Open access peer-reviewed chapter

Nutrient Composition and Aflatoxin Contamination of African Sourced Peanuts and Cashew Nuts: Its Implications on Health

By Modupeade C. Adetunji, Stephen A. Akinola, Nancy Nleya and Mwanza Mulunda

Submitted: September 19th 2020Reviewed: November 20th 2020Published: February 26th 2021

DOI: 10.5772/intechopen.95082

Downloaded: 167

Abstract

Edible nuts are popular worldwide based on their varied attributes such as desirable taste, high nutritional value as well as some health benefits. Globally, the most popular edible nuts are groundnuts or peanuts, almond, cashew nut among others. Due to the rich nutritional composition of nuts, they tend to be prone to contamination by toxigenic fungi which could ultimately results in the release of fungal metabolites known as mycotoxins into nuts. In view of the nutritional composition of nut and its high susceptibility to fungal attack, this chapter looks at the nutritional profile, mycotoxigenic fungi and aflatoxins contamination of peanuts, cashew nuts and their products with a central focus on Africa where the effect of aflatoxin contaminations is more prominent.

Keywords

  • public health
  • peanut
  • cashew nut
  • aflatoxigenic fungi
  • aflatoxin
  • mycobiota diversity
  • food safety
  • Africa

1. Introduction

Edible nuts are popular worldwide based on their varied attributes such as desirable taste, high nutritional value as well as some health benefits. Moreover, production of edible nuts can be done under various growing conditions and climates [1], however edible nut production is mainly in the tropical and subtropical regions of the world.

Globally, the most popular edible nuts are groundnuts or peanuts (Arachis hypogaea) and are classified as legumes [2] with several other tree nuts such as almond (Prunus dulcis), cashew (Anacardium occidentale), Brazil nut (Bertholetia excelssa), hazelnut (Corylus avellana), macadamia (Macadamia integrifolia), pecan (Carya illinoinensis), pine nut (Pinus pinea), pistachio (PistachiaVera), and walnut (Juglansregia) [1, 3]. Although nuts are considered as food with numerous health benefits, they are prone to contamination by toxigenic fungi which could ultimately results in the release of fungal metabolites known as mycotoxins into nuts [4].

Contamination of food commodities by mycotoxins has become a global food safety concern [5, 6]. Aflatoxins are secondary metabolites produced by members of the genus Aspergillusmainly A. flavus, A. parasiticusand A. nomius[7]. This genus is very ubiquitous and is known as a primary inhabitant of soil that contaminate a variety of agricultural commodities especially cereal grains and oil seeds including nuts [8]. Consumption of aflatoxin contaminated food results in a condition known as aflatoxicosis. The severity of aflatoxicosis symptoms ranges from vomiting, abdominal pains and liver damage in acute aflatoxicosis as a result of ingesting large doses of the toxin. Whereas ingestion of smaller doses leads to chronic aflatoxicosis which is asymptomatic and may result in hepatocellular carcinoma [9]. There over 20 aflatoxins but only four of them occur naturally i.e. aflatoxins (B1, B2, G1, G2). These aflatoxins are identified based on their fluorescence (B-blue or G-green) under ultraviolet light [10].

Aflatoxin contamination has led to reduced international markets especially in the developed nations, thereby advocating for stringent measures requiring import products to have very low concentrations of aflatoxins. Since nuts are used as food as well as food ingredients, regulatory limits have been established and set at 4 μg/kg for total aflatoxin (B1 + B2 + G1 + G2) and ≤ 2 μg/kg for aflatoxin B1 by the European Commission [11, 12]. Implementation of good manufacturing practices in the nut production chain is very important so that the nuts comply with limits of the importers [13]. As a result, many countries have conducted research on the diversity of aflatoxigenic fungi as well as the extent of aflatoxin contamination in edible nuts as well as their products to ensure that their produce meets the required standards [14]. This chapter looks at the nutritional profile, mycotoxigenic fungi and aflatoxins contamination of peanuts, cashew nuts and their products with a central focus on Africa where the effect of aflatoxin contaminations is more prominent.

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2. Nutritional profile of peanut

Peanut (Arachis hypogaeaL.), groundnut or monkey nut (Figure 1) is the fourth oilseeds crop and 13th food crop grown worldwide because of its nutritional, medicinal and economic values [17, 18]. Several delicacies could be prepared from peanut ranging from products like roasted peanuts, peanut butter, peanut oil, peanut paste, peanut sauce, peanut flour, peanut milk, peanut beverage, peanut snacks (salted and sweet bars) and peanut cheese analog (Figure 2). Raw peanut is subjected to different processing which could alter or determine the nutritional composition of the end products. Processing such as roasting of peanut enhance its colour, flavour, taste, aroma and crunchy texture [20]. It also reduces the bacteria load and aflatoxin-producing fungi in raw peanut [21].

