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Determination of nitrate in vegetables using an ion-selective electrode
JOURNAL
OF FOOD COMPOSITION
AND
ANALYSIS
(1992)
5,252-256
Determination of Nitrate in Vegetables an Ion-Selective Electrode
Using
A. CONSALTER,’ A. RIGATO, L. CLAMOR, AND P. GIANDON Centro Agrochimico-Ente via Baciocchi 9, 31033
di Sviluppo Castelfranco
Agricolo del Veneto, V.to (TV), Italy
Received May 31, 1991, and in revised form June 12, 1992 An ion-selective electrode was used to determine nitrate in vegetables after extraction with 0.01 A4 CuS04. The method proved to be sufficiently accurate and precise for assay of carrot, wild endive, chicory, spinach, parsley, and celery. The use of 2 M (NH&SO4 as an ionic strength adjustor was found to be unnecessary. The mean of recoveries was 104% and within sample the coefficients of variation ranged from 2.2 to 6.7%. Results obtained from different samples collected in the Veneto region of Italy indicated that nitrate content of vegetables is relatively low in the area. Nitrate content of vegetables decreased significantly after cooking. 0 1992 Academic PKSS, h.
INTRODUCTION
Determination of nitrate-nitrogen in food is very important because it is related to the amount of nitrate ingested by humans in a normal diet. The effects of nitrates on human health are clear (Bryan, 1982). After reduction to nitrites, they are absorbed by the blood where they combine with hemoglobine to form metahemoglobine which is not able to transport oxygen. The carcinogenic properties of nitrosamines compounds formed from nitrites and amines are also known, although, at present, significant epidemiological data, such as data to associate food and water nitrate level with toxic risk, are lacking (Aubert, 1983). In the Veneto Region of Italy there is a program to improve food quality. An easy, cheap, precise, and accurate method for determination of nitrate in vegetables is needed. The analytical method using a nitrate ion-selective electrode was selected because it works in a wide range of concentrations. Many authors reported results of water analysis carried out with a nitrate ionselective electrode (Hara and Okazaki, 1985), but there are very few papers dealing with determination of nitrate in vegetables using this method. Most of the authors reported vegetable analysis results obtained by ion, high pressure liquid or gas chromatography, or by a traditional reduction method. The present work aims to evaluate a nitrate ion-selective electrode for vegetable analysis, to increase our knowledge about the levels of nitrate-nitrogen present in vegetables from the Veneto Region of Italy, and to measure the effect of cooking on these levels. MATERIALS
AND
METHODS
Sampling operations, as all laboratory procedures, were carried out following or interpreting good laboratory practices (O.E.C.D., 1982). ’ To whom reprint requests should be addressed.
0889..1575/92 $5.00 Copyright 0 1992 by Academic Press. Inc. All rights of reproductmn in any form reserved
252
NITRATE
IN
VEGETABLES
253
Four to ten samples of each of six different vegetable species were purchased in 1990 from different markets of the Veneto Region: carrot (Daucus carota L.), wild endive (Chycoviu~z en&via L., ssp. latifolium Hot-t), celery (Opium graveolens L.), chicory (Chycorium intibus L., var. foliosum Bish.) of the “Trevisano” variety, spinach (Spinacia oleracea L.), and parsley (Apium petroselinum L.). Each sample was cleaned and washed and then divided into eight parts; one homogeneous sample was obtained by taking amounts from different parts to collect about 1 kg of edible. After homogenization 10 g of puree was taken. For spinach, celery, and carrot half of the sample was previously boiled in 2 liters of distilled water following traditional culinary procedures (Veronelli, 196 1): 60 min boiling for carrots and 30 for celery and spinach; after draining the normal procedure was followed. Apparatus An Orion 93-07 nitrate ion-selective electrode and an Orion 90-02 double-junction reference electrode (Orion Research, Cambridge, MA, 1986) were used. The outer filling solution of the reference electrode was 2 M ammonium sulphate solution. The potentials were measured to 0.1 mV with an Orion Model EA920 ionanalyzer. Reagents CuS04 X 5 HZ0 (2.497 g) was dissolved in 1 liter of distilled water to obtain the 