Ï94
FREEZE—DRYING
In both cases, reduced water binding at the isoelectric pH range resulted from
'
dehydration. The decreased rehydration resulted in signicant changes in tenderness
as measured with a Warner _Bratzler tenderometer (Wismer-Pedersen, 1965 b).
'The nature of the interactions which cause the decreased hydration is not fully under—
stood. Connell (1957) suggested that some of the increased aggregation is due to inter—
molecular disulde bridges. This view is supported by the work of Khan and Van Den‘Berg
ï
(1965) who observed that in frozen storage of chicken muscle, tenderness changes correlated
with decreased sulfhydryl content of muscle. Other mechanisms, however, must be operative,
_
particularly the formation of new electrostatic and hydrogen bonds between the chains
of muscle proteins, as suggested byHamm and Deatherage (1960). This appears likely
in view of the new ndings diScussed below which show the extreme sensitivity of the
rehydration and tenderness' characteristics of muscle tissues to the ionic environment
/
existing during the dehydration. WiSmer-Pedersen (1965 b) found that the rehydration
capacity and texture of pork muscle after freeze—dehydration were affected drastically by
pre-drying injections of= EDTA and; of pyrophosphate. In his studies, increased pH during
dehydration did not affect the rehydration and texture.
‘
'
Penny'ea—l.
1963) studied the properties of freeze-dried muscles in Which the pH
during drying‘
injections of adrenaline and found a very
'
substantia‘l improvement iii hÿdration due to the elevated pH. This was true in pork as well
as _in beef.
'
—
'- ”‘
,
_
‘
'
-
'
Adjustment‘of pH afær'dehydtation is ’cohsidérably less effective than that prior to
dehydration. This was obserVedïby all of the above authors, as well as by Suden et al. (1964)
who failed to observe improvements in rehydration of pork due to changes in pH of
rehydrating Solutions.
addition of EDTA to the rehydrating solution does not
improve rehydration, but EDTA inj‘é‘cted prior to dehydration signicantly improves
penetration of the rehydrating medium into the tissue and improves both rehÿdration and
texture (VVismerŒederSen, 1956 b).
“
"
:
'
WhateVer may be the meChanism Of crosslinking in dehydfa‘tion, it is evident that the
..
degree of deterioration may be‘controlled‘to some eXtent by processing parameters and” by
treatments "at
dehydration. In particular; temperature during» the dehÿdtati0n
*
.pt00ess ‘is’
important variable (Goldblith et al., 1963; Ttmmy andï Felder,
1964). The deleteoùS effect-of high*temperatures during ‘dr‘ÿing may arise “from the“fact
that denatured proteins shoWÿmore‘tendency to cresslink than do native proteins or mildly
*
denatui:€dpr0teins. Whileit is ‘ftrue thatdeatturaori “in the dry state “is consideràbly
retarded; conditions during freeze—fdryingf do result ‘in lÔCa1=liqùid
concentrations
_
which are substantial. This is,
non—‘fr02en water*when ”temperatures Of the
“frozen zone” are above — 25 °C during the proCess (Nemit‘Z, l964)»or tothe considerable
amounti’of ‘Ÿ‘bound’7"water‘fwhic‘his—retaiedin'thé f*diy”
the
crystals (Fusi, 1965). The effects Of the crosslinking or aggregation may .:be‘« counter—
‘
prôœœÿnc enzymes to the :rehydfation wateru‘This‘treatment
{to be; quite_iîefectiveà' by…«Sose‘bee et al; ‘
(1964), who applied two proteclÿtic
:,
Thework
that
myosrn
responsible forïî-îÏëliajiiges“duringïthe<“àffreeieïdehydratio‘n:aproceSsÀ It Jf
}‘h6wever; that‘frëcent’workï fo‘‘nff_roze1'i«%ïi‘Sl—t,’î m wh1chær alternativesexplan‘aticn
ofthesechangesrsadvancedmaÿaCtuallyhave apphcaüontodehydraüonInthISV1CW
_
sh
dUet‘o intefa£étio;df£thése“;proteins‘
FREEZE—DRYING
In both cases, reduced water binding at the isoelectric pH range resulted from
'
dehydration. The decreased rehydration resulted in signicant changes in tenderness
as measured with a Warner _Bratzler tenderometer (Wismer-Pedersen, 1965 b).
