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beverages
Review
Chemical Contaminants Associated with Palm Wine
from Nigeria Are Potential Food Safety Hazards
Ogueri Nwaiwu 1, * and Martin Itumoh 2
1Research Services, Alpha Altis, Sir Collin Campbell Building, University of Nottingham Innovation Park,
Triumph Road, Nottingham NG7 2TU, UK
2Department of Agribusiness and Management, Faculty of Agriculture, Federal University Ndufu Alike
Ikwo, Ebonyi 480101, Ebonyi State, Nigeria; martin.itumoh@funai.edu.ng
*Correspondence: ogueri.nwaiwu@alpha-altis.co.uk; Tel.: +44-785-317-9327
Academic Editor: Dimitrios Zabaras
Received: 30 November 2016; Accepted: 26 February 2017; Published: 3 March 2017
Abstract:
Recent analysis of palm wine, a traditional drink fermented mainly by yeasts, revealed the
presence of several chemicals that were not products of yeast fermentation. The chemicals included
styrene, benzene, trimethyldioxolane, dichloromethane, methylene fluoride, dichloroethanol,
benzylisoquinoline and tetraacetyl-D-xylonic nitrile. A review of the concentrations of these
compounds in palm wine found that the benzene concentrations in all samples reviewed ranged from
56–343 ppm and were within permissible limits, whereas the styrene values (1505–5614 ppm) in all
the palm wine samples evaluated were well over the recommended concentration that is immediately
dangerous to life or health. Other chemical compounds evaluated varied according to location or
sample source. The concentrations obtained are estimates only and a quantitative study needs to be
carried out before the impact of these chemicals on health is evaluated. A search on The PubChem
Project, the open chemical database, showed the description, properties and uses of these chemicals.
Further searches carried out within other databases like PubMed, Scopus and Google Scholar, using
each chemical’s name as a search term, showed possible hazards and adverse health conditions
caused by these chemicals, especially styrene, benzene and dichloromethane. The point at which
the chemicals are introduced into the drink is still not clear and requires further investigation. The
chemicals can be hazardous to humans and there is need to establish and maintain a system that
can guarantee permissible levels in the drink. This can be carried out using concentrations of the
chemicals that are already known to be immediately dangerous to life or health as a reference point.
Keywords: palm wine; chemicals; contaminant; styrene; benzene; food safety; hazard, plastic
1. Introduction
Palm wine is a traditional drink produced by different types of palm trees and is enjoyed by
many people living in sub-Saharan Africa. Around the world, the beverage is popular and is known
by different names. Increased microbiological studies of the product in the last five years has led to
more information on the diversity of Saccharomyces cerevisiae strains prevalent in the product [
1
,
2
] and
discovery of new microorganisms from the drink [
3
]. The tapping of the drink from the palm tree
provides a very important economic activity for people living outside of the cities, and the drink plays
an important role in the socio-cultural activities of people in Nigeria, where, in the southeastern region,
it is served in most traditional events. The drink is now beneficial to different groups of people in that
some people in Nigeria who are cutting alcohol consumption resort to freshly tapped product which is
sweet and without much alcohol.
The commercial production of the drink has increased and it is now canned. The drink is commonly
produced in beer like bottles in Nigeria and a good number of retailers sell the product with reused
Beverages 2017,3, 16; doi:10.3390/beverages3010016 www.mdpi.com/journal/beverages
Beverages 2017,3, 16 2 of 12
table water plastic bottles with the cap loosely fitted to reduce foaming. The vast production and sale
of the product is not regulated and this makes the drink predisposed to food safety hazards which
could be biological, chemical, physical, allergenic, nutritional or biotechnology-related [
4
]. It has
been reported that the drink can be contaminated at multiple steps in the production process and
should be regulated for quality control to avoid health risks [
5
]. In addition, plant material treated
with herbicides and pesticides can be present in the palm wine processing environment, and it is not
uncommon to see producers that use leaves to cover containers containing the drink. Leaves, stem and
bark can also get into the palm wine either when the incision is made to begin the tapping process or
when the sap is flowing into a container. In some palm wine processing environments, insects could
be a source of food safety hazards when they fly into bowls or containers containing the drink.
