Further insight into thermally and pH-induced generation of acrylamide from glucose/asparagine model systems

Dual functional roles of nutritional additives in nutritional fortification and safety of thermally processed food: Potential, limitations, and perspectives

The Maillard reaction (MR) has been established to be a paramount contributor to the characteristic sensory property of thermally processed food products. Meanwhile, MR also gives rise to myriads of harmful byproducts (HMPs) (e.g., advanced glycation end products (AGEs) and acrylamide). Nutritional additives have attracted increasing attention in recent years owing to their potential to simultaneously improve nutritional quality and attenuate HMP formation. In this manuscript, a brief overview of various nutritional additives (vitamins, minerals, fatty acids, amino acids, dietary fibers, and miscellaneous micronutrients) in heat-processed food is provided, followed by a summary of the formation mechanisms of AGEs and acrylamide highlighting the potential crosstalk between them. The main body of the manuscript is on the capability of nutritional additives to modulate AGE and acrylamide formation besides their traditional roles as nutritional enhancers. Finally, limitations/concerns associated with their use to attenuate dietary exposure to HMPs and future perspectives are discussed. Literature data support that through careful control of the addition levels, certain nutritional additives possess promising potential for simultaneous improvement of nutritional value and reduction of AGE and acrylamide content via multiple action mechanisms. Nonetheless, there are some major concerns that may limit their wide applications for achieving such dual functions, including influence on sensory properties of food products, potential overestimation of nutrition enhancement, and introduction of hazardous alternative reaction products or derivatives. These could be overcome through comprehensive assay of dose-response relationships and systematic evaluation of the diverse combinations from the same and/or different categories of nutritional additives to establish synergistic mixtures.

Acrylamide and hydroxymethylfurfural in cakes: An approach to reduce the formation of processing contaminants in sweet bakery products

In bakery products, beyond the heat treatment conditions, the type of flour and the combination with other ingredients in different ratios can increase or mitigate the formation of processing contaminants. In this study, a central composite design and a principal component analysis (PCA) were used to assess how the formulation affects the formation of acrylamide (AA) and hydroxymethylfurfural (HMF) in wholemeal and white cakes. The HMF levels (45-138 µg/kg) were up to 13 times lower than the AA (393-970 µg/kg) in cakes. The PCA showed that the proteins increased the AA formation during the dough baking, while the reducing sugar and the browning index were related to HMF formation in the cake crust. The total daily exposure of AA + HMF when consuming wholemeal cake is 1.8 times higher than white cake consumption, in which the values of margin of exposure (MOE), below < 10,000, demonstrated that AA showed a greater risk of exposure than HMF (MOE values > 10,000). Therefore, a good strategy to avoid high AA levels in cakes is to use of refined wheat flour and water in the formulation. In contrast, the advantage of wholemeal cake about their nutritional value should not be disregarded, thus, the use of water in its preparation and moderate consumption are strategies that could be adopted to reduce the risk of exposure to AA.

Influence of citral on acrylamide formation in model systems

This work aimed to evaluate the role of citral (Cit) in the formation of acrylamide (AA) in model systems. The asparagine (Asn)/glucose (Glc), Asn/Glc/ginger essential oil (GEO), and Asn/Glc/Cit model systems were prepared and analysed by UPLC-MS/MS. Cit was implicated to be a major product that contributed to the enhancement of AA formation by GEO. The addition of Cit significantly enhanced the formation of AA in the Asn/Glc model system in a dose-dependent manner. Further analysis showed Cit rather than its oxidation product played a major role in AA formation. Cit not only directly reacted with Asn via the Maillard reaction producing AA but also promoted the formation of AA between Asn and Glc.

