ArticlePDF Available

Oxalate Levels in Selected African Indigenous Vegetable Recipes from the Lake Victoria Basin, Kenya

Authors:

Abstract and Figures

African indigenous vegetables (AIVs) in Lake Victoria Basin that could provide micronutrients to fight malnutrition contain oxalates that reduce bioavailability. These can be reduced through appropriate traditional food processing techniques adopted by households. This study determined oxalate levels in formulated AIV recipes. Eleven selected AIVs and five AIV mixtures were each divided into two lots. One lot was boiled and fermented for 48 hours and other lot unfermented. The unfermented were subjected to three treatments; cooked by boiling in water, cooked by boiling with cow’s milk and lye and cooked by sautéing. Oxalate levels in recipes were determined using HPLC. Independent t-test was used to compare the mean oxalate levels between fermented and unfermented recipes. One-way ANOVA was used to compare mean oxalate levels between different methods of cooking. Oxalate levels in unfermented recipes ranged from 2.62-10.17 mg/100g FW and in fermented, 1.54-20.36 mg/100g FW. The mean levels in some fermented recipes were significantly lower than unfermented (p<0.05). Cooking methods differently affected oxalate levels. Cooking methods and fermentation do not have a uniform effect on oxalate level reduction in all AIV recipes but could still be employed as household procedures in reducing oxalate levels in a number of AIV recipes.
Content may be subject to copyright.
International Journal of Agriculture and Environmental Research
Volume:01,Issue:02
www.ijaer.in
www.ijaer.in Page 88
OXALATE LEVELS IN SELECTED AFRICAN INDIGENOUS
VEGETABLE RECIPES FROM THE LAKE VICTORIA BASIN, KENYA.
1Mr. Wakhanu A. John (MSc), 2Prof. Kimiywe Judith (PhD, CNS),
3Prof. Nyambaka Hudson (PhD)
1Applied Analytical Chemistry, School of Pure and Applied Sciences, Kenyatta University,
P.o Box 43844, Nairobi, Kenya.
2Nutritionist and Consultant, Food, Nutrition and Dietetics Department, Kenyatta University,
P.o Box 43844, Nairobi, Kenya.
3Chairman, Chemistry Department, Analytical/Nutritional Chemistry, Kenyatta University,
P.o Box 43844,Nairobi, Kenya.
ABSTRACT
African indigenous vegetables (AIVs) in Lake Victoria Basin that could provide micronutrients
to fight malnutrition contain oxalates that reduce bioavailability. These can be reduced through
appropriate traditional food processing techniques adopted by households. This study determined
oxalate levels in formulated AIV recipes. Eleven selected AIVs and five AIV mixtures were each
divided into two lots. One lot was boiled and fermented for 48 hours and other lot unfermented.
The unfermented were subjected to three treatments; cooked by boiling in water, cooked by
boiling with cow’s milk and lye and cooked by sautéing. Oxalate levels in recipes were
determined using HPLC. Independent t-test was used to compare the mean oxalate levels
between fermented and unfermented recipes. One-way ANOVA was used to compare mean
oxalate levels between different methods of cooking. Oxalate levels in unfermented recipes
ranged from 2.62-10.17 mg/100g FW and in fermented, 1.54-20.36 mg/100g FW. The mean
levels in some fermented recipes were significantly lower than unfermented (p<0.05). Cooking
methods differently affected oxalate levels. Cooking methods and fermentation do not have a
uniform effect on oxalate level reduction in all AIV recipes but could still be employed as
household procedures in reducing oxalate levels in a number of AIV recipes.
International Journal of Agriculture and Environmental Research
Volume:01,Issue:02
www.ijaer.in
www.ijaer.in Page 89
Keywords: African indigenous vegetables, oxalate levels, fermentation, cooking methods
INTRODUCTION
The African Indigenous vegetables (AIVs) in Vihiga County in Lake Victoria Basin (LVB)
include spider plant, African nightshade, pumpkin, cowpea, amaranths, jute mallow, and slender
leaf (Abukutsa-Onyango 2007). The potential of these AIVs as sources of micronutrients is
limited by the presence of anti- nutrients like phytate, oxalate, tannic acid, Ethylene diamine tetra
acetic acid (EDTA) and sapon in which bind to some micronutrients in the vegetables hence
limiting the micronutrient bioavailability (Makokha and Ombwara, 2005).Currently there is a lot
of research on bioavailability of micronutrients in AIVsand AIV anti-nutrient content and the
effects of these anti-nutrients on human health. It is only very recently that there has been a
significant interest toward Africa’s indigenous vegetables grown in home or backyard gardens
(Abukutsa-Onyango, 2010) otherwise AIVs normally face stiff competition with exotic
vegetables like cabbage, spinach, and lettuce among others (Maundu et al., 1999). The
introduction of exotic vegetables in the African continent had some negative impact on the
consumption and cultivation of indigenous vegetables. During the colonial time, a deliberate
suppression of the indigenous vegetables was done and a lot of efforts were made to promote the
exotic vegetables such as cabbage (Abukutsa-Onyango, 2010).The net effect of such suppression
flowed into the post independent era where the governments perpetuated the agricultural policies
developed by the colonial rulers. Changed food habits in favor of introduced temperate
vegetables lowered the demand of indigenous vegetables, due to the fact that the former fetched
higher prices in local markets (Abukutsa-Onyango, 2010). Indigenous vegetables were
considered out of fashion, poor man’s food that could only be used as a last resort. Thus they
enjoy less social prestige, being associated with the low-income group. As the poor sought to
imitate the eating habits of the affluent and were exposed to more fashionable exotic species, the
indigenous species became neglected (Abukutsa-Onyango, 2010). The neglect and stigmatization
was perpetuated by stakeholders like the policy makers, agricultural training institutions,
researchers, consumers and traders (Mnzava,1997). Having been branded and denoted by the
agriculturalists and researchers as weeds, the tendency was to eradicate them and not conserve
them as it were. However, the potential of AIVs for use in the eradication of malnutrition in poor
households has attracted a lot of research because of the numerous advantages these vegetables
possess over exotic ones.
AIVs adapt easily to harsh or difficult environments and require less input to grow as compared
to other crops. Furthermore AIVs are highly resistant to pathogens and require less attention
(Abukutsa-Onyango et al., 2006). This makes them appropriate for the alleviation of
International Journal of Agriculture and Environmental Research
Volume:01,Issue:02
www.ijaer.in
www.ijaer.in Page 90
malnutrition in people living in areas with high population density in LVB. Their mineral and
vitamin content exceed levels found in exotic vegetables like cabbage (Abukutsa-Onyango,
2010). They also contain ascorbic acid which has been known to enhance iron absorption.
