EFFECTS OF PROCESSING TREATMENTS ON THE NUTRITIVE COMPOSITION AND CONSUMER ACCEPTANCE OF SOME NIGERIAN EDIBLE LEAFY VEGETABLES

EFFECTS OF PROCESSING TREATMENTS ON THE NUTRITIVE
COMPOSITION AND CONSUMER ACCEPTANCE OF SOME NIGERIAN
EDIBLE LEAFY VEGETABLES.

H. D. Mepba1*, L. Eboh2 and D E.B. Banigo3



Horsfall Mepba




















*Corresponding author Email: mepba12002@yahoo.co.uk
1,3Department of Food Science and Technology
Rivers State University of Science and Technology
P.M.B. 5080, Port Harcourt, Nigeria

2Department of Home Economics
University of Uyo, Uyo,
Akwa Ibom, State, Nigeria
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ABSTRACT

Leafy vegetables are highly perishable food items and require special processing
treatments to prevent post harvest losses. Leafy vegetables to be preserved by
canning, freezing or dehydration are normally blanched in order to obtain good
quality products. In Nigeria, leafy vegetables are preserved by sun-drying and used
like freshly harvested vegetables in soups. The effects of these treatments on the
nutritive composition and sensory qualities of some edible Nigeria leafy vegetables
are reported. Samples (1kg each) of amaranths (Amaranthus hybridus), fluted
pumpkin (Talfaria accidentalis), gnectum vegetable (Gnectum africana), vine spinach
(Basella alba), bush okro (Corchorus olitorus), slippery vine (Asystacia gangetica)
and cocoyam leaves (Colocasia esculenta) were washed, cut into thin slices and sun-
dried for 5 hrs daily for 2 days. Samples (1kg) of tomatoes (Lycopersicon
esculentum) were similarly dried for 4 days. The fresh vegetables (1kg each) were
blanched in hot water at 100oC for 5-6 min and rapidly cooled to 20C in a freezer.
Samples (250g each) of fresh (raw), sun-dried or blanched vegetables were cooked
separately for 5min in soups. Sun-drying at 30 ± 10C and RH 80 – 85% for 10hr
resulted in a mean moisture loss of 35.6% with insignificant (P>0.05) increases of
protein, lipid, crude fiber and total ash. Gnectum vegetable, vine spinach, bush okoro,
cocoyam leaves and slippery vine had protein contents ranging from 3.0-5.0. K, Fe,
Na, Mg and Ca were the predominant mineral elements analysed while contents of Zn
and P were low. Blanching and cooking caused significant (P ? 0.05) reductions in the
K, Na, Ca, Mg, Zn, Fe, and P contents of the vegetables. The implications of these
results on the nutritive value of these vegetables are discussed. Among the treatments,
cooking accounted for 64.3 – 67.5% loss of vitamin C while blanching and sun-
drying accounted for 44.8-47.1% and 36.8 – 39.6% respectively. Panelists rated the
soups significantly (P? 0.05) higher for colour, taste, texture, flavour/aroma and
overall acceptability characteristics. Fresh fluted pumpkin soup was rated
significantly (P? 0.05) higher for colour, taste, texture and flavour/aroma
characteristics, while fresh gnectum vegetable soup was highly rated for taste,
flavour/aroma and overall acceptability characteristics. Compared with other dried
vegetable soups, dried gnectum vegetable soup had the highest score for colour and
taste while dried fluted pumpkin soup had the highest score for flavour/aroma and
overall acceptability characteristics. Generally, panelists preferred the fresh to dried
vegetable soups.

Key words: Blanching, Sun-drying, Cooked, Vitamin C, Sensory attributes.