0.0 1 M CuS04 X 5 HI0 solution. KN03 (7.1280 g) was dissolved in 1 liter of distilled water to obtain the 1000 ppm nitrate stock solution; it was diluted to prepare a standard series containing 0.2, 2, 20, and 200 ppm nitrate in 0.0 1 M CuS04. The or-ion nitrate ionic strength adjustor (ISA) was a 2 M (NH&SO4 solution. Procedure Puree (10 g) was extracted with 50 ml 0.0 1 CuS04 by shaking for 30 min (Cottenie et al., 1982). Extracts were filtered in 1OO-ml beakers. The calibrated nitrate electrode was immersed in the solution and the potential recorded against the reference electrode. The standard used for calibration depended on the working range chosen was 0.2-20 or 2-200 mg/liter. Four replicates of each sample were analyzed. For one sample of each considered species, recovery tests were carried on adding known amounts of nitrate before extraction: for each addition two replicates were analyzed. Fortifications varied with nitrate level in vegetables: the higher the nitrate level in some pretested samples, the higher the added nitrate. All these recovery tests were repeated twice with and without the addition of 2 ml ISA both to standards and to samples, as suggested by the electrode manual, to control the influence of this addition on the results of nitrate determinations. RESULTS AND
DISCUSSION
Preliminary tests were carried out to determine the different working ranges; 0.220 and 2-200 mg/liter of nitrate were chosen depending on the type of vegetable and the presumed nitrate concentration in it. Calibration was linear over the two working ranges using a semilogaritmic scale.
254
CONSALTER
ET
AL.
Table 1 shows the results of recovery tests. Recoveries vary from 100 to 1 lo%, with a mean of 104 and a SD of 4.5. An overestimation of nitrate is the most probable error. The sensitivity of the method is not as high as that of the HPLC method (Hunt and Seymour, 1985). Considering the correlation between added and measured nitrate (Table 2) we see that addition of ISA was not needed for these vegetables; thus its use was dropped for the remainder of the investigation. Results of the investigation of the nitrate content in the Veneto region are reported in Table 3. Excluding carrot, of which only roots were considered, all other vegetables are leafy; therefore carrot nitrate content is the lowest, less than one half of the nitrate content of chicory which is the poorest within leafy vegetables. These differ quite a lot in nitrate concentration; chicory seems to be a relatively low nitrate vegetable (50 mg/kg), while spinach and celery have relatively high nitrate contents within the studied vegetables (405 and 498 mg/kg of fresh product with maximum content of 671 and 7 15, respectively). There is a high variability between different samples of the same vegetable depending on cultivation techniques or environmental conditions during the plant growing season (Patruno, 1984); the higher the nitrate content the lower the variability between samples. Also, variability within samples that is between the replicates of each sample has the same trend, but coefficients of variability are quite low, confirming the good level of precision of the method.
TABLE RECOVERY TRACTION;
OFNITRATE EACH RESULT
I
ADDED TO VEGETABLE BEFORE ExIs THE MEAN OF Two SEPARATE AD-
DITIONS Vegetable
Carrot
Wild endive
Nitrate originally present 2
Nitrate added'
Total measured
Recovered
Recovery (%)b
3 10 20
5 13 24
3 11 22
100 110 110
51
3
54
3
100
10 20
62 73
11 22
110 110
Celery
163
10 20 40
173 163 203
10 20 40
100 100 100
Chicory
5
3 10 20
6 16 26
3 11 21
100 110 105
Spinach
109
10 20 40
119 129 149
10 a 40
100 100 100
Parsley
68
10 20 40
76 89 111
10 21 43
100 105 107
* mg/Kg fresh product b % of amount of nitrate added
NITRATE
IN
TABLE CORRELATION
NITRATE
ADDED
255
VEGETABLES 2
PARAMETERS
OF THE RELATIONSHIP
AND NITRATE
MEASURED
BETWEEN
IN RECOVERY
TESTS
WITH OR WITHOUT IONIC STRENGTH ADJUSTOR ((NHJZSO,) ADDITION TO SAMPLES AND STANDARD SOLUTIONS
ISA”
Vegetable Carrot
Measured value 2 2
rn yes
Wild
Intercept
Slope
1.7
1.1 1.0
1 .oo 1 .oo
1.6
Correlation coefficient
1x)
51
50
1.2
1 .oo
yes
52
53
1.0
1 .oo
nc yes
163 164
163 164
1.0 1 .l
1.00 0.99
Ix) yes
5
4
5 4
1 .o 1.1
1 .oo 1 .oo
t-a yes
109 100
109 100
1 .o 1 .o
1.00 1.00
rm
66
67
yes
57
57
1.1 1 .o
1.00 1 .oo
endive Celery
Chiiry
Spinach Parsley
a ISA=lonic Strength Adjustor (2M (NH4)2S04).