Figure 1.

Showing (a) the groundnut plant in the field, (b) harvested plant and (c) unshelled and shelled groundnuts [15,16].

Figure 2.

Various forms in which ground nut can be consumed, adopted from market insider with modifications [19].

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3. Proximate composition of peanut

Peanut is an excellent source of nutrients similar to other nuts with a substantial amount of lipid, protein and fibre content along with some amount of carbohydrate, vitamins, and minerals. The nutrient constituents and content of peanut have been previously reported; protein 20.7%–25.3%, crude fat 31–46%, ash 1.2%–2.3%, crude fibre 1.4%–3.9%, carbohydrate 21–37%, and moisture 4.9%–6.8%) [22]. Nuts including peanuts provide over 10% of the recommended dietary allowance of nutrients (protein, iron, thiamine and vitamin E) for adult males [23]. The nutritional composition of peanut is shown in Table 1.

PrincipleNutrientsNutrient valuePercentage of RDA
Macro nutrientsEnergy567 Kcal29
Carbohydrates16.13 g12
Protein25.80 g46
Total Fat49.24 g165
Cholesterol0 mg0
Dietary Fibre8.5 g22
VitaminsFolates240 μg60
Niacin12.066 mg75
Pantothenic acid1.767 mg35
Pyridoxine0.348 mg27
Riboflavin0.135 mg10
Thiamin0.640 mg53
Vitamin A0 IU0
Vitamin C00
Vitamin E8.33 mg55.5
MineralsSodium18 mg1
Potassium705 mg15
Calcium92 mg9
Copper1.144 mg127
Iron4.58 mg57
Magnesium168 mg42
Manganese1.934 mg84
Phosphorus76 mg54
Selenium7.2 μg13
Zinc3.27 mg30

Table 1.

Nutritional composition of groundnut.

Source: USDA 2014.

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4. Nutritional benefits of peanut on human health

The major components of peanut are Protein, fats, and fibre (Table 1), and are present in their most beneficial forms. The protein is plant-based, while the fat is unsaturated, and the fibre is composed of a complex carbohydrate that are beneficial for human nutrition.

4.1 Peanut protein

The nutritional value of a food protein is determined by its essential amino acid contents and its digestibility. The protein content in the cake could reach 50% after the peanut oil has been extracted [24]. Peanuts contain all the 20 amino acids in variable proportions [25]. According to its Protein Digestibility Corrected Amino Acid Score (PDCAAS) peanut proteins and other legume proteins such as soy proteins are nutritionally equivalent to meat and eggs and ideal for human growth and health [26]. The true protein digestibility of peanuts is comparable with that of animal protein [27].

4.2 Fatty acid composition of peanut oil

Although peanuts and tree nuts have high lipid contents, peanut oil is rich in unsaturated fat, predominantly, monounsaturated fats (MUFA which have been associated with lower cardio-vascular risk) [28]. The MUFA of the regular US peanuts is 49–57% while a medium (66–69%) and high oleic (78–80%) rich peanuts have been reported [29]. The consumption of MUFA promotes artery-clearing which keeps the flow of blood and lowers the risk of atherosclerosis, heart attack or stroke [30]. Clinical studies demonstrated that intakes of MUFAs and PUFAs are associated with low risk of cardiovascular diseases (CVD) and death, whereas saturated fat and trans-fat intakes are associated with high risk of CVD [28].

4.3 Dietary Fibre

There are soluble and insoluble dietary fibres which have health benefits such as lowering the risk of heart diseases, diabetes and maintenance of a healthy weight [31]. Other health benefits includes, the lowering of blood cholesterol, improvement of bowel movement and reduced risk of metabolic syndrome [32]. The dietary fibre content of dry roasted peanut was reported as 8.4 g per 100 g of peanut similar to that in soybean (9.3 g per 100 g) while the total dietary fibre of defatted peanut flour (15.8%) was comparable to that of defatted soybean flour (17.5%) [33]. This substantial amount of dietary fibre could help individuals reach their recommended daily allowance of 38 g for men and 25 g for women.

