- Teks
- Sejarah
10.4.3 INTERACTIONS OFAMYLOPECTIN A
10.4.3 INTERACTIONS OFAMYLOPECTIN ANDAMYLOSE
In a study in which retrogradation of gels from nongranular mixtures with
different amylose/amylopectin ratios were studied, synergistic interactions
were seen between amylopectin and amylose at a high amylose content [160].
Because the melting endotherm, as measured by the DSC method, has been
attributed to the recrystallization of the amylopectin fraction, one could expect
that the melting endotherm is proportional to the amount of amylopectin.
Gudmundsson and Eliasson [160], however, found unexpectedly high values
for the melting enthalpy of gels with very high amylose content (75 to 90%).
The possibility of limited cocrystallization has been proposed in relation to
retrogradation [161]. Such cocrystallization could be promoted when amylose
is found in high amounts. Schierbaum et al. [162] have found that linear
segments of amylopectin and amylose, or limit dextrins of certain critical
lengths, can interact in solution. Similar findings were reported by Seivert and
Würsch [159] in a study of the chain association of amylose and the effect of
amylopectin on that process in mixtures with different ratios of amylose to
© 2006 by Taylor & Francis Group, LLC
Starch: Physicochemical and Functional Aspects 419
amylopectin. They found that an increasing amount of amylopectin restricted
the chain association of amylose, and the authors attributed this finding to
either dilution or steric hindrance effects; however, the amylose and amylopectin in aqueous solution have been shown to be immiscible at moderate concentrations, and that encourages phase separation of the polymers [56]. Under
most circumstances, the interactions of amylose and amylopectin should be
limited in normal starch gels, as amylose is preferably leached out of the
granules, whereas the amylopectin is mainly retained within the granules.
10.4.4 STORAGETEMPERATURE ANDWATERCONTENT
Retrogradation is greatly affected by storage temperature. Storage of starch
gels with 45 to 50% water content at low temperatures but above the glass
transition temperature (Tg= –5.0°C) increases the retrogradation compared to
storage at room temperature, especially during the first days of storage. Storage
at freezing temperatures below the Tgvirtually inhibits recrystallization
[91,134]. Higher temperatures (above 32 to 40°C) effectively reduce retrogradation [134]. The Avrami equation has been frequently used to account for
the kinetics of the recrytallization process at different temperatures and water
contents [134,135,137]; however, the analysis of retrogradation kinetics
according to the Avrami equation requires thermodynamic equilibrium conditions, but that is not the case here and the method therefore has limited
applicability. Retrogradation is a nonequilibrium recrystallization process, as
indicated by the fact that at low temperatures (4 to 5°C) the crystallites formed
are less nearly perfect (i.e., they have lower melting temperature Tc) than
crystallites formed at higher storage temperatures [163,164]. A three-step
mechanism of initial nucleation (junction point of two or more starch molecules) followed by crystal growth and propagation and then crystal perfection
has been proposed [6].
Crystallization that follows such a mechanism is nucleation controlled
(i.e., the nucleation has to take place before the propagation can begin). Within
the range Tg
to Tc(e.g., –5.0 to 60°C for a gel with 50% water), both nucleation
and propagation exhibit an exponential dependence on temperature, such that
nucleation rate increases with decreasing temperature, down to the Tg, while
the propagation rate increases with increasing temperature, up to the Tc
[6].
This explains why crystallization occurs at low temperatures but only to a
limited degree at elevated temperatures (>30°C), because nucleation formation
is then retarded. For longer storage periods, the retrogradation should be
maximal at a temperature about midway between Tg
and Tc, as both nucleation
and propagation then take place at moderate rates. Both normal and waxy
starches seem to follow this mechanism; the rate of retrogradation was found
to increase during a 48-hour period with decreasing temperature in the interval
of 1 to 25°C [165]. Amylose gels stored at 6°C did not develop a staling
endotherm during 48 hours of storage [165], indicating that crystallinity melted
© 2006 by Taylor & Francis Group, LLC
420 Carbohydrates in Food
below 100°C is due to amylopectin. Results from NMR studies on the temperature dependence of retrogradation are consistent with these findings
[151,166].
Recrystallization of amylopectin is very sensitive to the water content in
starch gels. A starch content in the range of 10 to 80% is necessary for the
development of the DSC endotherm [137]. The maximum crystallization has
been measured at around 50% starch with DSC as well as with NMR [137,143,
145,151].
In contrast to a native starch suspensions, the gelatinized starch gel is
completely amorphous and its water is uniformly distributed. The recrystallization process depends on the temperature difference between the storage
temperature and the Tg
of the amorphous gel, as the mobility of the chains
determines their association rate. Because water is a plasticizer, it controls the
Tg
of the amorphous gel. At a very low water content, the Tgis above room
temperature, and the amorphous gel is in a highly viscous glassy state that
effectively hinders molecular mobility. Recrystallization increases with increasing water content until 45 to 50% water content is reached. Progressively more
effective plasticization (increased molecular mobility) is obtained, and finally
Tgis depressed below room temperature. Recrystallization then decreases with
a further increase in water content up to 90%, apparently due to dilution of the
crystallizable component in the plasticized amorphous matrix [6].
Due to their antiplasticizing effect, solutes (e.g., sugars) affect the retrogradation of starch gels compared to water alone [6]. They reduce the mobility
of the chains in the amorphous matrix by increasing the Tg
. As a consequence,
the rate of propagation can decline, decreasing the extent of retrogradation.
