complexes, it was shown that wheat

complexes, it was shown that wheat and barley starches gave the same type
of signal as the amylose–lipid complex [34]. When amylose and lipids were
present without forming an inclusion complex, no signal was obtained.
Although the hydrocarbon chain of the lipid in the complex is in the solid
state, the amylose–lipid complex is thought to be present as an amorphous
structure [34–36]. These complexes might thus serve as nuclei for crystallization during gelatinization and other heat treatments [33]. Cocrystallization
between the amylose–lipid complex and the amylopectin double helix cannot
occur; there must be different crystalline domains in a starch gel [37].
The protein present might very well be starch-degrading enzymes, and if
the conditions are such that the enzymes become active this will certainly
influence the functionality of the starch. Excess enzyme activity is usually not
preferred, and, particularly for baking, enzyme activity that is too high can be
disastrous. Other proteins have been identified as integral components of the
starch granule structure, located either in the interior [38] or at the surface
[39]. Examples of the latter type of protein are storage proteins, starch biosynthetic enzymes (e.g. starch-granule-bound starch synthase), and friabilin/
puroindolines [39a].
TABLE 10.2
Composition of Some Selected Starch Granules
Starch Amylose (%)
Protein
(g/100 g)
Lipids
(g/100 g) Ref.
Cassava 17 0.1 0.1 25
Potato 21 0.06 0.05 25
Rice 12.2–28.6 — 0.63–1.11 26
Waxy rice 0–2.32 — — 27
Wheat 28
29.2
0.3
—
0.8
0.85
28
29
A-granules 28.4–27.8 — 0.67–0.73 29
B-granules 27.5–24.5 — 0.73–0.91 29
Barley, waxy 2.1–8.3 — 0.30–0.49 26
Barley, normal 25.3–30.1 — 0.68–1.28 26
Barley, high amylose 38.4–44.1 — 1.05–1.69 26
Oat 25.2–29.4 — 1.35–1.52 26
Maize, normal 28.7 0.3 0.8 28
25.8–32.5 — 0.61–0.82 26
Maize, waxy 1.4–2.7 — 0.02–0.14 26
Maize, high amylose 42.6–67.8 — 1.01–1.09 26
Fava bean 33 0.9 0.1 28
Pea 33 0.7 0.1 28
© 2006 by Taylor & Francis Group, LLC
398 Carbohydrates in Food
10.2.2 STARCHCRYSTALLINITY
Starch granule crystallinity can be studied with the x-ray diffraction technique, and four different x-ray diffraction patterns have been described: the
A-pattern, obtained for cereal starches (except high-amylose varieties); the
B-pattern obtained for root and tubular starches (and for high-amylose varieties) and retrograded starch; the C-pattern, obtained for beans and peas; and
the V-pattern, obtained for gelatinized lipid-containing starches. The C-pattern
is described as a mixture of the A- and B-patterns but has also been regarded
as a structure of its own [33]. In normal starches (i.e., starches with both
amylose and amylopectin) and of course in waxy starches it is the branched
(amylopectin) molecules that constitute the crystallites. The branches of the
amylopectin molecules form double helices that are arranged in crystalline
domains [40]. The A-, B-, and C-patterns are thus different polymorphic forms
of starch that differ in the packing of the amylopectin double helices. Wheat
and rye starches have been reported to contain low levels of B-crystallites
(up to 10%), so the starch granules may be even more heterogeneous than
has previously been assumed [41].
Because of line broadening in the x-ray diffraction pattern, it can be
concluded that the starch crystals (crystallites) are very small and imperfect
[42]. The crystallites have been reported to be spherical in wheat starch as
well as in potato starch, with diameters of about 10 nm in wheat and somewhat
smaller in potato [43]. The level of crystallinity is also rather low; values in
the range of 15 to 45% have been reported for several starches [33], and the
crystallinity increases with the ratio of amylopectin in the starch [41]. It has
been observed that a greater number of double helices is present than the
number arranged in crystalline domains [44]. For wheat, the percentage of
double helices was 39% and the degree of crystallinity was 20%; for maize,
the corresponding values are 43 and 27%, respectively; and, for potato, the
corresponding values are 40 and 24% [45]. The degree of crystallinity is very
dependent on the water content, and the highest amount of crystallinity is
observed at some intermediate water content [7,46].
