Evaluación del valor nutricional y
factores antinutricionales de Dioscorea spp. silvestre
P.S. Shajeela1,
V. R. Mohan2*, L. Louis Jesudas3 and P. Tresina Soris2
1 PG & Research
Department of Botany, St. John's College, Palayamkottai, Tamil Nadu, India.
2 Ethnopharmacology
Unit, Research Department of Botany, V.O.Chidambaram College, Tuticorin, Tamil
Nadu, India. *Corresponding Author
3 PG & Research
Department of Botany, St. Xavier 's College, Palay amkottai, Tamil Nadu, India.
Abstract
The wild yam tubers
consumed by the tribes Kanikkars / Palliyars of South- Eastern slopes of Western
Ghats, Tamil Nadu (Dioscorea alata, D. bulbifera var vera, D.
esculenta, D. oppositifolia var dukhumensis, D.oppositifolia var. oppositifolia,
D. pentaphylla var. pentaphylla, D. spicata, D. tomentosa and D.
wallichi) were evaluated for its nutritional quality. From the present
investigation, it is observed that most of the wild edible yams were found to
be a good source of protein, lipid, crude fibre, starch, vitamins and minerals.
Antinutritional substances like total free phenolics, tannins, hydrogen
cyanide, total oxalate, amylase and trypsin inhibitor activities were
quantified.
Key words: Proximate and
mineral composition; vitamins; in vitro digestibility; antinutrients.
Resumen
Los tubérculos de
variedades silvestres de Dioscorea spp. Son consumidos por las tribus Kanikkars
/ Palliyars de la región sur y oriental de los Ghats Occidentales de Tamil
Nadu. Dioscorea alata, D. bulbifera var vera, D. esculenta, D.
oppositifolia var dukhumensis, D.oppositifolia var. oppositifolia,
D. pentaphylla var. pentaphylla, D. spicata, D. tomentosa y D.
wallichi fueron evaluados en cuanto a su calidad nutricional. Se encontró
que fueron una buena fuente de protein, lÃpidos, fibra cruda, almidón,
vitaminas y minerales. Adicionalmente se cuantificó el contenido de fenoles
totales libres, taninos, cianuro de hidrógeno y oxalatos totales. Se cuantificó
también la actividad de los inhibidores de amilasa y tripsina.
Palabras claves: composición
proximal; contenido de minerales; vitaminas; digestibilidad in vitro.
INTRODUCTION
With
ever-increasing population pressure and fast depletion of natural resources, it
has become extremely important to diversify the present-day agricultural in
order to meet various human needs (Janardhanan et al, 2003). The world
food crisis has been and will continue to be a major obstacle to humanity. The
observed interest in search for alternative / additional food and feed
ingredients is of paramount importance mainly for two reasons, one is the low
production of oil seeds and grains and another is the stiff competition between
man and the livestock industry for existing food and feed materials (Siddhuraju
et al, 2000). Root and tubers are the most important food crops since
time immemorial in the tropics and subtopics (Behera et al., 2009).
Roots and tubers refers to any growing plant that stores edible material in
subterranean root, corm and tuber. The nutritional value of roots and tubers
lies in their potential ability to provide one of the cheapest sources of
dietary energy in the form of carbohydrates in developing countries (Ugwu,
2009).
Yams (Dioscorea)
belong to Dioscoreaceae family. They are herbaceous plants with twine.
Approximately 600 Dioscorea species are eaten in various parts of the
world. (Agbor-Egbe and Treche, 1995). Yams, the edible starchy tubers, are of
cultural economic and nutritional importance in the tropical and subtropical
regions of the world (Coursey, 1967). Yam has been suggested to have
nutritional superiority when compared with other topical root crops. They are
reported as good sources of essential dietary nutrients (Baquar and Oke, 1976;
Bhandari et al, 2003; Shanthakumari et al, 2008; Maneenoon et
al, 2008; Arinathan et al, 2009). Earlier reports have also pointed
out that a few yam species contain some toxic compounds and can impact serious
health complications (Anthony, 2004). Some species of wild yams, particularly
wild forms, are toxic and / or unpalatable, taste bitter and cause vomiting and
diarrhoea when large amount are ingested without proper processing or if eaten
raw (Webster et al, 1984).