4.4 Vitamins and minerals

Peanut has been recognised as a great source of niacin, which is important for the proper functioning of the digestive systems, skin and the nerves. It helps in the conversion of food to energy and supposed to protect against Alzheimers disease and cognitive decline [34]. Peanut is an excellent source of vitamin E whose consumption in good quantities could lead to benefits against coronary heart disease [35]. Peanut also contains good amounts of folates which are important during infancy and pregnancy for the production and maintenance of cells. It was reported that a 100 g of peanut can provides the Recommended Dietary Allowance [36] levels of copper (127%), manganese (84%), iron (57%), phosphorus (54%) and magnesium (42%) intake which is associated with reduced inflammation [37, 38] decreased risk of metabolic syndrome [38] and type II diabetes [39]. They are also referred to as a nutrient dense food, rich in multiple natural micronutrients (Table 1) including bioactive compounds such as resveratrol, phytosterols, phenolic acids and flavonoids that are beneficial to health. This makes them a viable option for improving the nutrition status of the malnourished, neonates, growing, or those in need of critical nutrients [40].

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5. Health benefits of peanuts

Peanuts lipid profile is high in unsaturated fatty acids than the saturated fatty acids, trans- fat-free, cholesterol-free. Its low saturated fats thus qualify it as safe and desirable. Apart from basic benefits of daily nutrition, peanut consumption leads to long term health benefits such as the management of cancer [41], effective weight management [42] and lower body Mass Index [43] and management of hunger [44].

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6. Cashew nut

Cashew (Anacardium occidentaleL.) is one of the most traded processed tree nuts on the global market [45] and has become a source of income to people in the producing countries through export markets [13]. Cashew nuts are among tree nuts which are known to possess many health benefits such as reduced chances of cardiovascular diseases, diabetes, metabolic syndrome, weight gain and obesity as well as mental instability [46, 47]. This is mainly because tree nuts contain several nutrients needed for the proper functioning of the human body such as unsaturated fatty acids, proteins, mineral, vitamins, phenolic compounds and fibre [47, 48].

Following an analysis of raw cashew nuts from Brazil, India, Vietnam, East and West Africa, Rico, Bulló [47] highlighted fat as the major constituents of cashew nuts with an average of 48.3% of its total weight. However, in another study, Abubakar, Abubakar [46] reported a much higher percentage of total fats (56.4%) in raw cashew nuts from Nigeria. Nevertheless their findings were within the range (40–57%) reported in literature [49]. Fats are known to play several roles in the diet such as provision of energy, essential fatty acids as well as fat soluble vitamins [50].

The cashew tree produces the nut (kidney shaped) as the main fruit and an accessory fruit known as the cashew apple (Figure 3) [52, 53]. The main traded cashew products are the raw nut, the seed and the cashew nut shell liquid (CNSL) whereas the apple is converted into various beverages [54].

Figure 3.

Showing (a) cashew tree, (b) developing fruit, (c) cashew nut and apple, (d) roasting of shelled nuts, (e) raw shell nuts [51].

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7. Contamination of peanuts and cashew nuts by toxigenic Aspergillusspecies

Despite the fact that developing countries cover the world’s greatest peanut producing area, yield is very low especially in Africa because of poor socio-economic factors as well as the prevailing weather conditions [55]. The climatic conditions in the tropics and subtropics promote the proliferation of diverse pathogenic fungi capable of producing aflatoxins [56, 57, 58]. Extensive research on aflatoxins began in the 1960s with analysis on peanuts after poultry deaths in the United Kingdom, Kenya and India. This death was linked to the consumption of contaminated peanut meal [59]. The analysis of mould contaminants in peanut meals from various countries, implicated Aspergillus flavus[58] as the chief mould contaminant. Aspergillusspecies are ubiquitous group of soil borne fungi that can be found in agricultural soils, storage and food processing facilities as well as in the distribution systems [7, 60]. Aspergillus parasiticusis a soil inhabitant normally associated with pod and seed contamination whereas A. flavusthrives well in aerial environment and are therefore more likely to contaminate tree nuts [61]. Nuts can be colonised by fungi before harvest (Figure 4). Several authors have reported the presence of diverse Aspergillusspecies in the groundnuts and cashew nuts (Table 2).

Figure 4.

Colonisation of peanuts byAspergillusat different production stages, (a) showing pods and kernels already contaminated before harvesting, (b) contaminated unshelled peanuts and (c) contaminated shelled peanuts in storage [36,62,63].

