Maataloustieteellinen Aikakauskirja Vol. 59: 425—430, 1987 The nitrate concentration of domestic vegetables on Helsinki market in summer and autumn 1984 SEIJA AHONEN and IRIS KUOKKANEN Helsinki University Dept, for Horticulture SF-00710 Helsinki PIRJO-LIISA PENTTILÄ Nat. Board of Trade and Consumer Interest, PB 9 SF-00531 Helsinki Abstract. Nitrate concentration of some domestic vegetables at Helsinki district market was studied during the summer and autumn months of the year 1984. The species were cabbage (Brassica oleracea var capitata), Chinese cabbage ( Brassicapekinensis) , kohlrabi (Brassica oleracea var gongylodes), turnip (Brassica rapa), carrot (Daucus Carola subsp. salivas) and crisp- head and butter head lettuce (Lactuca saliva var. capitata). The 395 samples were analysed with an ion specific electrode. There was a wide range of nitrate concentrations within each species. The mean con- centrations mg nitrates/kg of fresh weight were the following: butter head lettuce 1835, Chinese cabbage 1057, kohlrabi 1008, crisphead lettuce 964, turnip 908, cabbage 607 and carrot 264. The nitrate concentration of butter head lettuce in the autumn was more than twice as high as that in the summer, and vice versa as tocabbage samples. The nitrate concentration of carrot samples in the summer was about 40 % higher than in the autumn. Index words: butter head lettuce, cabbage, carrot, Chinese cabbage, crisphead lettuce, kohlrabi, nitrate, turnip Introduction cording to Codex Alimentarius-commission Nitrate and nitrite in human food might the acceptable daily intake or ADI-value for have some negative influences on health. Ac- potassium and sodium nitrate is o—s0—5 mg and This investigation was committed at Helsinki Uni- versity, Department for Horticulture, on the initial of Na- tional Board of Trade and Consumer Interest, its Depart- ment of Consumer Affairs. The responsible person at the Board was Pirjo-Liisa Penttilä. Vegetable samples were provided by this board, the study was planned and lead at Helsinki University by Seija Ahonen, and the samples analysed and data calculated by Iris Kuokkanen. 425 JOURNAL OF AGRICULTURAL SCIENCE IN FINLAND https://www.c-info.fi/en/info/?token=Bo_GPBrg1IZDfnBh.k8aEZr2M8LdUFey5SkFmng.b4QiQNadpluBIDWnLumcoxXrscV-vAPiX7Zp6PsVbDwUXzfXROBW4SSEcGejfA1m9uBguAjB7zQ-M2jfvT74WEkagTYhewaV-mRiWNQNU7HFK8tkGvqbAJHXl0BxwUAM9UIo5lQG4h_m-VjJHhwZaGFoJm-vuXEwnAEigsi7QGJpQcBcRxU8IQvmlWbFpsqYm-KpZ9F9JDBJEbgGaA3XtA5U4dt-qOA that of corresponding nitrites 0—0,2 mg per kilogram of body weight. The major part of nitrates in human nutri- tion is of vegetable origin. Specially fresh vegetables can contain considerable amounts of nitrates. There are several factors affecting the NOj-concentration of vegetables: spe- cies, cultivar, part of the plant, source of the nutrient nitrogen, other nutrients, time of harvest and several environmental factors as light, temperature and humidity. There has been few studies on the nitrate concentration of vegetables in Finland. In one earlier Finnish review (Anon 1983) it has been calculated, that potato is, because of its great consumption, the most important vegetabil source of nitrates. The NO,-con- centration of potatoes on Finnish market was studied by means of the National Board of Trade and Consumer Interest in the year 1983 (Mäkäräinen 1984). As regards the major vegetable species, there hasn’t recently been studies of this kind in our country. So the Na- tional Board of Trade and Consumer Interest commanced in the year 1984 a study on the nitrate concentration of domestic vegetables on Helsinki district fresh market. tion. Species that are known to contain little nitrates, e.g. onion, were excluded, and so were those that are mainly rawmaterial for food industry, e.g. spinach and redbeet. Vegetable species chosen and numbers of samples gathered were the following: cabbage (89), Chinese cabbage (60), kohlrabi (21), turnip (32), carrot (96), crisphead lettuce (43) and butter head lettuce (54), 395 samples in all. From them 78 samples were organically grown vegetables. Nitrate concentrations were measured with the ion specific Orion Research electrode, the reference electrode being Double Junction Reference Electrode type 92-02. Sample size of different species varied from 3 to 15 pieces, the mean size being 5 pieces. Two parallel nitrate determinations were made from each sample. The nitrate concentration of each sample was determined of fresh weight by extracting nitrate ions into 0,01 N KH 2P04-solution: 50 grams’ sample to 200 millilitres was ho- mogenized for two minutes, and the nitrate concentration was measured immediately after filtering. It was calculated as mg nitrates in a kilogram of fresh weight (FW). Material and methods The study aimed at determining the average nitrate contents of some vegetable species on Helsinki district fresh market and the pos- sible variation in this contents due to time of harvest and method of growing (conven- tional vs. organic). All the samples were of domestic origin. The samples from con- ventionally grown products were taken main- ly from the vegetable market of the food wholesale market centre of Helsinki city, preferably straight from growers. Samples were also taken from market places and retail stores. Samples from vegetables that were announced to be organically grown were taken at health food industry wholesale and retail stores. Both leaf and root vegetables typical of freshmarket were taken into the investiga- Results Range of nitrate concentrations The range of the nitrate concentrations of each vegetable species is presented in table 1. Butter head lettuce had the highest mean concentration of nitrates, 1 835 mg/kg FW, and carrot the lowest, 264 mg/kg FW. The widest range in concentrations was found in crisphead lettuce and cabbage, and the smallest in kohlrabi and Chinese cabbage. Effect of sampling time on nitrate concentration In five of the seven species nitrate con- centration was higher in the summer samples 426 Table 1. Range of nitrate concentration of different vegetable species on Helsinki market summer and autumn 1984. Species Number of Nitrates mg/kg FW samples mean range Butter head lettuce 55 1835 175—3898 Chinese cabbage 60 1057 173—2126 Kohlrabi 21 1008 195—1737 Turnip 32 908 124—2658 Crisphead lettuce 40 964 85—3544 Cabbage 89 607 64—1949 Carrot 96 264 39—744 (table 2). The mean concentration of cabbage samples taken in the summer was almost twice as high as that of the samples taken in the autumn. The mean value for carrot samples in the summer was roughly 40 % higher than for those taken in the autumn. In two species there was a trend clearly opposite to the other species. In the autumn crisphead lettuce samples had a mean nitrate concentration 62 % higher than in the sum- mer. The difference was even more clear in butter head lettuce: the autumn samples' con- centration of nitrates was about 2.3-fold com- pared with that of the summer samples. Table 2. NOj-concentration mg NO,/kg FW of each vegetable species in summer (18. 6.—17. 8. 84) and au- tumn (26. 9.-28. 11. 84) samples. Species Summer samples Autumn samples n mean range n mean range Butter head lettuce 24 1050 175—2126 31 2443 284—3367 Chinese cabbage 12 964 230—1488 48 1081 266—2126 Kohlrabi 16 923 195—1737 5 734 390—1063 Turnip 14 1094 137—2304 18 762 124—2658 Crisphead lettuce 17 662 85-2481 23 1070 443-3544 Cabbage 32 812 120—1772 57 412 64—1949 Carrot 33 326 53—744 63 231 39—567 Table 3. The distribution (%) in various N03 -concentration classes of cabbage, Chinese cabbage and carrot. O = organically, C = conventionally grown. Samples taken 26. 9. 28. 11. 