Journal of Scientific Innovations for Development Volume 1(1), p.12-21
www.novelpublications.com
ISSN: 2026-6553
PROXIMATE, MINERAL AND ANTI-NUTRIENT COMPOSITION OF
PHASEOLUS VULGARIS LEAF
Emmanuel O. Oyelude*, Nicholas P. Gli and Jeremiah Amafo
Department of Applied Chemistry and Biochemistry, Faculty of Applied Sciences,
University for Development Studies, Navrongo Campus,
P.O. Box 24, Navrongo, Ghana.
Abstract
The leaf of Phaseolus vulgaris was analysed to determine its proximate, mineral and anti-nutrient
composition. The fresh edible leaf was rich in moisture (78.25 g/100 g), protein (7.96 g/100 g), crude
fibre (1.43 g/100 g), potassium (717.84 mg/100 g), sodium (224.62 mg/100 g) and iron (4.59 mg/100g).
The leafy vegetable could be a good source of protein and crude fibre. It has low calorific value (78.12
kcal/100 g) and may be suitable for those who are watching their weight. The levels of anti-nutritional
components in the vegetable are low and will not impact negatively on the bioavailability of calcium, zinc
and iron in the body. The consumption of the vegetable could help to reduce the prevalence of protein
energy malnutrition and anaemia in sub-Saharan Africa countries where it is available.
Key words: Leafy vegetable, Sub-Saharan Africa, Bioavailability, RDA, Anaemia
1.0
INTRODUCTION
Leafy vegetables are leaves of plants often cooked and consumed with dish made from
tubers, cereals or plantain. The nutritional content of vegetables varies considerably,
though generally they contain little protein or fat and varying proportions of vitamins,
dietary minerals, fibre and carbohydrate (Gruda, 2006). Many households in subSaharan Africa are poor and rely heavily on vegetables to meet a good portion of their
daily meals. However, the frequency of consumption of leafy vegetables has decreased
probably because they are often considered to be inferior in their taste and nutritional
value compared to exotic vegetables (Weinberger and Msuya, 2004).
Sub-Saharan Africa has the highest prevalence of malnutrition in the world, with one in
three people chronically hungry (Food and Agriculture Organisation, 2008). Although
green leafy vegetables are not good sources of protein, they can contribute to meet part
of the daily requirements of our body. The nutrition quality of a number of African
leafy vegetable is still unknown making it impossible for people to know their
importance and how to make the best use of them. Phaseolus vulgaris isaherbaceous
plant grown for its edible bean and leaf. Many well known varieties belonging to this
species include: black beans, pinto beans, pink beans, red or kidney beans, white beans
and yellow beans. In northern Ghana, leaves of Phaseolus vulgaris are often combined
with groundnut paste or okroto make palatable soup and served with staples such as
“tuo-zafi”, “fufu” and gari. This paper examines the nutritional and anti–nutritional
composition of the leaf ofPhaseolus vulgaris grown in the northern part of Ghana.
Corresponding Author: Emmanuel O. Oyelude E-mail:[email protected]
Emmanuel O. Oyelude, (2012). Proximate, mineral and anti-nutrient composition of phaseolus
vulgaris leaf
2.0
MATERIALS AND METHODS
2.1
Collection and Preparation of Samples
Fresh samples of Phaseolus vulgaris vegetables were harvested from five randomly
selected farms in Navrongo and Tono, both located in the Kassena-Nankana East
District, Upper East Region, Ghana. This was done to even out the effects of different
environment and soil types on nutrition (Asibey-Berko&Tayie, 1999). The plant was
authenticated at the Department of Applied Biology, University for Development
Studies, Navrongo, Ghana. The samples were carefully and thoroughly rinsed under
running tap, and later rinsed with distilled water and blotted dry. Healthy leaves were
plucked from plant stalk and dried to a constant weight at 70 °C in an air oven. The
dried samples were pooled, ground into fine powder with pestle and mortar, sieved and
kept in air-tight glass bottles. This sample was used for proximate, mineral and antinutritional composition of the vegetable.
