European Journal of Clinical Nutrition (1998) 52, 489±493
ß 1998 Stockton Press. All rights reserved 0954±3007/98 $12.00
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Nitrate and nitrite content in daily hospital diets during the
winter season Ð comparison of analytical and calculation
methods
M Borawska, R Markiewicz and A Witkowska
Laboratory of Bromatology, Medical University, 1 Kilinskiego St., 15-230 Bialystok, Poland
A comparison of two methods: analytical and calculation on an estimation of dietary intakes of nitrate and nitrite
from six different types of general hospital diets was studied. Studies were performed in the winter season of
1996 ±1997.
It was found that the mean daily intake of nitrates was 85 mg per person in the analytical method, and 65 mg per
person in the calculated method. The estimation of average dietary intakes of nitrite was adequate: 1.67 mg per
person (the analytical method) and 1.18 mg per person (the calculated method). The main source of nitrates were
vegetables, whereas the main source of nitrites was meat and meat-containing products.
We suggest that the different methodologies, analytical and calculation methods, for measuring dietary intakes of
nitrate and nitrite from diets make it possible to make direct comparisons of intakes.
Descriptors: nitrate; nitrite; hospital diets; different methods
Introduction
diets in the winter season by using two methods:
Diet constitutes an important source of human exposure to
nitrate and nitrite present in food either as natural components or as preserving additives. Chronic administration of
nitrates in low doses may result in dyspepsia, mental
depression and headache (Magee, 1983). In some pathological conditions (diarrhoea and lambliasis) an increase of
endogenous nitrate biosynthesis has been found (Wagner &
Tannenbaum, 1982; Wetting et al, 1987). Nitrites may
evoke methemoglobinemia (Bruning-Fann & Kaneene,
1993), anaemia (Ruddell et al, 1978), hypovitaminosis
(Lhuissier, 1976; Philips, 1968) and increase of risk of
goiter (Hoering et al, 1988). However, dietary nitrate can
also have positive effect on human organism. It has been
established that nitrates are reduced to nitrites by tongue
surface bacteria and then, in the acidic conditions of the
stomach, are chemically reduced to nitric oxide (NO),
which is an important protective factor against gut pathogens (Benjamin et al, 1994). NO readily diffuses through
cell membranes, deranges bacterial metabolism and
damages bacterial DNA (Wink et al, 1991). Conversion
of dietary nitrate into nitrite and nitric oxide plays protective role against microbial pathogens in the mouth and
lower gut (Benjamin et al, 1994; Liew et al, 1990; Duncan
et al, 1995).
It should be noted that different methodologies for
measuring dietary intakes of nitrate and nitrite have been
reported. As a consequence, it is not always possible to
make a direct comparison of dietary intakes between
countries. For these reasons we decided to estimate mean
dietary intake of nitrate and nitrite from general hospital
(1) analytical estimation of nitrate intake in all components
of the duplicate portion of diet from the patient's plate
(analytical method);
(2) the daily nitrate intake was calculated using our databank of contaminants in food with our results on the
mean nitrate levels in food products from 1990 ±1997
in the winter season, according to the list of products
delivered from the hospital stores for preparing meals
(calculation method).
Correspondence: Dr M Borawska.
Received 9 January 1998; revised 27 February 1998; accepted 10 March
1998
Materials and methods
Studies were performed on six whole day general diets
prepared for patients at the Teaching Hospital in Bialystok,
at the end of December, 1996 and January, 1997. In the
analytical method each component of hospital diet, consisting of breakfast, lunch, afternoon snack and evening
meal were submitted to investigation (grain products, milk
and milk-derived products, eggs, meat and sausages, ®sh,
butter and other fats, potatoes, vegetables and fruits, sugar
and sweets, soft drinks).
The amounts of nitrates and nitrites in these products
were determined by a standard spectrofotometric procedure, recommended by the following `Polish Norms' (PN):
(1) PN-92/A-75112Ðgrain products, potatoes, vegetables,
fruits, sugar, soft drinks (Polish Norm, 1992).
(2) PN-74/A-82114Ðmeat, sausages and other meat products, ®sh, eggs, lard (Polish Norm, 1974).
(3) PN-81/A-86234Ðmilk and milk-derived products,
butter, margarine (Polish Norm, 1981).
