Metal analyses of ash derived alkalis from banana and plantain peels (Musa spp.) in soap making

Abstract

The objective of this work was to determine the metal content of plantain and banana peels ash derived
alkali and the possibility of using it as alternate and cheap source of alkali in soap industry. This was
done by ashing the peels and dissolving it in de-ionised water to achieve the corresponding hydroxides
with pH above 12. The solution was then analyzed using Atomic Absorption Spectroscopy (AAS). The
analytical measurements were carried out in triplicate and the multi elemental solution was used for
calibration of equipment. The abundance of essential metals was in these orders in both the banana
and plantain alkalis: K > Fe > Ca > Mg > Mn > Zn > Na and Fe > K > Ca > Mg > Zn > Mn > Na,
respectively. The presence of other metals besides K and Na at higher concentrations limits the
foamability of the soaps but could be adapted as thickeners and emulsifiers in greases. The
concentrations of elements with health risk in the ash derived alkalis are within the allowable range of
the Commission of European Communities (2008) limit.

Full text

African Journal of Biotechnology Vol. 11(99), pp. 16512-16518, 11 December, 2012
Available online at http://www.academicjournals.org/AJB
DOI: 10.5897/AJB12.2255
ISSN 1684–5315 ©2012 Academic Journals
Full Length Research Paper
Metal analyses of ash derived alkalis from banana and
plantain peels (Musa spp.) in soap making
I. Oluremi Olabanji*, E. Ayodele Oluyemi and O. Solomon Ajayi
Department of Chemistry, Obafemi Awolowo University, Ile-Ife, Nigeria.
Accepted 10 October, 2012
The objective of this work was to determine the metal content of plantain and banana peels ash derived
alkali and the possibility of using it as alternate and cheap source of alkali in soap industry. This was
done by ashing the peels and dissolving it in de-ionised water to achieve the corresponding hydroxides
with pH above 12. The solution was then analyzed using Atomic Absorption Spectroscopy (AAS). The
analytical measurements were carried out in triplicate and the multi elemental solution was used for
calibration of equipment. The abundance of essential metals was in these orders in both the banana
and plantain alkalis: K > Fe > Ca > Mg > Mn > Zn > Na and Fe > K > Ca > Mg > Zn > Mn > Na,
respectively. The presence of other metals besides K and Na at higher concentrations limits the
foamability of the soaps but could be adapted as thickeners and emulsifiers in greases. The
concentrations of elements with health risk in the ash derived alkalis are within the allowable range of
the Commission of European Communities (2008) limit.
Key words: Banana, plantain, ash derived alkali, major elements, minor elements.
INTRODUCTION
Nigeria is one of the largest plantain producing countries
in the world (FAO, 2006). Despite this large production,
she does not export plantain because its production is
largely consumed locally. The rise in cottage industries
that made use of plantain for snacks (plantain chips) in
the non-farming urban population coupled with the
demand for easy and convenient foods made from
plantain locally, made its consumption to be on the
increase (Akinyemi et al., 2010). The high demand for
plantain also generates wastes which are often
discarded, and sometimes used for animal feeds. FAO
(1988) estimated 5,879,000 metric tonnes of banana
peels and 17,397,000 metric tonnes of plantain peels in
African countries which could be put into use for
generation of ethanol, alkali for soap production and
other medicinal use.
Soap production started around 2500 BC with boiling of
*Corresponding author. E-mail: ioolabanji@yahoo.com. Tel:
+2348034620878.
fats with ashes. The formula for soap consisting of water,
alkali and cassia oil was written on a Babylonian clay
tablet around 2200 BC (SDA, 1981; Willcox, 2000). In
ancient times, lubricating greases were made by reacting
lime with olive oil (Cavitch and Miller, 1995) these are
non synthetic and agricultural based materials like
banana peels, plantain peels, palm oil and palm kernel
oil, and therefore agricultural wastes such as banana
peels, plantain peels reacting with oil (palm oil and palm
kernel) could also serve the same purpose.
In chemistry, soap is a salt of a fatty acid (IUPAC,
1997). Ester hydrolyzed in the presence of an alkali
produces the carboxylates (salts of parent carboxylic
acids) and alcohols. The reaction is irreversible and can
be represented as shown below
RCOOR’ + OH- → RCOO- + R’OH
This reaction is used in the soap-making process, in
which fats or oils (or triesters) are hydrolyzed to produce
sodium carboxylates (soap) (Wong et al., 1998). The
alkaline solution promotes what is known as saponifica-

