STUDIES ON THE NITRATE CONTENT OF VEGETABLES AT SOURCE AND UNDER DIFFERENT METHODS OF STORAGE AND ENVIRONMENT

(1)

AND UNDER DIFFERENT METHODS OF STORAGE AND ENVIRONMENT

Indira Sarangthem

Department of Soil Science and Agricultural Chemistry, College of Agriculture, Central Agricultural University, Imphal.

Abstract

Studies on the nitrate content of vegetables at source and under different methods of storage and environment under Manipur condition was taken up to study in five district of Manipur 1) Imphal East, 2) Imphal West, 3) Bishnupur, 4) Thoubal and 5) Senapati districts. Random sampling was adopted due to the unavailability of requisite no. of farmers in each village as the particular crop was not cultivated widely. Fudge and Truman methods with some modification was used for estimation of Nitrite and nitroxylenol method of Lip and Dolberg for Nitrate. Fresh vegetables contain higher levels of Nitrate compare to Nitrite. However the vegetables under storage condition contain higher values of Nitrite compare to Nitrate. Wide variation of nitrate content in freshly harvested sample may be due to difference in cultivation practices. Rulkawska B reported that significantly lower nitrate content in patoto was observed in ecological farm and almost twice higher in conventional farm. Decrease in Nitrate content after storage may be due to the reduction of Nitrate by micro-organism during storage into Nitrite. This finding was similar with the finding of Chung J.C. et al.

Key wards : Nitrite, Nitrate, Vegetables,.

I. INTRODUCTION

In the recent years people eat more fresh vegetable than in past as the supermarkets having proper storing facilities for vegetables have responded to provide a wide range of vegetables year round. Out of various nutrients, these fresh vegetables are also known to contain a number of anti-nutritional or toxic substances of which nitrate is one (National Academy of Science 1973) Nitrate content has a wide variation between species. It is also found in trace in drinking water. The presence of nitrate in soil is essential for the existence of plant which in turn also accumulates nitrate. The degree of accumulation was responded to be effective by different agro-climatic and environmental factors (Barker et al 1971). If excess nitrogen is present in the soil the nitrate content may be too high, particularly when some other nutrients are not adequate, whereas nitrite content may be low. However the plant that accumulates very high amount of nitrate may also content significant amount of nitrite (Rechardson et al 1970, Seciliano et al 1975).Post-harvest or improper storage of vegetable may lead to the accumulation of nitrite arising from the reduction of nitrate caused by plant enzymes or microbial activity (Heisler et al 1974, Phillips 1968).

Excessive dietary nitrate may cause a life threatening haemoglobin malfunction in infant and may convert to carcinogenic nitrosomines during digestion. Vegetables are main source of dietary nitrate and researchers agree that efforts to lower nitrate level in leafy vegetables are warranted. The 1974, W.H.O. established an acceptable daily intake of 220 mg nitrate for an adult.

II. MATERIALS AND METHODS

(2)

Volume 02, Issue 12, [December- 2016]

February for Rabi from five districts of Manipur viz. Imphal East, Imphal West, Bishnupur, Thoubal and Senapati to be used the next day and adequate amount of the same sample were stored for 10 days for using as “Stored Sample”.

For estimation of nitrate Fredge and Trueman method with certain modification was adopted. Nitroxylenol method of Lip and Dolberg for nitrite as given by Heisler et al was adopted with some modifications.

20 g of dried, washed and cut sample was blended with 20 ml of water and filtered. The filtrate was treated with activated charcoal to decolourise. The volume was made up to 50 ml and pH was determined. Then volume was finally made up to 100 ml and 3-4 drops of toluene was added to avoid fungal growth and kept in the refrigerator.