Food safety hazards [
6
] occur when food is exposed to hazardous agents and results in
contamination of the food. It may occur through air, soil and water in the environment. Furthermore,
in the food industry, there are various types of chemical hazards and they include mycotoxins, natural
toxins, marine toxins, environmental contaminants, food additives, processing-induced chemicals,
pesticides, agricultural products and veterinary drug residues [
5
]. Currently, there is no evidence
that hazard analysis and critical control points (HACCP), a systematic preventive approach to food
safety from biological, chemical, and physical hazards, are used during the production of palm wine
among local processors. Many workers [
7
–
9
] have studied the microbial and biochemical constituents
of the drink, especially compounds of microbial fermentation, and they are not currently regarded
as hazards.
There are rarely any reports on the chemical contaminants of the product. The metal concentrations
of 13 elements in the drink have been determined, and it was found that, from the estimated target
hazard, no long life health concerns of metals are associated with the consumption of Raphia palm
wine [
10
]. The chemical contaminants per se were not analyzed in that study. However, it was found
that the individual and combined metal target hazard quotient values of Raphia palm wine were
higher in other traditional alcoholic drinks. The lack of information on chemical contaminants of
palm wine has created a paucity of information on the properties of non-ethanol and non-microbial
components associated with the drink as well as other food safety hazards linked with unregulated
processing of the beverage.
In a previous study [
11
], some chemical compounds were not identified as products of yeast
fermentation in palm wine after a search on the yeast metabolome database (YMDB) was carried
out [
12
], and it was suggested that the contaminants were artifacts from the environment. Irrespective
of how the chemical contamination occurred, the presence of these substances in palm wine is not
desirable. Therefore, the aim of this review was to focus on these chemical contaminants and highlight
safety concerns that should be addressed for the health benefits of palm wine consumers. To this
end, the properties, uses, toxicity, and health issues associated with palm wine chemical contaminants
detected in the previous study were explored in more detail in order to raise more awareness on the
possible hazards that could arise from consumption of the beverage.
2. Methods
The chemical contaminants found in palm wine (Figure 1) are listed in Table 1. In the absence
of actual sources of these contaminants, the hypothetical sources are specified. An investigation [
11
]
reported that palm wine obtained from trees of Elaeis sp. and Raphia sp. were purchased (1.5 L
pack size) from six different open markets in southeastern Nigeria. Using a wide range of analytical
techniques, the microbial and chemical contents were determined. In particular, the use of gas
chromatography-mass spectrometry (GC-MS) revealed that all the palm wine samples contained
chemical compounds that are known carcinogens. There is a paucity of data on palm wine contaminants
in literature. However, an earlier study [
13
] reported some of the compounds listed (Table 1) and it
included styrene and dimethylbenzene. Another investigation reported [
14
] the presence of phenyl
compounds among other volatiles. A search was conducted within The PubChem Project, the open
Beverages 2017,3, 16 3 of 12
chemical database [
15
], to establish the description and uses of candidate chemicals (Table 1). The main
reason for including these chemicals in the search was because they are not associated with yeast
fermentation of palm wine. The compound identifier and uses of these chemicals were captured.
Beverages2017,3,163of12
presenceofphenylcompoundsamongothervolatiles.AsearchwasconductedwithinThePubChem
Project,theopenchemicaldatabase[15],toestablishthedescriptionandusesofcandidatechemicals
(Table1).Themainreasonforincludingthesechemicalsinthesearchwasbecausetheyarenot
associatedwithyeastfermentationofpalmwine.Thecompoundidentifierandusesofthese
chemicalswerecaptured.
