resistant starch
TRANSCRIPT
Resistant starch
Starch
Starch is widely distributed in various plant organs as a storage carbohydrate. As an
ingredient of many foods, it is also the most important carbohydrate source in human
nutrition(1). In plants, starch occurs as granules, storing the carbohydrates in an insoluble
and tightly packed manner. Chemically, starches are polysaccharides composed of alpha
glucopyranosyl units linked together with α
Starch is composed of amylos
residues linked with α-D-(1–
branched molecule with α-D-(1
polymerization of 100–10,000 DP, whereas, amylopectin has an average DP of 2 millions.
Amylopectin isthe major component of starch, whereas, amylose typically constitutes 15
30% of the starch. Pure waxy starches are almost 100% amylopectin and high amylose
varieties of maize and rice have 30
tarch in foods and its health benefits
Starch is widely distributed in various plant organs as a storage carbohydrate. As an
ingredient of many foods, it is also the most important carbohydrate source in human
. In plants, starch occurs as granules, storing the carbohydrates in an insoluble
and tightly packed manner. Chemically, starches are polysaccharides composed of alpha
anosyl units linked together with α-D-(1–4) or α D-(1–6) linkages.
Starch is composed of amylose, which is essentially a linear polymer with glucose
(1–4) linkages (Fig. 1), and amylopectin which is the larger
(1–4) and α-D-(1–6) linkages (Fig. 2). Amylose has a degree of
00 DP, whereas, amylopectin has an average DP of 2 millions.
Amylopectin isthe major component of starch, whereas, amylose typically constitutes 15
30% of the starch. Pure waxy starches are almost 100% amylopectin and high amylose
ce have 30–70% amylose.(18)
Fig. 1 Structure of amylose
Fig. 2 Structure of amylopectin
1
in foods and its health benefits
Starch is widely distributed in various plant organs as a storage carbohydrate. As an
ingredient of many foods, it is also the most important carbohydrate source in human
. In plants, starch occurs as granules, storing the carbohydrates in an insoluble
and tightly packed manner. Chemically, starches are polysaccharides composed of alpha-D-
6) linkages.(18)
e, which is essentially a linear polymer with glucose
, and amylopectin which is the larger
. Amylose has a degree of
00 DP, whereas, amylopectin has an average DP of 2 millions.
Amylopectin isthe major component of starch, whereas, amylose typically constitutes 15–
30% of the starch. Pure waxy starches are almost 100% amylopectin and high amylose
In the native form of starch, amylose and amylopectin molecules are organised in
granules as alternating semi-
semi-crystalline layer consists of of double helices formed by short amylopectin b
most of which are further ordered
lamellae. The amorphous regions of the semi
composed of amylose and non
Fig. 3 Structure of a starch granule, with alternating amorphous and semi
zones constituting the growth rings
Starch can be categorized in to 3 groups by
1) Type A has amylopectin chain lengths of 23 to 29 glucose units formed as a
double helix with amylose moieties packed inside, common in cereals.
2) Type B structure consists of amylopectin of chain lengths of 30 to 44 glucose
units with water interspersed and
3) Type C appears to be a mixture of both A and B forms as found in legumes
In the native form of starch, amylose and amylopectin molecules are organised in
-crystalline and amorphous layers that form growth rings.
crystalline layer consists of of double helices formed by short amylopectin b
most of which are further ordered into crystalline structures known as the crystalline
lamellae. The amorphous regions of the semi-crystalline layers and the amorphous layers are
composed of amylose and non-ordered amylopectin branches (Fig. 3). (11)
tructure of a starch granule, with alternating amorphous and semi
zones constituting the growth rings (11)
Starch can be categorized in to 3 groups by X-ray diffraction pattern (Fig. 4):
Type A has amylopectin chain lengths of 23 to 29 glucose units formed as a
double helix with amylose moieties packed inside, common in cereals.
Type B structure consists of amylopectin of chain lengths of 30 to 44 glucose
units with water interspersed and is usually found in raw potato and green banana starch.
