Seeds of species from the ‘caatinga’: proteins, oils and fatty acid contents

Seeds of species from the ‘caatinga’: proteins, oils and fatty acid contents

MARCO AURÉLIO S. MAYWORM¹ , ANDRÉA SERRA DO NASCIMENTO² and ANTONIO SALATINO¹

(recebido em 20/01/98; aceito em 24/06/98)

ABSTRACT - (Seeds of species from the ‘caatinga’: proteins, oils and fatty acid contents). The seeds of 14 species from the ‘caatinga’, a dry forest ecosystem of the semiarid region of northeast Brazil, were analysed for total protein and total lipid contents, as well as fatty acid distribution. The seeds of Argemone mexicana L., an introduced and naturalized species in Brazil, commonly found in ‘caatingas’ and other vegetation, were also analysed. The protein contents ranged from 123 g.kg^-1 to 551 g.kg^-1, higher contents being found in species of Leguminosae, but also in Jatropha mollissima (Pohl) Baill. (Euphorbiaceae, 409 g.kg^-1). Oil contents ranged from 10 g.kg^-1 to 400 g.kg^-1. The contents of protein and oil were found to be inversely proportional in the seeds of most species, the figures for proteins being generally higher than those of oils. Most species presented either oleic or linoleic as predominant fatty acids. Cardiospermum cf. corindum L. presented eicosenoic acid as the predominant fatty acid.

RESUMO - (Sementes de espécies da "caatinga": teores de proteínas, óleos e ácidos graxos). Sementes de 14 espécies da caatinga, um ecossistema de floresta seca do semiárido do nordeste do Brasil, foram analisadas para proteína total, teor de lipídeos e distribuição de ácidos graxos. As sementes de Argemone mexicana L., uma espécie introduzida e naturalizada no Brasil, geralmente encontrada na caatinga e em outras vegetações, foram também analisadas. Os teores de proteínas variaram de 123 g.kg^-1 a 551 g.kg^-1, teores mais elevados sendo encontrados nas espécies de Leguminosae, mas também em Jatropha molissima (Pohl) Baill. (Euphorbiaceae, 409 g.kg^-1). Teores de óleo variaram de 10 g.kg^-1 a 400 g.kg^-1. Os teores de proteína e óleo encontrados foram inversamente proporcionais na maioria das espécies, sendo os números para proteínas geralmente superiores que aqueles de óleo. A maioria das espécies apresentou ácido oléico ou linoléico como predominante. Cardiospermum cf. corindum L. apresentou ácido eicosenóico como ácido graxo predominante.

Key words - ‘Caatinga’, semiarid ecosystems, seed proteins, seed oils, fatty acids

Introduction

The ecosystem of the regions of Brazil with the lowest availability of edaphic water is called ‘caatinga’, a South-American Indian name that means ‘white forest’, because of the deciduous habit of most of its species. It covers an area of 834,666 km² of northeast Brazil (Andrade-Lima 1981). The ‘caatingas’ as a whole correspond to 80% of the ‘Polígono das Secas’ (drought polygon), an economic-social designation of the semiarid region of the Brazilian northeast, inhabited by approximately 23 million people and corresponding to the largest demographic semiarid area of the world located in a single country (Batista Filho & Batista 1996). The ‘caatingas’ are conditioned by the BSH Koeppen’s climate, with a high evapotranspiration potential (1500-2000 mm annually) all over the year and low pluviometric precipitation (300-1000 mm annually), usually concentrated in 3-5 months (Reddy 1983).

Few crops are commercially exploited in the region, mainly beans, cassava and corn. The circumscription of commercial food production to a reduced number of plants contributes to the long standing condition of undernourishment of a significant proportion of the population, which has characterized the Brazilian semiarid (Castro 1946, EMBRATER 1980, Batista Filho & Batista 1996). Some seed oil palms, like oiticica (Licania rigida Benth.) and licuri (Syagrus coronata (Mart.) Becc.) are grown in the area and their products industrialized. Unfortunately, the market for their oils has recently followed a downward direction, with low prices and reduced production. Several species of Cnidosculus (Euphorbiaceae) are native in the region and furnish high quality oils. However, there is as yet no commercial production of Cnidosculus seed oils, because the fruits are dehiscent and the plants are extremely spiny. Copernicia prunifera (Miller) H.E. Moore, the carnaúba palm, is a local traditional source of the high prized carnaúba wax (the ‘queen of the waxes’), which has however suffered from competition by the synthetic and petroleum derived products (Hamilton 1995).