These wild yams
make a significant contribution in the diets of the tribal people of India. The
tubers were found with a high amount protein, a good proportion of essential
amino acids and appeared as a fairly good source of many dietary minerals.
However, their wider utilization is limited due to the presence of some toxic
and antinutritional factors. In India the cooked wild tubers are known to be
consumed by the Palliyar and Kanikkar tribes (Arinathan et al, 2007;
Shanthakumari et al., 2008) living in South-Eastern slopes of Western
Ghats, Tamil Nadu. Information regarding the chemical and nutritional content
of wild edible tuber is meager (Babu et al., 1990; Nair and Nair, 1992;
Rajyalakshmi and Geervani, 1994; Shanthakumari et al, 2008; Alozie et
al, 2009; Arinathan et al, 2009). Studies of nutritional value of
wild plant food are of considerable significance since it may help to identify
long forgotten food resources. In this context, an attempt was made to
understand the chemical composition and antinutritional factors of the under
utilized tubers of nine species of Dioscorea to suggest ways and means
to remove the antinutritional / toxins and make the edible tubers as the safe
food sources for mass consumption.
MATERIALS AND
METHODS
Nine samples of
wild yam tubers {Dioscorea alata, D. bulbifera var vera, D.
esculenta, D. oppositifolia var dukhumensis, D.oppositifolia var. oppositifolia,
D. pentaphylla var. pentaphylla, D. spicata, D. tomentosa and D.
wallichi) grown in sandy loam soil consumed by the tribal Kanikkars /
Palliyars were collected using multistage sampling technique in three
consecutive rainy seasons during August and January 2009 from the South Eastern
Slopes of Western Ghats, Virudhunagar district, Madurai district and
Kanyakumari district, Tamil Nadu.
Moisture content
was determined by drying the samples in an oven at 80°C for 24hrs and was
expressed on a percentage basis. The samples were powdered in Willey mill 60
mesh sizes and stored in screw cap bottles at room temperature for further
analysis. Nitrogen content was estimated by the micro-kjeldhal method
(Humphries, 1956) and crude protein was calculated (N x 6.25).
The contents of
crude lipid, crude fibre and ash were estimated by AOAC (2005) methods.
Nitrogen free extract was obtained by difference method by subtracting the sum
of the protein, fat, ash and fibre from the total dry matter (Muller and Tobin,
1980). The energy value of the tuber was estimated (KJ) by multiplying the
percentages of crude protein, crude lipid and NFE by the factors 16.7, 37.7 and
16.7 respectively (Siddhuraju et al, 1996). From the triple acid
digested sample, sodium, potassium, calcium, magnesium, iron, copper, zinc and
manganese were analyzed using an atomic absorption spectrophotometer (Perkin
Elmer Model 5000) (Issac and Johnson, 1975). Phosphorus was estimated
colorimetrically (Dickman and Bray, 1940). The total starch was determined by
the titrimetric method of Moorthy and Padmaja (2002). The antinutritional
factors, total free phenolics (Sadasivam and Manickam, 1996), tannins (Burns,
1971), hydrogen cyanide (Jackson, 1967), total oxalate (AOAC, 1984), trypsin
inhibitor activity (Sasikaran and Padmaja, 2003) and amylase inhibitor activity
(Rekha and Padmaja, 2002). In vitro protein digestibility was determined
using the multi-enzyme technique (Hsu et al, 1977) and in vitro
starch digestibility was assayed by Padmaja et al. (2001).
