Protein, amino acid, ash and mineral contents in Brassica spp. grown in Northwest Spain

International Journal of Food Science and Technology 2011, 46, 146–153

146

Original article Protein, amino acid, ash and mineral contents in Brassica spp. grown in Northwest Spain Sidonia Martı´nez,* Pedro Losada, Inmaculada Franco & Javier Carballo A´rea de Tecnologı´ a de los Alimentos, Facultad de Ciencias de Ourense, Universidad de Vigo, 32004 Ourense, Spain (Received 17 June 2010; Accepted in revised form 20 September 2010)

Summary

The protein, amino acid, ash, and mineral composition of different Brassica spp. grown in several areas of Galicia (Northwest Spain) were studied. The highest protein values were observed in Galega kales (crude protein: 29.66 g per 100 g) and turnip greens and turnip tops (27.74–31.46 g per 100 g), whereas the leaves showed higher protein contents than the stems. Glutamic acid was the most abundant amino acid present (14.53% in turnip greens to 18.45% in white cabbage). Other amino acids such as arginine, aspartic acid, lysine, alanine and glycine were also observed in higher quantities. The stems contained the same amino acid as the leaves but at a lower level. Furthermore, differences in amino acid contents were observed among varieties. The proportion of essential amino acids was high (41% in leaves of turnip top to 47% in external leaves of oxheart cabbage). The studied varieties are also a good source of some minerals, which include as main element potassium (27.24–37.57 mg g)1 in whole plants), followed by calcium (4.27–17.48 mg g)1 in whole plants) and magnesium (1.62–2.92 mg g)1 in whole plants). Significant differences among varieties and edible portions were found concerning ash and mineral contents.

Keywords

Amino acid, ash, cabbage, kale, minerals, protein, turnip.

Introduction

Brassica spp. occupy an important position among food because of its nutritional properties, highly beneficial for the maintenance of health and prevention of diseases. Their high nutritive and dietetic value derives from its particular chemical composition. They are a rich source of fibre, carbohydrate, phenolic compounds, ascorbic acid, b-carotene, a and b-tocopherols as well as glucosinolates. In addition, vegetable leaves such as Brassica spp. are in general considered to be a notable protein and mineral source compared to other vegetables. Furthermore, Brassica spp. contain lots of minerals (Glew et al., 2005; Tıras¸og˘lu et al., 2005). Brassica spp. form an indispensable constituent of diet in Spain in general and in Galicia (Northwest Spain) in particular. Traditional Brassica vegetables in Galicia include numerous landraces which are well adapted to soil and climate conditions. Turnip (Brassica rapa var. rapa L.), Galega kales (Brassica oleracea L. var. acephala), white cabbage (Brassica oleracea L. convar. capitata L. Alef. var. capitata L. f. alba DC.) and oxheart cabbage (Brassica oleracea L. convar. capitata *Correspondent: Fax: +34 988 387001; e-mail: [email protected]

var. alba DC. subvar. conica) are commonly grown and consumed throughout Galicia. It is well known that environmental conditions as well as time of harvest, maturity at harvest and postharvest storage conditions may greatly influence the nutrient composition of plants. There is also variation in protein and mineral content in different groups of Brassica. On the other hand, different parts of Brassica spp. are edible and there may be significant differences in the nutrient contents of these parts (Martı´ nez et al., 2010). The cabbage leaves, which form a compact head, are the edible portion. In the case of the turnips and the Galega kales, the leaves as well as the stems are consumed. In addition, the type of leaf may also influence the composition. The internal and external leaves differ regarding organoleptic and nutritive characteristics (Ferreres et al., 2006). In the available literature, there are some works that contain information about morphological and agronomic attributes, genetic diversity and some compounds and sensory quality of Brassica spp. grown in Northwest Spain. However, no information is available on the content of mineral and amino acid in different edible portions of these Brassica spp. In addition, proteins, amino acids and minerals are the important nutrient of a healthy diet, and the vegetables are a natural source of

doi:10.1111/j.1365-2621.2010.02463.x  2010 The Authors. International Journal of Food Science and Technology  2010 Institute of Food Science and Technology

Protein, amino acid, ash and mineral contents S. Martı´nez et al.