10.4.5 BOTANICALSOURCE
The botanical source is of great importance for the retrogradation of starch
gels [22,167–173]. This is true not only for starches with very different amylose content, but also for starches with similar amylose contents. Some of the
differences among, for example, cereal starches can be attributed to differences
in the amylose/amylopectin ratio and lipid contents; however, these factors
account for only some of the differences. Structural differences found in the
amylopectin molecule can explain some of the differences in the rate and
extent of recrystallization.
Some studies indicate that the rate, and sometimes the extent, of retrogradation increases with increasing amounts of amylose. Although the amylopectin is considered responsible for the long-term retrogradation, some
waxy starch types are reported to retrograde slowly, but pea and potato
starches with high amylose contents retrograde to a greater extent
[151,174,175]. It is possible that the initial rate of retrogradation could be
accelerated because of synergistic interactions between amylopectin and amylose, as discussed earlier. Other studies have failed to show this relation of
In a study in which retrogradation of gels from nongranular mixtures with
different amylose/amylopectin ratios were studied, synergistic interactions
were seen between amylopectin and amylose at a high amylose content [160].
Because the melting endotherm, as measured by the DSC method, has been
attributed to the recrystallization of the amylopectin fraction, one could expect
that the melting endotherm is proportional to the amount of amylopectin.
Gudmundsson and Eliasson [160], however, found unexpectedly high values
for the melting enthalpy of gels with very high amylose content (75 to 90%).
The possibility of limited cocrystallization has been proposed in relation to
retrogradation [161]. Such cocrystallization could be promoted when amylose
is found in high amounts. Schierbaum et al. [162] have found that linear
segments of amylopectin and amylose, or limit dextrins of certain critical
lengths, can interact in solution. Similar findings were reported by Seivert and
Würsch [159] in a study of the chain association of amylose and the effect of
amylopectin on that process in mixtures with different ratios of amylose to
© 2006 by Taylor & Francis Group, LLC
Starch: Physicochemical and Functional Aspects 419
amylopectin. They found that an increasing amount of amylopectin restricted
the chain association of amylose, and the authors attributed this finding to
either dilution or steric hindrance effects; however, the amylose and amylopectin in aqueous solution have been shown to be immiscible at moderate concentrations, and that encourages phase separation of the polymers [56]. Under
most circumstances, the interactions of amylose and amylopectin should be
limited in normal starch gels, as amylose is preferably leached out of the
granules, whereas the amylopectin is mainly retained within the granules.
10.4.4 STORAGETEMPERATURE ANDWATERCONTENT
Retrogradation is greatly affected by storage temperature. Storage of starch
gels with 45 to 50% water content at low temperatures but above the glass
transition temperature (Tg= –5.0°C) increases the retrogradation compared to
storage at room temperature, especially during the first days of storage. Storage
at freezing temperatures below the Tgvirtually inhibits recrystallization
[91,134]. Higher temperatures (above 32 to 40°C) effectively reduce retrogradation [134]. The Avrami equation has been frequently used to account for
the kinetics of the recrytallization process at different temperatures and water
contents [134,135,137]; however, the analysis of retrogradation kinetics
according to the Avrami equation requires thermodynamic equilibrium conditions, but that is not the case here and the method therefore has limited
applicability. Retrogradation is a nonequilibrium recrystallization process, as
indicated by the fact that at low temperatures (4 to 5°C) the crystallites formed
are less nearly perfect (i.e., they have lower melting temperature Tc) than
crystallites formed at higher storage temperatures [163,164]. A three-step
mechanism of initial nucleation (junction point of two or more starch molecules) followed by crystal growth and propagation and then crystal perfection
has been proposed [6].
Crystallization that follows such a mechanism is nucleation controlled
(i.e., the nucleation has to take place before the propagation can begin). Within
the range Tg
to Tc(e.g., –5.0 to 60°C for a gel with 50% water), both nucleation
and propagation exhibit an exponential dependence on temperature, such that
nucleation rate increases with decreasing temperature, down to the Tg, while
the propagation rate increases with increasing temperature, up to the Tc
[6].
This explains why crystallization occurs at low temperatures but only to a
limited degree at elevated temperatures (>30°C), because nucleation formation
is then retarded. For longer storage periods, the retrogradation should be
maximal at a temperature about midway between Tg
and Tc, as both nucleation
and propagation then take place at moderate rates. Both normal and waxy
starches seem to follow this mechanism; the rate of retrogradation was found
to increase during a 48-hour period with decreasing temperature in the interval
of 1 to 25°C [165]. Amylose gels stored at 6°C did not develop a staling
endotherm during 48 hours of storage [165], indicating that crystallinity melted
© 2006 by Taylor & Francis Group, LLC
420 Carbohydrates in Food
below 100°C is due to amylopectin. Results from NMR studies on the temperature dependence of retrogradation are consistent with these findings
[151,166].
Recrystallization of amylopectin is very sensitive to the water content in
starch gels. A starch content in the range of 10 to 80% is necessary for the
development of the DSC endotherm [137]. The maximum crystallization has
been measured at around 50% starch with DSC as well as with NMR [137,143,
145,151].