Nitrate concentrations found in this investigation are relatively low; according to Corm and Breimer (1979) carrot has a nitrate content varying between 500 and 1000 mg/kg of fresh product, parsley and endive between 1000 and 2500 mg/kg, and spinach and celery over 2500 mg/kg. Also Lorenz (1978) reported a nitrate content of more than 22 15 mg/kg fresh product for spinach, parsley, celery, and endive, and between 886 and 22 15 mg/kg for carrot. The loss of nitrate with cooking of three of the vegetables is reported in Table 4; the decrease in nitrate content after cooking is high for carrot (-54%) and spinach (-70%) while it is not very significative for celery (-23%). CONCLUSIONS
The ion-selective electrode method seems to be sufficiently precise and accurate in the determination of nitrate in vegetables. The method is easy and quick for use in TABLE NITRATE
Veg&bkS
n. Of
samples= carrot Wild endive Celery Chicory Spinach ParSleV
a b c d
10 10 5 5 5 4
(mg/kg
3
OF FRESH PRODUCT) DIFFERENT VEGETABLES
General
moist.
mean
1%)
max. value
min. value
17 121 498 xl 405 224
a7 96 95 a9 94 90
45 166 715 123 671 301
3 59 369 13 235 114
Four replicates of each sample were assayed. SD=Standard Deviation. CV=Coefficient of Variability (SD/Mean). Replicate variability is reported as within sample
CONTENTS
SDb CVC between tehveen SamPIes samples
12.3 40.1 136 40.1 162 76
70 33 27 79 40 34
SD and CV.
OF
SD cv withind within samples samples
0.3 1.5 1.7 0.4 3.9
i .a
6.7 5.5 2.2 3.5 3.5 4.6
256
CONSALTER
ET AL.
TABLE
4
NITRATE CONTENT (mg/kg OF FRESHPRODUCT) OF SOME VEGETABLESBEFOREAND AFTER COOKING Veg&blGTS
CarrOt Spinach CdWY
biting time
60 30 30
fresh
fresh
prOdUCt
pPJdlJCt
SD
boiled prodUct mean
bolfsd product SD
meal
63 255 766
42 60 131
29 76 604
15 36 149
nitrate depletion ( )
5? 70 23
routine analysis of nitrate content of vegetables on a large scale. Vegetables in the Veneto Region have a relatively low nitrate content. Cooking reduces the nitrate level in vegetables but the amount of reduction varies considerably between species. REFERENCES AUBERT, M. C. (1983). Nitrates in vegetables: Some possible toxic effects. Nutr. ffcdth 2, 77-84. BRYAN, F. L. (1982). Diseases transmitted by foods, a classification and summary. U.S. Dept. of Health and Human Services, Atlanta. CORR~, W. J.. AND BREIMER, T. (1979). Nitrate and nitrite in vegetables. P.U.D.O.C.. Wageningen. COTTENIE,A., VERLOO, M., KIENKES, L., VELGHE, G., AND CARNERLYNCK, R. (1982). Chemical analysis of plants and soils. I.W.O.N.L., Brussels. HARA. H., AND OKAZAKI, S. (1985). Effect of surfactants on the determination of nitrate in stream waters by using a nitrate ion-selective electrode. Analyst 110, I l-14. HUNT, J., AND SEYMOUR, D. J. (I 985). Method for measuring nitrate-nitrogen in vegetables using anionexchange high-performance liquid chromatography. Analysf 110, I3 l-1 33. LORENZ, 0. A. (1978). Nitrate levels in edible plant parts. In Nielsen and MacDonald’s Nitrogen in the Environment, Vol. 2, pp. 20 l-2 19. Academic Press, New York. O.E.C.D. (1982). Good laboratory practice in the testing of chemicals, Paris. PATRUNO, A. (1984). Influenza dei fattori agronomici sul contenuto di nitrati nei prodotti agricoli. Riv. di .4,gron. 18, 79-9 I. VERONELLI, L. (196 1). Curnacrna. Garzanti. Italia.
