Acrylamide in Food

Analysis, Content and Potential Health Effects

Vural Gokmen

• Publisher: Academic Press
• Year: 2015
• ISBN:
  9780128028759
• Topic: Technology & Engineering
• Subtopic: Food Science
• Index: Technology & Engineering

Acrylamide in Food: Analysis, Content and Potential Health Effects provides the recent analytical methodologies for acrylamide detection, up-to-date information about its occurrence in various foods (such as bakery products, fried potato products, coffee, battered products, water, table olives etc.), and its interaction mechanisms and health effects.

The book is designed for food scientists, technologists, toxicologists, and food industry workers, providing an invaluable industrial reference book that is also ideal for academic libraries that cover the domains of food production or food science.

As the World Health Organization has declared that acrylamide represents a potential health risk, there has been, in recent years, an increase in material on the formation and presence of acrylamide in different foods. This book compiles and synthesizes that information in a single source, thus enabling those in one discipline to become familiar with the concepts and applications in other disciplines of food science.

• Provides latest information on acrylamide in various foods (bakery products, fried potato products, coffee, battered products, water, table olives, etc.)
• Explores acrylamide in the food chain in the context of harm, such as acrylamide and cancer, neuropathology of acrylamide, maternal acrylamide and effects on offspring and its toxic effects in tissues
• Touches on a variety of subjects, including acrylamide, high heated foods, dietary acrylamide, acrylamide formation, N-acetyl-S-(2-carbamoylethyl)-cysteine (AAMA), acrylamide removal, L-asparaginase, and acrylamide determination
• Presents recent analytical methodologies for acrylamide determination, including liquid chromatographic tandem mass spectrometry and gas chromatography-mass spectrometry

Chapter 1

Acrylamide Formation Mechanisms

Richard H. Stadler¹, and Alfred Studer^{2 1}Nestec Ltd, Corporate Quality Management, Vevey, Switzerland ²Nestlé Research Centre, Vers-chez-les-Blanc, Switzerland

Abstract

The formation of acrylamide via the Maillard pathway at temperatures typically above 120 °C is today the most prominent route of formation. The key precursor of acrylamide, asparagine, provides the chemical backbone of acrylamide, in essence through decarboxylation and loss of a nitrogen moiety. Stable isotope-labeled experiments conducted in model foods have corroborated the asparagine pathway, as well as studies on the use of the enzyme asparaginase as a mitigation approach, that have resulted in the successful reduction of acrylamide across many food categories. The chemistry involved has demonstrated different possible intermediates (decarboxylated Amadori product, 3-aminopropionamide) en route to acrylamide, partly driven by the structures of the reacting carbonyls (reducing sugars or dicarbonyl compounds). Techniques such as mass spectrometry and Fourier-transform infrared spectroscopy have aided to detect and measure the key intermediates. Lower-temperature reactions have also been proposed; for example, in the formation of acrylamide in prune concentrates heated over a longer period of time and subject to drying at a relatively low temperature (<100 °C). Further efforts are, however, still required to assess the significance of such marginal pathways.

Keywords

3-aminopropionamide; Acrolein; Acrylamide; Acrylic acid; Decarboxlated Amadori product; Dicarbonyl; Mitigation; Reducing sugar

Introduction

Since the discovery of acrylamide in certain types of food cooked at high temperatures in April 2002 by the Swedish National Food Authority [1,2], extensive work has been done to identify the molecular precursors and to elucidate the reaction mechanism(s) leading to acrylamide. The very early studies dealing with the formation of acrylamide in food identified the Maillard reaction as a key driver of acrylamide formation [3,4]. The Maillard reaction is the reaction between naturally present amino acids and reducing sugars (e.g., glucose or fructose) when foods are heated. It is responsible for the development of the desirable flavor and color in many cooked foods subjected to baking, frying, or roasting. Acrylamide is mainly formed from the amino acid asparagine and reducing sugars (glucose and fructose) both of which occur naturally in plant materials including, for example, cereal grains, vegetables (such as potatoes), cocoa, and coffee (for in-depth reviews see Refs [5–8]).

The first research papers on the formation of acrylamide had in common that they identified asparagine as the key amino acid that furnishes the acrylamide backbone [3,4,9], although the initial proposals of the chemical pathways described by the authors were divergent, providing only little evidence of the key intermediates. Stadler et al. [3] provided evidence of the involvement of the free amino acid asparagine through stable isotope dilution assays using ¹⁵N-labeled asparagine, showing that >98% of the label is incorporated into acrylamide. The same paper showed that N-glycosides (N-(D-glucos-1-yl)-1-asparagine and N-(D-fructos-2-yl)-L-asparagine) are effective precursors of acrylamide, yielding >1.3 mmol acrylamide per mol of N-glycoside. Mass spectra of the pyrolysate of asparagine and glucose confirmed the presence of the corresponding N-glycoside [3].