Figure1.RepresentativesamplesofpalmwinebottlessoldinNigeria.Thesamplesinglassbottles
(right)arenowexportedaroundtheworld.Samplesinpolyethyleneterephthalatebottles(left)with
polystyrenecapsarenormallyfoundinsmallretailoutlets.
Toverifysafelevels,anothersearchwasperformedontherevisedlistofimmediatelydangerous
tolifeorhealthconcentrations(IDLH)ofchemicalsheldbytheCenterforDiseasesControland
Prevention,UnitedStatesofAmerica[16].Wheretheexactcompoundofinterestwasabsentonthe
list,acloselyrelatedcompoundwashighlighted.Inthepreviouswork[11],thechemicalabundance
wasdeterminedbycomparingGC‐MSpeakareasacrosssamples.Inthisreview,weusedthepeak
areaswithinsamplestoestimatethepercentageconcentrationbeforeconvertingtopartspermillion
(Table1)andthencomparedvaluesobtainedwithIDLHlimits.Furthersearcheswerecarriedouton
otherdatabaseslikePubMed,ScopusandGoogleScholarusingeachchemical’snameasasearch
term.Thesearchstrategyemployedfocusedmainlyonarticlesfromthelast10yearsandonly
articlesthathadinformationonhowthesechemicalsaffectpublichealthwereselected.Thecapacity
tocauseharmbythechemicalsofinterestwasnoted.Possiblehazardsfrompolyethylene
terephthalate(PET),acommonretailingcontainer,werehighlighted.
Table1.Estimatedconcentrationsofchemicalcontaminantsassociatedwithpalmwinesamples.
CompoundsPubChem
CID
1
EstimatedConcentrations
2
inPalmWine
(ppm)IDLH
3
(ppm)UsesPossibleSources
S1S2S3S4S5S6S7
1.Styrene750144954299 3132 1938 1867 1505 5614 700PlasticsPlasticcontainer
2.Benzene241332268 173 87121 56343 500SolventBenzoicacid+
VitaminC
3.Trimethyldioxolane1258632811533 789 3560 462 2298 3581 500
4
SolventDerivative
4.Dichloromethane6344108168 367 835 151 135 301 2300SolventEnvironment
5.Methylenefluoride634512628482146140 5825
5
refrigerantEnvironment
6.Dichloroethanol11718693118 134 158 70390 125 3000
6
SolventEnvironment
7.Dimethylhydrazine59769264889 9162 7238 352 766 540 50PesticidesEnvironment
8.Dimethylhydrazine1668069673138 210 169 127 53116 66.1
7
PharmacyLeavesortissue
9.
Tetraacetyl‐
D
‐xylonic5415688768132 96118 88152 250
8
PlantpartPlantcompound
nitrile
1
CID=compoundidentifier;InformationsourcedfromPubChemopenchemistrydatabase[15].
2
ConcentrationsestimatedinpalmwinefromNwaiwuetal.study[11].
3
IDLH=Immediatelydangeroustolifeor
health;S=sample.
4
IDLHforDioxane.
5
IDLHforFluorine.
6
IDLHforDichloroethane.
7
IDLHforQuinone.
8
IDLH
forPhenol.
Figure 1.
Representative samples of palm wine bottles sold in Nigeria. The samples in glass bottles
(
right
) are now exported around the world. Samples in polyethylene terephthalate bottles (
left
) with
polystyrene caps are normally found in small retail outlets.
Table 1. Estimated concentrations of chemical contaminants associated with palm wine samples.