The formation of A-crystals is favored by a short average chain length in
amylopectin, a high temperature of formation, a high concentration, the presence of a salt with a high number in the lyothropic series, or the presence of
water-soluble alcohols and organic acids [47]. Transitions from an A-structure
to a B-structure through a C-structure have been observed [48]. The polymorphs
are thus related to each other in such a way that the A-structure is most stable:
melt →B-structure →C-structure →A-structure
For isolated crystallites that melt unrestricted, a lower melting temperature
has been observed for B-crystallites compared with A-crystallites [49]. Crystalline A-spherulites were found to melt at 90°C and B-spherulites at 77°C
© 2006 by Taylor & Francis Group, LLC
Starch: Physicochemical and Functional Aspects 399
[50]. The dissolution temperature of the B-polymorph of amylose in water is
related to the chain length [50a].
In the crystalline and amorphous regions in starch granules, three types
of structures can be identified (Figure 10.1): (1) crystalline domains, (2)
amorphous regions containing branching points alternating with crystalline
domains, and (3) a second amorphous phase surrounding the alternating crystalline and amorphous regions.
Microscopy studies have further elaborated the details regarding the organization of starch granules [50b], and the organization of amylopectin lamellae in blocklets (20 to 500 nm) has been visualized. The organization of
amylopectin in the crystalline domains has been described using the sidechain liquid–crystalline model for synthetic polymers [50c]. In this model,
three components are used to describe the polymer: rigid units, flexible
spacers, and a flexible backbone. The model must be linked to the chemical
structure of the amylopectin molecule which is becoming increasingly better
understood with time.
Amylopectin constitutes the crystalline domains, with the double helices
arranged in the A-, B-, or C-pattern. The branching regions in the amylopectin
molecules constitute the amorphous layer that separates the crystallites from
each other. Because of the size of the amylopectin molecule, the same molecule might take part in several crystalline domains. Surrounding these alternating crystalline and amorphous domains is another amorphous structure,
FIGURE 10.1Arrangement of crystalline and amorphous regions within a growth ring
in the starch granule. The enlargement shows the organization within a crystalline layer.
(Adapted from Eliasson, A.-C. et al., Starch/Stärke, 39, 147, 1987.)
Granule surface
Alternating crystalline
and
amorphous regions
© 2006 by Taylor & Francis Group, LLC
400 Carbohydrates in Food
causing what has been described as “growth rings.” It has been suggested
that a Bragg peak at 10 nm, which disappears on gelatinization, is due to the
alternating amorphous and crystalline layers [51]. The Bragg peak has been
detected around 10 nm for several starches by both x-ray diffraction techniques and optical diffraction [52], although d-spacings at 26 to 30 nm have
also been reported [53]. It has also been suggested that the size of the
combined crystalline and amorphous parts (9 nm) is a fundamental feature
of the packing of starch molecules and is approximately constant for all
starches [54]. To account for the spherical shape of crystallites and for the
existence of a layered structure, a curved crystal structure has been proposed
[55]. The curvature is the result of a translatory displacement of the helices
in the parallel packing.
The structure of the amorphous regions is not known. An interesting aspect
that has implications for the organization of the starch granule is that incompatibility has been observed for amylose and amylopectin. In aqueous solutions
of these components, phase separation into an upper, clear, amylose-rich phase
and a lower, opalescent, amylopectin-rich phase was observed after 24 hours
at 80°C [56]. For binary amylose–water systems, the introduction of a third
component (amylopectin) has always been accompanied by the aggregation
of amylose [57].
