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Pakistan Journal of Nutrition 2 (2): 82-88, 2003
© Asian Network for Scientific Information 2003
82
The Level of Organic Acids in Some Nigerian Fruits and their Effect on
Mineral Availability in Composite Diets
Olumuyiwa S. Falade , Olusoga R. Sowunmi , Adewale Oladipo , Ayo Tubosun and Steve R. A. Adewusi *
1 1 2 2 1
Department of Chemistry, Obafemi Awolowo University, Ile-Ife, Nigeria
1
Centre for Energy Research and Development, Obafemi Awolowo University, Ile-Ife, Nigeria
2
E-mail: sadewusi@oauife.edu.ng
Abstract: The pH, ascorbic, citric and total organic acid content of some local fruits in Nigeria were
determined. The mineral content of the fruits, amaranthus vegetable and cowpea (Vigna unguiculata L. Walp)
were also determined. Orange juice had the highest level of ascorbic acid but low in citric acid while lime
juice is very rich in citric acid. Pine apple juice contained a low level of the organic acids. The effect of the
juice from the different fruits on the amaranthus and cowpea composite diets were investigated and
correlated with the acids content of the fruits. Orange and grapefruit enhanced Fe and Cu from both
amaranthus and cowpea but seem impaired by pine apple and lime juice. All fruit juices enhanced Mg and
Zn availability from amaranthus vegetable and cowpea composite diets except that Zn was inhibited by all
the fruit juice from cowpea meals. There was generally a strong correlation between ascorbic, citric and total
organic acid content of the fruits and the enhancement of mineral availability.
Key words: Ascorbic acid, citric acid, amaranthus, cowpea, mineral availability
Introduction
Minerals play a vital role in the maintenance of human
health (Schrimshaw, 1991). Iron, for instance, is an
important component of blood and enzymes involved in
electron transfer. Its deficiency results in fatigue,
headache and sore tongue in addition to anemia.
Calcium is needed for bone formation while zinc is
essential for protein and nucleic acid synthesis,
carbohydrate metabolism, successful pregnancy,
delivery and normal development (Wintrobe and Lee,
1974). Magnesium serves a key role in most reactions
involving phosphate transfer, structural stability of
nucleic acids and intestinal absorption of nutrients
(Battiflora et al., 1968).
In most African and other developing countries, mineral
deficiency especially that of iron is still a public health
issue probably due to the over dependence on plant
food sources, which contain more than enough minerals
to meet the daily requirement of man but have a low
bioavailability for physiological purposes (Adewusi and
Falade, 1996; Adewusi et al., 1999). The low
bioavailability of minerals from plant foods has been
attributed to the presence of anti-nutritional factors such
as tannin, phytate and oxalic acid (Awoyinka et al., 1995;
Santamaria et al., 1999) while ligands such as ascorbic
and other organic acids (Adewusi et al., 1999; Hazell
and Johnson, 1987) and some amino acids have been
reported to enhance mineral bioavailability (Reinhold et
al., 1981).
Fruits, such as oranges, banana, grapefruit and pine
apple abound in the tropical environment of Africa and
other developing areas of the world and are consumed
heavily when in season because storage technology is
not available to preserve the excess production. Fruits
contain organic acids especially ascorbic and citric
acids with the latter predominating. Hallberg et al. (1986)
reported the optimum concentration of ascorbic acid in
iron enhancement to be 50 mg per meal while
unpublished results from our laboratory indicated 100
mg ascorbic acid as the optimum concentration to
enhance iron availability in legume and vegetable
samples. Ascorbic acid has no effect on the absorption
of inorganic zinc (Solomons et al., 1979) while its effect
on copper availability has been reported to be negative
(Van den Berg et al., 1994). In addition to its limited
culinary use, lime is also used as a solvent medium in
many local herbal preparations for cough, cold,
indigestion and gastroenteritis especially for children.
Only a limited number of studies have been initiated into
tropical fruits, their chemical composition and the
possible effect of the juices on mineral availability from
composite diets of plant origin. This report therefore
represents the first attempt in the series of
investigations to bridge the gap in the knowledge of
Nigerian fruits and their probable role in nutrition in the
tropics.