Determination of nitrate (Fredge and Trueman method):

2 ml of Al(OH)3 suspension was added to 5 ml of the solution and the volume was made up to 50 ml from which 5 ml was pipetted out into 50 ml volumetric flask. Diluted with about 30 ml of distilled water, then 5 ml freshly prepared sulphanilamide solution and finally added 2 ml of freshly prepared solution of N-(1-naphthyletlylenediaminedihydrochloride (0.5%)) and the volume was finally made upto the mark. The contents were mixed well and after standing for 20 min, absorvance was read at 540 nm. A blank determination was also carried out. A standard curve was similarly prepared using a standard solution containing 0-10 mg nitrate/ml the result was expressed as ppm. Determination of Nitrate (The nitroxylenol method of Lip and Dolberg as given by Heisler et al) :

2 ml of vegetable extract was pipetted into a conical flask (100 ml) wrapped with aluminium foil. 0.1g of 3,4-Dimethylphenol was added and followed by careful addition of 10 ml concentrated H2SO4. The flask was placed in an ice bath and 25 ml of distilled water was added slowly. The reaction was allowed to proceed for 30 min. The entire reaction mixture with washing was then transferred in previously cleaned distillation tube of auto analyzer. The nitroxylenols were distilled off for 9 min and the distillate was collected in 150 ml conical flask containing 6 ml of 50% NaOH. The distillate was put in hot water bath till the volume was about 20-30 ml. Cooled the distillate and transferred into a 50 ml volumetric flask and made up the volume with distilled water. The absorbance was measured at 430 nm. A blank determination was also carried out.

Nitrate and Nitrite content of potato at Source and Storage Conditions.

Name of the District

Name of the Village

Samples Source Storage

pH (ppm

)

NO3¯ (ppm)

NO2¯ (ppm)

pH NO3¯ (ppm)

NO2¯ (ppm)

Thoubal Kakching Keirak

S1 6.09 35.0 22.5 6.11 17.5 32.5

- do - S2 6.14 57.5 40.0 6.13 17.5 32.5

Imphal West Mayang Imphal

S3 6.26 22.5 40.0 6.13 10 60.0

- do - S4 6.05 2

Bishnupur Khoijuman S5 6.18 35.0 35.0 6.01 42.5 32.5

- do - S6 6.15 30.0 27.5 6.02 42.5 40.0

Nitrate and Nitrite content of Chillies at Source and Storage Conditions Name of the

District

(3)

(ppm )

(ppm) (ppm) (ppm) (ppm)

Thoubal Kakching Keirak

S7 5.85 62.50 5.63 5.79 54.00 8.13 S8 6.13 50.00 5.63 6.12 41.50 7.95 S9 5.66 43.75 1.88 5.50 38.75 5.35 S10 5.94 50.00 5.00 5.95 42.00 9.25 S11 6.23 43.75 5.63 6.20 45.50 5.13 S12 5.86 67.50 5.00 5.96 51.75 6.75 S13 5.18 75.00 8.00 5.25 70.00 9.00 S14 5.55 37.00 6.00 5.43 39.00 6.50 S15 5.65 50.00 6.50 5.50 42.00 8.00 S16 5.58 100.00 6.50 5.60 80.00 7.00 S17 5.55 97.50 5.00 5.39 77.50 6.50 S18 5.78 35.00 125.00 5.65 22.5 130.00 S19 6.92 22.5 2.5 6.50 17.5 4.00

Nitrate and Nitrite content of Cabbage Name of the

District

pH (ppm

)

NO3¯ (ppm)

NO2¯ (ppm)

pH NO3¯ (ppm)

NO2¯ (ppm)

Thoubal Thoubal S20 5.31 35.00 85.00 5.62 50.00 35.00 Bishnupur Khoijuman S21 6.50 155.00 3.00 6.23 145.00 3.00

Senapati Tispari S22 6.17 35.00 4.00 6.20 47.50 5.00 S23 6.02 35.00 4.00 6.25 60.00 7.00 Nitrate and Nitrite content of Cauliflower

Name of the District

pH (ppm

)

NO3¯ (ppm)

NO2¯ (ppm)

pH NO3¯ (ppm)

NO2 -(ppm)

Thoubal Lilong S24 6.46 5.00 170 6.71 5.00 185.00

S25 6.34 35.00 45.00 6.30 5.00 40.00

Bishnupur S26 6.92 155.00 3.00 6.85 140.00 3.00

Imphal West Mayang Imphal

(4)

Volume 02, Issue 12, [December- 2016] III. DISCUSSION

Nitrate content of potato differ between the freshly collected sample of different places. It may be due to the difference in the amount of nitrogeneous fertilizers used. The same comment was also given by Mark Schonbeck 1988.

