192
FREEZE-DRYING
The present paper is devoted to
review of recent literature and of recent work in the
authors’ laboratories "Which further elucidates the’importance” of the above reaCtions,
and in some cases allows new insight into factors which may modify the extent of deteriœ
ration due to these reactions.
Loss of Volales
‘
‘
'
Many of the avor compounds
"
present in foOds have—vapor pressures exceeding those of
water at the temperatures involved in primary and secondary stages of freeze—dehydration.
Other compounds have vapor pressures comparable to those of water. It might be expected,
therefore, that dehydration at low total pressures would result in very substantial removal
of avor from freeze-dried foods.
—
Kallistratos and Von Sengbusch (1964) subjected a number of pure compounds, selected
from” among tho‘se occurring naturally in foods, to conditions simulating the freeze—dehydration proceSs. (Total pressure 200 p., temperatures from— 30 °C to + 30 °C). They found
that many of the compounds were completely sublimated or evaporated. Among the
compounds showing 100 % loss were n—butyric
iso-amyl butyrate, ethyl acetate,
‘
and benzaldehyde, to name only a few.
These results would be fully expected for pure compounds, and in fact, approximate
;
conditions which occur in s0me simple, model systems. In our laboratories, for instance,
:
a model system consisting of 1 % gelatin, water, and 1 % iso—amyl acetate was subjected
-
to freeze—dehydraüonat a—pr685}1t@9f 400
and it was found that at the time needed to
reduce water content;to
of
acetate Was lost (Holland, 1964).
It should be‘pointçd
__and simplemodels
adequately- represent the situation
using a model System containing
glucose, acetone,
the presence of glucose, 45
the, acetone‘
'
was retained after
secondary dehydration_ at low pressures;
In subsequen“t experiments
these observations of Prof—… Rey
and have, in…ddition,
banana
sliœs,ç and ill—…
in…the,presçncc
Qf;addôdr$ùçf_056— We have
-
found a very substantial retention of a number of highly volatile compounds, including
ethanol, ethyl acetate, 2—pentanone, butanol, iso-amy1 acetate, iso-amyl alcohol, and
n—amyl acetate. The
of some of the alcohols.
These experiments, as well as the well known tenacitÿ with which certain volatile solvents
1nd10ate t…o
Qf dehydraonmw
.
volatile Côpbnènf‘s‘ ofthefoodsthelocal water contentandthetemperature
pféèèiité
:
'gràîents existing in the fooddurmgdehydratwnWearecunentîyeugaged
‘
'
: Onejofjtfheiiirajbhdefects of
is the
.
—
assoc1ated
‘WätÇr—holdingaCapacity and «described ais l'OSS-i11. “juicinesä’.
,
‘
‘
mereasedtwghnessappearancwfawoodytextureandsxmarsubjectwedescnpü°ns
‘
FREEZE-DRYING
The present paper is devoted to
review of recent literature and of recent work in the
authors’ laboratories "Which further elucidates the’importance” of the above reaCtions,
and in some cases allows new insight into factors which may modify the extent of deteriœ
ration due to these reactions.
Loss of Volales
‘
‘
'
Many of the avor compounds
"
present in foOds have—vapor pressures exceeding those of
water at the temperatures involved in primary and secondary stages of freeze—dehydration.
Other compounds have vapor pressures comparable to those of water. It might be expected,
therefore, that dehydration at low total pressures would result in very substantial removal
of avor from freeze-dried foods.
—
Kallistratos and Von Sengbusch (1964) subjected a number of pure compounds, selected
from” among tho‘se occurring naturally in foods, to conditions simulating the freeze—dehydration proceSs. (Total pressure 200 p., temperatures from— 30 °C to + 30 °C). They found
that many of the compounds were completely sublimated or evaporated. Among the
compounds showing 100 % loss were n—butyric
iso-amyl butyrate, ethyl acetate,
‘
and benzaldehyde, to name only a few.
These results would be fully expected for pure compounds, and in fact, approximate
;
conditions which occur in s0me simple, model systems. In our laboratories, for instance,
:
a model system consisting of 1 % gelatin, water, and 1 % iso—amyl acetate was subjected
-
to freeze—dehydraüonat a—pr685}1t@9f 400
and it was found that at the time needed to
reduce water content;to
of
acetate Was lost (Holland, 1964).
It should be‘pointçd
__and simplemodels
adequately- represent the situation
using a model System containing
glucose, acetone,
the presence of glucose, 45
the, acetone‘
'
was retained after
secondary dehydration_ at low pressures;
In subsequen“t experiments
these observations of Prof—… Rey
and have, in…ddition,
banana
sliœs,ç and ill—…
in…the,presçncc
Qf;addôdr$ùçf_056— We have
-
found a very substantial retention of a number of highly volatile compounds, including
ethanol, ethyl acetate, 2—pentanone, butanol, iso-amy1 acetate, iso-amyl alcohol, and
n—amyl acetate. The
of some of the alcohols.
These experiments, as well as the well known tenacitÿ with which certain volatile solvents
1nd10ate t…o
Qf dehydraonmw
.
volatile Côpbnènf‘s‘ ofthefoodsthelocal water contentandthetemperature
pféèèiité
:
'gràîents existing in the fooddurmgdehydratwnWearecunentîyeugaged
‘
'
: Onejofjtfheiiirajbhdefects of
is the
.
—
assoc1ated
‘WätÇr—holdingaCapacity and «described ais l'OSS-i11. “juicinesä’.
,
‘
‘
mereasedtwghnessappearancwfawoodytextureandsxmarsubjectwedescnpü°ns
‘