2.2
Experimental Method
Proximate composition analysis of the samples was carried out according to the
methods recommended by the Association of Official Analytical Chemists (1999). All
determinations were carried out at least thrice. Moisture content was determined by
drying 5 g fresh leaves to a constant weight at 105 °C in an air oven. The level of total
nitrogen in the vegetable was determined by micro Kjeldahl method. The value obtained
for total nitrogen was multiplied by the conversion factor of 6.25 to calculate the level
of crude protein (Pearson, 1976). Crude lipid was determined by extracting 5 g sample
with petroleum ether for 6 h using a Soxhlet apparatus (Akwaowo, Ndon, &Etuk, 2000).
Crude fibre was determined using 5 g of the dried defatted sample according to the
method of Abara, Obochi, Malu, & Obi-Abang (2009). The level of ash in the vegetable
was determined by incinerating 5 g sample in a muffle furnace at 550 °C for 5 h
(Abaraet al., 2009). Carbohydrate content was calculated by subtracting the sum of
moisture, crude protein, crude lipid, crude fibre and ash from 100. The calorific value
(kCal/100 g) of the vegetable was estimated by multiplying the levels of crude protein,
crude fat and carbohydrate by a factor of 4, 9 and 4, respectively. These three values
were added together as recommended by Grubben (1978).
Microwave-assisted digestion of sample was accomplished in the presence of
concentrated HNO3 and 30 % H2O2. Iron, manganese, zinc, copper, lead, mercury,
calcium and magnesium were determined using atomic absorption spectrophotometer
(Varian AA 240 FS) and sodium and potassium were determined using Jenway PFP7
flame photometer (Abaraet al., 2009). Phosphorus was determined colometrically using
the molybdovanadate method (AOAC, 1999).
Total oxalates were determined by slight modification of the procedure of Day &
Underwood (1986). 150 mL of 7.5 M H2SO4 was added to 2 g of powdered sample
contained in 250 mL Erlenmeyer flask. The flask was shaken on a mechanical shaker at
100 rpm for 4 h. The mixture was then filtered using Whatman No. 1 filter paper and 25
mL of the filtrate was titrated against 0.1 M KMnO4 solution till a faint pink colour
which persisted for 30 s was observed.The level of alkaloids was determined as
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Emmanuel O. Oyelude, (2012). Proximate, mineral and anti-nutrient composition of phaseolus
vulgaris leaf
described by Harborne(1973) andEdeogaet al.(2005).The concentration of flavonoids
was determined by the method of Bohm&Kocipai (1994).
The content of tannins in the sample was determined by the method of van Buren &
Robinson, (1969) and reported byObadoni&Ochuko, (2002).Crude saponins were
determined by the method credited to Harborne (1973) and described by
Obadoni&Ochuko (2002).The content of phytates was determined by the procedure of
Reddy and Love (1999) as described by Umaru, Adamu, Dahiru&Nadro (2007).The
level of hydrocyanic acid (HCN) in the vegetable sample was determined by the method
of Joslyn (1970) and described by Abaraet al. (2009). The concentration of phenols in
the sample was determined using the method earlier described by Edeoga, Okwu,
&Mbaebie(2005).
2.3
Statistical Analysis
The mean and standard deviation of the data were calculated.
3.0
RESULTS AND DISCUSSION
3.1
Proximate Composition
The proximate composition together with the calorific value of Phaseolus vulgaris leaf
is presented in Table 1. The average moisture content of 78.25 g/100 g falls within the
range of 72-94 mg/100g reported for selected African leafy vegetables by Uusiku,
Oelofse, Duodu, Bester & Faber (2010). This implies that the vegetable cannot be kept
for long at room temperature. The result shows that Phaseolus vulgaris leaf is rich in
protein. The average crude protein content of 7.96 mg/100 g was higher than the range
of 1-7 g/100 g reported for African leafy vegetables by Uusikuet al. (2010). According
to Oniang’o, Mutuku, &Malaba, (2003), many households in sub-Sahara Africa are
poor and depend on diet composed primarily of staple foods prepared from cereals,
tubers and plantain. The diet is generally of poor protein content. The crude protein
content of Phaseolus vulgaris leaf was much higher than the values reported by AsibeyBerko&Tayie (1999) for Corchorustridens (2.7 g/100 g), Amaranthusincurvatus (2.1
g/100 g). Therefore, consumption of Phaseolus vulgaris may help to reduce protein
energy malnutrition in sub-Sahara Africa (Uusikuet al. (2010).
