Hans Lingnert

A Review of Acrylamide: An Industry Perspective on Research, Analysis, Formation, and Control

Acrylamide is a synthetic monomer with a wide scope of industrial applications, mainly as a precursor in the production of several polymers, such as polyacrylamide. The main uses of polyacrylamides are in water and wastewater treatment processes, pulp and paper processing, and mining and mineral processing. The announcement by the Swedish National Food Administration in April 2002 of the presence of acrylamide predominantly in heat-treated carbohydrate-rich foods sparked intensive investigations into acrylamide, encompassing the occurrence, chemistry, agricultural practices, and toxicology, in order to establish if there is a potential risk to human health from the presence of this contaminant in the human diet. The link of acrylamide in foods to the Maillard reaction and, in particular, to the amino acid asparagine has been a major step forward in elucidating the first feasible chemical route of formation during the preparation and processing of food. Other probably minor pathways have also been proposed, including acrolein and acrylic acid. This review addresses the analytical and mechanistic aspects of the acrylamide issue and summarizes the progress made to date by the European food industries in these key areas. Essentially, it presents experimental results generated under laboratory model conditions, as well as under actual food processing conditions covering different food categories, such as potatoes, biscuits, cereals, and coffee. Since acrylamide formation is closely linked to food composition, factors such as the presence of sugars and availability of free amino acids are also considered. Many new findings that contribute towards a better understanding of the formation and presence of acrylamide in foods are presented. Many national authorities across the world are assessing the dietary exposure of consumers to acrylamide, and scientific projects have commenced to gather new information about the toxicology of acrylamide. These are expected to provide new scientific knowledge that will help to clarify whether or not there is a risk to human health from the consumption of foods containing low amounts of acrylamide.

Acrylamide in food: mechanisms of formation and influencing factors during heating of foods

Background: In April 2002, the Swedish National Food Administration and a scientific group at the University of Stockholm jointly announced that they had shown acrylamide to be formed during the preparation of food and found it to occur in many foodstuffs. These new findings were clearly of concern to many types of industrial food processing as well as to home cooking. The Swedish Food Federation (Li) initiated and financed the formation of an expert committee to look into the chemical mechanisms. The present review is the final report of that expert committee. Design: The study identified, examined and put together facts and present knowledge on reaction routes for acrylamide formation in food and causal connections to cooking and food processing conditions. The results are based on literature surveys, examination of the analytical data published by the Swedish National Food Administration and other follow-up studies, contacts with international scientific networ ks, and observations from food companies. Results: The exact chemical mechanism(s) for acrylamide formation in heated foods is unknown. Several plausible mechanistic routes may be suggested, involving reactions of carbohydrates, proteins/amino acids, lipids and probably also other food components as precursors. With the data and knowledge available today it is not possible to point out any specific routes, or to exclude any possibilities. It is likely that a multitude of reaction mechanisms is involved. Acrolein is one strong precursor candidate, the origin of which could be lipids, carbohydrates or proteins/amino acids. Acrylamide is a reactive molecule and it can readily react with various other components in the food. The actual acrylamide level in a specific food product, therefore, probably reflects the balance between ease of formation and potential for further reactions in that food matrix. There are indications in support of that the Maillard reaction being an import a nt reaction route for acrylamide formation, but lipid degradation pathways to the formation of acrolein should also be considered. Conclusions: Reliable analytical methods to measure acrylamide in foods are available. Model studies are needed to identify precursors and reaction route(s) based on current hypotheses and to elucidate possible further reactions between acrylamide and other food components. Studies are needed to optimize formulation and processing conditions to minimize acrylamide levels, taking other product quality properties into consideration. Keywords: Acrylamide, cooking, food processing, heated foods, Maillard reaction.