Compounds PubChem
CID 1
Estimated Concentrations 2in Palm Wine (ppm) IDLH 3
(ppm) Uses Possible
Sources
S1 S2 S3 S4 S5 S6 S7
1. Styrene 7501
4495 4299 3132 1938 1867 1505 5614
700 Plastics Plastic container
2. Benzene 241 332 268 173 87 121 56 343 500 Solvent Benzoic acid +
Vitamin C
3. Trimethyldioxolane 12586
3281 1533
789
3560
462
2298 3581
500 4Solvent Derivative
4. Dichloromethane 6344 108 168 367 835 151 135 301 2300 Solvent Environment
5. Methylene fluoride 6345 126 28 48 21 46 140 58 25 5
refrigerant
Environment
6. Dichloroethanol 11718 693 118 134 158 70 390 125 3000 6Solvent Environment
7. Dimethylhydrazine 5976 926
4889 9162 7238
352 766 540 50 Pesticides Environment
8. Dimethylhydrazine 16680696 73 138 210 169 127 53 116 66.1 7
Pharmacy
Leaves or tissue
9. Tetraacetyl-D-xylonic 541568 87 68 132 96 118 88 152 250 8Plant part Plant compound
nitrile
1
CID = compound identifier; Information sourced from PubChem open chemistry database [
15
].
2
Concentrations
estimated in palm wine from Nwaiwu et al. study [
11
].
3
IDLH = Immediately dangerous to life or health; S = sample.
4IDLH for Dioxane. 5IDLH for Fluorine. 6IDLH for Dichloroethane. 7IDLH for Quinone. 8IDLH for Phenol.
To verify safe levels, another search was performed on the revised list of immediately dangerous
to life or health concentrations (IDLH) of chemicals held by the Center for Diseases Control and
Prevention, United States of America [
16
]. Where the exact compound of interest was absent on the
list, a closely related compound was highlighted. In the previous work [
11
], the chemical abundance
was determined by comparing GC-MS peak areas across samples. In this review, we used the peak
areas within samples to estimate the percentage concentration before converting to parts per million
(Table 1) and then compared values obtained with IDLH limits. Further searches were carried out
on other databases like PubMed, Scopus and Google Scholar using each chemical’s name as a search
term. The search strategy employed focused mainly on articles from the last 10 years and only articles
that had information on how these chemicals affect public health were selected. The capacity to cause
harm by the chemicals of interest was noted. Possible hazards from polyethylene terephthalate (PET),
a common retailing container, were highlighted.
Beverages 2017,3, 16 4 of 12
3. Styrene
According to the United States Department of Energy [
17
], styrene monomer is a colorless oily
liquid, large-volume chemical used in making polyesters, resins, and chemical intermediates with a
global market value of approximately $32.5 billion. Most PET bottles used for retailing palm wine have
a polystyrene cap, which is a safety concern if styrene migrates to the drink. An
in vitro
genotoxicity
investigation to evaluate the genotoxicity of styrene oligomers extracted from polystyrene intended for
use in contact with food has been conducted [
18
], and it was concluded that the risk of the genotoxicity
of styrene oligomers migrating from polystyrene food packaging into food is likely very low.
Styrene Exposure
In all samples, the estimated styrene concentration was over the concentration immediately
dangerous to life or health (Table 1). Although styrene exposure will occur mainly to those that are
involved in the manufacturing of plastics and composites, the detection of high concentrations of
the monomer in palm wine suggests that there is some form of exposure to palm wine consumers.
It also indicates that not all containers used for the drink are food grade. Adverse properties of
styrene exposure have been reported and styrene has been linked to eosinophilic bronchitis [
19
] and
transient bilateral vestibular dysfunction [
20
]. It has also been reported that styrene has an effect on
hearing loss [
21
,
22
] and may affect neurological behavior [
23
,
24
]. The effect of occupational exposure
to styrene on frequencies of chromosomal aberrations and binucleated cells with micronuclei and on
single-strand break levels in peripheral blood lymphocytes has also been studied in styrene-exposed
lamination workers [
25
]. It was found that positive correlation between exposure parameters and
DNA repair rates suggests that particular DNA repair pathways may be affected by styrene exposure.
4. Benzene
4.1. Benzene as a Carcinogen
Even though all samples evaluated were within permissible limits (Table 1), the exact route of
entry of benzene into palm wine needs to be established due to the carcinogenic nature of the drink.