these nutrients, and so the study is important in these Brassica spp. The aim of this study is to determine the protein, amino acid, ash and mineral composition of different edible portions of Brassica spp. grown and consumed in Galicia (NW Spain). These plants play an important role in local diets, and the data presented in this report could illustrate the nutritional value of this food relative to other green vegetables with the purpose of promoting the consumption of these Brassica spp. Materials and methods

Plant material and preparation of samples

The edible portions (leaves and stems) of turnip greens (young leaves and stems of B. rapa var. rapa L. when they start to grow), turnip tops (fructiferous stems with the flower buds and surrounding leaves of B. rapa var. rapa L. obtained immediately before flowering), Galega kales (B. oleracea L. var. acephala harvested in the vegetative growth period), oxheart cabbage (B. oleracea L. convar. capitata var. alba DC. subvar. conica) and white cabbage (B. oleracea L. convar. capitata var. alba) were harvested from five different plantations in four areas of production in the province of Ourense (Galicia, NW Spain). Samples were collected in the autumn ⁄ winter season in 2008 and 2009 since this time of the year corresponds to the period of highest production. Three samples of each type were collected at random in three different sites in the different plantations. They were washed with deionised water and separated from the inedible parts. The edible portion was further sorted into leaves and stems (turnip and Galega kale) and into external and internal leaves (oxheart cabbage and white cabbage). The different portions were then weighed. The samples were lyophilised, vacuum packed and maintained at )20 C (±2 C) until analysis. Chemical analysis

Crude protein was assessed by determining the N content using the Kjeldahl method with a conversion factor of 6.25 using a digestion apparatus (Kjeldatherm; Gerhardt Laboratory Instruments, Bonn, Germany). Net protein was calculated by summing-up the amounts of the amino acids. The identification and quantification of the individual amino acids were carried out by high-performance liquid chromatography (HPLC) techniques according to Alonso et al. (1994) with some modifications. For the total amino acid analysis, a lyophilised sample (0.2 g) was hydrolysed under vacuum in 6 N HCl at 102 C for 24 h. Then, 10 mL of internal standard solution (5 mm hydroxyproline) was added, and the volume was adjusted to 250 mL with water. A volume of 0.2–0.4 mL was concentrated and dried under N2 at 37 C, and the

residue was suspended in 20 lL of a mixture consisting of ethanol, triethylamine, water and phenyl isothiocyanate (7:1:1:1, v ⁄ v). Subsequently, after remaining 20 min at 25 C, the material was evaporated under N2 current and suspended in 500 lL of 5 mm sodium phosphate pH 7.4 and acetonitrile (HPLC grade) in a 95:5 (v ⁄ v) proportion. The mixture was then filtered through a 0.45-lm filter (Milipore, Molsheim, France). Then, 20 lL aliquots were injected into a Water C-18 column (5 lm particles; 4.6 · 250 mm) reversed phase type (Milford, MA, USA). The liquid chromatography equipment consisted of a Spectra System chromatograph (Thermo Finnigan, San Jose, CA, USA), equipped with a SCM 1000 degasser, a P4000 pump, an AS 3000 automatic injector and a Photodiode Array UV6000LP detector. The temperature of the column was controlled to 50 ± 10 C with a column heater (Spectra Physics 8792; Spectra Physics, San Jose, CA, USA). The wavelength of the detector was settled down at 254 nm. Standards of the nineteen different amino acids were supplied by Sigma Chemical Co. (St Louis, MO, USA). All samples and standards were injected in triplicate (at least). Repeatability tests were performed by injecting a standard and a sample consecutively six times a day. Ash content was determined after the incineration of samples in a muffle furnace (Hobersal 10-PR ⁄ 300 serie B, Barcelona, Spain) at 550 ± 25 C for 6 h. Mineral macroelements (K, Mg and Ca) and microelements (Fe, Zn, and Cu) were extracted with wet digestion (samples of 0.2 g were extracted with 10 mL concentrated nitric acid over night) (Cavero et al., 1993). The samples were treated at 90 C for 5 h, and after cooling down, they were centrifuged. An aliquot of 5 mL of supernatant was mixed with 5 mL of distilled water. Minerals were assessed using an atomic absorption spectroscope (Varian model 220 Fast Sequential; Mulgrave, Victoria, Australia). Dry matter was determined by drying the samples to constant weight in an oven at 70 C. Statistical analysis

To determine any significant differences between the different Brassica spp. and edible portions, a variance analysis (anova) was performed with a confidence interval of 95% (P < 0.05). Means were compared by the least squares difference test, by using of the Statsoft Inc 5.1 computer programme for Windows (Statsoft Inc. 1996, Tulsa. OK, USA). Results and discussion

Protein and amino acids

Protein and amino acids contribute to the nutritive value and flavour of foods. Brassica spp. have high

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Protein, amino acid, ash and mineral contents S. Martı´nez et al.