In contrast to a native starch suspensions, the gelatinized starch gel is
completely amorphous and its water is uniformly distributed. The recrystallization process depends on the temperature difference between the storage
temperature and the Tg
of the amorphous gel, as the mobility of the chains
determines their association rate. Because water is a plasticizer, it controls the
Tg
of the amorphous gel. At a very low water content, the Tgis above room
temperature, and the amorphous gel is in a highly viscous glassy state that
effectively hinders molecular mobility. Recrystallization increases with increasing water content until 45 to 50% water content is reached. Progressively more
effective plasticization (increased molecular mobility) is obtained, and finally
Tgis depressed below room temperature. Recrystallization then decreases with
a further increase in water content up to 90%, apparently due to dilution of the
crystallizable component in the plasticized amorphous matrix [6].
Due to their antiplasticizing effect, solutes (e.g., sugars) affect the retrogradation of starch gels compared to water alone [6]. They reduce the mobility
of the chains in the amorphous matrix by increasing the Tg
. As a consequence,
the rate of propagation can decline, decreasing the extent of retrogradation.
10.4.5 BOTANICALSOURCE
The botanical source is of great importance for the retrogradation of starch
gels [22,167–173]. This is true not only for starches with very different amylose content, but also for starches with similar amylose contents. Some of the
differences among, for example, cereal starches can be attributed to differences
in the amylose/amylopectin ratio and lipid contents; however, these factors
account for only some of the differences. Structural differences found in the
amylopectin molecule can explain some of the differences in the rate and
extent of recrystallization.
Some studies indicate that the rate, and sometimes the extent, of retrogradation increases with increasing amounts of amylose. Although the amylopectin is considered responsible for the long-term retrogradation, some
waxy starch types are reported to retrograde slowly, but pea and potato
starches with high amylose contents retrograde to a greater extent
[151,174,175]. It is possible that the initial rate of retrogradation could be
accelerated because of synergistic interactions between amylopectin and amylose, as discussed earlier. Other studies have failed to show this relation of
5000/5000
10.4.3 INTERACTIONS OFAMYLOPECTIN ANDAMYLOSE
In a study in which retrogradation of gels from nongranular mixtures with
different amylose/amylopectin ratios were studied, synergistic interactions
were seen between amylopectin and amylose at a high amylose content [160].
Because the melting endotherm, as measured by the DSC method, has been
attributed to the recrystallization of the amylopectin fraction, one could expect
that the melting endotherm is proportional to the amount of amylopectin.
Gudmundsson and Eliasson [160], however, found unexpectedly high values
for the melting enthalpy of gels with very high amylose content (75 to 90%).
The possibility of limited cocrystallization has been proposed in relation to
retrogradation [161]. Such cocrystallization could be promoted when amylose
is found in high amounts. Schierbaum et al. [162] have found that linear
segments of amylopectin and amylose, or limit dextrins of certain critical
lengths, can interact in solution. Similar findings were reported by Seivert and
Würsch [159] in a study of the chain association of amylose and the effect of
amylopectin on that process in mixtures with different ratios of amylose to
© 2006 by Taylor & Francis Group, LLC
Starch: Physicochemical and Functional Aspects 419
amylopectin. They found that an increasing amount of amylopectin restricted
the chain association of amylose, and the authors attributed this finding to
either dilution or steric hindrance effects; however, the amylose and amylopectin in aqueous solution have been shown to be immiscible at moderate concentrations, and that encourages phase separation of the polymers [56]. Under
most circumstances, the interactions of amylose and amylopectin should be
limited in normal starch gels, as amylose is preferably leached out of the
granules, whereas the amylopectin is mainly retained within the granules.
10.4.4 STORAGETEMPERATURE ANDWATERCONTENT
Retrogradation is greatly affected by storage temperature. Storage of starch
gels with 45 to 50% water content at low temperatures but above the glass
transition temperature (Tg= –5.0°C) increases the retrogradation compared to
storage at room temperature, especially during the first days of storage. Storage
at freezing temperatures below the Tgvirtually inhibits recrystallization
[91,134]. Higher temperatures (above 32 to 40°C) effectively reduce retrogradation [134]. The Avrami equation has been frequently used to account for
the kinetics of the recrytallization process at different temperatures and water
contents [134,135,137]; however, the analysis of retrogradation kinetics
according to the Avrami equation requires thermodynamic equilibrium conditions, but that is not the case here and the method therefore has limited
applicability. Retrogradation is a nonequilibrium recrystallization process, as
indicated by the fact that at low temperatures (4 to 5°C) the crystallites formed
are less nearly perfect (i.e., they have lower melting temperature Tc) than
crystallites formed at higher storage temperatures [163,164]. A three-step
mechanism of initial nucleation (junction point of two or more starch molecules) followed by crystal growth and propagation and then crystal perfection
has been proposed [6].
Crystallization that follows such a mechanism is nucleation controlled
(i.e., the nucleation has to take place before the propagation can begin). Within
the range Tg
to Tc(e.g., –5.0 to 60°C for a gel with 50% water), both nucleation
and propagation exhibit an exponential dependence on temperature, such that
nucleation rate increases with decreasing temperature, down to the Tg, while
the propagation rate increases with increasing temperature, up to the Tc
[6].
This explains why crystallization occurs at low temperatures but only to a
limited degree at elevated temperatures (>30°C), because nucleation formation
is then retarded. For longer storage periods, the retrogradation should be
maximal at a temperature about midway between Tg
and Tc, as both nucleation
and propagation then take place at moderate rates. Both normal and waxy
starches seem to follow this mechanism; the rate of retrogradation was found
to increase during a 48-hour period with decreasing temperature in the interval
of 1 to 25°C [165]. Amylose gels stored at 6°C did not develop a staling
endotherm during 48 hours of storage [165], indicating that crystallinity melted
© 2006 by Taylor & Francis Group, LLC
420 Carbohydrates in Food
below 100°C is due to amylopectin. Results from NMR studies on the temperature dependence of retrogradation are consistent with these findings
[151,166].