Type C appears to be a mixture of both A and B forms as found in legumes
Fig. 4 X-ray diffraction
diagrams of A-
type starch (1)
2
In the native form of starch, amylose and amylopectin molecules are organised in
crystalline and amorphous layers that form growth rings. The
crystalline layer consists of of double helices formed by short amylopectin branches,
into crystalline structures known as the crystalline
crystalline layers and the amorphous layers are
(11)
tructure of a starch granule, with alternating amorphous and semi-crystalline
pattern (Fig. 4):
Type A has amylopectin chain lengths of 23 to 29 glucose units formed as a
Type B structure consists of amylopectin of chain lengths of 30 to 44 glucose
is usually found in raw potato and green banana starch.
Type C appears to be a mixture of both A and B forms as found in legumes.
ray diffraction
-type and B-
3
Starch digestion
The digestion of starch is mediated by salivary and pancreatic α- amylases that release
glucose, maltose, oligosaccharides, and higher dextrins into the lumen of small intestine.(18)
The remaining hydrolysis takes place by the action of enzymes located in the brush border of
the intestinal mucosa. Only monosaccharides can enter the mucosal cell. Glucoamylase
(maltase) hydrolyzes maltose and the straight chain oligosaccharides to glucose. Sucrose is
hydrolyzed by sucrase to fructose and glucose. Lactose is similarly hydrolyzed by lactase
(beta-galactosidase) to glucose and galactose. The limit dextrins are hydrolyzed to glucose by
alpha-(1,6)-glucosidase.(22)
Resistant starch
Before the early 1980s, starch was assumed to be fully digestible in human intestine.
In 1982, Englyst et al. first recognized the presence of starch fraction resistant to enzymic
hydrolysis during their research on measurement of nonstarch polysaccharides. The name
“Resistant starch” was defined as all starch and starch degradation products that resist small
intestinal digestion and enter large bowel in normal humans.(18)
Enzymatic resistance of starch may affect by several intrinsic or extrinsic factors.
Intrinsic factor included food particle size, amylose-lipid complex, enzyme inhibitors, starch
granule structure, amylose/amylopectin ratio. Extrinsic factor included different processing
treatments to foods.(18)
Depending on the various reasons for the enzyme resistance, the resistant starch can
be categorized into four groups:(18)
RS1 (physically inaccessible starch) represents the starch granules which enclosed in
the intact cell walls and inaccessible to the digestive enzymes. It is found in partly milled
grains and seeds. This type of starch is heat stable in normal cooking operations. But can be
totally digested if properly milled.
RS2 (resistant starch granule) is raw, ungelatinized native starch molecule in granular
form with B-type crystallinity.
RS3 (retrograded starch) is mainly the retrograded amylose formed during cooling of
gelatinized starch. It can only be dispersed with KOH or dimethyl sulfoxide. It can be found
in the heat-processed foods such as cooked and cooled potatoes and breads. Starch
digestability can by improved by reheating.
RS4 (chemically modified starch) has cross-bonding with chemical reagents such as
ether and ester. This type of starch cannot be broken down by digestive enzyme since the
structure of the starch molecule is modified.
Measurement of resistant starch
Many methods were developed for measurement of resistant starch including Englyst
et al. (1982), Berry (1986), Englyst et al. (1992), Champ (1992), Muir and O'Dea (1992),
Faisant et al. (1995), Goñi et al. (1996), Akerberg et al. (1998) and Champ et al. (1999).
4
McCleary and Monaghan (2002) developed a method for measurement of RS. Many
factors which affect RS result were studied included pepsin pretreatment, pH of incubation,
shaking or stirring, effect of maltose and inclusion of amyloglucosidase.
In the physiological digestive process, foods are subjected to protease (pepsin)
hydrolysis in stomach at about pH 2.0 before entering small intestine. The use of pepsin may
be need because in food high in protein such as beans, protein may partially encapsulate the
starch. However, the result (Table 1) demonstrated that protease pretreatment had no
insignificant effect on RS values. Because crude pancreatic α-amylase contains active
proteases (trypsin 50 mU/mg, chymotrypsin 325 mU/mg pancreatic α-amylase) which is
probably adequate for release starch from the protein matrix.
Table 1 Effect of pepsin pretreatment on determined RS content of sample
Sample type Pepsin pretreatment RS, % (w/w)
Batchelors kidney beans (canned, lyophilized) Yes 5.10 ± 0.1
No 5.00 ± 0.1
Rob Boy flageolet beans (canned, lyophilized) Yes 4.55 ± 0.05
No 4.40 ± 0.10
Native potato starch Yes 73.9 ± 0.06
No 75.6 ± 1.05
Green banana (lyophilized) Yes 50.8 ± 0.51
No 48.0 ± 0.20
Maltose occurred originally in foods or by activity of α-amylase can inhibit pancreatic
α-amylase by competitive inhibition, thus caused higher RS values (Table 2). After addition
of maltase, RS value were lower, indicated that pancreatic α-amylase was more active (Table
3).