The method of analysis for nitrate in foodstuffs is
generally based on the reduction of nitrate ion to nitrite
85.240
124.770
24.180
126.280
45.040
60.540
115.010
1.760
0.880
10.530
0.000
4.490
12.310
5.000
0.761
3.810
13.200
Ð
Ð
Ð
15.430
7.040
11.890
0.090
1.070
Ð
4.400
Ð
5.020
Ð
Ð
4.710
0.117
0.550
263.210
19.780
167.130
38.160
88.110
140.710
119.520
0.527
62.990
45.200
Ð
38.220
61.590
19.790
30.350
39.030
0.219
8.550
37.470
20.340
29.590
20.340
29.590
48.090
30.900
0.025
0.770
11.080
14.160
28.800
35.560
10.340
4.470
17.400
0.104
1.810
Ð
Ð
Ð
Ð
Ð
Ð
Ð
Ð
Ð
Eggs
5.490
6.170
3.510
0.000
15.410
6.600
6.200
0.433
2.680
1
2
3
4
5
6
Mean nitrates concentration (mg/kg)
Product consumption (kg/person/d)
Nitrates intake (mg/person/d)
Milk
Number of diet
8.640
20.340
3.700
5.920
5.920
11.840
9.390
0.396
3.720
Legumes
Vegetables
Potatoes
Butter
and other
fats
Six different samples of hospital diets were determined by
analytical method for nitrate and the results of these
analyses are presented in Table 1. The concentration of
nitrate in individual samples of food groups was generally
less than 50 mg/kg, even in vegetables and potatoes. The
vegetable group, which was mainly cabbage, beets and
carrots contained average nitrate concentrations of 140.71,
167.13, 263.21 mg/kg respectively and only one sample
of the potatoes contained high concentrations of nitrate
(61.59 mg/kg). The estimated average total dietary intake of
nitrate was 85 mg per patient per day with about 83% of this
derived from vegetables including potatoes, 4% from milk,
4% from soft drinks and 3% from cereal products. As
presented in Table 1 vegetables and potatoes are the
major source of nitrate intake in the average diet. The
range of estimated intakes from the individual hospital total
diets was 24 ±126 mg of nitrate per person per day; mean
daily intake was 85 mg per person per day.
Figure 1 shows the mean nitrate content assayed in food
products available on sale in the north-east region of Poland
in the winter season. The concentration of nitrate in food
groups was generally less than 50 mg/kg, although potatoes
and vegetables were exceptions. The vegetables group
which was mainly potatoes, and the other vegetables
group (fresh and frozen), contained average nitrate concentrations of 536 mg/kg.
The results of the analysis of the hospital diet samples
for nitrate by calculated method and analytical method are
presented in Figure 2. The calculated average total dietary
intake of nitrate from food products was 65 mg per person,
82% of which was derived from vegetables including
potatoes. The range of calculated intakes of nitrate from
the general hospital diets was 39±115 mg per person per
day. Comparisons between the two methods made by t-test
for dependent samples and Mann±Whitney U-Wilcoxon
Test were not signi®cantly different.
In various European countries the daily intake of nitrates
varies from 42±179 mg per day (Gislason & Dahle, 1980;
Jagerstad & Nilsson, 1976; Ministry of Agriculture, Fisheries and Food, 1987; Nabrzyski & Gajewska, 1989;
Stephany & Schuller, 1978) and vegetables can account
for up to 85% of the nitrate intake from food (Cornee et al,
1992).
Table 2 presents the analytical method results for the
analyses of hospital diets study food groups for nitrite. In
potatoes and fresh fruit nitrite was not detected. The intake
Meats,
meat prod.,
®sh
Results and discussion
Cereal
products
Concentration of nitrate (mg NaNO3/kg) in the total diet food groups
Sugar and
sweets
Non-alcoholic
beverages
ion by the use of spongy cadmium.
According to the list of products without tap water,
delivered from the hospital stores for preparing meals, we
calculated the content of nitrate and nitrite in diets. This
theoretical method was based on assessment according to
our databank containing levels of nitrate and nitrite in food
products (1064 of product trials) available on sale in the
north-east region of Poland from 1990 ±1997 in the winter
season. Information on the loss of a fresh weight basis of
potatoes and vegetables (Los-Kuczera, 1990) was taken
into account in calculating intakes.
In the literature, the dose of nitrate or nitrite is expressed
in various ways. In these papers and ours nitrate and nitrite
are expressed as a weight of sodium salt.
