A Review of Acrylamide Concentrations in Different Food Products; Associated Risks and Mitigation Strategies

Mechanisms of Acrylamide Formation in Foods

Acrylamide could be formed from naturally-occurring substances like carbohydrate, fat, protein) in certain foods as the result of high temperature processing [5]. During the typical heating of foods, reducing sugars react with amino acids initiating a cascade of events leading to the browning of foods known as the Maillard reaction [6]. Maillard reaction is a non-enzymatic browning reaction occurring in foods during extrusion cooking, roasting, popping, baking, pan- frying, deep-fat frying, barbecuing and autoclavation. This happens at existent of necessary starter reactants that is amino acids: proteins and reducing sugar [2].

The major mechanistic pathway in the formation of acrylamide in foods is a part of the Maillard reaction with free amino acid (asparagine) and reducing sugars (mainly glucose and fructose) [2, 5, 6]. Glycoconjugates of asparagine are the major source of Acrylamide in foods under low moisture conditions at elevated temperatures in the presence of reducing sugars or a suitable carbonyl source [7]. Zyzak, et al. [6] also suggested the necessity of carbonyls in the formation of acrylamide, from asparagine.

In addition to asparagine, other amino acids have been implicated in the formation of acrylamide. Preliminary studies have shown that other amino acids such as L-alanine and L-arginine are also capable of releasing acrylic acid at temperatures above 180°C, with yields within the same order of magnitude as aspartic acid [8].

Factors Affecting Acrylamide Formation in Processed Foods

The variations in varieties and quality of raw materials, formulations, process strategies, and process parameters could impact the formation of acrylamide in foods [9]. But the rate of acrylamide formation is affected by concentration of reactant, reactant ratio, temperature, pH, and water contained [5]. Water impacts the chemical route (Example hydrolysis of the imine) as well as the molecular mobility of the chemical constituents which indirectly contributes to the formation of acrylamide [10].

Glucose and fructose are the major reducing sugars in plant foods, and have the greater influence on acrylamide formation [5]. During the Study of Factors Affecting Acrylamide Levels in Model Systems; Ciesarova, et al. [10] reported that acrylamide is formed from fructose at lower temperatures and on the contrary, in the case of glucose high temperatures (above 140°C) were required to observe acrylamide.

A more important factor which affect the acrylamide yield appeared is the water content. According to Ciesarova, et al. [10] the minimum amount of acrylamide formation is observed in the range of the initial moisture content between 15 and 45%.

It has also been shown that PH affects acrylamide formation in processed foods. Studies on the effect of PH on the yield of acrylamide have reported reduced acrylamide content due to the lowering of the pH [11].

Temperature is another important factor which affects the acrylamide formation in processed foods. Higher amount of acrylamide formation occur at high temperature processing of foods. Ciesarova, et al. [10] obtained high yields of acrylamide at high temperatures in the mixture of potato starch with asparagine and glucose and/or fructose without water after 20 min heat treatment. Mikulikova, et al. [12] also reported that the acrylamide concentration in malt is dependent on the kilning temperatures and with the increasing temperature of kilning, the acrylamide content in malt increased to the temperature of 180 °C.

Acrylamide in Processed Food Products

A wide range of acrylamide levels, which may be achieved using different raw materials, ingredients, and cooking methods, were reported all over the world [9]. Acrylamide was found in many heat processed food items like processed vegetables, processed cereals, animal products and hot drinks.

Acrylamide in Processed Vegetables

Potato products are the most important contribution to the acrylamide exposure both on a high consumption of the products and on a relatively high content of acrylamide. Studies have been performed to determine the level of acrylamide in various fried foods of vegetable origin. Acrylamide content of vegetable based food items are presented in Table 1. Shamla & Nisha [13] conducted a research on acrylamide content of deep-fried snacks of India and obtained acrylamide content of potato chips ranging from 82.0 to 4245.6 µg/kg, acrylamide content of jack chips ranging from 46.2 to 2431.4 µg/kg, and acrylamide content range of 14.7 to 1690.5 µg/kg and 24.8–1959.80 µg/kg, for Plantain chips and Sweet plantain chips respectively.