Populations who consume AIVs are less likely to suffer cardiovascular diseases, diabetes and
other diseases and this property is attributed to the presence of non-nutrient bioactive
phytochemicals (Smith and Eyzaguire, 2007). Some studies have also shown that AIVs contain
health promoting compounds such as anti-cancer factors, minerals, vitamins and anti-
oxidants(Abukutsa-Onyango, 2003). This boosts the body’s immune system if consumed. Apart
from providing important nutrients, AIVs can also play an important role in improving income
and subsistence to people (Adebooye and Parody, 2004). However, the potential of AIVs in their
use to fight malnutrition is limited by the anti-nutrients they contain. Anti-nutrients in vegetables
which include phytate, oxalate, tannic acids and hydrocyanic acids are associated with less
bioavailability of zinc, calcium, iron and magnesium in vegetables (Broadhurst and Jones,
1978;Akindahunsi, 2005). Anti-nutrients are organic in nature and chelate with mineral elements
to form insoluble complexes which interfere with absorption and assimilation of these mineral
elements in the human body (Munro and Bassir, 1969). AIVs also contain polyphenols such as
phenolic acids, flavonoids and their polymerization products. They form insoluble complexes
with iron and inhibit iron absorption. Tannin is a phenolic compound (Brown et al., 1990). Anti-
nutrient levels increase with age in stems, roots and seeds (Ekpedema et al., 2000; Weinberger
and Msuya, 2004).One anti-nutrient that has attracted study is the oxalate whose ionposes two
main problems: it reduces the bioavailability of essential elements in the human body such as
calcium, iron and zinc and its crystals block the kidney as kidney stones and also cause gout,
rheumatoid arthritis and vulvodynia (Franceschi and Nakata, 2005). Oxalate is distributed in
plants and this levels range in 3-15 % w/w of their dry weight (Franceschi and Nakata, 2005).
Some plants like rice accumulate oxalate to detoxify aluminium, lead, strontium, copper and
cadmium (Yang et al., 2000; Choi et al., 2001).Oxalate is actually a compound of oxalic acid
(ethanedioic acid); oxalic acid is a colourless and toxic organic compound that belongs to the
family of dicarboxylic acids whose formula is (COOH)2.2H2O. It is soluble in water, alcohol and
ether. It occurs as oxalate in plants and more so in green leafy foods.
Lack of knowledge on the correct choice of food, dietary diversity and anti-nutrient levels in
AIVs has led to underutilization of AIVs (Abukutsa-Onyango, 2003; Waudo et al., 2006;
Kimiywe et al., 2007). Diets in households within the LVB are primarily composed of cereals
and legumes that are high in anti-nutrients that inhibit micronutrient absorption. This can be
reduced through appropriate traditional food processing techniques adopted in households
(Walingo, 2009). The mineral and anti-nutrient content of local foods within LVB needs further
research to identify suitable sources of absorbable minerals and possible suitable dietary
combinations that can contribute towards the reduction of mineral deficiency (Walingo, 2009).
International Journal of Agriculture and Environmental Research
Volume:01,Issue:02
www.ijaer.in
www.ijaer.in Page 91
Traditional food processing methods and diet combinations usually reduce the levels of mineral
anti-nutrients in the plant diets thus increasing mineral bioavailability. Household food
processing methods that promote nutrient content and bioavailability for improved health and
nutrient situation of rural populations whose diets are basically plant based with high anti-
nutrient content should be identified (Walingo, 2009). Some of these processes include thermal
processing, germination, milling/household pounding, microbial fermentation, and soaking.
Cooking has been shown as one of the factors that affect anti-nutrient and nutrient contents of
vegetables. The main methods of cooking in the study area involve boiling in unspecified
amounts of water contributing to nutrient loss and using additives like bicarbonate of soda, lye
(traditional salt),milk, sesame and groundnut paste whose effects are unknown. Cooking in study
area households is done by use of pots rather than pans as pots retain heat and give better
simmering effects (Abukutsa-Onyango, 2010). Also, the covering of the cooking pot is preceded
by sealing it completely with banana leaves and this helps to retain steam, which escapes with
some volatile nutrients and the aroma (Musotsi et al., 2005). Results also show that the recipes in
study area households are based on a mixture of different vegetables (Musotsi et al., 2005).
There is some evidence that boiling vegetables induce losses of 5%-15% of phytate and that
thermal processing can also enhance bioavailability of vitamins and carotenoids by releasing
them from entrapment in the plant matrix (Sandberg, 1991). Microbial fermentation is also one
of the food processing methods employed in the study area. Fermentation can induce phytate
hydrolysis via action of microbial phytase enzymes, which hydrolyze phytate to lower
inositolphosphates that do not affect mineral absorption (Sandberg, 1991). Microbial phytases
originate from micro flora on the surface of cooked food (Sandberg, 1991). Studies also reveal
that the enzyme phytase is affected by anti-nutrients like tannin hence interfere with hydrolysis
of phytate (Sandberg, 1991). Employing both cooking and fermentation of AIVs may contribute
to the increased bioavailability of micronutrients (Gibson et al., 2010). Kimiywe and Waudo
(2007) documented preparation and cooking procedures that could lead to a decrease in the
nutritive value of cooked food. These includes chopping before washing which leads to loss of
vitamin C and vitamin B complex since they are water soluble vitamins, repeated boiling and
frying destroys vitamin C and addition of sodium bicarbonate leads to loss of vitamin B
complex i.e. B1, B2 and niacin.There is a delicate balance between loss of nutrients and
reduction of anti-nutrients by traditional food processing methods adopted in LVB households.
Oke and Bolarinwa (2011) studied the effect of fermentation on oxalate content of cocoyam
flour. It was demonstrated that 48 hour fermentation reduced calcium oxalate significantly by
approximately 58%-65% and that the longer the fermentation period the higher the microbial
population and the higher the reduction of oxalate in the cocoyam. Iwuoha and Kalu (1995)
reported 82.1% and 61.9% oxalate reduction in cocoyam flour produced from boiled and roasted
International Journal of Agriculture and Environmental Research
Volume:01,Issue:02
www.ijaer.in
www.ijaer.in Page 92
cocoyam respectively. The study concluded that high temperatures during cooking significantly
reduced the levels of oxalate in vegetables. Muchoki et al (2010) also demonstrated that high
temperatures reduced oxalate levels in Vigna unguiculata leafy vegetable. The effects of cooking
and microbial fermentation on levels of anti-nutrients needed a study. This study investigated the
oxalate levels in selected African indigenous vegetable recipes from the Lake Victoria Basin,
Kenya.
MATERIALS AND METHODS
Study site
The study was carried out in Vihiga County of Western part of Kenya in the LV Band is located
at longitude 34o 30” East and latitude 00o 11” and 00o 15” North and occupies an area of 563 km2
(CBS, 2001). It has four sub-counties: Emuhaya, Vihiga, Hamisi and Sabatia. It lies between
1300 m and 1500 m above sea level with an equatorial climate and a forest cover of 4 percent
and an annual precipitation of 1900 mm (District Strategic Plan, 2005). Land is arable and
supports a variety of crops (CBS, 1997). It is the third most densely populated County in Kenya
with a population of 595,180 people as per 2005 census. Population density is 975 persons per
sq. km (CBS, 2001). The County is dependent on food relief and its high population growth rate
cannot be sustained by its infrastructure and productivity. Adverse poverty indicators hinder
attainment of food security, as demand grows every year. With an average land size of 0.4
hectares per household, the county can no longer produce enough food. Malnutrition is a
common feature here (Akelola et al., 2007). Land is scarce and 60 percent of the population lives
below the poverty line. The main economic activity by residents is farming of maize, millet, tea,
cassava, sweet potatoes, beans and a variety of vegetables and fruits. Dairy farming is practiced
on small scale, as many people have been restricted to keeping one or two animals because of
inadequate pasture. Uneconomical land use and HIV/AIDS contributes to poverty, and
malnutrition is high due to wide spread poverty, poor feeding habits and over reliance on starchy
foods. Nearly 133 children per 1000 children die before their fifth birthday due to maternal
malnutrition (CBS, 2002). Despite having favorable climate and soils the area is not sufficient in
food production.
