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Degree of Starch Gelatinization, Digestion Rate of Starch in Vitro, and Metabolic Response in Rats



Glycemic response after ingestion of starchy foods varies. Starch in many common ready-to-eat foods is only partly gelatinized. In view of this, the relationships among degree of starch gelatinization, in vitro digestion rate, and in vivo metabolic response in rats were studied. Wheat starch with different degrees of gelatinization was used in the experiments. Plasma glucose and insulin responses as well as the rate of in vitro hydrolysis with alpha-amylase were strongly correlated to the degree of starch gelatinization (r = 0.88, r = 0.90, and r = 0.96, respectively). Plasma glucose and insulin responses were also positively correlated to the rate of hydrolysis with alpha-amylase in vitro (r = 0.98 and r = 0.76, respectively). These results suggest that the degree of starch gelatinization is an important determinant both for the rate of starch hydrolysis in vitro and for the metabolic response in vivo.
1010 Am J C/in Nuir l988;47: 1010-6. Printed in USA. © 1988 American Society for Clinical Nutrition
Degree of starch gelatinization, digestion rate of starch
in vitro, and metabolic response in rats1’2
J#{246}rgenHo/rn, MSc; Jngmar Lundquist, MD, PhD; Inger Bj#{246}rck,PhD;
Ann-Charlotte Eliasson, PhD; and Nils-Georg Asp, MD, PhD
ABSTRACI’ Glycemic response after ingestion of starchy foods varies. Starch in many
common ready-to-eat foods is only partly gelatinized. In view ofthis, the relationships among
degree of starch gelatinization, in vitro digestion rate, and in vivo metabolic response in rats
were studied. Wheat starch with different degrees ofgelatinization was used in the experiments.
Plasma glucose and insulin responses as well as the rate ofin vitro hydrolysis with a-amylase
were strongly correlated to the degree ofstarch gelatinization (r =0.88, r=0.90, and r=0.96,
respectively). Plasma glucose and insulin responses were also positively correlated to the rate
ofhydrolysis with a-amylase in vitro (r =0.98 and r=0.76, respectively). These results suggest
that the degree of starch gelatinization is an important determinant both for the rate of starch
hydrolysis in vitro and for the metabolic response in vivo. Am J C/in Nuir 1988;47:
KEY WORDS Starch gelatinization, starch digestion rate, a-amybolysis, plasma glucose,
plasma insulin
The variable glycemic response after ingestion of
starchy foods has been the subject of much interest re-
cently, especially in relation to diabetes. So far, however,
not much attention has been paid to the importance of
the degree ofstarch gelatinization (DG).
In plant cells starch is present as granules. Starch poby-
mers (amybose and amybopectin) are tightly packed in
granules with a high degree of molecular order and are
associated by hydrogen bonding. Raw granules contain
highly crystalline regions and are birefringent in polar-
ized bight. The granules are insoluble in cold water.
When exposed to heat in the presence ofwater, the starch
granules undergo an irreversible swelling and destruction
of the internal crystalline structure and birefringence is
lost. This transformation is termed gelatinization. With
excessive treatment the granules may even rupture and
disintegrate and a fraction of the starch is then sobubi-
Raw starch is only slowly digested by enzymes in vitro
whereas cooking increases the susceptibility considera-
bly because ofthe rupture and disintegration ofthe com-
pact crystalline granular structure (1-4). Furthermore,
the glucose and insulin responses in vivo are significantly
greater after ingestion of cooked compared with raw
starches(3-7). Consequently, DG is an extremely impor-
tant factor in the rate ofstarch hydrolysis and metabolic
However, in many common plant foods the starch is
only partly gelatinized, because ofthe limited water con-
tent during processing. The starch granules are only
slightly swollen and the internal structure is partly intact.
Examples of such foods are breakfast flakes of cereal
grains (3) and several baked products (8- 1 1). The starch
granules in legumes may swell incompletely during pro-
cessing (12, 13). In view of the increased attention to
starchy foods and the nutritional advantages of carbohy-
drates that are slowly digested and absorbed (14-19), the
nutritional properties of incompletely gelatinized starch
are of interest.
This paper describes the close relationship between the
DG of pure wheat starch and the enzymatic susceptibil-
ity in vitro as well as the glucose and insulin responses
to starch in rats. The results are discussed in terms of a
IFrom the departments ofFood Chemistry and Food Technology,
University of Lund, Lund, and the Department ofCell Biology, Urn-
versity ofLink#{246}ping, Link#{246}ping,Sweden.
2Address reprint requests to J#{246}rgenHolm, Department of Food
Chemistry, Chemical Center, University ofLund, P 0 Box 124, S-22l
00 Lund, Sweden.
ReceivedFebruary2, 1987.
Accepted for publication June 16, 1987.