Acrylamide in widely consumed foods - a review

Acrylamide (AA) is considered genotoxic, neurotoxic and a 'probable human carcinogen'. It is included in group 2 A of the International Agency for Research on Cancer (IARC). The formation of AA occurs when starch-based foods are subjected to temperatures higher than 120 °C in an atmosphere with very low water content. The aim of this review is to shed light on the toxicological aspects of AA, showing its regulatory evolution, and describing the most interesting mitigation techniques for each food category involved, with a focus on compliance with EU legislation in the various classes of consumer products of industrial origin in Europe.

Effects of Formulation and Baking Process on Acrylamide Formation in Kolompeh, a Traditional Cookie in Iran

Thermal treatments and recipes are two critical aspects for the formation of acrylamide at ordinary household cooking conditions and industrial level. Kolompeh is a traditional Iranian cookie, and the aim of this study was to monitor acrylamide formation in four different recipes: traditional sugary Kolompeh (TSK), traditional simple Kolompeh (TSIK), industrial sugary Kolompeh (ISK), and industrial simple Kolompeh (ISIK). Along with the measurement of reducing sugars, moisture, and pH, acrylamide was quantified by gas chromatography mass spectrometry (GC-MS). Results indicated that acrylamide content was 1758, 1048, 888, and 560 μg/kg for TSK, TSIK, ISK, and ISIK, respectively, revealing that the kind of thermal treatment in combination with higher concentrations of reducing sugars were the major driver for acrylamide formation. In particular, acrylamide concentration in TSIK direct heating was 1.87 times higher than industrial indirect heating treatment, highlighting that domestic preparation of Kolompeh required a specific attention as a source of potential toxic molecule formation.

Support vector regression-guided unravelling: antioxidant capacity and quantitative structure-activity relationship predict reduction and promotion effects of flavonoids on acrylamide formation

We used the support vector regression (SVR) approach to predict and unravel reduction/promotion effect of characteristic flavonoids on the acrylamide formation under a low-moisture Maillard reaction system. Results demonstrated the reduction/promotion effects by flavonoids at addition levels of 1–10000 μmol/L. The maximal inhibition rates (51.7%, 68.8% and 26.1%) and promote rates (57.7%, 178.8% and 27.5%) caused by flavones, flavonols and isoflavones were observed at addition levels of 100 μmol/L and 10000 μmol/L, respectively. The reduction/promotion effects were closely related to the change of trolox equivalent antioxidant capacity (ΔTEAC) and well predicted by triple ΔTEAC measurements via SVR models (R: 0.633–0.900). Flavonols exhibit stronger effects on the acrylamide formation than flavones and isoflavones as well as their O-glycosides derivatives, which may be attributed to the number and position of phenolic and 3-enolic hydroxyls. The reduction/promotion effects were well predicted by using optimized quantitative structure-activity relationship (QSAR) descriptors and SVR models (R: 0.926–0.994). Compared to artificial neural network and multi-linear regression models, SVR models exhibited better fitting performance for both TEAC-dependent and QSAR descriptor-dependent predicting work. These observations demonstrated that the SVR models are competent for predicting our understanding on the future use of natural antioxidants for decreasing the acrylamide formation.

Role of plant polyphenols in acrylamide formation and elimination

Acrylamide found in thermal-treated foods has led to an intensive and persistent research effort, since it is a neurotoxic, genotoxic and probable carcinogenic compound to humans. Plant polyphenols are the most abundant antioxidants in human diet. Several researches indicated that the polyphenols affected the acrylamide formation during heating. However, the controversial effects of the polyphenols on acrylamide formation were related to their structure, concentrations, and antioxidant capacity, as well as reaction condition. Polyphenols can inhibit acrylamide formation through trapping of carbonyl compounds and preventing against lipid oxidation, while some special polyphenols can enhance the acrylamide content by providing carbonyl groups, accelerating the conversion from 3-aminopropionamide (3-APA) to acrylamide and inhibiting acrylamide elimination. This review concludes the effects of polyphenols in the Maillard reaction and food systems conducted so far, aimed to give an overview on the role of plant polyphenols in acrylamide formation and elimination.