All statistical evaluations of the results were based on
the software statistical program: Statistica v. 5.0.
Table 1 Assessment of dietary hospital intake of nitrate (mg/person/d) by analytical method
490
Intake from
a diet (mg/
person/d)
Nitrate and nitrite content in hospital diets
M Borawska et al
Nitrate and nitrite content in hospital diets
M Borawska et al
of nitrite was estimated to be 1.67 mg per person per day,
with meat, ®sh and meat products representing the main
source of the intake (69%).
Figure 3 shows the mean nitrite content in food products
available on sale. In contrast to the results for nitrate, nitrite
was not detected in eggs, fruits and there was a very low
concentration in potatoes (0.16 mg/kg) and in milk and
dairy products (0.17 mg/kg). Nitrite content was higher in
vegetables (20.10 mg/kg).
On the basis of the hospital stores for preparing meals
and the information on average residual nitrite levels in
food products, the calculated nitrite intakes from hospital
diets (in comparison to the analytical method) are presented
Figure 1 Nitrate levels (mg NaN3O/kg) in food groups.
Figure 2 Nitrite levels (mg NaN2O/kg) in food groups.
in Figure 4. The average daily intake of nitrite from diets in
the calculated method was found to be 1.18 mg (range:
0.47±2.59 mg) per person. The ®gure was similar to the
results in the analytical method. In the calculated method
37% of nitrite was derived from meats and ®sh products,
25% from soft drink products and 16% from vegetables
including potatoes.
The higher effect of nitrite derived from meat and ®sh
products in the diets in the analytical method was `diluted'
by the nitrite levels found in other components of food
groups in the calculated method. This is also possible, in
view of the dif®culty in accurately determining nitrite
concentrations in food groups after preparation of the meals.
491
1.670
0.000
0.000
0.000
1.570
0.430
0.000
0.330
0.761
0.250
0.000
Ð
Ð
Ð
0.000
0.360
0.120
0.090
0.010
Ð
0.000
Ð
0.000
Ð
Ð
0.000
0.117
0.000
0.000
0.000
0.000
0.000
0.720
0.000
0.120
0.527
0.060
0.000
Ð
0.000
0.000
0.000
0.000
0.000
0.219
0.000
1.500
0.000
0.000
0.000
1.500
1.500
0.750
0.025
0.020
0.000
0.000
4.100
39.100
23.600
0.000
11.130
0.104
1.160
Potatoes
Vegetables
Legumes
Non-alcoholic
beverages
Sugar and
sweets
Butter
and other
fats
Meats,
meat prod.,
®sh
Figure 3 Estimation of dietary hospital intake of nitrate (mg/person/d)
by analytical and calculation methods.
Figure 4 Estimation of dietary hospital intake of nitrite (mg/person/d)
by analytical and calculation methods.
Number of diet
Ð
Ð
Ð
Ð
Ð
Ð
Ð
Ð
Ð
0.660
0.000
0.300
0.000
0.660
0.660
0.380
0.396
0.150
0.000
0.000
0.000
0.290
0.000
0.000
0.050
0.433
0.020
1
2
3
4
5
6
Mean nitrites concentration (mg/kg)
Product consumption (kg/person/d)
Nitrites intake (mg/person/d)
Milk
Eggs
Conclusions
Cereal
products
Table 2 Assessment of dietary hospital intake of nitrite (mg/person/d) by analytical method
Concentration of nitrite (mg NaNO2/kg) in the total diet food groups
Intake from
a diet (mg/
person/d)
492
0.270
0.000
0.500
6.320
1.950
0.320
Nitrate and nitrite content in hospital diets
M Borawska et al
The estimated level of nitrite ranges from 0.87±13.05 mg/d
in various European countries (Ministry of Agriculture,
Fisheries and Food, 1987; Gislason & Dahle, 1980;
Jagerstad & Nilsson, 1976; Stephany & Schuller, 1978;
Nabrzyski & Gajewska, 1989).
A comparison of dietary intakes of nitrate and nitrite
from general hospital diets in multiple regression double
paired test showed a positive correlation coef®cient
between analytical and calculated methods; r values
varied from 0.55 for nitrite to 0.72 for nitrate.
We suggest that the different methodologies, analytical
and calculation methods, for measuring dietary intakes of
nitrate and nitrite from diets are possible to make direct
comparisons of intakes.
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