CountryProductSample sizeNumber of strainsIsolates’ IdentityAflatoxigenic (%)Reference
AlgeriaShelled peanuts855Aspergillussection Flavi40[64]
Cashew nuts84Apergillussection Flaviand Nigrin.c[65]
BeninCashew nuts150A. tubingensis, A. niger, A. brasiliensis, A. carbonarius, A. luchuensis, A. aculeatus, A. aculeatinus.0[66]
BotswanaPeanuts120A flavusand A. parasiticus69[67]
EgyptPeanuts (raw, roasted and roasted with salt)60170A. niger, A. flavus, A. fucuum, A. oryzae and A parasiticus23[68]
Peanuts4588Aspergillussection Flavi90[11]
Peanuts1015A. flavus, A. niger, A. terreusand A.candidus80[69]
Peanuts8A. flavusand A. niger[70]
Peanuts4017A flavusand A. parasiticus29[71]
KenyaPeanuts and peanut butter82A. flavus S strain, A. flavus L strain, A. parasiticus, A. niger, A. tamarii, A. alliaceus and A. caeletusn.c[2]
Peanuts (raw, roasted coated and roasted decoated)228Aspergillus flavus L strain, A. flavus S strain, A. parasiticus, A. tamarii, A. caelatus, A. alliaceusand A.nigern.c[72]
Peanuts (roasted,
shelled raw, spoilt, fried, boiled podded, spoiled podded, peanut butter and peanut flour.
7051027A. flavus S-strain, A. flavus L-strain,
A. niger, A. tamari, A. alliaceus, A. parasiticusand A. caelatus
73[73]
NigeriaCashew nuts3214A. niger, A. restrictus, A. flavus, A. fumigatusand Aspergillus sp.n.c[74]
Cashew nuts108A. flavus, A. glaucus, A. niger30[75]
Peanut kernels, Peanut cake, Peanut oil189A. niger, A. flavusand A. fumigatusn.c[76]
Peanuts84140A. flavus64–88[77]
Peanuts cake4848A. flavus, A. parasiticus, A. niger, A. tamarii, A. fumigatusn.c[78]
Cashew nuts
Peanuts
15
9
9
7
A. carbonarius, A. nigerand A. flavus.56
-
[79]
Cashew nutsA. niger, A. flavus, A. tereus[80]
South AfricaCashew nuts36A. flavus, A. fumigatus, A. oryzae, A. nigerand other Aspergillus spp15[81]
UgandaPeanuts (clean)
Peanuts (rejects)
-
-
45A flavus, A. parasiticus, A. niger, A. ochraceus, A. tamarii.24[82]
Peanuts24096A flavus, A. parasiticusand section Nigri34[83]
ZambiaSoils cropped to peanuts49991A. flavus (S) and (L) strains), A. parasiticus, A. nomius.56–100[84]

Table 2.

Incidence of Aflatoxigenic Aspergillusspp. in peanuts and cashew nuts from Africa.

Keys: n.c – not counted, 0 = none was aflatoxin positive.

Initially aflatoxin production was linked to A. flavus[85], therefore most researchers use A. flavusas an indicator of possible aflatoxin contamination in food commodities. For example, Sultan and Magan, [11] isolated several Aspergillusspecies from Flavi, Circumdatiand Nigrisections, but performed aflatoxin producing potential tests only on the isolates from section Flavi.Similarly, Oyedele and co-workers [77] also isolated three Aspergillusspecies (A. flavus, A. parasiticusand A. tamarii) from peanut samples. However, determination of the toxigenicity of the isolates was carried out on those identified as A. flavusonly. In another survey by Riba and colleagues [64] isolated species belonging to Flavi, Circumdati, Terreiand Nigrisections from shelled peanuts. Despite the fact that species from section Nigrihad the highest incidence of occurrence, toxigenicity tests were done only for isolates from Flavisection. However some authors have reported aflatoxin production by species outside the section Flavi[86, 87, 88, 89]. Therefore, it is important for researchers to determine the aflatoxigenicity of all isolates even if they do not belong to the Flavisection.