SOURCE OF THE AFRICAN INDIGENOUS VEGETABLES
The eleven AIVs selected for use in recipe formulations were spider plant (Cleome gynandra),
pumpkin leaves (Curcubita moschata), cowpea (Vigna unguiculata), green amaranth
(Amaranthusblitum), jute mallow (Corchorus olitorius), sweet potatoes leaves (Ipomea batatas),
African nightshade (Solanum nigrum), and cassava leaves (Manihot esculenta), slender leaf
(Crotolaria ochroleuca), vine spinach (Basella alba) and African kales (Brassica carinata).
International Journal of Agriculture and Environmental Research
Volume:01,Issue:02
www.ijaer.in
www.ijaer.in Page 93
These vegetables were identified and about 1 kg of each purchased from markets within the
study area: Chavakali, Shisejeri, Shamakhokho, Gambogi, Kiboswa, Wemilabi, Luanda and
Majengo. Leaves of sweet potatoes (Ipomea batatas), cassava (Manihot esculenta) and nderema
(Basella alba) were identified and purchased from small vegetable farms in homes within the
study area. The purchased vegetables were de-stalked and the leaves washed with distilled water
to remove dirt. Vegetables of the same species from different markets were mixed to get a
representative sample for each species and transported to Kenyatta University in cool boxes for
recipe preparation. Exactly 1kg of each vegetable sample was weighed and blanched in one litre
of boiling water for two minutes to inactivate enzymes responsible for vitamin degradation
(Mosha et al., 1997 and Nyambaka and Ryley, 1996) and immersed in ice cold water for two
minutes to minimize premature cooking process.
PREPARATION OF LYE
Lye was prepared from pods of beans (Habwe et al., 2009). Pods of green beans were dried after
removing the mature seeds. The dry pods were then burnt over a hot dry pan and the ash
collected after complete burning. The ash was put in a container whose bottom had small holes
and distilled water poured through the ash into another container underneath and filtrate (lye)
collected.
PREPARATION OF RECIPES
There were five vegetable mixtures formulated, each containing 40g of the unmixedAIV as
follows: First mixture (S. nigrum + A. blitum), second mixture (C. ochroleuca + C. olitorius),
and third mixture (C. ochroleuca + C. olitorius + V. unguiculata), fourth mixture (A. blitum + C.
gynandra + S. nigrum) and fifth mixture (C. gynandra + C. moschata).Each of these blanched
five vegetable mixtures and each of the eleven unmixed selected AIVS were divided into two
lots. One lot was fermented and the other lot unfermented. The lot to be fermented was boiled,
cooled and left in the open to allow microbial fermentation to occur for 48 hours. The
unfermented lot was divided into three portions for cooking. One portion was cooked by boiling
in water, another cooked by boiling with lye and milk and the other cooked by sautéing
according to the household cooking procedures commonly employed in the study area. The
unfermented group was refrigerated at 40C. This generated 16 AIV recipes for study.
Vegetable cooked by boiling in water
Exactly 40 g of the vegetable was boiled in 100 ml of distilled water for 10 minutes at 40ºC and
recipe obtained was cooled to room temperature and sealed in black polythene bags to keep out
light and refrigerated at - 4ºC, awaiting extraction to obtain the sample for laboratory analysis.
International Journal of Agriculture and Environmental Research
Volume:01,Issue:02
www.ijaer.in
www.ijaer.in Page 94
Vegetable cooked by boiling with lye and milk
Exactly 40 g of the blanched AIV to which 30 ml of traditional salt (lye) had been added was
boiled for 7 minutes in 40 ml of distilled water at a moderate temperature of 40ºC. Exactly 30 ml
of fresh milk was added and mixture simmered for three more minutes. The boiled mixture was
left to cool to room temperature, sealed in a black polythene bag and refrigerated at - 4ºC
awaiting extraction to obtain the sample for laboratory analysis.
Vegetable cooked by sautéing
Exactly 20 ml of vegetable cooking oil was transferred by means of clean plastic syringe to a
clean cooking pan and placed on electric cooker plate set at a temperature of 40ºC to heat. One
onion bulb was peeled to remove dry outer skin, washed, sliced and was sautéed in the oil till
golden brown and a pinch of common salt added. Two tomatoes with intact skin were washed
with distilled water, chopped and added to the mixture in the pan. Exactly 40 g blanched AIV
was then added, stirred and mixture heated for 10 minutes. The sautéed AIV was left to cool to
room temperature, sealed in a black polythene bag and refrigerated at - 4ºC awaiting extraction
to obtain the sample for laboratory analysis.
Fermented recipe
Exactly 40 g of the blanched single AIV or AIV mixture was boiled for 10 minutes in 100 ml of
distilled water and left to cool to room temperature, sealed in a black polythene bag to keep out
light and kept in open air for 48 hours to allow microbial fermentation. After the fermentation
period the fermented recipe was refrigerated at - 4ºC awaiting extraction to obtain the sample for
laboratory analysis.
SAMPLE PREPARATION FOR OXALATE ANALYSIS
Glassware was initially washed with a detergent, chromic acid and further washed in 1:1 nitric
acid before rinsing in distilled water. The glassware was dried overnight at 50 0 C. Plastic
containers were washed in 1:1 nitric acid and also rinsed in distilled water before drying them in
an oven at 30 0 C. Standards of oxalic acid were of analar grade and were sourced from Aldrich
Chemicals. Exactly 0.2 g of vegetable sample was homogenized in 1 ml of 0.5 N HCl. The
homogenate was heated at 80 ° C for 10 min with intermittent shaking. To the homogenate 5 ml
of distilled water was added. About 2 ml of the solution was withdrawn and centrifuged at 12
000 g for 10 min. 1 ml of supernatant was passed through a filter (0.45 µm) before HPLC
analysis. Standards were prepared at varying concentrations for quantification.
STANDARDS AND CALIBRATION CURVES
International Journal of Agriculture and Environmental Research
Volume:01,Issue:02
www.ijaer.in
www.ijaer.in Page 95
A stock solution of the standard containing 10 mg/ml of oxalic acid was prepared for calibration.
The peak area was determined and used to obtain the concentration levels of oxalate in the
samples. The regression coefficient (R) was obtained and from it the coefficient of determination
(R2) was worked out.