84. Cabbage mg N0 3/kg FW x n <250 250—500 500—750 750—1000 1000—1250 > 1250 O 394 17 53 29 12 0 0 6 C 422 40 25 51 18 2 2 2 Chinese cabbage mg NO,/kg FW \ n <5OO 500—1000 1000—1500 1500—2000 >2OOO O 892 12 25 42 8 17 8 O 1115 36 8 36 39 11 6 Carrot mg NO,/kg FW x n 5OO O 127 15 13 60 20 7 0 0 C 206 48 17 46 17 10 8 2 427 Nitrate concentration of organic and conventional samples As the number of organically grown sam- ples in the summer was small, one to six, com- pared to that of conventionally grown, only the autumn samples of three species are given attention to (table 3). Half of the organic cabbage samples in the autumn had nitrates less than 250 mg/kg FW, while half of the conventional samples belonged to the con- centration class 250—500. In both groups 94 % of samples had nitrates less than 750 mg/kg FW. A fourth of organic Chinese cabbage sam- ples had nitrates less than 500 mg/kg FW, and of conventional samples 8 %. On the other hand, a fourth of organic samples had nitrates over 1500mg/kg FW, while the corresponding percentage for conventional samples is 17. About two thirds of both organic and conven- tional carrot samples had nitrates less than 200 mg/kg FW. The development of nitrate concentrations throughout the sampling period In cabbage and carrot a diminishing trend is found in nitrate concentrations towards autumn (figure 1). However, the last two monthly means of nitrate concentration in cabbage are higher than that from the pre- vious month. The nitrate concentration of carrot samples was usually about a half of that of cabbage. From butter head lettuce least nitrates were found in samples taken in June (x 885 mg/ kg FW) and highest concentrations in No- vember (x 2685 mg/kg FW) (figure 2). The corresponding nitrate concentrations for crisp- head lettuce are 447 mg/kgFW in August and 1976 mg/kg FW in November. From August to October the mean concentrations for butter head lettuce nitrates were more than twice as high as those of crisphead lettuce. Discussion Corre and Breimer (1979) grouped vege- table species according to the so called natural limits for their maximum nitrate concentra- tions. According to them these limits, as mg NQ 3/kg FW, are the following: lettuce and Chinese cabbage over 2500, kohlrabi 1000— 2500, carrot and cabbage 500—1000. In cer- tain unfavourableconditions these concentra- tions can, however, rise even threefold (Anon 1984). The maximum concentrations detected in our investigation fitted quite well in these frames. Only cabbage had a maximum value, 1772, higher than the natural limits for it. Different types and cultivars within one Fig. 1. Monthly nitrate concentration means and num- ber of cabbage and carrot samples. Fig. 2. Monthly nitrate concentration means and num- ber of butter head and crisphead lettuce samples. 428 vegetable species are known to contain nitrates in different amounts. For example crisp- head lettuce has earlier been found to con- tain more nitrates than butter head types (Maynard et al. 1976). In agreement with the results of Lönberg et ai. 1985, in our in- vestigation crisphead lettuce contained nitrates less than butter head lettuce did, specially in the autumn months. Light has an effect on nitrate accumulation in a plant, as it in- fluences the activity of its nitrate reducing enzymes (Corre & Breimer 1979). The au- tumn months of the year 1984 were excep- tionally cloudy. This might to some extent explain the high nitrate concentration of lettuce and crisphead lettuce harvested in November. Moreover, samples late in the au- tumn were mostly taken from greenhouse grown products. Lettuce grown in greenhouse has been found to contain greater amounts of nitrates than field grown (von Seitz 1984). The nitrate concentration means of organi- cally grown products were usually lower than those of conventionally grown. Flowever, also among these samples there were some with high nitrate concentration. Nitrate concentration means received in this study were equal to or lower than those from earlier studies in Finland. The mean nitrate concentrations mg/kg FW