The compound is a known human carcinogen for all routes of exposure and is a widely used chemical
formed from both natural processes and human activities [
26
]. It is also believed to rank in the top
20 chemicals for production volume. Furthermore, industries use benzene to make other chemicals
that are used to make plastics, resins, and nylon and other synthetic fibers. Benzene is found in the air
from emissions from burning coal and oil, gasoline service stations, cigarette smoke and motor vehicle
exhaust. Inhalation exposure of humans to benzene may cause drowsiness, dizziness, headaches,
as well as eye, skin, respiratory tract irritation, and unconsciousness [
15
]. The specific hematologic
malignancies that benzene is associated have been outlined and they include acute myeloid leukemia,
myelodysplastic syndrome, acute lymphoblastic leukemia and chronic myeloid leukemia [27].
4.2. Benzene Formation in Beverages
It has been previously reported [
28
] that the reaction of benzoic acid and ascorbic acid (vitamin C)
can induce benzene formation in vitamin C drinks. There is ascorbic acid inherent in fresh palm
wine [
29
] and benzoic acid from plant material [
30
] can get into the drink at any point in the production
process. This provides an opportunity for both compounds to combine and form benzene, which could
be hazardous to health. The actual source of benzene in palm wine is still unclear and needs to be
investigated further.
A survey of over 100 soft drinks and other beverage samples with a focus on soft drinks that
contain both benzoate salts and ascorbic or erythorbic acid has been carried out [
31
] in the United States
of America. It was found that four beverage products contained benzene levels above the 5 ppb quality
standard for drinking water. It was also reported that these products with high benzene content were
reformulated by the manufacturers, and, following a re-test, samples of these reformulated products
Beverages 2017,3, 16 5 of 12
showed that benzene levels were less than 1 ppb. The level of benzene in the bottled (Figure 1) and
canned products is important because benzoates are likely to be used as preservatives. Corrective
actions should be taken if the levels are found to be above acceptable thresholds.
5. Trimethyldioxolane
It is known that dioxolanes are highly flammable liquid and vapor that can easily be prepared
from carbonyl compounds with 1,3-propanediol or 1,2-ethanediol in the presence of a Brönsted or
a Lewis acid catalyst [
32
]. It is not clear if its occurrence in palm wine is through reaction between
other compounds present in the palm wine or reaction between extraneous materials. However, the
properties of the compound indicate that it should be avoided. The hazard warnings for the chemical
states that it can cause harm if swallowed and it is suspected of causing genetic defects and damage of
an unborn child [
15
]. Apart from one sample that was within permissible limits (Table 1), all the other
samples were over the recommended IDLH limit for dioxanes. The key to reduction of this compound
in the drink may be to avoid the entry of extraneous materials.
6. Dichloro Methane
According to Gribble et al. [
33
], dichloro methane or methylene chloride is among organohalogen
compounds that were once dismissed as accidents of nature or isolation artifacts and natural sources
include oceanic sources, macroalgae or wetlands. In addition, the majority of dichloromethane in the
environment is the result of industrial emissions, and its occurrence in palm wine could be from plant
material or environmental pollution. Even though the compound is reasonably implicated as a human
carcinogen [
34
], it has many industrial uses that include insect sprays, postharvest fumigant for grains,
manufacture of drugs, and decaffeination of coffee [
35
]. The compound can be dangerous if the lethal
dose is reached as exemplified by the reported death of 14 workers who used the product to refinish
bath tubs [
36
]. The estimated concentration levels seen in all palm wine samples analyzed is far less
than the dangerous concentration limit (Table 1).