Rapid mixed mode solid phase extraction method for the determination of acrylamide in roasted coffee by HPLC-MS/MS

In this work, a rapid and reliable purification method based on a single mixed solid phase extraction (SPE) column, for the determination of acrylamide in roasted coffee by liquid chromatography-tandem mass spectrometry, was developed. Deuterium labelled d(3)-acrylamide was used as internal standard. Acrylamide was extracted by 10 mL of water and the extract purified by a single SPE column consisting of 0.5 g of an in-house prepared mixture of C18, strong cation (SCX) and anion exchange (SAX) sorbents in the ratio 2/1.5/1.5 (w/w/w). The amount of the three sorbents was optimised in order to eliminate the main interfering compounds present in coffee extracts, such as melanoidins, trigonelline, chlorogenic acids and caffeine. The SPE procedure was very simple and consisted of pushing 1 mL of an aqueous coffee extract through the SPE column followed by 1 mL of water which was collected for the analysis. The method was tested on six samples of roasted coffee of different composition and roasting level. The repeatability of the method, expressed as relative standard deviation (n=6), was lower than 5%. The recovery of acrylamide at three spiked levels ranged from 92% to 95%. The limits of detection (LOD) and quantitation (LOQ) were 5 and 16 μg kg(-1), respectively.

Role of curcumin in the conversion of asparagine into acrylamide during heating

This study aimed to investigate the ability of curcumin to convert asparagine into acrylamide during heating at different temperatures. Binary and ternary model systems of asparagine-curcumin and asparagine-curcumin-fructose were used to determine the role of curcumin on acrylamide formation in competitive and uncompetitive reaction conditions. The results indicated that curcumin could potentially contribute to acrylamide formation under long-term heating conditions as long as asparagine was present in the medium. The amount of acrylamide formed in the ternary system was slightly higher than in the binary system during heating (p < 0.05), because of the higher concentrations of carbonyl compounds initially available. The kinetic trends were similar in both model systems evidencing that fructose reacted with asparagine more rapidly than curcumin. The data reveal that acrylamide formation in the temperature range of 150-200°C obeys Arrhenius law with activation energy of 79.1 kJ/mole. Data of this work showed the possibility that antioxidants having a carbonyl compound can react directly with ASN leading to acrylamide. The addition of antioxidants to foods may increase the formation of acrylamide upon long-term heating if free sugar concentration is low and ASN concentration is relatively high.

Acrylamide in foods: a review of the science and future considerations

Acrylamide occurs in foods commonly consumed in diets worldwide. It is formed from the reaction of reducing sugars (e.g., glucose or fructose) with the amino acid asparagine via the Maillard reaction, which occurs during heat processing of foods, primarily those derived from plant origin, such as potato and cereal products, above 120°C (248°F). The majority of epidemiological studies concerning potential relationships between acrylamide consumption and different types of cancer have indicated no increased risk, except with a few types that warrant further study. Efforts to reduce the formation of acrylamide in food products have resulted in some successes, but there is no common approach that works for all foods. Reduction in some foods is probably not possible. The results from a major toxicological study (aqueous intake of acrylamide by rats and mice) are in the process of being released. The status of current knowledge in these areas is reviewed.

Asparagine decarboxylation by lipid oxidation products in model systems

The decarboxylation of asparagine in the presence of alkanals, alkenals, and alkadienals, among other lipid derivatives, was studied in an attempt to understand the reaction pathways by which some lipid oxidation products are able to convert asparagine into acrylamide. Asparagine was converted into 3-aminopropionamide in the presence of lipid derivatives as a function of reaction conditions (pH, water content, time, and temperature), as well as the type and amount of lipid compound involved. Alkadienals (and analogous ketodienes) were the most reactive lipids followed by hydroperoxides and alkenals. Saturated carbonyls and polyunsaturated fatty acids, or other polyunsaturated derivatives, also exhibited some reactivity. On the other hand, saturated lipids or monounsaturated alcohols did not degrade asparagine. A mechanism for the decarboxylation of asparagine in the presence of alkadienals based on the deuteration results obtained when asparagine/2,4-decadienal model systems were heated in the presence of deuterated water was proposed. The activation energy (E(a)) of asparagine decarboxylation by 2,4-decadienal was 81.0 kJ/mol, which is higher than that found for the conversion of 3-aminopropionamide into acrylamide in the presence of 2,4-decadienal. This result points to the decarboxylation step as the key step in the conversion of asparagine into acrylamide in the presence of alkadienals. Therefore, any inhibiting strategy for suppressing the formation of acrylamide by alkadienals should be mainly directed to the inhibition of this step.