from earlier Finn- ish studies (Anon 1983) and those in our study, correspondingly, are the following: Chinese cabbage 3475/1057, kohlrabi 2210/ 1008, carrot 279/264 and butter head lettuce 2124/1835. Only cabbage had a mean value, 607, a little higher than that of earlier studies, 561. The Swedish study mentioned above (Lön- berg et ai. 1985) deals with an annual de- velopment of nitrate concentration in some vegetable species on market. It gives a nitrate concentration mean for cabbage (620 mg/kg FW) and Chinese cabbage (1100 mg/kg FW) very similar to those of our investigation (607 and 1057 mg/kg FW, correspondingly). The Swedish study gives a nitrate concentration mean for carrot, 1100 mg, fourhold to ours, and that of butter head lettuce, 2900 mg/kg FW, about 60 ®7o higher than the Finnish mean concentrations. However, in our study the sampling period didn’t exceed in winter months with poorest light conditions, which might have an effect on the butter head lettuce concentrations of nitrates. During the past few years some European countries have set the highest acceptable ni- trate concentration for lettuce on the market. The upper limits, depending on the country, are between 3500 to 5000 mg nitrates/kg FW. Only two samples in our study had concentra- tions higher than 3500 mg/kg. Conclusions Time of year seems to have an influence on the nitrate concentration of some vegetable species. When growing lettuce in poor light conditions, much attention should be paid to cultural practices, specially nitrogen fer- tilizing. Domestic fresh market vegetables in sum- mer and autumn can be regarded safe as regards their nitrate concentration. References Anon 1983. NONO-työryhmän mietintö. Nitraatti, nit- riitti ja N-nitrosoyhdisteet elintarvikkeissa. Elinkeino- hallitus. 66 p. Helsinki. Anon 1984. Nitrat-Kongress in Karlsruhe. Deutscher Gartenbau 39: 1726. Corre, W.J. & Breimer, T. 1979. Nitrate and nitrite in vegetables. 85 p. Wageningen. Lönberg, E., Everitt, G. & Mattsson, P. 1985. Nitrat i grönsaker. Vär föda 37: 316—322. Maynard, D.N., Barker, A.V., Minotti, P.L. & Peck, 429 N,H. 1976. Nitrate accumulation in vegetables. Adv. in Agron. 28: 71—llB. Seitz, P. von 1984. Ergebnisse von Nitratuntersuchungen. Gemiise 12; 420—421. Mäkäräinen, E. 1984. Suomalaisen ruokaperunan nit- raattipitoisuus. Elinkeinohallitus, Kuluttaja-asiain osas- ton julkaisuja. Sarja A 6/84. 84 p. Helsinki. Ms received October 15, 1987 SELOSTUS Kotimaisten vihannesten nitraattipitoisuus Helsingin markkinoilla kesällä ja syksyllä 1984 Seija Ahonen ja Iris Kuokkanen Helsingin yliopisto Puutarhatieteen laitos SF-00710 Helsinki Pirjo-Liisa Penttilä Elinkeinohallitus Kuluttaja-asiainosasto PL 9. SF-00531 Helsinki Eräiden Helsingin seudulla kaupan olevien kotimaisten vihannesten nitraattipitoisuutta seurattiin Elinkeinohal- lituksen toimesta kesällä ja syksyllä 1984. Vihanneslajit olivat keräkaali (Brassica oleracea var. capilala), salaat- tikiinankaali ( Brassica pekinensis), kyssäkaali ( Brassica oleracea var, gongylodes), nauris (Brassica rapa), pork- kana (Daucus carota subsp. Carola) sekä pehmeä jara- pea keräsalaatti (Lactuca saliva var. capilala). Näytteitä oli 395, joista viidesosa oli ilmoitettu luonnonmukaisesti viljellyiksi. Näytteiden nitraattipitoisuus määritettiin ionispesifisellä elektrodilla Helsingin yliopiston puutar- hatieteen laitoksella. Kunkin vihanneslajinnitraattipitoisuus vaihteli suuresti. Näytteiden nitraattipitoisuuden keskiarvot milligrammoi- na nitraatteja tuorepainokiloa kohti olivat seuraavat: peh- meä keräsalaatti 1835, kiinankaali 1057,kyssäkaali 1008, rapea keräsalaatti 964, nauris 908, keräkaali 607 japork- kana 264. Syksyn pehmeän keräsalaatin näytteiden nit- raattipitoisuus oli yli kaksinkertainen verrattuna kesän näytteisiin, keräkaalilla päin vastoin. Kesällä porkkana- näytteiden nitraattipitoisuuden keskiarvo oli noin 40 % suurempi kuin syksyllä. 430