Maataloustieteellinen A ikakauskirja Vol. 56: 23—31, 1984 Experiments on the cultivation of dandelion for salad use. II The nutritive value and intrinsic quality of dandelion leaves TAINA KUUSI, 1 KIRSTI HÄRDH2 and HELENA KANON 2 ' Technical Research Centre of Finland, Food Research Laboratory, SF-02150 ESPOO 15, Finland 2 Department of Horticulture, University of Helsinki, SF-00710 HELSINKI 71, Finland Abstract. In an extensive investigation concerning the utilization of dandelion, the feasi- bility of cultivating the dandelion for salad use has been studied. Properties making up the intrinsic quality, viz., nutritive value and content of nitrates, have been used as one criterion of suitability. The study material consisted of 11 Finnish agamospecies selected for their mild taste, and two middle-European cultivars, ’Vollherziger verbesserter’ and ’Vert de Mont- magny’. The effects of cultivation methods were also studied: two levels of fertilization, and covering with black polyethelene film, black fibre cloth and bark humus layers of various thicknesses were compared. As criteria of the nutritive value, dry matter, soluble solids, mineral contents, in particular Ca, Mg, Fe and Mn, and vitamin C, were measured. The nitrate content as a criterion of intrinsic quality was also studied. In spring, the dry matter of the rosettes averaged 12.3 %, in late summer 17.1 %. In spring the average content of soluble solids was 5.5 %, the mineral content 1.6 %. The amounts of the individually analyzed minerals Ca, Mg, Fe and Mn deviated somewhat from values in the literature, probably due to the methods of cultivation. The amount of vitamin C in spring was on average 42 mg/100 g, varying between 29 and 53 mg/100 g. The nitrate content was low: at highest 660 mg N03 /kg fresh weight. The influence of fertilizing level was slight. Even the levels of minerals and nitrates were not increased at the higher level of fertilization. Coverings had clear-cut effects. Where the covering effectively eliminated light, i.e. when black film, black fibre cloth or thick bark humus layer was used, the dry matter, soluble so- lids, mineral content and vitamin C values were decreased and the nitrate values increased. Compared with other plants used as salad greens, the nutritive value and particularly the amount of vitamin C in dandelion are much higher, although the values are considerably decreased if the leaves are bleached. If the mild tasting types studied here were cultivated, bleaching would not be necessary. The nitrate content in dandelion is generally low as com- pared with many other plants used as salad greens. Index words: dandelion, salad greens, agaraospecies, cultivation methods, fertilization, bleaching, nutritive value, vitamin C, nitrates 23 JOURNAL OF AGRICULTURAL SCIENCE IN FINLAND https://www.c-info.fi/en/info/?token=DsuwYyY-kGFnhJtG.JFIMwlPNpj1iz6uEgEq4ag.6DYU2b-tROZTTjkQ9vWs4sMaFwcLmLAa-hk4P5mjVZijGVO3XcD36X_ldRcNl89ybtv6GZ2c5dqpF8J3VGppxYkV8KkXxXKzuwY4YaOhDxW4mzQlTBvDt9I3QztE2yPT1J4SBAT5Ij_LBm4mnCq4gXBagnSF7853tj2u0GPiC6iYrwQV3_r_fRx3zEhCIrXKoeDLHR0H_apC0SJzUQ Introduction The dandelion is a wild-growing plant which has long been collected for its food and therapeutic value. A Finnish working group has for several years now been investi- gating the possibility of its extended use, par- ticularly the cultivation of mild-tasting types for use as a salad green. The main results of this part of the investigation are reported separately (see Kuusi et ai 1984; Kanon 1982). Here the nutritive value and some other properties making up the ’intrinsic quality’ will be reported. Although