BROCCOLI AS THE SOURCE OF PHYTOSTEROLS IN NUTRITION

Transcription

1 Buletin USAMV-CN, 64/27(-) ISSN BROCCOLI AS THE SOURCE OF PHYTOSTEROLS IN NUTRITION Gajewski M., J. L. Przybył, P. Szymczak Department of Vegetable and Medicinal Plants, Warsaw Agricultural University ul. Nowoursynowska 166, Warszawa, Poland Key words: broccoli, sterols, vegetables, cultivation, nutrition Abstract. The aim of this work was to determine free sterols content in different parts of the main and lateral branches of plants of broccoli cultivars, grown as an autumn crop. Cultivars chosen for the experiment were: Chevalier F 1, Milady F 1 and Cezar F 1. Broccoli plants were cultivated as an autumn crop on the experimental field of Warsaw Agricultural University. Fertilization was done according to results of soil analysis. Sterols were determined immediately after harvest, in the main branches and lateral branches of the plants, separately for the top part of broccoli plant (florets) and in lower part (stems) separately, as well as in the whole edible part of this vegetable. HPLC method was used for the analysis. Results showed that florets of broccoli contain much higher amount of sterol compounds than stems. The main branches of the plants contained more sterol compounds than lateral branches. The dominant sterol compound in broccoli was β-sitosterol, both in florets and stems, but the sterols composition was differentiated between cultivars. Total amount of sterols reached 23 mg g 1 d.w. in florets of the plants. Chevalier was the cultivar of the highest content of sterols in florets and Cezar was the cultivar of the lowest content of sterols in stems. INTRODUCTION Broccoli became a very popular vegetable crop in temperate climate regions. In literature authors indicate high nutritional value of this vegetable [6, 1, 13]. Also phytosterols were found in this vegetable in high amount. Plant sterols have antiinflammatory properties and β-sitosterol works against prostate diseases. In the United States the daily intake of phytosterols is approximately 18 mg, while in Japan it reaches 4 mg [7]. Sitosterol and campesterol account for up to 95% of dietary phytosterols. In a plant, sterols are essential structural and functional components of cell membranes [8, 11, 16]. Sterol glucosides found in plants are essentially cholesterol, campesterol and sitosterol glucosides [14]. Total sterols content in vegetable plants varies from 25 to 4 mg kg -1 d.m., and in cauliflower the highest concentration of these compounds was found [12]. Sterols content in fresh broccoli edible part equals 18 mg g -1 f.w [1]. Median total amount of plant sterols in the vegetables is equal to 16 mg mg -1 [9]. The use of phytosterols as cholesterol-lowering food additives is considered [7]. Sitosterol is the predominant sterol (43-86% of total) for most vegetable species. No significant differences in sterols content between raw and cooked vegetables were found [9]. During storage a decline of free sterols concentration was observed in the case of zucchini [16] or increase of free sterols in the case of chicory heads [5]. Also an increase of stigmasterol to sitosterol ratio during the ageing of plant tissues was observed [5, 17]. There was found that free sterols content in cauliflower, which is relative to broccoli, depends on growing season and storage conditions [3]. Broccoli cultivars differ in chemical composition and sensory traits [4]. Most broccoli are grown for the main crop in autumn, as well as cauliflower, and only a short-term storage for this produce is applied, due to quality deterioration of the florets [2].

