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Several enzymes involved in the metabolism of xenobiotic substances are polymorphic in humans. Inter-individual differences in response to certain chemicals, such as acrylamide, as a result of such genetic polymorphisms might affect health-risk assessments. Detoxification by, for example, conjugation with glutathione (GSH) will decrease the concentration. The dose of the compound and enzymes that enhance the conjugation with GSH will increase the detoxification rate. The dose of acrylamide or glycidamide has been measured in blood samples from individuals with defined genotypes for the glutathione transferases GSTT1 and GSTM1 after in vitro incubation with these compounds. The results indicate that these enzymes have no significant effect on the blood dose, measured as Hb adducts over time, after exposure to acrylamide or glycidamide.

The heat-induced reaction of amino groups of amino acids, peptides, and proteins with carbonyl groups of reducing sugars such as glucose results in the concurrent formation of so-called Maillard browning products and acrylamide. For this reason, reported studies of adverse biological effects of pure acrylamide may not always be directly relevant to acrylamide in processed food, which may contain Maillard and other biologically active products. These may either antagonize or potentiate the toxicity of acrylamide. To stimulate progress, this paper presents an overview of selected reported studies on the antiallergenic/allergenic, antibiotic, anticarcinogenic/carcinogenic antimutagenic/mutagenic, antioxidative/oxidative, clastogenic (chromosome-damaging), and cytotoxic activities of Maillard products, which may adversely or beneficially impact the toxicity of acrylamide. The evaluation of biological activities of Maillard products and of other biologically active food ingredients suggests that they could both enhance and/or ameliorate acrylamide toxicity, especially carcinogenicity, but less so neurological or reproductive manifestations. Future studies should be directed to differentiate the individual and combined toxicological relationships among acrylamide and the Maillard products, define individual and combined potencies, and develop means to prevent the formation of both acrylamide and the most toxic Maillard products. Such studies should lead to safer foods.

This paper summarizes the progress made to date on acrylamide research pertaining to analytical methods, mechanisms of formation, and mitigation research in the major food categories. Initial difficulties with the establishment of reliable analytical methods have today in most cases been overcome, but challenges still remain in terms of the needs to develop simple and rapid test methods. Several researchers have identified that the main pathway of formation of acrylamide in foods is linked to the Maillard reaction and in particular the amino acid asparagine. Decarboxylation of the resulting Schiff base is a key step, and the reaction product may either furnish acrylamide directly or via 3-aminopropionamide. An alternative proposal is that the corresponding decarboxylated Amadori compound may release acrylamide by a beta-elimination reaction. Many experimental trials have been conducted in different foods, and a number of possible measures identified to relatively lower the amounts of acrylamide in food. The validity of laboratory trials must, however, be assessed under actual food processing conditions. Some progress in relatively lowering acrylamide in certain food categories has been achieved, but can at this stage be considered marginal. However, any options that are chosen to reduce acrylamide must be technologically feasible and also not negatively impact the quality and safety of the final product.

The formation of acrylamide (AA) from L-asparagine was studied in Maillard model systems under pyrolysis conditions. While the early Maillard intermediate N -glucosylasparagine generated ∼2.4 mmol/mol AA, the Amadori compound was a less efficient precursor (0.1 mmol/mol). Reaction with α-dicarbonyls resulted in relatively low AA amounts (0.2–0.5 mmol/mol), suggesting that the Strecker aldehyde pathway is of limited relevance. Similarly, the Strecker alcohol 3-hydroxypropanamide generated low amounts of AA (0.2 mmol/mol). On the other hand, hydroxyacetone afforded more than 4 mmol/mol AA, indicating that α-hydroxycarbonyls are more efficient than α-dicarbonyls in transforming asparagine into AA. The experimental results are consistent with the reaction mechanism proposed, i.e. (i) Streckertype degradation of the Schiff base leading to azomethine ylides, followed by (ii) β-elimination of the decarboxylated Amadori compound to release AA, The functional group in β-position on both sides of the nitrogen atom is crucial. Rearrangement of the azomethine ylide to the decarboxylated Amadori compound is the key step, which is favored if the carbonyl moiety contains a hydroxyl group in β-position to the N-atom. The β-elimination step in the amino acid moiety was demonstrated by reacting under pyrolysis conditions decarboxylated model Amadori compounds obtained by synthesis.