Materials and Methods
Ripe fruits [Orange (Citrus sinensis), Grape fruit (Citrus
paradisi), Lime (Citrus aurantifolia), Pine apple (Ananas
comosus)] and Amaranthus esculentus vegetable were
bought in the local markets in Ile-Ife. Cowpea (Vigna
unguiculata L. Walp IT82D-699) was donated by the
International Institute of Tropical Agriculture (IITA),
Ibadan, Nigeria. The fruits were washed with distilled
water, peeled, cut opened and the juice extracted. The
Falade et al.: Organic Acids in Some Nigerian Fruits and Mineral Availability
83
sieved juice was stored frozen at -15 C in a plasticspectrophotometer.
o
container until used. The vegetable and cowpea were
prepared as previously described (Adewusi et al., 1999;
Adewusi and Falade, 1996).
Analytical Procedure:
aMoisture content was determined by the Association
of Official Analytical Chemist (AOAC, 1984) method.
bAscorbic acid was determined by the method of Roe
and Kuether (1943) with some modifications thus:
Five gram wet weight of each sample was extracted
with 25 mL of 0.1% oxalic acid, the residue washed
with 10 mL extraction solvent twice and the extract
centrifuged and made up to 50 mL in a standard
flask. The extract was thoroughly mixed with 4%
trichloroacetic acid (ratio 1:9) and 0.75 g acid
washed Norit and filtered through a No 1 Whatman
filter paper. 0.5 mL of 10% thiourea solution was
added to 1.0 mL of the filtrate, followed by 0.5 mL of
2.0% 2,4-dinitro phenylhydrazine (DNP) reagent in
4.5 M HSO . The test tubes were incubated in a
2 4
Buchi water bath (Model No. 887196; Type B465)
and incubated at 37 C for 3 h and cooled in ice. To
o
each test tube was added 2.5 mL of 85% HSO .
2 4
The tubes were shaken thoroughly in ice and left for
30 min for colour formation. Absorbance was read
at 540nm using a Pharmacia LKB
spectrophotometer against a reagent blank
prepared by adding the DNP reagent after the
addition of 2.5 mL 85% H SO . A standard curve of
2 4
ascorbic acid 0-100 mg per liter was established.
c Determination of Citric Acid Content was carried out
by the UV method using the Boehringer Mannheim
kit catalog No. 139076.
dDetermination of Total Titratable Acidity: 20 mL
aliquot of clear juice was titrated in a 250 mL
Erlenmeyer flask against 0.3 M NaOH solution to an
end point of pH 8.1 using a PYE Unicam pH meter
(Model 290 MK 2). Total organic acid was calculated
as the anhydrous citric acid equivalent.
eDetermination of Total and Available Mineral
Content: Total mineral content was determined from
4 g of each of the fruit juice and vegetable samples
and 0.5 g of the cowpea weighed in triplicate. 10 mL
conc. HNO was added to each sample in a
3
digestion flask and allowed to stand overnight. The
samples were heated carefully until the production
of brown nitrogen (iv) oxide fume has ceased. The
flasks were cooled and (2-4 mL) of 70% perchloric
acid was added. Heating was continued until the
solutions turned colorless. The solutions were
transferred into 50 mL standard flasks and diluted
to mark with distilled water. Total mineral content
was then analyzed by ALPHA 4 Atomic absorption
Available mineral content was determined by method of
Miller et al. (1981) with some modifications.
(i) Preparation of test meals: 20 g fresh sample was
mixed with 80 g water to make 100 g meal (fruit
juice or amaranthus) while 10 g of cowpea (dry
weight) was mixed with 90 g of water to make a 100
g meal. The mixture was homogenized in a
Kenwood KW 10 food blender to a creamy
consistency, adjusted to 40 g meal aliquots and
frozen until used.
(ii) Simulated digestion of test meals: Pepsin-HCl
digestion: The frozen meal from (i) above was
thawed at 37 C and divided into 20 g aliquots.
o
Pepsin digestion was continued as previously
described (Adewusi et al., 1999).