Inhibitory mechanism of naringenin against carcinogenic acrylamide formation and nonenzymatic browning in Maillard model reactions

Chemical model reactions were carried out to investigate the effect of a citrus flavonoid, naringenin, on the formation of acrylamide under mild heating conditions. Results showed that naringenin significantly and dose dependently inhibited the formation of acrylamide (20-50% relative to the control), although not in a linear manner. Moreover, the presence of naringenin in acrylamide-producing models effectively reduced the extent of browning. Careful comparison of the HPLC chromatograms of samples from the chemical model reactions revealed that naringenin likely reacted with Maillard intermediates, giving rise to new derivatives. Subsequent LC-MS analyses suggested that the proposed derivatives have a predicted molecular mass of 341 Da. Eventually, two derivatives were purified and characterized with LC-MS/MS and NMR spectroscopy as 8-C-(E-propenamide)naringenin and 6-C-(E-propenamide)naringenin, respectively. In other words, naringenin, a rather weak antioxidant, strongly inhibited acrylamide formation probably by directly reacting with acrylamide precursors, thus diverting them from the pathways that lead to acrylamide formation.

Formation of Pent-4-en-1-amine, the counterpart of acrylamide from lysine and its conversion into piperidine in lysine/glucose reaction mixtures

Isotope labeling studies performed using lysine/glucose model systems have indicated that lysine can generate piperidine, a reactive amine capable of undergoing Maillard type interactions. Two possible mechanisms were identified for the formation of piperidine: one arising through decarboxylation of lysine alone to generate cadaverine (1,5-diaminopentane) followed by deamination to form pent-4-en-1-amine which in turn can cyclize into piperidine where both Nepsilon and Nalpha atoms of lysine can be equally involved in its generation due to the symmetrical nature of the precursor diamine. On the other hand, in the presence of sugars, lysine, similarly to asparagine and phenylalanine, can undergo carbonyl-assisted decarboxylative deamination reaction to generate pent-4-en-1-amine, the counterpart of acrylamide. The pent-4-en-1-amine can then cyclize to form piperidine through the Nepsilon atom of lysine. To confirm the formation of pent-4-en-1-amine in the lysine/glucose model system, a useful strategy based on Py-GC/MS analysis was developed using isotope labeling technique to identify sugar adducts of pent-4-en-1-amine. Products simultaneously possessing five lysine carbon atoms (C2'-C6') and the Nepsilon-amino group from lysine in addition to glucose carbon atoms were targeted using specifically labeled precursors such as [(15)Nalpha]lysine.2HCl, [(15)Nepsilon]lysine.2HCl, [U-(13)C(6)]lysine.2HCl, [(13)C-6]lysine.2HCl and [U-(13)C(6)]glucose. The complete labeling studies along with structural analysis using synthetic and other available precursors have shown the presence of a peak that satisfies the above criteria, and the peak was tentatively identified as N-(5-methylfuran-2-yl)methylidene]penta-1,3-dien-1-amine incorporating pent-4-en-1-amine in its structure.