The high prevalence of the black Aspergillusi.e. section Nigrihas been reported in many peanuts samples. Mohammed and Chali [55] reported the prevalence rates of A. nigerranging from 35 to 66% in peanut samples from the fields, storages and in market places. According to Riba and colleagues [64], A. nigeris mainly used in fermentations. Riba and associates [64] also reported high incidence of A. nigerin analysed peanut samples. Although there are no reports on aflatoxin production by A. niger,there have been reports on ochratoxin A production by some A. nigerstrains [90, 91]. On the other hand, Akinola and co-workers [92] highlighted the possibility of gene transfer between toxigenic and atoxigenic strains in feedlots resulting in strains previously known as non aflatoxigenic becoming toxigenic. Acquisition of aflatoxin producing genes by A. nigermay become a threat to the fermentation industry where it is mainly used.

The quality of the edible part of cashew nut is of great importance as it is used as either as food or ingredients in processed products. However, like others cashew nuts are also prone to fungal contamination with consequent mycotoxin production. Table 2 shows the presence of Aspergillusspecies especially the section Nigribeing present in most of the samples. Lamboni and others [65] highlights the implication of this section in food deterioration. The same author reported production of mycotoxins by some isolates from cashew nuts in Benin belonging to the section Nigrisuch as Aspergillus tubingensis, A. niger, A. brasiliensis, A. carbonarius, A. luchuensis, A. aculeatus, A. aculeatinus, however none of the isolates were able to produce aflatoxins in culture. A similar observation was noted by El-Samawaty and colleagues [93] where the majority of the Aspergillusspecies in cashew nuts from Saudi Arabia belonged to section Nigri.Adeniyi and Adedeji [94], emphasised the importance of moisture in the kernels during storage as it may contribute to the colonisation of the nuts by mycotoxigenic fungi.

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8. Aflatoxin contamination of groundnut and cashew nut

Aflatoxin B1 is the most potent and commonly produced naturally occurring aflatoxin [95], hence its presence in most of the samples and the most reported by researchers (Table 3).African countries especially those in Southern Africa namely Botswana [98], Democratic Republic of Congo [100, 101], Malawi, Mozambique [56], South Africa [101], Zambia [123, 124] and Zimbabwe [125, 126, 127, 128] had the highest incidence of aflatoxins in the samples analysed. Most batches had more than 50% of the samples testing positive to one or more of the naturally occurring aflatoxins (Table 3).

