- Teks
- Sejarah
as added lipids. These lipids are e
as added lipids. These lipids are either on the surface or inside the granules
[242,243] and consist mainly of phospholipids or free fatty acids [244]. Ionic
surfactants interact in a similar way with starch as monoacyl lipids by complex
formation, but their being charged complicates their effects [236,245]. When
amylose leaches out of the granules during gelatinization, the lipids, either
native or added, form complexes with the exuded amylose, probably on the
surface of the granules, and retard their swelling [246,247]; as a result, the
gelatinization temperature is somewhat increased. Because the complex formation is an exothermic process that probably takes place during gelatinization, the enthalpy of the gelatinization measured via DSC could be observed
to be lower than it really is [5,232a,235,236]. Certain surfactants (i.e., sodium
dodecyl sulfate [SDS]) have been observed to decrease the gelatinization
temperature of starches [245,247,248].
10.6.1.4.3 Rheological Properties
Monoacyl lipids and surfactants affect the rheological properties of the
starches. They do so probably by changing the swelling and solubility of the
starch granules. Previous studies on various lipids and surfactants have shown
that they increase or decrease the starch viscosity, depending on the type of
lipid and source of starch as well as experimental conditions [192,249–251].
The monoacyl lipids and ionic surfactants have a similar interaction mechanism, except that the ionic surfactants have an additional effect due to their
charged nature [201,236,245]. Furthermore, when the lipids are introduced,
whether they are heated with the starch suspension from the beginning or
added at later stages (e.g., after the gelatinization), is a critical factor.
The volume occupied by the swollen granules is a dominant factor at low
starch concentrations, as discussed in Section 10.5. In a system of low starch
concentration, the effect of the lipids should be decreased viscosity because of
the retarded swelling and solubility; however, a decrease in viscosity is only
obtained as long as the lipids or surfactants can retard the swelling and solubility
of the granules. At high temperatures (e.g., above 95°C), starches with added
lipids or surfactants can have higher viscosity than starch pastes without added
lipids [236]. At 95°C in systems with excess or intermediate water contents,
many amylose–lipid complexes begin to melt [201,232,252], allowing for rearrangement of the complex [252], and the retardation effects disappear. At lower
temperatures (e.g., 85°C), the lipids effectively retard the swelling and decrease
the viscosity compared to starches without added lipids [236]. If the lipids or
surfactants are added at later stages, when the starch has already been heated,
smaller effects should be seen because the granules have swelled unrestricted.
Ionic surfactants have somewhat different effects, as they destabilize the
starch granule; for example, increased swelling and solubility are observed
when starch is heated in their presence [253]. This could be the result of an
amylose extraction effect of the ionic surfactants, because of the charged and
highly hydrophilic head group [109,192,245]. The viscosity should therefore
© 2006 by Taylor & Francis Group, LLC
Starch: Physicochemical and Functional Aspects 439
increase in their presence, and the charged head group further stabilizes the
starch paste because of electrostatic repulsive forces. At 85°C, the viscosity
increase is only due to the charged nature of the ionic surfactants, as their
effect can be completely canceled by the addition of salt before heating. At
95°C, the addition of salt makes the ionic surfactants behave similarly to
nonionic surfactants [236].
At high concentrations the situation is different. Granule-to-granule contact, and thus granule deformability, is the most important factor. The lipids
or surfactants make the starch granules more rigid until a certain temperature
is reached; therefore, starch pastes should become more viscous when lipids
or surfactants are added, and gels should be firmer than starch pastes or gels
without added lipids or surfactants. Lipids and surfactants that are added at
later stages could be expected to affect only the continuous amylose phase.
Other rheological properties (e.g., stickiness) are also affected when lipids are
added because the complex on the surface of the starch granule reduces
stickiness by decreasing the hydrogen bonds available.
10.6.1.4.4 Retrogradation
Monoglycerides and other related compounds are known to have an antistaling effect on bread and to extend its shelf-life [241,255,256]. It is believed
that the retarding mechanism of lipids and surfactants on retrogradation is
related to their ability to form complexes with the amylose fraction
[140,241,255,256]. The effects of added lipids or surfactants on retrogradation can be measured with many different techniques, such as x-ray diffraction, DSC, or various rheological methods. The effect of lipids added to bread
is an increase in V-type x-ray pattern compared to control bread without such
an addition. The V-type pattern is virtually unchanged with time but is superimposed by a B-type x-ray diffraction pattern that increases on aging [140].
The effect of lipids or surfactants on retrogradation as observed with DSC
is a decreased melting endotherm of recrystallized amylopectin, as well as an
increased size of the endotherm associated with the amylose–lipid complex
transition [143,144]. Rheological measurements (mostly firmness measurements) usually show that added lipids decrease the firmness of breads on aging
compared to breads without added lipids [257]. Other rheological measurements have shown that surfactants can have varied effects on the rheological
properties of starch gels depending on the type of surfactant [236,241]. The
presence of emulsifiers in concentrated starch gels (40%, w/w) slows down
the increase in firmness during aging, although the elasticity modulus initially
is higher than for the control without emulsifiers [256a].
As discussed in Section 10.4, the amylopectin fraction is responsible for
retrogradation [132], and the long-term effects associated with retrogradation
are related to the amylopectin fraction. The obvious question then arises as to
how lipids or surfactants can affect retrogradation, as they are believed to form
complexes with the amylose molecule [140,255,258]. The possible alternatives
© 2006 by Taylor & Francis Group, LLC
440 Carbohydrates in Food
are that either the lipids act through an amylose–lipid complex in various ways
or the lipids interact directly with the amylopectin.