The group of Mottram [4] proposed the involvement of the Strecker reaction in the formation of acrylamide, using 2,3-butanedione as the dicarbonyl source reacting with asparagine. Strecker aldehydes are formed via the oxidative deamination and decarboxylation of α-amino acids, driven by deoxysones. Model system studies showed that carbonyls furnish acrylamide under both wet (phosphate buffer) and dry conditions. The authors also proposed acrolein/acrylic acid as potential intermediates, albeit at lower yields due to the likely limitation of ammonia in the reaction [4].

Zyzak et al. [9] were the first to show that 3-aminopropionamide (3-APA), a biogenic amine formed during the Maillard reaction, may be one of the key precursors of acrylamide. The researchers also showed through experiments with 2-deoxy-glucose that carbonyls, but not dicarbonyls, are essential in the Maillard route to acrylamide: that is, Amadori rearrangement products are not needed. Further studies by other researchers [10] corroborated this early work on 3-APA, first in model systems and then in actual food samples such as cheese and cocoa [11,12].

Major Pathways of Acrylamide Formation

Experiments based on binary mixtures of short carbon chain carbonyls and hydroxycarbonyls are useful to compare the efficacy of precursors and gain insight into the possible reaction mechanisms governing the formation of acrylamide. Several reports have shown that both dicarbonyls and hydroxycarbonyls react rapidly with asparagine to release acrylamide. These earlier studies provided useful information on the impact of temperature, moisture, pH, and other reactants on the pathway to acrylamide, conducted under both wet and dry conditions.

Aldo versus Keto Sugars

Binary model systems demonstrate that about equal amounts of acrylamide are formed when asparagine is added to fructose or glucose; significantly lower amounts of acrylamide are formed when sucrose is employed as reactant. The different reactivities of carbonyls have been reported by several authors [13,14]. However, the data of the reports are difficult to compare, due to the fact that heating conditions vary. However, there seems consensus in different reports that lower amounts of acrylamide are formed in glucose mixtures versus fructose. This may be due to the lower melting point of fructose (and hence higher mobility) and consequently faster interaction of the precursors to afford the early Maillard intermediates [14]. Alternatively, keto sugars such as fructose form the fructose Schiff intermediate that stabilizes the azomethyine ylide (H bonding), see also Figure 2. This extra stabilization can increase the rate of its formation and consequently acrylamide formation versus glucose systems. Yaylayan and Stadler [15] suggest that the reactivity is reversed in aprotic solvents, supporting the hydrogen-bonding theory.

Pyruvic acid (2-oxopropionic acid) and hydroxyacetone are highly efficient reactants that afford >6 mmol acrylamide/mol reactant, whereas mixtures containing glyoxal, methylglyoxal, or propanal yield about 2 mmol/mol [16,17]. Interestingly, pentosans and cellulose may also contribute to acrylamide formation when incubated together with asparagine; mixtures with pentosans providing even more acrylamide than mixtures with comparable concentrations of glyoxal.

Table 1

Comparison of the efficacy of different carbonyl reactants in the formation of acrylamide (mmol/mol reactant)

Reactant^a	Acrylamide (mmol/mol)
2-Hydroxy-1-butanal	15.8
Hydroxyacetone	3.97
Glucose	2.22
Methylglyoxal	0.52
Glyoxal	0.38
Diacetyl	0.26
3-Hydroxy-propanamide	0.24
Glyoxylic acid	0.08
1-Butanal	0.01

^a Samples heated at 180 °C for 5 min.

Adapted from Refs [13,18]

As depicted in Table 1, α-dicarbonyls are effective reactants that generate acrylamide. However, compounds such as glyoxylic acid without a dicarbonyl moiety may also lead to the formation of acrylamide in binary mixtures with asparagine.

Interestingly, hydroxyacetone afforded significantly more (ca. 10-fold) acrylamide in this dry model versus short carbon chain dicarbonyls. Similarly, only relatively low conversion rates were observed in incubations with the Strecker alcohol (3-hydroxy-propamanide). Such models are useful to compare relative reactivities under give...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• List of Contributors
• Preface
• Introduction: Potential Safety Risks Associated with Thermal Processing of Foods
• Chapter 1. Acrylamide Formation Mechanisms
• Chapter 2. Challenges in Estimating Dietary Acrylamide Intake
• Chapter 3. Secular Trends in Food Acrylamide
• Section A. Acrylamide, The Food Chain in the Context of Harm
• Section B. Acrylamide in Foods
• Section C. Interactions and Reductions
• Section D. Methods of Analysis
• Index