informa- tion on the nutritive value of dandelion leaves can be found in various nutrition tables (Turpeinen 1978; European Produc- tivity Agency 1961; Souci et al. 1962), the influence of methods of cultivation on the nutritive value has not been reported. These questions have been explored here. Other re- sults, e.g. the botanical-genetic investiga- tions of the dandelion material (Rousi et al. 1984) are being reported elsewhere. The properties chosen to indicate the nu- tritive value and intrinsic quality properties were in part chemical, in part sensory. Chem- ical nutritive properties were the dry mat- ter, soluble dry matter, vitamin C and mineral content. In addition, in a small series the contents of calcium, magnesium, iron and manganese were studied. Concerning the in- trinsic quality, the amount of nitrate was as- sayed in a small series. The sensory proper- ties, including the general evaluation as salad green and measure of bitterness, are reported in part I of this article (see Kuusi et ai. 1984). Material and methods The material consisted of 11 Finnish mild- tasting agamospecies, chosen from 69 agamo- species for cultivation experiments on the basis of taste, vigour of growth and several other properties (see Rousi et al. 1984,Kuusi et ai. 1984, Kanon 1982). Two commercial varieties, ’Vollherziger, verbesserter’ of Swiss origin and ’Vert de Montmagny’ of French origin, were included for compari- son. The list of the agamospecies and varie- ties is seen in the tables. Seeds were ger- minated in peat pots and grown in a glass- house for 6 weeks before being transferred to the open field at the end of May. The experi- mental design was the split plots method. The properties of the different agamo- species and varieties were compared in a first experiment, and the influence of fertilization at 2 levels of application, using ’Vert de Montmagny’, in a second. At the same time, the influence of various covering methods was investigated, with the alternatives being no covering, different thicknesses of bark humus, black polyethylene film and black fibre cloth. The details are given in part I of this article (Kuusi et al. 1984) and in the pro gradu-work of Kanon (1982). The quality analyses and evaluations were done in August of the first summer and the main investigations at harvest the following May and June. The analytical methods were those regular- ly used in the Food Research Laboratory. Dry matter was obtained after drying at 100 —lO5°C. Soluble solids were measured by refractometry (Horwitz 1975) from extracts obtained as follows: leaves were washed and homogenized with a Bamix mixer, and the homogenates were kept frozen in gauze bags. After thawing, the juice was pressed out and the sediment allowed to settle to the bottom. The clear top liquid was taken for the mea- surement. Mineral content was assayed by ashing at 550°C (Horwitz 1975), and acid- insoluble ash was also assayed when necessary (Anon, 1942). Ca, Mg, Fe and Mn were as- sayed from acid-soluble ash by atomic ab- sorption spectrophotometry. Nitrates were as- sayed with an Orion 93—07 nitrate-specific electrode (Anon. 1977). Vitamin C was as- sayed from metaphosphoric acid extracts of the leaves colorimetrically by using Till- mann’s reagent (Freed 1966). In some cases 24 the reductone correction was done, but de- hydroascorbic acid was not taken into ac- count. Results The analytical results are presented in Tables I—61 —6 for each property separately. First, the different agamospecies and varie- ties are compared for that property and then the influence of fertilization and covering is