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ABSTRAIT

Des légumes verts à feuilles sont des denrées tres périssable donc, ils demandent des
traitements spéciaux pour éviter des pertes aprés moissure. Des legumes verts à
feuilles à conservation: en boîte, congélation ou déshydration sont normalement
blanchis pour avoir des produits de bonne qualities. Au Nigéria des légumes verts à
feuilles sont conservés par le séchage solaire et utilisés pour la préparation des
potages comme des légumes frais. L’effet des traitements sur les qualités de la
composition nutritionelle et sensorielle de certains légumes verts à feuilles
comestibles sont prresentés: Les échantillons (1 kilo chacun) de amaranths
(Amaranthus hybridus), La citrouille (annelée) (Telfaria occidentalis), Légume
gnectum (Gnectum africana), épinard (Basella alba), feuille de vigne (Asystacia
gangetica) et des feuilles de taro (Colocasia esculenta) sont lavés, coupés en petits
tranches et séchés sous le soleil 5h par jour pour deux jours. Echantillon (1 kilo) de
tomates (Lycopersicon esculentum) sont égalements séchés pendant quatre jours. Ces
légumes (1 kilo chacun étaient blanchis dans l’eau chaude à 100°C pour 5 à 6 minutes
et rapidement surgélés à 2°C dans un congélateur. Les échantillons (250g chacun) de
légumes frais (crus) séchés dans le soleil ou blanchis étaient preparés séparément pour
5 minutes dans les potages. Séchant en soleil à 30 + 1°C et RH80 – 85% pour 10hs
on a noté une perte moyenne en moisissure de 35. 6% avec une augmentation
insignifiante (P>0.05) en protéine lipide, fibre cru et cendre total. G. africana, B.
alba, Corchorus olitolus, Asystacia gangetica, C. esculanta out des protéines qui
varies entre 3.0 à 5.0. K, Fe, Na, Mg et Ca étaient les éléments miniraux prédominants
analisés; alors que la composition en Zn et P étailent basses. Le blanchiment et le
séchage out causé une réduction significative (P?0.05) en K, Na, Ca, Mg, Zn, Fe et P
dans la composition des légumes traités. Les implications de Ces résultats sur la
valeur nutritionelle des légumes sont objets de discussions. Parmi les traitements, la
preparation contribue en une perte de 64.3 à 67.5% en vitamines C alors que le
blanchiment et le séchage en soleil contribuent une perte de 44.8 à 47.1% et 36.8 à
39.6% respectivement. Les juris out fortement estimé les potages pour la couleur,
goût, contexture saveur/arôme et l’acceptabilité dans l’ensemble. Le potage préparé
avec la citrouille cannelée (Telfaria occidentalis) frais a été plus considéré (P?0.05)
en couleur, goût, saveur/arôme et. L’acceptabilité dans l’ensemble que les autres
potages préparés avec des légumes séchés, le potage préparé avec du Gnectum
africana seché a été estimé le meilleur pour la couleur et le goût alors que le potage
préparé avec (Telfaria occidentalis) séché a été estimé le meilleur en saveur/arôome et
l’acceptabilité dans l’ensemble. En général les juris out préférés les potages aux
légumes frais aux potages aux légumes séchés.
Les mots clés: Blanchiment, séchage au soleil, Préparé ou cuisinié Vitamin C,
sensoriel, Attribut.


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INTRODUCTION

Leafy vegetables are important items of diet in many Nigerian homes. Apart from
the variety which they add to the menu. They are valuable sources of nutrients
especially in rural areas where they contribute substantially to protein, mineral,
vitamins, fiber and other nutrients which are usually in short supply in daily diets [1].
Besides, they add flavour, variety, taste, colour and aesthetic appeal to what would
otherwise be a monotonous diet. They are in abundance shortly after the rainy season
but become scarce during the dry season during which cultivated types are used.
Some eventually find their way to urban markets.

In Nigeria leafy vegetables are rarely processed, presumably due to the general lack
of basic preservation facilities for freezing, canning or dehydration. A relatively small
quantity of harvested leafy vegetables are however, sun-dried resulting in poor
quality products with variable moisture contents and microbial loads thus affecting
storage stability. Freezing is generally regarded as the best method of preservation
from quality stand-point and for long term preservation of foods. For perishable
commodities with very high moisture contents, dehydration results in substantial
reduction in weight and bulk with consequent savings in storage and distribution
costs. Echetama et al [2] reported that Okra dehydrated in a see- saw solar dryer with
appropriate pre-drying treatments compared favourably in quality with frozen okra.