Three possibilities exist with regard to the amylose–lipid complex and
retrogradation. First, it could be that the intact complex (i.e., as one entity)
interferes with the crystallization of amylopectin and retards the retrogradation
[259]. Second, the amylose–lipid complex could change or retard the water
distribution and hence the retrogradation [260]. Third, a cocrystallization of
amylose and amylopectin is possible to some extent, and substances that
complex with amylose eliminate the contribution of amylose in the recrystallizing process [161]. On the other hand, the interaction of amylopectin and
lipids means that lipids interact directly with the amylopectin fraction, at least
to a small extent, and retard retrogradation through the formation of an amylopectin–lipid complex [6,160,171,172,236,261,262].
The possibility of retarding the retrogradation of some starches (maize,
potato, and waxy maize) and nongranular amylopectin by adding an intact
cetyltrimethylammonium bromide (CTAB)–amylose complex has been
explored [259]. It was found that CTAB–amylose complexes added to a cooled
gelatinized starch gel or to starch suspensions that were heated to temperatures
below the transition temperature of the CTAB–amylose complex had little
effect on retrogradation; however, starch gels or starch suspensions with added
CTAB–amylose complexes that were heated to temperatures above the transition temperature (i.e., the complex melted) showed a decreased retrogradation. This mechanism is therefore unlikely.
Because lipids and some surfactants retard or delay gelatinization, probably by complexing with leached amylose on the surface of the starch granules,
it is possible that lipids or surfactants also retard the retrogradation by a similar
mechanism (i.e., by acting as a barrier against water transport) [260]. This
mechanism could be involved in retarding the retrogradation of normal starches
because it is known that the water content is very important for recrystallization; however, it does not explain the effect of lipids and surfactants on
decreasing the retrogradation of waxy starches, unless they are able to interact
with the surface molecules of the waxy starch granules. Furthermore, nongranular amylopectin gels have also been shown to decrease in retrogradation
when surfactants and monoglycerides are added [160,261], which shows that
the granule form is not a limiting factor. If lipids and surfactants are added
after the gelatinization is concluded, such a barrier effect should not be
obtained and the retrogradation should progress in a way similar to that for
starch gels without additives; however, pregelatinization of the starches before
the addition of a surfactant was found to decrease retrogradation compared to
starch gels without such an addition [171,172]. This indicates that lipids or
surfactants affect the retrogradation even after the starch suspensions are fully
gelatinized. This alternative, therefore, has only limited value as an explanation
of the effects of lipids or surfactants on retrogradation.
© 2006 by Taylor & Francis Group, LLC
Starch: Physicochemical and Functional Aspects 441
Russell [161] has suggested that a possible cocrystallization of amylose
and amylopectin contributes to retrogradation, and the role of l
[242,243] and consist mainly of phospholipids or free fatty acids [244]. Ionic
surfactants interact in a similar way with starch as monoacyl lipids by complex
formation, but their being charged complicates their effects [236,245]. When
amylose leaches out of the granules during gelatinization, the lipids, either
native or added, form complexes with the exuded amylose, probably on the
surface of the granules, and retard their swelling [246,247]; as a result, the
gelatinization temperature is somewhat increased. Because the complex formation is an exothermic process that probably takes place during gelatinization, the enthalpy of the gelatinization measured via DSC could be observed
to be lower than it really is [5,232a,235,236]. Certain surfactants (i.e., sodium
dodecyl sulfate [SDS]) have been observed to decrease the gelatinization
temperature of starches [245,247,248].
10.6.1.4.3 Rheological Properties
Monoacyl lipids and surfactants affect the rheological properties of the
starches. They do so probably by changing the swelling and solubility of the
starch granules. Previous studies on various lipids and surfactants have shown
that they increase or decrease the starch viscosity, depending on the type of
lipid and source of starch as well as experimental conditions [192,249–251].
The monoacyl lipids and ionic surfactants have a similar interaction mechanism, except that the ionic surfactants have an additional effect due to their
charged nature [201,236,245]. Furthermore, when the lipids are introduced,
whether they are heated with the starch suspension from the beginning or
added at later stages (e.g., after the gelatinization), is a critical factor.
The volume occupied by the swollen granules is a dominant factor at low
starch concentrations, as discussed in Section 10.5. In a system of low starch
concentration, the effect of the lipids should be decreased viscosity because of
the retarded swelling and solubility; however, a decrease in viscosity is only
obtained as long as the lipids or surfactants can retard the swelling and solubility
of the granules. At high temperatures (e.g., above 95°C), starches with added
lipids or surfactants can have higher viscosity than starch pastes without added
lipids [236]. At 95°C in systems with excess or intermediate water contents,
many amylose–lipid complexes begin to melt [201,232,252], allowing for rearrangement of the complex [252], and the retardation effects disappear. At lower
temperatures (e.g., 85°C), the lipids effectively retard the swelling and decrease
the viscosity compared to starches without added lipids [236]. If the lipids or
surfactants are added at later stages, when the starch has already been heated,
smaller effects should be seen because the granules have swelled unrestricted.