reported. Table 1 shows the results for dry matter. It is seen that the average dry matter for all agamospecies and varieties in spring was 12.3 °/o when cultivation was in light and 7.4 % when cultivation was in darkness. In late summer the average in light was still higher, 17.1 %. In tables of the literature the values vary between 14 and 15 °/o (Turpei- nen 1978; Anon. 1961; Souci 1962), while for leaves of spring dandelionFranke and Kens- bock(l9Bl) give 13 and 15.7 %. The content of dry matter evidently depends on the growth phase of the leaves, and is lower in young spring leaves, which are best for salad use, than in the mature leaves of late sum- mer. Darkness decreases the dry matter be- cause photosynthesis is hindered. No clear differences were observed between the Fin- nish and the foreign dandelions. The fertilizing level had no influence on the dry matter, but the method of cover- ing was important: black film, black fibre cloth and thick bark humus covering de- creased the dry matter due to the darkening effect and the thinner bark humus layer had no effect. The results for soluble solids in Table 2 vary in a similar way to the dry matter with light/darkness and spring/late summer. In spring in light the average was 5.5 %, in darkness 3.8 %, and in late summer in light higher at 6.2 °/o. The average values of the foreign varieties were the highest of the series both in spring and in late summer, but many of the Finnish agamospecies had values at the same level. In spring the soluble solids content was lowest in the small agamospecies T. hjeltii. Comparison of these values with the litera- ture is difficult, since the tables give only the calculated total carbohydrate. This varies between 7.5 and 8.6 % and is higher than the refractometric soluble solids give here. The influence of fertilizing level on the sol- uble solids was only slight. Influence of co- Table I. Dry matter (per cent) in leaves of different dandelion agamospecies and varieties, and the effect of different methods of cultivation DRY MATTER IN THE DIFFERENT AGAMOSPECIES AND VARIETIES Spring 1981 Summer 1980Agamospecies or variety In light In darkness In light Taraxacum aculeatum 12.9 7.3 16.0 T. datum 11.7 6.8 14.8 T. amplum 13.3 7.6 17.2 T. ancistrolobum 11.5 15.5 T. ekmanii 11.8 17.3 T. hemicydum 13.1 15.3 T. hjeltii 10.2 22.7 T. pallidipes 13.0 15.4 T. piceatum 13.1 18.2 T. sublaeticolor 13.2 18.4 T. tanyphyllum 12.3 8.4 17.1 ’Vollherziger’ 11.9 6.8 15.6 ’Vert de Montmagny’ 12.3 7.5 19.0 Averages: Finnish 12.4 7.5 17.1 12.1 7.2 17.3Foreign 12.3 7.4 17.1All EFFECT OF DIFFERENT METHODS OF CULTIVA- TION (VARIETY ’VERT DE MONTMAGNY’) Covering Fertilizing level 1x 2 x No covering 11.3 12.1 Bark humus 2.5 cm 13.0 12.7 » 5 cm 11.7 12.1 » 5 + 5 cm 9.5 8.9 Black film 6.6 6.4 —» and bark humus scm 7.7 8.8 Black fibre cloth 7.4 7.1 Average 9.6 9.7 25 Table 2. Soluble solids (per cent) in leaves of different dandelion agamospecies and varieties, and the effect of different methods of cultivation SOLUBLE SOLIDS OF DIFFERENT AGAMOSPECIES AND VARIETIES Spring 1981 Summer 1980Agamospecies or variety In light In darkness In light Taraxacum aculeatum 5.4 3.9 7.0 T. alatum 4.9 3.3 4.7 T. amplum 6.0 3.7 6.2 T. ancistrolobum 5.3 6.4 T. ekmanii 5.3 6.3 T. hemicyclum 5.7 6.3 T. hjeltii 3.8 5.7 T. pallidipes 5.8 6.5 T. piceatum 5.8 5.8 T. sublaeticolor 6.0 5.5 T. tanyphyllum 5.7 4.1 6.5 ’Vollherziger’ 6.3 3.6 6.9 ’Vert de Montmagny’ 5.8 4.0 6.5 Averages: Finnish 5.4 3.8 6.1 6.1 3.8 6.73.8 6.7Foreign 3.8 6.25.5All EFFECT OF DIFFERENT METHODS OF CULTIVA- TION (VARIETY ’VERT DE MONTMAGNY’) Covering Fertilizing level 