Carbohydrate is an important part of a balanced diet. It is required to produce energy
needed for the smooth functioning of the body. The average carbohydrate content of
Phaseolus vulgaris leaf (10.58 g/100 g) was within the range of between 1 and 16 g/100
g reported for selected African leafy vegetables (Uusikuet al., 2010). This value was
approximately equal to 10.56 g/100 g reported for Boerhaviadiffusa leaf (Ujowundu,
Igwe, Enemor, Nwaogu, &Okafor, 2008).The average crude fat content of Phaseolus
vulgarisleaf was 0.44 g/100 g. This makes the vegetable a poor source of fat and may be
recommended for persons suffering from overweight. However, the value was within
the range of 0.1-5.0 g/100 g reported for a number of African leafy vegetables (Uusikuet
al., 2010).
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Emmanuel O. Oyelude, (2012). Proximate, mineral and anti-nutrient composition of phaseolus
vulgaris leaf
Emebu&Anyika (2011) stated a number of benefits of fibre in diet. These include:
adding bulk to food, preventing absorption of excess starchy food and cholesterol,
keeping blood sugar levels under control and cleansing of digestive tract by removing
potential carcinogens from the body. The average crude fibre content of
Phaseolusvulgaris was 1.43 g/100 g. This is comparable to the level of fibre found in
selected African leafy vegetables ranging from 1-8 g/100 g (Uusikuet al., 2010).
However, it was much lower than the value of about 4 g/100 g reported for
Vignaunguiculata (Kruger, Sayed, Langenhoven& Holing, 1998).
Table 1.Average composition of fresh edible Phaseolus vulgaris leaf.
Parameter
Moisture
Crude protein
Crude fat
Crude fibre
Ash
Carbohydrate
Composition (g/100 g)
78.25 ± 0.56
7.96 ± 0.11 (36.60 ± 0.42)
0.44 ± 0.08 (2.02 ± 0.07)
1.43 ± 0.14 (6.57 ± 0.23)
1.34 ± 0.11 (6.16 ± 0.21)
10.58 ± 0.22 (48.65 ± 0.56)
Calorific value (kCal/100 g)
78.12 (359.18)
Note:Values are expressed as mean ± SD for three determinations; concentration on dry weight basis in
brackets.
The average level of ash in the vegetable was 1.34 g/100 g. This value is approximately
the same as 1.33 g/100 g reported forBrassica oleracea (Emebu&Anyika, 2011) but
slightly lower than 1.4 g/100 g and 1.5 g/100 g reported for Amaranthusincurvatus and
Corchorustridens, respectively (Asibey-Berko and Tayie, 1999). The low value of ash
is an indication that the mineral content of Phaseolus vulgaris leaf is small
(Emebu&Anyika, 2011) and the vegetable has high nutrient quality (Ukam, 2008). The
calculated calorific value of Phaseolus vulgaris leaf (78.12 kcal/100 g) was comparable
to the range of 23-91 kcal/100 g reported for selected African leafy vegetables
(Uusikuet al., 2010).
3.2
Mineral Composition
The mineral composition of Phaseolus vulgaris leaf is presented in Table 2. The
vegetable possessed low levels of minerals except potassium, sodium and iron.
Potassium (717.84 mg/100 g) was the most abundant mineral in the vegetable followed
by sodium (224.62 mg/100 g). The levels of potassium and sodium in Phaseolus
vulgaris were much higher than those reported for almost all other African leafy
vegetables including: Brassica oleraceae (Emebu and Anyika, 2011),
Boerhaviadiffusaand
Commelinanudiflora
(Ujowunduet
al.,
2008),
and
Amaranthushybridus (Akubugwo, Obasi, Chinyere, &Ugbogu, 2007a). The World
Health Organisation (1973) recommended that adults should take on daily basis 500 mg
sodium and 2000 mg potassium. This implies that consumption of Phaseolus vulgaris
leaf could assist to meet the daily requirements for both potassium and sodium. Sodium
assists to regulate body fluid and to maintain electric potential in the body tissue, while
potassium is important in the regulation of heart beat, neurotransmission and water
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Emmanuel O. Oyelude, (2012). Proximate, mineral and anti-nutrient composition of phaseolus
vulgaris leaf
balance of the body (Alinnor&Oze, 2011). Lower level of sodium to potassium in the
body is recommended to lower blood pressure. Therefore, food with Na/K value lesser
than one is considered to be good for consumption. The calculated value of Na/K for
Phaseolus vulgaris leaf is 0.31 implying that the vegetable has the potential of lowering
blood pressure and therefore good for consumption.