Pancreatin digestion: The frozen 20 g pepsin digest
from (b) above was thawed and placed into a 100 ml
beaker. Dialysis tubing (12,400 molecular weight cut off
obtained from Sigma) which contained 10 mL distilled
water and an amount of NaHCO equivalent to the
3
measured titratable acidity was placed into the beaker
containing 20 g pepsin digest sample. The beaker was
sealed with parafilm and incubated in a Buchi water bath
model No. 887196, type B 465 at 37 C with continuous
o
agitation until pH was about 5 (approx. 30 min).
Pancreatin-bile extract mixture (6.25 mL) was then
added to the beaker and incubated for 2 h with gentle
shaking. The volume of the dialysate was noted and
then frozen until used.
(iii) Preparation of composite test meals: 16 g fruit (wet
weight) was separately mixed with 4 g (dry weight)
of vegetable or cowpea. Water was added to the
mixture to make a 100 g meal and then blended to
a creamy consistency. The resulting mixture was
treated as in (a) and (b) above.
Determination of titratable acidity was carried out as
described by Miller et al. (1981).
(iv) Estimation of available mineral: Protein from the
dialysate was precipitated as previously described
(Adewusi et al., 1999) and the supernatant was
diluted as required for available mineral
determination using ALPHA 4 Atomic Absorption
Spectrophotometer.
Statistical Analysis of Data: The results were
expressed as a mean of three determinations with the
exception of dietary fiber and available minerals that
were presented as the mean of four determinations ±
SD. Correlation analysis was carried out using the
Pearson test.
Results and Discussion
The moisture content presented in Table 1 ranged
between 87 and 92% for fruit juice samples, which
agreed with arrange of 82 to 90% reported earlier (FAO,
Falade et al.: Organic Acids in Some Nigerian Fruits and Mineral Availability
84
Table 1: Percentage Moisture, pH value, Ascorbic, Citric and Total Organic Acid (mg/100 g) Content of Fruit Juice,
Amaranthus Vegetable and Cowpea*
Sample % Moisture pH Ascorbic acid Citric acid Total organic acid
a b c
Pineapple 87.3 ± 1.5 3.5 11.7 ± 1.5 218 ± 4.0 246 ± 6.3
Orange 90.2 ± 0.5 3.5 55.3 ± 1.5 452 ± 31 497 ± 5.2
d
Grape fruit 92.3 ± 0.7 3.2 45.4 ± 1.2 1312 ± 18 1382 ± 39.4
Lime 91.2 ± 0.5 1.4 29.4 ± 1.4 4124 ± 78 4187 ± 35.1
e
Amaranthus 89.7 ± 0.5 - - - -
f
Cowpea 10.6 ± 0.4 - - - -
g
*Mean ± standard deviation of quadruplicate analysis expressed on wet weight basis.
a. expressed in mg/100 g
b. expressed in mg/100 g (expressed as anhydrous citric acid)
c. Total organic acid expressed as anhydrous citric acid/100 g juice.
d. The pH of unripe oranges plucked for transportation was 2.7 and the total organic acid content was 561mg/100
g juice.
e. pH, Ascorbic, Citric and total organic acid content could vary by up to 29% depending on the stage of fruit maturity
and ripeness.
f. values are on wet weight basis (balanced vegetable)
g. Sample was cooked and dried at 50 C prior to analysis.
o
Table 2: Total and Percent Available Iron Content of Some Fruit Juice, Amaranthus Vegetable, Cowpea together with
the Theoretical and Experimental Available Iron of the Composite Diets1
Sample Total Iron % available Available iron (mg/kg) in fruit-amaranthus and fruit-cowpea composite
(mg/kg) Iron diets
-----------------------------------------------------------------------------------------------
Fruit Juice + Amaranthus Fruit Juice +Cowpea
2 3
----------------------------------------------- -------------------------------------------
Theoretical Exptal %Df Theoretical Exptal %Df
4 4
Pineapple 4.8 ± 0.9 48 3.9 ± 0.1 3.6 ± 0.8 -8 4.2 ± 0.1 3.2 ± 0.5 - 24
Orange 8.9 ± 1.2 32 2.6 ± 0.2 3.4 ±0.4 31 2.9 ± 0.2 3.4 ± 0.8 17
Grape fruit 10.7 ± 1.8 31 4.1 ± 0.1 4.5 ± 0.1 10 4.6 ± 0.2 6.9 ± 0.6 50
Lime 4.2 ± 0.7 31 7.0 ± 0.7 6.4 ± 1.0 - 9 5.6 ± 0.6 5.4 ± 0.5 -4
Amaranthus 86 ± 1.4 12 - - - - - -
Cowpea 157 ± 1.4 3- - - - - -
5
Mean±standard deviation of quadruplicate analysis. Composite diet = fruit juice and amaranthus mixed in ration
1 2
4:1. Composite diet = fruit juice and cowpea mixed in ratio 9:1. Df = difference between theoretical and experimental
3 4
values. Sample was cooked and dried at 50 C prior to analysis.