Comparison between methods using low-toxicity solvents for the extraction of lipids from herring (Clupea harengus)

Three alkane/alcohol/water-based lipid extraction systems were evaluated to determine which would be the best replacement for the frequently used chloroform/methanol/water system, nowadays known to be very toxic. All the methods were applied to samples of minced herring (Clupea harengus) differing in quality and composition. In addition to comparisons of total lipid yield, the extracted lipids were compared with respect to content of triglycerides, phospholipids, free fatty acids, α-tocopherol, lipid hydroperoxides and conjugated dienes. The content of phospholipids was found to differ most between the lipids extracted by the four methods. Here, the chloroform/methanol/water system was the most efficient, followed by heptane/ethanol/water/sodium dodecyl sulphate (SDS) and then iso-propanol/hexane. However, by decreasing the level of SDS, the efficiency of the heptane/ethanol/water/SDS system in extracting phospholipids was increased to the same level as that of the chloroform/methanol/water system. This decrease in SDS also resulted in a higher recovery of free fatty acids. The lack of correlation between yields of phospholipids and yields of lipid oxidation products throughout this study was surprising because of the often-described susceptibility of phospholipids to oxidation.

Influence of skinning on lipid oxidation in different horizontal layers of herring (Clupea harengus) during frozen storage

This study was conducted to evaluate the effect of skinning and of compositional differences on the oxidative stability of various horizontal layers from herring (Clupea harengus) during frozen storage. Herring fillets, with and without skin, were stored at -18°C for 0, 3, 9, 16 and 28 weeks. After each storage period, the fillets were divided horizontally into three layers: ‘under skin’, ‘middle part’ and ‘inner part’. Each layer was then extracted for total lipids, in which peroxide value (PV), absorbance at 234 nm (A234) and 268 nm (A268) as well as lipid-soluble fluorescent oxidation products (FP) were measured. Prior to storage, the fat content, fatty acid pattern and α-tocopherol were also analysed. During storage of skinless fillets, the under skin layer increased most in PV, A234, A268 and FP (P<0·05), followed by the inner and middle parts. In fillets stored with skin, the high oxidation rate of the under skin layer lipids was suppressed, but this layer still gave rise to the highest responses. Firstly, these results point to the protective properties of the skin and, secondly, to the unfavourable composition of the under skin layer: a lot of dark muscle; the silver surface; the highest fat content and the lowest level of α-tocopherol. Concerning the fatty acid pattern in the three layers, the amount of C20: 5, C18:1 and C20:1 in the fat gradually decreased from the under skin layer towards the inner part of the fillet, whereas the opposite was true for C22: 6.

Fenton reagents may not initiate lipid peroxidation in an emulsified linoleic acid model system

This study includes two parts. First, the Fe2+ autooxidation and chelation processes in the presence of the chelators ethylenediaminetetraacetic acid (EDTA) and diethylenetriamine pentaacetic acid (DTPA) were studied by measuring UV light absorbance alterations. Competition for Fe3+ between chelators and water or phosphate buffer (PB) ions was confirmed. The addition of EDTA or DTPA to Fe3+ in water or PB only slowly turned the water/PB-Fe3+ complexes to EDTA-Fe3+ or DTPA-Fe3+ complexes. In the second part of this study, the initiation mechanisms of Tween 20 emulsified linoleic acid peroxidation under stimulation by chelator-Fe-O2 complexes were studied by measuring changes in UV light absorbance following diene conjugation. Fe3+ in the presence of EDTA or DTPA did not stimulate diene conjugation. Fe2+ (0.10 mM) and EDTA (0.11 mM) stimulated diene conjugation of the linoleic acid emulsion, but only after apparent Fe2+ autooxidation. Fe2+ and DTPA, as well as premixed DTPA-Fe2+ complex, resulted in very fast diene conjugation in a wide range of concentrations. A nonlinear, mainly square root relation between Fe2+ concentration and peroxidation rate was noted. Superoxide dismutase (SOD), catalase, and mannitol did not prevent the lipid peroxidation. H2O2 substantially decreased the DTPA-Fe2+ stimulated, otherwise rapid, diene conjugation but slightly enhanced the slower one stimulated by EDTA-Fe2+. Without ambient oxygen, Fenton reagents did not result in .H abstraction-related diene conjugation. The findings suggest that .OH resulting from Fenton reagents may not be the main cause for the initiation of peroxidation in this model system. Furthermore, a study with different combinations of Fe2+ and Fe3+ did not support the Fe2+/Fe3+ (1:1) optimum ratio hypothesis. We therefore conclude that perferryl ions or chelator-Fe-O2 complexes may be responsible for the first-chain initiation of lipid peroxidation, at least in this model system.