Unit operations that intentionally separate the component of foods alter the nutritional
and sensory qualities of each fraction compared with the raw material. Blanching
which is an important pre-processing heat –treatment of vegetable destined for
freezing, canning or dehydration inevitably causes separation and losses [3] of water
soluble nutrients (minerals, water soluble vitamins and sugars).

According to fellows [3] blanching at 880C stop all life process, inactivates enzymes,
fixes green colour and removes certain harsh flavours common in vegetables.
Cooking also cause significant changes in the nutritional properties of foods as well
as gelatinisation of starches and coagulation of proteins to improve their digestibility
and sensory properties [3]. To the consumer, the most important attributes of a food
are its sensory characteristics. These determine an individuals preference for specific
products, and small difference between brands of similar products can have a
substantial influence on acceptability. Vegetables play crucial roles in alleviating
hunger and food security by contributing bulk of the nutritional components in the
diets of people where animal products are scarce.

They present unique problems which negatively confront attempts to extend their post
harvest useful life span on account of their fragile texture and high moisture contents
both of which are responsible for their rapid deterioration, drying difficulties with loss
of heat sensitive nutrients. The outstanding preservative method practiced in many
homes in Nigeria is sun-drying. This along with blanching and cooking of vegetables
in soup preparation have considerable effects on the nutritive value and sensory
acceptability of final products. The objective of this investigation was to evaluate the
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effect of these processing treatments on the nutritive and sensory properties of edible
Nigerian vegetables.

MATERIALS AND METHODS

Source
Eight types of indigenous leafy vegetables that are widely used in soup preparation
were procured from farmers on June 2004. The vegetables were harvested fresh from
farms at Aka, Afaha Offot, Mbak, Ikpa, Ikot oku Nsit, Afaha ube, in Uyo urban area.
Samples were young and tender at harvest and each species were packed loosely in
two-ply polythene (HDPE) bags to minimise heat build-up. Tomatoes (Lycopersicon
esculentum) were collected in plastic buckets. Samples were separated for
identification and only sound samples (leaves and stalk) were used for analysis and
soup preparation, samples used are listed in Table 1 with their local and
common/scientific names.

Sample Preparation
One kilogramme each of leafy vegetables were washed and cut into thin slices and
spread on medium density (0.926 – 0.940 g/cc) polythene bags on a concrete floor.
Samples were sun-dried for 5hrs daily for two days at 30-320C and RH, 80-85%.
Similarly tomato (Lycopersicon esculentum) slices were dried for four days. In
another experiment one kilogramme each of the vegetables were blanched following
the methods described by Ajayi and Onayemi [4]. Briefly, Ikg each of the vegetables
were blanched in hot water at 1000C for 5-6mins and rapidly cooled to 20C in a
freezer. The minimum blanching time which is a function of enzyme inactivation was
determined by testing for peroxides activity after introducing the vegetables into hot
water at 1000C for periods of time up to six minute [5].

Soup Preparation
Two hundred and fifty grammes each of sliced, fresh and sun-dried gnetum vegetable
(Gnectum africana) were separately pounded in a mortar. Similarly, 250g each of
fresh and dried fluted pumpkin (Telfaria occidentalis), amaranths (Amaranthus
hybridus) and cocoyam leaves (Colocasia esculenta) were sliced and dried. Two
hundred and fifty and grammes of fresh vine spinach,(Basella alba), which is
traditionally used in vegetable soups, were similarly treated and used as control. Both
fresh and dried vegetable soups were prepared using standard ingredients (Table 2) as
described by Eboh [6]. Briefly, fresh meat cuts were washed and steamed with salt,
onions and crushed maggi (spice) for 30 mins, Deboned dried fish was added and
cooked in the meat broth for 5 mins, then water was added and cooking sustained for
15 mins before ground crayfish was added. The soup was stirred about 2-3 times then
cut vegetables were added and cooked for further 5 mins before oil was added and
cooking sustained for further 5 mins.

