ABSTRACT
The effects of fermentation and toasting on the nutrients
and antinutrients composition of Senna obtusifoliai seeds were
investigated. Senna obtusifolia seeds were fermented with Aspergillus
niger at an ambient (27-30°C) temperature for five days. Senna
obtusifolia seeds were also toasted at 80oC in open pan
using hot plate for 10 min. Raw Senna obtusifolia seeds contained
7.45mg/100g moisture, 33.33mg/100g crude protein, 17.25mg/100g lipid,
9.49mg/100g dietary fibre, 4.50mg/100g ash, 37.99mg/100g nitrogen free extract.
Antinutrients composition of raw Senna obtusifolia was 3.95mg/100g
tannins, 3.74mg/100g phytates, 2.13mg/100g oxalates and 2.62mg/100g
saponins, 11.23 TUI/mg trypsin inhibitor and 5.77 IC50 (mg/ml) alpha
amylase inhibitor. Fermentation increased the crude protein of Senna
obtusifolia but reduced nitrogen free extract, moisture, lipid and dietary
fibre. Toasting reduced moisture, dietary fibre, crude protein but increased
lipid, ash and nitrogen free extract. Toasting/fermentation (toasting followed
with fermentation) increased moisture, nitrogen free extract and ash but
reduced crude protein, dietary fibre and lipid. Fermentation reduced the
tannins by 38%, phytates by 84%, oxalates by 36%, saponins by 37%, trypsin
inhibitor by 12% and α-amylase inhibitor to 6.40 IC50 (mg/ml) while
toasting reduced tannins by 63%, phytates by 89%, oxalates by 61%, saponins by
66%, trypsin inhibitor by 40% and α-amylase inhibitor to 13.05 IC50
(mg/ml). Toasting/fermentation reduced tannins by 70%, phytates by 93%,
oxalates by 54%, saponins by 91%, trypsin inhibitor by 43% and α-amylase
inbitor to 19.54 IC50 (mg/ml). The in vitro protein
digestibility of raw Senna obtusifolia was 7.80%. The reduction
in antinutritional factors was concomitant with a significant (P
≤ 0.05) increase in protein digestibility after processing of the samples,
fermentation, toasting and toasting/fermentation increased the in vitro
protein digestibility of Senna obtusifolia to 45%, 22%, and 25%,
respectively. Raw Senna obtusifolia seeds contained both essential and
non essential amino acids with fermentation and toasting increasing the amino
acids content respectively but toasting/fermentation slightly reduced the amino
acid content. The total minerals contents Senna obtusifolia seeds (Ca,
Zn, K, Na, Fe and Mg) were reduced after processing. Fermentation reduced all
the total mineral contents, toasting increased Fe, Mg, K and Na but reduced Ca
and Zn. Toasting/fermentation reduced Ca, Mg, Zn, K and Na but increased Fe.
Results obtained indicated that fermentation had significant influence on the
proximate composition, in vitro protein digestibility, antinutritional
factors, amino acids and mineral contents of Senna obtusifolia seeds.
CHAPTER
ONE
1.0. INTRODUCTION
Food-based approaches such as dietary diversification,
fortification and biofortification are necessary strategies to prevent the
debilitating effects of malnutrition by promoting the consumption of foods that
are naturally rich in micronutrients. Dietary diversification has been
advocated internationally for the improvement of micronutrient intake and
status (Hedwig et al., 2012). An increase in meat and animal products
consumption is eminent in emerging and developing economies (Delgado et al.,
1999), yet the consumption of animal protein is still low in developing
countries like Nigeria (Okojie, 1999; FAO, 2001). One reason often advanced for
this scenario is the high cost of animal proteins often beyond the purchasing
power of the majority and poor people of these countries. In order to boost the
animal protein consumption of developing countries and achieve Millennium
Developmoent Goal 1 (MDG 1), there is need to reduce the cost of livestock
products by bringing down the cost of their feed. Soybean which is the main
source of plant protein in the diets of farm animals is increasingly finding
new uses as biodiesel stock in response to the deepening world energy crisis (Sasson, 2012). In addition, the use of soybean for
food and energy by man often takes precedence over its use for livestock
feeding. This dilemma has encouraged livestock nutritionists and feed millers
to seek for alternatives to soybean as plant protein source in livestock diets.