Figure 1: Calibration curve for oxalate
METHOD VALIDATION
The following performance parameters were evaluated for method validation: linearity domain
of the concentration: limit of detection (LOD), precision (reproducibility), and accuracy (by
recovery tests):
Linearity test of concentration: limit of detection
The linearity of the calibration curve is given by the equation y=mx-c, where the calculated
blank sample absorbance is c and the method sensitivity (the slope) is m and the correlation
coefficient is R. Limit of detection (LOD) was calculated using equation (i) (Eurachem guide,
1998). Absorbance values for 10 replicates of the blank solution were determined and
transformed into concentration values in order to be compared with the data obtained from the
calibration curve. The results are displayed in table 1.
International Journal of Agriculture and Environmental Research
Volume:01,Issue:02
www.ijaer.in
www.ijaer.in Page 96
LOD = X
̄blank + 3Sblank........................................ (1)
X
̄blank is the mean absorbance obtained with the blank solutions:
Sblank is the standard deviations of the blank:
Xi are the values of the blank solutions while n is the number of replicates i.e. n=10.
Table 1: Limit of detection, equation of calibration curve, coefficient of
determination (R2) and regression coefficient (R)
Parameter
LOD(µg/ml)
Equation
R2
R
Oxalate
0.002
Y=3684x+2881
0.997
0.99849
The R2 values hence R values indicate that the established calibration curves are linear over the
respective range of concentrations as R tends to unity. The method detection limits at 3 standard
deviations for all the parameters were < 1 µg/ml which clearly indicates that the method was
reliable for the determination of the levels of oxalates.
Precision
Reproducibility of results was calculated for 10 measurements. Precision was evaluated by
Relative Standard Deviation (%RSD), according to the equation 2 (Eurachem guide, 1998). The
results are given in table 2.
RSD =𝑠
x 100........................................... (2)
Table 2: Method precision
Parameter
mean
s
%RSD
Oxalate
5.34
0.02
0.37
The obtained results show good precision for the parameter under determination.
International Journal of Agriculture and Environmental Research
Volume:01,Issue:02
www.ijaer.in
www.ijaer.in Page 97
Accuracy
Accuracy was evaluated by recovery test, according to equation3 (Eurachem guide, 1998). The
results are presented in table 3.
% Recovery = 𝐶𝐹−𝐶𝑈
𝐶𝐴 x 100............................................ (3)
Where CU is the concentration in unfortified sample; CA is the concentration of Fortification
(added solution); CF is the concentration determined in fortified sample.
Table 3: Accuracy by Recovery test
CU
(mg/g)
CA
(mg/g)
CF
(mg/g)
%Recovery
0.20
0.70
0.89
98.40
The percentage recovery lies within the range (98.40−102.10). This confirms that the method is
accurate and fit for analysis of the parameter.
ANALYSIS OF OXALATE
Analysis was done at Jomo Kenyatta University of Agriculture and Technology’s Home
economics laboratory by reversed-phase HPLC using Hypsil C-18 SUPELCO column (5 µM,
4.6 mmx250 mm) equipped Waters 550 (Waters, MA, USA) as the static phase and the mobile
phase was a solution containing 0.5 % KH2PO4 and 0.5 mM TBA (tetrabutylammonium
hydrogen sulphate) buffered at pH 2.0 with orthophosphoric acid. Flow rate was 1 ml min-1
(Libert, 1981; Yu et al., 2002) and detection wavelength was at 220nm.
DATA ANALYSIS
The data obtained was analyzed by SPSS software (version 17) where it was subjected to
independent t-test to compare whether there was any significant difference in the mean levels of
oxalates between fermented and non-fermented AIVs and one-way ANOVA to compare the
mean values between different AIVs and cooking methods. Where one- way ANOVA showed
significant difference it was followed by multiple range test (Student Newman Keul Test). All
the significance tests were performed at 95% confidence level.
International Journal of Agriculture and Environmental Research
Volume:01,Issue:02
www.ijaer.in
www.ijaer.in Page 98
RESULTS AND DISCUSSION
The mean concentration levels of oxalate in fermented and unfermented AIV recipes
The mean levels of oxalate between fermented and unfermented AIV recipes were compared
(Table 4). Unfermented Amaranthus blitum and C. gynandra+C. moschata recipe formulation
recorded significantly higher mean levels of oxalate than any other unfermented recipes
(p<0.001). Fermented Amaranthus blitum recorded significantly higher mean levels of oxalate
than any other fermented recipes (p=0.107). The mean levels of oxalate in fermented Ipomea
batatas, Solanum nigrum,Manihot esculenta, Cleome gynandra and Basella alba were
significantly lower than in the unfermented ones (p<0.05). The mean levels of oxalate in the five
recipe mixtures that were fermented were significantly lower than in the unfermented ones
(p<0.001). There was no significant difference in the mean oxalate levels between fermented and
unfermented Vigna unguiculata (p=0.569) and Amaranthus blitum (p=0.107) (Table 4). Apart
from 2 AIV recipes (Vigna unguiculata and Amaranthus blitum) all the fermented AIV recipes in
the study had significantly lower mean levels of oxalate than the unfermented ones. However,
when the mean value of all unfermented vegetables was compared with the mean value of all
fermented AIVs (table 5), there was no significant difference (p=0.280, t-test).It was observed
that fermentation reduced oxalate levels in someunmixedAIV recipes and some recipe mixtures.
The observations inthose recipes in which there was a significant reduction in mean levels of
oxalates agreed withfindings of Oke and Bolarinwa (2011) who studied the effect of
fermentation on oxalate content of cocoyam flour. The study showed that 48 hour fermentation
reduced calcium oxalate significantly by approximately 58%-65% and that longer fermentation
period resulted in higher microbial population leading to higher reduction of oxalate
concentration levels.
Table 4: Mean concentration levels of oxalate in fermented and unfermented AIVs
Oxalate
AIVs
Unfermented
(Mean±SE)mg/100g
(n=9)
Fermented
(Mean±SE)mg/100g
(n=9)
P value
Curcubita moschata
9.20±1.61a
6.55±1.53b
0.030
Vigna unguiculata
2.62±.43a
2.24±.01a
0.569
Amaranthus blitum
15.42±1.56b
20.36±.01c
0.107
Corchorus olitorius
10.17±3.73a
3.04±.01a
0.001
Ipomea batatas
3.45±.53a
1.56±.08a
0.038
Solanum nigrum
6.72±.41a
2.69±.02a
<0.001
International Journal of Agriculture and Environmental Research
Volume:01,Issue:02
www.ijaer.in
www.ijaer.in Page 99
Mean ± SE values within the same column followed by the same superscripts are not
significantly different at α=0.05, while values within the same row with p<0.05 are significantly
different, 95% confidence level, independent t-test.