7. Methylene Fluoride
Methylene fluoride or difluoromethane (HFC32) is a colorless hydrofluorocarbon gas that is
slightly toxic in rats [
37
]. It is based on methane, the most abundant hydrocarbon in the atmosphere,
and it is an important greenhouse gas except that two of the four hydrogen atoms have been replaced
by fluorine atoms [
38
]. In the YMDB [
12
], fluoride (YMDB 01518) is listed as a product of yeast
anaerobic fermentation of Saccharomyces cerevisiae. Fluoride is a ubiquitous environmental toxin that
all biological species must cope with, and protection is achieved through fluoride export proteins that
protect organisms from fluoride toxicity by removing it from the cell [
39
]. Therefore, one way of its
occurrence in palm wine may be through the reaction of methane in the atmosphere and fluoride, a
product of anaerobic fermentation by yeasts.
All samples analyzed were above the IDLH limit for fluorine apart from one sample (Table 1).
Environmental contamination appears to be the route of entry into palm wine. Screening the process
environment for fluorides may prevent contamination. According to Tsai et al. [
40
], hydrofluorocarbons
(HFCs) are now used as replacements for chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons
(HCFCs) that cause significantly stratospheric ozone depletion and global warming. In addition,
they are used commercially in cleaning solvents in the electronic components, blowing agent in the
foamed plastics, and refrigerant in the air conditioning units and refrigerators. It has been reported
that high concentrations [
41
] may cause asphyxia from lack of oxygen or act as a narcotic causing
central nervous system depression. The report added that overexposure can cause dizziness, headache,
tiredness, nausea, unconsciousness, and cessation of breathing.
Beverages 2017,3, 16 6 of 12
8. Dichloroethanol
Dichloroethanol is regarded as a biohazard and it is flammable corrosive and harmful [
15
].
In rats, it is formed during the metabolism of an air borne chemical 1,2-dichloroethene by the hepatic
mixed function oxidase system [
42
]. In this reaction, cis and trans isomers are metabolized to an
epoxide and the aldehyde formed from the cis isomer yields dichloroethanol. It is also a metabolite of
trichlorfon, an insecticide used to control a variety of insects on an extensive range of crops [
43
]. It is
possible that it is an intermediate product from other reactions in the palm wine drink and not a direct
contaminant. The contamination levels varied in different samples and were all within permissible
limits for dichloroethane (Table 1).
9. Dimethylhydrazine
The estimated concentrations of dimethyl hydrazine found in all samples were far above
the recommended limits (Table 1). This suggests a serious issue of environmental contamination.
The compound is currently used in many cancer studies [
44
,
45
] because it is a known carcinogen that
can cause sporadic forms of colon carcinoma in rats resulting in a reproducible experimental models
for pre-clinical screening of test compounds based on its metabolism [
46
]. It has been reported that the
metabolism of dimethyl hydrazine leads to the formation of azoxymethane methylazoxymethanol and
methyl diazonium ions, which can cause alkylation of the DNA in the colon mucosa [
47
]. Dimethyl
hydrazine is associated with rocket fuels, cigarette smoke, tobacco products and plant pesticides [
29
].
Using a theoretical approach, Carlsen et al. [
48
] carried out a preliminary assessment of the potential
environmental and human health impact of unsymmetrical dimethylhydrazine as a result of space
activities. It was revealed that inside the fall region of burned-out rocket stages constitute a significant
threat to both environmental and human health, the latter as a result of the carcinogenic, mutagenic,
convulsant, teratogenic and embryotoxic characteristics of dimethylhydrazine.
Apart from rocket fuel, other aforementioned substances in dimethyl hydrazine can occur in palm
wine processing environment. The impact from rockets may not be a concern for now considering that
Nigeria’s space technology is still developing. However, smoking, use of tobacco and application of
plant pesticides should be avoided in the palm wine processing environment.
10. 3-Methyl-6,7-benzylisoquinoline
Only one sample out of the seven samples analyzed was within the recommended limit for
quinone (Table 1). Avoiding extraneous leaves making contact with the drink may eliminate the
problem. According to Galanie and Smolke [
49
], the compound benzylisoquinoline is a class l-tyrosine
derived plant alkaloids. Benzylisoquinoline alkaloids have a pharmaceutical value and they are large
and structurally diverse family of plant secondary metabolites [
50
] that includes the opiates such as
morphine [
51
]. Using synthetic chemistry and biology approaches, a strain of Saccharomyces cerevisiae,
the dominant yeast species found in palm wine has been engineered to synthesize the key intermediate
reticuline and other metabolites from benzylisoquinoline [52].