The search for new sources of food and industrial products derived from the local biota is essential for promotion of the economic and social development of the Brazilian semiarid. The present work presents data of the contents of seed proteins and oils, as well as the distribution of the seed fatty acids of some common species of the ‘caatingas’. In addition to the nutritional and industrial interest connected to the seed proteins and oils, it is hoped that the data on distribution of fatty acids may contribute to taxonomic discrimination at various hierarchic levels (Shorland 1963, Harborne & Turner 1984).

Material and methods

Samples of mature fruits were collected in an area of ‘caatinga’ located in Itatim, state of Bahia, Brazil. All the species studied are native of the ‘caatinga’, except Argemone mexicana L., which was introduced from North America and is presently naturalized in many environments of the Brazilian territory. Specimens of A. mexicana are very often found in ‘caatingas’, probably because of their xerophilous characteristics. Voucher specimens of each sample are deposited in the Herbarium of the Departamento de Ciências Biológicas of the Universidade Estadual de Feira de Santana - HUEFS (table 1). The fruits were kept in the shade until dehiscence and the seeds were maintained in a refrigerator prior to analysis.

The contents of total nitrogen was determined by the micro-Kjeldahl method and the results were expressed as total proteins, using the factor 6.25 (AOAC 1995).

Oil extraction was done in duplicate. For each sample, 10 g of seeds were ground and homogenized with mortar and pestle. The divided material was extracted in Soxhlet with n-hexane for 10 h, protected from the light. The solvent was evaporated under reduced pressure, transferred to amber vials, where the remaining solvent was eliminated under a N₂ flow. The vials were kept in a desiccator until constant weight (Zygadlo & Guzman 1986, Ferlay et al. 1993). The glycerides were saponified during 2 h with 100 g.l^-1 KOH under reflux. After acidification of the resulting solution with 2 M HCl until pH 4.0 - 5.0, the fatty acids were extracted with chloroform (Grunwald & Endress 1988) and the solvent evaporated, first in a rotatory evaporator under reduced pressure and then under a N₂ flow. The fatty acids were derivatized to the corresponding methyl esters with a freshly prepared ether solution of diazomethane. The methyl esters were analyzed by GC-MS in a 5890 ser. II Plus HP chromatographer interfaced with a ChemStation System 5889B HP mass spectrometer, using a HP Ultra-1 capillary column (25 m X 0.25 mm) of fused silica and helium as carrier gas at a flow of 1 cm³.min^-1. The temperatures of the column involved a program starting at 150^oC for 5 min, then rising the temperatures until 210^oC at 4^oC min^-1 and maintaining an isothermal period of 60 min. The temperature of injector and detector was 250^oC. The ionization was accomplished by the electron impact technique at 70 eV. The identification of the compounds was achieved by comparison with standards and comparison of the mass spectra obtained with those of the Wiley 275 library.

Results and Discussion

Table 1 presents the contents of seed proteins and oils and the distribution of the fatty acids of the seed glycerides of the examined plants. It is clear that the seeds of most species present a higher protein than oil content. As expected, seeds of Leguminosae species yielded in general relatively high contents of proteins, outstanding examples being Senna spectabilis var excelsa (Schrad) Irwin & Barneby, Canavalia brasiliensis (Mart.) Benth. and Mimosa arenosa (Willd) Poir., all with protein contents above 400 g.kg^-1 (table 1). Surprisingly, the lowest protein content found (123 g.kg^-1) was also in a member of species of Leguminosae (Poecilanthe ulei (Horms) Arroyo & Pudd, table 1). The seeds of Jatropha mollissima (Pohl) Baill. (Euphorbiaceae) rivalled those of Leguminosae species in protein content (409 g.kg^-1). Relatively high contents of proteins were found also in seeds of Capparis yco Mart. (316 g.kg^-1) and Cardiospermum cf. corindum L. (301 g.kg^-1). These results must be viewed with caution, because the contents of proteins were calculated on the basis of total nitrogen, and not all the seed nitrogen corresponds necessarily to proteins. For example, there are species of Canavalia extremely rich in toxic non protein amino acids, specially canavanine (Harborne & Turner 1984).

Relatively high oil content was found in seeds of Argemone mexicana (400 g.kg^-1), Aspidosperma pyrifolium Mart. (344 g.kg^-1) and Jatropha mollissima (378 g.kg^-1) (table 1). With the exception of J. mollissima, which has seeds with both high oil and protein content, species rich in seed proteins (considered as such those with contents above 300 g.kg^-1) have low seed oil content and vice versa (table 1). The low protein content of Pilosocereus gounellei (F.A.C. Weber) Byles & Rowley (175 g.kg^-1) seems to follow a general trend in Cactaceae seeds (Serrano & Guzman 1991, 1994).