Table1: Summary of reported amounts of acrylamide (μg/kg) in vegetable based food products.

Acrylamide in Processed Cereals

Cereals and cereal products are the second largest group of products contributing to acrylamide exposure [14]. Boyacı Gündüz & Cengiz [9] conducted a research on acrylamide contents of commonly consumed bread types in Turkey and obtained acrylamide content of (479 ± 325 µg kg−1) in whole wheat breads and 432 ± 214 µg kg−1 in rye bread samples. From the work of Fredriksson, et al. [15] free asparagine in wheat parts are reported to be 0.48 to 0.51, 4.88 to 4.99, 1.48, and 0.14 to 0.17 g kg-1 in the fraction of Whole grain flour, germ, bran, and Sifted flour, respectively .In addition free asparagine in rye was reported to be 1.07, 0.53 to 0.68, and 2.61 to3.18 in the fraction of Whole grain, Sifted flour, and bran of rye respectively. Since Acrylamide formation is related to free asparagine content existence of high concentration of acrylamide in whole grain may be due to the concentration of free asparagine in the bran parts of these grains. Boyac Gündüzand Cengiz [9] reported Acrylamide concentration of Wheat bran bread ,stone oven wheat bread, and white wheat bread to be 307 ± 258 µg kg−1, 171 ± 184 µg kg−1,and 121 ± 103 µg kg−respectively. Chen, et al. [16] obtained average acrylamide content of 22.62–44.92 µg/kg for rice roll, noodle, roasted bread, wafer biscuit and sauted nuts samples from China. Acrylamide contents in different processed cereal based foods were summarized in Table 2.

Studies on acrylamide content of alcoholic or non- alcoholic fermented beverages are very limited and only few surveys are available on acrylamide in alcoholic beverages. Dibaba, et al. [17] reported acrylamide content of 3440 µg/kg for Keribo (Ethiopian traditional fermented beverage) which is prepared from deep roasted unmalted barley at higher level of added sugar (1.5 kg/10 L) and 1320 µg/kg for Keribo prepared from light roasted unmaltedsample. Mikulikova, et al. [12] reported acrylamide content of 630–660 µg.kg-1, and 2210 µg.kg-1 for pale malts and Melanoidin malt respectively. It was revealed that Rye malts have lower acrylamide values in caramel and roasted malts compared to barley malts prepared at the same temperatures. Despite high acrylamide level in malts it was reported that it’s content in all the analyzed samples of beers were under the LOQ (< 25 µg.l-1).

Acrylamide in Animal Products

Acrylamide can be produced as a result of thermal processing of meat products but abundantly lower contents were reported. Chen, et al. [16] reported great variation between acrylamide content of processed and cooked meat and reported average values of 22.62 µg/kg and 25.03 µg/ kg for processed meat and cooked meat respectively. They also reported maximum values of 49.06 µg/kg and 78.57 µg/ kg and minimum values of 2.31µg/kg and 2.71µg/kg in the samples of processed meat and cooked meat respectively. The acrylamide contents of animal based food groups are given in Table 3 & 4 below.

Milk is rich in protein and sugar. So it is obvious that processing of milk at high temperature may lead to acrylamide formation. After examination of Acrylamide in milk samples with different types of additives using Spectrophotometry Method, Tomovska, et al. [18] reported acrylamide content starting with a range from 129.58 µg/l in a homogenized milk with instant coffee as additive, and up to 144.95 µg/l in pasteurized milk with instant coffee as additive, while the lowest value of 13.42 µg/l in chocolate milk (which already contains cocoa/chocolate).But without additives acrylamide content of 8.79 and 14.97 µg/l was reported for pasteurized milk and homogenized milk respectively.

