The
best cell recovery by flotation was obtained in cultures with P-limitation and
just below the critical dilution rate where no lipids were excreted at all. The high
molecular weight and strongly acidic glycoproteins enriched in the foam and
the low molecular weight ones in the residue liquid. The proteins played a role
as „foamer“ and „collector“ as defined by the flotation technique. Since
Hansenula polymorpha has a hydrophilic surface (see below), its flotation is
only possible with collectors. Exoproteins adsorb at the cell surface and act as
collectors.
4.1.3
Influence of the Flotation Equipment, Construction and Operational Parameters
The column height and diameter, as well as the operational conditions, influence the performance of the flotation process [113]:
– S * and C S * are improved by diminishing feed rate (reduction of water content)
– C R * is reduced, but C S * is not influenced, hence S * is improved by increasing
aeration rate
– C * S and C R * are reduced with diminishing bubble size, and S * passes a slight
maximum at 100–175 mm pore diameter (increasing water content in foam)
– temperature increase up to 50 °C slightly improves C S * but has no effect on C R *
– C S * and S * have maxima at pH 5.0–5.5
– the dilution of cultivation medium increases C S * (diminution of the water
content in foam) and C R * (due to the dilution)
– increase in the foam layer height up to 15 cm enlarges C S * and C R * , above that
they are constant
– increasing height of the aerated liquid layer reduces C S * slightly, but C R * considerably, separation is improved
– enlargement of the foam column diameter improves C S * and S * (reduction of
wall effect)
– addition of structure-maker salts to the medium increases the foaminess and
reduces C S *
– addition of structure-breaker salts to the medium decreases the foaminess
and increases C S * , but does not influence C R *
Recovery of Proteins and Microorganisms from Cultivation Media by Foam Flotation
223
excreted proteins was observed. The foam stability increased in the sequence
C-, N- and P-limited growth cultures.
In cultures with C- and N-growth limitation, the foaminess was influenced
by the dilution rate. At low dilution rate, the foaminess was low, and the
foam consisted of large foam lamellae that were unstable. This phenomenon
was not caused by the change in the proteins, because the dilution rate did not
influence the protein pattern, but by extracellular lipids that were excreted by
the yeast at low dilution rates. The main proteins (75 kD) excreted at P-limitation had a significantly different electrophoretic behavior than those excreted
during C- and N-limitation. They were quantitatively enriched in the foam.
With increasing dilution rate the amount of excreted lipids diminished. The
best cell recovery by flotation was obtained in cultures with P-limitation and
just below the critical dilution rate where no lipids were excreted at all. The high
molecular weight and strongly acidic glycoproteins enriched in the foam and
the low molecular weight ones in the residue liquid. The proteins played a role
as „foamer“ and „collector“ as defined by the flotation technique. Since
Hansenula polymorpha has a hydrophilic surface (see below), its flotation is
only possible with collectors. Exoproteins adsorb at the cell surface and act as
collectors.
4.1.3
Influence of the Flotation Equipment, Construction and Operational Parameters
The column height and diameter, as well as the operational conditions, influence the performance of the flotation process [113]:
– S * and C S * are improved by diminishing feed rate (reduction of water content)
– C R * is reduced, but C S * is not influenced, hence S * is improved by increasing
aeration rate
– C * S and C R * are reduced with diminishing bubble size, and S * passes a slight
maximum at 100–175 mm pore diameter (increasing water content in foam)
– temperature increase up to 50 °C slightly improves C S * but has no effect on C R *
– C S * and S * have maxima at pH 5.0–5.5
– the dilution of cultivation medium increases C S * (diminution of the water
content in foam) and C R * (due to the dilution)
– increase in the foam layer height up to 15 cm enlarges C S * and C R * , above that
they are constant
– increasing height of the aerated liquid layer reduces C S * slightly, but C R * considerably, separation is improved
– enlargement of the foam column diameter improves C S * and S * (reduction of
wall effect)
– addition of structure-maker salts to the medium increases the foaminess and
reduces C S *
– addition of structure-breaker salts to the medium decreases the foaminess
and increases C S * , but does not influence C R *
Recovery of Proteins and Microorganisms from Cultivation Media by Foam Flotation
223