Phaseolus vulgaris leaf is poor in calcium (3.80 mg/100 g), phosphorus (0.11 mg/100 g)
and magnesium (0.04 mg/100 g). These values are negligible compared to the
Recommended Dietary Allowance (RDA) for calcium, phosphorus and magnesium of
800, 800 and 350 mg/100 g, respectively for adults. The levels of calcium, phosphorus
and magnesium in Phaseolus vulgaris were much lower than those reported for almost
all other African leafy vegetables including: Brassica oleraceae (Emebu and Anyika,
2011) and Boerhaviadiffusaand Commelinanudiflora (Ujowunduet al., 2008).
According to Alinnor and Oze (2011), food is considered to be “good” if Ca/P value is
greater than 1 and “poor” if the value is lesser than 0.5. The calculated Ca/P value for
Phaseolus vulgaris leaf is 34.55 making it good for consumption.
Table 2.Mineral composition of fresh edible Phaseolus vulgaris leaf.
Element
Composition (mg/100 g)
Na
224.62 ± 21.56 (1032.75 ± 91.84)
K
717.84 ± 64.11 (3300.40 ± 151.31)
Ca
3.80 ± 0.26
(17.47 ± 1.63)
Mg
0.04 ± 0.01
(0.18 ± 0.04)
P
0.11 ± 0.02
(0.51 ± 0.09)
Fe
4.59 ± 0.31
(21.10 ± 1.78)
Mn
1.30 ± 0.17
(5.98 ± 0.51)
Zn
0.30 ± 0.04
(1.38 (0.20)
Cu
0.22 ± 0.03)
(1.01 ± (0.16)
Pb
0.06 ± 0.01)
( 0.28 ± (0.03)
Hg
bdl
Na/K
0.31
Ca/P
34.55
Ca/Mg
95.00
Note:Values are expressed as mean ± SD for three determinations; concentration on dry weight basis in
brackets; bdl = below detection level.
Iron (4.59 mg/100 g) was the third most abundant mineral in Phaseolus vulgaris leaf.
This value was within the range of 0.2-12.8 mg/100 g reported for selected African
leafy vegetables (Uusikuet al., 2010). Iron is needed for formation of blood and equally
important for normal functioning of the central nervous system (Adeyeye&Fagbohun,
2005). It is an important trace element that binds oxygen in haemoglobin (Geissler&
Powers, 2005). Iron is essential in the diet of pregnant women, nursing mothers, infants
and elderly to prevent anaemia. According to WHO (2008), Africa has the highest
proportion of persons affected by anaemia. The RDA for iron in adult men and children
is 10 mg/100 g while it is 15 mg/100 g for adult females. Therefore, consumption of
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Emmanuel O. Oyelude, (2012). Proximate, mineral and anti-nutrient composition of phaseolus
vulgaris leaf
Phaseolus vulgaris leaf could assist to meet part of the daily requirement of iron in the
diet.
The levels of manganese (1.30 mg/100 g), zinc (0.30 mg/100 g) and copper (0.20
mg/100 g) in Phaseolus vulgaris leaf were too low. Hence, the vegetable can be
considered as a poor source of these minerals. The level of zinc was within the range of
0.02-2.9 mg/100 g for most selected African leafy vegetables (Uusikuet al., 2010). The
levels of zinc, copper and manganese in Phaseolus vulgaris leaf were lower than the
levels
reported
for
Ocimumgrattissimum
and
colocassiaesculenta
leaf
(Adepoju&Oyewole, 2011). Mercury was not detected in the vegetable and the level of
lead (0.06 mg/100 g) would not have any negative impact on the body if the vegetable is
consumed.
3.3
Anti-nutritional Composition
The result of antinutritional composition of Phaseolus vulgaris leaf is presented in
Table 3.