)1

Table 1 Crude protein (g N · 6.25 per 100 g dry weight), net protein (g per 100 g dry weight), amino acid (mg g

dry weight) contents and

essential amino acid composition (%) of different Brassica spp (whole plants) Galega kale Ala Arg Asp Glu Gly His Ile Leu Lys Met Phe Pro Ser Thr Tyr Val % Essential amino acids Net protein (SAAs) (g 100 g)1) Crude protein (g N · 6.25 100 g)1 DM) Dry matter (g 100 g)1 of product)

17.13 22.36 21.89 34.47 10.89 11.26 10.78 15.08 24.95 1.35 8.19 17.05 11.70 11.27 5.68 11.22 43 23.53

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

0.51ab 2.68abc 0.17ac 0.36ac 1.92a 0.34a 0.32a 0.11a 1.95a 0.16a 0.74a 0.35a 1.01ac 1.39a 0.39a 1.06ac 0.1abc 0.13a

Turnip top 15.80 25.73 24.98 43.08 12.95 12.14 11.70 17.56 27.12 1.23 8.85 17.88 16.42 13.88 5.16 12.02 41 26.65

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

Turnip green

0.45a 1.24a 3.00a 5.52b 0.58b 0.63a 0.39a 1.18a 1.08a 0.02a 0.26a 0.11a 0.82b 0.76a 0.04a 0.34a 0.5b 0.20b

19.02 24.61 24.36 37.72 11.37 12.95 15.81 16.14 24.69 1.36 9.20 14.28 14.46 12.39 6.76 14.43 44 25.95

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

Oxheart cabbage

3.16b 0.84ac 0.80ac 0.54ab 0.99ab 0.87a 1.52b 2.71a 1.20a 0.05a 0.99a 1.77b 0.89ab 2.99a 0.72b 0.51b 0.8ac 0.17b

9.84 18.28 14.09 29.36 5.47 8.37 9.45 9.63 14.21 1.86 5.50 7.71 8.97 7.83 5.23 9.43 45 16.52

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

White cabbage

0.98c 2.11b 1.29b 3.32c 0.29c 0.59b 0.10a 0.10b 0.90b 0.56b 0.26b 0.12c 0.44c 0.89b 0.29a 0.59c 0.6c 0.79c

8.65 21.32 18.98 34.07 5.31 8.42 9.99 9.77 14.12 1.93 5.28 14.43 9.38 7.86 5.64 9.54 42 18.47

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

0.72c 3.25bc 0.96bc 4.25ac 0.77c 0.36b 1.97a 0.24b 3.43b 0.07b 0.53b 0.50b 2.19c 0.73b 0.31a 0.99c 2.7ab 0.83c

29.66 ± 5.21a

27.74 ± 1.95a

31.46 ± 2.38a

21.08 ± 2.84b

20.61 ± 2.24b

8.20 ± 0.74a

8.84 ± 0.21a

9.19 ± 0.70a

5.50 ± 0.26b

5.28 ± 0.53b

a–c

Mean values of at least three determinations ± standard deviation with different superscript in the same row were significantly different (P < 0.05).

protein contents compared to other vegetables, and the nutritional quality is better than that of other plant proteins such as soy, sunflower, pea and wheat proteins (Sarwar et al., 1984). The crude protein (g N · 6.25 per 100 g), net protein (total amino acids), amino acid contents and essential amino acids composition of different Brassica spp. (whole plant) grown in Galicia (NW Spain) are shown in Table 1. As expected, the obtained results show that the net protein content was inferior to the one of crude protein; however, differences were not important. This indicates that nonprotein nitrogen is very low in these vegetables. On the other hand, regression analysis showed good correlation between crude protein and net protein (Fig. 1). Most protein values given in the literature are for crude protein, by assessing the total nitrogen and using a nitrogen-to-protein conversion factor (usually 6.25). However, not all nitrogen in foods is found in proteins. Vegetables can contain a nonprotein nitrogen-component, such as free amino acids. Thus, crude protein does not necessarily represent the true protein content. Proteins are made up of chains of amino acids, whereas the sum of the amino acids then represents the protein content (net protein) (Pellett & Young, 1980; SaloVaananen & Koivistoinen, 1996).