The highest nitrate content (57.5 ppm) is recorded in S2 and it is must lower than that in slovenia (i.e. 158 mg/kg recorded by Surin J et al 1988) and the lowest (22.5) one is recorded in S3.

Nitrite content if potato in our observation is much higher than the result of investigation obtained in Slovenia (0.5 ppm) and other countries. The highest nitrite content is observed (40 ppm) in S2 and S3 and the lowest (22.5 ppm) in S1. No direct relationship has been established for the accumulation of nitrates and nitrites in vegetable. These findings are in the same trend with the finding of Murokh VI.

Nitrate content of the potato after 10 days of storage decreases and Nitrite content increases in almost all sample. It may be due to the reduction of nitrate by plant enzyme or microbial activity which is similar to the finding of M.S. teotia et al 1988.

After 10 days of storage, the highest content of nitrate and nitrite are found in S5, S6 (42.5 ppm) and S3 (60.00 ppm) respectively. The lowest content of nitrate and nitrite are found in S3 (10 ppm) and S1, S2 (32.5 ppm) respectively. Range of nitrate in the fresh potato is 22.5-40 ppm and that of nitrite is 22.5-40 ppm. On the other hand that of nitrate and nitrite under storage condition are in the range of (10-42.5 ppm) and (32.5-60.00 ppm).

Wide variation of nitrate content in freshly harvested sample of chillies may be due to the difference in cultivation practices. The highest content of nitrate in chillies recorded 100 ppm in S16 and the lowest as 22.5 ppm in S19. Except in one sample (S18), nitrite content in freshly harvested sample is 8 ppm or less. In fresh samples, the highest nitrite content is 125 ppm (S18) and the lowest is 1.88 ppm (S9).

Nitrate content of chillies after 10 days of storage decreases and nitrite increases in almost all the sample similar trend was also reported by Chung J.C. et al. After storage the highest nitrate content was 80 ppm (S16) and the lowest was 17.5 (S19); the highest nitrite content was 130.0 (S18) and the lowest was 4.00 ppm (S19).

The highest nitrate content in fresh cabbage was found in S21 and the lowest as 35.00 ppm in S20, S22, S23. The highest nitrite content was found as 85.00 ppm in S20 and the lowest as 3.00 ppm in S21.

After storage of cabbage for 10 days, the highest nitrate content was 145.00 ppm is S21 and the lowest was 47.50 ppm in S22. The highest nitrite content was 35.00 ppm in S20 and the lowest content was 3.00 ppm in S22. After storage in most of the sample nitrate content decreases and nitrite content increases Chung J.C. reported a similar finding that during storage at ambient temperature (22 ± 1OC) nitrate level in vegetable dropped significantly from the third day while nitrite levels increased dramatically from the fourth day of storage.Nitrate content of freshly harvested cauliflower also varies. This may be due to different agricultural practices.

In fresh cauliflower, the highest nitrate content was 190.00 ppm and the lowest was 5.00 ppm in S27 and S24 respectively and highest Nitrite content was 170 (S24) and the lowest was 3 ppm (S26, S27). After storage, the highest nitrate content was 165.00 ppm (S27) and the lowest was 5.00 ppm (S24, S25); The highest nitrite content was 185.00 ppm (S24) and the lowest was 3.00 ppm (S26).

Both Nitrate and Nitrite content in fresh vegetable observed so far in the state of Manipur are very must lower than that of others reported in literature.