OF FOOD COMPOSITION
AND
ANALYSIS
(1992)
5,252-256
Determination of Nitrate in Vegetables an Ion-Selective Electrode
Using
A. CONSALTER,’ A. RIGATO, L. CLAMOR, AND P. GIANDON Centro Agrochimico-Ente via Baciocchi 9, 31033
di Sviluppo Castelfranco
Agricolo del Veneto, V.to (TV), Italy
Received May 31, 1991, and in revised form June 12, 1992 An ion-selective electrode was used to determine nitrate in vegetables after extraction with 0.01 A4 CuS04. The method proved to be sufficiently accurate and precise for assay of carrot, wild endive, chicory, spinach, parsley, and celery. The use of 2 M (NH&SO4 as an ionic strength adjustor was found to be unnecessary. The mean of recoveries was 104% and within sample the coefficients of variation ranged from 2.2 to 6.7%. Results obtained from different samples collected in the Veneto region of Italy indicated that nitrate content of vegetables is relatively low in the area. Nitrate content of vegetables decreased significantly after cooking. 0 1992 Academic PKSS, h.
INTRODUCTION
Determination of nitrate-nitrogen in food is very important because it is related to the amount of nitrate ingested by humans in a normal diet. The effects of nitrates on human health are clear (Bryan, 1982). After reduction to nitrites, they are absorbed by the blood where they combine with hemoglobine to form metahemoglobine which is not able to transport oxygen. The carcinogenic properties of nitrosamines compounds formed from nitrites and amines are also known, although, at present, significant epidemiological data, such as data to associate food and water nitrate level with toxic risk, are lacking (Aubert, 1983). In the Veneto Region of Italy there is a program to improve food quality. An easy, cheap, precise, and accurate method for determination of nitrate in vegetables is needed. The analytical method using a nitrate ion-selective electrode was selected because it works in a wide range of concentrations. Many authors reported results of water analysis carried out with a nitrate ionselective electrode (Hara and Okazaki, 1985), but there are very few papers dealing with determination of nitrate in vegetables using this method. Most of the authors reported vegetable analysis results obtained by ion, high pressure liquid or gas chromatography, or by a traditional reduction method. The present work aims to evaluate a nitrate ion-selective electrode for vegetable analysis, to increase our knowledge about the levels of nitrate-nitrogen present in vegetables from the Veneto Region of Italy, and to measure the effect of cooking on these levels. MATERIALS
AND
METHODS
Sampling operations, as all laboratory procedures, were carried out following or interpreting good laboratory practices (O.E.C.D., 1982). ’ To whom reprint requests should be addressed.
0889..1575/92 $5.00 Copyright 0 1992 by Academic Press. Inc. All rights of reproductmn in any form reserved
252
NITRATE
IN
VEGETABLES
253
Four to ten samples of each of six different vegetable species were purchased in 1990 from different markets of the Veneto Region: carrot (Daucus carota L.), wild endive (Chycoviu~z en&via L., ssp. latifolium Hot-t), celery (Opium graveolens L.), chicory (Chycorium intibus L., var. foliosum Bish.) of the “Trevisano” variety, spinach (Spinacia oleracea L.), and parsley (Apium petroselinum L.). Each sample was cleaned and washed and then divided into eight parts; one homogeneous sample was obtained by taking amounts from different parts to collect about 1 kg of edible. After homogenization 10 g of puree was taken. For spinach, celery, and carrot half of the sample was previously boiled in 2 liters of distilled water following traditional culinary procedures (Veronelli, 196 1): 60 min boiling for carrots and 30 for celery and spinach; after draining the normal procedure was followed. Apparatus An Orion 93-07 nitrate ion-selective electrode and an Orion 90-02 double-junction reference electrode (Orion Research, Cambridge, MA, 1986) were used. The outer filling solution of the reference electrode was 2 M ammonium sulphate solution. The potentials were measured to 0.1 mV with an Orion Model EA920 ionanalyzer. Reagents CuS04 X 5 HZ0 (2.497 g) was dissolved in 1 liter of distilled water to obtain the 0.0 1 M CuS04 X 5 HI0 solution. KN03 (7.1280 g) was dissolved in 1 