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50 45 Crude protein = 61.5208 + 0.9099 * net protein

Crude protein (g per 100 g dry weight)

148

r = 0.94

40

95% confidence

35 30 25 20 15 10 5 0

0

5

10

15

20

25

30

35

40

45

50

Net protein (g per 100 g dry weight) Figure 1 Linear regression analysis between net protein and crude protein Kjeldahl-nitrogen.

Galega kale, turnip top and turnip green showed high contents of crude and net protein. Crude protein varied from 20.61 (white cabbage) to 31.46 g per 100 g (turnip green), and net protein from 16.52 (oxheart cabbage) to 26.65 g per 100 g dry weight (turnip top). These data are consistent with the results reported by other authors for

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Protein, amino acid, ash and mineral contents S. Martı´nez et al.

other Brassica varieties. Ayaz et al. (2006) showed that the protein (sum of individual amino acids) reached values of 27.1 g per 100 g dry weight in B. oleracea L. var. acephala. Cartea et al. (2008) reported values of crude protein between 16.5 and 25.5 g per 100 g dry weight in Brassica napus var pabularia. Hanif et al. (2006) obtained crude protein contents of 20 and 22.5 g per 100 g in Brassica oleracea var. capitata and Brassica oleracea var. botrytis, respectively. Vilar et al. (2008) reported crude protein contents for Galega kales between 10.4 and 24.5 g per 100 g dry weight. Glutamic acid was the most abundant amino acid in all samples, ranging from 17.76 (oxheart cabbage) to 14.53% (turnip green) of the total amino acids. Turnip top and turnip green showed the highest glutamic acid values (43.08 and 37.72 mg g)1 dry matter, respectively). Galega kale, turnip top and turnip green were also rich in arginine, aspartic acid and lysine, and they had medium values of alanine, glycine, histidine, isoleucine, leucine, proline, serine, threonine and valine. Methionine showed the lowest percentages. Compared with the kales and turnips, oxheart cabbages and white cabbages contained significantly less alanine, glycine, histidine, leucine, lysine, phenylalanine and valine; however, they contained more methionine. Oxheart cabbages had lower proline content than white cabbages. The nutritive value of the nitrogenous component depends on its content of essential amino acids. The green leaves of plants may supply most of the essential amino acids consumed by the man. The proportion of essential amino acids (arginine, phenylalanine, histidine, isoleucine, lysine, methionine, threonine and valine) in total amino acids was between 41 (turnip top) and 45% (oxheart cabbage) in the whole plants. Eppendorfer & Bille (1996) showed that the proportion of essential amino acids depended on the availability of nutrients during the development, and they observed that the methionine was the most limited essential amino acid in kale. The protein and amino acid content can vary significantly between the plant parts. Total crude protein, net protein, amino acid contents and essential amino acids composition of different edible portions (leaves and stems) are shown in Table 2. Much higher crude protein and net protein contents were found in the leaves than in the stems of kales and turnips. The crude protein content was between 35.43 (turnip green) and 19.70 g per 100 g dry weight (external leaves of white cabbages) in the leaves studied, and between 20.92 (turnip green) and 18.91 g per 100 g dry weight (turnip top) in the stems. The net content ranged between 32.89 (turnip top) and 15.99 g per 100 g dry weight (external leaves of oxheart cabbages) in the leaves, and between 17.50 (Galega kale) and 16.60 g per 100 g dry weight (turnip green) in the stems. No significant differences were observed between the crude protein and net protein of external and internal leaves in