1x 2 x No covering 5.1 5.3 Bark humus 2.5 cm 5.5 6.1 » 5 cm 5.6 6.0 » 5 + 5 cm 4.9 4.9 Black film 4.0 4.1 —» and bark humus scm 4.5 4.6 Black fibre cloth 4.3 4.5 Average 4.8 5.1 Table 3. Mineral content (per cent) of leaves in dif- ferent dandelion agamospecies and varieties, and the effect of different methods ofcultiva- tion MINERAL CONTENT OF DIFFERENT AGAMOSPECIES AND VARIETIES Spring 1981 Summer 1980Agamospecies or variety In light In darkness In light Taraxacum aculeatum 1.80 0.83 1.85 T. alatum 1.73 0.79 1.68 T. amplum 1.79 0.94 2.33 T. ancistrolobum 1.36 1.82 T. ekmanii 1.64 2.24 T. hemicyclum 1.62 1.85 T. hjeltii 1.71 3.19 T. pallidipes 1.40 1.89 T. piceatum 1.58 2.33 T. subiaeticolor 1.61 2.30 T. tanyphyllum 1.58 1.00 2.05 'Vollherziger' 1.44 0.74 1.78 'Vert de Montmagny' 1.57 0.90 2.15 Averages: Finnish 1.62 0.89 2.14 1.52 0.82 1.97Foreign 1.60 0.87 2.11All EFFECT OF DIFFERENT METHODS OF CULTIVA- TION (VARIETY ’VERT DE MONTMAGNY’) Covering Fertilizing level 1x 2 x No covering 1.39 1.41 Bark humus 2.5 cm 1.60 1.49 » 5 cm 1.37 1.45 » 5 + 5 cm 1.04 0.89 Black film 0.65 0.61 —» and bark humus scm 0.76 0.88 Black fibre cloth 0.84 0.74 Average 1.09 1.07 vering was similar to that for dry matter: ef- fective darkening lessened the values at both levels of fertilization, but the thin bark hu- mus layers had no effect. The mineral contents are shown in Table 3. Again, in spring the average values were higher in light (1.60 %) than in darkness (0.87 %) and in late summer higher still (2.11 °7o). The values of the Finnish dan- delions were somewhat higher than the for- eign ones in each series. The literature value of 2 % is between the spring and summer values obtained here. The mineral content responded to fertiliza- tion and covering in the same way as the dry matter: the higher level of fertilizing had no 26 effect, effective covering decreased the con- tent, and the thin bark humus layers had no effect. The contents of Ca, Mg, Fe and Mn deter- mined in one Finnish agamospecies and one forcing variety and shown in Table 4 are in good agreement. Relative to the literature (Souci 1962) values for Ca, 150—190 mg/ 100 g, the values obtained here, 182—195 mg/100 g, are at the upper limit. Conversely, for Mg the literature gives 36 mg/100 g, and our values of 29 mg/100 g are somewhat low. The differences may be due to the cultivation methods, particularly the addition of lime to the acid soils of Finland. For Fe, the tables give 3.0—3.1 mg/100 g, and thus the values of 9—14 mg/100 g obtained here are consid- erably higher. The high content of iron in the irrigation water may have been a contribut- ing factor. For Mn, Souci’s earlier value of 58 mg/100 g was obviously erroneous and it has since been corrected (1981/82) to 0.34 mg/100 g. The values obtained here, 0.58— 0.68 mg/100 g, are at the same level as this. The nitrate contents are seen in Table 5. Because it was assumed that dandelion does not accumulate nitrates, analyses were per- formed on only a few random samples. The values varied between 80 and 660 mg N0 3/kg fresh weight, which is a comparatively low level. No clear differences were found between the different agamospecies and varieties. Darkening caused a rise in the nitrate values, as expected (e.g. Mengel 1979). Values for comparison have not been found in the literature. The fertilizing level had no consistent ef- fect on the nitrate content in this restricted series. Covering increased the content, as darkening did in the above series. Table 4. Contents of selected metals in dandelion leaves (mg/100 g) Agamospecies or variety Ca Mg Fe Mn Taraxacum piceatum ’Vert de Montmagny’ 195 29.0 14 0.58 182 28.5 9 0.68 Vitamin C results are given in Table 6. To simplify the table, the values of vitamin C after formalin correction have been omitted, al- though such analyses were done in the later summer series. The difference between the total and corrected vitamin C was small: the average total vitamin C in 13 samples was 20.0 mg/100 g, while the corresponding cor- rected value was 18.2 mg/100 g. The diffe- rence was maximally 4 mg/100 g. According- ly, in all later analyses, separate assay for corrected vitamin C was considered unneces- sary. The average spring values in light were 42 mg/100 g with a range of 29—53 mg/100 g, and in darkness 14 mg/100 g, ranging from 11 to 16 mg/100 g. Cultivation in darkness Table 5. Nitrate content (mg NO,/kg fresh weight) of dandelion leaves in different agamospecies and varieties, and the effect of different methods of cultivation NITRATE CONTENT OF DIFFERENT AGAMOSPECIES AND VARIETIES Agamospecies or Spring 1981 Summer 1980 variety In lighi In darkness In light Taraxacum amplum 130 660 90 T. hemicyclum 80 260 610 T. hjeltii 200 T. subtaeticolor 90 180 270 T. (anyphyllum 300 'Vollherziger' 120 'Vert de Montmagny' 480 Averages: Finnish 100 367 294 Foreign 296 All 100 367 296 EFFECT OF DIFFERENT METHODS OF CULTIVA- TION (VARIETY ’VERT DE MONTMAGNY’) Covering Fertilizing level 1x 2 x No covering 100 160 Bark humus 5 + 5 cm 370 660 Black film 520 150 Average 330 323 27 28 Table 6. TotalvitaminCcontents(mg/100g)ofleaves of different dandelion agamospecies and varieties, and the effect of different methods of cultivation VITAMIN C CONTENT OF DIFFERENT AGAMOSPECIES AND VARIETIES Agamospecies or Spring 1981 Summer 1980 In light In darkness In light Taraxacum aculeatum 46 13 19 T. alatum 47 15 21 T. amplum 53 16 18 T. ancistrolobum 44 18 T. ekmanii 42 26 T. hemicyclum 35 17 T. hjellii 33 17 T. pallidipes 43 T. picealum 48 26 T. sublaeticolor 37 23 T. lanyphyllum 29 11 19 'Vollherziger' 49 14 24 'Vert de Montmagny' 41 13 25 Averages: Finnish 42 14 19 Foreign 45 14 25 All 42 14 20 EFFECT OF DIFFERENT METHODS OF CULTIVA- TION (VARIETY ’VERT DE MONTMAGNY’) Covering Fertilizing level 1x 2 x No covering 35 52 Bark humus 2.5 cm 36 48 » - 5 cm 42 49 » 5 + 5 cm 26 5 Black film 8 10 —» and bark humus scm 18 19 Black fibre cloth 11 10 Average 25 28 thus considerably decreased theascorbic acid content. In late summer the average was 20 mg/100 g and range 7—26 mg/100 g. Al- though the average values of the foreign dan- delions were slightly higher than those of the Finnish agamospecies, the values of some of the latter were fully comparable or even higher. The influence of the level of fertilizing was slight on the average. Where enough light was available (no covering and thin bark humus layer), the higher level increased the vitamin C content. If the covering caused ef- fective darkening, the content was strongly decreased. According to literature tables, vitamin C content in dandelion leaves varies between 5 and 40 mg/100 g. In Finland, Simola (1945) found 49 mg/100 g and Erkama (1946) 73 mg/100 g. Recent values from Germany (Franks and Kensbock 1981) vary between 51 and 110 mg/100 g, and if dehydroascorbic acid is taken into account, between 74 and 137 mg/100 g. The amount is much lower in the leaf nerve than the lamina, the former va- lue being 15—31 mg/100 g, the latter 93— 159 mg/100 g, without dehydroascorbic acid. The German values are high in com- parison with other literature values and also the present values, which may depend on the analytical method used. Discussion As the main conclusions concerning