RESULTS AND
DISCUSSION
The crude protein (Table
1) content of the various species of Dioscorea tubers investigated in
the present study was found to be in agreement with the earlier investigation
in the species of Dioscorea tubers (Onyilagha and Lowe, 1985;
Rajyalakshmi and Geervani, 1994; Akissoe et al, 2001; Shanthakumari et
al, 2008; Alozie et al, 2009; Arinathan et al, 2009). Among
the two varieties of D. oppositifolia tubers, the variety dukhumensis
contained more crude protein than the variety oppositifolia. This value
is found to be consonance with earlier reports (Arinathan et al, 2009).
The crude lipid content of D. oppositifolia var dukhumensis was
found to be higher when compared to the presently investigated other Dioscorea
species. The content of crude lipids in the tubers oà Dioscorea species
exhibited more crude lipid content than the earlier reports in the tubers of D.
alata (Udensi et al, 2008); D. oppositifolia, D, bulbifera, D.
pentaphylla, D. hispida (Rajyalakshmi and Geervani, 1994) and D.
rotundata (Akissoe et al, 2001); D. calicola, D. daunea,
D.wallichi, D. stemonoides and D. glabra (Maneenoon et al,
2008). The crude fibre content in the presently investigated tubers of D.
esculenta, D. oppositifolia var oppositifolia, D. pentaphylla var
pentaphylla, D.spicata andD. wallichi were found to be more than that in
the earlier reports inD. bulbifera (Pramila et al, 1991); D.
oppositifolia, D. pentaphylla (Murugesan and Ananthalakshmi, 1991); D.
alata (Udensi et al, 2008); D. bulbifera, D. deltoidea, D.
versicolor and D. triphylla (Bhandari et al, 2003). The
nitrogen free extractives (NFE) in the tubers of D. alata, D. bulbifera
var vera, D. pentaphylla var pentaphylla, D. spicata and D.
tomentosa were higher (above 75%).
Table 2
This value was
found to be higher than that of the previous studies in the Dioscorea
spp (Rajyalakshmi and Geervani, 1994; Akissoe et al, 2001; Pramila et
al, 1991). The calorific value of all the investigated Dioscorea
spp. was less than that of earlier studies in the tubers oà Dioscorea
spp. (Arinathan et al, 2009). Robinson (1987) reported that a diet that
meets two-third of the RDA (Recommended Dietary Allowance) values is considered
to be adequate for an individual. The tubers of D. oppositifolia var. oppositifolia
and D. wallichi were found to contain higher calcium content than that
of RDA's of NRC/NAS, (1980) for infants and children. The magnesium content of D.
alata was found to be more when compared to that of the other Dioscorea
species.All the investigated tubers were found to contain higher magnesium
content than that of RDA's of NRC/NAS (1980) for infants and children. The
tubers of D. bulbifera var vera, D. esculenta, D. oppositifolia
var dukhumensis and D. oppositifolia var oppositifolia were found
to contain higher level of potassium when compared with RDA's of infants and
children (<1550mg) (NRC/NAS, 1980). The high content of potassium can be
utilized beneficially in the diets of people who take diuretics to control
hypertension and suffer from excessive excretion of potassium through the body
fluid (Siddhuraju et al., 2001). The manganese content of D.
bulbifera var vera was found to be high when compared to that of the
other investigated Dioscorea species. All the investigated tubers
appeared to have a higher level of manganese content compared to ESADDI of
infants, adults and children of NRC/NAS (1989).
The amount of
starch (Table 3) estimated in the tubers of Dioscorea sp. were higher
than that of the earlier reports in the species of Dioscorea
(Rajyalakshmi and Geervani, 1994; Arinathan et al., 2009). The niacin
content in the tubers of Dioscorea alata, D. bulbifera var vera, D,
esculenta, D. oppositifolia var oppositifolia, D. pentaphylla var pentaphylla,
D. spicata and D. wallichi were found to be higher than in the
tubers of Dioscorea species (Rajyalakshmi and Geervani, 1994; Arinathan et
al., 2009). The starch content of D. bulbifera var vera, D.
oppositifolia var dukhumensis, D. pentaphylla var pentaphylla
and Dioscorea tomentosa was found to be more when compared with the
earlier reports of same wild edible yams (Arinathan et al., 2009). This
difference may be due to some edaphic factors. Among the investigated tubers D.
bulbifera var vera, D. oppositifolia var dukhumensis and D.
pentaphylla var pentaphylla registered the highest ascorbic acid
content than the earlier studied tubers of D. alata (Udensi et al.,
2008).