Model reactions of acrylamide with selected amino compounds

The reaction of acrylamide with amines, amino acids, and polypeptides was studied in an attempt to understand the role of amino compounds on acrylamide fate. The obtained results showed that amino compounds are added to acrylamide by means of a Michael addition to produce the corresponding 3-(alkylamino)propionamides. Although 3-(alkylamino)propionamides can also be added to a new molecule of acrylamide to produce a new adduct, this last adduct was not detected under the employed conditions in which the concentration of acrylamide was much lower than the concentration of the amino compounds. The produced 3-(alkylamino)propionamides were not stable, and the addition reaction was easily reversed by heating. Thus, acrylamide was produced from 3-(alkylamino)propionamides by means of an elimination reaction. However, the activation energies (E(a)) of both reactions are not the same. In fact, acrylamide seems to be converted into its Michael adduct with a lower activation energy than the elimination reaction of the Michael adduct. For this reason, when acrylamide was stored in the presence of glycine at 60 degrees C, acrylamide disappeared after 14 days. However, when these samples were heated again for 20 min at 180 degrees C, the equilibrium was reestablished and a significant amount of acrylamide was detected. All of these results suggest that amino compounds may play a significant role in the changes observed in acrylamide content in foods upon storage. In addition, they also point to 3-(alkylamino)propionamides as possible compounds in which acrylamide might be potentially hidden.

Effect of pyridoxamine on acrylamide formation in a glucose/asparagine model system

The effect of pyridoxamine (PM) on the reduction of acrylamide (AA) formation in a low-moisture equimolar glucose/asparagine model system was investigated. Formation/elimination kinetics of acrylamide was carried out at temperatures between 120 and 180 degrees C. Time courses of glucose, asparagine, pyridoxamine, 3-aminopropionamide (3-APA), acrylamide, and browning were measured to get more insight on the mechanism of action of PM. PM exhibited an inhibitory effect on AA formation at all temperatures studied, but became more relevant at 160 and 180 degrees C (up to 51% reduction). Degradation rates of glucose and asparagine were not significantly affected by PM, but PM was rapidly consumed in the glucose/asparagine system. Browning was significantly suppressed by addition of PM in the system, and formation of 3-APA was increased as compared to control. In comparison with pyridoxal, pyridoxine, and ascorbic acid, PM exerted the highest inhibition activity against AA formation, and a clear dose-response was observed. The nucleophilic aminomethyl group of PM was crucial for the exertion of an inhibition effect more than double those other B6 vitamers. The action mechanism of PM was attributable to its structural features that have the capacity to scavenge intermediary dicarbonyls formed during sugar degradation and advanced stages of the Maillard reaction. These findings open new possibilities for strategies in acrylamide mitigation where formation of reactive dicarbonyls should be carefully considered.

FTIR monitoring of oxazolidin-5-one formation and decomposition in a glycolaldehyde-phenylalanine model system by isotope labeling techniques

Imines or Schiff bases formed through the interaction of reducing sugars with amino acids are known to play a critical role not only in initiating the Maillard reaction but also in its propagation through isomerization reactions initiated by the intermediate oxazolidin-5-one. FTIR spectroscopic evidence for the formation of this intermediate in a phenylalanine-glycolaldehyde model system was provided by taking advantage of a strong absorption band centered at 1778 cm(-1). The identity of this peak was confirmed by observing a shift to 1736 cm(-1) when [(13)C-1]phenylalanine was used. The intensity of this peak decreased over time with concomitant increase of two bands in the carbonyl absorption region, one centered at 1730 and the other at 1720 cm(-1). The former band was shifted to 1685 cm(-1), while the band at 1720 remained unchanged when [(13)C-1]phenylalanine was used. The simultaneous formation of a carboxylic acid and a carbonyl band is consistent with the formation of an Amadori rearrangement product. Furthermore, time-dependent analysis of the formation and decomposition of the oxazolidin-5-one intermediate suggests that it is an important precursor of the Amadori rearrangement product. In addition, through the use of appropriate model systems, [(15)N]phenylalanine and second-derivative spectral analysis, evidence was also provided for the formation of decarboxylated imines at 80 degrees C.