Table 5: oxalate levels in all non-fermented and all fermented recipes
Microbial Fermentation
Mean Oxalate level ±SE
All Non-fermented AIVs
5.48±0.87
All Fermented AIVs
3.88±1.16
p-value
0.280
Independent t test
The mean concentration levels of oxalate in AIVs by different cooking methods
Boiled Curcubita moschata recorded significantly higher mean levels of oxalate than in
Amaranthus blitum, Ipomea batatas, Brassica carinata, Solanum nigrum, Crotolaria ochroleuca
and Cleome gynandra (Table 6). There was no significant difference in mean oxalate levels in
boiled Curcubita moschata compared to boiled Vigna unguiculata, Corchorus olitorius and
Basella alba (p>0.05). Curcubita moschata boiled with lye and milk recorded significantly
higher mean oxalate levels than in Corchorus olitorius, Ipomea batatas, Brassica carinata and
Amaranthus blitum cooked the same way (p<0.05). However, there was no significant difference
in mean oxalate levels in Curcubita moschata boiled with lye and milk when compared with
Vigna unguiculata, Solanum nigrum, Manihot esculenta, Cleome gynandra and Basella alba
cooked the same way (p>0.05). SautéedCorchorus olitorius recorded significantly higher mean
oxalate levels than sautéed, Ipomea batatas, Solanum nigrum, Manihot esculenta, Crotolaria
ochroleuca, Brassica carinata, Cleome gynandra and Basella alba. The mean oxalate levels in
sautéed Amaranthus blitum were not significantly different from sautéed Vigna unguiculata,
Curcubita moschata and Basella Alba (p>0.05).
Manihot esculenta
3.07±.25a
1.94±.08a
0.006
Crotolaria ochroleuca
4.37±.58a
3.01±.00a
<0.001
Brassica carinata
6.10±1.65a
3.18±.06a
0.003
Cleome gynandra
5.12±.09a
1.54±.01a
<0.001
Basella alba
5.24±.52a
2.06±.45a
0.001
S. nigrum+A. blitum
3.04±.00a
2.06±.01a
<0.001
C. ochroleuca+ C. olitorius
2.53±.02a
2.04±.01a
<0.001
C. ochroleuca +C. olitorius+V. unguiculata
3.44±.01a
1.70±.03a
<0.001
A. blitum+C. gynandra+S. nigrum
4.14±.01a
2.30±.01a
<0.001
C. gynandra+C. moschata
5.88±.086b
3.02±.08a
<0.001
p-value
<0.001
<0.001
International Journal of Agriculture and Environmental Research
Volume:01,Issue:02
www.ijaer.in
www.ijaer.in Page 100
Table 6: The mean concentration levels of oxalate in AIVs by different cooking methods
Mean±SE values within the same row followed by the same superscripts are not significantly
different at α=0.05, p<0.001, SNK test.
Sautéed recipes had significantly lower oxalate levels than those boiled with lye and milk except
Amaranthus blitum and Corchorus olitorius (p<0.05) (Table 6).AIVs boiled with water had
significantly lower mean oxalate levels than those boiled with lye and milk except boiled
Brassica carinata which recorded significantly higher mean concentration levels of oxalate than
Brassica carinata boiled with lye and milk (Table 6). The higher levels of oxalate in sautéed
vegetables and in vegetables boiled with lye and milk compared to boiled ones could be
attributed to addition of oxalate to the recipes present in lye, milk, tomatoes and onions during
cooking. The results also showed that high temperatures during boiling and sautéing reduce
doxalate levels in some recipes and not others. The observations in those recipes in which there
was a significant reduction in mean levels of oxalates agreed with findings of Muchoki et al
(2010) that high temperatures reduced oxalate levels in Vigna unguiculata leafy vegetable.
Iwuoha and Kalu (1995) also reported 82.1% and 61.9% oxalate reduction in cocoyam flour
produced from boiled and roasted cocoyam respectively. The mean levels of all boiled AIVs, all
AIVs boiled with lye and milk and all sautéed AIVs were compared (table 7).The results show
that there was no significant difference in the mean values of oxalates by different methods of
cooking(p=0.986, one-way ANOVA).
OXALATE
AIVs
Boiled
(Mean±SE)
mg/100g
(n=3)
Lye+milk
(Mean±SE)
mg/100g
(n=3)
Sautéed(Mean±SE)
mg/100g
(n=3)
Curcubita moschata
7.13±.01a
17.26±.46c
9.86±.18b
Vigna unguiculata
1.66 ±.01a
3.57±.01c
2.15±.06b
Amaranthus blitum
19.78±.01c
9.37±.02a
17.11±.06b
Corchorus olitorius
1.82±.00a
3.66±.01b
25.03±.32c
Ipomea batatas
7.14±.01c
3.53±.01b
1.40±.04a
Solanum nigrum
6.77±.09b
8.09±.02c
5.29±.02 a
Manihot esculenta
2.61± .03b
3.60±.08c
2.00±.02a
Crotolaria ochroleuca
4.04±.02b
6.52±.01c
2.55±.02a
Brassica carinata
15.18±.01c
5.14±.01b
3.22±.03a
Cleome gynandra
5.04±.01b
5.47±.06c
4.86±.01a
Basella alba
4.65±.03a
7.91±.06c
5.28±.01b
International Journal of Agriculture and Environmental Research
Volume:01,Issue:02
www.ijaer.in
www.ijaer.in Page 101
Table 7: mean levels of oxalate in all AIVs by different cooking methods
One-way ANOVA
CONCLUSION
Fermentation of AIVs differently affected oxalate levels. In some recipes a decrease was
observed while in others there was no significant change, suggesting that reduction of oxalate
levels in AIVs may depend on other factors within the recipes other than microbial fermentation.
Cooking methods also differently affected oxalate levels. In some recipes a decrease was
observed while in others there was no significant change, suggesting that the degree of oxalate
degradation may depend on other factors within the recipes apart from heat during cooking.
Cooking methods and fermentation do not have a uniform effect on oxalate level reduction in all
AIV recipes but could still be employed as household procedures in reducing oxalate levels in a
number of AIV recipes.
ACKNOWLEDGEMENTS
The authors would like to thank the following for their contributions during the study: Mr.
Katweo Wambua of Mines and Geology, Nairobi for his support while using the Atomic
Absorption Spectrometer, Paul Karanja (Jomo Kenyatta University Of Agriculture And
Technology) for facilitating the use of HPLC equipment, Denis Osoro, Cornelius Waswa, Kevin
Odhiambo, Eunice Oduor (technicians in the Chemistry Department, Kenyatta University). Ann
Mwangi, John Gachoya and Patrick Kamande (Technicians in the Department of Food, Nutrition
and Dietetics, Kenyatta University) for assisting in recipe preparations from indigenous
vegetables, Dr.Mildred Nawiri, Dr. Ruth Wanjau, Prof Jane Murungi, Dr. Daniel Oyoo, Dr.
Charles Onindo, and Dr. Margaret Ng’an’ga for their advice.
REFERENCES
1. Abukutsa-Onyango, M. O. (2003). Unexploited potential of Traditional African
vegetables in Western Kenya. Maseno Journal of Education, Arts and Sciences, 4: 103-
122.
Cooking Method
Mean oxalate level ± SE
All AIVs Boiled
6.89±1.71
All AIVs boiled with Lye andMilk
6.74±1.22
All AIVs Sauteed
7.16±2.26
p-vlaue
0.986
International Journal of Agriculture and Environmental Research
Volume:01,Issue:02
www.ijaer.in
www.ijaer.in Page 102
2. Abukutsa-Onyango, M. O., Tushaboomwe, K., Onyango, J. C and Macha, S. E. (2006).
Improved community Land use for sustainable production and utilization of African
indigenous vegetables in the Lake Victoria region. In: proceedings of the Fifth Workshop
on Sustainable Horticultural Production in the Tropics, 23rd-26th November, 2005, ARC,
Egerton University.