With regard to the distribution of seed fatty acids, oleic acid was predominant in Aspidosperma pyrifolium Mart., Cordia glabrata A. DC., Capparis yco and in the three species of Fabaceae; linoleic acid predominated in Pilosocereus gounellei, Jatropha mollissima, Argemone mexicana, and in all species of Caesalpiniaceae and Mimosaceae investigated. Relatively high contents of stearic acid were found in seeds of Aspidosperma pyrifolium (271 g.kg^-1), Caesalpinia pyramidalis Teel. (153 g.kg^-1) and Capparis yco (180 g.kg^-1, table 1). Cardiospermum cf. corindum is notable for the predominance of eicosenoic acid (table 1). Such fatty acid pattern is probably a characteristic of the Sapindaceae, since similar results were observed in other species of Cardiospermum (e.g. Mayworm & Salatino 1996a), and in species of Serjania and Urvillea (Abburra & Guzman 1986, Abburra et al. 1992).

It is interesting to note that the species of Caesalpiniaceae and Mimosaceae all presented a predominance of linoleic acid, while all the studied species of the related family Fabaceae showed predominance of oleic acid in their seeds (table 1). In addition, in the species of Fabaceae here studied there is a consistent presence, albeit in low levels, of fatty acids with chains C₂₀ or longer. There seems to be a difference in the distribution of fatty acids of Caesalpiniaceae and Mimosaceae from the ‘caatinga’ vs. ‘cerrado’ habitat, for in the species of the latter vegetation a trend was observed for the predominance of palmitic acid in seeds of both taxa (Mayworm & Salatino 1996a).

Aspidosperma pyrifolium is similar to A. tomentosum Mart., a species of the ‘cerrado’, in that both have oleic acid as the predominant seed fatty acid, although apparently only the former presents a relatively high stearic acid content (271 g.kg^-1, table 1), a pattern not observed in the latter (Mayworm & Salatino 1996a).

The predominance of oleic acid, as in Cordia glabrata (table 1), is not always observed in other Boraginaceae, even in species of Cordia. For example, in seeds of Cordia rothii Roem & Schult. linoleic acid predominate (Daulatabad et al. 1992) and linolenic acid is the main seed fatty acid of Cordia myxa L. (Mukarram et al. 1986).

The fatty acid pattern of Pilosocereus gounellei (table 1) is very similar to that of another species of Cactaceae from the ‘caatinga’ (Cereus jamacaru DC., Mayworm & Salatino 1996b) and resembles those of species from Argentina, although the relative contents of oleic acid in the latter is much lower (Serrano & Guzman 1991, 1994).

The present results concerning the seed oils of Jatropha mollissima are in general agreement with the fatty acid patterns found by Teixeira (1987), although the content of oil found in the present investigation is substantially higher than the contents reported by that author for the same species.

Argemone mexicana seeds also had a predominance of linoleic acid (table 1), a pattern common to some species of Papaver (Deninsenko & Stepanenko 1977, Singh et al. 1990). The high content of seed oil (400 g.kg^-1, actually the highest yield found in this survey, table 1), herbaceous habit, high seed production and hardiness of Argemone mexicana are characteristics that recommend this species (which is regarded as a noxious weed in Brazil, Lorenzi 1991) as a possible commercial source of seed oils to be grown under the climatic and edaphic conditions of the ‘caatinga’. With exception of the habit, similar comments apply also to Jatropha mollissima, a tree species which is one of the most common Euphorbiaceae in the ‘caatingas’. It is noteworthy that their seeds were the only ones which showed contents of oils and proteins above 300 g.kg^-1. Other favorable characteristics of Jatropha mollissima as seed oil source are the relatively large size of its seeds, thin tegument and high capacity of the seeds to germinate under ‘caatinga’ conditions, as judged by the relatively high numbers of plantlets found in the natural environment (Suzene I. da Silva, personal communication). The high economic potential of Jatropha mollissima has already been emphasized (Teixeira 1987).

Acknowledgements - The authors wish to acknowledge Mr Luciano Q. Paganucci for the identification of plant material, and financial support provided by FAPESP (Fundação de Amparo à Pesquisa do Estado de São Paulo), CAPES (Fundação Coordenação de Aperfeiçoamento de Pessoal de Nível Superior) and CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico).

2. Departamento de Ciências Biológicas, Universidade Estadual de Feira de Santana, Km 3 BR116, Feira de Santana, BA, Brasil.

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1

. Instituto de Biociências, Universidade de São Paulo, Caixa Postal 11461, 05422-970 São Paulo, SP, Brasil.

Publication Dates

• Publication in this collection
  25 Feb 1999
• Date of issue
  Dec 1998

History

• Accepted
  24 June 1998
• Received
  20 Jan 1998