Table 3.Average anti-nutritional composition of fresh edible Phaseolus vulgaris leaf.
Parameter
Composition (g/100 g)
Phytates
0.77 ± 0.06
Oxalates
2.15 ± 0.12
Tannins
3.07 ± 0.15
Saponins
0.94 ± 0.10
Phenols
1.94 ± 0.14
Alkaloids
2.86 ± 0.21
Hydrocyanic acid
0.21 ± 0.02
Flavonoids
0.79 ± 0.0.07
Steroids
51.69 ± 3.02
Note:Values are expressed as mean ± SD for three determinations.
Steroids are the most abundant anti-nutritional constituents found in Phaseolus vulgaris
leaf. The level of steroids in Phaeolus vulgaris leaf was 51.69 mg/100 g. This value is
much higher than 0.05 mg/100 g found in the leaves of SolanumnigrumL. Var. virginicu
(Akubugwo, 2007b), Steroids are important because of their relationship with sex
hormones (Aberoumand, 2011; Okwu, 2001). Tannins are the second most abundant
anti-nutritional constituents present in Phaseolus vulgaris leaf. The concentration of
tannins in the vegetable (3.07 mg/100 g) was much higher than 0.63 mg/100 g in
Colocassiaesculenta leaves and 0.44 mg/100 g in Ocimumgratissimum leaves
(Adepoju&Oyewole, 2008). However, the level of tannins in Phaseolus vulgaris leaf
was much lower than the concentration range of 168-1222 mg/100 g reported for
selected African leafy vegetables by Uusikuet al., (2010). Tannins have been noted to
complex with proteins, starches and digestive enzymes and thus reducing the nutritional
value of foods (Chung, Wong, Wei, Huang & Lin, 1998). They also reduce the
availability of iron and interfere with protein absorption (Serrano, Pupponen-Pimiä,
Dauer, Aura &Saura-Calixto, 2009).
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Emmanuel O. Oyelude, (2012). Proximate, mineral and anti-nutrient composition of phaseolus
vulgaris leaf
An average of 3.07 mg/100 g of alkaloids was found in Phaseolus vulgaris leaf. This
value (fresh basis) is higher than 3.54 mg/100 g (dry basis) reported for
Amaranthushybridus leaves (Akubugwoet al., 2007a) but lower than 1.62 mg/100 g
(dry basis) reported for SolanumnigrumL. Varvirginicum leaves (Akubugwo, Obasi,
Ginika, 2007b). According to Edeoga&Eriata (2001), alkaloids are very important in
medicine and are have marked physiological effect on animals. Alkaloids are implicated
for the bitter taste of some African leafy vegetables (Wallace, Marfo&Plahar, 1998).
The concentration of phytates in Phaseolus vulgaris leaf was 0.77 mg/100 g. This
concentration was higher than 0.47 mg/100 g in Colocassiaesculenta leaves and 0.63
mg/100 g in Ocimumgratissimum leaves (Adepoju&Oyewole, 2008). Uusikuet al.,
(2010) reported the level of phytate in selected African leafy vegetables to fall between
0.1 mg/100 g and 481 mg/100 g. Phytates in food can bind to some essential mineral
nutrients in the digestive tract which may lead to deficiency of the minerals (Bello,
Falade, Adewusi&Olawore, 2008). The level of phytates in Phaseolus vulgaris leaf is
very low and may therefore not be injurious to health if the vegetable is consumed.
The level of oxalates in the Phaseolus vulgaris leaf was 2.15 mg/100 g. The
concentration of oxalates (as oxalic acid) in selected African leafy vegetables reviewed
by Uusikuet al., (2010) was between 1 mg/100 g and 1115 mg/100 g. Oxalates in food
may be either soluble or insoluble; soluble oxalates are absorbed by the body while the
insoluble ones are excreted in the faeces. According to Gupta, Lakshmi,
Manjunath&Prakash (2005), soluble oxalates form strong chelates with dietary calcium,
making it unavailable for absorption and assimilation. The oxalates content in
Phaseolus vulgaris leaf is low and unlikely to have adverse effect on the absorption of
calcium in the body. The concentration of saponins in Phaseolus vulgaris leaf was 0.94
mg/100 g. Saponins are reputed to possess cholesterol lowering effect (van
Duyn&Pivonka, 2000). They equally possess haemolytic, anti-inflammatory,
antifungal/antiyeast, antibacterial/antimicrobial and antiviral activities (Sparg, Light &
van Staden, 2004). This concentration was approximately equal to 0.93 mg/100 g in
Colocassiaesculenta leaves and 0.92 mg/100 g in Ocimumgratissimum leaves
(Adepoju&Oyewole, 2008). The level of saponins in Phaseolus vulgaris is small making
the vegetable safe for consumption.