Chemical Analysis
Ground samples of raw, sun-dried, blanched and cooked vegetables were analysed for
their proximate contents using the AOAC (7) method. The moisture content was
determined by air-oven drying at 130oC for 1 hr, and the crude protein contents by
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microKjeldah method (% protein = N x 6.25). The lipid content was determined using
petroleum ether (bp. 60-80oC) in a soxhlet extraction apparatus and crude fiber
content by dilute acid and alkali hydrolysis. Carbohydrate contents was calculated by
difference of total contents from 100. Five (5) grammes of dried powdered sample
was dissolved in 6 M HCl solution and the resulting solution was made up to a
definite volume (20ml) and used for the determination of minerals. Phosphorus was
determined by the phosphomolybdate method of Yuen and Polland (8). Sodium and
potassium were determined by flame photometer (Jenway, PF 7, Essex UK) while
calcium, magnesium, iron and zinc were determined by Atomic absorption
spectrophotometer (Unicam Analytical system, Model 919, Cambridge, UK. Vitamin
C was determined by taking a 5g sample, grinding it in a mortar using 100ml of 10%
trichloroacetic acid. The ascorbic acid was assayed by visual titration with 2,6
dichlorophenol solution.

Sensory Evaluation
A twenty member sensory panel consisting of 12 male and 8 female students who are
regular consumers of vegetable soups and familiar with the attributes, investigated the
sensory qualities of the prepared soups. Panelists evaluated the soup attributes against
a control soup prepared with a popular vegetable (Basella alba). Panelists were
comfortably seated in booths and served with separate plates of soup and garri (a
common starchy staple). The soup samples were coded with four digit letters, spoons,
fork and water were provided. Panelists evaluated soup samples for colour, taste,
flavour/aroma, texture and overall acceptability characteristics on a 9 = point
descriptive scale with 9 = excellent, 7 = very good, 5 = good 3 = fair and 1 = bad as
proposed by Larmond (9).

Statistical Analysis
Experimental Design: A split- plot arrangement fitted with a complete randomization
design with species = Whole unit and Treatments (preparations) = subunits was used
for the analysis of proximate composition and mineral contents of samples . A
randomized complete block design was used for the evaluation of sensory data. Data
for all determinations were subjected to analysis of variance (ANOVA) as outlined by
Wahua [10]. Fisher’s least significant difference (LSD) test was used to identify
significant differences among treatment means (P ? 0.05).

RESULTS

List of selected indigenous soup vegetables identified in Akwa Ibom State are given
in Table 1. The vegetables were identified by their local, English and Scientific names
as well as the plant types.

Table 2 presents the recipe for the preparation of vegetable soups. Steaming of fresh
meat cuts with salt and other spicies facilitated penetration of spicies into the meat
cuts and generation of meat broth. Saltiness of meat broth was reduced after addition
of water and fish while the addition of crayfish further improved the taste/flavour
properties of the broth. Further thickening of soups resulted from the addition of
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vegetables while palm oil addition improved flowability of soups during subsequent
stirring.

Data in Table 3 show the effects of processing treatments on nutrient contents of the
indigenous vegetables. The protein contents of amaranths ranged from 4.0 -
4.6mg/100g while the crude fiber contents ranged from 1.6 -3.4mg/100g.

The moisture contents of the sun-dried sample decreased significantly (P? 0.05) with
corresponding increase in the contents of dry matter. Tomatoes and fluted pumpkin
had protein contents ranging from 2.5 – 3.2 and 1.4-2.2mg/100g respectively.
Generally, sun-dried and cooked vegetables had significantly (P?0.05) lower moisture
contents than raw and blanched vegetables. Gnectum vegetable and vine spinach had
protein contents ranging from 4.5- 5.2 and 3.7 – 4.2mg/100g respectively while bush
okro and slippery vine had protein contents ranging from 1.4 -2.4 and 2.8 –
3.4mg/100g respectively. Sun-drying resulted in a loss of 31.3% moisture but an
increase of 0.2% protein and 1.1% crude fiber in cocoyam leaves.