Chemical modification (crosslinking) has shown that the amylose molecules are not located together in bundles [58]. This conclusion was reached
because no crosslinking was observed between amylose molecules, only
between amylopectin molecules and between amylopectin and amylose. The
latter observation also indicates that amylose molecules might be rather evenly
distributed in the starch granule.
Due to the leaking of amylose and amylopectin during gelatinization, it
has been suggested that the location of amylose differs among starches. For
oat starch, amylose and amylopectin were found to coleach from the granule
during heating, whereas in barley starch the amylose was preferentially leached
[59]. For wheat starch heated to 95°C, most of the amylose leached out of the
granules [60], whereas in potato starch the amylose diffused toward the aqueous center of the granule [61]. For maize starch, it has been observed that
annealing causes an increase in the differential scanning calorimetry (DSC)
endotherm attributed to the melting of crystalline amylose, indicating that in
this starch the location of amylose molecules is such that it is possible to
obtain an ordered, crystalline structure [62].
Although the structures of the amorphous phases are largely unknown,
they certainly influence the properties of the starch. A higher water content in
the B-polymorph, not only in the unit cell but also in the amorphous regions,
could contribute to the lower stability of this polymorph [49]. As will be
discussed later, a glass transition of t

Hasil (Bahasa Indonesia) 1:

kompleks, itu menunjukkan bahwa Pati gandum dan jelai memberikan jenis yang samasinyal sebagai kompleks amilosa – lipid [34]. Ketika amilosa dan lipid yangsekarang tanpa membentuk kesatuan kompleks, tidak ada sinyal diperoleh.Meskipun rantai hidrokarbon lipid di kompleks padatannegara, kompleks amilosa – lipid dianggap dapat hadir sebagai amorfstruktur [34-36]. Kompleks ini mungkin sehingga berfungsi sebagai inti untuk kristalisasi selama gelatinization dan perawatan panas lainnya [33]. Cocrystallizationantara kompleks amilosa – lipid dan amilopektin heliks ganda dua tidakterjadi; harus ada domain kristal yang berbeda dalam pati gel [37].Protein ini mungkin sangat baik menjadi Pati-merendahkan enzim, dan jikakondisi yang sedemikian rupa sehingga enzim menjadi aktif ini pasti akanmempengaruhi fungsi dari Pati. Aktivitas enzim kelebihan ini biasanya tidakdisukai, dan, khususnya untuk baking, aktivitas enzim yang terlalu tinggi dapatbencana. Protein lain telah diidentifikasi sebagai komponen integralstruktur granula Pati, terletak di pedalaman [38] atau pada permukaan[39]. contoh kedua jenis protein adalah penyimpanan protein, Pati biosynthetic enzim (misalnya terikat Pati granula Pati sintase) dan friabilin /puroindolines [39a].10.2 TABELKomposisi dari beberapa dipilih PatiAmilosa Pati (%)Protein(g/100 g)Lipid(g/100 g) REF.Cassava 17 0.1 0.1 25Potato 21 0.06 0.05 25Rice 12.2–28.6 — 0.63–1.11 26Waxy rice 0–2.32 — — 27Wheat 2829.20.3—0.80.852829A-granules 28.4–27.8 — 0.67–0.73 29B-granules 27.5–24.5 — 0.73–0.91 29Barley, waxy 2.1–8.3 — 0.30–0.49 26Barley, normal 25.3–30.1 — 0.68–1.28 26Barley, high amylose 38.4–44.1 — 1.05–1.69 26Oat 25.2–29.4 — 1.35–1.52 26Maize, normal 28.7 0.3 0.8 2825.8–32.5 — 0.61–0.82 26Maize, waxy 1.4–2.7 — 0.02–0.14 26Maize, high amylose 42.6–67.8 — 1.01–1.09 26Fava bean 33 0.9 0.1 28Pea 33 0.7 0.1 28© 2006 by Taylor & Francis Group, LLC398 Carbohydrates in Food10.2.2 STARCHCRYSTALLINITYStarch granule crystallinity can be studied with the x-ray diffraction technique, and four different x-ray diffraction patterns have been described: theA-pattern, obtained for cereal starches (except high-amylose varieties); theB-pattern obtained for root and tubular starches (and for high-amylose varieties) and retrograded starch; the C-pattern, obtained for beans and peas; andthe V-pattern, obtained for gelatinized lipid-containing starches. The C-patternis described as a mixture of the A- and B-patterns but has also been regardedas a structure of its own [33]. In normal starches (i.e., starches with bothamylose and amylopectin) and of course in waxy starches it is the branched(amylopectin) molecules that constitute the crystallites. The branches of theAmilopektin molekul membentuk helices ganda yang disusun dalam kristaldomain [40]. A, B, dan C-pola adalah bentuk polimorfik yang berbedaPati yang berbeda dalam pengepakan amilopektin ganda helices. Gandumdan rye Pati telah dilaporkan mengandung tingkat rendah B-crystallites(hingga 10%), sehingga butiran Pati mungkin bahkan lebih heterogen daripadasebelumnya telah diasumsikan [41].Karena baris memperluas pola Difraksi sinar x, hal ini dapatmenyimpulkan bahwa kristal Pati (crystallites) sangat kecil dan tidak sempurna[42]. crystallites telah dilaporkan menjadi bulat di Pati gandum sebagaiserta Pati kentang, dengan diameter sekitar 10 nm gandum dan agakkecil dalam kentang [43]. Tingkat bagian kristalinitas juga agak rendah; nilai-nilaikisaran 15-45% telah dilaporkan untuk beberapa Pati [33], danbagian kristalinitas meningkat dengan rasio amilopektin di Pati [41]. Memilikitelah mengamati bahwa sejumlah besar double helices hadir daripadanomor diatur dalam kristalin domain [44]. Gandum, persentaseDouble helices adalah 39% dan tingkat bagian kristalinitas 20%; untuk jagung,nilai yang sesuai adalah 43 dan 27%, masing-masing; dan, untuk kentang,nilai yang sesuai adalah 40 dan 24% [45]. Tingkat bagian kristalinitas sangattergantung pada kadar air, dan jumlah tertinggi bagian kristalinitas adalahdiamati pada air menengah konten [7,46].The formation of A-crystals is favored by a short average chain length inamylopectin, a high temperature of formation, a high concentration, the presence of a salt with a high number in the lyothropic series, or the presence ofwater-soluble alcohols and organic acids [47]. Transitions from an A-structureto a B-structure through a C-structure have been observed [48]. The polymorphsare thus related to each other in such a way that the A-structure is most stable:melt →B-structure →C-structure →A-structureFor isolated crystallites that melt unrestricted, a lower melting temperaturehas been observed for B-crystallites compared with A-crystallites [49]. Crystalline A-spherulites were found to melt at 90°C and B-spherulites at 77°C© 2006 by Taylor & Francis Group, LLCStarch: Physicochemical and Functional Aspects 399[50]. The dissolution temperature of the B-polymorph of amylose in water isrelated to the chain length [50a].In the crystalline and amorphous regions in starch granules, three typesof structures can be identified (Figure 10.1): (1) crystalline domains, (2)amorphous regions containing branching points alternating with crystallinedomains, and (3) a second amorphous phase surrounding the alternating crystalline and amorphous regions. Microscopy studies have further elaborated the details regarding the organization of starch granules [50b], and the organization of amylopectin lamellae in blocklets (20 to 500 nm) has been visualized. The organization ofAmilopektin dalam kristalin domain dideskripsikan menggunakan model cairan – kristal sidechain untuk Polimer sintetik [50c]. Dalam model ini,tiga komponen yang digunakan untuk menggambarkan polimer: unit kaku, fleksibelspacer, dan tulang punggung yang fleksibel. Model harus dihubungkan dengan bahan kimiastruktur molekul amilopektin yang menjadi semakin lebih baikdipahami dengan waktu.Amilopektin merupakan domain kristal, dengan double helicesdiatur dalam A, B, atau C-pola. Kawasan-kawasan yang bercabang di amilopektinmolekul merupakan lapisan amorf yang memisahkan crystallites dariSatu sama lain. Karena ukuran molekul amilopektin, molekul sama mungkin ambil bagian dalam beberapa kristalin domain. Sekitar bergantian kristal dan amorf domain adalah struktur amorf lainnya,GAMBAR 10.1Arrangement kristal dan amorf daerah dalam pertumbuhan cincindi the granula Pati. Pembesaran menunjukkan organisasi dalam lapisan kristalin.