liter of distilled water to obtain the 1000 ppm nitrate stock solution; it was diluted to prepare a standard series containing 0.2, 2, 20, and 200 ppm nitrate in 0.0 1 M CuS04. The or-ion nitrate ionic strength adjustor (ISA) was a 2 M (NH&SO4 solution. Procedure Puree (10 g) was extracted with 50 ml 0.0 1 CuS04 by shaking for 30 min (Cottenie et al., 1982). Extracts were filtered in 1OO-ml beakers. The calibrated nitrate electrode was immersed in the solution and the potential recorded against the reference electrode. The standard used for calibration depended on the working range chosen was 0.2-20 or 2-200 mg/liter. Four replicates of each sample were analyzed. For one sample of each considered species, recovery tests were carried on adding known amounts of nitrate before extraction: for each addition two replicates were analyzed. Fortifications varied with nitrate level in vegetables: the higher the nitrate level in some pretested samples, the higher the added nitrate. All these recovery tests were repeated twice with and without the addition of 2 ml ISA both to standards and to samples, as suggested by the electrode manual, to control the influence of this addition on the results of nitrate determinations. RESULTS AND
DISCUSSION
Preliminary tests were carried out to determine the different working ranges; 0.220 and 2-200 mg/liter of nitrate were chosen depending on the type of vegetable and the presumed nitrate concentration in it. Calibration was linear over the two working ranges using a semilogaritmic scale.
254
CONSALTER
ET
AL.
Table 1 shows the results of recovery tests. Recoveries vary from 100 to 1 lo%, with a mean of 104 and a SD of 4.5. An overestimation of nitrate is the most probable error. The sensitivity of the method is not as high as that of the HPLC method (Hunt and Seymour, 1985). Considering the correlation between added and measured nitrate (Table 2) we see that addition of ISA was not needed for these vegetables; thus its use was dropped for the remainder of the investigation. Results of the investigation of the nitrate content in the Veneto region are reported in Table 3. Excluding carrot, of which only roots were considered, all other vegetables are leafy; therefore carrot nitrate content is the lowest, less than one half of the nitrate content of chicory which is the poorest within leafy vegetables. These differ quite a lot in nitrate concentration; chicory seems to be a relatively low nitrate vegetable (50 mg/kg), while spinach and celery have relatively high nitrate contents within the studied vegetables (405 and 498 mg/kg of fresh product with maximum content of 671 and 7 15, respectively). There is a high variability between different samples of the same vegetable depending on cultivation techniques or environmental conditions during the plant growing season (Patruno, 1984); the higher the nitrate content the lower the variability between samples. Also, variability within samples that is between the replicates of each sample has the same trend, but coefficients of variability are quite low, confirming the good level of precision of the method.
TABLE RECOVERY TRACTION;
OFNITRATE EACH RESULT
I
ADDED TO VEGETABLE BEFORE ExIs THE MEAN OF Two SEPARATE AD-
DITIONS Vegetable
Carrot
Wild endive
Nitrate originally present 2
Nitrate added'
Total measured
Recovered
Recovery (%)b
3 10 20
5 13 24
3 11 22
100 110 110
51
3
54
3
100
10 20
62 73
11 22
110 110
Celery
163
10 20 40
173 163 203
10 20 40
100 100 100
Chicory
5
3 10 20
6 16 26
3 11 21
100 110 105
Spinach
109
10 20 40
119 129 149
10 a 40
100 100 100
Parsley
68
10 20 40
76 89 111
10 21 43
100 105 107
* mg/Kg fresh product b % of amount of nitrate added
NITRATE
IN
TABLE CORRELATION
NITRATE
ADDED
255
VEGETABLES 2
PARAMETERS
OF THE RELATIONSHIP
AND NITRATE
MEASURED
BETWEEN
IN RECOVERY
TESTS
WITH OR WITHOUT IONIC STRENGTH ADJUSTOR ((NHJZSO,) ADDITION TO SAMPLES AND STANDARD SOLUTIONS
ISA”
Vegetable Carrot
Measured value 2 2
rn yes
Wild
Intercept
Slope
1.7
1.1 1.0
1 .oo 1 .oo
1.6
Correlation coefficient
1x)
51
50
1.2
1 .oo
yes
52
53
1.0
1 .oo
nc yes
163 164
163 164
1.0 1 .l
1.00 0.99
Ix) yes
5
4
5 4
1 .o 1.1
1 .oo 1 .oo
t-a yes
109 100
109 100
1 .o 1 .o
1.00 1.00
rm
66
67
yes
57
57
1.1 1 .o
1.00 1 .oo
endive Celery
Chiiry
Spinach Parsley
a ISA=lonic Strength Adjustor (2M (NH4)2S04).