Recrystallization of amylopectin is very sensitive to the water content in
starch gels. A starch content in the range of 10 to 80% is necessary for the
development of the DSC endotherm [137]. The maximum crystallization has
been measured at around 50% starch with DSC as well as with NMR [137,143,
145,151].
In contrast to a native starch suspensions, the gelatinized starch gel is
completely amorphous and its water is uniformly distributed. The recrystallization process depends on the temperature difference between the storage
temperature and the Tg
of the amorphous gel, as the mobility of the chains
determines their association rate. Because water is a plasticizer, it controls the
Tg
of the amorphous gel. At a very low water content, the Tgis above room
temperature, and the amorphous gel is in a highly viscous glassy state that
effectively hinders molecular mobility. Recrystallization increases with increasing water content until 45 to 50% water content is reached. Progressively more
effective plasticization (increased molecular mobility) is obtained, and finally
Tgis depressed below room temperature. Recrystallization then decreases with
a further increase in water content up to 90%, apparently due to dilution of the
crystallizable component in the plasticized amorphous matrix [6].
Due to their antiplasticizing effect, solutes (e.g., sugars) affect the retrogradation of starch gels compared to water alone [6]. They reduce the mobility
of the chains in the amorphous matrix by increasing the Tg
. As a consequence,
the rate of propagation can decline, decreasing the extent of retrogradation.
10.4.5 BOTANICALSOURCE
The botanical source is of great importance for the retrogradation of starch
gels [22,167–173]. This is true not only for starches with very different amylose content, but also for starches with similar amylose contents. Some of the
differences among, for example, cereal starches can be attributed to differences
in the amylose/amylopectin ratio and lipid contents; however, these factors
account for only some of the differences. Structural differences found in the
amylopectin molecule can explain some of the differences in the rate and
extent of recrystallization.
Some studies indicate that the rate, and sometimes the extent, of retrogradation increases with increasing amounts of amylose. Although the amylopectin is considered responsible for the long-term retrogradation, some
waxy starch types are reported to retrograde slowly, but pea and potato
starches with high amylose contents retrograde to a greater extent
[151,174,175]. It is possible that the initial rate of retrogradation could be
accelerated because of synergistic interactions between amylopectin and amylose, as discussed earlier. Other studies have failed to show this relation of
In a study in which retrogradation of gels from nongranular mixtures with
different amylose/amylopectin ratios were studied, synergistic interactions
were seen between amylopectin and amylose at a high amylose content [160].
Because the melting endotherm, as measured by the DSC method, has been
attributed to the recrystallization of the amylopectin fraction, one could expect
that the melting endotherm is proportional to the amount of amylopectin.
Gudmundsson and Eliasson [160], however, found unexpectedly high values
for the melting enthalpy of gels with very high amylose content (75 to 90%).
The possibility of limited cocrystallization has been proposed in relation to
retrogradation [161]. Such cocrystallization could be promoted when amylose
is found in high amounts. Schierbaum et al. [162] have found that linear
segments of amylopectin and amylose, or limit dextrins of certain critical
lengths, can interact in solution. Similar findings were reported by Seivert and
Würsch [159] in a study of the chain association of amylose and the effect of
amylopectin on that process in mixtures with different ratios of amylose to
© 2006 by Taylor & Francis Group, LLC
Starch: Physicochemical and Functional Aspects 419
amylopectin. They found that an increasing amount of amylopectin restricted
the chain association of amylose, and the authors attributed this finding to
either dilution or steric hindrance effects; however, the amylose and amylopectin in aqueous solution have been shown to be immiscible at moderate concentrations, and that encourages phase separation of the polymers [56]. Under
most circumstances, the interactions of amylose and amylopectin should be
limited in normal starch gels, as amylose is preferably leached out of the
granules, whereas the amylopectin is mainly retained within the granules.
10.4.4 STORAGETEMPERATURE ANDWATERCONTENT
Retrogradation is greatly affected by storage temperature. Storage of starch
gels with 45 to 50% water content at low temperatures but above the glass
transition temperature (Tg= –5.0°C) increases the retrogradation compared to
storage at room temperature, especially during the first days of storage. Storage
at freezing temperatures below the Tgvirtually inhibits recrystallization
[91,134]. Higher temperatures (above 32 to 40°C) effectively reduce retrogradation [134]. The Avrami equation has been frequently used to account for
the kinetics of the recrytallization process at different temperatures and water
contents [134,135,137]; however, the analysis of retrogradation kinetics
according to the Avrami equation requires thermodynamic equilibrium conditions, but that is not the case here and the method therefore has limited
applicability. Retrogradation is a nonequilibrium recrystallization process, as
indicated by the fact that at low temperatures (4 to 5°C) the crystallites formed
are less nearly perfect (i.e., they have lower melting temperature Tc) than
crystallites formed at higher storage temperatures [163,164]. A three-step
mechanism of initial nucleation (junction point of two or more starch molecules) followed by crystal growth and propagation and then crystal perfection
has been proposed [6].
Crystallization that follows such a mechanism is nucleation controlled
(i.e., the nucleation has to take place before the propagation can begin). Within
the range Tg
to Tc(e.g., –5.0 to 60°C for a gel with 50% water), both nucleation
and propagation exhibit an exponential dependence on temperature, such that
nucleation rate increases with decreasing temperature, down to the Tg, while
the propagation rate increases with increasing temperature, up to the Tc
[6].
