*2.2.3. Soil properties and fertilization*

the degradation of amino acids. Although based on experiments with ammonium salts, acrolein and oils, this mechanism suggested might be inappropriate for ACR formation in foods [20]. Nevertheless, there are a number of factors that impact on the development of ACR in foods.

Food processing conditions such as time and temperature are vital factors affecting the formation and levels of ACR in food [21, 22]. However, the manner of heat transfer to foods (for instance, baking, frying, microwave heating and roasting) does not, however, necessarily impact the rate of ACR formation [23]. An exponential increase in ACR levels from 265 to 2130 μg/kg in French fries was observed when temperature increased from 150 to 190°C [21]. In potato slices with low and high surface-to-volume ratios (SVRs), ACR levels increased with increasing frying temperature and time, reaching maximum levels of 2500 and 18,000 μg/kg, respectively [24]. Studies on the effect of time and temperature on ACR formation in bread revealed that more ACR was formed in the crust layer and the levels increased with baking temperature and time [20, 25]. Roasting temperature and time had an impact on ACR formation in

In Africa, traditional food processing operations and techniques are commonly applied but vary among different ethnic groups, communities and settlements. Heat processing operations such as frying, roasting and baking are common processes used in preserving and processing foods for further use. Thus, this presents a significant risk of ACR exposure. Elsewhere, it has been observed that concentrations of ACR are highly correlated with the degree of crust surface browning of processed foods [20]. These authors asserted that because ACR and brown colour of foods are formed due to Maillard reaction, it is most likely that ACR is formed in parallel with browning. Thus, the degree of surface browning (though may not necessarily indicate amount of ACR) could be used as a visual indicator of ACR formation in foods during

The formation of ACR intermediates is usually determined by the amount and form of amino acids and sugars present [27]. It has thus been postulated that ACR formation and consequent concentration are relative to amino acid and sugar composition in the substrate [21, 27]. While these precursors affect ACR formation, the presence of other compounds that compete with amino acids and reducing sugars in the Maillard reaction are also vital compositional factors [21]. In potato and cereal products, ACR levels are highly correlated with glucose/fructose and asparagine concentrations [28]. Varieties in crop cultivar could also affect the reducing sugar content in the produce [29]. Short-term storage of potatoes at 4°C significantly increased the potential for ACR formation [30, 31]. Cooling potatoes to temperatures less than 10°C causes reducing sugars to increase, thereby increasing the potential for ACR formation [21, 30, 31]. Temperature and moisture levels in the food substrate are also other factors that affect ACR

Such factors are subsequently reviewed.

*2.2.1. Processing conditions*

154 Acrylic Polymers in Healthcare

coffee beans [23, 26].

cooking [25].

*2.2.2. Substrate composition*

**2.2. Factors affecting formation of acrylamide**

Both nitrogen and sulphur are important compositions of the soil, and subsequent concentrations and amount have significant effect on the formation of ACR precursors [33–36]. According to Halford et al. [34], increasing soil sulphur levels and reducing nitrogen levels can effectively decrease the levels of ACR precursors, such as asparagine [34]. In a study conducted by De Wilde et al. [33] on the influence of soil enrichment on ACR formation in potatoes, differences occurred in ACR formation from crops grown on different soils. The effect of nitrogen fertilizer usage on crops has been reported in the literature to have an impact on asparagine and reducing sugar concentrations [37]. A decrease in nitrogen fertilizer resulted in a 30–65% increase in ACR formation [33, 38]. Moderate nitrogen fertilizer with a good provision of potassium may result in low levels of free asparagine and reducing sugars in tubers [39]. This clearly indicates that mineral composition due to either fertilizer employed or soil composition may impact on the presence and concentrations of ACR precursors. Deficiencies in phosphorus, potassium and magnesium can cause asparagine levels to rise in potato and wheat [34]. An appropriate balance between levels of fertilizer application and minimum requirements of the crop while taking into account possible environmental impacts and legal fertilizer limits should be reached to obtain food products less prone to ACR formation [33].