2 The aim of this study was to determine sterols content in three different cultivars of broccoli grown as an autumn crop, and to determine differences in sterols content between parts of the plant. MATERIAL AND METHODS Broccoli plants were grown in the experimental field of Warsaw Agricultural University on a medium mud soil, of ph 7.. Fertilization was applied according to results of soil analysis. Three cultivars, two of Dutch and one of Polish origin, were chosen for the experiment: Chevalier F 1 (late yielding cultivar, above 7 days of vegetation), Milady F 1 (semi-early yielding cultivar, about 6 days of vegetation), and Cezar F 1 (early-yielding cultivar of Polish breeding, about 55 days of vegetation). Broccoli plants were grown as an autumn crop, which is the most popular method of their growing in Poland. They were sown, planted out and harvested at the followed terms: sowing 3 rd decade of May, planting out - 3 rd decade of June, harvesting 3 rd decade of September. During harvest broccoli florets with 1 cm upper part of a stem (according to the EU quality standard for broccoli) were cut out at their optimal marketable stage. Sterols were was determined immediately after harvest time in a raw material. Sterols content was determined in the main branches and lateral branches of the plants, in the whole edible part of the plant, in the top part of the plant (florets) and in lower part of the plant (stems). Sterols content was determined with HPLC method (Toivo et al. 21, with modification). All analyses were made on representative samples of plant material, in two replicates. 1 g of air-dry raw material was extracted with ml of hexane in Büchi B-811 Extraction System. Twenty five extraction cycles were used. After evaporation of solvent, the residue was dissolved in 1 ml of chloroform-methanol (4 : 1) mixture. The obtained extract was filtered (Supelco IsoDisc PTFE 25 mm x.45 µm) and subjected to HPLC. The analysis was carried out using the Shimadzu chromatograph with SPD-M1A VP DAD detector and Luna C8(2) RP 18 column, 5 µm, 25 mm x 4,6 mm (Phenomenex). The following conditions were applied: mobile phase A methanol (LabScan), mobile phase B ACN (LabScan), flow rate 1 ml/min., temperature 31ºC, time of analysis 2 min. Detection wave applied: 21 nm. Peak identification was confirmed by comparison of retention time and spectral data with adequate parameters of standards from ChromaDex. Dry matter of samples was determined by drying in temperature of 15 o C until stable weight. Free sterols content was expressed per g of dry matter. Results of the experiment were statistically evaluated by ANOVA, with StatgraphicsPlus 4.1 program. The homogenous groups of means were identified with LSD test, at probability level P <.5. Presented data are the means of the two seasons of the experiment. RESULTS AND DISCUSSION Broccoli cultivation as an autumn crop is the most popular method of their growing in temperate climate zone conditions, e.g. in Poland and in other middle-europe countries. It results from the fact that broccoli is a plant of the temperate climate and grows especially well when temperatures are below 25 o C. Results of the experiment showed a considerable variation of phytosterols content for different parts of the plant and for the cultivars. Free sterols content in florets of broccoli plants varied from about 8 to 23 mg g -1 d.m., and in stems varied from about 1 to 65 mg g -1 d.m, depending on the cultivar (Fig 1). So, sterols content in florets was much higher than in stems. Obtained data for sterols content in the plant are in agreement with those presented in literature. According to published data, in the edible part of fresh broccoli florets amount of 39 mg g 1 of sterols was found and in the boiled sample - 68 mg g 1 [9]. In literature we found no data concerning differentiation of sterols content in different parts of broccoli plants. According to literature,

3 the range in the plant sterol contents in vegetables and fruits is higher when the concentrations are calculated on a dry weight basis, than on fresh weight basis [12]. Similar relation for sterols content in the top part and the stem of the plant can be noticed for the main branches of the plants, which are the main crop of this vegetable, and for lateral branches as well. Lateral branches are sometimes harvested as the second, minor crop of this vegetable. However, the main branches of the three cultivars contained significantly more free sterols than lateral branches. The differences between main and lateral branches were not so big, as between florets and stems and between cultivars. Since a high dietary intake of sterols might have a positive impact on human health, it can be concluded that florets of broccoli plant have higher biological value than stems, and are more valuable from nutritional aspect. However, the plant sterol concentration in vegetables and fruits commonly consumed in European countries is generally low. Therefore, seeking of plants of higher sterols content is important from consumer s point of view. Of cultivars chosen for the experiment, Chevalier was the cultivar of the highest content of sterols in florets, in the main branches of the plant, as well as in the lateral branches. The differences between sterols concentration for stems of the chosen cultivars were not so big as for florets. Polish cultivar Cezar, which was an example of early-yielding cultivar, showed the lowest sterols content in stems. High differentiation between cultivars in free sterols concentration was observed also for cauliflower plants [3]. It was found that the green cultivars of cauliflower showed higher free sterols concentration in curds than the white ones. There are no data available in literature on the impact of broccoli cultivar, geographic location of growing, agricultural practices and processing on sterols content in the plant. Since Chevalier is the latest yielding cultivar of the three cultivars investigated in the experiment, and Cezar the earliest yielding cultivar, it can be concluded that free sterols content may be related to the vegetation period of broccoli. 25 mg/ g d.w Florets Stems Chevalier Milady Cezar LSD Cultivars Fig. 1. Phytosterols content in florets and stems of main branches of broccoli cultivars The chemical composition of sterol compounds was a little differentiated among cultivars and parts of the plant (Fig. 2). The compound found in the highest concentration was β-sitosterol, followed by brassicasterol, campesterol or stigmasterol, depending on the cultivar. In cv. Chevalier brassicasterol was the second sterol compound in respect of its amount in both florets and stems, but in florets of cv. Milady stigmasterol was presented in a higher amount that brassicasterol. Sterol compounds we found in broccoli are usual