each property have already been drawn, we turn here to a more general discussion of the nutritive value and intrinsic quality of dande- lion leaves. According to the tables of the literature, the nutritive value of dandelion leaves is high compared with cultivated lettuce. As the dry matter value of the dandelion leaves is 2—3 times higher, the values of the different nutri- tive components are quite naturally higher. The present results are in basic agreement with the values in the literature, but go farther in indicating the effect of different cultivation methods. It is not specified in the literature tables whether the analyses concern wild or cultivated dandelions, but since cultiva- tion is uncommon it may be assumed that they were wild. High vitamin C values have been reported for leaves of wild dandelions (Franke and Kensbock 1981, Erkama 1946). Cultivation may to some degree change the nutritive values, and vitamin C content may indeed be higher in the wild plant. Corre- spondingly, the slightly higher values found here for calcium and iron and lower values for magnesium may be related to the addi- tion of lime and use of irrigation water con- taining iron. The nutrient level of the dandelion leaves is high, partly because of the high dry matter content. This alone is not a decisive criterion of quality, however. The dry matter content of leaves is highest in late summer, but the vitamin C content is then lower and the sen- sory quality poorer than in the spring. Like dry matter, soluble solids and mineral con- tent are high in late summer, but also the nitrate content tends to be higher. Here the decisive properties for usefulness are the sen- sory properties and vitamin C content. Darkness had the effect of decreasing the values of vitamin C as well as dry matter, soluble solids and mineral content, but in- creased the nitrate values. The sensory prop- erties were improved by darkness. Compared with other salad greens, such as lettuce and Chinese cabbage, dandelion leaves show definitely higher nutrient con- tents. The main difficulty with dandelion leaves picked wild is the bitter taste, which varies in an apparently random way among different individuals. The results obtained here based on the comparatively mild-tasting agamospecies selected for cultivation indicate that strong bitter taste and high value of vita- min C are connected. If dandelions are grown in darkness, both bitterness and con- tent of vitamin C are decreased. Thus, a compromise is necessary to obtain an accep- table low level of bitterness together with as high vitamin C content as possible. In the present agamospecies the bitterness was in general so slight that cultivation in darkness is not essential. However, such cultivation also has the favourable effect of producing a crisp texture. A choice may thus have to be made between light green rosettes with higher vita- min C content and a texture like soft lettuce leaves, and bleached rosettes with lower vita- min C content and crisp texture like iceberg lettuce. In both cases the bitterness is barely noticeable. Dandelion leaves collected wild in spring have high vitamin C content, but because of the bitterness they are best used together with other, mild-tasting salad vege- tables. One positive feature of dandelion leaves compared with other salad greens is that dan- delion does not accumulate nitrates. Al- though the nitrate content increases if cul- tivation takes place in darkness, even then the level is only ca. 600 mg nitrate/kg fresh weight. In contrast, our investigations (Kuu- si, Virtanen and Kleemola 1980) showed a level of 