**2. Discovery and properties of acrylamide**

Acrylamide (IUPAC name—prop-2-enamide) (**Figure 1**) was accidentally discovered in foods in April 2002 by a group of researchers in Sweden working on heat processing technology of carbohydrate-rich foods [1, 7]. It is a white, odourless and crystalline compound with the chemical formula C3 H5 NO, molar mass of 71.08 g/mol, melting point of 84.5°C, vapour pressure of 0.007 mmHg at 25°C and boiling point at 136°C [8]. ACR is soluble in chloroform, ether, ethanol and water and decomposes in the presence of acids, oxidizing agents, bases, iron and iron salts [9] to form ammonia, carbon dioxide, carbon monoxide and oxides of nitrogen [10]. ACR is a heat-induced contaminant naturally formed during industrial processing and home cooking of many foods daily consumed around the world [8, 11].

ACR is used as a chemical intermediate in the production of polyacrylamides, which are used as a flocculating agent for sewage/wastewater treatment and other industrial applications

**Figure 1.** Chemical structure of acrylamide.

such as those in the formulation of several cosmetics [12]. Its application as a grouting agent is also extended to the construction of dam foundations, sewers and tunnels and cosmetics and in electrophoresis gels [13]. It has also been used in pesticide production, cement formulations, ore processing, sugar manufacturing, food packaging, plastic and paper production and for the prevention of soil erosion [2]. Sequel to its detection in foods and potential toxic effects, several studies have been initiated and reported worldwide, some of which will be highlighted in the succeeding sections of this chapter.

#### **2.1. Formation of acrylamide**

principally in carbohydrate-rich foods, was first reported by Tareke et al. [1] and has since been identified as a global challenge in the food industry. It has been classified as a potential occupational (Group 2A) carcinogen by the International Agency for Research on Cancer (IARC) and some US government agencies [2]. This is due to the fact that ACR is known to potentially exhibit carcinogenic effects in experimental animals, albeit its dietary link to human cancer. Its neurotoxicity in humans is well known from accidental and occupational exposures and experimental studies in animals which have shown genotoxic, reproductive and carcinogenic

For over a decade since its discovery, several studies have been published in the literature on its formation, presence in various food products and toxicity in different parts of the world [1, 4–6]. In contrast, there is a dearth of information on its incidence and prevalence in Africa. This is probably why no information regarding limits regulating ACR in foods has not been established or enforced. Although other regions of the world can be affected by ACR contamination, it could be easily identified that Africa can be the most affected. It can, however, be difficult to affirm this assertion considering the lack of well-established or insufficient data on ACR levels in processed foods, degree of human exposure and risk assessment in the continent. This chapter appraises studies presenting information on the formation of ACR in foods and toxicity associated with it in other parts of the world. The main strategies for controlling or preventing its occurrence in the literature are also reviewed herein with a view of their

Acrylamide (IUPAC name—prop-2-enamide) (**Figure 1**) was accidentally discovered in foods in April 2002 by a group of researchers in Sweden working on heat processing technology of carbohydrate-rich foods [1, 7]. It is a white, odourless and crystalline compound with the

sure of 0.007 mmHg at 25°C and boiling point at 136°C [8]. ACR is soluble in chloroform, ether, ethanol and water and decomposes in the presence of acids, oxidizing agents, bases, iron and iron salts [9] to form ammonia, carbon dioxide, carbon monoxide and oxides of nitrogen [10]. ACR is a heat-induced contaminant naturally formed during industrial processing

ACR is used as a chemical intermediate in the production of polyacrylamides, which are used as a flocculating agent for sewage/wastewater treatment and other industrial applications

and home cooking of many foods daily consumed around the world [8, 11].

NO, molar mass of 71.08 g/mol, melting point of 84.5°C, vapour pres-

effects [3].

152 Acrylic Polymers in Healthcare

possible adoption in Africa.

chemical formula C3

**2. Discovery and properties of acrylamide**

H5

**Figure 1.** Chemical structure of acrylamide.

ACR is principally formed via Maillard reaction involving asparagine and carbonyl sources such as reducing sugars [14]. Although asparagine may be converted to ACR by thermally induced deamination and decarboxylation, carbohydrates are necessary to effect its conversion to ACR (**Figure 2**) [15]. While several other carbonyl compounds can enhance this reaction, α-hydroxyl carbonyl compounds such as glucose or fructose are more efficient [16]. Claus et al. [14] indicated that the first step in this reaction is the formation of a Schiff base intermediate as a low-energy alternative in decarboxylating this product intact. The formed Schiff base intermediate can either hydrolyze to form 3-aminopropionamide, a precursor of ACR, or further undergo elimination reaction leading to direct formation of ACR [17]. Nevertheless, the formation of ACR from reducing sugars and asparagine in the Maillard reaction represents the main formation route [14].

The formation of acrolein and acrylic acid through the dehydration of fats when heated at high temperature has been proposed as another mechanism of ACR formation [6, 14]. The studies of Becalski et al. [19] also indicated that ACR can be formed along with ammonia from

**Figure 2.** Proposed mechanism for the formation of the acrylamide in heat-treated foods. Adapted from Vleeschouwer et al. [18].

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. Such factors are subsequently reviewed.

#### **2.2. Factors affecting formation of acrylamide**

#### *2.2.1. Processing conditions*

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 coffee beans [23, 26].

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 cooking [25].

#### *2.2.2. Substrate composition*

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 formation. While temperature has been discussed in the preceding section, Matthaus et al. [32] reported that a quick reduction of the water content in the outer layers of the product (as a consequence of high temperatures) favours ACR formation.