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Physical and morphological characteristics ofwheat-starch samples used in the experiments
temperaturet Heat ofgelatinization En)
Degree of gelatinization
power [nJ Solubility [n] Microscopical
(DSC)[nJ Enzymatic
method [n]
C J/g(cal/g) % % %
10.52 ± 0.29 (2.5 1 ± 0.07) [3]
9.02 ± 0. 17 (2. 15 ± 0.04)[4)
6.64 ±0.25 (1 .59 ±0.06) [5]
3.04 ± 0.03 (0.73 ±0.01 ) [3]
1.59 ±0.02 (0.38 ±0.0 1) [21
0.42 (0. 10) [2]
0 [2]
0 [2]
Ot [3]
l4.2 [4]
36.9t [5]
7 1.1f [3]
85.0 [21
96.Of [2]
l00 [2]
l00 [21
0. 1 ± 0.4t [4]
14. 1 ±1.3f [4]
47.3 ±1.9f (6]
91 .9 ±0.4f [4J
97.2 ±0.7f [2]
97.8f [2]
2.0 [4]
2.4 [4]
2.8 [3)
3.9 [31
5.4 ±0. 1 [3]
6. 1 ± 0.2 [3]
6.9 ±0.2 [3]
0.2 [4J
0.4 ±0. 1 [4J
0.6 ±0. 1 [3]
0.8 ±0. 1 [3]
1.4 ±0. 1 [3]
1.6 [3J
2.8 [3)
35.0 ±4.0(3J
Intact birefringent
Increased swelling and
decreased number of
granules showing
Extensively swollen
Granules disintegrated
tPartly gelatinized.
§Completely gelatinized.
physical and morphological characterization of the
Materials and methods
Preparation ofstarch samples
Raw commercial wheat starch was obtained from KEBO
Lab AB (Stockholm, Sweden). The starch content was 98.2 g/
100 g (polymer weight, dry basis), determined as glucose after
incubating the sample with a thermostable a-amylase at 95 #{176}C
and amyloglucosidase at 60 #{176}C(20). To obtain starch with
different DOs, 100 g/L suspensions ofwheat starch in distilled
water were heated under gentle agitation at 47, 50, 53, 56, 59,
or 65 C. After 20 mm the samples were cooled to room tern-
perature. A boiled sample was prepared by boiling a 50 g/L
suspension for 20 mm.
Degree ofstarch gelatinization
The DO was measured by two different methods. Duplicate
analyses were performed on each preparation. With the cabori-
metric method (differential scanning calorimetry [DSC]) we
measured the heat ofgelatinization (H) ofthe starch samples,
ie, the energy that has to be supplied to obtain complete starch
gelatinization. Ten to 15 mg of a bOO g/L suspension was
heated from 22 to 80 #{176}Cat a scanning rate of 10 C/min in
coated sample pans. H was calculated from the peak area of
the thermogram. The instrument used was a Perkin-Elmer
DSC-2 (Perkin-Ebmer Corp, Eden Prairie, MN). The DG was
calculated by comparing iH for raw starch with that for heat-
treated starch:
DG (%) =(1 -x100 (1)
The enzymatic method is based on the principle that gelatin-
ized starch is easily digested by glucoamybase to form glucose.
A small amount of the heat-treated starch suspensions corre-
sponding to 20 mg of starch was withdrawn and analyzed ac-
cording to Chiang and Johnsson (21). DO was expressed as the
percentage ofthe total starch content that was immediately sus-
ceptible to glucoarnylase.
Swelling and solubi/itypauerns
The heat-treated suspensions were carefully transferred to
weighed centrifuge bottles and diluted with distilled water to
30 g/L starch concentration. A suspension of raw starch was
kept for 20 mm at room temperature under gentle agitation.
The samples were centrifuged for 15 mm at 700 Xg. The super-
natant was decanted and evaporated to dryness in the oven and
the amount ofsolute was measured. Granule swelling and solu-
bility were calculated according to Leach et al (22):
Swelling power
=weight ofgel/(total starch -weight ofsolutes) (g/g) (2)
Solubility (%)
=100 X weight ofsolutes/total starch (gig) (3)
A few drops ofa 10 g/L suspension were examined by light
microscopy and by polarized light microscopy to further char-
acterize the morphology ofthe granules.
Experiments in vitro
A porcine pancreatic a-amylase preparation (27 mg protein/
mL, 1200 units/mg; Sigma Chemical Co, St Louis, MO) was
diluted 1:20 or 1:400 before incubation. The heat-treated sam-
ples were diluted with distilled water to 50 gIL. Forty-five milbi-
liters of0.05 mob/L Na,K-phosphate buffer(0.025 mol/L each
of KH2PO4 and Na2HPO4) containing 0.4 g/L NaC1 (pH 6.9)
and 1.25 mL ofdiluted a-amylase preparation were added to a
lO-mL subsample corresponding to 500 mg starch. Samples
were taken before and after 5-60 mm incubation (under gentle
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50 -
05 15 30 60
agitation at 37 #{176}C)and analyzed with dinitrosalicylic acid for
content ofreducing sugar (23). A standard curve was prepared
using maltose. The extent of hydrolysis (the proportion of
starch degraded to maltose, or percent maltose equivalents)
was calculated as 100 times milligrams of maltose equivalents
times 0.95 divided by milligrams ofstarch in sample.