This explains why crystallization occurs at low temperatures but only to a
limited degree at elevated temperatures (>30°C), because nucleation formation
is then retarded. For longer storage periods, the retrogradation should be
maximal at a temperature about midway between Tg
and Tc, as both nucleation
and propagation then take place at moderate rates. Both normal and waxy
starches seem to follow this mechanism; the rate of retrogradation was found
to increase during a 48-hour period with decreasing temperature in the interval
of 1 to 25°C [165]. Amylose gels stored at 6°C did not develop a staling
endotherm during 48 hours of storage [165], indicating that crystallinity melted
© 2006 by Taylor & Francis Group, LLC
420 Carbohydrates in Food
below 100°C is due to amylopectin. Results from NMR studies on the temperature dependence of retrogradation are consistent with these findings
[151,166].
Recrystallization of amylopectin is very sensitive to the water content in
starch gels. A starch content in the range of 10 to 80% is necessary for the
development of the DSC endotherm [137]. The maximum crystallization has
been measured at around 50% starch with DSC as well as with NMR [137,143,
145,151].
In contrast to a native starch suspensions, the gelatinized starch gel is
completely amorphous and its water is uniformly distributed. The recrystallization process depends on the temperature difference between the storage
temperature and the Tg
of the amorphous gel, as the mobility of the chains
determines their association rate. Because water is a plasticizer, it controls the
Tg
of the amorphous gel. At a very low water content, the Tgis above room
temperature, and the amorphous gel is in a highly viscous glassy state that
effectively hinders molecular mobility. Recrystallization increases with increasing water content until 45 to 50% water content is reached. Progressively more
effective plasticization (increased molecular mobility) is obtained, and finally
Tgis depressed below room temperature. Recrystallization then decreases with
a further increase in water content up to 90%, apparently due to dilution of the
crystallizable component in the plasticized amorphous matrix [6].
Due to their antiplasticizing effect, solutes (e.g., sugars) affect the retrogradation of starch gels compared to water alone [6]. They reduce the mobility
of the chains in the amorphous matrix by increasing the Tg
. As a consequence,
the rate of propagation can decline, decreasing the extent of retrogradation.
10.4.5 BOTANICALSOURCE
The botanical source is of great importance for the retrogradation of starch
gels [22,167–173]. This is true not only for starches with very different amylose content, but also for starches with similar amylose contents. Some of the
differences among, for example, cereal starches can be attributed to differences
in the amylose/amylopectin ratio and lipid contents; however, these factors
account for only some of the differences. Structural differences found in the
amylopectin molecule can explain some of the differences in the rate and
extent of recrystallization.
Some studies indicate that the rate, and sometimes the extent, of retrogradation increases with increasing amounts of amylose. Although the amylopectin is considered responsible for the long-term retrogradation, some
waxy starch types are reported to retrograde slowly, but pea and potato
starches with high amylose contents retrograde to a greater extent
[151,174,175]. It is possible that the initial rate of retrogradation could be
accelerated because of synergistic interactions between amylopectin and amylose, as discussed earlier. Other studies have failed to show this relation of
Sedang diterjemahkan, harap tunggu..
10.4.3 INTERAKSI OFAMYLOPECTIN ANDAMYLOSE
Dalam sebuah studi di mana retrogradasi gel dari campuran nongranular dengan
rasio amilosa / amilopektin yang berbeda dipelajari, interaksi sinergis
yang terlihat antara amilopektin dan amilosa pada kadar amilosa tinggi [160].
Karena endoterm mencair, yang diukur dengan metode DSC, telah
dikaitkan dengan rekristalisasi dari fraksi amilopektin, satu bisa berharap
bahwa endoterm mencair sebanding dengan jumlah amilopektin.
Gudmundsson dan Eliasson [160], bagaimanapun, menemukan nilai-nilai yang tak terduga tinggi
untuk entalpi leleh gel dengan kadar amilosa sangat tinggi (75 sampai 90%).
Kemungkinan cocrystallization terbatas telah diusulkan dalam kaitannya dengan
retrogradasi [161]. Cocrystallization tersebut dapat dipromosikan ketika amilosa
ditemukan dalam jumlah tinggi. Schierbaum et al. [162] telah menemukan bahwa linear
segmen amilopektin dan amilosa, atau batas dekstrin kritis tertentu
panjang, dapat berinteraksi dalam larutan. Temuan serupa juga dilaporkan oleh Seivert dan
Würsch [159] dalam studi asosiasi rantai amilosa dan pengaruh
amilopektin pada proses yang dalam campuran dengan rasio yang berbeda dari amilosa untuk
© 2006 oleh Taylor & Francis Group, LLC
Pati: fisiko dan Fungsional Aspek 419
amilopektin. Mereka menemukan bahwa peningkatan jumlah amilopektin dibatasi
asosiasi rantai amilosa, dan penulis dikaitkan temuan ini ke
salah pengenceran atau efek halangan sterik; Namun, amilosa dan amilopektin dalam larutan air telah terbukti bercampur pada konsentrasi moderat, dan yang mendorong pemisahan fase polimer [56]. Dalam
sebagian besar keadaan, interaksi amilosa dan amilopektin harus
dibatasi dalam gel pati normal, seperti amilosa lebih disukai tercuci keluar dari
butiran, sedangkan amilopektin ini terutama dipertahankan dalam butiran.
