Oxalate Content of Egyptian Grown Fruits and Vegetables and Daily Common Herbs

Abstract

Egyptian dieticians typically rely on foreign databases to find out oxalate content of food due to unavailability of local databases. The soil, fertilizers, climate and cultivars are often very different. Therefore, the purpose of this study is to establish a local database of oxalate content in Egyptian grown fruits and vegetables and selected daily common herbs. The current study analysed the total and the soluble oxalate in 37 Egyptian grown fruits, vegetables and 9 commonly used herbs. Two methods were used for screening the Egyptian foods for oxalate concentration; the first method was AOAC 1999 and the second was enzymatic method. Total oxalate varied greatly among the vegetables examined, ranging from 4 to 917 mg/100 g F.W. Total oxalate of analysed fruits ranged from 9 to 50 mg/100 g F. W. There is a strong correlation found between the two methods used. Vegetables were classified into 4 categories; low oxalate concentration containing less than 10 mg of oxalic acid /100 g F.W., such as cabbage, courgette, cucumbers, garlic, spring onions and turnip. Moderate oxalate concentration vegetables containing 10-25 mg/100 g F. W., such as aubergine, field bean, corn, peppers and watercress. High oxalate concentration vegetables containing 26-99 mg/100g F.W., such as f?l, green beans, celery, mallow, okra and sweet potatoes. Very high oxalate concentration containing 100-900 mg/100g F.W. such as Swiss chard, molokhia, purslane and vine leaves (fresh). Extensive amounts of total oxalate (201-4014 mg/100 g D.W.) were found in daily common herbs such as caraway seed, green cardamom, cinnamon, coriander seeds, cumin, curry powder, ginger and turmeric powder.

Full text

Journal of Food Research; Vol. 3, No. 3; 2014
ISSN 1927-0887 E-ISSN 1927-0895
Published by Canadian Center of Science and Education
66
Oxalate Content of Egyptian Grown Fruits and Vegetables and Daily
Common Herbs
Aly R. Abdel-Moemin1
1 Nutrition and Food Science Department, Faculty of Home Economics, Helwan University, Cairo, Egypt
Correspondence: Aly R. Abdel-Moemin, Nutrition and Food Science Department, Faculty of Home Economics,
Helwan University, Cairo, Egypt. Tel: 202-3560-1762. E-mail: dralymoemin@yahoo.co.uk
Received: February 25, 2014 Accepted: March 13, 2014 Online Published: April 10, 2014
doi:10.5539/jfr.v3n3p66 URL: http://dx.doi.org/10.5539/jfr.v3n3p66
Abstract
Egyptian dieticians typically rely on foreign databases to find out oxalate content of food due to unavailability of
local databases. The soil, fertilizers, climate and cultivars are often very different. Therefore, the purpose of this
study is to establish a local database of oxalate content in Egyptian grown fruits and vegetables and selected daily
common herbs. The current study analysed the total and the soluble oxalate in 37 Egyptian grown fruits, vegetables
and 9 commonly used herbs. Two methods were used for screening the Egyptian foods for oxalate concentration;
the first method was AOAC 1999 and the second was enzymatic method. Total oxalate varied greatly among the
vegetables examined, ranging from 4 to 917 mg/100 g F.W. Total oxalate of analysed fruits ranged from 9 to 50
mg/100 g F.W. There is a strong correlation found between the two methods used. Vegetables were classified into 4
categories; low oxalate concentration containing less than 10 mg of oxalic acid /100 g F.W., such as cabbage,
courgette, cucumbers, garlic, spring onions and turnip. Moderate oxalate concentration vegetables containing
10-25 mg/100 g F.W., such as aubergine, field bean, corn, peppers and watercress. High oxalate concentration
vegetables containing 26-99 mg/100g F.W., such as fūl, green beans, celery, mallow, okra and sweet potatoes. Very
high oxalate concentration containing 100-900 mg/100g F.W. such as Swiss chard, molokhia, purslane and vine
leaves (fresh). Extensive amounts of total oxalate (201-4014 mg/100 g D.W.) were found in daily common herbs
such as caraway seed, green cardamom, cinnamon, coriander seeds, cumin, curry powder, ginger and turmeric
powder.
Keywords: total oxalate, soluble oxalate, enzymatic method, fruits and vegetables, herbs
1. Introduction
Oxalic acid (ethanedioic acid), the name comes from the plant Oxalis (wood sorrel) from which it was first isolated
(Liebman, 2002), occurs ubiquitously in nature, sometimes as a free acid, but more commonly as soluble
potassium, sodium or ammonium oxalate or as insoluble calcium oxalate. Biosynthesis of oxalate occurs in
members of all five kingdoms. Oxalate is associated with metabolic disorders and infectious diseases (Holmes &
Assimos, 1998; Nakagawa et al., 1999).