Experiments in vivo
The availability of starch for digestion and absorption in
vivo in male rats (Sprague-Dawley, 120-150 g) was studied by
analyzing concentrations of glucose and insulin in plasma at
various time intervals after gastric intubation. The starch sam-
ples were diluted with a NaCl solution to 40 gIL. The final con-
centration of NaCI was 9 gIL. After being starved for 24 h un-
anesthetized rats were intubated with a starch suspension (2.5
mL) corresponding to 100 mg starch. Nine rats were used for
each sample tested. Blood was obtained from the rats by multi-
pIe serial sampling from the retroorbital venous plexus. After
135 mm the rats were killed by a blow on the head and a piece
of the liver (‘-0.5 g) was taken from the ventral part of the
left lateral lobe for analysis ofglycogen content. Estimation of
plasma glucose concentration was done with a glucose-oxidase
method (24). Plasma insulin levels (IRI) were analyzed with
a radioirnmunoassay (25). Liver glycogen concentration was
determined by the method ofRerup and Lundquist (26).
St atistical evaluation
The results are given as mean ± SEM. The significance of
differences was tested with Student’s ttest.
The physical and morphological characterization of
the starch samples used in the in vitro and in vivo experi-
ments are presented in Table 1. With increasing DG
there was an increased susceptibility to glucoamylase as
well as a gradual boss ofbirefringence, indicating that the
highly ordered structure within the granules was de-
stroyed to different extents. The soluble starch fraction
was only slightly increased for the partly gelatinized sam-
ples and for the completely gelatinized sample heated at
65 #{176}C(just above the gelatinization temperature range).
In contrast, after boiling, a large fraction of the starch
was soluble, indicating disintegration of the granular
The susceptibility of starch with different DGs to hy-
drobysis by porcine pancreatic a-amylase (added at a
concentration of200 units/g starch where 1 unit liberates
1mg maltose from soluble starch in 3 mm at pH 6.9 and
at 20 #{176}C)is shown in Figure 1. Raw starch was hydro-
lyzed most slowly and the susceptibility to a-amylase in-
creased with DO. The two completely gelatinized sam-
ples(DG =100%)and starch with a DG of96% displayed
the highest availability; no significant difference was oh-
served between these three samples.
When a large excess ofenzyme was used by increasing
the enzyme concentration 20-fold to 4050 units/g starch,
the initial hydrolysis rate increased as did the extent of
hydrolysis (Fig 2). However, the differences in availabil-
ity between the samples, especially in the initial hydroly-
Incubation time (mm)
FIG 1. Hydrolysis ofstarch with different DOs by porcine pancreatic
a-amylase added at a concentration of 200 units/g starch. Percentage
hydrolysis is expressed in terms of maltose equivalents. DG (%): #{149},0
(raw); A, 14.2; #{149},36.9; 0, 71.1; t, 85.0. The bars represent the interval
obtained with 96.0, lOO(heated at 65 ‘C,just above gelatinization tem-
perature range), and 100% (boiled). The SEM did not exceed 3.4 for
any experimental point. n=2-3.
sis rate, were still very pronounced. The boiled sample
was hydrolyzed to 75% (maltose equivalents) within 5
mm and reached a plateau at 80% after 30 mm, whereas
the hydrolysis values at 5 mm for raw starch and starch
with DGs of 14 and 37% were b2, 30, and 48%, respec-
The course of the plasma glucose and insulin re-
sponses in rats after intubation with starch with different
DGs are shown in Figures 3 and 4 and the area under
the curves are presented in Table 2. The plasma glucose
response after intubation with boiled starch (DG
=100%) was much greater than after raw starch (DG
=0%). The responses to the partly gelatinized products
were intermediate. The response to the partly gelatinized
starch with a DG of 37% was greater than to that with a
DG of 14%. With raw starch the glucose peak was de-
bayed (peak value at 60 mm), whereas the peak values
for the partly and completely gelatinized starch samples
were obtained after only 15 mm. The insulin responses
were closely associated with the glucose responses. The
rise in plasma glucose (0-60 mm) and plasma insulin (0-
30 mm) reflect the early rates of digestion and absorp-
tion, where the largest differences are found. The liver
glycogen contents 1 35 mm after intubation were 4.1
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___0 5 15 30 60
Incubatmon tmme (1Tn)
smgnifmcant dmfferences
_i aQ (mm)
.-Ap<0.00 1 p <0.001
.-Up<0.00 1 p <0.00 1p<0.001
.- 0 p<0.00 1p<0.00 1po.oo i
A-I p<0.01
A- 0p< 0001 p< 0.001 p< 0.05
1-0 p<o.o5
1#{149} I I I I
015 30 60 120
starch was hydrolyzed almost completely within 5 mm,
barge differences in the rate of hydrolysis remained (Fig
2). Starch hydrolysis with a-amylase results in the forma-
tion ofglucose, maltose, maltotriose, and alimit dextrins
(branched obigosaccharides with four glucose monomers
or more). Therefore, 75-80% hydrolysis expressed as
maltose equivalents corresponds to an almost complete
hydrolysis. Once the highly organized structures within
the swollen granules were completely destroyed, as in the
sample treatedjust above the gelatinization temperature
range, the availability ofstarch was not increased further
by swelling, rupture, and disintegration of the granular
structure (boiled sample) (Fig 1). The increased suscepti-
bility to a-amylase was not rebated to increased sobubility
because the soluble starch fraction did not exceed 3% in
any sample, except for boiled starch.