Table 2 Effect of added maltose on determined RS values
Sample Added maltose, mg Determined RS, % (w/w)
Hi Maize 1043 0 45.4
50 51.2
CrystaLean 0 42.6
50 45.1
Potato amylose 0 41.2
50 43.6
Novelose 330 0 41.8
50 45.9
Potato starch 0 9.1
50 9.7
Regular maize starch 0 9.5
50 15.3
100 19.6
5
Table 3 Effect of added maltase enzyme on the determined level of RS for RMS and HAMS
Sample RS, % *w/w)
No maltase added With maltase
RMS 6.2 0.8
HAMS (60107) 46.3 38.0
Maltase added at a level of 500 units/test
However, addition of amyloglucosidase (AMG) in incubation mixture resulted in
lower amount of RS than that added with maltase, indicated that AMG can also remove
inhibitory effect of maltose. In many in vitro method AMG is added to ensure complete
hydrolysis of soluble starch fragments and maltosaccharides to glucose. Using either pure or
crude pancreatic α-amylase in the presence of AMG, similar RS values were obtained,
confirmed that purity of RS was not an issue (Table 4).
Table 4 Effect of amyloglucosidase (AMG) and maltase on the determined level of RS in
HAMS
Pancreatic α-amylase AMG or maltase RS, % (w/w)
Pure (Sigma Cat. No. A-2643) Neither 58.2/59.6
Maltase (500 U) 47.6/49.4
AMG (12 U) 39.0/41.1
Crude (pancreatin) AMG (12 U) 42.2/43.4
The method of McCleary and Monaghan (2002) was adopted by Association of
Official Analytical Chemists (AOAC) as a first action of official method for measurement of
resistant starch in starch and plant materials by enzymatic method (Method 2002.02). The
method consists of 2 main steps – hydrolysis of non-resistant starch and measurement of RS.
Brief steps of the method were shown as follows:
1) Hydrolysis of non-resistant starch
Sample grinding
↓
Pancreatic α-amylase + amyloglucosidase 16 h at 37°C
with shaking 200 stroke/min
↓
Enzyme termination by ethanol or industrial methylated spirit
↓
Centrifugation
↓
Decant supernatant
6
2) Measurement of RS
Starch pellet
↓
Dissolve in 2M KOH by stirring in ice-water bath
↓
Neutralize with acetate buffer
↓
Hydrolyzed to glucose with amyloglucosidase
↓
Measure glucose with glucose oxidase-
peroxidase reagent (GOPOD)
In addition, non-resistant starch (solubilized starch) can be measured by pooling
supernatant and measure glucose with GOPOD.
Results obtained by this method are in best agreement with currently available in vivo
data and other published in vitro data as shown in Table 5. Most methods used pancreatic α-
amylase with amyloglucosidase and a shaking-tube format.
Table 5 Comparison of RS values obtained using several in vitro analytical methods and in
vivo results
Source of starch
RS (in vitro method/results) RS
(in vivo
results) Englyst Faisant Champ McCleary Goni
Potato starch (native) 66.5 83.0 77.7 77.0 – 78.8
Amylomaize starch
(native)
71.4 72.2 52.8 51.7 – 50.3
Amylomaize starch
(retrograded)
30.5 36.4 29.6 42.0 37.8 30.1
Bean flakes 10.6 12.4 11.2 14.3 15.3 9-10.9
Corn flakes 3.9 4.9 4.3 4.0 4.7 3.1-5.0
Canned beans 17.1 – 17.1 16.5 – 16.5
ActiStar 63 – 57 58.0 57 59
Values are presented as a percentage of total starch content of sample.
From: McCleary and Monoghan (2002)
Resistant starch content in foods
Resistant starch content in foods varies by type and variety of raw materials, and
processing condition, as shown in Table 6. Raw bananas have high resistant starch, more than
50% by dry basis, and vary by varieties. Raw rice has RS range from 4 to 34. But RS in
cooked or processed rice were less than 10%. Studies of RS in legumes are quite extensive.