3. Abukutsa-Onyango, M.O. (2007). The diversity of cultivated African leafy vegetables in
three communities in western Kenya. African Journal of Food Agriculture, Nutrition and
Development (AJFAND) 7 (3) online journal www.ajfand.net.7-179. Njoro: Egerton
University.
4. Abukutsa-Onyango, M.O. (2010). African Indigenous Vegetables in Kenya: Strategic
Repositioning in the Horticultural Sector. Inaugural lecture, April 30th, 2010, Assembly
Hall, Main Campus, JKUAT-Juja,
5. Adebooye, O. C and Parody, J. T. (2004). Status of conservation of the traditional leaf
vegetables and fruits of Africa. African Journal of Biotechnology, 3: 103-122.
6. Akelola, R., Karuri, N. M. and Mwaniki, D. 2007. The effect of otange fleshed sweet
potato on vitamin A nutritional status of pre-school children in Nambale Division, Busia
District, Proceedings of the 13th ISTRC Symposium 13:721-727.
7. Akindahunsi, S. (2005). Phytochemical screening and nutrient-anti-nutrient composition
of selected tropical green leafy vegetables. African Journal of Biotechnology, 4: 497-501.
8. Broadhurst, R. and Jones, W. T. (1979). Analysis of condensed tannins using acidified
vanillin. Journal of the Science Food and Agriculture, 29: 783-798.
9. Brown, R. C., Klein, A.K., Simons, W. K and Hurrel, K. F. (1990). The influence of
Jamaican herbal teas and other polyphenols containing beverages on iron absorption in
the rat. Nutrition Research Reviews, 10: 343-353.
10. Central Bureau of Statistics (1997). Vihiga District Plan 1997-2001. Government
Printers, Nairobi: 114-119.
11. Central Bureau of Statistics and Ministry of Planning and National Development (2001).
Population distribution by administrative areas and urban centers, Kenya, 1999
Population and Housing census vol. 1, 13-25.
12. Central Bureau of Statistics and Ministry of Planning and National Development (2002).
Kenya 1999 Population and Housing Census. Analytical report on mortality vol. V, 115-
122.
13. Choi, Y. E., Harada, E., Wada, M., Tsuboi, H., Morita, Y., Kuusano, T and Sano, H.
(2001). Detoxification of Cadmium in tobacco plants: formation of active excretion of
crystal containing cadmium and calcium through trichomes. Journal of Plant physiology,
213: 45-50.
International Journal of Agriculture and Environmental Research
Volume:01,Issue:02
www.ijaer.in
www.ijaer.in Page 103
14. District Strategic Plan (2005). Implementation of the national population policy for
sustainable development. National coordinating Agency for population and development,
Nairobi, Kenya.
15. Ekpedema, U., Akwaowo, Ndun, A and Ekaete, U. (2000). Minerals and anti-nutrients in
fluted Curcubita moschata (Telfairia occidentalis Hook f.) Analytical, Nutritional and
Clinical Methods Section. Food Chemistry Journal, 70: 235-240.
16. Eurachem (1998). The Fitness of Purpose of Analytical methods, A Laboratory Guide to
Method Validation and Related Topics, Internet edition: 46-49.
17. Franceschi, V. R and Nakata, P. A. (2005). Calcium oxalate in plants: formation and
function. Annual Review of Plant Biology, 56:41-71.
18. Gibson, R. S., Bailey, K. B., Gibbs, M and Ferguson, E. L. (2010). A review of Phytate,
iron, zinc and calcium concentrations in plant based complementary foods used in low-
income countries and implications for bioavailability. Food and Nutrition Bulletin, 31:
S134-46.
19. Habwe, F. O., Walingo, M. K., Abukutsa-Onyango, M. O and Oluoch, M. O. (2009). Iron
content of the formulated East African Traditional AIV recipes. African Journal of. Food,
Agriculture, Nutrition and Development, 3: 393-397.
20. Iwuoha, C. I and Kalu, F. A. (1995). Calcium oxalate and physicochemical properties of
cocoyam tuber flours as affected by processing. Food Chemistry Journal, 54: 61-66.
21. Kimiywe, J., Waudo, J., Mbithe, D and Maundu, P. (2007). Utilization and medical value
of traditional leafy vegetables consumed in Urban and peri-urban Nairobi. African
Journal of. Food, Agriculture, Nutrition and Development. ISSN, 7: 1684-5374.
22. Libert, B and Franceschi, V. R. (1987). Oxalate in crop plants. Journal of Agriculture and
Food Chemistry, 35:926-938.
23. Libert, B. (1981). Rapid determination of oxalic acid by reversed-phase high performance
liquid chromatography. Journal of chromatography, 210:540-543.
24. Makokha, A.O. and F. Ombwara, (2005). Potential for increased use of indigenous
Kenyan Vegetables as functional foods. In: In: Proceedings of the third
HorticultureWorkshop on Sustainable Horticultural Production in the Tropics, 26th -29th
November 2003. Maseno University MSU, Maseno, Kenya. ISBN: 9966-758-11-9. pp.
102-116.
25. Maundu, P.M, G.W. Ngugi and C.H.S. Kabuye, 1999.Traditional Food Plants of Kenya.
KENRIK National Museums of Kenya, Nairobi, Kenya. 270 pages.
26. Mnzava, N.A. (1997). Vegetable crop diversification and the place of traditional species.
In: Guarino Editor 1997, Traditional African vegetables. Promoting the conservation and
use of Underutilized and neglected crops. 16. Proceedings of the IPGRI International
Workshop on Genetic Resources of Traditional Vegetables in Africa. Conservation and
International Journal of Agriculture and Environmental Research
Volume:01,Issue:02
www.ijaer.in
www.ijaer.in Page 104
use, 29-31 August 1995, ICRAF-HQ, Nairobi, Kenya. Institute of Plant Genetic and Crop
Plant Research, Gatersleben/International Plant Genetic Resources Institute, Rome. Italy.
Pages 1-15.
27. Mosha, T. C., Pace, R. D., Adeyeye, S., Laswai, H. S and Mtebe, K. (1997). Plant Foods
for Human Nutrition. , Journal of Agriculture and Food Chemistry, 50: 189-201.
28. Muchoki, C. N., Lamuka, P. O and Imungi. (2010). Reduction of nitrates oxalate and
phenols in fermented solar- dried store Vigna unguiculata (Vigna unguiculata) leaf
vegetables. African Journal of. Food, Agriculture, Nutrition and Development, 10: 4398-
4412.
29. Munro, A and Bassir, O. (1969). Oxalate in Nigerian vegetables. West African Journal of
Biological and Applied Chemistry, 12: 14-18.