10.4.4 STORAGETEMPERATURE ANDWATERCONTENT
retrogradasi sangat dipengaruhi oleh suhu penyimpanan . Penyimpanan pati
gel dengan 45 sampai 50% kadar air pada suhu rendah tetapi di atas kaca
suhu transisi (Tg = -5,0 ° C) meningkatkan retrogradasi dibandingkan dengan
penyimpanan pada suhu kamar, terutama pada hari-hari pertama penyimpanan. Penyimpanan
pada suhu beku di bawah Tgvirtually menghambat rekristalisasi
[91134]. Suhu yang lebih tinggi (di atas 32 sampai 40 ° C) secara efektif mengurangi retrogradasi [134]. Persamaan Avrami telah sering digunakan untuk menjelaskan
kinetika proses recrytallization pada temperatur yang berbeda dan air
isi [134135137]; Namun, analisis kinetika retrogradasi
menurut persamaan Avrami memerlukan kondisi kesetimbangan termodinamika, tapi itu tidak terjadi di sini dan oleh karena itu metode ini memiliki keterbatasan
penerapan. Retrogradasi adalah proses rekristalisasi nonequilibrium, sebagaimana
ditunjukkan oleh fakta bahwa pada suhu rendah (4 sampai 5 ° C) kristalit yang terbentuk
kurang hampir sempurna (yaitu, mereka memiliki suhu yang lebih rendah leleh Tc) dari
kristal yang terbentuk pada suhu penyimpanan yang lebih tinggi [163164] . A tiga langkah
mekanisme nukleasi awal (titik persimpangan dari dua atau lebih molekul pati) diikuti oleh pertumbuhan kristal dan propagasi dan kemudian kristal kesempurnaan
telah diusulkan [6].
Kristalisasi yang mengikuti mekanisme seperti itu nukleasi dikendalikan
(yaitu, nukleasi memiliki terjadi sebelum propagasi dapat mulai). Dalam
rentang Tg
ke Tc (misalnya -5,0 sampai 60 ° C untuk gel dengan 50% air), baik nukleasi
dan propagasi pameran ketergantungan eksponensial pada suhu, sehingga
laju nukleasi meningkat dengan menurunnya suhu, turun ke Tg, sedangkan
meningkat tingkat propagasi dengan meningkatnya suhu, hingga Tc
[6].
Hal ini menjelaskan mengapa kristalisasi terjadi pada suhu rendah tetapi hanya sampai
tingkat yang terbatas pada suhu tinggi (> 30 ° C), karena pembentukan nukleasi
kemudian terbelakang. Untuk periode penyimpanan lama, retrogradasi harus
maksimal pada suhu tentang antara Tg
dan Tc, baik sebagai nukleasi
dan propagasi kemudian mengambil tempat pada tingkat moderat. Kedua normal dan lilin
pati tampaknya mengikuti mekanisme ini; tingkat retrogradasi ditemukan
meningkat selama periode 48-jam dengan penurunan suhu dalam interval
dari 1 sampai 25 ° C [165]. Gel amilosa disimpan pada 6 ° C tidak mengembangkan staling
endoterm selama 48 jam penyimpanan [165], menunjukkan bahwa kristalinitas meleleh
© 2006 oleh Taylor & Francis Group, LLC
420 Karbohidrat dalam makanan
di bawah 100 ° C karena amilopektin. Hasil dari studi NMR pada ketergantungan suhu retrogradasi konsisten dengan temuan ini
[151166].
Rekristalisasi dari amilopektin sangat sensitif terhadap kadar air dalam
pati gel. Sebuah kadar pati di kisaran 10 sampai 80% diperlukan untuk
pengembangan DSC endoterm [137]. Kristalisasi maksimum yang
diukur pada sekitar 50% pati dengan DSC serta dengan NMR [137143,
145151].
Berbeda dengan suspensi pati asli, pati gel gelatinized adalah
benar-benar amorf dan air didistribusikan secara merata. Proses rekristalisasi tergantung pada perbedaan suhu antara penyimpanan
suhu dan Tg
gel amorf, seperti mobilitas rantai
menentukan tingkat hubungan mereka. Karena air adalah plasticizer, ia mengendalikan
Tg
gel amorf. Pada kadar air yang sangat rendah, TGIs atas ruang
suhu, dan gel amorf dalam keadaan kaca yang sangat kental yang
efektif menghambat mobilitas molekul. Rekristalisasi meningkat dengan meningkatnya kadar air sampai kadar air 45 sampai 50% tercapai. Semakin lebih
Plasticization efektif (mobilitas molekul meningkat) diperoleh, dan akhirnya
TGIs tertekan di bawah suhu kamar. Rekristalisasi kemudian menurun dengan
peningkatan lebih lanjut dalam kadar air hingga 90%, tampaknya akibat dilusi dari
komponen dikristalisasi dalam matriks amorf plasticized [6].
Karena efek antiplasticizing mereka, zat terlarut (misalnya, gula) mempengaruhi retrogradasi pati gel dibandingkan dengan air saja [6]. Mereka mengurangi mobilitas
rantai dalam matriks amorf dengan meningkatkan Tg
. Akibatnya,
laju penjalaran bisa menurun, penurunan tingkat retrogradasi.