tion. Soaps for cleansing are obtained by treating
vegetable or animal oils and fats with a strongly alkaline
solution. Soap is mainly used for washing, bathing, and
cleaning but soaps are also important components of
lubricants. Therefore, it is important to note the metal
constituents of the ash from agricultural waste for the
production of locally made soaps.
Studies have been conducted on metal composition of
personal care products, soaps and detergents and
cosmetics in Nigeria (Ayenimo et al., 2010; Abulude et
al., 2010; Oyedeji et al., 2011) but there was little or no
information on metal constituents of locally made soaps
or its alkali. The toxic effects of heavy metals on human
health and ecosystem are well documented (Turkdogan
et al., 2003; Kawata et al., 2007; Liu et al., 2009). At low
concentration, some of these elements cause internal
body organ damage in animals and humans, since
metals’ pollution is through ingestion, inhalation and skin
contact, therefore, metals in agricultural waste could get
accumulated in man through the above route and their
by-products.
The abundance of plantain and banana peels could
generate ash derived alkali solution as alternative to
inorganic alkali, such as NaOH and KOH. Irvine (1965)
stated that agricultural waste materials contain a good
percentage of potash. These materials include palm
bunch waste, cocoa pod, plantain peels, banana leaves,
banana peels, maize cob, wood, sugar beet waste and
many others. When these materials are burnt in air, the
ashes contain oxides of potassium and sodium which
when dissolved in water yield the corresponding
hydroxides (Onyegbado et al., 2002) according to the
equations:
Na2O + H2O → 2NaOH
K2O + H2O → 2KOH
Environmental factors can affect the quality of locally
made soap, since they are made of raw or unprocessed
materials from agricultural waste. Agriculture and
aquaculture have been reported to affect the environment
due to fertilizer, contaminated sewage and the use of
herbicides (Falandysz et al., 2005). It is therefore
pertinent to assess the composition of the ash-derived
alkali and its suitability for human use. This will enable us
to have information on the heavy metal that can be
absorbed into the body through the use of the product
made from the alkali and possible danger man may face
through their use.
MATERIALS AND METHODS
Pretreatment and sterilization of apparatus
The beakers, volumetric flask, sample bottles, measuring cylinder,
pipette, burette, stirring rod, spatula, were soaked with 10% HNO3
and liquid soap for 48 h and rinsed with double distilled water after
Olabanji et al. 16513
which they were left to dry in the oven at 105°C ± 2 (Ogunfowokan
et al., 2005). Other materials used include an oven, a furnace,
crucibles, weighing balance, a large shallow tray called “combustion
pot” and a sieve set.
Reagents
All reagents used are of analytical grade. They include, alcoholic
KOH, sodium carbonate, sodium chloride were all from BDH
Chemicals Limited, Poole England, Hydrochloric acid (Riedel-de
Haen).
Sample collection and preparation
Unripe plantains (Musa balbisiana) Figure 1 and unripe banana
(Musa acuminate) Figure 2 were collected from the same farmland
within Obafemi Awolowo University Ile-Ife, Nigeria. They were
peeled and the peels were washed with double distilled water dried
in an oven at 105°C ± 2 for two days to constant weight. The dried
peels were ashed in a porcelain crucible placed in a Gallenkamp
muffle furnace for 6 h by stepwise increase of the temperature up to
500°C (Crosby, 1977). The ashed samples (grey in colour) were
homogenized in porcelain mortar and pestle and sieved. Sixty (60)
g of each of the sample were weighed into poly ethylene buckets of
2000 L capacities and one liter of water were added (Kuye and
Okorie, 1990; Onyegbado et al., 2002). They were covered to
prevent contamination for 24 h for maximum extraction. The
extracts were carefully decanted and double distilled water were
added in ratios of 1:4 of sample to double distilled water and were
analyzed by atomic absorption spectrophotometer (AAS) Buck
Model 205 at the International Institute for Tropical Agriculture
(IITA), Ibadan. These extracts were alkaline to litmus paper and
gave yellow colour when two drops of methyl orange were added.
The remaining extracts were used in the determination of molarities
and in preparation of soaps.
Determination of molarities
Ten gram (10 g) of anhydrous Na2CO3 was placed in a crucible and
heated between 250 to 270°C for 30 min in the oven and allowed to
cool in desiccator. 2.65 g was weighed into 500 cm3 standard flasks
and double distilled water was added and shaken at interval until
the salt dissolved and made to the mark. This solution was titrated
against HCl using methyl orange as indicator to determine its
molarity. The HCl of known molarity was titrated against each of the
extract using Phenothpthalein indicator to determine its molarities.
Determination of pH and conductivity
The pH of the extracts were determined using Hannah instruments,
pH 210 Microprocessor pH meter. The pH meter was calibrated
using buffer solutions of pH 4, 7 and 9, the pH meter of each extract
subsequently determined. The conductivity meter (CD210, WPA,
UK) model was calibrated following the manual instructions and the
extracts conductivities were determined.
Oil blend preparation and characterization
Four hundred gram (400 g) of palm oil and 100 g of palm kernel oil
purchased from the retail market at Oroki, Ile-Ife, Osun State,
Nigeria, were blended to give a ratio of 4:1 by weight (Onyegbado
et al., 2002). Forty gram (40 g) of the blended oil was heated to
70°C and poured into a cell in a Tri-stimulus Colorimeter (Model:

16514 Afr. J. Biotechnol.
Figure 1. Plantain (Musa balbisiana).
Macbeth-Munsell disk colorimeter) at the Chemical Engineering
Department, Obafemi Awolowo University, Ile-Ife, Osun State,
Nigeria. The readings were taken when the meter colour matched
the blended sample colour. Forty gram (40 g) each of the
unbleached palm oil, unbleached palm kernel oil, bleached palm oil,
bleached palm kernel oil, and unbleached oil blend were also
poured into the Tri-stimulus Colorimeter at intervals, and the colours
units were recorded to ascertain the actual colour of the blended oil.
Determination of saponification value of blended oil
Five gram (5 g) of blended oil sample was accurately weighed into
a 250 mL flask, 50 mL of alcoholic KOH solution was added and the
content was refluxed. Test for complete saponification was carried
out by dropping the mixture in water at interval; whenever the
traces of oil are seen, it shows incomplete saponification. Reflux
was continued until saponification was completed at 80°C. The
mixture was cooled and 10 cm3 of the mixture was pipette into a
conical flask, two drops of phenolphthalein indicator was added. 0.5
M HCl was put in the burette and titrated against the mixture. This
was done in triplicates and the average value was recorded.
Saponification reaction using the ash-extracts
One hundred and ten milliliter (110 mL) of the ashed peel (Banana
and plantain separately) extract was heated to half of the original
volume (concentrated to 50% alkali) by heating and evaporating in
a beaker (saponification pot) (Babayemi et al., 2011). This is
because in soap making, a slight excess of alkali is usually
recommended in order to ensure that all the fat is saponified and
also because of the antibacterial effect of the alkalis (Kirk et al.,
1954). The concentrated extract was heated to 80°C and 7.0 g of
bleached oil blend was gradually charged into the pot. The
temperature was maintained at 80°C and 5 mL of distilled water
was added intermittently while the mixture was continuously stirred.
Saponification continued until the solution became creamy. This
took approximately 40 min. About 10 mL of sodium chloride brine
was charged into the beaker content (saponification pot) and the
soap was completely homogenized and maintained at the
temperature of 70°C for 30 min. The crude soap was separated by
allowing the beaker and its content to cool. The soap formed a layer

Olabanji et al. 16515
Figure 2. Banana (Musa acuminate).
on the surface of the beaker while lye (a solution of glycerol and
brine) was below. The lye was removed by scooping the surface
into another container. The neat soap was then cooled.
RESULTS AND DISCUSSION
Analytical validation
The pH of banana and plantain peels ash derived
solutions are 12.05 and 12.88, respectively which
confirmed alkali production from banana and plantain
peels, the molarities of the banana and plantain ash
extract were 0.45 and 0.49, respectively and the metal
analysis (Table 1) showed metals of varying
concentrations.
Thorsten et al. (2002) stated that soaps are key
components of most lubricating greases, which are
usually emulsions of calcium soap or lithium soaps and
mineral oil. These calcium- and lithium-based greases
are widely used. Other metallic soaps are also useful,
including those of aluminium, sodium, and mixtures of
them. Such soaps are also used as thickeners to
increase the viscosity of oils. The ash derived alkali
contains varying concentrations of different metals (as
shown by conductivity values of 61.7 µS/cm in banana
peels and 64.2 µS/cm in plantain peels). Since emulsion
of Ca, Li and many other metal soaps and their mixtures
are used in most lubricating greases and are often called
thickener (Cavitch and Miller, 1995; Thorsten et al.,
2002), the soap made from these ash derived alkali of
banana and plantain could be useful as a thickener in
lubricating greases and will be more economical than
those from inorganic sources.
Although the soaps produced from the ash-derived
alkalis were not solid, they were soft and jelly-like, this is
expected as the percentage concentration of K in banana
and plantain were 41.45 and 32.54% and that of sodium
were 0.72 and 0.37%, respectively (Table 1) of the total
metal ions analyzed in each sample. Almost as a rule, the

