Nutrient and fatty acid composition of wild edible bladder campion populations [Silene vulgaris (Moench.) Garcke]

Introduction

The use of edible wild species Silene vulgaris has been reported by several authors (Launert, 1982; Facciola, 1998). The consumption as a leafy vegetable of bladder campion is present in Turkey, Italy, Austria, Germany and Spain (Laghetti & Perrino, 1994). Several ethnobotanical studies (Rivera & Obón, 1991; Tardío et al., 2002) reveal that bladder campion is very much appreciable in the traditional gastronomy of many Spanish regions. The tender leaves are prepared by cooking, like spinach in vegetable pies or used raw in salads.

Edible wild plants are rich sources of essential fatty acids such as α-linolenic acid (18:3ω-3) and linoleic acid (18:2ω-6) (Simopoulos, 1988; Glew et al., 1997; Guil-Guerrero & Rodríguez-García, 1999; Zeghichi et al., 2003) and in addition, provide higher amounts of α-linolenic acid and antioxidant vitamins than cultivated plants (Simopoulos, 2004). In nutritional terms, the presence of ω-3 fatty acids are essential for normal growth and development and may play an important role in the prevention and treatment of coronary artery disease, hypertension, arthritis, other inflammatory and autoimmune disorders and cancer (Hamazaki & Okuyama, 2001).

In S. vulgaris, as in many other Caryophyllaceae, hermaphrodite and male sterile plants coexist in the same population (gynodioecy) and plants are alogamous. Thus, a considerable between-population variation has been detected in vegetative habit, phenology, seed morphology, leaf shape, leaf size (Wall & Morrison, 1990; Runyeon & Prentice, 1997, 2000).

This work attempts to contribute to the knowledge of the nutritional properties of wild edible Spanish bladder campion, which have not been, as far as we know, documented to date. Considering the possible domestication and the enlargement of their consumption, the present study examines the macronutrient and fatty acid composition of ten S. vulgaris wild populations collected at different sites from Central Spain.

Materials and methods

Samples

Seed samples from ten bladder campion populations were collected in July 2003 at ten different locations from Central Spain. Plant populations were located following Plant Information System in Spain (Proyecto Anthos, 2003) and seed samples from twenty to thirty plants were collected at each site. In October seeds were sown in an indoor greenhouse, in organic production system. Tender leaves were collected in March 2004, and at least twenty separate plants from each population were pooled to form a single population sample.

Before analysis, the leaves were washed and residual moisture was evaporated at room temperature, and plant material were freeze-dried and ground in a mortar. The finely ground materials were then analysed for proximate and fatty acid composition in three replicates. Mean and standard errors of three values are reported.

For comparative purposes nutrient parameters of green vegetables were taken from USDA National Nutrient Database for Standard Reference (US Department of Agriculture, Agricultural Research Service, 2004). As their same edible use, Spinacia oleracea and Beta vulgaris data were selected among leafy green vegetables.

Proximate analysis

The following analyses were carried out. Moisture content was determined by drying a representative 3 g of sample in a oven with air circulation at 103 °C for 24 h. Total ash was determined by incineration of a representative 0.5 g of sample in an oven at 450 °C for 48 h. Total dietary fibre content was determined by the neutral detergent fibre method (Goering & Van Soest, 1970). Available carbohydrates were estimated by the anthrone method, with spectrophotometric measurement (Osborne, 1986). Crude protein was estimated by the Kjeldhal method. A factor of 6.25 was used to convert nitrogen content to protein values. The lipid content was determined by petroleum ether extraction in a Soxhlet apparatus. A representative 5 g of dried sample was extracted during 24 h.

Fatty acid analysis

For fatty acid analysis, fat extracts were methylated using a mixture of boron-trifluoride, hexane and methanol as described by Morrison & Smith (1964). The resultant fatty acid methyl esters were analysed by gas chromatography using a Chrompack CP-9001 gas chromatograph (Chrompack Instrumental Bv, Middelburg, The Netherlands) equipped with a 30-m narrow bore 0.32-mm (ID) WCOT capillary column (0.50-μm film thickness, Chrompack). Analyses were performed with a temperature programme from 170 to 250 °C at a rate of 3.5 °C min⁻¹, and the carrier gas (N₂) at flow rate of 4.5 mL min⁻¹. Pentadecanoic acid was used as internal standard.