(Diadaptasi dari Eliasson, A.-C. et al., Pati/Stärke, 39, 147, 1987.)Granul permukaanBergantian kristaldanamorf daerah© 2006 oleh Taylor & Francis Group, LLC400 karbohidrat dalam makananmenyebabkan apa yang telah digambarkan sebagai "pertumbuhan rings." Telah diusulkanBragg puncak 10 nm, yang menghilang pada gelatinization, adalah karenabergantian amorf dan kristal lapisan [51]. Puncak Bragg telahdetected around 10 nm for several starches by both x-ray diffraction techniques and optical diffraction [52], although d-spacings at 26 to 30 nm havealso been reported [53]. It has also been suggested that the size of thecombined crystalline and amorphous parts (9 nm) is a fundamental featureof the packing of starch molecules and is approximately constant for allstarches [54]. To account for the spherical shape of crystallites and for theexistence of a layered structure, a curved crystal structure has been proposed[55]. The curvature is the result of a translatory displacement of the helicesin the parallel packing.The structure of the amorphous regions is not known. An interesting aspectthat has implications for the organization of the starch granule is that incompatibility has been observed for amylose and amylopectin. In aqueous solutionsof these components, phase separation into an upper, clear, amylose-rich phaseand a lower, opalescent, amylopectin-rich phase was observed after 24 hoursat 80°C [56]. For binary amylose–water systems, the introduction of a thirdcomponent (amylopectin) has always been accompanied by the aggregationof amylose [57].Chemical modification (crosslinking) has shown that the amylose molecules are not located together in bundles [58]. This conclusion was reachedbecause no crosslinking was observed between amylose molecules, onlybetween amylopectin molecules and between amylopectin and amylose. Thelatter observation also indicates that amylose molecules might be rather evenlydistributed in the starch granule. Due to the leaking of amylose and amylopectin during gelatinization, ithas been suggested that the location of amylose differs among starches. Foroat starch, amylose and amylopectin were found to coleach from the granuleduring heating, whereas in barley starch the amylose was preferentially leached[59]. For wheat starch heated to 95°C, most of the amylose leached out of thegranules [60], whereas in potato starch the amylose diffused toward the aqueous center of the granule [61]. For maize starch, it has been observed thatannealing causes an increase in the differential scanning calorimetry (DSC)endotherm attributed to the melting of crystalline amylose, indicating that inthis starch the location of amylose molecules is such that it is possible toobtain an ordered, crystalline structure [62].Although the structures of the amorphous phases are largely unknown,they certainly influence the properties of the starch. A higher water content inthe B-polymorph, not only in the unit cell but also in the amorphous regions,could contribute to the lower stability of this polymorph [49]. As will bediscussed later, a glass transition of t

Hasil (Bahasa Indonesia) 2:

kompleks, itu menunjukkan bahwa gandum dan pati barley memberikan jenis yang sama
dari sinyal sebagai amilosa-lipid kompleks [34]. Ketika amilosa dan lipid yang
hadir tanpa membentuk kompleks inklusi, tidak ada sinyal diperoleh.
