mined [13]. By means of a change in the turbidity temperature of the protein
solution with the salt concentration, a specific constant k can be determined for
each salt. The change in the foaminess with the salt concentration was calculated by means of this constant k and the dependence of the turbidity temperature on the PEO concentration. The calculated and measured foaminess
values were in good agreement [14]. The applicability of the turbidity temperature for the calculation of foaminess indicates that the influence of salts on
the foaminess is mainly due to their effect on the structure of water.
The influence of organic solvents on the foaminess is more complex. They
control not only the water structure, and by that the protein solubility, but also
the protein structure. In spite of this, it is possible to calculate the foaminess as
a function of the concentrations of various alcohols by means of the turbidity
temperature change, which is corrected by a factor for the direct alcohol/protein
interaction [15].
2.1.5
Influence of Foam Stability
Foam stability is important for foam suppression as well as for foam flotation.
According to Mokrushin and Zhidkova [16], foaminess and foam stability are
complementary properties. This was proved by Bumbullis and Schügerl [17] for
BSA foam. They found that salts which increase the foaminess reduce the foam
stability. There is a relationship between the foam stability and the drainage rate
of liquid from the foam lamellae [1]. With increasing viscosity of the bulk
liquid, the drainage rate diminishes. To evaluate the influence of the surface
viscosity of the liquid on the drainage rate, surface rheological measurements
were performed according to the method of the authors [18–20].
Highly viscoelastic surface viscosity was found with BSA solutions [21].
Above the threshold concentration, the surface viscosity is independent of the
BSA concentration. Below this critical concentration the surface viscosity
increases with diminishing BSA concentration. This could be caused by an
increase in the coordination number of the hydration complex of the protein
[5]. The surface viscosity increased with time, during which the surface tension
remained constant. This may be caused by the conformation change and
denaturation of the protein on the surface [21]. With increasing concentration
of a structure forming salt (Na 2 SO 4 ), foaming and surface viscosity are enhanced and surface tension is diminished [22].
2.2
Foams of Cultivation Media
All industrial biotechnological production processes use complex cultivation
media which consist of agricultural by-products (beet or cane molasses, cornsteep liquor, cottonseed meal, whey permeate, peanut flour, soybean meal,
distillation residues, etc.). In addition polysaccharides (starch, dextrose, malt
extract, maltodextrins, etc.) and proteins (e.g. caseinate, yeast autolysates, etc.)
are used as energy sources for the microorganisms and cells. These systems
Recovery of Proteins and Microorganisms from Cultivation Media by Foam Flotation
197
solution with the salt concentration, a specific constant k can be determined for
each salt. The change in the foaminess with the salt concentration was calculated by means of this constant k and the dependence of the turbidity temperature on the PEO concentration. The calculated and measured foaminess
values were in good agreement [14]. The applicability of the turbidity temperature for the calculation of foaminess indicates that the influence of salts on
the foaminess is mainly due to their effect on the structure of water.
The influence of organic solvents on the foaminess is more complex. They
control not only the water structure, and by that the protein solubility, but also
the protein structure. In spite of this, it is possible to calculate the foaminess as
a function of the concentrations of various alcohols by means of the turbidity
temperature change, which is corrected by a factor for the direct alcohol/protein
interaction [15].
2.1.5
Influence of Foam Stability
Foam stability is important for foam suppression as well as for foam flotation.
According to Mokrushin and Zhidkova [16], foaminess and foam stability are
complementary properties. This was proved by Bumbullis and Schügerl [17] for
BSA foam. They found that salts which increase the foaminess reduce the foam
stability. There is a relationship between the foam stability and the drainage rate
of liquid from the foam lamellae [1]. With increasing viscosity of the bulk
liquid, the drainage rate diminishes. To evaluate the influence of the surface
viscosity of the liquid on the drainage rate, surface rheological measurements
were performed according to the method of the authors [18–20].
Highly viscoelastic surface viscosity was found with BSA solutions [21].
Above the threshold concentration, the surface viscosity is independent of the
BSA concentration. Below this critical concentration the surface viscosity
increases with diminishing BSA concentration. This could be caused by an
increase in the coordination number of the hydration complex of the protein
[5]. The surface viscosity increased with time, during which the surface tension
remained constant. This may be caused by the conformation change and
denaturation of the protein on the surface [21]. With increasing concentration
of a structure forming salt (Na 2 SO 4 ), foaming and surface viscosity are enhanced and surface tension is diminished [22].
2.2
Foams of Cultivation Media
All industrial biotechnological production processes use complex cultivation
media which consist of agricultural by-products (beet or cane molasses, cornsteep liquor, cottonseed meal, whey permeate, peanut flour, soybean meal,
distillation residues, etc.). In addition polysaccharides (starch, dextrose, malt
extract, maltodextrins, etc.) and proteins (e.g. caseinate, yeast autolysates, etc.)
are used as energy sources for the microorganisms and cells. These systems
Recovery of Proteins and Microorganisms from Cultivation Media by Foam Flotation
197