The plasma glucose and insulin concentrations in rats
were raised to different extents depending on the DG. An
already bow DG (14%), which caused only slight swelling
and internal disorganization of the granules (Table 1),
raised the glycemic response far above that ofraw starch.
The decline in plasma glucose concentration was slower
for partly gelatinized starch than for completely gelatin-
FIG 2. Hydrolysis ofstarch with different DGs using a large excess
of porcine pancreatic a-amylase (4050 units/g starch). DG (%): #{149},0
(raw); A, 14.2; ,36.9; 0, 100 (boiled). The SEM did not exceed 3.4
for any experimental point. n=2-3.
± 0.7 (raw), 6.9 ± 0.8 (DG =14%), 6.1 ± 1.1 (DG
=37%), and 6.3 ± 0.5 (boiled) mg/g wet wt ofliver. The
glycogen content was significantly bower with raw starch
than with boiled starch or starch with DG of 14% (p
<0.05). The liver glycogen content in control rats(n =4)
intubated with 0.9% NaCb solution was 0.3 ±0.1.
The plasma glucose and insulin responses were posi-
tiveby correlated with the rate of hydrolysis with a-
amylase in vitro, and both the plasma glucose and insu-
lin responses as well as the rate ofhydrolysis with a-amy-
lase were positively correlated with the DG (Table 3).
During gelatinization inter- and intramolecular hy-
drogen bonds are broken. This results in a loosening up ___________________________________
of the compact granular structure and allows different
degrees of swelling and absorption of water, fully hy-
drated starch molecules leach from the granule. Conse- Time after intubation (mm)
quently, the availability of the starch granules to diges- FIG 3. Plasma glucose responses at various intervals in rats given
tive enzymes increases to different levels with increasing h with different DOs (100 mg as a 40 g/L suspension in 9 g/L
DG. Even when we used an enzyme concentration in our NaCI). DG (%): #{149},0 (raw); A, 14.2; #{149},36.9; 0, 100 (boiled). Nine rats
in vitro system that was so high that the boiled wheat were used for each sample tested. (Mean ±SEM.)
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significant differences
i. 122 (mm)
#{149}-A p<0.05
#{149}-o p<0.01
A-D p<0.01
1-0 p<0.05
Correlation coefficients between DO, digestion rate ofstarch in vitro,
and plasma glucose and plasma insulin responses in rats
DO with digestion rate (n =7)t 0.96
DO with plasma glucose(n =4) 0.88
DO with plasma insulin (n =4) 0.90
Digestion rate with plasma glucose (n =4) 0.98
Digestion rate with plasma insulin (n =4) 0.76
015 30 60
Time after intubation (mm)
FIG 4. Plasma insulin (IRI) responses at various intervals in rats
given starch with different DOs (100 mg as a 40 g/L suspension in 9
g/L NaG). DG (%): #{149},0(raw); A, 14.2; I, 36.9; 0, 100 (boiled). Nine
rats were used for each sample tested. (Mean ±SEM.)
ized starch, which confirms that digestion and absorp-
tion are prolonged when swelling is limited. Raw starch
was absorbed very slowly and elicited a flattened plasma
glucose curve with a delayed and less pronounced peak
and a very slow decline.
The effect ofcompbete gelatinization on metabolic re-
sponse has been studied in humans, both in diabetic and
nondiabetic subjects(5-7)and in animals(3, 4). Potatoes
and corn starch give much lower postprandial glucose
and insulin responses in raw form than after cooking (5-
7). In fact, raw corn starch has been used clinically to
Area under the curve after gastric intubation ofrats with starch with
different DG5
*DO was calculated from calorimetric measurement ofthe heat of
starch gelatinization. Digestion rate =degree ofhydrolysis after 60 mm
incubation with a-amylase (added at a concentration of 200 units/g
starch). Plasma glucose =area under the curve, 0-60 mm. Plasma insu-
lin =area under the curve, 0-30 mm.
tn=number of starch samples with different DGs on which the
calculations were based.
provide glucose with prolonged absorption in the treat-
ment of type 1 glycogenosis (27). The effect of raw
starchy foods on the glycemic response may be more fa-
vorable than supplementation with gel-forming types of
dietary fiber. The use of raw plant food in the nutrition
ofdiabetic patients was discussed (28).
Despite a low enzymatic availability, raw wheat starch
is almost completely digested and absorbed in the rat
small intestine (29). Raw potato starch, on the other
hand, is poorly digested (30).
In some processed food products the starch is only
partly gelatinized with a slightly swollen granular struc-
ture and the internal granular organization partly intact.