Ionic surfactants have somewhat different effects, as they destabilize the
starch granule; for example, increased swelling and solubility are observed
when starch is heated in their presence [253]. This could be the result of an
amylose extraction effect of the ionic surfactants, because of the charged and
highly hydrophilic head group [109,192,245]. The viscosity should therefore
© 2006 by Taylor & Francis Group, LLC
Starch: Physicochemical and Functional Aspects 439
increase in their presence, and the charged head group further stabilizes the
starch paste because of electrostatic repulsive forces. At 85°C, the viscosity
increase is only due to the charged nature of the ionic surfactants, as their
effect can be completely canceled by the addition of salt before heating. At
95°C, the addition of salt makes the ionic surfactants behave similarly to
nonionic surfactants [236].
At high concentrations the situation is different. Granule-to-granule contact, and thus granule deformability, is the most important factor. The lipids
or surfactants make the starch granules more rigid until a certain temperature
is reached; therefore, starch pastes should become more viscous when lipids
or surfactants are added, and gels should be firmer than starch pastes or gels
without added lipids or surfactants. Lipids and surfactants that are added at
later stages could be expected to affect only the continuous amylose phase.
Other rheological properties (e.g., stickiness) are also affected when lipids are
added because the complex on the surface of the starch granule reduces
stickiness by decreasing the hydrogen bonds available.
10.6.1.4.4 Retrogradation
Monoglycerides and other related compounds are known to have an antistaling effect on bread and to extend its shelf-life [241,255,256]. It is believed
that the retarding mechanism of lipids and surfactants on retrogradation is
related to their ability to form complexes with the amylose fraction
[140,241,255,256]. The effects of added lipids or surfactants on retrogradation can be measured with many different techniques, such as x-ray diffraction, DSC, or various rheological methods. The effect of lipids added to bread
is an increase in V-type x-ray pattern compared to control bread without such
an addition. The V-type pattern is virtually unchanged with time but is superimposed by a B-type x-ray diffraction pattern that increases on aging [140].
The effect of lipids or surfactants on retrogradation as observed with DSC
is a decreased melting endotherm of recrystallized amylopectin, as well as an
increased size of the endotherm associated with the amylose–lipid complex
transition [143,144]. Rheological measurements (mostly firmness measurements) usually show that added lipids decrease the firmness of breads on aging
compared to breads without added lipids [257]. Other rheological measurements have shown that surfactants can have varied effects on the rheological
properties of starch gels depending on the type of surfactant [236,241]. The
presence of emulsifiers in concentrated starch gels (40%, w/w) slows down
the increase in firmness during aging, although the elasticity modulus initially
is higher than for the control without emulsifiers [256a].
As discussed in Section 10.4, the amylopectin fraction is responsible for
retrogradation [132], and the long-term effects associated with retrogradation
are related to the amylopectin fraction. The obvious question then arises as to
how lipids or surfactants can affect retrogradation, as they are believed to form
complexes with the amylose molecule [140,255,258]. The possible alternatives
© 2006 by Taylor & Francis Group, LLC
440 Carbohydrates in Food
are that either the lipids act through an amylose–lipid complex in various ways
or the lipids interact directly with the amylopectin.
Three possibilities exist with regard to the amylose–lipid complex and
retrogradation. First, it could be that the intact complex (i.e., as one entity)
interferes with the crystallization of amylopectin and retards the retrogradation
[259]. Second, the amylose–lipid complex could change or retard the water
distribution and hence the retrogradation [260]. Third, a cocrystallization of
amylose and amylopectin is possible to some extent, and substances that
complex with amylose eliminate the contribution of amylose in the recrystallizing process [161]. On the other hand, the interaction of amylopectin and
lipids means that lipids interact directly with the amylopectin fraction, at least
to a small extent, and retard retrogradation through the formation of an amylopectin–lipid complex [6,160,171,172,236,261,262].
The possibility of retarding the retrogradation of some starches (maize,
potato, and waxy maize) and nongranular amylopectin by adding an intact
cetyltrimethylammonium bromide (CTAB)–amylose complex has been
explored [259]. It was found that CTAB–amylose complexes added to a cooled
gelatinized starch gel or to starch suspensions that were heated to temperatures
below the transition temperature of the CTAB–amylose complex had little
effect on retrogradation; however, starch gels or starch suspensions with added
CTAB–amylose complexes that were heated to temperatures above the transition temperature (i.e., the complex melted) showed a decreased retrogradation. This mechanism is therefore unlikely.
Because lipids and some surfactants retard or delay gelatinization, probably by complexing with leached amylose on the surface of the starch granules,
it is possible that lipids or surfactants also retard the retrogradation by a similar
mechanism (i.e., by acting as a barrier against water transport) [260]. This
mechanism could be involved in retarding the retrogradation of normal starches
because it is known that the water content is very important for recrystallization; however, it does not explain the effect of lipids and surfactants on
decreasing the retrogradation of waxy starches, unless they are able to interact
with the surface molecules of the waxy starch granules. Furthermore, nongranular amylopectin gels have also been shown to decrease in retrogradation
when surfactants and monoglycerides are added [160,261], which shows that
the granule form is not a limiting factor. If lipids and surfactants are added
after the gelatinization is concluded, such a barrier effect should not be
obtained and the retrogradation should progress in a way similar to that for
starch gels without additives; however, pregelatinization of the starches before
the addition of a surfactant was found to decrease retrogradation compared to
starch gels without such an addition [171,172]. This indicates that lipids or
surfactants affect the retrogradation even after the starch suspensions are fully
gelatinized. This alternative, therefore, has only limited value as an explanation
of the effects of lipids or surfactants on retrogradation.