3000 mg/kg in lettuce heads, and in November as much as ca. 4500 mg/kg. Cor- respondingly, Liukkonen and other (1976) obtained for lettuce values between 2000 and 5200 mg/kg. Values were also high for Chi- nese cabbage, between 750 and 6660 mg/kg (Kuusi and Hautala, unpublished). In this respect, then, dandelion leaves are superior to other salad greens. Other properties making up the ’intrinsic quality’ are contents of harmful substances such as residues of heavy metals and pestici- des. Though these have not been investigated here, it is known from the literature that if dandelions grow near heavily trafficked roads, they pick up lead from engine ex- hausts (Haney, Carlson and Rolfe 1974). In parks in Cracow dandelions were found to accumulate cadmium, lead and iron, emitted by a near-by steel plant (Grodzinska and Kazmierczakowa 1977). In Japan a local species, Taraxacum japonicum, was shown to pick up cadmium in the neighbourhood of an old mine (Narita and others, 1976). As regards pesticides, their use in dandelion cul- tivation may in general be unneccessary, since dandelion seems to be relatively re- sistant against insects and plant diseases. If such pests do appear, they will probably do so in late summer, whereas the crop of young rosettes will be harvested the following spring. Dandelion seems to be resistant against many 29 herbicides. Where herbicides effective against dandelion have been used however, collecting of dandelions would not be recom- mended. In such cases the growth of dan- delions would be anomalous, and pickers would probably discard such individuals. Acknowledgements.The authors are indebted to Ant- ti Mustranta, Tuomo Kiutamo and Helena Liukkonen- Lilja of the Food Research Laboratory for the analyses of nutritive value and nitrates. Financial support was re- ceived from the Juho Vainio Säätiö. References Anon. 1942. The Pharmacopoeia of the U.S.A. 1942, 12th Rev., p. 629. Easton, Pa. LXXXVIII, 880 p. Anon. 1961. European Productivity Agency Organiza- tion for European Economic Co-operation, Docu- mentation Food & Agriculture, 1960 Series: Nutritive and therapeutic value of fruit and vegetables. 148 pp. Paris, 1961. Anon. 1977. Nitrate ion electrode model 93—07. Orion Research. Instruction Manual. Erkama, J. 1946. Kolorimetrisestä C-vitamiinin määri- tyksestä 2,6-diklorfenoli-indofenolilla. Suomen Ke- mistilehti 19: 21 —25. Franke, W. & Kensbock, A. 1981. Vitamin C-Gehalt von heimischen Wildgemiise- und Wildsalatarten. Er- nährungs-Umschau 28/6; 187—191. Freed, M. 1966. Methods of vitamin assay. New York- London-Sydney, Interscience Publishers. Ed. by The Association of Vitamin Chemists, Inc. Grodzinska. K. & Kazmierczakowa, P. 1977. Heavy metal content in the plants of Kracow parks. Bull. Acad. Pol. Scie., Ser. Sci. Biol. 25/4: 227—34. Haney, A., Carlson, J.A. & Rolfe, G.L. 1974—1975. Lead contamination of soils and plants along highway gradients in east central-lllinois. Trans 111 State Acad Sci 67/3: 323—335. Horwitz, W. (Ed.). 1975. Official methods of analysis of the Association of Official Agricultural Chemists, 12th ed. Washington. P. 129, 7.003; p. 397, 22.024, p. 339, 22.025. Kanon, H. 1982. Salaattivoikukka. Pro gradu -tutkiel- ma. Helsingin yliopiston puutarhatieteen laitos. 