5 o
1968; Beyond vegetarianism, 1994). The moisturethese earlier studies but lower in many instances than
content of amaranthus was equally high (85.4%). Thisthe values of FAO (1968). The ascorbic acid content of
value agreed favorably with 86.7% reported forfruits varies appreciably with the fruit maturity, genetic
amaranthus (Awoyinka et al., 1995). The pH of the fruitvariety, climate and sunlight (Vanderslice and Higgs,
juices was between 1.4 and 3.8 (Table 1) which1990; de Ariola et al., 1980) and may be responsible for
compared well with earlier values (Lark, 2001). The pHthe variation in ascorbate content quoted in literature.
of the juice is dependent on the maturity and stage ofThe recommended daily intake (RDI) for ascorbic acid -
ripeness of the fruits as indicated in Table 1 for oranges. 30 mg/day for healthy women and 40 mg/day for men
Ascorbic acid content was least in pine-apple and(NHMRC, 1991) - can be supplied by 100 mL of all the
highest in oranges (Table 1). Machlin (1991) reportedfruit juices investigated except pine-apple.
the ascorbic acid content of pine-apple to be 20-40The constituent organic acids in fruits include ascorbic,
mg/100 g. The values; 53-55 mg and 27-29 mg/100 gmalic, lactic, malonic, succinic and citric acids with the
had also been reported for orange and lime juicelatter predominating. In this study, citric acid was highest
respectively (The Natural Food Hub, 1999; Vanderslicein lime and lowest in pine apple but generally
et al., 1990; Oyenuga, 1968; Mathoko and Kiniiya, 2002). constituted at least 90% of the total organic acid content
The figures reported in this study agreed essentially with of the selected fruits (Table 1).
Falade et al.: Organic Acids in Some Nigerian Fruits and Mineral Availability
85
Total and Available Iron Content: The total iron content composite diets could be due to the presence of high
presented in Table 2 ranged between 4.2 for lime andsoluble dietary fiber (0.8%) which is known to bind iron
10.7 mg/kg for grape fruit. The iron content of grape fruit making it unavailable (Fernandez and Phillips, 1982;
reported in this study (Table 2) was higher than the 7Falade et al., unpublished results). This inhibitory effect
mg/kg reported earlier; that of orange was marginallyis expected to cancel out the enhancing power of the
lower than the 11 mg/kg while the iron content reportedascorbic and other organic acids present in the pine-
for pine-apple agreed with the 4 mg/kg value publishedapple juice hence the small values of inhibition mostly
by FAO (1968). The total iron content of orange juice was observed in both composite diets. Overall, there was
at least twice as high as the 4 mg/kg quoted in Beyondhigh positive correlation (r = 0.99) and a significant r =
vegetarianism (1994) on the internet. The total iron0.49 between citric acid content and iron availability from
content of amaranthus and cowpea was 86 and 157juice-amaranthus and juice-cowpea composite diets
mg/kg respectively. The value for the former sample was respectively while the correlation between ascorbic acid
lower and that of the latter higher than values previously and iron availability from composite diets was not
obtained in our laboratory (Adewusi and Falade, 1996;significant.