CountryProductSample
size
Positive
(%)
Total Aflatoxin
(range μg/kg)
Aflatoxins Detected (μg/kg)Analysis
Method
Reference
B1B2G1G2
AlgeriaShelled peanuts
Unshelled peanuts
Shelled nuts
37
12
8
49
83
100
0.34–26LOD-175
0.53–47
0.2–21
10–193
-
n.d
n.d
n.d
n.d
HPLC[96]
[64]
BeninPeanut cake1510033–346˂LOQ282˂LOD-31˂LOD-796–96LC–MS/MS[97]
Cashew nuts84˂LOD˂LOD˂LOD˂LOD˂LODUHPLC–MS/MS[65]
BotswanaPeanuts1207812.0–3291.3–2230.5–2030.6–2591.0–164HPLC[67]
Peanuts
Peanut Butter
29
21
52
71
3.2–48
1.6–64
0.8–16
3.2–16
1.6–16
0 1.6–20
1.6–8
3.2–20
1.6–16
1.6–20
TLC & HPLC[98]
CameroonPeanuts9029n.d6–125n.dn.dn.dLC–MS/MS[99]
DRCPeanuts6072n.d1.5–937n.dn.dn.dTLC[100]
Peanuts201002.19–12582.19–5430–2110–3100–193HPLC[101]
EgyptPeanuts (roasted)36750–390–330–40–30–0.2HPLC[102]
Peanuts8100n.d210–600250–400n.dTLC[70]
EthiopiaPeanuts1207615–11,900n.dn.dn.dn.dELISA[103]
Peanut cake5050n.d0–1580–158UPLC[104]
GambiaPeanuts367n.d2–31n.dn.dn.dHPLC[105]
GhanaRaw peanuts2400–1546n.dn.dn.dn.dELISA[106]
KenyaPeanuts [121]
Peanuts (roasted)
Peanut butter
63
8
11
74
50
73
0–365
2–298
0–2377
n.d
n.d
n.d
n.d
n.d
n.d
n.d
n.d
n.d
n.d
n.d
n.d
ELISA[2]
Peanuts (raw, roasted coated and roasted decoated)228810–2345n.dn.dn.dn.dELISA[72]
Peanuts769360–7525n.dn.dn.dn.dELISA[107]
Shelledraw peanuts
Spoilt peanuts
Roasted peanuts
Fried peanuts
Peanut butter
Peanut flour
705410–820
2.2–1628
0–757
0–22
0–582
0–820
n.d
n.d
n.d
n.d
n.d
n.d
n.d
n.d
n.d
n.d
n.d
n.d
n.d
n.d
n.d
n.d
n.d
n.d
n.d
n.d
n.d
n.d
n.d
n.d
ELISA[73]
Peanuts204990.1–5910.0–5100–480–440.1–26HPLC[108]
MalawiRaw peanuts
Peanut flour
Peanut butter
28
26
13
LOD-1200
LOD-820
LOD-180
-
-
-
-
-
-
-
-
-
-
-
-
Vicam-Fluorometer[109]
Mozambique57100n.d0–73n.dn.dn.dELISA[56]
MoroccoPeanuts2050.30.17n.dn.dn.dLC[110]
NigeriaPeanut kernels (A*)
Peanut kernels(B*)
Peanut pellets
Peanut oil (crude)
Peanut oil (refined)
-
-
-
-
-
100
100
100
100
100
Max 600
Max 450
Max 860
Max 98
Max 9
+
+
+
+
±
+
+
+
+
±
+
-
+
+
±
+
-
+
+
±
TLC[111]
Peanut cake20–455TLC[112]
Peanut kernels
Peanut pellets
Peanut oil (crude)
Peanut oil (refined)
-
-
-
-
-
-
-
-
-
-
-
-
281–680
389–793
16–26
0–7
135–782
391–513
14–18
0
182–502
218–530
14–19
0
217–590
196–320
11–13
0–5
TLC[113]
Dry roasted peanut106645–1656–265–207–10TLC[114]
Cashew nuts (roasted)
Peanut (roasted)
Peanut (hulled)
Peanut (dehulled)
10
10
7
7
0–0.4
0-˃20
0–0.2
0-˃20
n.d
n.d
n.d
n.d
n.d
n.d
n.d
n.d
n.d
n.d
n.d
n.d
n.d
n.d
n.d
n.d
ELISA[115]
Peanut841000.4–20760.9–7100.4–1290.4–120218.3–123LC–MS/MS[77]
Peanut
Cashew nuts
9
15
29–34
0.1–6.8
n.dn.dn.dn.dELISA[79]
Cashew nuts390.01–0.28n.dn.dn.dn.dHPLC[81]
South AfricaPeanut20900–730–350–160–100–8HPLC[101]
Cashew nuts360.03–0.77n.dn.dn.dn.dHPLC[81]
SudanPeanut butter120100n.d17–170n.dn.dn.dVicam fluorometer[116]
Peanut6058n.d17.57–404n.dn.dn.dTLC[117]
Peanut oil (unrefined)
Peanut oil (semi-refined)
Peanut oil (refined)
8
18
2
13
0
0
n.d
n.d
n.d
0.2
-
-
-
-
-
-
-
-
-
-
-
HPLC[118]
Peanut
Peanut (roasted)
Peanut butter
Peanut cake
400
400
400
400
2
11
64
14
3–8
4–12
32–54
7–10
-
-
+
+
-
+
+
+
-
-
+
-
TLC & HPLC[119]
TunisiaPeanut425HPLC[120]
UgandaPeanut15257n.d0.3–11n.dn.dn.dTLC[121]
Peanut152181–1000++++TLC[122]
ZambiaPeanut butter
Raw peanuts
24
92
100
55
n.d
0.014–48.67
≤20–10,740
0.015–46.60
n.d
0.006–13
n.d
0.005–0.5
n.d
0.006–0.04
ELISA
HPLC
[123]
[124]
ZimbabwePeanut44179n.d0–25n.d0–25n.dTLC[125]
Peanut18176.6–6226.3–528n.dn.dn.dHPLC[126]
Peanut butter11910–2470–1860–250–470–9
Peanut202139–6980.7–1761.3 to 32021--27229–378HPLC[127]

Table 3.

Aflatoxin contamination of groundnuts, cashew nut and their products in African countries.

Keys: - = absent, + = present, n.d = not determined, LOD = limit of detection, LOQ = limit of quantification, Max = maximum, A* = kernels from government supply, B* = kernels from miscellaneous supply.

In samples from Northern Africa, aflatoxins were detected though incidences of contamination were less than those reported in Southern Africa. Most samples from the batches analysed had less than 50% aflatoxin contamination occurrence rate with a few exceptions like Sudan in peanut butter. Weather conditions in Northern African countries are characterised by high temperature and humidity [129], due to being surrounded by the Mediterranean Sea and the Atlantic Ocean which promotes growth, occurrence of toxigenic moulds and subsequent aflatoxin production [130].