Acrylamide in Hot Drinks

Acrylamide contents of coffee and tea samples are mostly dependent on various factors including roasting conditions and its origion. Mojska & Gielecinska [19] demonstrated roasting process had the most significant effect on acrylamide levels in natural coffee. Different studies reported higher acrylamide levels in Robusta coffee than Arabica coffee. Soares, et al. [20] reported higher acrylamide levels in Robusta coffee than Arabica coffee for a similar roast degree, and suggested this could be probably due to a higher initial amount of asparagine in Robusta coffee. Bagdonaite & Murkovic [21] also reported highest amount of acrylamide in Robusta coffee than Arabica coffee beans. In addition to this they reported that high quality Arabica coffee beans (Columbian Excelso and Uganda Organic Biocoffee) had a lower amount of acrylamide compared to lower quality Arabica coffee beans (Santos Brasil).

Khan, et al. [22] conducted studies on different brands and origin of coffees, and obtained acrylamide content of 152- 682 μg/kg in coffee, 73-108 μg/kg in Arabic coffee. Soares, et al. [23] reported some preliminary data on acrylamide levels of standard espresso coffee (0.32–1.46 lg/30 mL or 10.7–48.7 lg/L).During quantification of acrylamide level of Turkish Black Tea, Instant and Turkish Coffee Samples . Canbay, et al. Obtained acrylamide content ranging from 4.48 to 15.71 µg/kg and 3.89 to 88.44 µg/kg in instant coffee and coffee samples respectively. Mojska & Gielecinska [19] reported acrylamide concentrations of 358 µ/kg in instant coffee and 179 µ/kg in ground roasted coffee samples in determining the acrylamide level in commercial samples of roasted and instant coffee and in coffee substitutes by LC- MS/MS method.

Khan, et al. [22] conducted studies on a total of 22 tea samples of two classes (black and green) and were found acrylamide content of <100 μg kg−1.It is reported that the acrylamide content of green types of tea samples were in the range of (10–18 μg kg−1) while in black tea acrylamide content in the range of 35 - 97 μg kg−1 were reported. Similar result was also reported by Liu, et al. [24] during quantitative analysis of acrylamide in tea by liquid chromatography coupled with electrospray ionization tandem mass spectrometry. Acrylamide content less than 100μg/kg were reported30tea samples; while acrylamide content of Black, oolong, and white and yellow tea samples were less than 20μg/kg. Acrylamide content of sun-dried green tea samples were also reported to be in the range of 46–94 µg/kg. Canbay, et al. also determined the acrylamide contents of Turkish black Tea Samples and reported that black Tea samples had acrylamide content ranging from 6.09 to19.85 µg/kg.

Health Risks of Acrylamide Intake

Acrylamide was found to cause extensive DNA damage in lymphocytes of ACR-fed rats. it was reported that the tail moment for lymphocytes of acrylamide -fed rats was 112.35 while that of the control acrylamide 0 and the mean amount of DNA in the tail of lymphocytes was 86.7% while that of the control was 0.87% [25].

Duan, et al. [26] studied toxic effects of Acrylamide on mouse oocyte quality and fertility in vivo and reported that acrylamide-treated mice had reduced Ovary weights and DNA methylation levels, resulted in oxidative stress and oocyte early stage apoptosis and aberrant oocyte cytoskeletons. ALKarim, et al. [25] detected acrylamide induced significant genotoxicity by using the alkaline comet test and in acrylamide fed rats Significant Ovarian shrinkage, uterine horns irregularities and kinking were reported compared to the control .It was reported that Ovaries of pregnant acrylamide -fed group showed vascularization of corpus luteum compared to the control ones and Significant differences were observed regarding the number and size of fetuses in the ACR fed rats compared to the control. In addition induced adverse effects were reported on male reproductive system for acrylamide administrated with the ordinary rat food that absolute weights of testes and seminal vesicles were significantly reduced in group treated with acrylamide, and decrease in male rat fertility were reported. Aras, et al. [27] reported significantly higher M-II stage oocytes in the control group compared to the Acrylamide treated groups during their study of ‘’In Vivo acrylamide exposure may cause severe toxicity to mouse oocytes through its metabolite glycidamide’ and Concluded that systemic exposure of mice to acrylamide have toxic effects on mouse oocytes.