Results and discussion

The proximate composition of ten S. vulgaris populations analysed, locations of collected populations and registered data from S. oleracea and B. vulgaris are given in Table 1. Data are reported as nutrient value per 100 g of edible portion of fresh weight. Coefficients of variation across S. vulgaris populations are shown in the table.

In general, different nutrient contents were found in a similar range among populations, showing low levels of coefficients of variation. Populational variability was higher for available carbohydrates and ashes and lower for moisture content. Highest values for moisture content, ashes, lipids, fibre and available carbohydrates were found in SV-8 (88.5%), SV-4 (0.4%), SV-3 (0.8%), SV-7 (3.1%) and SV-6 (3.9%) populations respectively. Regarding protein content the highest value (3.6%) corresponded to SV-3 and SV-9 populations. Moisture content, fibre and protein were found to be in the range of that for S. oleraceae. Lipid content was found to be higher in S. vulgaris populations (between 0.6% and 0.8%) than in B. vulgaris (0.1%) and S. oleraceae (0.3%). Conversely, data from ashes showed lower values in S. vulgaris (between 0.2% and 0.4%) than in B. vulgaris (1.1%) and S. oleraceae (1.7%) and in turn, available carbohydrate values were lower for S. vulgaris (between 2.9% and 3.9%) than for B. vulgaris (6.7%), however, higher than for S. oleraceae (1.4%).

Fatty acid contents of S. vulgaris populations, S. oleracea and B. vulgaris species and coefficients of variation across populations are recorded in Table 2. The fatty acids found in S. vulgaris populations studied were palmitic (C16:0), stearic (C18:0), oleic (C18:1), linoleic (C18:2), linolenic (18:3) and erucic (C22:1) acids. Other fatty acids of undetermined structure ranging from 3% to 4% were present in S. vulgaris populations.

The saturated fatty acids palmitic and stearic acids were found in lower amounts than those reported for spinachs and beets. Palmitic acid values ranged from 10.6% to 15.1% and the percentages of stearic acid among populations showed a high coefficient of variation (50.2%) and ranged from 0.2% to 0.8%. The monounsaturated fatty acids found in S. vulgaris populations were oleic and erucic acids. With regard to oleic acid values were found to be similar to S. oleracea (2.1%) and lower than that for B. vulgaris (27.2%). Coefficients of variation showed high differences among populations for erucic acid (from 2.1% to 5.5%). Intraspecific comparison in this alogamous species reveals that, under the same environmental growth conditions, variability at the populational level in fatty acids stearic and erucic may be related to genetic variation. Erucic acid, is a toxic acid which induces the development of myocarditis (Concon, 1988). For domestication purposes, selection of S. vulgaris populations with low contents of erucic acid can be conduced.

High amounts of polyunsaturated fatty acids linoleic and α-linolenic acids were found across populations. Linoleic acid content of S. vulgaris populations had higher values (from 18.9% to 24.4%) than that for S. oleracea and in turn, α-linolenic acid content (from 51.2% to 56.9%) was similar to the levels reported for S. oleraceae, but higher than that for B. vulgaris. In addition essential fatty acid contents from S. vulgaris were higher than those found in leafy wild edible species previously reported (Guil-Guerrero & Rodríguez-García, 1999; Guil-Guerrero et al., 2003; Glew et al., 2005).

To our knowledge the present work is the first report on the proximate and fatty acid composition of tender leaves of S. vulgaris. The remarkable high content on essential fatty linolenic and linoleic acids must be emphasised. These results reinforce the growing awareness that wild edible plants can contribute with useful amounts of essential nutrients to human diets and agree with previous reports, which show that wild edible species are rich sources of essential fatty acids (Simopoulos, 1988; Glew et al., 1997; Zeghichi et al., 2003). Moreover, aggressive, industrialised agricultural management techniques have decreased the essential fatty acid content in many cultivated species. Our data show that the wild edible species S. vulgaris exhibited a good nutritional potential although further research will be needed to complete the nutritional profile of this species. Furthermore, in developing new sources of food, the assessment of the bioavailability of essential nutrients and study of dietary composition in this species needs to be undertaken.

References