Most raw legumes have RS more than 10%, except chickpea and lentil. Soaking, cooking and
sprouting cause lower RS content. Among tubers, taro has high RS about 43%, sorghum has
RS about 5-6%. Bakery products have very low RS.
7
Table 6 Resistant starch content in various foods
Food Starch content (% DB)
Method Ref. Total Resistant
Rice and rice products
Saohai cultivar (hard rice), raw 52.0 34.8 Goni (1996) (21)
Dookmali cultivar (soft rice), raw 67.5 11.6
Brown rice, raw 66.6 4.2
White rice, cooked 64.7 7.1
Khanomjean, cooked 41.9 8.5
Kaotung, fried 75.9 2.6
Kaokreupvor, roasted 54.6 2.9
Kaokreup, fried 44.9 2.0
Extruded rice snack 4.2 0.4
Noodle type products, uncooked
Glass noodles 59.0 11.3 Goni (1996) (21)
Instant glass noodles 60.7 9.1
White rice noodles 67.0 3.0
Brown rice noodles 73.7 2.2
Instant rice noodles 57.1 2.4
Vermicelli 58.5 4.4
Rice sheet 41.3 2.4
Spaghetti <1 (6)
Legumes
Mungbeans, raw 44.3 22.9 Goni (1996) (21)
Red kidney bean, raw 41.6 35.0 Englyst (1992) (5)
Red kidney bean, soaked and boiled 46.0 2.5
Black bean, raw 39.8 18.3 Goni (1996) (21)
Black bean, steam heated 38.7 6.0 Tovar (1990) (20)
Mothbean, raw 39.54 12.20 Goni (1996) (2)
Mothbean, cooked 46.24 3.90
Mothbean, water soaked and cooked 47.88 3.72
Mothbean, sprouted and cooked 44.75 2.67
Horse gram, raw 36.03 26.42
Horse gram, cooked 47.32 5.21
Horse gram, water soaked and cooked 46.29 5.69
Horse gram, sprouted and cooked 44.66 4.44
Black gram, raw 37.87 19.66
Black gram, cooked 40.73 3.40
Black gram, water soaked and cooked 41.02 3.68
Black gram, sprouted and cooked 38.99 3.03
Green pea, raw 53.4 32.1 Englyst (1992) (5)
Green pea, soaked and boiled 53.1 5.8
Yellow pea, raw 57.1 36.2
Yellow pea, soaked and boiled 63.9 10.3
Chickpea, raw 3.39 Faisant et al. (4)
Lentil, raw 3.25
Tubers
Taro 43.2 AACC (1995) (17)
Sweet potato 9.05
Cassava chip 52.4 Englyst (1992) (15)
Cassava pellet 40.9
Tapioca pearls (sago) 44.7 4.5 Goni (1996) (21)
8
Food Starch content (% DB)
Method Ref.
Total Resistant
Banana
Namwa 53.0 AACC (1995) (17)
Hom Thong 47.2
Banana flour (green 90-120 days) Goni (1996) (21)
Namwa 79.7 56.6
Hom 91.0 57.7
Kai 80.5 52.2
Lepmurnang 72.1 57.0
Hugmuk 72.3 61.4
Hin 72.7 68.1
Ngachaeng 75.5 64.6
Lepchaengkut 88.7 50.7
Nangphaya 91.0 66.8
Phamahagkuk 91.4 60.1
Thepparod 82.4 58.5
Seeds and grains
Sorghum 6.46 McCleary(2002) (10)
Sorghum (autoclaved 130°C) 5.24
Job’s tears 66.5 6.4 Goni (1996) (21)
Bakery products
Biscuit 1.8 Goni (1996) (6)
White bread (crumb) 2.3
Crispbread <1
Effects of processing on resistant starch content in foodstuffs
1. Heating
Cooking of presoaked legumes decrease RS level in pea (Pisum sativum L. cv.
Maria), common bean (Phaseolus vulgaris L. cv. IAC carioca Eté), chickpea (Cicer
arietinum L.) and lentil (Lens culinaris Med. cv. Silvina). The grains of the legumes were
chosen to eliminate external material, immature seeds and damaged grains. Part of the grains
of each legume was ground raw into flour. The rest were washed in running water, soaked for
a period of 16 h (1:2w/v) and then cooked with the addition of one volume of water.