© 2006 by Taylor & Francis Group, LLC
Starch: Physicochemical and Functional Aspects 441
Russell [161] has suggested that a possible cocrystallization of amylose
and amylopectin contributes to retrogradation, and the role of l
0/5000
sebagai menambahkan lipid. Lipid ini yang baik pada permukaan atau di dalam butiran[242,243] dan terdiri terutama dari fosfolipid atau asam lemak bebas [244]. Ioniksurfaktan berinteraksi dalam cara yang mirip dengan pati sebagai lipid monoacyl oleh komplekspembentukan, tetapi mereka dikenakan merumitkan efek mereka [236,245]. Kapanamilosa leaches dari butiran selama gelatinization, lipid, baikasli atau ditambahkan, membentuk kompleks dengan amilosa exuded, mungkin padapermukaan granul, dan menghambat mereka pembengkakan [246,247]; Akibatnya,gelatinization suhu agak meningkat. Karena formasi kompleks adalah proses eksotermik yang mungkin terjadi selama gelatinization, entalpi gelatinization diukur melalui DSC dapat dilihatuntuk lebih rendah daripada benar-benar adalah [5, 232a, 235, 236]. Surfaktan tertentu (yakni, natriumlauryl sulfate [SDS]) telah diamati untuk mengurangi gelatinizationsuhu Pati [245,247,248].10.6.1.4.3 rheological padaMonoacyl lipid dan surfaktan mempengaruhi rheological padaPati. Mereka melakukan jadi mungkin dengan mengubah pembengkakan dan kelarutanbutiran Pati. Studi sebelumnya pada berbagai lipid dan surfaktan telah menunjukkanbahwa mereka menambah atau mengurangi viskositas Pati, tergantung pada jenislipid dan sumber Pati serta kondisi eksperimental [192,249-251].Monoacyl lipid dan ionik surfaktan memiliki mekanisme interaksi mirip, kecuali bahwa surfaktan ionik memiliki efek tambahan karena merekadibebankan alam [201,236,245]. Selain itu, Kapan lipid diperkenalkan,Apakah mereka yang dipanaskan dengan suspensi Pati dari awal atauditambahkan pada tahap selanjutnya (misalnya, setelah gelatinization), merupakan faktor penting.Volume yang ditempati oleh butiran bengkak adalah faktor dominan di rendahPati konsentrasi, seperti yang dibahas dalam bagian 10.5. Dalam sistem rendah Patikonsentrasi, efek lipid harus penurunan viskositas karenapembengkakan terbelakang dan kelarutan; Namun, penurunan viskositas adalah hanyaDiperoleh selama lipid atau surfaktan dapat menghambat pembengkakan dan kelarutanbutiran. Pada suhu tinggi (misalnya, di atas 95° C), Pati dengan ditambahkanlipid atau surfaktan dapat memiliki kekentalan tinggi dari Pati pasta tanpa ditambahkanlipid [236]. Di 95° C dalam sistem dengan isi air kelebihan atau menengah,banyak kompleks amilosa – lipid mulai mencair [201,232,252], memungkinkan untuk penataan ulang kompleks [252], dan efek keterbelakangan menghilang. Lebih rendahsuhu (misalnya, 85° C), lipid efektif menghambat pembengkakan dan penurunanviskositas dibandingkan Pati tanpa ditambahkan lipid [236]. Jika lipid atausurfaktan ditambahkan pada tahap selanjutnya, ketika Pati sudah dipanaskan,efek kecil harus dilihat karena butiran telah membengkak terbatas.Ionik surfaktan memiliki efek yang agak berbeda, karena mereka mengacaukangranula Pati; sebagai contoh, peningkatan pembengkakan dan kelarutan diamatiwhen starch is heated in their presence [253]. This could be the result of anamylose extraction effect of the ionic surfactants, because of the charged andhighly hydrophilic head group [109,192,245]. The viscosity should therefore© 2006 by Taylor & Francis Group, LLCStarch: Physicochemical and Functional Aspects 439increase in their presence, and the charged head group further stabilizes thestarch paste because of electrostatic repulsive forces. At 85°C, the viscosityincrease is only due to the charged nature of the ionic surfactants, as theireffect can be completely canceled by the addition of salt before heating. At95°C, the addition of salt makes the ionic surfactants behave similarly tononionic surfactants [236].At high concentrations the situation is different. Granule-to-granule contact, and thus granule deformability, is the most important factor. The lipidsor surfactants make the starch granules more rigid until a certain temperatureis reached; therefore, starch pastes should become more viscous when lipidsor surfactants are added, and gels should be firmer than starch pastes or gelswithout added lipids or surfactants. Lipids and surfactants that are added atlater stages could be expected to affect only the continuous amylose phase.Other rheological properties (e.g., stickiness) are also affected when lipids areadded because the complex on the surface of the starch granule reducesstickiness by decreasing the hydrogen bonds available.10.6.1.4.4 RetrogradationMonoglycerides and other related compounds are known to have an antistaling effect on bread and to extend its shelf-life [241,255,256]. It is believedthat the retarding mechanism of lipids and surfactants on retrogradation isrelated to their ability to form complexes with the amylose fraction[140,241,255,256]. The effects of added lipids or surfactants on retrogradation can be measured with many different techniques, such as x-ray diffraction, DSC, or various rheological methods. The effect of lipids added to breadis an increase in V-type x-ray pattern compared to control bread without suchan addition. The V-type pattern is virtually unchanged with time but is superimposed by a B-type x-ray diffraction pattern that increases on aging [140].The effect of lipids or surfactants on retrogradation as observed with DSCis a decreased melting endotherm of recrystallized amylopectin, as well as anincreased size of the endotherm associated with the amylose–lipid complextransition [143,144]. Rheological measurements (mostly firmness measurements) usually show that added lipids decrease the firmness