198
FREEZE—DRYÏNG
oxidation extended into the bimolecular phase ‘of oxidation in addition to
affecting the early stages. The inhibition of the catalyzed reaction by water is interpreted
.
as due to deactivation of metal catalysts by hydration of their coordination shells (Labuza,
1965).
A schematic summary of the mechanisms of inhibition of oxidation, based on our recent
work, is presented below :
,
Inhibition (A)
initiation :
i
/ H2O
[ROOH]A [ÎMl
RO - + - OH
free radicals
_
t
Propagation :
k
_
R ‘ + 02 "
ROz ‘
k
R02- + RH _2> [ROOH]A + [ROOH]3
Inhibition (B) :
water—li id
[ROOHIB
[ROOH]A
interface
Tèrmination :
’
2 R02 —
non radical products
-
(from Labuza, 1965)
'
It can be seen that tWo separate mechanisms may be effective simultaneously in the case
of oxidation catalyzed by metals. In both cases the rate of initiation is lowered, either by
'
inactivating the metal catalyst (Inhibition A) or by binding a fraction of the total hydroperoxides at a water—lipid interface (Inhibition B).
'
Since many of the
freeZe—dried foods susceptible to oxidation are also rich in proteins,
we have also been interested in intera‘ctibn of lipid oxidation products and proteins and
amino acids; The possible interactions of lipid oxidation and proteins have already been
alluded to previously, and it
is known that lipid oxidationproducts can impair quality of
proteins in dehydrated foods. A reCentdemonstrati0n “of interactions of this type is presented
by El—Bhargawi and Bugan (1965) =
‘
'
'
‘
'
Another effect of possible signicance
is the antioxidant effect of amino acids and pro—
teins.”
Such eectshàve “bee'n'shoWn‘for*gelatin by Bishov et al. (1961) and for emulsions
by-* Marcuse (1961): Recently, We have -undertaken
on oxidation of methyl linoleate
in>a freeze—dried
model system based
on microorystalline cellulose, in the presence and
-infàtheÇJ-absencezàof amino —cäi*bôXylib
-‘ compounds—_—added in* concentrations ranging from
‘1_O*3ft0
4 10”?
observedthatSever*al—arino carboxylic
compounds had- «substatialantioxidant'
such activity Was
observed included: histidine,
alanine, lysinè“;
gamma
amino‘ïbutync
”amino
acid;
Jantioxidant ac't‘iVity‘was obserVed
“
‘
7
'
°
»
»
FREEZE—DRYÏNG
oxidation extended into the bimolecular phase ‘of oxidation in addition to
affecting the early stages. The inhibition of the catalyzed reaction by water is interpreted
.
as due to deactivation of metal catalysts by hydration of their coordination shells (Labuza,
1965).
A schematic summary of the mechanisms of inhibition of oxidation, based on our recent
work, is presented below :
,
Inhibition (A)
initiation :
i
/ H2O
[ROOH]A [ÎMl
RO - + - OH
free radicals
_
t
Propagation :
k
_
R ‘ + 02 "
ROz ‘
k
R02- + RH _2> [ROOH]A + [ROOH]3
Inhibition (B) :
water—li id
[ROOHIB
[ROOH]A
interface
Tèrmination :
’
2 R02 —
non radical products
-
(from Labuza, 1965)
'
It can be seen that tWo separate mechanisms may be effective simultaneously in the case
of oxidation catalyzed by metals. In both cases the rate of initiation is lowered, either by
'
inactivating the metal catalyst (Inhibition A) or by binding a fraction of the total hydroperoxides at a water—lipid interface (Inhibition B).
'
Since many of the
freeZe—dried foods susceptible to oxidation are also rich in proteins,
we have also been interested in intera‘ctibn of lipid oxidation products and proteins and
amino acids; The possible interactions of lipid oxidation and proteins have already been
alluded to previously, and it
is known that lipid oxidationproducts can impair quality of
proteins in dehydrated foods. A reCentdemonstrati0n “of interactions of this type is presented
by El—Bhargawi and Bugan (1965) =
‘
'
'
‘
'
Another effect of possible signicance
is the antioxidant effect of amino acids and pro—
teins.”
Such eectshàve “bee'n'shoWn‘for*gelatin by Bishov et al. (1961) and for emulsions
by-* Marcuse (1961): Recently, We have -undertaken
on oxidation of methyl linoleate
in>a freeze—dried
model system based
on microorystalline cellulose, in the presence and
-infàtheÇJ-absencezàof amino —cäi*bôXylib
-‘ compounds—_—added in* concentrations ranging from
‘1_O*3ft0
4 10”?
observedthatSever*al—arino carboxylic
compounds had- «substatialantioxidant'
such activity Was
observed included: histidine,
alanine, lysinè“;
gamma
amino‘ïbutync
”amino
acid;
Jantioxidant ac't‘iVity‘was obserVed
“
‘
7
'
°
»
»