by means of the surface tension vs. pH diagram. However, because of a strong
overlapping of the protein peaks their separation was not possible.
Liu et al. [77] investigated the separation of BSA and hemoglobin by flotation
in batch operation. An optimal separation factor a = S 1 (BSA)/S 2 (HBB) = 14 was
obtained at pH 3.9. Brown et al. [73] investigated the separation of binary
mixtures of b-casein, lysozyme and BSA and obtained fairly good separations
(Table 5).
The isolation and purification of human placental homogenate was investigated by Sarkar et al. [78] in a batch foam column. They found the
optimum near to the IEP (pH 8.0). Column diameter and height were optimized. At a low gas flow rate the best separation from accompanying proteases
was obtained.
3.3
Application of Additives
Miranda and Berglund [79] used a food grade polymer, (hydroxypropyl)methyl
cellulose (HPMC), and ammonium sulfate as additives for the recovery of
recombinant a-amylase by flotation. The enzyme was removed from the liquid
phase by partition to a salted-out HPMC phase and the enzyme-containing
polymer flocs were recovered by flotation. This system behaved in a manner
similar to the flotation of mineral systems. The problem with this technique is
the cost of the polymer and the separation of the enzyme from the polymer
phase. Both of them complicate the process and increase the separation cost. In
general, for protein recovery and separation, especially in the pharmaceutical
industry, it is not proper to add chemicals to the feed, because they have to be
removed from the product completely and this separation causes problems and
additive costs.
3.4
Protein Denaturation
The application of foam flotation for the recovery of enzymes is often impaired
by their denaturation and activity loss. By using nitrogen or carbon dioxide as
sparging gas, respectively, instead of air, low volumetric flow rates (0.79 cm s –1 )
and operating at 16 °C and pH 3, denaturation can be suppressed. In the case of
catalase the loss of enzyme activity was reduced to 0% and in the case of
trypsin to 10% [80].
Varley and Ball [81] investigated the activities of lysozyme, pepsin and
trypsin during foam separation. They found that with increasing protein
concentration the enzyme activity loss diminished. According to Graham and
Phillips [82, 83] the surface concentration of a protein at the gas/liquid interface
changes with its bulk concentration. At higher bulk concentrations a multiprotein layer with high surface coverage is formed. A bubble surface covered by
a multi-layer obviously reduces the residence time of the protein in the foam
phase and protects the enzymes from denaturation. With increasing flow rate,
the activity loss was reduced. 99% of the initial activity of lysozyme, 92% of
Recovery of Proteins and Microorganisms from Cultivation Media by Foam Flotation
217
overlapping of the protein peaks their separation was not possible.
Liu et al. [77] investigated the separation of BSA and hemoglobin by flotation
in batch operation. An optimal separation factor a = S 1 (BSA)/S 2 (HBB) = 14 was
obtained at pH 3.9. Brown et al. [73] investigated the separation of binary
mixtures of b-casein, lysozyme and BSA and obtained fairly good separations
(Table 5).
The isolation and purification of human placental homogenate was investigated by Sarkar et al. [78] in a batch foam column. They found the
optimum near to the IEP (pH 8.0). Column diameter and height were optimized. At a low gas flow rate the best separation from accompanying proteases
was obtained.
3.3
Application of Additives
Miranda and Berglund [79] used a food grade polymer, (hydroxypropyl)methyl
cellulose (HPMC), and ammonium sulfate as additives for the recovery of
recombinant a-amylase by flotation. The enzyme was removed from the liquid
phase by partition to a salted-out HPMC phase and the enzyme-containing
polymer flocs were recovered by flotation. This system behaved in a manner
similar to the flotation of mineral systems. The problem with this technique is
the cost of the polymer and the separation of the enzyme from the polymer
phase. Both of them complicate the process and increase the separation cost. In
general, for protein recovery and separation, especially in the pharmaceutical
industry, it is not proper to add chemicals to the feed, because they have to be
removed from the product completely and this separation causes problems and
additive costs.
3.4
Protein Denaturation
The application of foam flotation for the recovery of enzymes is often impaired
by their denaturation and activity loss. By using nitrogen or carbon dioxide as
sparging gas, respectively, instead of air, low volumetric flow rates (0.79 cm s –1 )
and operating at 16 °C and pH 3, denaturation can be suppressed. In the case of
catalase the loss of enzyme activity was reduced to 0% and in the case of
trypsin to 10% [80].
Varley and Ball [81] investigated the activities of lysozyme, pepsin and
trypsin during foam separation. They found that with increasing protein
concentration the enzyme activity loss diminished. According to Graham and
Phillips [82, 83] the surface concentration of a protein at the gas/liquid interface
changes with its bulk concentration. At higher bulk concentrations a multiprotein layer with high surface coverage is formed. A bubble surface covered by
a multi-layer obviously reduces the residence time of the protein in the foam
phase and protects the enzymes from denaturation. With increasing flow rate,
the activity loss was reduced. 99% of the initial activity of lysozyme, 92% of
Recovery of Proteins and Microorganisms from Cultivation Media by Foam Flotation
217