Adewusi et al., 1999). This is probably a reflection of the
soil / location in which these samples were grown. Total and Available Magnesium Content: The total
Percent available iron was high in fruit juices (31-48%)magnesium content of the juice from the selected fruits
compared to 12% availability of iron for amaranthus and (Table 3) fell within the range of 140-640 mg/kg reported
3% for cowpea (Table 2). The values of iron availabilityearlier while the value for orange in this report is higher
obtained for amaranthus and cowpea are similar tothan the content reported earlier (Beyond vegetarianism,
those obtained earlier (Adewusi and Falade, 1996;1994). Blanching as a processing method for
Adewusi et al., 1999) and close to the 4.1% iron amaranthus vegetable leaches out minerals, the rate
availability reported for green bean (Martinez et al., 1998) depending on many uncontrollable factors such as the
and a range of 6-12% iron availability reported byvalency of the mineral; whether the metal is bound or
Rangarajan and Kelly (1998) for amaranthus. free, the binding state and the period of exposure to
The correlation between ascorbic acid and percent ironboiling water. The magnesium value for the present
availability in the fruit juices was negative (r = -0.80)blanched amaranthus sample was lower than the
probably due to the presence of other organic acidsearlier value quoted for a similar sample (Adewusi et al.,
which probably masked its ability as an antioxidant. At1999) but higher than 1024 mg/kg obtained for a sample
high concentration, most anti-oxidants exhibit pro-of amaranthus vegetable obtained from another source
oxidant activities as observed with ascorbic acid in our(Falade, unpublished results). The total magnesium
laboratory (Falade, unpublished results). Indeed, therecontent of cowpea now reported is similar to 2270 mg/
was also a negative correlation (r = -0.52) between thekg reported earlier (Falade and Adewusi, 1996) and
percent iron availability and the citric acid content of thewithin the range observed by Martinez et al. (1998).
fruit juices though Hazell and Johnson (1987) hadPercent available magnesium was high in all the fruit
indicated earlier that citric acid enhanced iron availability juices (Table 3) with no significant correlation (r = -0.07)
from wheat flour better than a correspondingbetween Mg availability and ascorbic acid but a positive
concentration of ascorbic acid. correlation (r = 0.45, p< 0.05) between availability and
Availability of Iron from Composite Meals: Orange and from amaranthus and cowpea (18 and 23% respectively)
grape fruit juice each enhanced iron availability inwere lower than the values obtained for similar samples
amaranthus by 31 and 10% and in cowpea by 17 andin earlier studies (Adewusi et al., 1999) and 27-37%
50% respectively probably due to the presence of higher reported for green beans by Martinez et al. (1998).
levels of ascorbic and citric acids. On the other hand,
lime and pine-apple juice had only a minor negativeComposite Meals: Lime juice produced the highest
(<10%) effect on the iron availability from bothenhancement of magnesium availability in both
amaranthus and cowpea composite diets except theamaranthus and cowpea composite diets while pine
24% inhibition of iron availability in pine-apple juice-apple juice enhanced magnesium availability by a
cowpea composite diet. Earlier studies have alsomarginal 4-5% in both samples (Table 3). The negligible
revealed the enhancement of iron availability by theincrease in magnesium availability in the presence of
addition or presence of ligands such as ascorbic acidpine apple juice may be directly connected to the
(Hazell and Johnson, 1987; Derman et al., 1977), lacticpresence of soluble dietary fiber in the pine apple juice
acid (Adewusi et al., 1999) and some amino acids(Falade, unpublished results). There was no significant
(Reinhold et al., 1981). The observed lack of effect orcorrelation between ascorbic acid content and available
inhibition of iron availability of iron in pine-apple juicemagnesium of the fruit juice-amaranthus composite diet
citric acid content. The percent available magnesium
Falade et al.: Organic Acids in Some Nigerian Fruits and Mineral Availability
86
Table 3: Total and Percent Available Magnesium Content of Some Fruit Juice, Amaranthus Vegetable, Cowpea
together with the Theoretical and Experimental Available Magnesium of the Composite Diets1
Sample Total Magnesium % available Available Magnesium (mg/kg) in Fruit-Amarathus and Fruit -
mg/kg Magnesium Cowpea Composites Diets
-------------------------------------------------------------------------------------
Fruit Juice + Amaranthus Fruit Juice + Cowpea
2 3
---------------------------------------- ----------------------------------------
Theoretical Exptal Df Theoretical Exptal %Df
4 4
Pineapple 302 ± 28 36 150 ± 18 157 ± 18 5181± 13 189 ± 25 4
Orange 220 ± 23 26 106 ± 5 146 ± 17 38 126 ± 25 160 ± 15 27
Grape fruit 155 ± 6.8 53 126 ± 14 169 ± 30 34 162 ± 37 205 ± 61 27
Lime 161 ± 23 39 107 ± 8 159 ± 21 49 143 ± 30 192 ± 28 34
Amaranthus 1356 ± 26 18 - - - - - -
Cowpea 2330 ± 3.8 23 - - - - - -
5
Mean ± standard deviation of quadruplicate analysis. Composite diet = fruit juice and amaranthus mixed in ration
1 2
4:1. Composite diet = fruit juice and cowpea mixed in ratio 9:1. Df = difference between theoretical and experimental
3 4
values. Sample was cooked and dried at 50 C prior to analysis.