of breads on agingcompared to breads without added lipids [257]. Other rheological measurements have shown that surfactants can have varied effects on the rheologicalproperties of starch gels depending on the type of surfactant [236,241]. Thepresence of emulsifiers in concentrated starch gels (40%, w/w) slows downthe increase in firmness during aging, although the elasticity modulus initiallyis higher than for the control without emulsifiers [256a].As discussed in Section 10.4, the amylopectin fraction is responsible forretrogradation [132], and the long-term effects associated with retrogradationare related to the amylopectin fraction. The obvious question then arises as tohow lipids or surfactants can affect retrogradation, as they are believed to formcomplexes with the amylose molecule [140,255,258]. The possible alternatives© 2006 by Taylor & Francis Group, LLC440 Carbohydrates in Foodare that either the lipids act through an amylose–lipid complex in various waysor the lipids interact directly with the amylopectin.Three possibilities exist with regard to the amylose–lipid complex andretrogradation. First, it could be that the intact complex (i.e., as one entity)interferes with the crystallization of amylopectin and retards the retrogradation[259]. Second, the amylose–lipid complex could change or retard the waterdistribution and hence the retrogradation [260]. Third, a cocrystallization ofamylose and amylopectin is possible to some extent, and substances thatcomplex with amylose eliminate the contribution of amylose in the recrystallizing process [161]. On the other hand, the interaction of amylopectin andlipids means that lipids interact directly with the amylopectin fraction, at leastto a small extent, and retard retrogradation through the formation of an amylopectin–lipid complex [6,160,171,172,236,261,262].The possibility of retarding the retrogradation of some starches (maize,potato, and waxy maize) and nongranular amylopectin by adding an intactcetyltrimethylammonium bromide (CTAB)–amylose complex has beenexplored [259]. It was found that CTAB–amylose complexes added to a cooledgelatinized starch gel or to starch suspensions that were heated to temperaturesbelow the transition temperature of the CTAB–amylose complex had littleeffect on retrogradation; however, starch gels or starch suspensions with addedCTAB–amylose complexes that were heated to temperatures above the transition temperature (i.e., the complex melted) showed a decreased retrogradation. This mechanism is therefore unlikely.Because lipids and some surfactants retard or delay gelatinization, probably by complexing with leached amylose on the surface of the starch granules,it is possible that lipids or surfactants also retard the retrogradation by a similarmechanism (i.e., by acting as a barrier against water transport) [260]. Thismechanism could be involved in retarding the retrogradation of normal starchesbecause it is known that the water content is very important for recrystallization; however, it does not explain the effect of lipids and surfactants ondecreasing the retrogradation of waxy starches, unless they are able to interactwith the surface molecules of the waxy starch granules. Furthermore, nongranular amylopectin gels have also been shown to decrease in retrogradationwhen surfactants and monoglycerides are added [160,261], which shows thatthe granule form is not a limiting factor. If lipids and surfactants are addedafter the gelatinization is concluded, such a barrier effect should not beobtained and the retrogradation should progress in a way similar to that forstarch gels without additives; however, pregelatinization of the starches beforethe addition of a surfactant was found to decrease retrogradation compared tostarch gels without such an addition [171,172]. This indicates that lipids orsurfactants affect the retrogradation even after the starch suspensions are fullygelatinized. This alternative, therefore, has only limited value as an explanationof the effects of lipids or surfactants on retrogradation.© 2006 by Taylor & Francis Group, LLCStarch: Physicochemical and Functional Aspects 441Russell [161] has suggested that a possible cocrystallization of amyloseand amylopectin contributes to retrogradation, and the role of l
Sedang diterjemahkan, harap tunggu..
as added lipids. These lipids are either on the surface or inside the granules
[242,243] and consist mainly of phospholipids or free fatty acids [244]. Ionic
surfactants interact in a similar way with starch as monoacyl lipids by complex
formation, but their being charged complicates their effects [236,245]. When
amylose leaches out of the granules during gelatinization, the lipids, either
native or added, form complexes with the exuded amylose, probably on the
surface of the granules, and retard their swelling [246,247]; as a result, the
gelatinization temperature is somewhat increased. Because the complex formation is an exothermic process that probably takes place during gelatinization, the enthalpy of the gelatinization measured via DSC could be observed
to be lower than it really is [5,232a,235,236]. Certain surfactants (i.e., sodium
dodecyl sulfate [SDS]) have been observed to decrease the gelatinization
temperature of starches [245,247,248].
10.6.1.4.3 Rheological Properties
Monoacyl lipids and surfactants affect the rheological properties of the
starches. They do so probably by changing the swelling and solubility of the
starch granules. Previous studies on various lipids and surfactants have shown
that they increase or decrease the starch viscosity, depending on the type of
lipid and source of starch as well as experimental conditions [192,249–251].