From West African States, Nigeria and Benin had majority of their peanuts and cashew nuts contaminated with aflatoxins and with almost 100% incidence rates. Total aflatoxin contamination in peanut cake from Benin exceeded the stipulated EC regulatory limit (4 μg/kg) whereas in cashew nuts the concentration was below the limit of detection (LOD). Studies have shown that peanut production in Africa is faced with so many challenges such as poor resources and field management which resulted to the nut being neglected. Peanuts harvest and marketing are often delayed thereby exposing the peanuts to high levels of aflatoxin contamination [95]. Contamination of nuts by aflatoxin can either be before or after harvest and a gradual increase in aflatoxin content with prolonged storage [131] could be expected. In an analysis of aflatoxin levels in peanuts at farms and markets in Uganda, Kaya and co-workers [132] reported the presence of aflatoxins at farm level in ≥60% of the peanuts. Results from analysis of raw peanuts, peanut flour, roasted peanuts and peanut butter [73, 109] showed a decrease in aflatoxin concentration in the order raw peanuts ˃ peanut flour ˃ roasted peanuts ˃ peanut butter. These results are in agreement with those of Siwela and colleagues [133] who reported a 51% reduction in aflatoxin after roasting of peanuts during large scale peanut production.

Peanut oil is the most utilised oil by people in the tropics due to its affordability [134, 135]. Analyses of peanut oil samples have shown the presence of aflatoxins especially in the unrefined oils. It has also been reported that oils extracted from peanuts often have higher aflatoxin contamination [136]. Abalaka [113], highlighted the use of crude oils by the majority of the Nigerian population hence their exposure to aflatoxins [113]. Most of the analyses in oils were from Nigeria and Sudan. Sudan is known as a major vegetable oil producer.

Cashew nut production in Africa is dominated by West African countries [137] hence the high number of reports from this quarters. Most of the studies in Africa were from Nigeria as it is one of the leading producers of cashew nuts worldwide. The result of analyses on aflatoxins in cashew nuts showed that they were within the EU and FDA regulatory limit of 15 μg/kg for total aflatoxin in nuts intended for further processing. However Milhome and associates [14] highlighted some samples from Brazil having total aflatoxins greater than this limit.

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9. Impact of Aflatoxin on health

Mycotoxins finds their way into human and animal body through the consumption of mycotoxin contaminated foods [138]. Mycotoxins causes significant decline in animal productivity and general health performance. Out of the over 400 mycotoxins identified in food and animal feeds, those capable of causing significant health effect in humans and animals includes aflatoxin (AFs), fumonisins (FUM), zearalenone (ZEA), T-2/HT-2, deoxynivalenol [139] and ochratoxin A [15], they are of great concern for their effects on animal and human health [140]. Aflatoxins are naturally occurring chemical contaminants of foods such as cereals, legumes and nuts; groundnuts and cashew nuts [141], Aspergillus parasiticusand Aspergillus flavusare the primary producers of aflatoxin in crops [142]. The consumption of contaminated peanuts and cashew nuts which serves the function of food ingredients and as snacks could results in mycotoxicosis in humans and animals. Similarly, the detection of aflatoxin in animals carcases have been related to the ingestion of aflatoxin contaminated feed ingredients such as peanut [143]. Aside food substrates, mycotoxin occurrence have been reported in animal feed, animal feedlots and animal derived food products [92, 144, 145]. Aflatoxin is regarded as the chief of mycotoxins based on their degree of toxicities [146]. They have been classified as class 1 human carcinogens based on their deleterious effect on the health of both humans and animals [147, 148].