For example, some baked products and breakfast cereals
contain incompletely gelatinized starch granules, which
is attributed to the limited water available (10-60 g/lOO
g) when these products are produced. Cereal flakes are
produced by steaming whole kernels and then flaking
them between rollers. Starch in breakfast cereals or pre-
cooked convenience foods produced under more severe
conditions (elevated temperatures, pressures, and shear
forces, eg, extrusion cooking or popping) is normally
completely gelatinized despite the bow water content. A
recent study (3) found that the plasma glucose and insu-
bin responses in rats were lower after ingestion of wheat
flakes with a DG of45%, as measured by DSC, than after
boiled completely gelatinized whole-grain wheat flour.
The in vivo responses were closely related to the in vitro
digestibility with pepsin and a-amylase.
According to Wootton and Chaudhry (1 1) DGs in
short bread, hard sweet cookies, soda crackers, crisp-
bread, wafer, fruit cake, and bread crumbs were 1,2, 3,
33, 40, 50, and 60%, respectively. The corresponding in
vitro digestibility values with porcine pancreatic a-
amybase were 18, 25, 33, 43, 56, 66, and 69%, respec-
tively whereas pregelatinized wheat starch was digested
to 90%. The variations in gelatinization were explained
in terms ofprebaking water content, baking time at high
moisture bevel favoring high DG, and the presence of
added ingredients that restrict gelatinization. Lineback
Area under the curve
Plasma glucoset Plasma glucose Plasma insulin
DO (0-60 mm) (0-120 mm) (0-30 mm)
%mmol/L Xmm mmol/L Xmm nmo!/L Xmm
111248±15 It
1381±19 t
§1465±22 t
t1512±25 t
§1 2.12±0.68 §
IMean ±5EM; n=9. For each bracket, values without footnotes were sig.
nificantly different from values with footnotes.
t <0.001.
tp <0.01.
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and Wongsrikasem (10) found DOs between 4 and 97%
in several commercial U.S. baked products. Hagander et
al (3 1) observed that extruded crispbread elicited larger
glucose and insulin responses than a conventionally
baked bread in diabetic patients, possibly because the
conventionally baked bread had a bower DG.
Snow and O’Dea (1) obtained a more rapid hydrolysis
of starch in vitro in commercial breads compared with
homemade breads and suggested that this might have
been due to a greater exposure to heat in the commercial
breadmaking process. L#{252}deret al (32) reported signifi-
cantby lower blood glucose bevels in healthy subjects after
ingestion of 85% rye-15% wheat bread with a baking
time of35 mm compared with bread with a baking time
of 45, 55, or 65 mm. These differences in glycemic re-
sponse were probably caused by differences in DO that
were caused by the variations in baking time.
The extent ofstarch gelatinization also varies within a
given bakery product because ofa moisture gradient (8).
Thus, starch gelatinization in white pan bread ranged
from 33% in the crust to 70% in the center ofthe crumb
(8). The crust contained many unswollen birefnngent
starch granules whereas starch granules in the crumb
center were deformed and only slightly birefringent. The
differences in DG between crumb and crust is the proba-
ble reason for differences in postprandial hyperglycemia
after ingestion ofbread with different crust-to-crumb ra-
tios (33). Bread rolls with high crust-to-crumb ratios
raised the blood glucose level more slowly with a later
peak and a slower decline than loaves with bow crust-to-
crumb ratios.
Dreher et al (34) obtained a higher in vitro digestibility
and more extensive gelatinization of starch in potato
chips compared with starch in baked potato. The in vitro
digestibility of potato chips, baked potato, and raw po-
tato were 66.3, 53.6, and 228%, respectively.
Differences in the extent of gelatinization after pro-
cessing legumes in different ways was suggested as a plau-
sible explanation for differences in in vitro starch digest-
ibility (2). It has been suggested that the low metabolic
response and in vitro starch digestibility of legumes is
caused by the entrapment of starch in the cells (12, 13,
35). The cell walls may limit the hydrolysis rate because
of steric hindrance to enzymatic attack (13). Further-
more, the cell walls may also inhibit starch gelatinization
by physically limiting the degree ofswelling ofthe starch
granules and by limiting the water transport necessary
for complete gelatinization (12, 13). Grinding raw be-
gumes, thus disrupting the cell walls, followed by cook-
ing resulted in an increased swelling ofthe granules, and
it was proposed that this could increase the rate of starch
digestion as well as the glycemic response (12, 13).
DSC is a calorimetric method based on the physical
course of gelatinization but it requires equipment not
usually available in most nutritional laboratories. How-
ever, the values for DU obtained with the simple and
rapid enzymatic method using glucoamylase were
closely correlated (r =0.99) with those obtained with
DSC (Table 1).
The characterization ofthe starch, especially regarding
the degree ofgebatinization, would be desirable in studies
concerned with the rate of digestion and absorption of
starchy foods. Light microscopy in combination with po-
barized light microscopy as webb as enzymatic methods
like that used in this study are rapid methods that are
well suited for this purpose.