30. Musotsi, A.A., Sigot, A. and M.O.A. Onyango (2005). African Indigenous Vegetables
Recipe Documentation and their role in food security. In: Proceedings of the third
Horticulture Workshop on Sustainable Horticultural Production in the Tropics, 26th -29th
November 2003. Maseno University MSU, Maseno, Kenya. ISBN: 9966-758-11-9. pp.
105-111.
31. Nyambaka, H and Ryley. (1996). an isocratic reversed-phase HPLC separation of stereo
isomers of the provitamin A carotids (α and β carotene) in dark green vegetables, Journal
of Food Chemistry, 55: 63-72.
32. Oke, M. O and Bolarinwa, I. F. (2012). Effect of fermentation on physicochemical
properties and oxalate content of cocoyam (Colocasia esculenta) flour.
33. Sandberg, A. S (1991). Phytate hydrolysis by phytase in cereals; effects on in vitro
estimation of iron availability. Journal of Food Science, 56: 1330-1333.
34. Smith, I. F and Eyzaguire, P. (2007). African heavy vegetables; their role in the World
Health Organization Global Fruit and Vegetable Initiative. African Journal of. Food,
Agriculture, Nutrition and Development, 7: 1674-1684.
35. Walingo, M. K. (2009). Traditional food processing methods that improve zinc
absorption and bioavailability of plant diets consumed by the Kenyan population. African
Journal of. Food, Agriculture, Nutrition and Development, 9: 523-535.
36. Waudo, J., Tuitoek, P., Msuga, J and Kikafunda, J. (2006). Food consumption patterns
and nutrient intakes by women and children under five in the wetlands of Lake Victoria
Basin. Research week, Egerton University, July 2006.
37. Weinberger, K and Msuya. (2004). Indigenous vegetables in Tanzania-Significance and
Prospects. Shanhua, Taiwan: AVRDC-The world vegetable centre. Technical Bulletin no.
31, AVRDC publication 04-600. p. 70.
International Journal of Agriculture and Environmental Research
Volume:01,Issue:02
www.ijaer.in
www.ijaer.in Page 105
38. Yang Y. Y., Jung, J. Y., Song, W. Y., Suh, H. S and Lee, Y. (2000). Identification of rice
varieties with high tolerance or sensitivity to lead and characterization of the mechanism
of tolerance. Plant Physiology Journal, 124: 1019-1026.
39. Yu, L., Peng, X. X., Yang, C., Liu, Y. H and Fan, Y. P. (2002). Determination of oxalic
acid in plant tissue and root exudates by reversed phase high performance liquid
chromatography. Chinese Journal of Analytical Chemistry, 30: 1119-1122.
... ANS contains antinutritional factors such as oxalates, tannins, cyanogenic glycosidase, phytate, glycoalkaloids, and nitrates (Table 5) (Amalraj & Pius, 2015;Essack et al., 2017;Mwanri et al., 2018;Wakhanu et al., 2015). Some of them, for example, tannin, phytate, and glycoalkaloids, exhibit functional properties, for example, anticancer, antibacterial, antivirus, and anti-inflammatory properties (Delimont et al., 2017;Silva & Bracarense, 2016), also elaborated in Section 4.2. ...
... Nonetheless, the amount of oxalate in ANS leaves is significantly lower than in some exotic vegetables (Akhtar et al., 2011;Faudon & Savage, 2014). Fermentation and boiling reduce oxalate content in ANS and other AIVs (Essack et al., 2017;Muchoki et al., 2010;Owade et al., 2019;Wakhanu et al., 2015). Likewise, blanching at 95 • C and steam blanching for 5 min reduce oxalate in ANS by 42% to 75% (Managa et al., 2020). ...
Article
Full-text available
Achieving zero hunger in sub‐Saharan Africa (SSA) without minimizing postharvest losses of agricultural products is impossible. Therefore, a holistic approach is vital to end hunger, simultaneously improving food security, diversity, and livelihoods. This review focuses on the African nightshades (ANS) Solanum spp. contribution to improving food and nutrition security in SSA. Different parts of ANS are utilized as food and medicine; however, pests and diseases hinder ANS utilization. African nightshade is rich in micronutrients such as β‐carotene, vitamins C and E, minerals (iron, calcium, and zinc), and dietary fiber. The leaves contain a high amount of nutrients than the berries. Proper utilization of ANS can contribute to ending hidden hunger, mainly in children and pregnant women. Literature shows that ANS contains antinutritional factors such as oxalate, phytate, nitrate, and alkaloids; however, their quantities are low to cause potential health effects. Several improved varieties with high yields, rich in nutrients, and low alkaloids have been developed in SSA. Various processing and preservation techniques such as cooking, drying, and fermentation are feasible techniques for value addition on ANS in SSA; moreover, most societies are yet to adopt them effectively. Furthermore, promoting value addition and commercialization of ANS is of importance and can create more jobs. Therefore, this review provides an overview of ANS production and challenges that hinder their utilization, possible solutions, and future research suggestions. This review concludes that ANS is an essential nutritious leafy vegetable for improving nutrition and livelihoods in SSA.
... Even though most people consume amaranth frequently, not for its nutritional attributes but because it is cheap and available or because of circumstance related to poverty, there has been notable change in cooking from the traditional methods. e traditional methods involved long boiling time extending to hours, coupled with fermentation for several days [17,[33][34][35]. It was noted by the key informants that training and advise on cooking are taken seriously and there have been some changes in attitudes. ...
Article
Full-text available
African leafy vegetables such as amaranth have been utilized since time immemorial both as food and as medicine. These vegetables grew naturally in most rural environments, but currently most of them are cultivated both for home consumption and for sale. The aim of this study was to identify the most preferred amaranth species and cooking and utilization practices, as well as the beliefs and attitudes that encourage or discourage use of this vegetable. The study was carried out in seven counties of Kenya and in three regions in Tanzania. Twenty Focus Group Discussions (FGDs) with members of the community and twenty Key Informant Interviews (KIIs) with agricultural and nutrition officers were conducted in the study areas to obtain information on preferred varieties, sources of amaranth vegetables, common cooking methods, alternative uses, beliefs and taboos surrounding amaranth consumption, and the challenges experienced in production and consumption. The findings of the study showed that amaranth is one of the most commonly consumed indigenous vegetables in Kenya and Tanzania. The preference for varieties and cooking habits differs depending on the community and individuals. Amaranthus dubius and Amaranthus blitum were most common in Kenya, while Amaranthus dubius and Amaranthus hypochondriacus were most common in Tanzania. Most people consumed these vegetables because they were affordable and available or because of circumstance of lacking other foods. Regarding cooking, final taste was mostly considered rather than nutritional attribute. Several alternative uses of amaranth such as uses as medicine and livestock feed were also reported, as well as some beliefs and taboos surrounding the vegetable. Training on nutritional attributes and promotion of food preparation practices that ensure maximum nutrient benefits from amaranth is needed at the community level to realize the nutritional importance of the vegetables. Hands-on training and demonstrations were the most preferred modes of passing information.