#### **2.3. Occurrence and levels of acrylamide in foods**

There have been considerable efforts made since the discovery of ACR in foods by regulatory agencies such as the US Food and Drug Administration (FDA), the World Health Organization (WHO) and the European Commission (EC) to gather data on food levels of ACR [40, 41]. However, none of these were reported from the continent of Africa. Prevalent sources of ACR differ among countries due to differences in the diet, method of preparing foods and the nature of soil/agricultural practices [42]. Cereal-, tuber- and coffee-related products contribute mostly to the sources of ACR intake [43]. Since ACR is present in a variety of food products which are consumed on a daily basis, the risks of exposure apply to almost all consumers. Children may be more vulnerable due to their smaller body mass as compared to adults [44].

Though a summary of reports on the incidence of ACR have been reported in other parts of the world [40, 41, 43, 44], a search of literature revealed few reports from Africa. The different studies reported are summarized in **Table 1** on ACR incidence levels reaching 12626, 9499, 7310 and 6968 μg/kg in South America, Africa, the Middle East and Europe, respectively. Of the very few incidences reported so far, only a few reported on African commodities were in Ghana [45], Kenya [46] and South Sudan (**Table 1**) [47, 48]. Though majority of these commodities were mainly baked and fried, this does not suggest that other heat-intense processed foods do not lead to ACR. The death of dogs after consuming the burnt part of maize meal is worth noting [49]. The death of these dogs was ascribed to ACR poisoning by the authors and should awaken intensive research on this. Further considering the fact that maize meal is a

#### 156 Acrylic Polymers in Healthcare



**Product/produce Region of the world Acrylamide content Reference** Arabica Europe 48–3210 [50] Baby biscuit Europe 588 [51] Baby bread—rusks Europe 660 [51] Baby food Europe 0–130 [41] Baked *gorasa* Africa 20 [48] Baked *minnan* Africa 17 [48] Baked *hilmur* Africa 59 [48] Baked potato chips Middle East 329–7310 [52] Biscuit Asia 119 [53]

156 Acrylic Polymers in Healthcare

Bread Asia 103 [55]

Bread and rolls Europe 400 [58] Breakfast cereal Asia 117.3 [53]

Cakes Europe 13–50 [61] Candy bars Europe 39–61 [61] Cantonese moon cake Asia 207 [62] Cereal-based baby foods Europe 353 [56]

Cereals Europe 52–1057 [41] Cereal bar Europe 820 [58] Chocolate Europe 750 [58]

487 [54] 232 [55]

1177 [51] 214 [57] 1514 [58]

695 [51]

762 [51] 674 [58]

11–16 [61]

Europe 4200 [56]

South America 3180 [59]

Middle East 90–802a [60] Europe 2430 [56]

Europe 1600 [56]

South America 2288 [59]



c Average value.

**Product/produce Region of the world Acrylamide content Reference** Fried instant noodle Asia 54 [54] Fried potato Africa 750 [47]

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Fried potato chips Middle East 375–7024 [52] Fried puffs Asia 524 [55] Fried sweet potato Africa 1043 [45] Fried *taamia* Africa 68 [47] Fries Europe 3300 [58] Gingerbread Europe 2100 [58] Home-cooked potato products Europe 2175 [56] Hot beverages Europe 93–5399 [41] Infant biscuits Europe 3–516 [67] Infant cereals in powder Europe 65–296 [67]

Infant cereals (ready to eat) 11–52a Infant cereal with follow-on formula in powder 17–260 Infant cereal with follow-on formula (ready to eat) 3–46

Infant powdered formula South America 1821 [59] Instant cereal-based baby food Europe 19.2–34.7 [61] Jarred baby foods Europe 162 [56]

Juice Europe 267 [41] *Mahua* Asia 234 [62] Moon cake Asia 201 [62] Non-fried instant noodles Asia 5 [54] Nuts products Asia 105 [53] *Paicha* Asia 214 [62] Plantain chips Africa 568 [45] Popcorn Europe 1100 [58]

Potato Europe 131–5360 [78] Potato-based chips Middle East 375–7310 [52] Potato chips Asia 1021 [54]

227 [48]

2–162 [67]

South America 781 [59]

**Table 1.** Reported occurrence of acrylamide in foods by regions.

staple food in Southern African and gets burnt during its preparation, there are indications of a huge risk of ACR exposure to millions of individuals consuming this product daily.