Oxalic acid and its salts occur as an end product of metabolism in a number of plants. When these plants are eaten
they may have an adverse effect on humans and animals because oxalate binds calcium and other minerals and may
cause stone formation in the urinary tract when the acid is excreted in the urine (Noonan & Savage, 1999).
Oxalate-producing plants, which include many crop plants, accumulate oxalate in the range of 3%-80% (w/w) of
their dry weight (Libert & Franceschi, 1987). The oxalate production pathways the cleavage of isocitrate,
hydrolysis of oxaloacetate, glycolate/glyoxylate oxidation, and/or oxidative cleavage of L-ascorbic acid
(Hodgkinson, 1977). Of these pathways, the cleavage of ascorbic acid appears to be the most common (Yang &
Loewus, 1975; Nuss & Loewus, 1978; Li & Franceschi, 1990; Keates et al., 2000).
The diversity of calcium oxalate crystal shapes and sizes, as well as their prevalence and spatial distribution, have
led to a number of hypotheses regarding crystal function in plants. The proposed functions include roles in ion
balance, in plant defense, in tissue support, in detoxification, and in light gathering and reflection (Franceschi &
Horner, 1980). Recently, (Nakata & McConn, 2000) hypothesized the roles of calcium oxalate formed in plants in
supporting tissue structure and in regulating excess tissue calcium.

www.ccsenet.org/jfr Journal of Food Research Vol. 3, No. 3; 2014
67
Figure 1. The chemical structure of different forms of oxalic acid
The oxalate content of food such as spinach can vary considerably between plants of the same species, due to
differences in climate, soil quality, state of ripeness, or even which part of the plant is analyzed. Variations also
may be caused by the different methods used for measuring oxalate in food (Eheart & Massey, 1962).
Insoluble oxalate crystals formed in the gut are not absorbed and are carried out with the feces, thus reducing the
bioavailability and absorption of calcium and iron in diets (Bataille & Fournier, 2001). Human urine always
contains small levels of calcium oxalate (Oke, 1969) that may be deposited in the kidneys of certain people as a
common form of kidney stones (Massey et al., 1993).
In Egypt we have not enough data about how much oxalate in local grown fruits and vegetables or execrated
oxalate in urine that comes from endogenous metabolic synthesis. On the other hand, healthy adults, with U.S. or
European type western diets, 90% of oxalic acid excreted in the urine comes from endogenous metabolic synthesis
(Massey et al., 1993). However, establishing a local database of oxalate content in Egyptian grown fruits and
vegetables and daily common herbs may help Egyptian patients with hyperoxaluria to make more accurate dietary
modifications.
2. Materials and Methods
2.1 Experimental Procedure
Thirty seven fruits and vegetables were analysed, the selection of which was based on those listed in the USDA
Table 1984 with some modification to suit Egyptian food habits. The individual products were purchased from the
same batch within the supermarket. On the day of purchase, where applicable, the edible parts of the fruits or
vegetables were washed, dried, cut finely and weighed. For the purposes of this study three replicate samples of
each product were used. In the case of products such as, cauliflower, and onions, the products were of a sufficient
size and weight to allow for individual items to be used as single replicate. In the case of apricots, three individual
fruits were taken as one replicate due to the small size, chopped up and a composite sample prepared from which
the required sample weight was taken. Three replicates of each product were analysed in the dried state. Herbs
were treated similarly apart from washing process. Following sampling and preparation as described above, three
sub-samples of each ground product were prepared for the analysis. All results were expressed as mg oxalate/100
fresh weight (F.W.) of each fruit or vegetable or mg oxalate/100 dry weight (D.W.) for daily common herbs.
2.2 Drying Food Samples
A fruit or vegetable was dried at 28 °C from 2-7 days, depending on the type of food in a vacuum dryer
(Remplissage evacuation, Arthermo Gessate MI, temperature and density guide, Italy). For example, spinach
leaves and upper part of stalk of spinach were dried at 28 °C, for 3h then broken into small pieces by hand, and
mixed spinach and left in the vacuum dryer for about 27 hours until dried. Moisture and dry matter were
determined in all foods (Infrared Moisture Determination Balance FD-610-Japan).

www.ccsen
2.3 Optim
i
Four meth
b
est meth
o
and enzy
m
p
ilot stud
y
compared
2.4 Deter
m
Accordin
g
mixed wit
h
was adde
d
suspensio
n
with 2 ml
0.1M KM
n
seconds.