Considering that Benzylisoquinoline alkaloids are plant metabolites that are present in plant
cells [
53
], its presence in the palm wine may be from the palm tree from which the palm wine was
obtained. More knowledge may be gained if an investigation is carried out to establish if Saccharomyces
cerevisiae from palm wine can naturally synthesize the compound. It has been reported that many plant
species are currently recognized as toxic for both animals and humans, and some of them are known
to cause their toxic effects due to their alkaloid content [
54
]. The report pointed out that the alkaloid
content may include pyrrolizidine alkaloids and neurotoxins. Diseases associated with alkaloids
from plant seeds have been reported [
55
] and so contact of the palm wine with plant seeds should be
avoided during the palm wine production process.
Beverages 2017,3, 16 7 of 12
11. Tetraacetyl-D-xylonic Nitrile
The compound tetraacetyl-d-xylonic nitrile has been found in the ethanolic leaf extract of
Croton bonplandianum [
56
] and has been associated with metabolism of Aspergillus niger after methanolic
extracts were analyzed with gas chromatography-mass spectrometry [
57
]. It is also a volatile metabolite
of the endophytic fungi Fusarium sp. [
58
] and has been listed as one of the nitrogenous products
from fermented soy bean meal with Trichoderma sp. [
59
]. Furthermore, it has been found in trace
amounts when the chemical composition of essential oils from aerial parts of Sisymbrium irio from
Jordan was determined [
60
]. It is evident that this compound is very present in the environment and
appears harmless in small amounts. However, it has been implicated in the
in vitro
cytotoxicity of
Indian bee propolis on cancer cell lines [
61
]. As the compound is associated with several plants and
fungal organisms, it could have entered the palm wine drink at any point in the production process.
The concentration (Table 1) estimated in all of the palm wine samples is below the limit for phenols
found in most plants.
12. Physical and Other Chemical Contaminants
Chemical contaminants in food [
62
] can come from pesticides and veterinary medicines used in
farming, acrylamides used in processing, natural aflatoxin that occur during storage and pollutants
such as dioxins in the environment. Physical and other contaminants can get into the drink through the
water used for dilution. A frequent complaint by palm wine consumers is adulteration of the product
with water to boost product volume followed by addition of artificial sweeteners [
10
]. This is why
undiluted palm saps are generally more expensive than diluted ones. Due to no portable water at some
palm wine processing centers in Africa, water may be sourced from nearby open wells and streams or
transported with plastic containers, and, if the container has been used to store other materials, there
is the possibility of introduction of extraneous materials into the drink. The extraneous items may
include plant leaves, twigs and dead insects.
Ukhun et al. [
63
] compared the heavy metal profile of fresh palm wine and those of seven brands
of bottled palm wine using atomic absorption spectroscopy in Benin City, Nigeria and found that the
bottled samples contained toxic levels of either lead or cadmium. Both metals were detected in fresh
palm wine and it was suggested that most of the metals detected were as a result of dilution with
contaminated water. The suspicion that the water used for bottling was from questionable sources was
strong, given that around the time the study was carried out, there were reports that the ground water
in Benin City was reported to be contaminated with unacceptable levels of lead, cadmium, chromium
and zinc [64].
13. Toxicity Concerns with Use of Plastic Containers
13.1. Plastic Degradation
Finally, there are concerns about the use of PET and other plastic containers as the main storage vessels
of palm wine from the tapping process up until consumption because some of the aforementioned
chemicals may be constituents of a PET or plastic container used in the production process. In Europe,
European regulation No. 10/2011 [
65
] ensures the safety of plastic materials in contact with foodstuffs.