128 pp. Kuusr.T., Hardh.K. & Kanon.H. 1984. Experiments of the cultivation of dandelion for salad use. I. Study of cultivation methods and their influence on yield and sensory quality. J. Agric Sci Finl. 56; 9—22. Kuusi, T., Virtanen, T. & Kleemola, K. 1980. Tutki- muksia salaatin, tomaatin ja porkkanan sisäisestä laa- dusta markkinoinnin aikana. J. Scient. Agric. Soc. Finl. 52: 339—356. Kuusi, T. & Hautala, H. (to be published). Liukkonen, H., Rajama, J. & Nikkilä, O.E. 1976. Kas- visten ja kasvisvalmisteiden nitraattipitoisuuksia. Ympäristö ja Terveys 7/7: 640—643. Mengel, K. 1979. Influence of exogenous factors on the quality and chemical composition of vegetables. Acta Horticulturae 93: 133—151. Narita, M., Naoaya, M., leiri, K., Takeuchl H. & Miyata, S. 1976. Studies on the environmental pollu- tion by the trace heavy metals from the old mine area. 11. Cd contents in plants. Acta Schol. Med. Univ. Gifu 24/I—2, 71—80. Ref. Chem. Abstr. 86 (1977) p. 216, 86: 46977c. Rousi, A., Huttunen, H. & Hyrkäs-Lyytikäinen, K. 1984. Chromosomes and reproductive behaviour of Finnish Taraxacum agamospecies. Nordic Journal of Botany (in press). Simola, P.E. 1945. Suomalaisten ruoka-aineiden vita- miinipitoisuudesta. Suomen Kemistilehti 18/1 —2: 4—lo. Souci. S.W., Fachmann, W. & Kraut, H. 1962. Die Zusammensetzung der Lebensmittel. Nahrwert-Ta- bellen. Stuttgart. Souci, S.W., Fachmann, W. & Kraut, H. 1981. Die Zusammensetzung der Lebensmittel. Nährwert-Ta- bellen 1981/82. Stuttgart. Compiled by H. Scherz & G. Kloos. 1352 pp. Turpeinen, O. 1978. Ruoka-ainetaulukko. 16. painos. Keuruu, Otava. Ms received January 9, 1984 30 SELOSTUS Tutkimuksia salaattivoikukan viljelystä. II Voikukan lehtien ravintoarvo ja sisäinen laatu Taina Kuusi 1, Kirsti Härdh2 ja Helena Kanon2 ' Valtion teknillinen tutkimuskeskus, Elintarvikelaboratorio, SF-02150 Espoo 15 2 Puutarhatieteen laitos, Helsingin yliopisto, SF-00710 Helsinki 71 Voikukan hyötykäyttöäkoskevassa tutkimuksessa on selvitetty voikukan viljelymahdollisuuksia salaattina käytettäväksi. Tässä yhteydessä on eräänä kriteerinä käytetty sisäiseen laatuun kuuluvia ominaisuuksia kuten ravintoarvoa sekä nitraattipitoisuutta. Tutkimuksessa on verrattu keskenään 11 kotimaista miedon makuista pikkulajia sekä kahta keskieurooppalaista salaattivoi- kukkakantaa, ’Vollherziger, verbesserter’ ja ’Veri de Montmagny’. Lisäksi on tutkittu viljelymenetelmien vaikutusta, niin että lannoitusta kokeiltiin kahdella ta- solla, ja ruusukkeiden vaalentamiseksi käytettiin erilai- sia katteita kuten mustaa muovikalvoa, kuitukangasta ja eri paksuisia kuorihumuskatteita. Ravintoarvon kri- teereinä olivat kuiva-aine, liukoinen kuiva-aine, kiven- näisainepitoisuus sekä erikseen Ca-, Mg-, Fe- ja Mn- määrät, nitraatti sekä C-vitaraiini. Salaattivoikukan kuiva-aineen todettiin kevätsadossa olevan keskimäärin 12.3 %, loppukesällä jopa 17.1 %. Liukoinen kuiva-aine oli keväällä keskimäärin 5.5 °7o ja kivennäisainepitoisuus 1.6 %. Nitraatin määrä oli alhai- nen, korkeimmillaan 660 mg NO/kg tuorepainoa. C- vitamiinin määrä oli kevätsadossa keskimäärin 42 mg/100 g ja vaihteli rajoissa 29—53 mg/100 g. Tutkittujen kivennäisaineiden, Ca, Mg, Fe ja Mn, määrät poikkesivat jossakin määrin kirjallisuuden ar- voista johtuen otaksuttavasti viljelyn vaikutuksista. Lannoitustason vaikutus on ollut vain vähäinen. Kor- keampi lannoitustaso ei ole kohottanut edes kivennäis- aineiden eikä nitraatin määriä. Katteiden vaikutuksesta voitiin todeta, että silloin kun kattaminen oli tehokkaasti vähentänyt valon saantia (muovi- ja kuitukangaskate sekä paksuin kuorihumus- kate), olivat kuiva-aineen, liukoisen kuiva-aineen ja C- vitamiinin arvot alentuneet ja nitraattimäärä kohonnut. Voikukkasalaatin etuina muihin salaattina käytettyi- hin kasveihin verrattaessa on korkea ravinnepitoisuus, erityisesti C-vitamiinin korkea taso, joka tosin vaalen- nettaessa melkoisesti alenee. Tutkittuja mietoja voikuk- kakantoja viljeltäessä vaalentaminen ei ole välttämätön- tä. 31