The monoacyl lipids and ionic surfactants have a similar interaction mechanism, except that the ionic surfactants have an additional effect due to their
charged nature [201,236,245]. Furthermore, when the lipids are introduced,
whether they are heated with the starch suspension from the beginning or
added at later stages (e.g., after the gelatinization), is a critical factor.
The volume occupied by the swollen granules is a dominant factor at low
starch concentrations, as discussed in Section 10.5. In a system of low starch
concentration, the effect of the lipids should be decreased viscosity because of
the retarded swelling and solubility; however, a decrease in viscosity is only
obtained as long as the lipids or surfactants can retard the swelling and solubility
of the granules. At high temperatures (e.g., above 95°C), starches with added
lipids or surfactants can have higher viscosity than starch pastes without added
lipids [236]. At 95°C in systems with excess or intermediate water contents,
many amylose–lipid complexes begin to melt [201,232,252], allowing for rearrangement of the complex [252], and the retardation effects disappear. At lower
temperatures (e.g., 85°C), the lipids effectively retard the swelling and decrease
the viscosity compared to starches without added lipids [236]. If the lipids or
surfactants are added at later stages, when the starch has already been heated,
smaller effects should be seen because the granules have swelled unrestricted.
Ionic surfactants have somewhat different effects, as they destabilize the
starch granule; for example, increased swelling and solubility are observed
when starch is heated in their presence [253]. This could be the result of an
amylose extraction effect of the ionic surfactants, because of the charged and
highly hydrophilic head group [109,192,245]. The viscosity should therefore
© 2006 by Taylor & Francis Group, LLC
Starch: Physicochemical and Functional Aspects 439
increase in their presence, and the charged head group further stabilizes the
starch paste because of electrostatic repulsive forces. At 85°C, the viscosity
increase is only due to the charged nature of the ionic surfactants, as their
effect can be completely canceled by the addition of salt before heating. At
95°C, the addition of salt makes the ionic surfactants behave similarly to
nonionic surfactants [236].
At high concentrations the situation is different. Granule-to-granule contact, and thus granule deformability, is the most important factor. The lipids
or surfactants make the starch granules more rigid until a certain temperature
is reached; therefore, starch pastes should become more viscous when lipids
or surfactants are added, and gels should be firmer than starch pastes or gels
without added lipids or surfactants. Lipids and surfactants that are added at
later stages could be expected to affect only the continuous amylose phase.
Other rheological properties (e.g., stickiness) are also affected when lipids are
added because the complex on the surface of the starch granule reduces
stickiness by decreasing the hydrogen bonds available.
10.6.1.4.4 Retrogradation
Monoglycerides and other related compounds are known to have an antistaling effect on bread and to extend its shelf-life [241,255,256]. It is believed
that the retarding mechanism of lipids and surfactants on retrogradation is
related to their ability to form complexes with the amylose fraction
[140,241,255,256]. The effects of added lipids or surfactants on retrogradation can be measured with many different techniques, such as x-ray diffraction, DSC, or various rheological methods. The effect of lipids added to bread
is an increase in V-type x-ray pattern compared to control bread without such
an addition. The V-type pattern is virtually unchanged with time but is superimposed by a B-type x-ray diffraction pattern that increases on aging [140].
The effect of lipids or surfactants on retrogradation as observed with DSC
is a decreased melting endotherm of recrystallized amylopectin, as well as an
increased size of the endotherm associated with the amylose–lipid complex
transition [143,144]. Rheological measurements (mostly firmness measurements) usually show that added lipids decrease the firmness of breads on aging
compared to breads without added lipids [257]. Other rheological measurements have shown that surfactants can have varied effects on the rheological
properties of starch gels depending on the type of surfactant [236,241]. The
presence of emulsifiers in concentrated starch gels (40%, w/w) slows down
the increase in firmness during aging, although the elasticity modulus initially
is higher than for the control without emulsifiers [256a].
As discussed in Section 10.4, the amylopectin fraction is responsible for
retrogradation [132], and the long-term effects associated with retrogradation
are related to the amylopectin fraction. The obvious question then arises as to
how lipids or surfactants can affect retrogradation, as they are believed to form
complexes with the amylose molecule [140,255,258]. The possible alternatives
© 2006 by Taylor & Francis Group, LLC
440 Carbohydrates in Food
are that either the lipids act through an amylose–lipid complex in various ways
or the lipids interact directly with the amylopectin.
Three possibilities exist with regard to the amylose–lipid complex and
retrogradation. First, it could be that the intact complex (i.e., as one entity)
interferes with the crystallization of amylopectin and retards the retrogradation
[259]. Second, the amylose–lipid complex could change or retard the water
distribution and hence the retrogradation [260]. Third, a cocrystallization of
amylose and amylopectin is possible to some extent, and substances that
complex with amylose eliminate the contribution of amylose in the recrystallizing process [161]. On the other hand, the interaction of amylopectin and
lipids means that lipids interact directly with the amylopectin fraction, at least
to a small extent, and retard retrogradation through the formation of an amylopectin–lipid complex [6,160,171,172,236,261,262].