In conclusion, the rate ofstarch hydrolysis in vitro and
the glucose and insulin responses in vivo are increased to
different extents, depending on DO. Hence, starchy
foods with low DOs may be beneficial nutritionally be-
cause they favor a reduced rate ofstarch uptake. 13
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... Considering the calculated values of C ∞ were affected by the digestion time, the experimentally determined values of C 120 were also presented, which were similar as C ∞ (Table 5). Although Holm et al. (1988) found that the degree of starch gelatinization is an important determinant for the rate of starch hydrolysis in vitro (Holm et al., 1988) and Zhedagaozhi 1B was scarcely gelatinized, gelatinized and retrograded starch can benefit the formation of RS, which has been reported to be decisive for the glycemic index of rice (Kumar et al., 2018). The RS3 content should be the major *The results were expressed as mean ± SD (n = 3). ...
... Considering the calculated values of C ∞ were affected by the digestion time, the experimentally determined values of C 120 were also presented, which were similar as C ∞ (Table 5). Although Holm et al. (1988) found that the degree of starch gelatinization is an important determinant for the rate of starch hydrolysis in vitro (Holm et al., 1988) and Zhedagaozhi 1B was scarcely gelatinized, gelatinized and retrograded starch can benefit the formation of RS, which has been reported to be decisive for the glycemic index of rice (Kumar et al., 2018). The RS3 content should be the major *The results were expressed as mean ± SD (n = 3). ...
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The content of resistant starch (RS) was considered positively correlated with the apparent amylose content (AAC). Here, we analyzed two Indica rice mutants, RS111 and Zhedagaozhi 1B, similar in high AAC and found that their RS content differed remarkably. RS111 had higher RS3 content but lower RS2 content than Zhedagaozhi 1B; correspondingly, cooked RS111 showed slower digestibility. RS111 had smaller irregular and oval starch granules when compared with Zhedagaozhi 1B and the wild type. Zhedagaozhi 1B showed a B-type starch pattern, different from RS111 and the wild type, which showed A-type starch. Meantime, RS111 had more fa and fb1 but less fb3 than Zhedagaozhi 1B. Both mutants showed decreased viscosity and swelling power when compared with the parents. RS111 had the lowest viscosity, and Zhedagaozhi 1B had the smallest swelling power. The different fine structures of amylopectin between RS111 and Zhedagaozhi 1B led to different starch types, gelatinization properties, paste viscosity, and digestibility. In addition to enhancing amylose content, modifications on amylopectin structure showed great potent in breeding rice with different RS2 and RS3 content, which could meet the increasing needs for various rice germplasms.
... The shorter time taken to produce 50% of the asymptotic gas volume and higher molar proportion of propionate with the pelleted diets could be due to pelleting heat treatments and starch gelatinization in the process. It is known that starch gelatinization increases with pelleting heat treatments [36], with a subsequent increase in the rate of fermentation [37]. Unfortunately, it was not possible to estimate the rate of fermentation for specific nutrients from the in vitro work. ...
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Four formulations of concentrate feeds, three contrasting qualities of grass silages, and mixtures of the silages (55%) and concentrates (45%, dry weight) were tested for in vitro fermentation kinetics, in vitro dry matter degradation (IVDMD), utilizable crude protein (uCP), and metabolizable energy (ME) values. The concentrates were pelleted control concentrate for dairy cows (CONT-P); pelleted alkaline concentrate with ammoniated cereal grains (ALKA-P); mash form concentrate with ALKA-P main ingredients but with feed-grade urea and barley replacing ammoniated cereal grain (UREA-M); and mash form of ALKA-P ingredients prior to alkalization (ALKA-M). The grass silages were early cut, late cut, and a mixture (1:1) of early and late cut. The objectives were to test if the feeds differed in the tested parameters within each feed category and assess the modulatory effect of concentrate feeds on the grass silage fermentation characteristics in the mixed diets. No interaction effects of the concentrate feeds by silage quality were observed for the tested parameters in the mixed diets. For concentrates, the pelleted diets were higher (p < 0.05) in IVDMD and molar proportion of propionate but lower in butyrate. The ALKA-P produced the highest estimated uCP (p < 0.01). For silages, uCP, ME, total short-chain fatty acids (VFAs), and molar proportions of propionate and branched-chain VFAs decreased (p < 0.05) with increasing stage of maturity. In conclusion, the ALKA-P could match the CONT-P in uCP and ME values and fermentation characteristics. Results for silages and their mixtures with concentrates highlight the importance of silage quality in dietary energy and protein supply for ruminants.
... However, the digestion rate and the total digestibility of a starch depend on its structure [6,7]. In addition, starch digestibility increases with the degree of gelatinization, and raw ungelatinized starch has been proposed to be a source of slowly digestible starch (SDS) [8,9]. A recent in vitro study reported that common buckwheat (Fagopyrum esculentum Moench) starch (ST) could be used as a source of SDS in biscuits [10]. ...
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Low-GI biscuits are commonly produced using whole-grain flour, bran, or soluble dietary fibers, giving an undesirable texture. New low-GI biscuits containing dietary fibers and with improved palatability were formulated by substituting 60% of wheat flour (WF) with a native starch (ST) and 15% of WF with a resistant dextrin (RD), a source of dietary fibers. The botanical source of ST was common buckwheat (Fagopyrum esculentum Moench). Biscuits were also made with a single substitution by ST or by RD at the same level for comparison. The firmness of the biscuits was increased with the single substitution by RD due to its small average molecular size and high hygroscopicity, while it was decreased with the single substitution by ST. The double substitution by ST and RD not only produced the texture with the lowest firmness and brittleness, but also led to the lowest in vitro starch digestion rate and total starch digestibility. The human trial confirmed that the biscuits with the double substitution had a low GI of 47. The results indicated the additive or synergistic effects of ST and RD on the properties of the biscuits, demonstrating that low-GI biscuits can be produced with a substantial dietary fiber content without jeopardizing their palatability.