F
ml of 1M
H
as percent
2.5 Deter
m
An enzy
m
the total a
n
b
y the oxi
d
3-methyl-
2
maximum
The princ
i
The oxala
t
acid conc
e
described
sample w
a
min with
M
(10 mM,
p
p
urifying
t
min. The
s
tubes wer
e
(DMAB)
+
were adde
standard
w
all tubes a
n
of blank,
c
Tech, Tai
w
determine
d
oxalate co
n
b
asis for
h
et.org
/
jfr
i
zing Methods
ods were exp
e
o
ds for analys
i
m
atic method (
k
y
were obtain
e
to other meth
o
m
ination of O
x
g
to the metho
d
h
30ml of 1M
d
0.5ml of 5
%
n
was centrifu
g
of 0.35 M N
H
n
O4 with the
t
F
or soluble ox
a
H
Cl, the extra
c
of D.W.
m
ination of O
x
m
atic method (
T
n
d soluble oxa
d
ase enzyme a
n
2
benzotiazin
o
at 590 nm as
e
i
ple of enzym
a
t
e kit (Proced
u
e
ntrations in
t
by Palaniswa
m
a
s homogenize
M
PW-120 ho
m
p
H 7.6) (in or
d
t
ubes which c
o
s
upernatant w
a
e
labeled for b
l
+
(3-methyl-2-
d to each sam
p
w
ere added to t
h
n
d immediatel
c
ontrol, stand
a
w
an. Measure
m
d
by subtracti
n
n
centration in
h
erbs.
to Determine
e
rimented to c
o
i
ng oxalate in
k
it). Spinach s
a
e
d from the
m
o
ds.
x
alate by AOA
C
d
of AOAC 1
9
HCl. Each mi
x
%
calcium ch
l
g
ed at 800g f
o
H
4OH then dis
t
emperature b
e
a
lates, the sa
m
c
tion was with
x
alate by Enzy
m
T
rinity Biotec
h
late concentra
t
n
d the determ
i
o
lone and 3-d
i
e
xplained in
F
a
tic method fo
r
u
re No. 591; T
r
t
he fresh gro
w
m
y et al. (20
0
d in 5 mL dei
o
m
ogenizer at a
d
er to chelate
t
o
ntained activ
a
a
s collected vi
a
l
ank, control,
s
b
enzothiazoli
n
p
le tube; 50 μ
L
h
e standard tu
b
y mixed by g
e
a
rd, and samp
l
ments were t
a
n
g the blank ab
mg per 100 g
o
Journal
Oxalate Conc
o
mpare the ac
c
Egyptian foo
d
a
mple was us
e
m
ethods of AO
A
C
1999
9
99 oxalate w
a
x
ture was the
n
l
oride and th
o
o
r 15minutes
a
s
olved in 0.5
M
e
ing maintaine
m
e procedure
w
30 ml distille
d
m
atic Method
h
)
p
roposed f
o
t
ion in the exa
m
i
nation of the
r
i
methylamino
F
igure 2.
r
oxalate deter
m
r
inity Biotech
P
w
n produce of
0
4) and Quint
e
o
nized water (
f
maximum spe
t
he calcium w
i
a
ted charcoal
a
a
filtering thro
u
s
tandard and s
a
n
one hydrazo
n
L
deionized
w
b
e; 0.1 mL of
o
e
ntle inversion
.
l
e were deter
m
a
ken
t
wice to
sorbance fro
m
o
f fresh weig
h
of Food Resear
c
68
entration in
Fo
c
uracy and pre
c
d
s. These met
h
e
d to optimize
t
A
C 1999 and
a
s determined;
n
shaken in a
w
o
roughly mixe
a
nd the super
n
M
H
2
SO
4
. Th
e
d at 60 °C to
a
w
as used excep
d
water. The to
(Kit)
o
r the determi
n
m
ined foods.
T
r
esulting hydr
o
benzoic, giv
e
m
ination.
P
lc Bray, Co.
W
Egyptian fru
i
e
ros (2003)
w
f
or soluble ox
a
ed. The water
i
thin the samp
l
a
nd centrifug
e
u
gh filter pap
e
a
mple; 1mL o
x
n
e) MBTH, p
H
w
ater was adde
d
o
xalate reagen
t
.