Researchers have enabled the advanced understanding of acrylamide-induced neuropathies. Acrylamide requires multiple exposures to produce neurotoxicity. Evidence of neurological effect has been observed following single oral doses of 126 mg/kg in rats and rabbits and 100 mg/ kg in dogs [28]. Low-level, work-related exposure to ACR monomer is neurotoxic for humans [29]. Rodent studies (sub-chronic and chronic oral dosing), primate studies (oral and subcutaneous) and a human occupational study, support a NOAEL for acrylamide neuropathy of 0.5 mg/kg bw per day [3]. Workers in the People’s Republic of China, who were exposed to acrylamide and acrylonitrile for 2 or more years, were assessed for neurological signs and haemoglobin acrylamide adducts. A correlation was demonstrated between levels of haemoglobin adducts and degree of peripheral neuropathy.

For the first time; Bull, et al., [30] demonstrated that acrylamide possesses carcinogenic properties. It was reported that acrylamide is capable of acting as a tumor initiator in the mouse skin. In addition, increased lung tumor yield in the strain was reported in A/J mouse independent of promoting agents. During two-year carcinogenicity study of acrylamide in Wistar Han rats with in utero exposure Maronpot, et al. [31] reported increased incidence of thyroid follicular neoplasms in males and females and in a non- statistically significant increase in mammary fibro adenomas in females.

Mitigation Strategies of Acrylamide Occurrence in Processed Foods

When cooking foods, the amount of acrylamide formed can be minimized in several ways. Based on the knowledge about the formation mechanisms various methods were developed by Food scientists around the world to mitigate the presence of acrylamide in fried food products. The chitosan- immobilized asparaginase has shown pronounced action in the mitigation of acrylamide in fried kochchikesel banana chips. Granda, et al. [32] reported vacuum frying reduced acrylamide formation by 94% in fried potatoes and reducing frying temperature reduce acrylamide formation. It was reported that Acrylamide formation decreased significantly in potato chips as the frying temperature decreased from 180 °C to 150 °C for the traditional method and from 140 °C to 118 °C for the vacuum frying [32].

For production of French fries, potato crisps and potato snacks with minimized acrylamide formation it is recommended to use selected potato cultivars having low level reducing sugars, avoiding use of potatoes stored below 60c and treating with calcium salts before frying [33].

It was reported that using additives such as salts, amino acids, cations and organic acids along with blanching of foods have reduced the concentration of acrylamide [34]. From the experiments with the potato powder model system, Mestdagh, et al. [11] concluded that the addition of free glycine and L-lysine gave significant acrylamide reductions while keeping the pH of the mixture at its original level. It was also reported that addition of organic acids and sodium acid pyrophosphate significantly mitigated the final acrylamide content potato powder model system. But this should be evaluated in a real food system. Ismial, et al. [35] investigated a reduction of acrylamide formation in potato chips by blanching in hot water (65 and 85°C) or soaking in solutions containing 0.05M citric acid, 0.1 M CaCl2 or NaCl, 0.1M glycine, L-glutamine or L-cysteine and reported a reduction percentage of 90.40, 88.88, 90.40, 73.58, 76.91, 85.20 and 76.96% respectively.

Fredriksson, et al. [15] conducted a research on ‘Fermentation reduces free asparagine in dough and acrylamide content in bread’ by using doughs and breads made in a model system; and reported that long time fermentation with yeast reduced acrylamide content in bread made with whole grain wheat by 87% and by 77% for breads made with rye bran. To minimize acrylamide formation in cereal based products Alimentarius  [33]  recommended avoiding over baking, decreasing final baking temperature and avoiding using reducing sugar in bread production. It was recommended to use malted and light roasted barely to minimize the amounts of acrylamide in Ethiopian traditional beverage like keribo (barley based beverage) [17]. Selection of commercial blends with higher Arabica percentages, and preferring shorter brews instead of long ones also used to minimize the acrlymide intake from processed coffee [36].