FROZEN FOODS
149
solid or liquid foodstu”s.
Moreover, as a result of water freezing, the solutes always
present in the water phase of foods (sugars, salts, acids, etc.) are highly concentrated Or
even crystallized; the -residual liquid freezes at cryohydric point. Demixing effects take
place; but because of the relative short time no pronounced diffusion effects occur, except
mechanical or chemical damage or even rupture of cell membranes (walls) will. happen.
The freezing begins always in the extracellular space, and the cells are somewhat dehydrated
depending on the freezing rate.
/
,
The chemical and biochemical changes during the freezing can be neglected.
The
weight loss of adequately prepacked food is also negligible.
.
3. CHANGES DURING STORAGE
These changes are most important for the stability of froZen foodstus, especially as far
as the reversibility of water bindingability of the frozen tissues after thaWig is concerned.
The freezing denaturation of different proteins 8, which progresseS slowly but steadily
during storage and which is mainly caused by the e‘eet of concentrated eleCtrolytes, is
one of the main factors inuencing the Water holding ability of thaWed food; thepermeability of cell membranes and connective tissues also allows the drip formation. In products
such as meat the water holding capacity is better With higher pH—valueS. GlObülines are
usually more susceptible to freezing denàturation—Which is explàinéd as aggrçgatio
effect—than the albumines.
The extent of freeZing denaturation mainly depëñds on
temperature and length of storage.
‘
_
As special form of irreversible freezirig, a denaturation known as “freezer burn”
as result of sublimation of ice crystals, if a denaturation of structure proteins takes, place 9;it leads to a formation of spongy tissue With micropores and miCrôcapillaes Of a very
large internal surface. In many foodstù's the “freezer burn” is Visible because of acolo‘u'i‘
change on the surface, as bright spots; but very often it penetràtës
the tÏSSiie, leading
after defrosting to a strawy sometimes “wet paper like”-tasting Structure. Low temperature
and good and tightly enclosing packaging material help here.
1
_
_'
’
In many foods a complete inaCtivatioh of enzymes Cannot be done befoæ fræzing;
in such cases one also must expect enzymic changes in the range of commerciay applied
temperatures, even if they are kept at a low level. As an example
it maybe mentioned
that an autolysis of muscle tissue or lipase induced fat oxidation Will occur in froZe pro—'
ducts.
'
Besides also chemical reactions as fat oxidation and hydrolysis can take place, if oxygen
is available.
A good packaging can help, but usually it,does notpreventthis kind ofçhe—
mical reactions completely.
_
_
"
,
4.
;FROZENFOODS .
‘
.
_
_
”
4.1. Criteria of stabitÿ
'
_
_
,
_
__
;
“
The stability of frozen foods iS' usually judged -,by:théyacceptale change 9f_ftheîr quality;
occurring during the stora,geuder
givenor
.
-
fore, as main criteriarof stability
changes of
Such
149
solid or liquid foodstu”s.
Moreover, as a result of water freezing, the solutes always
present in the water phase of foods (sugars, salts, acids, etc.) are highly concentrated Or
even crystallized; the -residual liquid freezes at cryohydric point. Demixing effects take
place; but because of the relative short time no pronounced diffusion effects occur, except
mechanical or chemical damage or even rupture of cell membranes (walls) will. happen.
The freezing begins always in the extracellular space, and the cells are somewhat dehydrated
depending on the freezing rate.
/
,
The chemical and biochemical changes during the freezing can be neglected.
The
weight loss of adequately prepacked food is also negligible.
.
3. CHANGES DURING STORAGE
These changes are most important for the stability of froZen foodstus, especially as far
as the reversibility of water bindingability of the frozen tissues after thaWig is concerned.
The freezing denaturation of different proteins 8, which progresseS slowly but steadily
during storage and which is mainly caused by the e‘eet of concentrated eleCtrolytes, is
one of the main factors inuencing the Water holding ability of thaWed food; thepermeability of cell membranes and connective tissues also allows the drip formation. In products
such as meat the water holding capacity is better With higher pH—valueS. GlObülines are
usually more susceptible to freezing denàturation—Which is explàinéd as aggrçgatio
effect—than the albumines.
The extent of freeZing denaturation mainly depëñds on
temperature and length of storage.
‘
_
As special form of irreversible freezirig, a denaturation known as “freezer burn”
as result of sublimation of ice crystals, if a denaturation of structure proteins takes, place 9;it leads to a formation of spongy tissue With micropores and miCrôcapillaes Of a very
large internal surface. In many foodstù's the “freezer burn” is Visible because of acolo‘u'i‘
change on the surface, as bright spots; but very often it penetràtës
the tÏSSiie, leading
after defrosting to a strawy sometimes “wet paper like”-tasting Structure. Low temperature
and good and tightly enclosing packaging material help here.
1
_
_'
’
In many foods a complete inaCtivatioh of enzymes Cannot be done befoæ fræzing;
in such cases one also must expect enzymic changes in the range of commerciay applied
temperatures, even if they are kept at a low level. As an example
it maybe mentioned
that an autolysis of muscle tissue or lipase induced fat oxidation Will occur in froZe pro—'
ducts.
'
Besides also chemical reactions as fat oxidation and hydrolysis can take place, if oxygen
is available.
A good packaging can help, but usually it,does notpreventthis kind ofçhe—
mical reactions completely.
_
_
"
,
4.
;FROZENFOODS .
‘
.
_
_
”
4.1. Criteria of stabitÿ
'
_
_
,
_
__
;
“
The stability of frozen foods iS' usually judged -,by:théyacceptale change 9f_ftheîr quality;
occurring during the stora,geuder
givenor
.
-
fore, as main criteriarof stability
changes of
Such