All tubes we
r
m
ined at 590
n
obtain consis
t
m
absorbance r
e
h
t was calculat
e
c
h
Fo
ods
c
ision of oxal
a
h
ods were Ba
k
t
he methods i
n
enzymatic m
e
0.1 g of food
p
w
ater bath at 1
0
d to precipit
a
n
atant poured
o
e
solution was
a
faint violet c
o
t that instead
o
tal and solubl
e
n
ation of oxal
a
T
he method is
o
gen peroxide,
e
s an indamin
W
icklow, Irel
a
i
ts and veget
a
w
ith little mod
i
a
late) or in 5
m
soluble sampl
l
e). Diluted s
a
e
d in sample-
pu
e
r. Oxalate rea
x
alate reagent
A
H
= 3.1) was ad
d
d
to the blank
t
B (oxalate o
x
r
e incubated a
t
n
m in a CT-22
t
ent absorban
c
e
adings of sta
n
e
d on fresh fru
a
te methods in
k
er 1952, Oke
n
this study. T
h
e
thod (Kit) pr
e
p
owder sampl
0
0 °C for 30 m
i
a
te out the ca
l
o
ut. The pelle
t
titrated with s
o
lour that pers
o
f extracting t
h
e
oxalate cont
e
a
te in urine is
a
based on the
o
which in pres
e
e compound
w
a
nd) was used
t
a
bles and sele
c
i
fication. A
m
m
L 2N HCl (fo
r
e
s were dilute
d
a
mples were p
u
u
rifying tubes
g
ents were w
a
A
3-(dimethyl
a
d
ed to each tu
b
and control t
u
x
idase and per
o
t
37 °C for 5
m
00 Spectroph
o
c
es. Correcte
d
n
dard, control
a
its and vegeta
b
Vol. 3, No. 3;
order to choo
s
1969, AOAC
h
e best results
o
e
sented in Ta
b
e was weighe
d
i
n. To each mi
x
l
cium oxalate.
t
was washed
t
tandard soluti
o
isted for at le
a
h
e oxalates wi
t
e
nts were calc
u
a
dapted to est
i
o
xidation of o
x
e
nce of peroxi
w
ith an absor
p
t
o determine
o
c
ted daily her
b
m
ass of 0.01 g
r
total oxalate)
d
with 5 mL E
D
u
rified with s
a
at 3,500 rpm
a
rmed to 37 °
C
a
mino benzoi
c
b
e; 50 μL of s
a
u
bes; 50 μL o
x
o
xide) was ad
d
m
in. The absor
b
o
tometer, E-C
h
d
absorbances
a
nd the sample
b
les and dry
w
2014
s
e the
1999
o
f the
b
le 1,
d
and
x
ture
The
t
wice
o
n of
a
st 15
t
h 30
u
lated
i
mate
x
alate
dase,
p
tion
o
xalic
b
s as
food
for 8
D
TA
a
mple
for 5
C
; test
c
acid)
a
mple
x
alate
d
ed to
b
ance
h
rom
were
. The
w
eight

www.ccsenet.org/jfr Journal of Food Research Vol. 3, No. 3; 2014
69
Table 1. The amount of reagents used for blank the standard and the sample
Control (N-E*) Blank Standard Sample
1 mL Reagent A 1 mL Reagent A 1 mL Reagent A 1 mL Reagent A
---------------------------- ---------------------------- ---------------------------- 50 µL sample
50 µL deionized water 50 µL deionized water ---------------------------- ----------------------------
---------------------------- ---------------------------- 50 µL oxalate standard ----------------------------
0.1 mL Reagent B 0.1 mL Reagent B 0.1 mL Reagent B 0.1 mL Reagent B
*N= normal level-E elevated level.
2.7 Statistical Analysis
The results are presented as mean of three determinations ± standard error (± SEM). Pearson correlation
coefficients (r) were computed to assess the strength of the association between oxalate levels measured by AOAC
1999 and enzymatic methods. Oxalate values were analysed in transformed scale (log 10(X) for simple linear
regression Wessa (2012).
3. Results
The total and soluble oxalate content of the selected grown Egyptian fruits and vegetables and common herbs are
presented in Table 2 to Table 8. However, the amount of insoluble oxalate can be evaluated as the difference
between the total and the soluble oxalate (Rahman et al., 2008). It is noted that fruits and vegetables contain
varying amounts of total oxalate. The outcome of Pearson correlation in this study was strong correlation that
equal 1 between the two methods used for determination of oxalate in all foods examined. Linear regression
analysis of the total oxalate concentration in vegetables revealed a linear correlation (r2 = 1.006) between the two
methods (Figure 2). A similar correlation between the two methods occurred for the fruit samples (r2 = 0.8739),
(Figure 3) and (r2 = 0.9969) (Figure 4) for herbs.
