Lactalbumin. Lactalbumin has temperatures for heat coagulation similar
to that of egg albumin. The lactalbumin forms a flocculent precipitate,
whereas egg albumin forms a firm coagulum. Rupp has reported the fol-
lowing amount of lactalbumin coagulated when heated for 30 minutes.
Temperature,
Albumin rendered insoluble,
°c.
per cent
62.8
0.00
65.6
5.75
68.3
12.75
71.1
30.78
Casein. Casein is not coagulated by heat at ordinary temperatures or
when heated for short periods, though the heating may alter the casein.
Rogers states that it is necessary to heat milk about 12 hours at 100°C. to
bring about coagulation. It takes approximately 1 hour at 135°C. and
approximately 3 minutes at 155°C. The time and temperature vary some-
what with different milks.
The rate of coagulation depends upon the concentration of the casein as
well as the time and the temperature of heating. Rogers states that
evaporated milk, containing twice the concentration of solids-not-fat in
normal milk, and thus a higher concentration of casein, requires about 60
minutes for coagulation at 114.5°C., 10 minutes at 131 °C., and 7500
minutes at 80°C.
Rogers and Palmer both state that, in the evaporated-milk industry,
the forewarming of milk prior to processing increases its stability to heat.
"Rapid improvement in resistance to heat coagulation results in increase
in temperature for prewarming up to 90° to 100°C. Above 90°C. the
change is very small, but in some cases can be effected with increases in
temperature up to 120°C. for 10-minute periods of forewarming. When
time is chosen as the variable, improvement may be noted with increases in
the time up to 30 minutes at a temperature of 95 °C. At higher tempera-
tures the same improvement may be effected in shorter periods of time."
Fat. Rogers states that fat particles in relatively large aggregates may
act as nuclei about which coagulation of the casein can proceed. In un-
homogenized milk the fat affects the coagulation time and temperature but
slightly. But when a milk of higher fat content is homogenized the fat
clumps may act as nuclei about which the casein may gather during heat-
ing. With increase in homogenization pressure as well as fat content, other
conditions being the same, a marked decrease in stability to heat is noted.
In homogenized milk it was found that the maximum stability to heat
coagulation occurs if homogenization is carried out at 80°.
306 MILK AND CHEESE
Rogers adds that the feathering of some homogenized cream when
added to coffee may be caused by using too high homogenization pressure,
thus reducing the stability of the cream to heat.
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Lactalbumin. Lactalbumin has temperatures for heat coagulation similar
to that of egg albumin. The lactalbumin forms a flocculent precipitate,
whereas egg albumin forms a firm coagulum. Rupp has reported the fol-
lowing amount of lactalbumin coagulated when heated for 30 minutes.
Temperature,
Albumin rendered insoluble,
°c.
per cent
62.8
0.00
65.6
5.75
68.3
12.75
71.1
30.78
Casein. Casein is not coagulated by heat at ordinary temperatures or
when heated for short periods, though the heating may alter the casein.
Rogers states that it is necessary to heat milk about 12 hours at 100°C. to
bring about coagulation. It takes approximately 1 hour at 135°C. and
approximately 3 minutes at 155°C. The time and temperature vary some-
what with different milks.
The rate of coagulation depends upon the concentration of the casein as
well as the time and the temperature of heating. Rogers states that
evaporated milk, containing twice the concentration of solids-not-fat in
normal milk, and thus a higher concentration of casein, requires about 60
minutes for coagulation at 114.5°C., 10 minutes at 131 °C., and 7500
minutes at 80°C.
Rogers and Palmer both state that, in the evaporated-milk industry,
the forewarming of milk prior to processing increases its stability to heat.
"Rapid improvement in resistance to heat coagulation results in increase
in temperature for prewarming up to 90° to 100°C. Above 90°C. the
change is very small, but in some cases can be effected with increases in
temperature up to 120°C. for 10-minute periods of forewarming. When
time is chosen as the variable, improvement may be noted with increases in
the time up to 30 minutes at a temperature of 95 °C. At higher tempera-
tures the same improvement may be effected in shorter periods of time."
Fat. Rogers states that fat particles in relatively large aggregates may
act as nuclei about which coagulation of the casein can proceed. In un-
homogenized milk the fat affects the coagulation time and temperature but
slightly. But when a milk of higher fat content is homogenized the fat
clumps may act as nuclei about which the casein may gather during heat-
ing. With increase in homogenization pressure as well as fat content, other
conditions being the same, a marked decrease in stability to heat is noted.
In homogenized milk it was found that the maximum stability to heat
coagulation occurs if homogenization is carried out at 80°.
306 MILK AND CHEESE
Rogers adds that the feathering of some homogenized cream when
added to coffee may be caused by using too high homogenization pressure,
thus reducing the stability of the cream to heat.