The effects of processing treatments on mineral contents of test vegetables are given
in Table 4. Blanching and cooking caused significant (P? 0.05) reductions in the K,
Na,Ca, Zn, Fe and P contents of amaranths, tomatoes, fluted pumpkin gnectum
vegetable, spinach, slippery vine and cocoyam leaves, Sun-drying had variable
effects on the mineral contents of the experimental vegetables. K, Mg and Ca were
the predominant minerals analysed while contents of Zn and P were low. The
concentrations of minerals elements vary significantly (P?0.05) with treatments, with
higher concentrations in the raw and sun-dried samples. Amaranths, tomatoes and
fluted pumpkin had the highest contents of Fe, Ca and Na respectively.

Table 5 gives the Vitamin C contents of the treated vegetables. The Vitamin C
contents of raw vegetables ranged from 37.5 – 205.4mg/100g. The various treatments
(sun-drying, blanching and cooking caused significant (P?0.05) losses of Vitamin C.
Bush okro had a significantly (P? 0.05) higher vitamin C content than all the tested
samples. Among the treatments, cooking had the most adverse effect accounting for
64.3 – 67.5% losses of vitamin C while blanching and sun-drying accounted for 44.8 -
47.1% and 36.8-39.6% losses respectively. Amaranths, tomatoes and gnectum
vegetables had significantly (P?0.05) lower contents of vitamin C than other cooked
vegetables.

Summary of panel mean scores for the sensory characteristics of soups prepared with
fresh and dried vegetables are presented in Table 6. Panelists rated the vegetable
soups significantly (P? 0.05) higher for their colour, taste, texture, flavour/aroma and
overall acceptability characteristics. Soups prepared with fresh fluted pumpkin was
rated significantly (P?0.05) higher than other soups for colour while soups prepared
with dried amaranths and dried cocoyam leaves had the least score. Similarly, fresh
gnectum vegetable and fresh fluted pumpkin vegetable soups were rated significantly
(P? 0.05) higher than other soups for taste and texture attributes. Fresh gnectum
vegetable soups and soups prepared with fresh cocoyam yam leaves had the highest
scores for flavour/aroma while dried amaranths soup was down-graded for these
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attribute. Dried amaranths soup also had the least score for all the tested attributes
while fresh gnectum vegetable soups had the highest score for taste, texture,
flavour/aroma and overall acceptability characteristics. Considering panel rating of
the soups; fresh gnectum vegetable soups scored 85.0% while fresh fluted pumpkin
soup had 73.6% of the total attribute scores. Fresh amaranths and fresh cocoyam
leaves soup scored 79.1% and 85.3% respectively of the total scores for the attributes.
Preference for the vegetable soups was in the order of fresh gnectum vegetable ?
fresh fluted pumpkin ? fresh cocoyam leaves ?fresh amaranths soups while
preference for dried vegetable soups was in the order of dried fluted pumpkin ? dried
gnectum vegetable ? dried cocoyam leaves ?dried amaranths soup.


DISCUSSION

The local, English and scientific names of some indigenous vegetables of Akwa-Ibom
State are presented in Table 1. Based on their classification into plant types the
vegetables were characterised mostly as herbs with some climbers, then a shrub and
tree species, Lyimo et al [11] also observed that over 90% of the indigenous
vegetables of Tanzania were herbs while a few shrubs and trees were characterized.
Indigenous or wild vegetables are basically plants whose leaves, fruit or roots are
acceptable and used in the diet of rural and urban people as a function of custom,
habitat and tradition [12]. Nutritionally they contribute substantially to protein, crude
fiber, mineral and vitamin intakes as evident in the following results. Steaming of
fresh meat or fish with salt and other spices (Table 2) is a common practice in
traditional methods of soup preparation in southern Nigeria [13, 14]. Although the
ingredients used in the fish pepper soup [14] and bean soup [13] were similar with
those used in our vegetable soups, the concentrations of the ingredients were differed.
For instance, up to 14g and 16g of red pepper were used in bean and fresh fish pepper
soups respectively. Similarly, Onions (17g) and monosodium glutamate (1.5g) were
used in bean soup [13]. Similar to our observations of increased thickness, Akanbi
[13] observed that addition of drum dried cowpea paste to the soup increased the
viscosity of broths.