cabbages or between oxheart cabbages and white cabbages. Rosa & Heaney (1996) found crude protein contents of 26.7 and 17–17.2 g per 100 g dry weight in leaves of Galega kales and Portuguese cabbages, respectively. These authors also obtained values between 10.3 and 17.8 g per 100 g in stems of Portuguese cabbages and between 9.5 and 19.0 g per 100 g dry weight in stems of Galega kales. Livingstone et al. (1980) observed that the proportion of crude protein in cabbages was 23%. Glew et al. (2005) showed net protein content in cabbage leaves (Brassica oleracea var. capitata) of 18.6 g per 100 g. Stems contained the same amino acids as the leaves but at a lower level. Differences in the proportions of individual amino acids between varieties were observed. In general, the leaves of Galega kale, turnip top and turnip green showed the highest amino acid contents. The leaves of oxheart cabbages and white cabbages showed similar amino acid contents to the stems of Galega kale, turnip top and turnip greens. Glutamic acid was the most abundant amino acid in the leaves of Galega kale, turnip top and turnip green, followed by lysine, proline, arginine, aspartic acid, leucine and alanine. Glutamic acid was also the most abundant amino acid in the leaves of cabbages, however, in this case, followed by arginine, lysine and aspartic acid. Glutamic acid, arginine, lysine, aspartic acid and proline were the most abundant amino acids in the stems. There were differences between external and internal leaves, although they were not significant in the majority of the cases. One exception was the glutamic acid, which was higher in the internal leaves than in the external leaves of the cabbages. The proportion of essential amino acids was high, ranging between 47 (external leaves of oxheart cabbages) and 41% (leaves of turnip top). There are important differences in the content of protein and amino acids in Brassica spp. found by several authors. These differences could be in part because of various factors such as genotype, environmental factors, growing conditions, maturity and part of the plant analysed (Kmiecik et al., 1999; Gomes & Rosa, 2000; Ishida et al., 2000; Lisiewska et al., 2004; Sincik et al., 2007; Martı´ nez et al., 2010). Ayaz et al. (2006) reported that the most abundant amino acid in kale leaves was glutamic acid (33.2 mg g)1 dry weight), followed by aspartic acid (27.6 mg g)1 dry weight). Lisiewska et al. (2008) also observed that glutamic acid was the main amino acid in kale leaves, however, in this case followed by proline and aspartic acid. Oliveira et al. (2008) studied the free amino acid of external and internal leaves of B. oleracea var. costata, and they reported that the major amino acid was the arginine. Kre˛z_ el et al. (1998) found the highest proportion in proline. Ishida et al. (2000) observed that the leaves contain more amino acids than the stems. Gomes & Rosa (2000)

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a–f

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

0.82bc 0.88bde 1.91bd 1.78bcd 0.45b 0.77b 0.17b 0.32b 1.71b 0.06b 0.70b 0.85b 1.05b 1.13b 0.70bd 0.97b 0.2b 0.43b

5.43 ± 0.67b

8.95 18.90 14.12 33.47 6.40 9.37 7.62 9.43 18.22 1.17 5.43 12.46 8.88 8.51 4.13 8.42 44 17.50

8.98 ± 1.90a

1.18a 1.15ac 1.86a 1.13ab 1.12a 1.01a 0.81a 1.79a 3.29a 0.21a 0.97a 0.47a 0.44a 1.57a 0.49a 0.70a 0.2ab 0.22a 19.77 ± 4.65b

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

34.40 ± 5.18a

20.29 27.30 25.75 40.27 16.87 13.44 17.18 23.91 30.00 1.98 12.18 28.20 15.88 17.90 6.70 14.97 42 30.28 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

2.14a 3.87c 5.88c 6.20a 1.58a 3.35a 2.76a 2.80a 4.60a 0.02b 1.07c 0.90a 2.69a 2.92a 0.72a 0.81a 2.5a 0.22a 9.70 18.70 13.93 30.19 6.03 9.18 7.85 9.82 16.89 1.14 5.77 14.77 8.73 8.38 4.13 9.19 44 17.44

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

0.78bc 1.01bd 1.24bd 3.59cd 0.48bd 0.25b 1.60bc 0.72b 0.92bc 0.11b 1.06b 1.97cf 1.29b 0.67b 0.32bd 1.91bd 1.5ab 0.46bc

10.63 ± 0.88a

5.52 ± 0.86b

33.16 ± 0.48a 18.91 ± 1.56b

21.04 28.98 32.14 46.32 15.78 14.16 16.08 23.87 30.88 1.39 10.63 29.37 17.38 18.77 6.98 15.17 41 32.89

Stems ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

2.04a 1.03a 3.25a 3.71bc 0.90c 1.15a 1.13a 2.67a 4.31a 0.18cb 1.19d 0.51d 1.28a 1.34a 0.48c 1.95c 1.3bc 1.85a