The alternative protein source has to be cheap, locally available and
preferably not used as food by man. Dietary diversification reflects household
access to varieties of foods and can also act as a proxy for individuals’
nutrient adequacy. Wild plants play an important role in the diet of most rural
dwellers in Nigeria. These plants tend to be drought tolerant and are gathered
both in times of plenty as well as times of need. Throughout the year, the
plants play an important role in supplying nutrients and calories especially during the dry season when cultivated
vegetables are scarce (Freiberger et al., 1998). Although
commonly eaten in the rural areas they are also consumed by urban people who
buy from traders who also collect them from the wild.
The use of toxic plants as food after fermentation or heat
treatment is known in Africa and other parts of the world (Ganiyu, 2005).
Antinutritional factors such as enzyme inhibitors, hemagglutinin, flatulence
factors, polyphenols, tannins and phytic acid inhibit the proteolytic activity
of the digestive enzymes such as pepsin and trypsin as well as the availability
of minerals (Deshpande and Cheryan, 1983). Minerals from plant sources,
particularly those from plant seeds are less bioaccessible than those from
animal’s sources due in part to phytic acid, tannins and fiber content
(Moelijopawiro et al., 1998). These antinutritional factors chelate
dietary minerals in the gastrointestinal tract reducing bioaccessibility and
bioavailability (Frolich, 1995). Polyphenols can form complexes with metal
cations through carboxylic and hydroxylic groups and thus interfere with the
intestinal absorption of essential minerals such as calcium (Valencia et al.,
1999). Phytic acid is naturally occurring as a hexaphosphate derivative of
inositol found in plants and in almost all mammalian cells. It consists of six
phosphate moieties and chelates metal irons such as Ca, Mg, Zn, Mn, Cu and Fe
to form insoluble complexes that are not readily absorbed (Graf and Eaton,
1993). Tannins also complex with enzymes of the digestive tract adversely
affecting utilization of proteins and carbohydrates and resulting in reduced
growth, feeding efficiency, metabolizable energy and bioavailability of amino
acids (Onyango et al., 2005). Several treatments have been applied to
remove or reduce the amount of antinutrient from plant. Few examples among them
are: fermentation, germination, thermal treatments (cooking) and soaking
procedures (Abd El-Hady and Habiba, 2003; Martin-Cabrejas et al., 2004).
In general, these processing methods enhance the nutritive value, reduce the amount of undesirable compounds and
improve the protein digestibility of legumes (Martin- Cabrejas et al.,
2004). Sicklepod is rich in Ca, Mg and P as major minerals while Fe, Zn and Mn
were present at lower levels (Ousman et al., 2005).
The plant Senna obtusifolia belongs to the kingdom
plantae, family fabaceae, a common annual plant that grows wild in Northern
Nigeria. The plant is considered a serious weed to Agriculturists in many
places. It grows on well-drained fertile soil. Similarly, it is suited for
cleared coastal forest countries. Senna obtusifolia has been regarded as
indigenous leafy vegetable of the Sahel with potential of providing vegetable
to the rural population in the month of August and September (Pasternak et
al., 2006). The young tender of Senna obtusifolia occasionally used
as vegetable throughout Africa and elsewhere and the plant is cultivated in
homes for this purpose in several countries including Senegal, Ghana, Cameroon,
and Ethiopia. If eaten frequently or in large quantities could cause diarrhea
(Irwin and Barneby, 1982). In Nigeria the seeds and roots of Senna obtusifolia
of no doubt have some laxatives effects. It is used as decoction febrifuge and
for the treatment of scorpion stings, gingivitis, dysentery and diarrhea
(David, 2002; Fowler, 2006). As the seeds are reputedly poisonous (Crowhurst et
al., 1972), therefore processing is necessary before eating. The cooked
vegetable tastes bitter but has an attractive consistency. Senna obtusifolia
will probably remain a minor vegetable.
