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.kg1
, 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 150oC for 5
min, then rising the temperatures until 210oC at 4oC min-1 and maintaining an
isothermal period of 60 min. The temperature of injector and detector was 250oC. 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).
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1. Instituto de Biociências, Universidade de São Paulo, Caixa Postal 11461, 05422-970 São Paulo, SP,
Brasil.
2. Departamento de Ciências Biológicas, Universidade Estadual de Feira de Santana, Km 3 BR116, Feira
de Santana, BA, Brasil.