Meskipun rantai hidrokarbon dari lipid di kompleks adalah di padat
negara, kompleks amilosa-lipid dianggap hadir sebagai amorf
struktur [34- 36]. Demikian kompleks ini bisa berfungsi sebagai inti untuk kristalisasi selama gelatinisasi dan perawatan panas lainnya [33]. Cocrystallization
antara kompleks amilosa-lipid dan amilopektin heliks ganda tidak bisa
terjadi; harus ada domain kristal yang berbeda dalam gel pati [37].
Protein ini mungkin sangat baik menjadi pati degradasi enzim, dan jika
kondisinya sedemikian rupa sehingga enzim menjadi aktif ini tentu akan
mempengaruhi fungsi pati. Aktivitas enzim Kelebihan biasanya tidak
disukai, dan, khususnya untuk kue, aktivitas enzim yang terlalu tinggi dapat
bencana. Protein lain telah diidentifikasi sebagai komponen integral dari
struktur granul pati, terletak baik di pedalaman [38] atau pada permukaan
[39]. Contoh tipe yang terakhir dari protein adalah protein penyimpanan, pati enzim biosintesis (misalnya pati-pati-granul terikat sintase), dan friabilin /
puroindolines [39a].
TABEL 10.2
Komposisi Beberapa Dipilih Butir Pati
Pati Amilosa (%)
Protein
(g / 100 g)
Lipid
(g / 100 g) Ref.
Singkong 17 0,1 0,1 25
Kentang 21 0,06 0,05 25
Beras 12,2-28,6 - 0,63-1,11 26
Waxy beras 0-2,32 - - 27
Gandum 28
29,2
0,3
-
0,8
0,85
28
29
A- butiran 28,4-27,8 - 0,67-0,73 29
B-butiran 27,5-24,5 - 0,73-0,91 29
Barley, lilin 2,1-8,3 - 0,30-0,49 26
Barley, normal 25,3-30,1 - 0,68-1,28 26
Barley, amilosa tinggi 38,4-44,1 - 1,05-1,69 26
Oat 25,2-29,4 - 1,35-1,52 26
Jagung, normal 28,7 0,3 0,8 28
25,8-32,5 - 0,61-0,82 26
Jagung, lilin 1,4-2,7 - 0,02-0,14 26
Jagung, amilosa tinggi 42,6-67,8 - 1,01-1,09 26
Fava bean 33 0,9 0,1 28
Pea 33 0,7 0,1 28
© 2006 oleh Taylor & Francis Group, LLC
398 Karbohidrat dalam makanan
10.2.2 STARCHCRYSTALLINITY
Pati granul kristalinitas dapat dipelajari dengan teknik difraksi sinar-x, dan empat yang berbeda difraksi x-ray pola telah dijelaskan: the
A-pola, diperoleh untuk pati sereal (kecuali varietas amilosa); yang
B-pola yang diperoleh untuk root dan tubular pati (dan untuk varietas tinggi amilosa) dan retrograded pati; C-pola, diperoleh untuk buncis dan kacang polong; dan
V-pola, diperoleh untuk pati yang mengandung lipid gelatinized. C-pola
digambarkan sebagai campuran dari A- dan B-pola tetapi juga telah dianggap
sebagai struktur tersendiri [33]. Dalam pati normal (yaitu, kanji dengan baik
amilosa dan amilopektin) dan tentu saja di pati lilin itu adalah bercabang
(amilopektin) molekul yang merupakan kristal. Cabang-cabang dari
molekul amilopektin membentuk heliks ganda yang diatur dalam kristal
domain [40]. The A-, B-, dan C-pola demikian bentuk polimorfik yang berbeda
dari pati yang berbeda dalam kemasan heliks ganda amilopektin. Gandum
dan gandum hitam pati telah dilaporkan mengandung rendahnya tingkat B-kristalit
(hingga 10%), sehingga granula pati mungkin bahkan lebih heterogen daripada
sebelumnya telah diasumsikan [41].