Studies on model systems of amino acids and sugars have indicated that acrylamide can be generated from asparagine or from amino acids that can produce acrylic acid either directly such as β-alanine, aspartic acid and carnosine or indirectly such as cysteine and serine. The main pathway specifically involves asparagine and produces acrylamide directly after a sugar-assisted decarboxylation and 1,2-elimination steps and the second nonspecific pathway involves the initial formation of acrylic acid from different sources and its subsequent interaction with ammonia to produce acrylamide. Aspartic acid, β-alanine and carnosine were found to follow acrylic acid pathway. Labeling studies with [^13C-4]aspartic acid have confirmed the occurrence in aspartic acid model system, of a previously proposed sugarassisted decarboxylation mechanism identified in asparagine model systems. In addition, creatine was found to be a good source of methylamine and was responsible for the formation of N-methylacrylamide in model systems through acrylic acid pathway. Furthermore, certain amino acids such as serine and cysteine were found to generate pyruvic acid that can be converted into acrylic acid and generate acrylamide when reacted with ammonia.

The effectiveness of different compounds in the generation of acrylamide (AA) from asparagine, was determined by reacting asparagine with mono-, diand polysaccharides, as well as four different oxo-compounds known to be involved in carbohydrate metabolism/degradation. Quantitation of AA formed either under aqueous conditions or in low water model systems revealed glucose and 2-oxopropionic acid as the most effective compounds in AA generation, when reacted in model systems with a low water content (about 1 mol-% yield). Interestingly, heating of asparagine in the presence of 2-oxopropionic acid generated quite high amounts of 3-aminopropionamide (3-APA), which itself effectively generated AA upon heating in aqueous solution, as well as in low water systems. Because this is the first report on amounts of 3-APA generated by Maillard-type reactions, the general role of 3-APA as key intermediate in AA formation is discussed in detail. In addition, first results on the development and application of an HPLC/fluorescence method for AA quantitation are presented.

Heating amino acids with dietary oils or animal fats at elevated temperatures produced various amounts of acrylamide. The amount of acrylamide formation corresponded to the degree of unsaturation of the oils and animal fats. The decreasing order of acrylamide formation from dietary oils or animal fats with asparagine was sardine oil (642 μg/g asparagine) > cod liver oil (435.4 μg/g) > soybean oil (135.8 μg/g) > corn oil (80.7 μg/g) > olive oil (73.6 μg/g) > canola oil (70.7 μg/g) > corn oil (62.1 μg/g) > beef fat (59.3 μg/g) > lard (36.0 μg/g). Three-carbon unit compounds such as acrylic acid and acrolein, which are formed from lipids by oxidation also produced acrylamide by heat treatment with amino acids, in particular with asparagine. The results of the present study suggest that acrylamide forms in asparagine-rich foods during deep fat frying in the absence reducing sugars.

A kinetic model for the formation of acrylamide in potato, rye and wheat products has been derived, and kinetic parameters calculated for potato by multi-response modeling of reducing sugar (glucose and fructose), amino acid, asparagine and acrylamide concentrations with time. The kinetic mechanism shares, with Maillard browning, a rate limiting (probably dicarbonylic) intermediate, and includes reaction steps of this intermediate which are competitive with respect to acrylamide formation. A pathway representing physical and/or chemical losses of acrylamide accounts for the measured reduction of acrylamide yield at long reaction times. A mechanistic hypothesis regarding the competing reactions of Strecker aldehyde formation and tautomerization followed by beta-elimination to give acrylamide, features in the kinetic model and can be used to determine the factors which steer the reaction towards acrylamide. A predictive application of this model is for ‘what-if’ experiments to explore the conditions which lead to reduced acrylamide yields.

The relationship between acrylamide and its precursors, namely free asparagine and reducing sugars, was studied in simple cakes made from potato flake, wholemeal wheat and wholemeal rye, cooked at 180°C, from 5 to 60 min. Between 5 and 20 min, large losses of asparagine, water and total reducing sugars were accompanied by large increases in acrylamide, which maximized in all three products between 25 and 30 min, followed by a slow linear reduction. Acrylamide formation did not occur to any extent until the moisture contents of the cakes fell below 5%. A comparison of each type of cake with a commercial product, made from the same food material, showed that acrylamide levels in all three commercial products were well below the maximum levels in the cooked cakes.

Recent concerns surrounding the presence of acrylamide in many types of thermally processed food have brought about the need for the development of analytical methods suitable for determination of acrylamide in diverse matrices with the goals of improving overall confidence in analytical results and better understanding of method capabilities. Consequently, the results are presented of acrylamide testing in commercially available food products — potato fries, potato chips, crispbread, instant coffee, coffee beans, cocoa, chocolate and peanut butter, obtained by using the same sample extract. The results obtained by using LC-MS/MS, GC/MS (EI), GC/HRMS (EI) — with or without derivatization — and the use of different analytical columns, are discussed and compared with respect to matrix borne interferences, detection limits and method complexities.