BIBLIOGRAPHY

[1] Barker A.V.,Peck NH, Mac Donald GE(1971) “Nitrate accumulation in vegetable, Spinach grown in upland soil”

Agron J 63:126-129.

[2] Chung J.C., Chouss, Hwang DF “Changes in nitrate and nitrite content of four vegetables during storage at

(5)

[3] Kulkarni, S.G., Chauhan A.S. and Ramana K.V.R. “Nitrate and Nitrite Content in Some Important South Indian

Vegetables” J.Food Sci.Technol.,2003,Vol.40. No5, 518-520.

1988 New Alchemy Institute, Inc. 237 Hatchuille Road East Falmouth, MA02536. www. Fuzzylu.com/greencenter/

[5] M.S. Teotia, S.K. Berry, S.G. Kulkarni and Sukhuir kour 1988 “Nitrate and Nitrite contents in vegetable” J.of food

Sc. Technology 1988 vol 25 no. 7 Page 272-275.

[6] Murata M, Ishinaga M. “Nitrate and Nitrite contents in vegetable juice, tea beverage and mineral water on the

market” Hiroshima Bunka two year college, 3-5-1, Nagatsukanishi, Asaminami-ku, Hiroshimashi, Hiroshima 731-0136 Japan.

[7] Murokh VI “Nitrate and Nitrite content of food products of plant origin grown with the use of mineral fertilizers”

[8] National Academy of Science(1973) “Toxicants occurring naturally in Food” 2nd edn. Committee on Food

Protection, National Research Council, National Academy of Sience, Washington D.C.

[9] Ohtsuki R, Kikugawak.: “ Nitro samine formation from vegetables produce in Japan” School of Pharmacy Tokyo

University of Pharmacy and life science.

[10]Okafor PN, Abara CN, Nwabuko CU, Ogbonna U, “ Assessmnt of cyanogenic potential, nitrate and nitrite contents

and trypsin inhibitor activity of some Nigerian legumes” Department of Chemical Sciences (Biochemistry Unit), Fedenal University of Agriculture, Omudike, Nigeria, ezenomyeob@ Yahoo.com.

[11]Petersen A, Stoltzes. “Nitrate and Nitrite in vegetables on the Danish market: content and intake” of Food Research

and Nutrition Soborg, Denmark. [email protected].

[12]Phillips,W.E.J., Changes in the nitrate and nitrite contents of fresh and processed spinach during storage. J. agric.

Fd. Chem., 1968, 16, 88

[13]Richardson, W.D. The occurrence of “Nitrate in vegetable foods, cured meats and elsewhere”. J. Am. Chem. Soc.

1907. 29, 1757.

[14]Roszczenko A, Rogals Ka J, Potapczok L, Kleczyneska A : “Influence of thermal processing and storage on the

content of nitrates and nitrites in chosen vegetables from Padlasie Prouince” Zaklad Toksykologii AMul. Meckiewiecza ZC, 15-222 Bialys tok. Pikutin @ WP.Pl.

[15]Rulkawska B “ Nitrate and Nitrite content in Potatoes from Ecological and conventional farms” Katedra Dietetyki i

Zywnosci Fundkojonalnej Szkola Glowna Gospodarstwa Wiejskiego 02-787 Warszawa, ul. Nowoursynowska 166.

[16]Siciliano, J., Krulick, S., Heisler E.G., Schevartz, J.H. and White, J.H. Jr. Nitrate and nitrite contents of some fresh

and processed market vegetables. J. agric. Fd Chem., 1975, 23, 461.

[17]Susin J, Kmecl V, Gregorcic A: “A survey of nitrate and nitrite content of fruit and vegetables grown in Slowvia

during 1996-2002” Agriculture Institute of Slowvia, Central Laboratories, Ljubljana, Slowvia. [email protected].

[18]Zhong W, Huc, Wang M: “Nitrate and nitrite in vegetables from north China on content and intake” Laboratory of