Generally, the results (Table 3) indicate that the vegetables were good sources of
proteins, crude fiber and carbohydrates. Higher protein contents were recorded for
gnectum vegetable, amaranths, bush okro, slippery vine and cocoyam leaves. These
results are in accord with those in literature [15,16]. Lyimo et al [11] similarly
reported protein contents ranging from 3.0-5.0% in bush okro, cocoyam leaves,
amaranths and slippery vine. Our results also indicated that sun-drying at 30± 10C and
RH 80-85% for 10hr resulted in a mean moisture contents of 35.6% with
insignificant (P> 0.05) crude fiber and total ash contents of treated vegetables.
Similarly, Mandhyan et al [17] observed that sun-drying at 34-390C and RH40-75%
for 16hr caused significant reductions (60.5%) in moisture contents of spinach,
cabbage, carrots and peas. Accordingly, reductions in moisture contents resulted in
corresponding increases in dry matter contents due to concentration of soluble solids
with relatively chemically stable products. Ajayi and Onayemi [4] similarly observed
that blanching had variable effects on dry matter composition with insignificant
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(P>0.05) reductions in lipid, crude fiber, toal ash and carbohydrate contents but had
no effect on the protein content of the vegetables. Lisiewka and Kmicik [18] however
observed that blanching reduced the dry matter content of broccoli and cauliflower.

Heating is one of the most important methods developed to extend the shelf life of
foods and increasing the availability of nutrients to consumers. Thermal processes
such as blanching and pasteurisation increase storage life of foodstuffs and minimise
food-borne diseases [3] while cooking is aimed primarily at increasing palatability of
food. The reduced protein contents of cooked vegetables could be attributed to the
severity of thermal process during cooking [19].

Data on mineral analysis (Table 4) indicate that blanching and cooking caused
significant (P ?0.05) reductions in the K, Na, Ca, Zn and P contents of the vegetables.
Similarly, Oladunmoye et al [20] observed significant (P?0.05) reductions in K, Na,
Ca, P, Fe and vitamin C contents of blanched and cooked tender and matured cassava
leaves. Uzoekwe and Ukhun [21] also reported reductions in the Fe, and Zn contents
of scent leaf (Ocimum gratissmum), gnectum vegetable, bitterleaf (Veronica
amygdalina), bush okro and green pepper (Piper gunineense) that were used in soup
preparation. The result for mineral analysis of the vegetables suggest consumption of
large quantities to meet the Recommended Daily Allowance (RDA) for minerals. For
instance, adult minimum K requirement for health set by the 1989 RDA is 2000mg
daily. It would require up to 476.2 mg/100g of cooked amaranths to meet the RDA.
K is a primary electrolyte and major cation inside the cell and low blood K is a life –
threatening problem [22]. Similarly, consumption of large amounts of amaranths,
fluted pumpkin, tomatoes, or gnectum vegetable would be important to meeting the
RDA for Na. A Na intake of less than 2g/day increases calcium loss in urine and high
intakes can contribute to hypertension in some people [22] Therefore the low level of
Na in bush okro, slippery vine and cocoyam leaves make them suitable for use in Na
restricted diets. Calcium is probably mainly associated with the pectic substance of
the cell wall and could significantly influence texture. Its high content in fruit
vegetables such as tomatoes was expected. Its low contents in leafy vegetables
suggests a low intake by vegetarians that must seek alternative sources to meet their
needs for calcium. This is important because the cells need calcium and more than
99% of calcium in the body is used as a structural component of bones and teeth. This
represents about 40% of all the minerals present in the body [22]. Fluted pumpkin had
the highest magnesium content while moderate concentrations were recorded in other
leafy vegetables. Magnesium occur abundantly in chloroplasts as a constituent of
chlorophyll molecule. Its low concentrations in most of the vegetables could be
attributed to age of plants and cultural practices. The levels obtained in this studies is
low to meet the Recommended Daily Allowance (RDA) of 400mg/day for men 19-30
years old and 310mg/day for women 19-30 years old [23].