4 components of plant sterols and are found in all vegetable species, but their amount in various species is highly differentiated [9] mg/ g d.m. Florets Stems 5 Chevalier Milady Cezar LSD Cultivars Fig. 2. Phytosterols content in florets and stems of lateral branches of broccoli cultivars mg/ g d.w Chevalier Milady Cezar LSD 4 2 Florets Stems Florets Stems Florets Stems Florets Stems Florets Stems Cholesterol Brassicasterol Campesterol Stigmasterol ß-sitosterol Fig. 3. Phytosterols chemical composition in the three broccoli cultivars, for different parts of the plant

5 CONLUSIONS 1. Florets of late-yielding cultivar of broccoli showed much higher concentration of phytosterols than florets of the earlier-yielding ones. 2. Florets of broccoli plants contained more phytosterols than stems. 3. Main branches of broccoli plants contained higher amount of phytosterols than lateral branches. 4. The main phytosterol found both in florets and stems of the main as well as lateral branches of broccoli, was β-sitosterol. Note: Research was supported by Polish Ministry of Science and High Education, grant No. 2 PO6R BIBLIOGRAPHY (1) Anonymous, 23, Broccoli raw. USDA National Nutrient Database for Standard Reference, Rel. 16, (2) Gajewski M., 21, The influence of CA on green cauliflower quality. Folia Hortic., 13/1A, (3) Gajewski M., 24a, The influence of growing period, cultivar and storage conditions on free sterols content in cauliflower (Brassica oleracea L. var. botrytis). Ann. Univ. M. Curie-Skłodowska, Vol. 14, sec. EEE, (4) Gajewski M., 24b, Application of quantitative descriptive analysis (QDA) to modelling of sensory quality of broccoli (Brassica oleracea L. var. italica Plenck). Folia Univ. Agric. Stetinensis, Agricultura, 239, (5) Krebsky E., J.M. Geuns, M. DeProft, 1999, Polyamines and sterols in Cichorium heads. Phytochem., 5, (6) Leja M., A. Mareczek, A. Starzyńska, S. RoŜek, 21, Antioxidant ability of broccoli flower buds during short-term storage. Food Chem., 72, (7) Moghadasian M.H., 2, Pharmacological properties of plant sterols in vivo and in vitro observations. Life Sci., 67, (8) Mrugasiewicz K., A. Mścisz, 1984, Methods of sterols determination in corn (Zea mays L.). Herba Polon., 3 (2), 97-. (9) Normén L., M. Johnsson H., Y. Andersson, S. van Gameren., P. Dutta, 1999, Plant sterols in vegetables and fruits commonly consumed in Sweden. Eur. J. Nutr., 38, (1) Palace V.P., N. Khaper, Q. Qin, P.K. Singal, 1999, Antioxidant potentials of vitamin A and carotenoids and their relevance to heart disease. Free Rad. Biol. Med., 25, (11) Piironen V., D.G. Lindsay, T.A. Miettinen, J. Toivo, A.M. Lampi, 2, Plant sterols: biosynthesis, biological function and their importance to human nutrition. J. Sci. Food Agric., 8, (12) Piironen V., Toivo J., Puupponen-Pimia R., Lampi A.M., 23, Plant sterols in vegetables, fruits and berries. J. Sci. Food Agric., 83: (13) Podsędek A., 27, Natural antioxidants and antioxidant capacity of Brassica vegetables. LWT, 4: (14) Schaller H., 24, New aspects of sterol biosynthesis in growth and development of higher plants. Plant Physiol. Biochem., 42, (15) Starzyńska A., M. Leja, A. Mareczek, 23, Physiological changes in the antioxidant system of broccoli buds senescing during short-term storage, related to temperature and packaging. Plant Sci., 165, (16) Toivo J., K. Phillips, A.M. Lampi, V. Piironen, 23, Determination of sterols in foods: recovery of free, esterified, and glycosidic sterols. J. Food Comp. Anal. 14, (17) Wang C., G. Kramer, B. Whitaker, W. Lusby, 1992, Temperature preconditioning increases tolerance to chilling injury and alters lipid composition in zucchini squash. J. Plant Physiol., 14, (18) Whitaker B.D., 1995, Lipid changes in mature-green bell pepper fruit during chilling at 2 o C and after transfer to 2 o C subsequent to chilling. Physiol. Plant., 93,