Human exposure to aflatoxin occurs due to the consumption of contaminated agricultural produce and animal derived food product [143]. Aflatoxin ingestion have been reported to cause teratogenic, mutagenic, carcinogenic immunosuppressive, hepatotoxic, nephrotoxic, and genotoxicity effect in humans and animals [144]. The degree of toxicity of mycotoxins on health of animals or humans is a function of the aflatoxin type, species and sex [149]. The liver is the major target organs for aflatoxin toxicity and could show symptoms such as liver lesions and tumour upon exposure to low and moderate doses of aflatoxin [146, 150]. The consumption of aflatoxin contaminated nuts could impair the immunity, feed efficiency and cause a teratogenic and mutagenic effect in animals [151, 152, 153]. The consumption of this nuts could pose a threat to consumer’s health causing ill-health, immunosuppression, cancer and liver and kidney damage in humans and animals [150]. The consequences of aflatoxicosis accounts for more than 40% of the diseases in developing countries [9]. In tropical and subtropical countries with less or lack of regulatory activities governing the acceptable level of aflatoxin in food and feeds, the risk of human aflatoxicosis is huge. [154, 155]. The study of Ibeh et al.[156] reported the effect of aflatoxin on male fertility. In their study, males with high aflatoxin levels in their serum had abnormal sperm morphology, motility and sperm count. There are also evidence to the transfer of aflatoxin from mothers to babies. Authors [157, 158, 159] have reported the detection of aflatoxin M1 in breast milk of mothers exposed to aflatoxin contaminated foods in Gambian and United Arab Emirates respectively. Neonatal jaundice was reported in foetus exposed to aflatoxin in Nigeria and Iran [160, 161]. Studies have also shown the negative effect of aflatoxin on birth weight, gestational age, birth height, in blood samples obtained from mothers [158, 159].

Yousef and Lamplugh [162] have also reported mobility and mortality cases as a result of aflatoxin ingestion in humans. Chronic aflatoxicosis can results from the continuous exposure to aflatoxin contaminated foods and could cause reduction in life expectancy, cancer, immunosuppression and stunting in children [154].

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10. Aflatoxin regulation

After the discovery of aflatoxins and their effects on health of both humans and livestock, regulatory limits were set in the late 1960s [163]. The United States of America was the first country to set the aflatoxin limit of 20 μg/kg [164] and the EU limit (4 μg/kg) for total aflatoxin and 2 μg/kg for aflatoxin B1. However there was harmonisation of aflatoxin standards for the EU countries which took place in 1997 and implemented in 1998. Total aflatoxin for peanuts needing further processing which was previously set at 10 μg/kg was changed to 15 μg/kg and 4 μg/kg for nuts intended for human consumption. Aflatoxin B1 was set at 8 μg/kg and 2 μg/kg for nuts that required further processing and direct human consumption respectively [165]. Not all countries adopted the harmonised standards, for examples in Asia, China and the Philippines limit of aflatoxins set by these countries were 20 μg/kg while Indonesia set 15 μg/kg for aflatoxin B1 [166].

11. Conclusion

Nuts and nut products and specially peanuts and cashew nuts have long been recognised for their nutritional content and contribution to good health. One of the limitations to the role of these nuts in human nutrition and health is their susceptibility to Aspergillusspecies and related aflatoxins. Aflatoxins have continued to be a problem from the time of discovery as their presence in nuts especially in African countries is still above the limits. Nuts are sources of livelihood to most people in developing countries as they can be used in nutrition as well as for income generation but its high susceptibility to aflatoxin contamination poses a huge threat to the consumers as well as reducing its value economically especially at the International market [139]. As aflatoxins are not really a threat to the developed countries, because of their stringent rules on acceptable limits in foods meant for human consumption.

This chapter revealed that a larger percentage of the nuts produced in Africa are contaminated with aflatoxin concentration above the regulated permissible level, hence consumers of nuts especially peanuts in Africa are at risk of aflatoxicosis despite the nutritional importance of the nut. Hence, strategies to reduce the proliferation of aflatoxigenic fungi in nuts while on the field and at post-harvest level should be harnessed. Some suggested strategies to achieve this includes:

  • Good Agricultural practices such as planting of improved varieties of nuts that are resistant to drought and stress, good storage practices, proper drying of produce before storage, prevention of kernel damage during harvesting etc. should be encouraged.

  • Appropriate controls of storage parameters that could aid impedes Aspergillusspp. growth, contamination and aflatoxin production.

  • Application of biological techniques such as use of atoxigenic strains of Aspergillusto control the toxigenic strains.

It is recommended that future research should focus on the nutritional advantages of peanuts and cashew nuts and their related health benefits beyond the ones that have been identified in this chapter.

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution 3.0 License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Modupeade C. Adetunji, Stephen A. Akinola, Nancy Nleya and Mwanza Mulunda (February 26th 2021). Nutrient Composition and Aflatoxin Contamination of African Sourced Peanuts and Cashew Nuts: Its Implications on Health, Nuts and Nut Products in Human Health and Nutrition, Venketeshwer Rao, Leticia Rao, Md Ahiduzzaman and A. K. M. Aminul Islam, IntechOpen, DOI: 10.5772/intechopen.95082. Available from:

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