10.4.5 BOTANICALSOURCE
Sumber botani sangat penting untuk retrogradasi pati
gel [22,167-173]. Hal ini berlaku tidak hanya untuk pati dengan kadar amilosa sangat berbeda, tetapi juga untuk pati dengan kandungan amilosa yang sama. Beberapa
perbedaan di antara, misalnya, pati sereal dapat dikaitkan dengan perbedaan
dalam amilosa / amilopektin rasio dan lipid isi; Namun, faktor-faktor ini
menjelaskan hanya beberapa perbedaan. Perbedaan struktural yang ditemukan di
molekul amilopektin dapat menjelaskan beberapa perbedaan dalam tingkat dan
luasnya rekristalisasi.
Beberapa studi menunjukkan bahwa tingkat, dan kadang-kadang tingkat, dari retrogradasi meningkat dengan meningkatnya jumlah amilosa. Meskipun amilopektin dianggap bertanggung jawab atas retrogradasi jangka panjang, beberapa
jenis pati lilin dilaporkan retrograde perlahan, tapi kacang dan kentang
pati dengan kandungan amilosa tinggi retrograde ke tingkat yang lebih besar
[151174175]. Ada kemungkinan bahwa tingkat awal retrogradasi dapat
dipercepat karena interaksi sinergis antara amilopektin dan amilosa, seperti yang dibahas sebelumnya. Studi-studi lain telah gagal untuk menunjukkan hubungan ini
Dalam sebuah studi di mana retrogradasi gel dari campuran nongranular dengan
rasio amilosa / amilopektin yang berbeda dipelajari, interaksi sinergis
yang terlihat antara amilopektin dan amilosa pada kadar amilosa tinggi [160].
Karena endoterm mencair, yang diukur dengan metode DSC, telah
dikaitkan dengan rekristalisasi dari fraksi amilopektin, satu bisa berharap
bahwa endoterm mencair sebanding dengan jumlah amilopektin.
Gudmundsson dan Eliasson [160], bagaimanapun, menemukan nilai-nilai yang tak terduga tinggi
untuk entalpi leleh gel dengan kadar amilosa sangat tinggi (75 sampai 90%).
Kemungkinan cocrystallization terbatas telah diusulkan dalam kaitannya dengan
retrogradasi [161]. Cocrystallization tersebut dapat dipromosikan ketika amilosa
ditemukan dalam jumlah tinggi. Schierbaum et al. [162] telah menemukan bahwa linear
segmen amilopektin dan amilosa, atau batas dekstrin kritis tertentu
panjang, dapat berinteraksi dalam larutan. Temuan serupa juga dilaporkan oleh Seivert dan
Würsch [159] dalam studi asosiasi rantai amilosa dan pengaruh
amilopektin pada proses yang dalam campuran dengan rasio yang berbeda dari amilosa untuk
© 2006 oleh Taylor & Francis Group, LLC
Pati: fisiko dan Fungsional Aspek 419
amilopektin. Mereka menemukan bahwa peningkatan jumlah amilopektin dibatasi
asosiasi rantai amilosa, dan penulis dikaitkan temuan ini ke
salah pengenceran atau efek halangan sterik; Namun, amilosa dan amilopektin dalam larutan air telah terbukti bercampur pada konsentrasi moderat, dan yang mendorong pemisahan fase polimer [56]. Dalam
sebagian besar keadaan, interaksi amilosa dan amilopektin harus
dibatasi dalam gel pati normal, seperti amilosa lebih disukai tercuci keluar dari
butiran, sedangkan amilopektin ini terutama dipertahankan dalam butiran.
10.4.4 STORAGETEMPERATURE ANDWATERCONTENT
retrogradasi sangat dipengaruhi oleh suhu penyimpanan . Penyimpanan pati
gel dengan 45 sampai 50% kadar air pada suhu rendah tetapi di atas kaca
suhu transisi (Tg = -5,0 ° C) meningkatkan retrogradasi dibandingkan dengan
penyimpanan pada suhu kamar, terutama pada hari-hari pertama penyimpanan. Penyimpanan
pada suhu beku di bawah Tgvirtually menghambat rekristalisasi
[91134]. Suhu yang lebih tinggi (di atas 32 sampai 40 ° C) secara efektif mengurangi retrogradasi [134]. Persamaan Avrami telah sering digunakan untuk menjelaskan
kinetika proses recrytallization pada temperatur yang berbeda dan air
isi [134135137]; Namun, analisis kinetika retrogradasi
menurut persamaan Avrami memerlukan kondisi kesetimbangan termodinamika, tapi itu tidak terjadi di sini dan oleh karena itu metode ini memiliki keterbatasan
penerapan. Retrogradasi adalah proses rekristalisasi nonequilibrium, sebagaimana
ditunjukkan oleh fakta bahwa pada suhu rendah (4 sampai 5 ° C) kristalit yang terbentuk
kurang hampir sempurna (yaitu, mereka memiliki suhu yang lebih rendah leleh Tc) dari
kristal yang terbentuk pada suhu penyimpanan yang lebih tinggi [163164] . A tiga langkah
mekanisme nukleasi awal (titik persimpangan dari dua atau lebih molekul pati) diikuti oleh pertumbuhan kristal dan propagasi dan kemudian kristal kesempurnaan
telah diusulkan [6].
Kristalisasi yang mengikuti mekanisme seperti itu nukleasi dikendalikan
(yaitu, nukleasi memiliki terjadi sebelum propagasi dapat mulai). Dalam
rentang Tg
ke Tc (misalnya -5,0 sampai 60 ° C untuk gel dengan 50% air), baik nukleasi
dan propagasi pameran ketergantungan eksponensial pada suhu, sehingga
laju nukleasi meningkat dengan menurunnya suhu, turun ke Tg, sedangkan
meningkat tingkat propagasi dengan meningkatnya suhu, hingga Tc
[6].