1.1. Statement
of Research Problem
Soaring food prices have triggered an increase in hunger worldwide,
especially in sub-Saharan African countries like Nigeria. The increase in
prices of food has been attributed to several factors that include production
shortfalls due to drought and floods; impact of climate change; increased
demand for biofuel; emerging consumption habits of fast growing economics of
some nations as well as trade policies to stabilize the food market crisis
(FAO, 2008). According to the W. H. O. (2013), malnutrition is one of the leading causes
of death globally. It is well established that majority of people in developing
countries depend mainly on cereal grains as their staple food due to limited
income and high prices of animal foods (Sokrab et al., 2012). Senna
obtusifolia has some limitations due to the presence of antinutritional
factors, such as trypsin and amylase inhibitors, phytate and tannins.
These compounds are known to interfere with protein and carbohydrate digestion
and mineral bioavailability. Reduction or elimination of these undesirable
components is essential for improving the nutritional quality of Senna
obtusifolia and effectively utilizing their full potential as human food.
Efforts however, are directed at improving the nutritional value of Senna
obtusifolia seeds. Various simple processing methods such as soaking,
sprouting, cooking and fermentation have been found to improve the nutritional
value of plant (Yagoub and Abdalla, 2007; Mohamed Nour et al., 2010). It
is well known that fermentation decreased the values of antinutritional factors
as well as increased the in vitro protein and starch digestibilities and
thus improve the nutritional quality of plant (Elkhalifa et al., 2004;
Idris et al., 2005; Abdelseed et al., 2011; Mohammed et al.,
2011). Cooking on the other hand has been reported to reduce the in vitro
protein digestibility, whereas combining fermentation with cooking had
significantly improved protein digestibility over wet cooking alone (Taylor and
Taylor, 2002).
Since the seeds of Senna obtusifolia contain
antinutritional factors that can be harmful to human, this calls for the
adoption of effective processing methods like boiling, soaking, roasting,
fermentation and sprouting before inclusion in diets. It is also important to
use the seeds in a feeding trial with the aim of evaluating their biological
values to humans.
Presence of antinutritional factors in this plant is one of
the factors limiting its use in food formulation (Oladele and Aina, 2007).
However, there is few detailed information on the nutritional profile of the
seeds in relation to human consumption within the guinea savanna environment of
Nigeria, where this plant is prevalent. This is very important since the
nutritional and chemical value of this plant is partly influenced by
geographical location which is shaped by factors like soil and climatic
conditions (FAO, 2004). Therefore to gather reliable information regarding the
use of this plant as food, the chemical and nutritional characteristics of this
food needs to be carefully assessed in order to prevent errors in predicting
human health and environmental effects impairing the survival of mankind.
Also most developing tropical countries have depended upon
soybeans and other common legume grains as protein source for both humans and
animals (Vadivel et al., 2008) but, their production is not sufficient
to meet the protein requirements of the increasing population and expanding
livestock industries (Vijayakumari et al., 2007). The competition
between human and livestock for the consumption of soybean and the increasing
role of soybean in the world as biodiesel feedstock (Cotula et al.,
2008) have increased its cost and demand and heightened the competition between
human and animal for soybeans. Consequently, the search for a novel, high
quality, cheap and readily available source of plant protein to replace soybean
(Adeniji et al., 2005; Obun and Ayanwale, 2006). One of such legumes
with great prospect as alternative and replacement for soybean is Senna
obtusifolia (sickle pod).
1.3. Null
Hypothesis
Toasting and
fermentation have no effect on the nutritive value of (Senna obtusifolia)
sickle pod seeds
1.4. Aim
The aim of this
research is to propose an effective processing method for safe utilization of
sickle pod seeds.
1.5. Specific
Objectives
• To
determine the effect of processing (toasting, fermentation and toasting +
fermentation) on the proximate composition of Senna obtusifolia seeds.
• To
determine the effect of processing (toasting, fermentation and toasting +
fermentation) on the antinutritional factors content of Senna obtusifolia
seeds.
• To
determine the effect of processing (toasting, fermentation and toasting +
fermentation) on the in vitro protein digestibility of seeds of Senna
obtusifolia.
• To
determine the effect of processing (toasting, fermentation and toasting +
fermentation) on the amino acid profile of the of Senna obtusifolia
seeds.
• To
determine the effect of processing (toasting, fermentation and toasting +
fermentation) on the mineral composition of Senna obtusifolia seeds.
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