Article
Full-text available
The diversity of indigenous leaf vegetables and fruits of Africa is being seriously eroded as a result of multiplicity of environmental, political and socio-economic factors. This paper discusses some new development-related and crises factors that have interacted in concert to amplify the spate of loss of the indigenous leaf vegetables and fruits genetic resources in Africa. The paper also suggests urgent steps that nations individually and Africa in general can take to arrest the wave of loss of plant genetic resources and therefore ensure the conservation of our remaining indigenous leaf vegetables and fruits heritage.
Article
Full-text available
This study was conducted to determine the effect of fermentation, solar drying and storage duration on the levels of anti-nutrients: nitrates, oxalates and phenols, in cowpea leaf vegetables. The rationale was reduction of the anti-nutrients. Reduction of nutritional stress factors in plant foods increases bioavailability of nutrients, hence improving their quality as foodstuffs. The cowpea leaves were purchased from the local markets, sorted to remove blemished leaves and foreign materials, washed in running tap water. Then, the vegetables were drained and divided into three batches of 16 kg each. One batch was heat-treated in hot water for 3 minutes and then cooled to ambient temperatures, drained and solar-dried. The second portion was acidified to a pH of 3.8, heat-treated, and solar-dried. The third portion was fermented for 21 days, heat-treated, and solar-dried. The three batches of vegetables were spread at different times on drying trays at the rate of 4 kg/m2and dried in a solar drier to an approximate moisture content of 10%. The dried vegetables were packaged in either polyethylene bags or Kraft paper bags and stored for three months at 18oC, 22-26oC or 32oC. Fermentation, heat-treatment and drying of vegetables led to significant (P < 0.05) reduction in nitrates compared to fresh cowpea leaves, but the reduction in oxalates and phenols was not significant. Storage for three months led to significant (P < 0.05) reduction in nitrates in the fermented sample compared to the other samples. The acidified sample had significantly (P < 0.05) higher levels of phenols after three months of storage than the other samples. Samples stored at 18oC had higher levels of oxalates and phenols but lower levels of nitrates, compared to those stored at higher temperatures. Packaging material had no significant effect on the level of nitrates, oxalates and phenols. Data obtained in this study reveal a novel technique for the reduction of anti-nutrients in cowpea leaf vegetables, namely; fermentation followed by solar drying. The increased acceptability of these fermented-dried vegetables would help rural communities in providing better foodstuff with fewer anti-nutrients, thus alleviating micronutrient malnutrition. This novel long-term storage technology can greatly help to deal with the issue of seasonality and will increase food security, especially during the dry season. Key words: Fermentation, solar drying, vegetables, anti-nutrients
Article
Full-text available
The effect of fermentation on physicochemical properties and oxalate content of cocoyam (Colocasia esculenta) flour was evaluated. The cocoyam, white flesh was cleaned, washed, peeled, sliced into chips of 2–2.5 cm thickness, soaked in tap water and left to ferment for 24 h and 48 h. The fermented cocoyam was then drained, dried in cabinet dryer at 60∘C for 24 h and milled. The flour samples were passed through a 45 μm mesh size sieve. Unfermented cocoyam flour was also produced and served as a control. Calcium oxalate and some physicochemical properties of flours from the fermented cocoyam were compared with the unfermented flour. Results showed that fermentation effected a significant reduction in oxalate level (58 to 65%) depending on the fermentation period. The amylose content was higher in 48 h fermented flour (55.52%) than in 24 h (54.55%). Pasting (gelatinization) temperature decreased, and water absorption capacity increased markedly due to fermentation.
Book
The book deals mainly with naturally occurring, and some cultivated, species of food plants, with an emphasis on less known but locally important species that are indigenous to Kenya. It aims at unlocking the potential of these species by providing information on their value to different communities. Detailed information on their food value and utilization, including, among other uses, their medicinal, cultural, and household usage is presented. Additionally, the species description, illustration, distribution, ecology, availability, status, management and commercial potential are provided. Also included are a few exotic species that are of traditional, cultural and nutritional importance in Kenya
Article
Levels of some nutrients and antinutrients in 14 commonly consumed tropical green leafy vegetables were evaluated and also screened for some phytochemicals. Saponin was present in all the vegetables with the exception of Hibiscus esculentus, Solanum macrocarpon and Piper guineese while only tannin was absent in Crassocephalum crepidioides, Talinum triangulare, Corchorous olitorius and Piper guineese. Crude protein, fat, fibre and ash recorded ranges from 20.59 to 38.18, 5.90 to 12.73, 6.20 to 7.20 and 8.00 to 25.49%, respectively. Na (0.64 to 8.97 g/100 g) and P (1.34 to 3.34 g/100 g) recorded the highest values of minerals. The low levels of antinutrients (phytic acid, tannic acid and oxalate) coupled with high level of zinc biovalability indicates that the studied vegetables are good dietary supplements.
Article
An improved method was described for the determination of oxalic acid in plant samples by reversed-phase high performance liquid chromatography. A reversed-phase C18 column, an ultraviolet detector at 220 nm, and a mobile phase containing 0.5% KH2PO4 and 0.5 mmol/L tetrabutylammonium hydrogen sulfate (pH 2.0) were applied to the system, which allowed a good separation of oxalic acid from nitrate and other organic acids. The method was further tested for the analysis of the samples of soybean leaves and the root exudate, showing it is precise, sensitive and highly reproducible. The detection limit is 1.43 ng, relative standard deviation is 2.8% (n = 21). Recovery is around 100%. In addition, the collecting method of root exudate was improved to avoid loss of oxalic acid during the preparation, by which it is much easier to monitor the oxalic acid exuded from the non-oxalic acid accumulating plants.
Article
Zinc deficiency is a public health problem associated with pregnancy complications and birth outcomes, impaired immune function, and increased duration and severity of diarrhea in children. Zinc is an essential trace mineral that is a component of over 200 enzymes and is known to be necessary for normal collagen synthesis, mineralization of bones, and is also involved in vital processes such as mitosis, synthesis of DNA and protein, and gene expression and activation. In many low-income countries diets are composed primarily of cereals and legumes which contain phytate that inhibit zinc absorption. Most Kenyan diets are composed of cereals and legumes that have high content of zinc inhibitors, whose levels may be reduced through appropriate food processing technologies at the household level. Indigenous food processing methods like soaking, germination, drying, fermentation, boiling, and roasting, and diet combinations usually reduce the levels of zinc antagonists in the plant diets, thus increasing zinc absorption and bio-availability. These methods are used in combination to both enhance organoleptic properties of food, increasing acceptability and also promoting complementation of nutrients. There are food combination patterns that enhance nutrient bioavailability and complementation that was known to most traditional households and are quickly being forgotten due to changing lifestyles, food preparation methods and food tastes. This is worsened by lack of proper knowledge transfer from the older generation. However, the transfer of indigenous knowledge in food processing, preparation and diet combinations need to be profiled to identify processes that promote nutrient content and bioavailability for improved health and nutrient situation of rural populations whose diets are basically plant based. There is need to identify suitable sources of absorbable zinc and possible suitable dietary combinations that can contribute towards the reduction of zinc deficiency. This paper discusses the indigenous food processing methods that enhance zinc absorption and bioavailability of zinc in local dietary combinations that could reduce zinc deficiency.