Common bean and chickpea grains were cooked in a pressure cooker (14.7 psi) for 20 and 40
min, respectively. Pea and lentil legumes were cooked from 20 min at atmospheric pressure.
The cooked material was frozen, freeze-dried and ground into flour (60 mesh). Resistant
starch values (Table 7) show that legumes presented lower RS values after thermal treatment
(4).
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Table 7 Resistant starch (RS) values of raw and freeze-dried cooked legumes (g/100g)
Legume RS (g/100 g)
Raw Cooked
Pea 2.45±0.30b 1.89±0.71
a
Common bean 3.72±0.79a 2.33±1.23
a
Chickpea 3.39±0.96ab
2.23±1.15a
Lentil 3.25±0.42ab
2.46±0.16a
Different letters in the same column indicate a statistical difference (p<0.05).
Data represent means and standard deviation (n=6).
2. Cooling
Cooling rate has an effect on resistant starch content in waxy maize starch. Waxy
maize starch dispersion were gelatinized and debranched by pullulanase (20 U/g) for 6 h.
After enzyme inactivation by heating, debranched starch was stored for 2 days at 4 or 20°C.
Debranched starch stored at 20°C had 50.1% RS, higher than that of starch stored at 4°C
which had 24.4% RS (9).
3. Heating-cooling cycle
Amylomaize VII starch dispersion (starch:water = 1:3.5) was autoclaved at 134°C for
1h, then cool and store at 4°C overnight. The autoclaving-cooling cycle was done for 0 to 4
cycles. Treated sample was then freeze-dried. Resistant starch content and thermal
characteristics of amylomaize VII were shown in Table 8. Increasing of autoclaving-cooling
cycle increased RS and transition enthalpy of the starch (19).
Table 8 Effects of autoclaving-cooling cycles on resistant starch yield and thermal
characteristics of amylomaize VII starch.
Number of
autoclaving-cooling
cycles
Resistant starch
yields (%)
Transition
temperature (Tp, °C)
Transition enthalpy
(∆H, J/g)
0 15.8 nd nd
1 21.3 149.3 2.7
2 25.2 149.6 4.5
3 29.9 148.1 7.0
4 31.8 152.9 8.8
10
(A)
(B) (C)
(D) (E)
Fig. 5 Scanning electron micrographs of raw amylomaize VII starch (A), freeze-dried
amylomaize VII starch after one (B) and four autoclaving-cooling cycles (C),
oven- (D) and vacuum-dried resistant starch isolated from amylomaize starch after four
autoclaving-cooling cycles (E).
Scanning electron micrographs of raw, autoclaved-cooled starch and isolated RS were
shown Fig. 5. Raw amylomaize VII starch had a 5 µm starch granule. After autoclaving and
cooling, starch granule disappeared. Starch treated with 1 autoclaving-cooling cycle had a
irregular shaped particles with spongy-like porous network. A 4-cycle treated starch shown
more compact structure which related to higher melting enthalpy and its stabilization. For
isolated RS, porous structure was no longer visible. Oven-dried RS shown very compact and
dense particle. While vacuum dried RS formed an open, fluffy structure. Melting enthalpy of
vacuum-dried RS (28.7 J/g) was higher than oven-dried RS (19.7 J/g) because better
hydration capacity vacuum-drying (19).
11
4. Debranching by pullulanase
Pullulanase or pullulan 6-glucanohydrolase (EC 3.2.1.41) is a debranching enzyme in
starch processing. It cleaves α-1, 6 linkages in pullulan, amylopectin and other related
polysaccharides, results in linear starch chains. Thus, provide an increased opportunity for
molecule alignment or aggregation to form crystalline structures, and hence, RS formation
(23).
Pongjanta et al. (2009) tested the effects of pullulanase concentration on RS content in
high amylose rice starch. High amylose rice starch dispersion (15% w/w) were annealed at
30°C for 1 h with vigorously shaking, then autoclaved at 121°C for 30 min and cooled to
55°C. The cooked starch samples were debranched using pullulanase enzymeat 0, 8, 10, 12,
14 and 16 U/g starch at 55°C for 16 h in a shaker water bath. The debranched samples are
then heated at 100°C for 15 min and stored at 4°C for 16 h. Afterward, a one cycle of
freezing (-10°C) and thawing (30°C) process of the samples was applied to promote syneresis
of the retrograded starches. The retrograded starch was dried at 45°C to approximately 13%
moisture content and grounded through 100-mesh sieve.
