contain many proteins and surfactants besides several poorly defined components (e.g. solid particles) which influence the formation and properties of
foams [1, 23] in (volume-aerated) submersed cultures. However, because
protein foams dominate in cultivation media, it is expected that properties of
protein foams and cultivation foams will be similar and that results obtained
with model protein foams can be applied for foams of cultivation media.
2.2.1
Foaminess of Components of Cultivation Media
Szarka and Magyar [24] investigated the foaminess of various cultivation
medium components such as corn-steep liquor, peanut meal, soybean meal and
casein solutions and their dependence on the pH value and sterilization. The
foaminess passes a maximum with increasing concentration of these components in the range 3 to 5% and as a function of the pH value. The maximum
is at pH 4 in the case of soybean meal solutions. With increasing sterilization
time the foaminess is enhanced. After 100 min heat treatment at 125 °C, the
foaminess S increased by a factor of 7 in the case of a model cultivation medium
consisting of glucose soybean meal and CaCO 3 in water.
2.2.2
Foaminess of Microbial Cell Cultivation Systems
In this section the foam behavior of various cultivation media is investigated. The
surface tension s and foaminess S of cultivation media of Hansenula polymorpha
with unlimited, substrate limited and oxygen transfer limited growth in the presence and absence of antifoam agents were investigated using methanol, ethanol
and glucose substrates, respectively. The time dependence of s can be described
by the Avrami relationship: ln y = bt n , where y is the dimensionless surface
tension. The constants n and b are functions of the cultivation time t F as long as
the growth is unlimited, but they are constant in the state of limited growth. With
the glucose substrate, S can be presented as a definite function of the time t DG , as
in model protein foams. However, with methanol and ethanol substrates, no
definite S (t DG ) function was found, because their concentration varied during
the cultivation [25]. In the main, alcohols considerably influence foaminess, as
shown by Bumbullis and Schügerl [15]. Surface tension (about 45 mN m –1 ) and
surface viscosity (0.55 cP) were constant during the cultivation time with methanol as substrate in the presence of an antifoam agent. During cultivation with
ethanol as substrate, and in the presence of an antifoam agent, the surface tension
diminished slightly and the surface viscosity increased with the time.
During Escherichia coli cultivation on casein peptone, yeast and meat extract
as medium components and in presence of an antifoam agent, the surface
tension (36 mN m –1) and surface viscosity (1.9 cP) were constant and did not
depend on the cultivation time.
Similar investigations were performed with Penicillium chrysogenum
cultivation medium in the absence and presence of antifoam agents [26]. Again
the Avrami relationship was applied for the antifoam-free system. The foami198
K. Schügerl
foams [1, 23] in (volume-aerated) submersed cultures. However, because
protein foams dominate in cultivation media, it is expected that properties of
protein foams and cultivation foams will be similar and that results obtained
with model protein foams can be applied for foams of cultivation media.
2.2.1
Foaminess of Components of Cultivation Media
Szarka and Magyar [24] investigated the foaminess of various cultivation
medium components such as corn-steep liquor, peanut meal, soybean meal and
casein solutions and their dependence on the pH value and sterilization. The
foaminess passes a maximum with increasing concentration of these components in the range 3 to 5% and as a function of the pH value. The maximum
is at pH 4 in the case of soybean meal solutions. With increasing sterilization
time the foaminess is enhanced. After 100 min heat treatment at 125 °C, the
foaminess S increased by a factor of 7 in the case of a model cultivation medium
consisting of glucose soybean meal and CaCO 3 in water.
2.2.2
Foaminess of Microbial Cell Cultivation Systems
In this section the foam behavior of various cultivation media is investigated. The
surface tension s and foaminess S of cultivation media of Hansenula polymorpha
with unlimited, substrate limited and oxygen transfer limited growth in the presence and absence of antifoam agents were investigated using methanol, ethanol
and glucose substrates, respectively. The time dependence of s can be described
by the Avrami relationship: ln y = bt n , where y is the dimensionless surface
tension. The constants n and b are functions of the cultivation time t F as long as
the growth is unlimited, but they are constant in the state of limited growth. With
the glucose substrate, S can be presented as a definite function of the time t DG , as
in model protein foams. However, with methanol and ethanol substrates, no
definite S (t DG ) function was found, because their concentration varied during
the cultivation [25]. In the main, alcohols considerably influence foaminess, as
shown by Bumbullis and Schügerl [15]. Surface tension (about 45 mN m –1 ) and
surface viscosity (0.55 cP) were constant during the cultivation time with methanol as substrate in the presence of an antifoam agent. During cultivation with
ethanol as substrate, and in the presence of an antifoam agent, the surface tension
diminished slightly and the surface viscosity increased with the time.
During Escherichia coli cultivation on casein peptone, yeast and meat extract
as medium components and in presence of an antifoam agent, the surface
tension (36 mN m –1) and surface viscosity (1.9 cP) were constant and did not
depend on the cultivation time.
Similar investigations were performed with Penicillium chrysogenum
cultivation medium in the absence and presence of antifoam agents [26]. Again
the Avrami relationship was applied for the antifoam-free system. The foami198
K. Schügerl