Figure 2. Simple linear regression analysis of the total oxalate between AOAC 1999 and enzymatic methods for
vegetables; the values used were the log transformation

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70
Figure 3. Simple linear regression analysis of the total oxalate between AOAC 1999 and enzymatic methods for
fruits; the values used were the log transformation
Figure 4. Simple linear regression analysis of the total oxalate between AOAC 1999 and enzymatic methods for
herbs; the values used were the log transformation
Table 2. Effect of using different methods on the total oxalate concentration and precision of the method
(mg/100g)
Readings Baker (1952) Oke (1969) Enzymatic (Kit) AOAC 1999
1s
t
reading 668 750 921 905
2n
d
reading 650 700 914 900
3r
d
reading 550 740 916 895
Average of total reading 622.7 730 917 900
± *SEM 36.70 26.45 2.1 5
*standard error of the mean, each method was tested 9 times.
3.1 Recovery Studies
Known amounts of oxalate were added to 10 food samples tested before and known their amounts of oxalate, in
addition to testing the reagent recoveries in order to obtain percentage of oxalate recovery. The recovery of added
oxalate ranged from 93-107% for samples and 100.5% for reagent recoveries.

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71
The data represented in Table 3 shows the values of low concentration oxalate (less than 10 mg oxalic acid / 100g
fresh weight), such as cabbage, cauliflower, courgette, cucumbers, garlic, onions (white), onions (spring- leaves
only), peas (green) and turnip.
Table 3. Low oxalate concentration group (less than 10 mg oxalic acid / 100g fresh weight)
Vegetable/Taxonomic name
Total oxalate
(Kit)
*Soluble
oxalate
(Kit)
Total oxalate
(AOAC 1999)
*Soluble
oxalate
(AOAC 1999)
**Log transformation values (mg/100g fresh weight)
Cabbage (Brassica oleracea) (0.60)**
4±0.15
N
D(0.47)
3±0.06
N
D
Cauliflower (Brassica oleracea var. botrytis)(0.65)
4.5 ± 0.60
N
D( 0.69)
5±0.54
N
D
Courgette (Cucurbita pepo) (0.77)
6±0.40
(0.60)
4±0.09
(0.90)
8±0.20
(0.77)
6±0.52
Cucumbers (Cucumis sativus) (0.54)
3.5± 0.20
(0.30)
2± 0.74
(0.39)
2.5 ±0.07
(0.17)
1.5±0.04
Garlic (Allium sativum) (0.77)
6±0.53
N
D(0.84)
7±0.44
N
D
Onions (Allium cepa L.) (white) (0.69)
5 ±0.34
(0.54)
3.5±0.08
(0.69)
5±0.40
(0.47)
3±0.03
Onions (Allium cepa) (spring- leaves only) (0.84)
7±0.83
(0.60)
4±0.02
(0.77)
6±0.09
(0.47)
3±0.05
Peas (Pisum sativa) (green) (0.84)
7±0.33
(0.60)
4±0.67
(0.90)
8±0.70
(0.69)
5±0.56
Turnip (Brassica rapa var. rapa ) (0.39)
2.5±0.07
(0.30)
2±0.05
(0.65)
4.5±0.18
(0.47)
3±0.09
*Insoluble oxalate = total oxalate – soluble oxalate
** log transformation values
ND: not detected
The Table 4 shows moderate concentration group that contain 10-25 mg oxalic acid /100g fresh weight. This group
include aubergine, bean (field), broccoli, corn, lettuce, peppers (green), peppers (red), tomatoes and watercress.
The data presented in Table 5 shows the vegetables, that contain 26-99 mg oxalic acid /100 g fresh weight. This
group include beans, beans green, carrots, celery, mallow, okra, potatoes and sweet potatoes.

www.ccsenet.org/jfr Journal of Food Research Vol. 3, No. 3; 2014
72
Table 4. Moderate oxalate concentration group (10- 25 mg oxalic acid /100 g fresh weight)
Vegetable/Taxonomic name Total Oxalate
(Kit)
Soluble
Oxalate
(Kit)
Total Oxalate
(AOAC 1999)
Soluble Oxalate
(AOAC 1999)
Log transformation values (mg/100g fresh weight)
Aubergine (Solanum melongena) (1.19)
15.5±0.95
(0.95)
9±0.66
(1.20)
16±0.85
(0.84)
7±0.87
Bean (Field) (Phaseolus aureus
)
(seeds only)
(1.07)
12±0.83
(0.60)
4±0.41
(1.0)
10±0.63
(0.47)
3±0.32
Broccoli (Brassica oleracea var.
botrytis)
(1.30)
20±0.85
(0.84)
7±53
(1.30)
20±1.3
(0.69)
5±0.32
Corn, (Zea mays subsp. mays) (corn
seeds)
(1.09)
12.5±0.23
(0.77)
6±54
(1.07)
12±0.65
(0.60)
4±0.19
Lettuce (Lactuca sativa L.) (1.07)
12±0.76
(0.69)
5±.08
(1.0)
10±0.70
(0.47)
3±0.35
Peppers (green) Capsicum annum var.