The possibility of retarding the retrogradation of some starches (maize,
potato, and waxy maize) and nongranular amylopectin by adding an intact
cetyltrimethylammonium bromide (CTAB)–amylose complex has been
explored [259]. It was found that CTAB–amylose complexes added to a cooled
gelatinized starch gel or to starch suspensions that were heated to temperatures
below the transition temperature of the CTAB–amylose complex had little
effect on retrogradation; however, starch gels or starch suspensions with added
CTAB–amylose complexes that were heated to temperatures above the transition temperature (i.e., the complex melted) showed a decreased retrogradation. This mechanism is therefore unlikely.
Because lipids and some surfactants retard or delay gelatinization, probably by complexing with leached amylose on the surface of the starch granules,
it is possible that lipids or surfactants also retard the retrogradation by a similar
mechanism (i.e., by acting as a barrier against water transport) [260]. This
mechanism could be involved in retarding the retrogradation of normal starches
because it is known that the water content is very important for recrystallization; however, it does not explain the effect of lipids and surfactants on
decreasing the retrogradation of waxy starches, unless they are able to interact
with the surface molecules of the waxy starch granules. Furthermore, nongranular amylopectin gels have also been shown to decrease in retrogradation
when surfactants and monoglycerides are added [160,261], which shows that
the granule form is not a limiting factor. If lipids and surfactants are added
after the gelatinization is concluded, such a barrier effect should not be
obtained and the retrogradation should progress in a way similar to that for
starch gels without additives; however, pregelatinization of the starches before
the addition of a surfactant was found to decrease retrogradation compared to
starch gels without such an addition [171,172]. This indicates that lipids or
surfactants affect the retrogradation even after the starch suspensions are fully
gelatinized. This alternative, therefore, has only limited value as an explanation
of the effects of lipids or surfactants on retrogradation.
© 2006 by Taylor & Francis Group, LLC
Starch: Physicochemical and Functional Aspects 441
Russell [161] has suggested that a possible cocrystallization of amylose
and amylopectin contributes to retrogradation, and the role of l
[242,243] and consist mainly of phospholipids or free fatty acids [244]. Ionic
surfactants interact in a similar way with starch as monoacyl lipids by complex
formation, but their being charged complicates their effects [236,245]. When
amylose leaches out of the granules during gelatinization, the lipids, either
native or added, form complexes with the exuded amylose, probably on the
surface of the granules, and retard their swelling [246,247]; as a result, the
gelatinization temperature is somewhat increased. Because the complex formation is an exothermic process that probably takes place during gelatinization, the enthalpy of the gelatinization measured via DSC could be observed
to be lower than it really is [5,232a,235,236]. Certain surfactants (i.e., sodium
dodecyl sulfate [SDS]) have been observed to decrease the gelatinization
temperature of starches [245,247,248].
10.6.1.4.3 Rheological Properties
Monoacyl lipids and surfactants affect the rheological properties of the
starches. They do so probably by changing the swelling and solubility of the
starch granules. Previous studies on various lipids and surfactants have shown
that they increase or decrease the starch viscosity, depending on the type of
lipid and source of starch as well as experimental conditions [192,249–251].
The monoacyl lipids and ionic surfactants have a similar interaction mechanism, except that the ionic surfactants have an additional effect due to their
charged nature [201,236,245]. Furthermore, when the lipids are introduced,
whether they are heated with the starch suspension from the beginning or
added at later stages (e.g., after the gelatinization), is a critical factor.
The volume occupied by the swollen granules is a dominant factor at low
starch concentrations, as discussed in Section 10.5. In a system of low starch
concentration, the effect of the lipids should be decreased viscosity because of
the retarded swelling and solubility; however, a decrease in viscosity is only
obtained as long as the lipids or surfactants can retard the swelling and solubility
of the granules. At high temperatures (e.g., above 95°C), starches with added
lipids or surfactants can have higher viscosity than starch pastes without added
lipids [236]. At 95°C in systems with excess or intermediate water contents,
many amylose–lipid complexes begin to melt [201,232,252], allowing for rearrangement of the complex [252], and the retardation effects disappear. At lower
temperatures (e.g., 85°C), the lipids effectively retard the swelling and decrease
the viscosity compared to starches without added lipids [236]. If the lipids or
surfactants are added at later stages, when the starch has already been heated,
smaller effects should be seen because the granules have swelled unrestricted.
Ionic surfactants have somewhat different effects, as they destabilize the
starch granule; for example, increased swelling and solubility are observed
when starch is heated in their presence [253]. This could be the result of an
amylose extraction effect of the ionic surfactants, because of the charged and
highly hydrophilic head group [109,192,245]. The viscosity should therefore
© 2006 by Taylor & Francis Group, LLC
Starch: Physicochemical and Functional Aspects 439
increase in their presence, and the charged head group further stabilizes the
starch paste because of electrostatic repulsive forces. At 85°C, the viscosity
increase is only due to the charged nature of the ionic surfactants, as their
effect can be completely canceled by the addition of salt before heating. At
95°C, the addition of salt makes the ionic surfactants behave similarly to
nonionic surfactants [236].
At high concentrations the situation is different. Granule-to-granule contact, and thus granule deformability, is the most important factor. The lipids
or surfactants make the starch granules more rigid until a certain temperature
is reached; therefore, starch pastes should become more viscous when lipids
or surfactants are added, and gels should be firmer than starch pastes or gels
without added lipids or surfactants. Lipids and surfactants that are added at
later stages could be expected to affect only the continuous amylose phase.
Other rheological properties (e.g., stickiness) are also affected when lipids are
added because the complex on the surface of the starch granule reduces
stickiness by decreasing the hydrogen bonds available.