'The nature of the interactions which cause the decreased hydration is not fully under—
stood. Connell (1957) suggested that some of the increased aggregation is due to inter—
molecular disulde bridges. This view is supported by the work of Khan and Van Den‘Berg
ï
(1965) who observed that in frozen storage of chicken muscle, tenderness changes correlated
with decreased sulfhydryl content of muscle. Other mechanisms, however, must be operative,
_
particularly the formation of new electrostatic and hydrogen bonds between the chains
of muscle proteins, as suggested byHamm and Deatherage (1960). This appears likely
in view of the new ndings diScussed below which show the extreme sensitivity of the
rehydration and tenderness' characteristics of muscle tissues to the ionic environment
/
existing during the dehydration. WiSmer-Pedersen (1965 b) found that the rehydration
capacity and texture of pork muscle after freeze—dehydration were affected drastically by
pre-drying injections of= EDTA and; of pyrophosphate. In his studies, increased pH during
dehydration did not affect the rehydration and texture.
‘
'
Penny'ea—l.
1963) studied the properties of freeze-dried muscles in Which the pH
during drying‘
injections of adrenaline and found a very
'
substantia‘l improvement iii hÿdration due to the elevated pH. This was true in pork as well
as _in beef.
'
—
'- ”‘
,
_
‘
'
-
'
Adjustment‘of pH afær'dehydtation is ’cohsidérably less effective than that prior to
dehydration. This was obserVedïby all of the above authors, as well as by Suden et al. (1964)
who failed to observe improvements in rehydration of pork due to changes in pH of
rehydrating Solutions.
addition of EDTA to the rehydrating solution does not
improve rehydration, but EDTA inj‘é‘cted prior to dehydration signicantly improves
penetration of the rehydrating medium into the tissue and improves both rehÿdration and
texture (VVismerŒederSen, 1956 b).
“
"
:
'
WhateVer may be the meChanism Of crosslinking in dehydfa‘tion, it is evident that the
..
degree of deterioration may be‘controlled‘to some eXtent by processing parameters and” by
treatments "at
dehydration. In particular; temperature during» the dehÿdtati0n
*
.pt00ess ‘is’
important variable (Goldblith et al., 1963; Ttmmy andï Felder,
1964). The deleteoùS effect-of high*temperatures during ‘dr‘ÿing may arise “from the“fact
that denatured proteins shoWÿmore‘tendency to cresslink than do native proteins or mildly
*
denatui:€dpr0teins. Whileit is ‘ftrue thatdeatturaori “in the dry state “is consideràbly
retarded; conditions during freeze—fdryingf do result ‘in lÔCa1=liqùid
concentrations
_
which are substantial. This is,
non—‘fr02en water*when ”temperatures Of the
“frozen zone” are above — 25 °C during the proCess (Nemit‘Z, l964)»or tothe considerable
amounti’of ‘Ÿ‘bound’7"water‘fwhic‘his—retaiedin'thé f*diy”
the
crystals (Fusi, 1965). The effects Of the crosslinking or aggregation may .:be‘« counter—
‘
prôœœÿnc enzymes to the :rehydfation wateru‘This‘treatment
{to be; quite_iîefectiveà' by…«Sose‘bee et al; ‘
(1964), who applied two proteclÿtic
:,
Thework
that
myosrn
responsible forïî-îÏëliajiiges“duringïthe<“àffreeieïdehydratio‘n:aproceSsÀ It Jf
}‘h6wever; that‘frëcent’workï fo‘‘nff_roze1'i«%ïi‘Sl—t,’î m wh1chær alternativesexplan‘aticn
ofthesechangesrsadvancedmaÿaCtuallyhave apphcaüontodehydraüonInthISV1CW
_
sh
dUet‘o intefa£étio;df£thése“;proteins‘