grossum
(1.0)
10±034
(0.84)
7±0.33
(1.04)
11±0.43
(0.77)
6±0.21
Peppers (red) Capsicum annum var.
grossum
(1.04)
11±0.82
(0.77)
6±.05
(1.0)
10±0.6
(0.60)
4±0.01
Toma t o es (Lycopersicon esculentum) (1.27)
19±0.38
(1.20)
16±0.89
(1.11)
13±0.49
(1.07)
12±0.74
Watercress (Nasturium oficinale) (1.14)
14±0.76
(0.90)
8±0.43
(1.17)
15±0.74
(0.77)
6±0.54
Table 5. High oxalate concentration (26- 99 mg oxalic acid /10g fresh weight)
Vegetable/Taxonomic name
Total oxalate
(Kit)
Soluble
oxalate
(Kit)
Total oxalate
(AOAC 1999)
Soluble
oxalate
(AOAC 1999)
Log transformation values (mg/100g fresh weight)
Beans (Vic i a f aba) (1.75)
57±2.5
(1.64)
44±1.8
(1.74)
55±2.7
(1.60)
40±1.6
Beans, green (Phaseolus vulgaris) (1.60)
40±1.5
(1.49)
31±0.92
(1.54)
35±0.78
(1.38)
24±0.66
Carrots (Daucas carota) (1.61)
41±2.01
(1.55)
36±0.76
(1.57)
38±2.3
(1.50)
32±2.7
Celery (Apium graveolens var. dulce) (1.43)
27±1.58
(0.77)
6±0.54
(1.30)
20±0.87
(0.69)
5±0.21
Mallow (Malva sylvestris) (1.74)
56±1.10
(1.68)
48±1.89
(1.74)
55±1.66
(1.69)
50±1.57
Okra (Abelmoschus esculentus) (1.65)
45±0.56
(1.65)
45±0.22
(1.61)
41±0.40
(1.61)
41±0.40
Potatoes (Solanum tuberosum L.) (1.43)
27±0.08
(1.32)
21±0.04
(1.47)
30±0.56
(1.32)
21±0.32
Sweet potatoes (Ipomoea batatas) (1.68)
48±0.13
(1.57)
38±0.04
(1.71)
52±1.20
(1.54)
35±1.09
Fw: fresh weight; insoluble oxalate such as calcium oxalate can be calculated from subtraction total oxalate from
soluble oxalate

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73
In addition to this groups some leafy green vegetables showed in Table 6 an oxalic content over 99-900 mg oxalic
acid /100 g fresh weight. This oxalic acid content can be considered as very rich concentration, this group include
Swiss chard, molokhia, parsley, purslane, spinach and vine leaves (fresh).
Table 6. Very high oxalate concentration (more than 99-900 mg oxalic acid / 100g fresh weight)
Vegetable/Taxonomic name
Total Oxalate
(Kit)
Soluble
Oxalate
(Kit)
Total Oxalate
(AOAC 1999)
Soluble Oxalate
(AOAC 1999)
Log transformation values (mg/100g fresh weight)
Swiss char
d
(Beta vulgaris subsp. cicla) 
(2.90)
812±3.54
(2.77)
600±40.87
(2.90)
800±4.76
(2.75)
570±3.56
Molokhia (Corchorus olitorius L)
(leaves mainly)
(2.65)
457±3.60
(2.14)
140±0.85
(2.65)
450±2.50
(2.11)
130±1.09
Parsley (Petroselinum crispum) (2.19)
156±1.02
(1.51)
33±0.76
(2.17)
150±1.30
(1.47)
30±0.70
Purslane (Portulaca oleracea) (2.93)
862±3.10
(2.74)
559±1.46
(2.92)
850±7.31
(2.74)
550±3.10
Spinach (Spinacia oleracea) (2.96)
917±2.1
(2.89)
785±1.59
(2.95)
900±50
(2.88)
770±4.20
Vine leaves (fresh ) (2.48)
302±2.01
(2.30)
202±1.09
(2.46)
290±2.10
(2.26)
185±1.70
The data presented in Table 7. shows the concentration of oxalate (mg/100g) in a selected Egyptian grown fruits.
This group include apples, apricots fresh, guava, strawberries and mangoes.