The proportion of phenols present in Phaseolus vulgaris leaf was 1.94 mg/100g.
According to Wong, Leong &Koh (2006), plant extracts that contain high amount of
polyphenols also exhibit high antioxidant activity. The concentration of phenols in the
vegetable is unlikely to affect its dietary quality adversely. Flavonoids (0.79 mg/100 g)
are another class of phenolic compounds present in Phaseolus vulgaris leaf. Flavonoids
serve as flavouring ingredients of spices and vegetables (Enwere, 1998) and possess
anti-oxidation property. The concentration of hydrocyanic acid in the studied vegetable
was 0.21 mg/100 g. This level is low making the consumption of the vegetable safe.
Consumption of any food with high concentration of hydrocyanic acid may lead to a
neurological disease known as tropical ataxis neuropathy (TAN).
Table 4.Antinutrient to nutrient molar ratio for Phaseolus vulgaris leaf.
Antinutrient/Nutrient Ratio
Value
Critical Level
Page | 18
Emmanuel O. Oyelude, (2012). Proximate, mineral and anti-nutrient composition of phaseolus
vulgaris leaf
[Oxalates]/[Ca]
[Oxalates]/[(Ca + Mg)]
[Ca][Phytates]/[Zn]
[Phytates]/[Zn]
[Phytates]/[Fe]
[Phytates]/[Ca]
0.26
0.41
0.02
0.25
0.01
0.01
2.5
2.5
0.5
1.5
0.4
0.2
The bioavailability of divalent elements (calcium, magnesium, zinc and iron) can be
predicted by calculating the antinutrient to nutrient ratio for the elements (Dangoggo,
Bunu, Uba&Saidu, 2012). Table 4 presents the calculated nutrient to antinutrient factor
for Phaseolus vulgaris leaf.
The effect of oxalates on the bioavailability of calcium was predicted from the ratio of
[Oxalates]/[Ca] and [Oxalates]/[(Ca + Mg)]. The two ratios were calculated to be 0.26
and 0.41, respectively. These ratios are well below the critical level of 2.5 that implies
that the level of oxalates in Phaseolus vulgaris leaf will not hinder the bioavailability of
calcium if the vegetable is consumed. The effect of phytates on the bioavailability of
zinc in was estimated from the ratio of [Ca][Phytates]/[Zn] and [Phytates]/[Zn]. The
ratio of [Ca][Phytates]/[Zn] was 0.02 which is much lower than the critical level of 0.5.
Similarly, the ratio of [Phytates]/[Zn] was 0.25 which is much lower than the critical
level of 1.5. Therefore, consumption of Phaseolus vulgaris leaf will not affect the
bioavailability of zinc.
The impact of phytates on the bioavailability of iron and calcium was estimated using
the ratio of [Phytates]/[Fe] and [Phytates]/[Ca], respectively. The calculated ratio for
iron was 0.1 which is very low when compared with the critical ratio of 0.4. The ratio
for calcium was determined to be 0.01 which is much lower than the critical level of
0.2. Therefore, the phytates level in Phaseolus vulgaris leaf will not hinder availability
of iron and calcium.
4.0
CONCLUSION
The results from this study revealed that:
Phaseolus vulgaris leaf is a good source of protein and crude fibre.The vegetable has
low calories and may be suitable for those who are watching their weight. It is rich in
potassium, sodium and iron. Its consumption could help to reduce the prevalence of
protein energy malnutrition andanaemia in sub-Saharan Africa countries where it is
available.The levels of antinutritonal components in the vegetable are low and will not
impact negatively on the bioavailability of calcium, zinc and iron.
5.0
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