Karena garis memperluas dalam difraksi x-ray pola, dapat
disimpulkan bahwa kristal pati (kristalit) sangat kecil dan tidak sempurna
[42]. Kristalit telah dilaporkan bola di pati gandum sebagai
serta dalam tepung kentang, dengan diameter sekitar 10 nm gandum dan agak
lebih kecil dalam kentang [43]. Tingkat kristalinitas juga agak rendah; nilai dalam
kisaran 15 sampai 45% telah dilaporkan selama beberapa pati [33], dan
kristalinitas meningkat dengan rasio amilopektin dalam pati [41]. Ia telah
telah mengamati bahwa sejumlah besar heliks ganda hadir daripada
jumlah diatur dalam domain kristal [44]. Untuk gandum, persentase
heliks ganda adalah 39% dan derajat kristalinitas adalah 20%; untuk jagung,
nilai-nilai yang sesuai adalah 43 dan 27%, masing-masing; dan, untuk kentang, yang
nilai-nilai yang sesuai adalah 40 dan 24% [45]. Derajat kristalinitas sangat
tergantung pada kadar air, dan jumlah tertinggi kristalinitas yang
diamati di beberapa kadar air menengah [7,46].
Pembentukan A-kristal disukai oleh rata-rata panjang rantai pendek dalam
amilopektin, tinggi suhu pembentukan, konsentrasi tinggi, kehadiran garam dengan jumlah yang tinggi dalam seri lyothropic, atau adanya
alkohol larut dalam air dan asam organik [47]. Transisi dari A-struktur
ke B-struktur melalui C-struktur telah diamati [48]. Para polimorf
demikian berhubungan satu sama lain sedemikian rupa bahwa A-struktur yang paling stabil:
meleleh → B-struktur → C-struktur → A-struktur
kristalit Untuk terisolasi yang mencair terbatas, suhu leleh lebih rendah
telah diamati untuk B -crystallites dibandingkan dengan A-kristal [49]. Kristal A-spherulites ditemukan mencair pada suhu 90 ° C dan B-spherulites pada 77 ° C
© 2006 oleh Taylor & Francis Group, LLC
Pati: fisiko dan Aspek Fungsional 399
[50]. Suhu pembubaran B-polimorf dari amilosa dalam air
berhubungan dengan panjang rantai [50a].
Dalam kristal dan amorf daerah di granula pati, tiga jenis
struktur dapat diidentifikasi (Gambar 10.1): (1) domain kristal, (2)
daerah amorf yang mengandung poin bercabang bergantian dengan kristal
domain, dan (3) fase amorf kedua sekitar kristal bolak dan daerah amorf.
studi Microscopy telah dijabarkan lebih lanjut rincian mengenai organisasi granula pati [50b], dan organisasi amilopektin lamellae di blocklets (20-500 nm) telah divisualisasikan. Organisasi
amilopektin dalam domain kristal telah dijelaskan menggunakan Sidechain Model cair-kristal polimer sintetis [50 c]. Dalam model ini,
tiga komponen yang digunakan untuk menggambarkan polimer: unit kaku, fleksibel
spacer, dan tulang punggung yang fleksibel. Model harus terkait dengan kimia
struktur molekul amilopektin yang menjadi semakin lebih baik
dipahami dengan waktu.
amilopektin merupakan domain kristal, dengan heliks ganda
diatur dalam A-, B-, atau C-pola. Percabangan daerah di amilopektin
molekul merupakan lapisan amorf yang memisahkan kristal dari
satu sama lain. Karena ukuran molekul amilopektin, molekul yang sama mungkin mengambil bagian dalam beberapa domain kristal. Sekitar ini bolak kristal dan amorf domain adalah struktur lain amorf,
GAMBAR 10.1Arrangement daerah kristalin dan amorf dalam cincin pertumbuhan
dalam granula pati. Pembesaran menunjukkan organisasi dalam lapisan kristal.