The antinutritional
factors like total free phenolics, tannins, hydrogen cyanide, total oxalate,
amylase inhibitor and trypsin inhibitor activities are presented in Table 4.
Phenolic compounds inhibit the activity of digestive as well as hydrolytic
enzymes such as amylase, trypsin, chymotrypsin and lipase (Salunkhe, 1982).
Among the various species of Dioscorea, the tubers of D. bulbifera
var vera contained more free phenolics (Table 4). This value was found
to be higher than that of the earlier studies in the tubers of Ipomoea
batatus (Adelusi and Ogundana, 1987). D. esculenta, D. alata, D.
rotundata (Babu et al., 1990; Sundaresan et al., 1990); Manihot
esculenta and Ipomoea batatus (Babu et al., 1990). Recently
phenolics have been suggested to exhibit health related functional properties
such as anticarcinogenic, antiviral, antimicrobial, anti-inflammatory,
hypotensive and antioxidant activity (Shetty, 1997). The level of tannins,
hydrogen cyanide and total oxalate were found to be lower when compared with
the earlier reports of the tubers of Dioscorea alata, D. cayenensis, D.
rotundata and D. esculenta (Esuabana, 1982). The tubers of D.
oppositifolia var dukhumensis and D. oppositifolia var oppositifolia
contained more trypsin inhibitor activity when compared with earlier reports in
the tubers of D. dumetorum and D. rotundata (Sasikiran et al.,
1999). The phenolics and tannins are water soluble compounds (Uzogara et
al., 1990) and as such can be eliminated by soaking followed by cooking
(Singh, 1988; Murugesan and Ananthalakshmi, 1991; Kataria et al., 1989;
Singh and Singh, 1992; Shanthakumari et al, 2008). A lot of hydrogen
cyanide (known to inhibit the respiratory chain at the cytochrome oxidase level)
is lost during soaking and cooking (Shanthakumari et al, 2009) so that
its content in the tubers posses no danger of toxicity. Boiling for sufficient
time makes the tuber soft enough and inactivates all the trypsin inhibitor
(Bradbury and Holloway, 1988).
Table 5 shows the
data of in vitro protein digestibility and in vitro starch
digestibility. In all the presently investigated samples, the in vitro
protein digestibility (IVPD) is found to be very low. The in vitro
protein digestibility of D. oppositifolia var. oppositifolia and D.
spicata was found to be higher when compared with the earlier reports of D.
oppositifolia var. dukhumensis, D. pentaphylla var. pentaphylla,
D. tomentosa and D. spicata (Mohan and Kalidas, 2010). However, in vitro
starch digestibility (IVSD) of the tubers Dioscorea bulbifera var vera,
D. pentaphylla var. pentaphylla, D. spicata and D. tomentosa is
found to be higher than that of the previous reports of D. oppositifolia, D.
bulbifera, D. pentaphylla, D. hispida and the pith of Caryota urens
(Rajyalakshmi and Geervani, 1994).
CONCLUSIONS
Based on the
nutritive evaluation studies on the wild edible yams consumed by the tribals
Kanikkars and Palliyars, it can be summarized that most of them were found to
be a good source of protein, lipid, crude fibre, starch, vitamins and minerals.
All the investigated samples exhibited variations in the levels of total free
phenolics, tannins, hydrogen cyanide, total oxalate, amylase and trypsin
inhibitors. Except phenolics, tannins, hydrogen cyanide, total oxalate, amylase
and trypsin inhibitors, these antinutritional can be inactivated by moist heat
treatments. Phenolics, tannins, hydrogen cyanide and total oxalate can be
eliminated by soaking followed by cooking before consumption. It is recommended
as a means of removing harmful effects of these antinutritional.
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