5 o
Table 4: Total and Percent Available Zinc Content of Some Fruit Juice, Amaranthus Vegetable, Cowpea together with
the Theoretical and Experimental Available Zinc of the Composite Diets1
Sample Total Zinc % available Available Zinc (mg/kg) in Fruit - Amaranthus and Fruit-Cowpea
mg/kg Zinc Composite Diets
---------------------------------------------------------------------------------------------
Fruit Juice + Amaranthus Fruit Juice + Cowpea
2 3
------------------------------------------ ---------------------------------------------
Theoretical Exptal Df Theoretical Exptal % Df
4 4
Pineapple 3.5 ± 0.2 82 6.0 ± 0.3 6.7 ± 0.3 12 6.5 ± 0.2 5.3 ± 0.2 -18
Orange 3.6 ± 0.2 65 5.2 ± 0.01 7.2 ± 0.02 38 6.0 ± 0.1 5.1 ± 0.8 -15
Grape fruit 2.4 ± 0.3 88 6.5 ± 0.1 7.9 ± 0.3 22 7.9 ± 0.4 6.0 ± 0.5 -24
Lime 2.5 ± 0.0 84 7.2 ± 1.8 7.3 ± 2.6 17.6 ± 2.3 7.4 ± 0.1 -3
Amaranthus 50.6 ± 0.6 21 - - - - - -
Cowpea 67.0 ± 1.0 23 - - - - - -
5
Mean ± standard deviation of quadruplicate analysis. Composite diet = fruit juice and amaranthus mixed in ration
1 2
4:1. Composite diet = fruit juice and cowpea mixed in ratio 9:1. Df = difference between theoretical and experimental
3 4
values. Sample was cooked and dried at 50 C prior to analysis.
5 o
but a negative correlation with juice-cowpea diet (r = -juice and zinc availability was again negative (r = -0.50)
0.40). The correlation between citric acid content and
available magnesium of the composite diets were small
but positive r = 0.28 and 0.35 fruit juice-amaranthus and
-cowpea composite diets respectively.
Total and Available Zinc Content: The total zinc content
of the fruit juices presented in Table 4 was in the upper
ranges of or greater than 0.03-2.75 mg/kg earlier quoted
for fruits (Beyond vegetarianism, 1994) while the zinc
content of amaranthus and cowpea was about twice the
24 and 32 mg/kg values reported earlier from our
laboratory (Adewusi and Falade, 1996; Adewusi et al.,
1999).
Percent available zinc was high (65-88%) in all the fruit
juices while the availability from amaranthus and
cowpea was about half the 42% availability observed
earlier. Numerically however, the figures were identical
(Adewusi and Falade, 1996; Adewusi et al., 1999). The
correlation factor between ascorbic acid content of the
but positive for citric acid and zinc availability (r = 0.41).
Composite Meals: Contrary to the effect on magnesium,
lime juice did not seem to have any appreciable effect on
the enhancement of zinc from both composite diets.
