195
FREEZE—DRYÏNG
’
‘
and black currants. They observed rapid loss of ascorbic acid in all of. these materials;
when stored either under vacuum or under COz at 40 °C and at a water
of approxi—
{;
mately 4%. Apparently, hydrogen acceptors present in dehydrated‘ juices are capable
of participating in ascorbic acid degradation, even when molecular oxygen isinaintained
at-a low level.
‘
-
‘
-
'
Other types of browning have also been documented as occurring at relatively low water
contents. Huang and Draudt (1964), for instance, have studied carbonyl—ammobrowning
…
in freeze-dried peaches at 28 °C and were able to isolate browning intermediates sat Water
contents of 1.68 %, but none at 0.55 %, after 138
storage. The intermediates isolated
appeared “to be fructose—asparagine, fruCtose-aspartic
and a reaction productrïo‘f
Ÿ
ammonia and D—glucose.
.
»
‘
»
Y
Browning due to interactions of lipid oxidation products and amino acids or of lipid
oxidation products and proteins can' also occur
low moisture ”Contents. Among >the
studies showing such interactionsin
meal— Were those of Carpenter et al. (1962)
who demonstrated reacti0ns between lysine residues in the herring proteins and oxidation
products of lipids. Heating of themeal containing oxidizedlipid resulted‘ in substàntial
loss of lysine
of the bi010gical Value of the proteins. These reactions Were
strongly dependent “on moisture
and maximum loss of lysine occurred at 5 to
14%
L'F>“-'
…
,
,:
…,
4‘
'
Toyomizu and his
discolo'ràtiOn “of frœze—dried jack mackerel
and
that the dàrkenigŸ of the sh *was due in“part‘to changes in myoglobin but
thatpart of the disColora£tidhcould bea'œounted‘for«bybrowning reactions involving“the .
oxidation of lipids.
(1965) fstudi‘edv—amodel system containing
histidine, methyl linoleate and microcrystalline cellulose. After incubation at 37 °C in
complete absence of water (after freeze-drying), a fraction showing uorescence
brown color and containing carbon derived both from the lipid and the amino acid has
been isolated.;
.
,
…
,
_
«
£ipîd Oxidation
”
,_
In Îour previouslypublishedreVieW(‘KareL 1968) it
ont that oxidation “of lipids
in
foods présents wa::ïproblem” which ?is—- 1üiiCulayvdifcult = to:
The
reasons f0r this dicult}t—Linclude; among
oxidation? in
freeze-dried.
;
…
»
.i
»1. Extreme
“oxidation even “atsïV6tÿ»£Ÿlowpa‘rtial ; pressuresmf Oxygen.
'
2 Acceleration
‘
…
Wè suggested
commetCially ‘“efeaSiblé
of
to
signicantly lower rates of oxidation.This suggeâtiô was bas”edbtwork on médelëisystems
containing linoleic ï
of: publications? de’scribigëäthe
-
_,sterage
: of vacuu—dried m11k:Æàs
“published
dehÿdraitedfi tonar‘î
iliighly
.
_
contamerheadspace ? Also,thepro0xidatiyè
loW—aaWate“r
Was
_
»
'
]
Anumberofhypotheseshwe
wà“cer
1Thatwaœrhasapretectweeffœtdueto retardatwnofoxygend1ffusxon (Haito;
'
…
andFischer,l937)
FREEZE—DRYÏNG
’
‘
and black currants. They observed rapid loss of ascorbic acid in all of. these materials;
when stored either under vacuum or under COz at 40 °C and at a water
of approxi—
{;
mately 4%. Apparently, hydrogen acceptors present in dehydrated‘ juices are capable
of participating in ascorbic acid degradation, even when molecular oxygen isinaintained
at-a low level.
‘
-
‘
-
'
Other types of browning have also been documented as occurring at relatively low water
contents. Huang and Draudt (1964), for instance, have studied carbonyl—ammobrowning
…
in freeze-dried peaches at 28 °C and were able to isolate browning intermediates sat Water
contents of 1.68 %, but none at 0.55 %, after 138
storage. The intermediates isolated
appeared “to be fructose—asparagine, fruCtose-aspartic
and a reaction productrïo‘f
Ÿ
ammonia and D—glucose.
.
»
‘
»
Y
Browning due to interactions of lipid oxidation products and amino acids or of lipid
oxidation products and proteins can' also occur
low moisture ”Contents. Among >the
studies showing such interactionsin
meal— Were those of Carpenter et al. (1962)
who demonstrated reacti0ns between lysine residues in the herring proteins and oxidation
products of lipids. Heating of themeal containing oxidizedlipid resulted‘ in substàntial
loss of lysine
of the bi010gical Value of the proteins. These reactions Were
strongly dependent “on moisture
and maximum loss of lysine occurred at 5 to
14%
L'F>“-'
…
,
,:
…,
4‘
'
Toyomizu and his
discolo'ràtiOn “of frœze—dried jack mackerel
and
that the dàrkenigŸ of the sh *was due in“part‘to changes in myoglobin but
thatpart of the disColora£tidhcould bea'œounted‘for«bybrowning reactions involving“the .
oxidation of lipids.
(1965) fstudi‘edv—amodel system containing
histidine, methyl linoleate and microcrystalline cellulose. After incubation at 37 °C in
complete absence of water (after freeze-drying), a fraction showing uorescence
brown color and containing carbon derived both from the lipid and the amino acid has
been isolated.;
.
,
…
,
_
«
£ipîd Oxidation
”
,_
In Îour previouslypublishedreVieW(‘KareL 1968) it
ont that oxidation “of lipids
in
foods présents wa::ïproblem” which ?is—- 1üiiCulayvdifcult = to:
The
reasons f0r this dicult}t—Linclude; among
oxidation? in
freeze-dried.
;
…
»
.i
»1. Extreme
“oxidation even “atsïV6tÿ»£Ÿlowpa‘rtial ; pressuresmf Oxygen.
'
2 Acceleration
‘
…
Wè suggested
commetCially ‘“efeaSiblé
of
to
signicantly lower rates of oxidation.This suggeâtiô was bas”edbtwork on médelëisystems
containing linoleic ï
of: publications? de’scribigëäthe
-
_,sterage
: of vacuu—dried m11k:Æàs
“published
dehÿdraitedfi tonar‘î
iliighly
.
_
contamerheadspace ? Also,thepro0xidatiyè
loW—aaWate“r
Was
_
»
'
]
Anumberofhypotheseshwe
wà“cer
1Thatwaœrhasapretectweeffœtdueto retardatwnofoxygend1ffusxon (Haito;
'
…
andFischer,l937)