Table 7. Concentration of oxalate (mg/100g) in a selected Egyptian grown fruits
Fruit/Taxonomic name Total oxalate
(Kit)
Soluble oxalate
(Kit)
Total oxalate
(AOAC 1999)
Soluble oxalate
(AOAC 1999)
Log transformation values (mg/100g fresh weight)
Apples (Malus domestica) (1.04)
11±0.9
(0.77)
6±0.32
(0.95)
9±0.75
(0.60)
4±0.21
Apricots (Prunus armeniaca) (fresh) (1.68)
48±80
(1.61)
41±11
(1.69)
50±15
(1.64)
44±50
Guava (Psidium guajava L) (1.25)
18±20
(1.25)
18±20
(1.23)
17±1.5
(1.14)
14±1.7
Strawberries (Fragaria ananassa Duch) (1.39)
25±4
(1.27)
19±1.3
(1.36)
23±1.9
(1.30)
20±5
Mangoes (Mangifera indica) (1.07)
12±30
(0.84)
7±0.70
(1.0)
10±10
(0.90)
8±2.4
The data in Table 8. Showed the oxalate concentration of some common herbs (mg/100 g D.W.) of daily selected
common herbs that include caraway seed, cardamom (green), cinnamon, coriander seeds, cumin, curry powder,
ginger, nutmeg and turmeric powder.

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74
Table 8. Oxalate concentration of some common herbs (mg/100g D.W.) of daily selected common herbs
Herb/Taxonomic name Total oxalates
(Kit)
Soluble oxalates
(Kit)
Total oxalate
(AOAC 1999)
Soluble oxalate
(AOAC 1999)
Log transformation values (mg/100g dry weight)
Caraway seeds (Carum carvi) (2.95)
900 ±55
(1.77)
60 ±21
(2.94)
890±78
(1.76)
58±9
Cardamom (green)
(Elettaria cardamomum)
(3.60)
4014 ±102
(3.59)
3977 ±123
(3.60)
4000±115
(3.59)
3970±135
Cinnamon
(Cinnamomum zelanicum)
(3.50)
3200 ±117
N
D(3.50)
3195±146
N
D
Coriander seeds
(Coriandrum sativum)
(3.00)
1005±150
N
D(2.99)
995±56
N
D
Cumin (Cuminum cyminum) (3.17)
1505 ±150
(2.05)
114 ±11
(3.17)
1500±147
(2.02)
105±10
Curry powder
(Murraya koenigii)
(3.31)
1070 ±126
(1.81)
65 ±80
(3.31)
1065±96
(1.88)
77±12
Ginger (
Z
ingiber officinale)(3.17)
1488 ±88
(3.14)
1390 ±57
(3.17)
1480±81
(3.13)
1379±60
N
utmeg (
M
yristica fragrans)(2.30)
201 ±11
(1.66)
46 ± 6
(2.30)
200±32
(1.70)
51±8
Turmeric powder
(Curcuma domestica)
(3.28)
1910 ±68
(3.25)
1812 ±85
(3.28)
1914±67
(3.25)
1809±79
4. Discussion
Since absorbed dietary oxalate can make a significant contribution to urinary oxalate levels therefore the Egyptian
consumers and dieticians always rely on oxalate content of food but from oxalate analyzers that are different
circumstances because the unavailability of a local database. Consequently, the aim of this work was to establish a
local database of oxalate included the common foods in Egypt such as fūl, molokhia, baladi corn, vine leaves,
mallows, mangoes and guava. The total food analysed in this study were 37 fruits and vegetables and 9 daily
common herbs. The AOAC 1999 and Trinity biotech kit for oxalate in urine were used to evaluate the total and
soluble oxalate.
Advantages of selected methods; AOAC 1999 and enzymatic kit, were that they were time efficient and had
relatively fewer steps. Results indicate that oxalate kit accuracy and precision was higher than AOAC and given
higher values of oxalate than AOAC 1999. Enzymatic method is adequate to the analysis of oxalate contents in the
examined foods, and the inter-day precision of the method expressed as standard error of mean was good (2.1),
with an accuracy of the recovery of added oxalate ranged from 93-107% for samples and 100.5% for reagent
recoveries.
In Egypt, consumption of vegetables is an important part of food habits, therefore grown vegetables were screened
for total and water soluble oxalate that were divided into four groups:
(i) Low oxalate concentration vegetables that were less than 10 mg/100 g F.W., include cabbage, cauliflower,
courgette, cucumbers, garlic, onions, spring onions, peas and turnip, which are the most vegetables consumed in
Egypt and would have a beneficial effect on patients with calcium oxalate stones.
(ii) Moderate oxalate concentration vegetables that contained 10-25 mg/100 g F.W. include aubergine, field bean,
broccoli, baladi corn, lettuce, peppers (green and red), tomatoes, and watercress.
(iii) High oxalate concentration vegetables that contained 26- 99 mg/100 g F.W. include beans, green beans, carrots,
celery, mallow, okra, potatoes, and sweet potatoes.
(iv) Very high oxalate concentration vegetables that contained 100- 900 mg/ 100g F.W. oxalic acid include Swiss
chard, molokhia (leaves mainly), parsley, purslane, spinach, vine leaves (fresh).