The retrogradation from the 8 to 12 U/g starch hydrolysis of the high amylose rice
starch was dramatically lost expressible water and remained relatively constant thereafter
with 12–16 U/g starch (Fig. 6A). Resistant starch content increased sharply as the amount of
the enzyme increased from 0 to 12 U/g starch because debranching increase opportunity for
crystallization of amylose molecules. However, increasing enzyme concentration from 12 to
16 U/g starch decreased RS content (Fig. 6B). Too long debranching process cause release of
small amylose molecules. Short amylose chains with DP 6–9 glucose units inhibit
retrogradation. While a chain length of at least 10 glucose units is required for crystallization
and formation of double helices, DP 20–30 is suitable to form RSIII. The results were in
accordance with hydrolysis rate of starches (Fig. 7). Among debranched starches produced in
this experiment, starch debranched by 12 U/g starch had the lowest hydrolysis rate, while that
of control was the highest. These results indicate that the incompletely-debranched RSIII
sample was resistant to α-amylase digestion (14).
Fig. 6 Effect of pullulanase enzyme concentration on degree of syneresis (A)
and resistant starch content (B) in RS III samples.
12
Fig. 7 Effect of pullulanase enzyme concentration on α-amylase hydrolysis rate of
resistant starch type III samples, native high amylose rice starch (HARS),
commercial resistant starch (CRS; Hi-maize) and white bread (WB).
Resistant starch content was also affected by debranching time. In the study of Zhao
and Lin (2009) , 20% (w/v) maize starch dispersion was autoclaved at 121°C for 20 min and
cooled to 60°C. Then 1 ml of pullulanase solution (enzyme activity 30 PUN/ml) was added
and maize starch was kept at 60ºC in a water bath for 2 to 12 h with continuous agitation. The
starch paste was heated to 100ºC to inactivate the enzyme, then cooled to room temperature,
stored at 4ºC for 24h, before retreated with two autoclaving–cooling cycles. RS formation
was improved significantly as debranching time increased. The highest RS yield was
obtained with hydrolysis time of 12 h (Fig. 8a).
Fig. 8 Effects of pullulanase hydrolysis of gelatinized maize starch on RS formation.
a b
13
However, when maize starch was treated with one autoclaving–cooling cycle, then
hydrolyzed by pullulanase at 60°C for different time durations, and followed by two
autoclaving–cooling cycles, the highest RS yield was obtained when retrograded maize starch
was hydrolyzed by pullulanase for 10 h. Prolonging hydrolysis of pullulanase could lead to
the decrease in RS yield as shown in Fig. 8b (23).
Similar results were also found in high amylose corn starch – Hylon V (about 55%
amylose) and Hylon VII (about 70% amylose). Amount of RS3 increased with debranching
time (Table 9). Hylon VII, which had higher amount of amylose, had higher amount of RS3
than that of Hylon V. However, peak transition temperature (Tp) and transition enthalpy (∆H)
of debranched starch were lower than that of native starch. Among debranched starch, peak
temperature was not different, but transition enthalpy increased with increasing debranching
time (12).
Table 9 Resistant starch (RS) contents and thermal properties of native and debranched
starch samples
14
Health benefits of resistant starch
1. Resistant starch as a component of dietary fiber
By a definition of The American Association of Cereal Chemists (AACC), dietary
fiber is the edible parts of plants or analogous carbohydrates that are resistant to digestion and
absorption in human small intestine with complete or partial fermentation in large intestine.
When measure total dietary fiber by AOAC method, resistant starch is included in the result.
RS assays as an insoluble fiber but has the physiological benefits of soluble fiber. Like
soluble fiber, it has a positive impact on colonic health by increasing crypt cell production
rate or decreasing the colonic epithelial atrophy. It can also be used as vehicle for slow
release of glucose and reduction of serum cholesterol. Overall, it behaves physiologically as a
fiber (18).
2. Colonic production of short chain fatty acid (SCFA)
Resistant starch is the fraction of starch not hydrolyzed to D-glucose in the small
intestine within 2 hours, but is fermented in colon. RS is digested by bacterial amylases (i.e.