The most useful properties of food, i.e. the ones that are detected through look, touch and taste, are a manifestation of the food’s structure. Studies about how this structure develops or can be manipulated during food production and processing are a vital part of research in food science. This book provides the status of research on food structure and how it develops through the interplay between processing routes and formulation elements. It covers food structure development across a range of food settings and consider how this alters in order to design food with specific functionalities and performance. Food structure has to be considered across a range of length scales and the book includes a section focusing on analytical and theoretical approaches that can be taken to analyse/characterise food structure from the nano- to the macro-scale. The book concludes by outlining the main challenges arising within the field and the opportunities that these create in terms of establishing or growing future research activities. Edited and written by world class contributors, this book brings the literature up-to-date by detailing how the technology and applications have moved on over the past 10 years. It serves as a reference for researchers in food science and chemistry, food processing and food texture and structure.
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Research on the gut microbiome has gained high popularity and almost every disease has meanwhile been linked to alterations in microbiome composition. Typically assessed via stool samples, the microbiome displays a huge diversity with a multitude of environmental parameters already identified as contributing to its character. Despite impressive scientific progress, normal microbiome diversity remains largely unexplained and it is tempting to speculate some of the yet unexplained variance is hidden in normal gut physiology. Although a few genome/phenome-wide associations studies have recently highlighted physiological parameters such as stool frequency, known as contributing to microbiome diversity, there is a large knowledge base from decades of basic research on gut functions that can be explored for possible links to stool features and microbiome characteristics. And, when extrapolating findings from faecal samples to the biology in the intestinal lumen or the mucosal microenvironment, gut anatomy and physiology features need to be considered. Similarly, differences in anatomy and physiology between rodents and humans need attention when discussing findings in animals in relation to human physiology and nutrition.
To study the effects of cooking methods on the structure and digestion changes of starch encapsulated by cellular structure, intact potato parenchyma cells are successfully isolated and then subjected to different domestic cooking methods, including baking, frying, boiling, and autoclaving. The morphology, crystalline structure, thermal properties, and in vitro starch digestibility of cooked cell samples were investigated. Our results indicated that potato cell walls remained intact and performed as physical barriers preventing the diffusion/absorption of α-amylase to intracellular starch substrates after baking or frying treatment. However, boiling or autoclaving treatment destroyed cell wall structure, and the disrupted cellular structure reduced the digestion rate, likely by inhibiting diffusion of amylase through a weakened cell wall barrier, but could not lower the final digestion extent when compared to the pure starch. These findings suggested that potato products with lower glycemic index can be obtained by baking or frying treatment.
.Extruded food products are highly popular because of their convenience and low cost. A wide variety of food products like snacks, noodles, and pasta can be prepared using this technology. In extrusion, raw materials are passed through an extruder, where physical and chemical changes occur to form final products. Noodles and pasta are staple foods and are a type of extruded product usually made from cereal flour such as wheat flour. They have huge demand because of convenience but are high in carbohydrates and do not provide much health benefits for consumers. Due to high digestible starch, overconsumption can lead to overweight. Many studies have been conducted to develop enriched and fortified pasta and noodles with high nutritive value. This review focuses on noodles and pasta products developed using fish. Studies showed that functional pasta and noodles with high protein content can be made.
The high-amylose rice cultivar Dodamssal (DDS), a potentially nutritious functional food, contains resistant starch (RS). However, its RS content varies with the processing method used. In this study, heat treatment was used to produce rice powder with enhanced RS content. The rice powder quality was improved by steaming rough rice and brown rice for 30 min and roasting the brown rice at 240 °C for 10 min. Brown rice flour (BRF) made from steamed rough rice and roasted DDS (SRRD) had higher RS content (14%), ratio of fine particle sizes (0–20 μm), and gelatinization degree (GD), as well as lower mean particle size (51 μm) and in vitro glycemic index than did roasted DDS. Contrastingly, BRF prepared from steamed brown rice and roasted DDS with high GD had low RS content (12%) and high mean particle size (56 μm). Hence, SRRD-BRF improves powder quality and may be beneficial for nutritious functional food production.
Overnutrition or energy imbalance is a major problem in civilised communities. The energy potential of food depends not only on its energy content but also on its satiating capacity. In removing fibre from carbohydrate foods man creates foods which are artificially low in satiety. This has been demonstrated by compariso ns of equivalent meals of apple juice and whole apples and of white and wholemeal bread. Simply disruptit1g fibre by turning apples into a purée also reduces their satiety potential. Insulin is a hormone which favours the synthesis and deposition of fat. Fibre-depleted apple juice evokes a greater insulin response than whole apples, while purée has an intermediate effect. Refined carbohydrate probably causes hyperinsulinism by being readily and rapidly absorbed. This provides a further link between such foods and obesity, as well as a possible mechanism for the causation of diabetes and atherosclerosis.