13.52 ± 1.04a

35.43 ± 3.25a

21.14 25.25 26.26 38.84 13.75 13.70 17.18 22.50 30.21 1.52 13.53 17.50 16.79 17.96 8.70 17.48 45 30.23

Leaves

Turnip green

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

0.58b 0.38b 1.37be 2.94cd 0.72d 0.39b 0.10cd 0.10b 2.38bc 0.12b 0.76b 0.62e 1.30b 0.83b 0.19d 1.15bd 0.1b 0.60b

5.86 ± 0.62b

20.92 ± 2.90b

7.89 16.06 17.97 32.08 4.89 9.08 9.64 9.27 15.89 1.12 5.86 7.89 9.23 6.15 3.83 9.19 44 16.60

Stems

White cabbage

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

0.35bc 2.55bde 0.83d 3.49d 0.51bd 0.28b 0.98cd 0.08b 1.57c 0.50ac 0.99b 0.69e 0.67b 1.07b 0.22be 0.50bd 1.0c 1.45b

5.70 ± 0.99b

19.83 ± 0.73b

9.75 17.80 9.41 27.50 5.86 8.40 9.89 9.99 13.61 1.85 5.70 8.19 8.67 8.56 4.85 9.86 47 15.99

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

1.82c 1.98bde 3.37bde 1.14bc 0.60bd 0.33b 0.44bcd 0.56b 1.55bc 0.39a 0.54b 1.12e 1.20b 1.34b 0.51ef 0.56bd 0.1ab 1.62bc

5.39 ± 0.84b

22.59 ± 4.70b

11.29 19.40 14.38 35.81 5.42 8.26 9.31 9.39 14.60 2.18 5.39 7.79 9.95 7.94 5.33 9.70 43 17.62

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

0.32b 4.16de 2.93be 3.98cd 0.62bd 0.47b 0.24bcd 0.34b 2.61bc 0.62ac 0.17b 0.76bc 0.73b 1.13b 0.22ef 0.87bd 0.7ab 1.77bc

5.22 ± 0.17b

19.70 ± 3.06b

8.77 20.93 17.07 32.82 5.24 8.16 9.32 9.22 14.15 1.94 5.22 13.54 9.22 7.82 5.35 9.11 43 17.79

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

2.44bc 3.19e 2.32e 1.58ab 0.66bd 0.74b 0.84d 0.85b 1.96bc 0.52a 0.87b 0.82df 0.79b 1.09b 0.29f 0.70d 0.6a 1.14c

5.71 ± 1.01b

22.09 ± 0.93b

9.73 22.26 19.64 40.88 5.97 8.47 10.20 10.09 15.58 2.27 5.82 15.78 10.56 8.91 5.79 10.98 41 20.29

External Leaves Internal Leaves External Leaves Internal Leaves

Oxheart cabbage

Mean values of at least three determinations ± standard deviation with different superscript in the same row were significantly different (P < 0.05).

Ala Arg Asp Glu Gly His Ile Leu Lys Met Phe Pro Ser Thr Tyr Val % Essential AAs Net protein (SAAs) (g 100 g)1) Crude protein (g N · 6.25 100 g)1) Dry matter (g 100 g)1 product)

Leaves

Leaves

Stems

Turnip top

Galega kale

)1 )1 )1 Table 2 Crude protein (g N · 6.25 100 g dry weight), net protein (g 100 g dry weight), amino acid (mg g dry weight) contents and essential amino acid composition (%) of edible portions (leaves and stems) of different Brassica spp

150 Protein, amino acid, ash and mineral contents S. Martı´nez et al.

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Protein, amino acid, ash and mineral contents S. Martı´nez et al.

Table 3 Ash and minerals contents of the edible portions of different Brassica spp

Galega kale Whole Leaves Stems Turnip top Whole Leaves Stems Turnip green Whole Leaves Stems Oxheart cabbage Whole External leaves Internal leaves White cabbage Whole External leaves Internal leaves

Ash (g per 100 g)

K (mg g)1)

Ca (mg g)1)

Mg (mg g)1)

Fe (mg g)1)

Zn (mg g)1)

Cu (lg g)1)