α-amylases, glucoamylase, isomaltase) and then glucose is metabolized into short chain fatty
acids (SCFA) such as acetate, butyrate, propionate and gases like CO2, H2, and CH4 etc. via
formation of pyruvate. 30 to 70% of RS is degraded to SCFA in the colon by bacterial
amylases.
SCFA produces an acidic environment which promotes the healthy bacterial
proliferation and inhibit pathogenic bacteria. It is a fuel for colonocytes (cells lining the
colon). It can increase colonic blood flow and electrolyte uptake, prevent development of
abnormal colonic cells. Among SCFA, butyrate appears to be the preferred substrate for
colonocytes and RS contributes high level of butyrate as shown in Table 10.
Table 10 Pattern of short chain fatty acids (SCFA) production from various substrates
Substrates Percentage of SCFA
Acetate Propionate Butyrate
Resistant starch 41 21 38
Starch 50 22 29
Oat bran 57 21 23
Wheat bran 57 15 19
Cellulose 61 20 19
Guar gum 59 26 11
Ispaghula 56 26 10
Pectin 75 14 9
From: Sharma et al. (2008)
3. Resistant starch and colorectal cancer risk
Cassidy et al. (1994) conducted a nutritional epidemiology ecological study which
gathered information on starch, NSP, fat and protein intake and mean national cancer
incidence rate in 12 countries (Table 11). Strong inverse associations between starch
15
consumption and colon cancer (r = -0.76) and large bowel cancer (r = -0.70) incidence were
found (Fig. 9 and Table 11). While non-starch polysaccharide (NSP) also had inverse relation
but not significant. Fat and protein consumption increases risk of colorectal cancer. After
adjusting the effects of fat and protein intake, relationship still significant for RS and cancer
incidence (Table 12). The result suggested a potential protection role of resistant starch
against colorectal cancer and correspond with the hypothesis that fermentation in the colon is
the mechanism for prevention of colorectal cancer.(3)
Table 11 Dietary intake (g day-1) and cancer incidence (cases per 100,000 year-1
; age
standardized, world) in various populations
Fig. 9 The association between starch intake (g day-1) and colon cancer incidence (males and
females combined, n = 22) (cases per 100,000 age-standardised world population year-1).
16
Table 12 Pearson correlation coefficients between dietary intake of starch, NSPs, protein and
fat and incidence of colorectal cancer .
Table 12 t-values of multiple regression analysis after adjusting for fat and protein intakes
and after interaction term analysis.
Leu et al. (2005) studied the synbiotic effect of RS and probiotics on colorectal cancer
risk. The 96 Male Sprague-Dawley rats with carcinogen-damaged cells in the colon were fed
with low or moderate RS diet (Table 13) and with or without Lactobacillus acidophilus or
Bifidobacterium lactis for 4 weeks.
17
Table 13 Composition of experimental diet
The rats consuming the moderate-RS diet had higher (P< 0.001) total SCFA, acetate,
propionate, and butyrate concentrations in the feces compared with those fed the low-RS diet.
Probiotic bacteria supplementation did not affect fecal SCFA concentrations in rats fed either
the low or moderate-RS diets (Table 14).
Table 14 Effect of low- and moderate-RS diets supplemented with L. acidophilus (LA), B.
lactis (BL), or both (LA+BL) on fecal pH and fecal SCFA concentrations in rats.
Cecal pH was lower in rats fed the moderate-RS diets (P<0.001) compared with rats
fed the low-RS diets. Supplementation of probiotics to the RS diet did not affect pH. SCFA
concentrations in the cecum were greater in those fed moderate-RS diets (P<0.001). Probiotic
supplementation did not affect cecal SCFA concentrations (Table 15).
18
Table 15 Effect of low- and moderate-RS diets supplemented with L. acidophilus (LA), B.
lactis (BL), or both (LA+BL) on cecal pH and cecal SCFA concentrations in rats.
The level of dietary RS affected total anaerobes (P=0.021), total aerobes (P<0.001),
lactobacilli (P<0.001), bifidobacteria (P<0.001), and total coliforms (P<0.001) in the cecal
digesta. Furthermore, the type of bacteria supplemented to the diet had a significant effect on
lactobacillus species numbers (P=0.004). B.lactis supplementation increased Lactobacilli
numbers (Table 16).
Table 16 Effect of low- and moderate-RS diets supplemented with L. acidophilus (LA), B.
lactis (BL), or both (LA+BL) on cecal microbial populations.