16516 Afr. J. Biotechnol.
Table 1. Concentrations and percentage compositions of ash derived alkali from banana and plantain peels.
Element
Concentration in PP
(mg/kg) ± SD
Composition of
elements (%)
Concentration of BP
(mg/kg) ± SD
Composition of elements
(%)
Ca
106.78±0.00
14.98
76.86±0.00
17.50
Mg
66.48±0.00
9.33
32.33±0.01
7.36
K
231.93±0.00
32.54
181.99±0.0
41.45
Na
2.66±0.00
0.37
3.18±0.00
0.72
Mn
29.64±0.00
4.16
23.74±0.00
5.41
Fe
241.63±0.00
33.9
99.18±0.02
22.58
Cu
2.45±0.00
0.34
1.67±0.00
0.38
Zn
30.70±0.00
4.31
19.74±0.00
4.50
Pb
0.02±0.00
0.003
0.02±0.00
0.005
Cr
0.02±0.00
0.003
0.04±0.00
0.009
Cd
0.003±0.00
0.000
0± 0.00
0.00
Pd
0.07±0.03
0.01
0.05±0.02
0.01
Ni
0.06±0.02
0.0084
0.05±0.02
0.011
Ag
0.02±0.01
0.0028
0.02±0.00
0.005
B
0.23±0.02
0.03
0.19±0.01
0.04
Al
0.03±0.01
0.004
0.019±0.01
0.044
712.72
99.99
439.08
100.03
PP- Plantain peel, BP- banana peel.
solubility of soap in water increased in the size of the
monovalent cation (base); an increase in the size of a
divalent cation, (Mg, Ca) results in a decrease in the
foamability (Gupta and Wiese, 1997). Potassium soaps
are more soluble in water than sodium soaps; in
concentrated form they are called soft soap. Also, sodium
soaps prepared from sodium hydroxide are firm, whereas
potassium soaps, derived from potassium hydroxide are
soft. Because of their softness and greater solubility,
potassium soaps require less water to liquefy and thus
can contain more cleaning agent than liquefied sodium
soap and can be used as shampoos, shaving creams,
cleaning of dirty floors and cooking utensils, in emulsion
polymerization processes used in rubber and plastic
industries and in such other similar uses
(http://en.wikipedia.org/wiki/Potassium_hydroxide). The
presence of Ca and Mg ions limit its foam ability.
The palm oil/palm kernel oil had a saponification value
of 177.61. According to the study of Bailey et al. (2000),
fats and oils can be characterized by their saponification
numbers; one mole of fat requires three moles of KOH for
complete saponification. If a fat contains fatty acids of
relatively high molecular weights, then one gram of the
fat will consist of fewer moles. Thus, fats having greater
percentages of high molecular weight fatty acids will have
lower saponification numbers than fats having greater
percentages of lower molecular weight fatty acids.
Therefore, the palm oil/palm kernel oil was supposed to
have lower molecular weight fatty acid and high
saponification value (Palm oil 196 to 205 and Palm
Kernel oil 242 to 250, when free from moistures and
unsaponifiable matter (Lewkowitsch, 1922). Other unsapo-
nifiable matters present in the oil may be
responsible for lower saponification number.
Lewkowitsch (1922) said fats of different species of
animals and plants vary widely. Indeed, the fat, from a
given natural source, say a given species of animal or
plant, may contain the same triglycerides in slightly
different proportions, depending upon the conditions of
the environment prevailing while the fat was being
formed. It was pointed out that the properties of the fat of
an animal vary somewhat with the diet and also with the
tissue from which it is obtained. Fruit may yield two fats of
different properties, one from the pulp and one from the
kernel. In the case of plants, the fat may also vary with
the cultural variety of the plant and with the climatic and
soil conditions under which the plant was grown. Soaps
made from fatty acid of longer chain C16 to C18
contribute to the cleansing properties of soap (Gupta and
Wiese, 1997), thus the soaps made with palm kernel and
palm oil (with chain length C16 to C18) in this work will
have good cleansing properties.
The redness of the oil was considerably reduced by
bleaching, in which yellowness increased giving the oil a
light colour. The redness of the oil is as a result of high
carotenoid pigments which contribute to the colour of the
resulting soap. Onyekwere (1996) had shown that
bleaching of the oil removed carotenoid pigment and
odour of palm oil in resulting soap.
Spectrophotometry analysis of the metallic ions present
in ashed samples solution (Table 1) showed that the
alkali consist of ions that are essential diet components
by contributing iron, calcium, potassium and other
elements, which are usually in short supply in human in