11.82 ± 1.37ab 10.42 ± 0.98a 13.80 ± 0.05ab

28.16 ± 1.78ab 23.62 ± 2.46a 31.03 ± 3.49b

17.48 ± 6.29a 18.49 ± 5.22a 15.83 ± 4.56a

2.92 ± 0.45a 2.85 ± 0.55ab 2.90 ± 0.37ab

0.139 ± 0.030ab 0.145 ± 0.021a 0.126 ± 0.027abe

0.031 ± 0.012abf 0.037 ± 0.009abc 0.029 ± 0.009af

5.77 ± 1.26ad 6.57 ± 0.92ac 6.35 ± 1.31acd

11.58 ± 1.64ab 10.55 ± 1.14a 14.27 ± 3.11b

30.24 ± 5.76b 26.25 ± 2.12ab 38.32 ± 0.78c

10.39 ± 1.85b 10.73 ± 2.68b 10.94 ± 1.10b

2.38 ± 0.57bcf 2.08 ± 0.17cdf 2.48 ± 0.48abc

0.099 ± 0.034bcd 0.089 ± 0.021cd 0.090 ± 0.037cde

0.040 ± 0.012bc 0.045 ± 0.012c 0.031 ± 0.008abf

7.34 ± 1.16ac 9.68 ± 1.41b 5.37 ± 1.08ad

11.23 ± 1.07ab 10.31 ± 0.15a 12.21 ± 1.46ab

37.57 ± 4.58c 27.23 ± 4.77ab 54.77 ± 7.96d

16.81 ± 3.45a 16.77 ± 1.83a 17.11 ± 4.48a

2.44 ± 0.44abc 2.40 ± 0.56bcf 2.48 ± 0.75abc

0.113 ± 0.036abd 0.124 ± 0.046abd 0.069 ± 0.017c

0.061 ± 0.013d 0.074 ± 0.007e 0.044 ± 0.006c

7.02 ± 1.25ac 9.49 ± 2.92b 7.79 ± 0.77bc

5.11 ± 0.02cd 5.67 ± 0.23c 4.74 ± 0.09d

27.97 ± 3.33ab 33.40 ± 5.08bc 27.51 ± 4.87ab

10.83 ± 2.73b 13.05 ± 4.02b 7.19 ± 0.98d

1.62 ± 0.38de 1.74 ± 0.10de 1.40 ± 0.29e

0.129 ± 0.023abd 0.137 ± 0.046ab 0.108 ± 0.017bd

0.027 ± 0.006f 0.025 ± 0.005f 0.031 ± 0.008abf

5.99 ± 1.93ad 6.91 ± 1.96ac 5.58 ± 0.53ad

6.18 ± 0.01e 6.89 ± 0.02e 5.74 ± 0.03c

27.24 ± 1.25ab 29.78 ± 5.11ab 28.11 ± 1.83ab

1.84 ± 0.18cde 2.07 ± 0.26cd 1.80 ± 0.26edf

0.026 ± 0.001f 0.031 ± 0.007f 0.037 ± 0.013f

0.032 ± 0.008abcf 0.022 ± 0.002f 0.036 ± 0.005abc

4.31 ± 0.31d 4.70 ± 0.32d 5.21 ± 0.63ad

4.27 ± 0.05c 5.21 ± 1.27cd 4.33 ± 0.22c

a–f

Mean values of at least three determinations ± standard deviation (dry weight) with different superscript in the same column were significantly different (P < 0.05).

and Oliveira et al. (2008) showed that the distribution of amino acids is not similar in internal and external leaves in Brassica spp. Ash and minerals

Brassica spp. are the good sources of minerals. However, the mineral contents can vary largely depending on species, variety and plant part or environmental factors such as soil. Ash and mineral contents of different edible portions of Brassica spp. grown in Galicia (Northwest Spain) are shown in Table 3. Significant variation among the varieties was observed in ash and mineral contents. The mean values for the ash content in whole plants ranged from 5.11 to 11.82 g per 100 g dry weight. The highest values for this parameter were observed in Galega kales, turnips top and turnips green, and the lowest in oxheart cabbages and white cabbages. Stems had higher concentrations of ash than leaves. External leaves showed higher ash content than internal leaves in the cabbages. The ash levels found are consistent with those reported by other authors. United States Department of Agriculture Nutrient Database showed values of 9.04, 17.47, 8.84, 8.61 and 15.68 g per 100 g dry weight in cabbages, Chinese cabbages, kales, turnips and turnip greens, respectively (Davis et al., 2004). Hanif et al. (2006) observed ash content in cabbages and cauliflower of 7.5 g per 100 g dry weight. Kmiecik et al. (2007) obtained ash content of 7.01, 8.60, 8.52 and 8.28 g per