There was a significant interaction between the level of dietary RS and bacteria on the
acute apoptotic response to genotoxic carcinogen (AARGC) (P=0.002). The AARGC was
significantly elevated in the distal colon by B.lactis in rats fed RS, with or without L.
acidophilus (Fig. 10). L. acidophilus did not affect the AARGC nor did B. lactis in rats fed
low-RS. The level of dietary RS did not affect the AARGC (8).
19
Fig. 10 Apoptotic index in the distal colon of rats fed a low-RS or moderate-RS diet
supplemented with L.acidophilus, B.lactis, or both.
4. Resistant starch and postprandial glycemia and hormonal response.
A study using 10 healthy normal weight males fed with test meals containing either
50g starch free of RS (0%RS), or 50g starch containing a high level of RS (54% RS) proved
the ability of high RS meals to significantly lower the postprandial concentration of blood
glucose and insulin (Fig. 11) (16).
Fig. 11 Change in plasma concentrations of glucose and insulin after a raw potato starch meal
(54% RS) (R) and a pre-gelatinized potato starch meal (0% RS) (S).
20
5. Fecal bulking
A study on 11 healthy human consumed low- and high-RS diet (5 and 39 g RS/d,
respectively) found that high-RS diet caused a significant increase in fecal wet and dry
weight, and lowered fecal pH (Table 17). A significant correlation between RS consumed and
total output of feces (Fig. 12). For every 1 g RS consumed, fecal weight increase about 1.8 g
(13).
Table 17 Effect of a diet high in resistant starch (RS) on fecal output, pH, and starch and
nonstarch polysaccharide (NSP) concentrations1
Fecal variable Low-RS diet High-RS diet
Fecal output
(g wet wt/d) 138 ± 22 197 ± 372
(g dry wt/d) 38 ± 2 54 ± 72
Fecal pH 6.9 ± 0.1 6.3 ± 0.12
Fecal starch
(mg/g feces, wet) 10.0 ± 2.0 37.0 ± 7.02
(g/d) 1.7 ± 0.7 8.5 ± 2.02
Fecal NSP
(mg/g feces, wet) 65.5 ± 29.0 68.0 ± 27.0
(g/d) 7.6 ± 0.5 11.4 ± 0.12
1Mean ± SEM, n=11
2Significantly different from the low-RS dietary period, P < 0.01 (paired-difference t test)
Fig. 12 During the high-resistant starch (RS) dietary period there was a significant correlation
between dietary RS intake and fecal output (r = 0.70, P < 0.05).
21
6. Resistant starch and lipid metabolism
Resistant starch has been found to affect the metabolism of low-density lipoproteins
(LDL), cholesterol, triglycerides, triglyceride-rich lipoproteins and total lipids. Soluble fibers
may bind bile acids or cholesterol in the intestine, preventing their reabsorption in the body.
The liver responds by taking up more LDL cholesterol from the blood stream thereby
lowering the concentration of LDL cholesterol in blood (18). A study in male rat fed with
cholesterol-free diet containing 50 g cellulose power (CP) or RS fraction from adzuki (AS) or
tebou (TS) starch found that RS diet caused lower in serum total cholesterol, HDL, IDL, LDL
and VLDL cholesterol (Fig. 13). Fecal total bile acid concentration in the AS and TS groups
were higher than the CP group (Table 18). The result suggested that serum cholesterol-
lowering effect of RS is due to the enhanced levels of hepatic SR-B1 and cholesterol 7α-
hydroxylase mRNA (7).
Fig. 13 Serum total cholesterol, VLDL + intermediate density lipoprotein (IDL) + LDL
cholesterol, and HDL cholesterol concentrations in rats fed with cellulose powder (�),
enzyme-resistant fraction of adzuki starch (�) or of tebou starch (◆) for 4 weeks.
Table 18 Fecal steroid concentrations in rats fed with CP, AS, or TS for 4 weeks.
CP, cellulose powder; AS, enzyme-resistant fraction of adzuki starch; TS, enzyme-resistant fraction of
tebou starch
Means within the same rows bearing different superscript roman letters are significantly different (P <
0.05)
22
In conclusion, RS content in food varies by type and variety of raw food, and
processing conditions such as heating, cooling and debranching. RS has many health benefits
included reduction in risk of colon cancer, fecal bulking, modulation of glucose and lipid
metabolism and acting as a prebiotic.
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