#### **2.4. Toxicity of acrylamide**

The neurotoxicity of ACR in humans is well known from occupational and accidental exposures [79]. Owing to its low molecular weight and polarity, ACR is readily distributed and incorporated in mammals [80]. After ingestion, ACR is rapidly circulated throughout the whole body via the bloodstream [81] and can be found in the liver, kidney, thymus, brain, heart and human breast milk [82]. The conjugation of ACR to glutathione, and its epoxidation to glycidamide in the liver via cytochrome P450, is one of the major metabolic routes [83]. The formation of glycidamide is considered to be the critical step for the toxic effects of ACR and its metabolites. ACR and glycidamide, the latter at a much higher rate, can react with macromolecules such as haemoglobin and enzymes [80]. According to the European Food Safety Authority, ACR and its metabolite glycidamide have shown evidences of genotoxicity (DNA damage) and carcinogenicity [44]. Although evidence from studies on human exposure and possible causes of cancer is currently limited, epidemiological studies designed to target different populations and different organs in relation to cancer risks have been presented, with absolutely none reported from the African continent [84].

Calleman [85] reported peripheral neuropathy symptoms of highly exposed workers in China. Characterized by numbness of hands and feet, ataxia and skeletal muscle weakness, ACR has been shown to be toxic to both the central and peripheral nervous system [86]. ACR induces nerve terminal degeneration [79] and has deleterious effects on the thalamus, hippocampus and cerebral cortex [79, 86]. A recent study demonstrated evidence of ACR neurotoxic effects of fried potato chips on rat postnatal development, causing cerebellar cortical defects and myodegeneration of the gastrocnemius muscle during the postnatal development of pups [87]. It has been postulated that neurotoxicity of ACR might be cumulative as the same neurotoxic effects can be seen at low and high doses of ACR with the low doses requiring longer exposure [86, 88].

In 1994, ACR was classified by the International Agency for Research on Cancer (IARC) as Group 2A, indicating that it is probably carcinogen to humans (Group 2A) [89, 90]. This was based on positive bioassay results in rodents, buttressed by evidence that ACR is transformed in mammalian tissues to a more reactive genotoxic metabolite (glycidamide) [8]. Evidence on experimental rodents indicates that ACR causes tumours in the skin, uterus, lungs, brain, thyroid and mammary gland [91]. The genotoxicity of ACR and glycidamide is also manifested as both clastogenicity and mutagenicity. ACR has proven to be genotoxic in vivo to the somatic and germ cells as well as to cell cultures [8] and mammalian cells [81]. As indicated by Rice [91], the oxidation of this contaminant to glycidamide is the prerequisite for genotoxicity of ACR. This is attributed to the higher reactivity of this metabolite (glycidamide) to form adducts with DNA [83].

For cancer-related effects, the margin of exposures (MOEs) of ACR have been estimated to range from 50 for high-consuming toddlers to 425 for average adult consumers. These numbers indicate concerns for public health [44]. Essentially, since any level of exposure to a genotoxic substance could possibly cause DNA damage and lead to cancer, no tolerable daily intake (TDI) of ACR is set by European scientists [44], not to mention Africa. Nonetheless, Shipp et al. [13] reported that ACR administered to drinking water of rodents at doses of ≥5 mg/kg bw/day resulted in significant decreases in the number of live pups. At higher doses, signs of copulatory behaviour as well as effects on sperm motility and morphology were observed by these authors. ACR toxicity in male animals includes decrease in sperm number/ abnormal sperm, decrease in fertility rates, degeneration of the epithelial cells of the seminiferous tubules and retarded development of pups [92]. These reproductive toxic effects may be attributed to the interfering effect of ACR on the kinesin motor proteins, resulting in a reduced sperm motility and subsequent fertilization [92].