The digestibility of starch in white wheat bread was studied. Raw wheat starch and raw wheat flour were used as reference materials. The extent of digestion and absorption in vivo was evaluated through balance experiments in rats given test diets with and without addition of the antibiotic, Nebacitin, to reduce the fermentation in the hind-gut. As judged from a high faecal recovery of dietary fibre constituents in rats fed a wheat flour diet with Nebacitin, this drug significantly reduced the microbial activity in the hind-gut. Only minute amounts of starch could be detected in faeces of rats whether Nebacitin was present or not, indicating that pure wheat starch as well as starch in wheat bread and raw wheat flour was almost completely digested and absorbed in the rat small intestine. However, during baking, a fraction of the starch (0·6%–0·9%, dry basis) was rendered resistant to enzyme digestion in vitro unless solubilised in KOH. This modified starch fraction also remained undigested in vivo, but was readily metabolised by the hind-gut microorganisms, thus having physiological properties similar to those of dietary fibre. It is therefore recommended that resistant starch formed during baking (i.e. that rendered resistant to enzymic digestion as measured in vitro) should be regarded as dietary fibre rather than as dietary starch.
Im Rahmen ernährungsphysiologischer Untersuchungen von Backwaren wurde bei gesunden Versuchspersonen der Verlauf der alimentären Hyperglykämie nach Verzehr von Weizenbrot, Roggenmischbrot (85/15) und Roggenvollkornbrot verfolgt. Diese Brotsorten — mit und ohne Belag verabreicht — zeigten gleiche Verläufe der alimentären Hyperglykämie. Roggenmischbrot (85/15) ergab bei 35 min Backzeit ein eindeutig geringeres Glucoseangebot im Blut gegenüber Backzeiten von 45, 55 und 65 min. Frisches, ofenwarmes Roggenmischbrot (85/15) führte zu einem sehr hohen Glucoseangebot mit zeitlicher Verzögerung des Maximums gegenüber 1–5 Tage gelagerten Roggenmischbroten.
The availability for digestion of starch in vitro after flaking, steam cooking and popping of whole grain wheat was studied and compared with that of raw and boiled wheat. Some physical and morphological characteristics were also investigated and correlated with starch availability for amylolysis. In an in vitro assay using hog pancreatic α-amylase after preincubation with pepsin, starch in flaked wheat was less available than that in boiled, popped and steam-cooked wheat. The starch in raw wheat was digested only slightly. When pepsin was omitted, the availability to α-amylase of starch in raw and boiled wheat decreased substantially, indicating that a large fraction of the starch was encapsulated in a protein matrix. The starch in flaked wheat elicited lower plasma glucose and plasma insulin levels in rats in vivo than that in boiled wheat after a gastric load. With raw wheat, the plasma glucose peak was much delayed and of lower magnitude compared with that with the heat-treated samples. In order to obtain good agreement with the in vivo results, a pepsin step had to be included in the in vitro assay using α-amylase. Differential scanning calorimetry measurements indicated that starch in flaked wheat was not gelatinised completely and this fact probably accounted for the lower availability in flaked wheat compared with boiled, popped or steam-cooked wheat.
Amylose from potatoes was complexed with lysolecithin and oleic acid. The degradation of complexed amylose by hog pancreatic α-amylase in-vitro was studied, as well as the in-vivo absorption in the rat. The presence of a bacterial thermostable α-amylase in the gelatinization step increased the result of a starch analysis using glucoamylase. Complexed amylose displayed a substantially reduced susceptibility to α-amylase in-vitro. However, when adding a large excess of enzyme, the complex was completely hydrolyzed after 3 h. Amylose-lysolecithin complex disappeared from the gastrointestinal tract within 120 min. The complexed amylose was hydrolyzed and adsorbed to the same extent as free amylose in-vivo but somewhat slower. Verdaulichkeit von Amylose-Lipid-Komplexen in vitro und in vivo. Kartoffelamylose wurde mit Lysolecithin und Ölsäure komplexiert. Der Abbau komplexierter Amylose durch Schweine-Pankreas-α-Amylase in vitro sowie die in vivo-Absorption in der Ratte wurden untersucht. Die Anwesenheit von thermostabiler Bakterien-α-Amylase während der Verkleisterungsstufe erhöhte das Ergebnis einer Stärkeanalyse bei Verwendung von Glucoamylase. Komplexierte Amylose zeigte eine wesentlich verringerte Angreifbarkeit durch α-Amylase in vitro. Wenn jedoch ein großer Überschuß an Enzym zugegeben wurde, war der Komplex innerhalb von 3 h vollständig hydrolysiert. Der Amylose-Lysolecithin-Komplex verschwand innerhalb von 120 min aus dem Magen-Darm-Trakt, woraus zu ersehen ist, daß die komplexierte Amylose hydrolysiert und in gleichem Ausmaß absorbiert wurde wie freie Amylose in vivo.