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75
Some fruits (apples, apricots (fresh), guava, strawberries and mangoes) were also screened for total and water
soluble oxalate. Apples in this study were found to have higher amounts than previously reported studies with total
oxalate levels between 0-2 mg/100 g (Holmes & Kennedy, 2000; Hönow & Hesse, 2002). In the study conducted
by El-Wahsh et al. (2012) a range of 1.3-2.6 mg total oxalate/100 g for apples were found.
Several studies were conflicting with regard to the reported oxalate level of strawberries with total oxalate levels
ranging from 2.9 mg/100 g (Hönow & Hesse, 2002) to 23.4 mg/100g (Ogawa, Takahashi, & Kitagawa, 1984). In
El-Wahsh et al., 2012, strawberries were reported to contain 6.0 mg and 2.5 mg of total and soluble oxalate/100 g,
respectively. In the present study, amount of total oxalate ranged from 23-25 mg/100 g F.W. The variation in
oxalate values in different sources of plants can be affected by factors such as soil quality, climate or different state
of fruit ripeness (Libert & Franceschi, 1987). In addition, differences could also be due to dissimilarity in
preparation of the samples and analytical techniques.
In Egypt, sweet potato is a common food eaten as a dessert while potatoes are staple food served as a main dish.
The oxalate content of sweet potato and potatoes were found to be 48 and 27 mg/100g F.W., respectively, this is
similar to the results of a Taiwanese study (48.6 mg/100 g.) (Tsai et al., 2005).
fūl (Vicia faba) is a staple food in Egypt, especially for low income people, with the amount of soluble oxalate
ranges between 40-44 mg/100 g D.W. (total oxalate 55-57 mg/100 g D.W.) there is a possibility that through
soaking and cooking oxalates are lost, but care should be paid to the spices that are added to the ful, specifically
cumin which has mega amounts of oxalate that found to be (1505-1500 mg/100g D.W.) .
Molokhia is a leafy green vegetable, another traditional food in Egypt, served as a thick green soup beside the main
dish that is usually a meat source. Molokhia belongs to very high oxalate concentration group (450-457 mg/100 g
F.W.) about 31 % of it have water soluble oxalate, coriander seed is used to spice traditional molokhia that is found
to contain 995-1005 mg/100 g D.M. Spinach and mallow are traditional vegetables in Egypt that are eaten in
winter similarly to molokhia in terms of adding spices. Mangoes are summer fruit in Egypt that are eaten as whole
or as juices and contains from 8-12 mg/100 g fresh weights.
Oxalate concentration of some common herbs (mg/100 g D.W.) of a selected common herbs include green
cardamom, coriander seeds, caraway seeds, cinnamon, cumin, curry powder, ginger, nutmeg and turmeric powder
that also important values for Egyptian cuisine. The data presented in Table 8. Indicates to the concentration of
oxalate in some common herbs used in the Egyptian cuisine.
Noticeably most these herbs contain extensive amounts of oxalate that exceeds 1000 mg / 100 g dry weight that
may consumers, patients and dieticians focus on high and very high concentrations of vegetables apart from herbs
that added to food. High consumption of oxalate rich foods can lead to secondary hyperoxaluria, a major risk factor
for calcium oxalate stone formation, and even acute renal failure in the case of excessive dietary oxalate intake
(Simpson et al., 1999).
About 75% of all kidney stones are composed primarily of calcium oxalate (Williams & Wandzilak, 1989) and
hyperoxaluria is a primary risk factor for this disorder (Goldfarb, 1988; Robertson & Hughes, 1993). Urinary
oxalate originates from a combination of absorbed dietary oxalate and endogenous formation from oxalate
precursors such as ascorbic acid and glyoxylate (Williams & Wandzilak, 1989). Restriction of dietary oxalate
intake has been proposed to prevent the formation of calcium oxalate kidney stones.
5. Conclusion
This study analysed traditional foods to establish a local database of oxalate content in 37 Egyptian grown fruits
and vegetables and 9 selected daily common herbs. Two methods were used for screening the Egyptian foods for
oxalate concentration. This study was analysed the traditional foods in Egypt such as fūl, molokhia, baladi corn,
vine leaves, mallows, mangoes and guava. Total oxalate varied greatly among the vegetables examined, ranged
from 4 to 917 (mg/100 g F.W). Total oxalate of analysed fruits ranged from 9 to 50 (mg/100 g F. W). Extensive
amounts of total oxalate were found in daily common herbs 201-4014 (mg/100 g D.W.).We hope the data obtained
herein can help dieticians, patients and urologists to instruct the public on urolithiasis prevention.
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