The levels of phosphorus obtained were similarly low. Phosphrus is a constituent of
cytoplasm and nuclear protein, phospholipids and nucleic acids, as well as taking
important part in carbohydrate metabolism. Efficient absorption plus the wide
availability in foods makes phosphorus a much less important mineral than calcium
[23] in diet planning. Vegetables are generally poor sources of iron. However, Fe,
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contents of amaranths, fluted pumpkin and gnectum vegetable can be considered
adequate when viewed against an RDA of 8mg Fe/day for men (19 years and older)
and for women over 50 years, 18mg/day for girls and women 11 to 50 years old [24].
However, neither the total iron content nor the nutrient density of the individual food
constitute an accurate guide for choosing dietary sources of iron. Rather the
bioavailability of iron present in a meal, which depends on its form and the presence
or absence of factors that influence absorption and the body’s need for iron ultimately
determine how much iron that is actually delivered to the body. Zinc was one of the
lowest mineral content of the vegetables when considered against an average
requirement of 9.4mg/day for men and 6.8 mg/day for women [24]. Zinc deficiency in
developing countries is becoming a growing concern because it has been shown that
zinc deficiency is related not only to decreased growth but also increased morbidity.
Studies [25] have shown zinc supplementation to be effective in reducing the
morbidity associated with infections in infants and children, possibly improving
immune function.

Table 5 gives the Vitamin C contents of the treated vegetables. Vitamin C contents
(mg/100g) up to 20.0, 21.3, 25.3, 59.7, 42.3, and 38.7 have been reported in cabbage,
lettuce, endives, spinach, spinach beet, and spinach beet leaves respectively [26].
Values obtained in this study support the reports in literature [27- 30]. Addo [31]
observed significantly low level losses (21.3-36.5%) of ascorbic acid in sun-dried
than in cooked vegetables. He observed that losses varied with vegetable cultivars,
for instance, fresh pepper lost up to 45% of its vitamin C content while baobab leaves
retained up to 65% of its vitamin C contents. Blanching prior to freezing or drying to
inactive enzymes which could contribute to undesirable changes in colour, flavour or
nutritive value during storage also cause significant loss of vitamin C. However,
vegetables from the Lycopersicon family as represented by tomatoes with thick pulp
had longer blanching times in comparison to the smaller, thin – leaf vegetables from
Amaranthaceae family. This observation indicate that the thickness and size of
vegetable pieces determine, in part, the effectiveness of blanching treatment. For this
reason, most commercial vegetable plant chop their vegetables into smaller sizes prior
to blanching.

The reported losses of ascorbic acid during blanching or cooking are enormous and
may vary between 40 and 70% in some cooked vegetables when processed at 100°C
for 15 min [32] other researchers observed losses up to 66%. 63%to 73% and 62 to
93% ascorbic acid in cooked vegetables [29, 30]. These values support the results
obtained for this studies.

The high solubility of ascorbic acid in water and the relative ease with which it is
oxidized makes this vitamin particularly susceptible to processing conditions. The
route and rate of oxidation of ascorbic acid is influenced by several factors including
pH, trace metals, enzymes, presence of oxygen as well as time and temperature.
Precooking preparation of vegetables followed in this work exposed the tissue. Under
this conditions, ascorbic acid oxidase may react with molecular oxygen and cause
direct destruction of the vitamins. The traditional Nigerian soups are water-in-oil
emulsions, and consequently, the large quantities of water used often predispose
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