This regulation has a list of substances that are authorized for use in plastic materials and some
compounds are subject to restrictions according to their toxicological data. Such regulations can be
adopted to prevent plastic hazardous material from getting into the palm wine drink.
Plastic containers are used virtually in all processing steps. Even the palm wine calabash that
is popular in Nigerian folklore has been replaced by plastic containers. In a study by Obahiagbon
and Oviasogie [
66
], the initial palm wine exudate was collected with a plastic funnel and receptacle.
An investigation [
67
] with scanning electron microscopy and energy dispersive X-ray spectroscopy to
evaluate the interactions of palm wine with the surface of its PET containers did not find any pitting
or extensive corrosion. However, the PET container that was used for palm wine storage showed
Beverages 2017,3, 16 8 of 12
the presence of chlorine, whereas no chlorine was observed for the control sample that contained
water. It was suggested that, at some point in the palm wine supply chain, a polyvinyl chloride plastic
container may have been used to store the product.
Polyvinyl containers are degradable under high temperature. McNeill et al. [
68
] carried out a
thermal degradation study and found that analysis of the liquid fraction collected during pyrolysis
included hydrogen chloride, chlorine, tar, and benzene. There are other concerns that reused chemical
plastic containers may still contain traces of chemicals, which may react with palm wine and cause
corrosion of the plastic container. Although it is generally believed that PET bottles take a long time to
degrade, the degradation of PET bottles has been successfully achieved in 2 h using hydrotalcite as
catalyst and ethylene glycol as solvent [
69
]. Therefore, the various types of plastic used in the storage
of the product should be evaluated to establish if there are reactions with the container.
13.2. Other Plastic Constituents
Bach et al. [
70
] carried out a comprehensive literature review which showed that contradictory
results for chemical migration in PET-bottled water have been reported, and the differences can be
explained by the wide variety of analytical methods, bioassays and exposure conditions employed.
It was reported that analysis of PET reveals some non-intentionally added substances produced by
initial reactants and additives. In addition, plasticizers, formaldehyde, acetaldehyde and antimony
are related to migration from PET into bottled water, but the origin of these compounds has not been
clearly established. The compounds could be from PET containers, cap-sealing resins, background
contamination, water processing steps, and recycled PET bottles. The effect of sunlight exposure
on chemical migration into PET-bottled waters has been studied [
71
]. Bottled waters were exposed
to natural sunlight for 2–10 days, and it was found that migration was dependent on the type of
water. PET-bottled water extracts did not induce any toxic effects, cyto-genotoxicity, estrogenic,
or anti-androgenic activity in vitro at relevant consumer-exposure levels.
14. Conclusions
From the qualities of the chemicals outlined above, it is evident that the chemicals are potentially
hazardous. It will be beneficial to public health to determine if concentrations found in palm wine
are dramatically increased when compared to other food-associated samples. The concentrations of
the chemical compounds in palm wine given are estimates only and a quantitative study needs to
be carried out with the relevant chemical standard before the impact of these chemicals on health is
evaluated. Even though private processing of the product may be difficult to monitor, unregulated
commercial processing should be discouraged and only those who have been sensitized on the
microbiological, physical and chemical hazards should be allowed to process and sell the product to
the public. In addition, use of only food grade plastics, especially for bulk transportation of palm wine,
should be allowed. Agricultural extension and health officers would need to sensitize processors to
avoid reuse of plastic containers that have been used for storage of any toxic chemicals. A detailed
hazard analysis that covers palm wine processing and the whole palm wine supply chain will be
beneficial to public health.
Acknowledgments:
The work was supported by the International Development Fund grant to O.N. from Society
for General Microbiology (now Microbiology Society) UK. Grant No IDF 2012/12/3.
Author Contributions: O.N. conceived the paper; and O.N. and M.I. contributed to the paper.
Conflicts of Interest: The authors declare no conflict of interest.
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