100 g in Brussels sprouts, broccoli, white cauliflower and green cauliflower, respectively. Lisiewska et al. (2009) reported a value of 7.69 g per 100 g in Brassica oleracea var. acephala. Regarding the minerals elements, important differences were observed between varieties and plant parts. The potassium was, quantitatively, the most important element, followed by calcium and magnesium. The concentrations of potassium were higher in the stems. The greatest content of potassium was found in stems of turnip greens. In the leaves, potassium contents were between 23.62 (Galega kale) and 33.40 mg g)1 (external leaves of oxheart cabbage). In the stems, potassium content ranged from 31.03 (Galega kale) to 54.77 mg g)1 (turnip green). There were no significant differences observed between external and internal leaves in the potassium content of cabbages. Rosa & Heaney (1996) found also that potassium content was higher in the stems than in the leaves of Portuguese cabbages and Galega kales, and they observed similar values to those we have found. Kmiecik et al. (2007) observed potassium values of 30.35 mg g)1 in white cauliflower and 32.47 mg g)1 in green cauliflower. Puupponen-Pimia et al. (2003) obtained potassium content of 40.8 mg g)1 in cauliflower. Ayaz et al. (2006) and Lisiewska et al. (2009) reported lowest values in B. oleracea var. acephala (13.5 and 14.72 mg g)1 dry weight, respectively). Calcium was also found in an appreciable amount. The highest values were observed in Galega kales and turnip greens, while the lowest values were found in

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white cabbages. Calcium content was similar in stems and leaves. External leaves had a higher content of calcium than internal leaves in the cabbages, especially in oxhead cabbages. These data are consistent with the results reported by Ayaz et al. (2006) in B. oleracea var. acephala (19.7 mg Ca g)1 dry weight). Ekholm et al. (2007) found calcium contents between 4.2 and 4.9 mg g)1 in cabbages (Brassica oleracea var capitata). The results of the present study revealed similar magnesium contents for the leaves and the stems. The lowest magnesium content was observed in the cabbages. No significant differences were observed between internal and external leaves in the cabbages. These results are consistent with those of Rosa & Heaney (1996) in Galega kales and Portuguese cabbages. Ayaz et al. (2006) reported similar results in B. oleracea var. acephala. However, Ekholm et al. (2007) observed lower contents in Brassica spp. The greatest contents of iron were found in Galega kales, whereas the lowest contents were observed in white cabbages. Rosa & Heaney (1996) reported similar results; however, Ayaz et al. (2006), Ekholm et al. (2007) and Lisiewska et al. (2009) observed lower iron contents. The zinc concentrations were significantly higher in turnip greens, while cabbages had the lowest zinc concentrations. Zinc content was higher in the leaves than in the stems, and no significant differences between external and internal leaves were observed. These results were similar to those reported by Rosa & Heaney (1996), Ayaz et al. (2006), Ekholm et al. (2007) and Lisiewska et al. (2009) in Brassica oleracea. Turnip top and turnip green had the highest mean concentration of copper. Copper concentrations were significantly higher in leaves than in stems of turnip top. No significant differences were observed between external and internal leaves. Similar results were reported by Ayaz et al. (2006) and Ekholm et al. (2007). The health benefits of Brassica spp. are well known. The present results indicate that Brassica spp. grown and consumed in Galicia (NW Spain) are a good source of protein, amino acids and minerals. However, there are differences between varieties and edible parts. These results offer information that could be used to typify these varieties of Brassica spp. and to increase their consumption in other countries and regions. References Alonso, M.L., A´lvarez, A.I. & Zapico, J. (1994). Rapid analysis of free amino acids in infant foods. Journal of Liquid Chromatography, 17, 4019–4030. Ayaz, F.A., Glew, R.H., Millson, M. et al. (2006). Nutrient contents of kale (Brassica oleraceae L. var. acephala DC). Food Chemistry, 96, 572–579. Cartea, M.E., Rodrı´ guez, V.M., De Haro, A., Velasco, P. & Orda´s, A. (2008). Variation of glucosinolates and nutritional value in nabicol (Brassica napus pabularia group). Euphytica, 159, 111–122.

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