Nitrate concentrations found in this investigation are relatively low; according to Corm and Breimer (1979) carrot has a nitrate content varying between 500 and 1000 mg/kg of fresh product, parsley and endive between 1000 and 2500 mg/kg, and spinach and celery over 2500 mg/kg. Also Lorenz (1978) reported a nitrate content of more than 22 15 mg/kg fresh product for spinach, parsley, celery, and endive, and between 886 and 22 15 mg/kg for carrot. The loss of nitrate with cooking of three of the vegetables is reported in Table 4; the decrease in nitrate content after cooking is high for carrot (-54%) and spinach (-70%) while it is not very significative for celery (-23%). CONCLUSIONS
The ion-selective electrode method seems to be sufficiently precise and accurate in the determination of nitrate in vegetables. The method is easy and quick for use in TABLE NITRATE
Veg&bkS
n. Of
samples= carrot Wild endive Celery Chicory Spinach ParSleV
a b c d
10 10 5 5 5 4
(mg/kg
3
OF FRESH PRODUCT) DIFFERENT VEGETABLES
General
moist.
mean
1%)
max. value
min. value
17 121 498 xl 405 224
a7 96 95 a9 94 90
45 166 715 123 671 301
3 59 369 13 235 114
Four replicates of each sample were assayed. SD=Standard Deviation. CV=Coefficient of Variability (SD/Mean). Replicate variability is reported as within sample
CONTENTS
SDb CVC between tehveen SamPIes samples
12.3 40.1 136 40.1 162 76
70 33 27 79 40 34
SD and CV.
OF
SD cv withind within samples samples
0.3 1.5 1.7 0.4 3.9
i .a
6.7 5.5 2.2 3.5 3.5 4.6
256
CONSALTER
ET AL.
TABLE
4
NITRATE CONTENT (mg/kg OF FRESHPRODUCT) OF SOME VEGETABLESBEFOREAND AFTER COOKING Veg&blGTS
CarrOt Spinach CdWY
biting time
60 30 30
fresh
fresh
prOdUCt
pPJdlJCt
SD
boiled prodUct mean
bolfsd product SD
meal
63 255 766
42 60 131
29 76 604
15 36 149
nitrate depletion ( )
5? 70 23
routine analysis of nitrate content of vegetables on a large scale. Vegetables in the Veneto Region have a relatively low nitrate content. Cooking reduces the nitrate level in vegetables but the amount of reduction varies considerably between species. REFERENCES AUBERT, M. C. (1983). Nitrates in vegetables: Some possible toxic effects. Nutr. ffcdth 2, 77-84. BRYAN, F. L. (1982). Diseases transmitted by foods, a classification and summary. U.S. Dept. of Health and Human Services, Atlanta. CORR~, W. J.. AND BREIMER, T. (1979). Nitrate and nitrite in vegetables. P.U.D.O.C.. Wageningen. COTTENIE,A., VERLOO, M., KIENKES, L., VELGHE, G., AND CARNERLYNCK, R. (1982). Chemical analysis of plants and soils. I.W.O.N.L., Brussels. HARA. H., AND OKAZAKI, S. (1985). Effect of surfactants on the determination of nitrate in stream waters by using a nitrate ion-selective electrode. Analyst 110, I l-14. HUNT, J., AND SEYMOUR, D. J. (I 985). Method for measuring nitrate-nitrogen in vegetables using anionexchange high-performance liquid chromatography. Analysf 110, I3 l-1 33. LORENZ, 0. A. (1978). Nitrate levels in edible plant parts. In Nielsen and MacDonald’s Nitrogen in the Environment, Vol. 2, pp. 20 l-2 19. Academic Press, New York. O.E.C.D. (1982). Good laboratory practice in the testing of chemicals, Paris. PATRUNO, A. (1984). Influenza dei fattori agronomici sul contenuto di nitrati nei prodotti agricoli. Riv. di .4,gron. 18, 79-9 I. VERONELLI, L. (196 1). Curnacrna. Garzanti. Italia.