10.6.1.4.4 Retrogradation
Monoglycerides and other related compounds are known to have an antistaling effect on bread and to extend its shelf-life [241,255,256]. It is believed
that the retarding mechanism of lipids and surfactants on retrogradation is
related to their ability to form complexes with the amylose fraction
[140,241,255,256]. The effects of added lipids or surfactants on retrogradation can be measured with many different techniques, such as x-ray diffraction, DSC, or various rheological methods. The effect of lipids added to bread
is an increase in V-type x-ray pattern compared to control bread without such
an addition. The V-type pattern is virtually unchanged with time but is superimposed by a B-type x-ray diffraction pattern that increases on aging [140].
The effect of lipids or surfactants on retrogradation as observed with DSC
is a decreased melting endotherm of recrystallized amylopectin, as well as an
increased size of the endotherm associated with the amylose–lipid complex
transition [143,144]. Rheological measurements (mostly firmness measurements) usually show that added lipids decrease the firmness of breads on aging
compared to breads without added lipids [257]. Other rheological measurements have shown that surfactants can have varied effects on the rheological
properties of starch gels depending on the type of surfactant [236,241]. The
presence of emulsifiers in concentrated starch gels (40%, w/w) slows down
the increase in firmness during aging, although the elasticity modulus initially
is higher than for the control without emulsifiers [256a].
As discussed in Section 10.4, the amylopectin fraction is responsible for
retrogradation [132], and the long-term effects associated with retrogradation
are related to the amylopectin fraction. The obvious question then arises as to
how lipids or surfactants can affect retrogradation, as they are believed to form
complexes with the amylose molecule [140,255,258]. The possible alternatives
© 2006 by Taylor & Francis Group, LLC
440 Carbohydrates in Food
are that either the lipids act through an amylose–lipid complex in various ways
or the lipids interact directly with the amylopectin.
Three possibilities exist with regard to the amylose–lipid complex and
retrogradation. First, it could be that the intact complex (i.e., as one entity)
interferes with the crystallization of amylopectin and retards the retrogradation
[259]. Second, the amylose–lipid complex could change or retard the water
distribution and hence the retrogradation [260]. Third, a cocrystallization of
amylose and amylopectin is possible to some extent, and substances that
complex with amylose eliminate the contribution of amylose in the recrystallizing process [161]. On the other hand, the interaction of amylopectin and
lipids means that lipids interact directly with the amylopectin fraction, at least
to a small extent, and retard retrogradation through the formation of an amylopectin–lipid complex [6,160,171,172,236,261,262].
The possibility of retarding the retrogradation of some starches (maize,
potato, and waxy maize) and nongranular amylopectin by adding an intact
cetyltrimethylammonium bromide (CTAB)–amylose complex has been
explored [259]. It was found that CTAB–amylose complexes added to a cooled
gelatinized starch gel or to starch suspensions that were heated to temperatures
below the transition temperature of the CTAB–amylose complex had little
effect on retrogradation; however, starch gels or starch suspensions with added
CTAB–amylose complexes that were heated to temperatures above the transition temperature (i.e., the complex melted) showed a decreased retrogradation. This mechanism is therefore unlikely.
Because lipids and some surfactants retard or delay gelatinization, probably by complexing with leached amylose on the surface of the starch granules,
it is possible that lipids or surfactants also retard the retrogradation by a similar
mechanism (i.e., by acting as a barrier against water transport) [260]. This
mechanism could be involved in retarding the retrogradation of normal starches
because it is known that the water content is very important for recrystallization; however, it does not explain the effect of lipids and surfactants on
decreasing the retrogradation of waxy starches, unless they are able to interact
with the surface molecules of the waxy starch granules. Furthermore, nongranular amylopectin gels have also been shown to decrease in retrogradation
when surfactants and monoglycerides are added [160,261], which shows that
the granule form is not a limiting factor. If lipids and surfactants are added
after the gelatinization is concluded, such a barrier effect should not be
obtained and the retrogradation should progress in a way similar to that for
starch gels without additives; however, pregelatinization of the starches before
the addition of a surfactant was found to decrease retrogradation compared to
starch gels without such an addition [171,172]. This indicates that lipids or
surfactants affect the retrogradation even after the starch suspensions are fully
gelatinized. This alternative, therefore, has only limited value as an explanation
of the effects of lipids or surfactants on retrogradation.
© 2006 by Taylor & Francis Group, LLC
Starch: Physicochemical and Functional Aspects 441
Russell [161] has suggested that a possible cocrystallization of amylose
and amylopectin contributes to retrogradation, and the role of l
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- 10.3.3.2 AnnealingIf the water content i
- mater dei
- 10.3.3.2 AnnealingIf the water content i
- benedikta mater dei
- selamat hari lahir
- its rhyme and rhythm are beaautiful.unde
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- Ik wil niet om u te vertellen en kwaad d
- Por favor, no me dejas anhelo de su cora
- life is choice
- very much affect the commercial samples,
- That day
- mater christi
- very much affect the commercial samples,
- Let you go
- Thanks for your information and we wait
- selamat hari lahir
- very much affect the commercial samples,
- Saya tidak ingin bercerita dan menyusahk
- Por favor, no me dejas anhelo nostálgico
- gloriosa
- selamat hari lahir
- Thanks for your information and we wait
- selamat hari lahir