some cases. It had been stated that plantains and
banana are good sources of vitamins and minerals,
particularly iron (24 mg/kg), potassium (9.5 mg/kg),
calcium (715 mg/kg), vitamin A, ascorbic acid, thiamin,
riboflavin and niacin. The sodium content (351 mg/kg) is
low in dietary terms, hence recommended for low sodium
diets (Stover and Simmonds, 1987; Welford et al., 1988).
The essential elements in the banana and the plantain
alkali in this study were in the order K > Fe > Ca > Mg >
Mn > Zn > Na and Fe > K > Ca > Mg > Zn > Mn > Na.
The element with the least concentration in these series
was Na, which supported the claim in previous findings
(Stover and Simmonds, 1987; Welford et al., 1988) and
also showed that the unripe banana and plantain pulp
may contain metals in similar order, and a slight
difference may be due to the type of soil they are grown
and the type of agricultural practices at different places.
Elements such as Fe, Ca, Mg and Zn are essential for
building red blood cells, bone formation, growth and
development; Zn and Mn are key components of metallo-
enzyme or are involved in crucial biological functions,
such as oxygen transport, free radical scavenging or
hormonal activity also required for metabolism (Parsons
and Barosa, 2007).
In this study Zn was found in banana and plantain alkali
in concentration of 30.90 and 19.74 mg/kg, respectively.
Zinc is an essential trace metal for plants, animals and
human as it is associated with many enzymes and with
certain proteins. The major health concern for zinc in
general is marginal or deficient zinc intake rather than
toxicity. Zinc is considered as being of low toxicity due to
the wide margin between usual environmental
concentrations and toxic levels. However, high levels of
zinc are undesirable as it may lead to copper deficiency
by inhibiting copper absorption (Iwegbu et al., 2011). All
these elements could enrich/nourish the skin when
soaps, through the ash derived alkali, are used for
bathing. Other metals such as Pd and Ni were less than
0.1 mg/kg, Pb, Cr, Ag, B and Al were less than 0.05
mg/kg and Cd less than 0.01 mg/kg. The Commission of
European Communities (2008) stated 0.3 and 0.05 mg/kg
for Pb and Cd as the maximum contaminants level in
foodstuff, as contained in food supplement as sold.
In this study, the values for banana and plantain peels
were (Pb 0.02 mg/kg in both peels and Cd 0.00, 0.03
mg/kg in banana and plantain, respectively). These
values are lower compared with the CEC recommended
maximum levels. Cadmium had been associated with
hypertension, liver disease and kidney damage while Pb
causes brain damage (Asaolu et al., 2002); but the levels
in this work were far below the level that could cause
damage to humans. Chromium was relatively low in the
samples. The levels of chromium observed in these
samples do not pose any contamination hazard to users.
Since it is essential to keep contaminants at levels which
do not cause health concerns in order to protect public
health (CEC, 2008), any contact made by the soap
produced with banana and plantain ash derived alkali
Olabanji et al. 16517
with humans through absorption by skin when in use may
not likely pose health risk.
Conclusion
Neat soap, having physical properties as pure potassium
hydroxide soap is derivable from the water extract of
ashes of plantain and banana peels. The concentrations
of elements with health risks are within the allowable
range of CEC (2008) limit of elements concentration in
food stuff. Efforts need to be made to reduce the level of
other macro and micro elements that constitute impurities
in the alkali. This will make agricultural wastes more
useful, thereby cutting down on, and eventually
eliminating the need for importation of inorganic raw
materials for production of thickeners and cleaning
agents.
ACKNOWLEDGEMENT
The authors acknowledge the effort of Ms. Falade
Omolara in bench work and transporting the samples to
IITA for analysis.
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