Hal ini menjelaskan mengapa kristalisasi terjadi pada suhu rendah tetapi hanya sampai
tingkat yang terbatas pada suhu tinggi (> 30 ° C), karena pembentukan nukleasi
kemudian terbelakang. Untuk periode penyimpanan lama, retrogradasi harus
maksimal pada suhu tentang antara Tg
dan Tc, baik sebagai nukleasi
dan propagasi kemudian mengambil tempat pada tingkat moderat. Kedua normal dan lilin
pati tampaknya mengikuti mekanisme ini; tingkat retrogradasi ditemukan
meningkat selama periode 48-jam dengan penurunan suhu dalam interval
dari 1 sampai 25 ° C [165]. Gel amilosa disimpan pada 6 ° C tidak mengembangkan staling
endoterm selama 48 jam penyimpanan [165], menunjukkan bahwa kristalinitas meleleh
© 2006 oleh Taylor & Francis Group, LLC
420 Karbohidrat dalam makanan
di bawah 100 ° C karena amilopektin. Hasil dari studi NMR pada ketergantungan suhu retrogradasi konsisten dengan temuan ini
[151166].
Rekristalisasi dari amilopektin sangat sensitif terhadap kadar air dalam
pati gel. Sebuah kadar pati di kisaran 10 sampai 80% diperlukan untuk
pengembangan DSC endoterm [137]. Kristalisasi maksimum yang
diukur pada sekitar 50% pati dengan DSC serta dengan NMR [137143,
145151].
Berbeda dengan suspensi pati asli, pati gel gelatinized adalah
benar-benar amorf dan air didistribusikan secara merata. Proses rekristalisasi tergantung pada perbedaan suhu antara penyimpanan
suhu dan Tg
gel amorf, seperti mobilitas rantai
menentukan tingkat hubungan mereka. Karena air adalah plasticizer, ia mengendalikan
Tg
gel amorf. Pada kadar air yang sangat rendah, TGIs atas ruang
suhu, dan gel amorf dalam keadaan kaca yang sangat kental yang
efektif menghambat mobilitas molekul. Rekristalisasi meningkat dengan meningkatnya kadar air sampai kadar air 45 sampai 50% tercapai. Semakin lebih
Plasticization efektif (mobilitas molekul meningkat) diperoleh, dan akhirnya
TGIs tertekan di bawah suhu kamar. Rekristalisasi kemudian menurun dengan
peningkatan lebih lanjut dalam kadar air hingga 90%, tampaknya akibat dilusi dari
komponen dikristalisasi dalam matriks amorf plasticized [6].
Karena efek antiplasticizing mereka, zat terlarut (misalnya, gula) mempengaruhi retrogradasi pati gel dibandingkan dengan air saja [6]. Mereka mengurangi mobilitas
rantai dalam matriks amorf dengan meningkatkan Tg
. Akibatnya,
laju penjalaran bisa menurun, penurunan tingkat retrogradasi.
10.4.5 BOTANICALSOURCE
Sumber botani sangat penting untuk retrogradasi pati
gel [22,167-173]. Hal ini berlaku tidak hanya untuk pati dengan kadar amilosa sangat berbeda, tetapi juga untuk pati dengan kandungan amilosa yang sama. Beberapa
perbedaan di antara, misalnya, pati sereal dapat dikaitkan dengan perbedaan
dalam amilosa / amilopektin rasio dan lipid isi; Namun, faktor-faktor ini
menjelaskan hanya beberapa perbedaan. Perbedaan struktural yang ditemukan di
molekul amilopektin dapat menjelaskan beberapa perbedaan dalam tingkat dan
luasnya rekristalisasi.
Beberapa studi menunjukkan bahwa tingkat, dan kadang-kadang tingkat, dari retrogradasi meningkat dengan meningkatnya jumlah amilosa. Meskipun amilopektin dianggap bertanggung jawab atas retrogradasi jangka panjang, beberapa
jenis pati lilin dilaporkan retrograde perlahan, tapi kacang dan kentang
pati dengan kandungan amilosa tinggi retrograde ke tingkat yang lebih besar
[151174175]. Ada kemungkinan bahwa tingkat awal retrogradasi dapat
dipercepat karena interaksi sinergis antara amilopektin dan amilosa, seperti yang dibahas sebelumnya. Studi-studi lain telah gagal untuk menunjukkan hubungan ini
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- C'est un reportage sur# Émilie est dans
- hallo sayang,,,,bagaimana kabar hari ini
- Bad mood
- Boleh kah
- Tiga puluh lima
- because in this month,my father diedyang
- aku tidak bisa berada disamping my fathe
- Bolehkah
- Semoga tuhan membalas semua ucapannya
- aku benar benar merasa kehilangan yang l
- Kenapa
- aku benar benar merasa kehilangan yang l
- Tapi kalau aku ingin lebih dekat mengena
- Personality has different meanings for t
- Ketika saudara jadi bangsat
- Personality has different meanings for t
- Maaf mungkin kata kata ku kurang sopan
- makanya, kadang aku merasa benci pada bu
- Maaf mungkin kata kata aku kurang sopan
- Personality has different meanings for t
- Kurikulum 2013 merupakan kurikulum baru
- aku tidak bisa berada disampingnya, dan
- Empat puluh lima
- aku tidak bisa berada disamping my fathe