(Diadaptasi dari Eliasson, A.-C et al., Pati / Starke, 39, 147, 1987.)
permukaan Granule
Alternating kristal
dan
daerah amorf
© 2006 oleh Taylor & Francis Group, LLC
400 Karbohidrat dalam makanan
menyebabkan apa yang telah digambarkan sebagai "cincin pertumbuhan." Ia telah mengemukakan
bahwa puncak Bragg pada 10 nm, yang menghilang pada gelatinisasi, adalah karena
bolak amorf dan lapisan kristal [51]. Puncak Bragg telah
terdeteksi sekitar 10 nm selama beberapa pati oleh kedua teknik difraksi sinar-x dan difraksi optik [52], meskipun d-jarak di 26-30 nm telah
juga telah dilaporkan [53]. Ini juga telah menyarankan bahwa ukuran
kristal gabungan dan bagian amorf (9 nm) adalah fitur mendasar
dari kemasan molekul pati dan mendekati konstan untuk semua
pati [54]. Untuk menjelaskan bentuk bulat dari kristal dan untuk
keberadaan struktur berlapis, struktur kristal melengkung telah diusulkan
[55]. Kelengkungan adalah hasil dari perpindahan translatory dari heliks
dalam kemasan paralel.
Struktur daerah amorf tidak diketahui. Aspek yang menarik
yang memiliki implikasi untuk organisasi granul pati adalah bahwa ketidakcocokan telah diamati untuk amilosa dan amilopektin. Dalam larutan air
dari komponen ini, fase pemisahan menjadi, jelas, fase kaya amilosa atas
dan bawah, terbuat dr batu baiduri, fase kaya amilopektin diamati setelah 24 jam
pada suhu 80 ° C [56]. Untuk sistem amilosa air biner, pengenalan ketiga
komponen (amilopektin) selalu disertai dengan agregasi
dari amilosa [57].
modifikasi kimia (silang) telah menunjukkan bahwa molekul amilosa tidak berada bersama-sama dalam bundel [58]. Kesimpulan ini dicapai
karena tidak ada silang diamati antara molekul amilosa, hanya
antara molekul amilopektin dan antara amilopektin dan amilosa. Yang
terakhir pengamatan juga menunjukkan bahwa molekul amilosa mungkin agak merata
didistribusikan dalam granula pati.
Karena bocornya amilosa dan amilopektin selama gelatinisasi, itu
telah disarankan bahwa lokasi amilosa berbeda antara pati. Untuk
pati gandum, amilosa dan amilopektin ditemukan coleach dari granul yang
selama pemanasan, sedangkan pada barley pati amilosa itu istimewa tercuci
[59]. Untuk tepung gandum dipanaskan sampai 95 ° C, sebagian besar amilosa yang tercuci keluar dari
butiran [60], sedangkan di kentang pati yang amilosa menyebar menuju pusat berair dari granul [61]. Untuk pati jagung, telah diamati bahwa
anil menyebabkan peningkatan diferensial scanning kalorimetri (DSC)
endoterm dikaitkan dengan mencairnya amilosa kristal, menunjukkan bahwa dalam
pati ini lokasi molekul amilosa adalah sedemikian rupa sehingga adalah mungkin untuk
mendapatkan memerintahkan , struktur kristal [62].
Meskipun struktur dari fase amorf sebagian besar tidak diketahui,
mereka pasti mempengaruhi sifat pati. Sebuah kadar air yang lebih tinggi di
B-polimorf, tidak hanya dalam sel satuan, tetapi juga di daerah amorf,
dapat memberikan kontribusi untuk stabilitas yang lebih rendah dari polimorf ini [49]. Seperti yang akan
dibahas kemudian, transisi gelas t