Interestingly, the other fruit juice samples inhibited zinc
availability from cowpea while enhancing zinc availability
by 12-38% in amaranthus composite diets. There is no
doubt that the higher level of anti-nutritional factors in
cowpea (Adewusi and Falade, 1996) would account for
the lower mineral availability and or the no effect
syndrome observed with the fruit juices. The inhibition of
mineral availability could also be explained if the added
ligand increases the level of anti-nutrients that bind
minerals. There was a high positive correlation between
available zinc and ascorbic acid (r = 0.65) and citric acid
(r = 0.99) in the composite diets except in cowpea where
r = -0.16 between ascorbic acid and available zinc.
Falade et al.: Organic Acids in Some Nigerian Fruits and Mineral Availability
87
Table 5: Total and Percent Available Copper Content of Some Fruit Juice, Amaranthus Vegetable, Cowpea together
with the Theoretical and Experimental Available Copper of the Composite Diets1
Sample Total Copper % available Available Copper (mg/kg) in Fruit-Amarathus and Fruit-Cowpea
mg/kg Copper Composite Diets
------------------------------------------------------------------------------------------
Fruit Juice + Amaranthus Fruit Juice + Cowpea
2 3
-------------------------------------------- ------------------------------------------
Theoretical Exptal Df Theoretical Exptal %Df
4 4
Pineapple 0.4 ± 0.04 50 0.9 ± 0.13 0.8± 0.04 -11 1.1 ± 0.13 0.8 ± 0.2 - 27
Orange 0.2 ± 0.04 50 0.8 ± 0.04 0.9± 0.01 13 1.0 ± 0.17 1.1 ± 0.1 10
Grape fruit 0.4 ± 0.02 25 0.8 ± 0.13 0.9± 0.21 13 1.1 ± 0.02 1.3 ± 0.04 18
Lime 0.8 ± 0.13 50 1.2 ± 0.04 0.9± 0.23 -25 1.3 ± 0.05 1.3 ± 0.1 0
Amaranthus 1.1 ± 0.06 36 - - - - - -
Cowpea 12.8 ± 2.3 18 - - - - - -
5
Mean ± standard deviation of quadruplicate analysis. Composite diet = fruit juice and amaranthus mixed in ration
1 2
4:1. Composite diet = fruit juice and cowpea mixed in ratio 9:1. Df = difference between theoretical and experimental
3 4
values. Sample was cooked and dried at 50 C prior to analysis.
5 o
Total and Available Copper Content: The total copperjuice seem better in this respect than lime and pine
content was highest in lime and lowest in orange juice
(Table 5). The value for orange was below the 0.5-0.6
mg/kg quoted for fruits (Beyond vegetarianism, 1994)
while that of lime in the present study was marginally
above it. The copper content of amaranthus reported in
this study was in close agreement with that obtained
earlier for a similar sample (Falade, unpublished
results). The total copper content in cowpea was slightly
lower than the 16 mg/kg reported for green beans by
Martinez et al. (1998) and the 17 mg/kg value observed
for a similar sample of cowpea (Falade, unpublished
results).
Percent available copper was also high in all the fruit
juice samples (25-50%), amaranthus and cowpea
(Table 5). As expected, there was no significant
correlation either between copper availability and
ascorbic acid (r = -0.35; p < 0.05) or citric acid (r = -0.08;
p < 0.05).
Composite diets: Pine apple and lime juice both
impaired copper availability from the two composite
diets similar to the observation on the effect of fruit juice
on iron availability while orange and grape fruit juice
enhanced copper availability by 10 -18%. Ascorbic acid
has been reported to inhibit copper availability through
the reduction of copper (II) to copper (I) and its
subsequent precipitation (Van den Berg et al., 1994) but
in this study, there was a positive correlation between
copper availability and ascorbic acid (r = 0.83 and 0.58)
and (r = 0.49 and 0.69) in juice-amaranthus and
–cowpea composite diets respectively.
Conclusion
This study revealed that the consumption of fruit juice is
beneficial to mineral nutriture. Grape fruit and orange
apple. It is interesting to note that lime and pine apple
with the highest and least citric and total organic acid
content affect mineral availability in the same pattern.
The mechanism of action would probably be different;
the effect of pine apple juice is probably as a result of its
low content of anti-oxidant organic acids while the effect
of lime juice is presumably due to its large content of
organic acids which may act as pro-oxidants at high
concentration. Further work with animal models is
needed to confirm these results from in vitro studies.
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