Optimization of temperature, time, and lactic acid concentration to inactivate lipoxygenase and lipase and preserve phytase activity in barley (cv. Blenheim) during soaking

ABSTRACT A barley-soaking process was studied to find conditions that inactivate the prooxidative enzyme lipoxygenase and the lipolytic enzyme lipase but preserve phytase activity to develop possible procedures for production of barley products with potentially high mineral bioavailability and good oxidative stability. Lactic acid concentration, temperature, and soaking time were studied. The study was done using a multivariate experimental design. Lactic acid concentration varied between 0 and 1%, temperature varied between 45 and 70°C, and soaking time varied between 30 and 120 min. Although conditions under which lipoxygenase was inactivated were found, total inactivation of lipase was not obtained. Total lipoxygenase inactivation with 60% remaining phytase activity was reached after soaking in 1% lactic acid at suitable time-temperature combinations of 70–110 min and 53–58°C.

Lipid changes during the production of potato granules

Abstract Potato granules were produced by an add-back-process. The lipid composition of the potato tubers and the final potato granules were assessed in order to study the influence of the process. The extracted lipids were fractionated into three major classes, neutral lipids, galacto-lipids and phospholipids, on a silicic acid column. The free fatty acids were separated from the neutral lipids by high performance liquid chromatography (HPLC). The fatty acid composition of the three lipid classes as well as the free fatty acid fraction was analysed by gas chromatography. No changes could be observed in the galactolipids and the phospholipids but the free fatty acid content was found to be about ten times higher in potato granules than in the potato tubers.

Liberation of free fatty acids during production of potato granules

Abstract The amount of free fatty acids and their composition were studied during an add-back process of potato granules. Samples were taken at several different stages in the production, from raw tubers to final potato granules. Lipids were extracted and lipid classes separated by liquid chromatography. Free fatty acids were separated from the neutral lipid fraction by high performance liquid chromatography (HPLC). The fatty acid composition was analysed by gas chromatography (GC). The amount of free fatty acid increased in the first stages of the process and rose to its highest level in the samples from the steam-cooking step. During further processing the amounts of free fatty acids slowly decreased. Since enzymatic hydrolysis is one explanation for liberation of fatty acids, lipase activity was measured by a spectrofluorimetric method in the raw tubers, blanched slices and steam-cooked slices. After the blanching step, some enzyme activity was found but after steam-cooking there was none.

Influence of Hydrothermal Treatment on Lipid Oxidation in Barley

ABSTRACT A steeping process of barley grains was evaluated regarding lipid oxidation. The steeping process was evaluated with respect to the temperature during the first steep and second steep, and the lactic acid concentration of the steep solutions. The study was conducted using a central composition circumscribed design, and response surface models were estimated with the use of partial least square. The change in the concentration of hexanal was used to monitor the oxidation during processing and subsequent storage at 30°C. In all samples there was hexanal development during processing and the hexanal concentration increased considerably during storage. The results show that it is possible to optimize the process to get a lower oxidation during the subsequent storage. The temperature during the second steep in the hydrothermal process and the level of lactic acid addition were the most important factors. Both of them should be kept low to favor the oxidative stability.

Lipid oxidation in potato slices under conditions simulating the production of potato granules

The formation of volatile compounds in potato slices was analyzed by means of gas Chromatographie headspace analysis. The experimental variables selected for the treatment of the potato slices were chosen to simulate the conditions during the first stages of an “add-back type” of process for production of potato granules. The potato slices (2 cm thick) were exposed to air of low temperature (4°C) and water at blanching temperature (76°C). Both the surface and the middle of each slice were analyzed for volatile compounds. Hexanal was the most abundant aldehyde formed. At the elevated temperature, in particular, there was an obvious formation of hexanal. After 15 min of blanching, the amount of hexanal was higher in the middle of the slices than at the surface. This difference in hexanal concentration was probably due both to the leakage of hexanal into the blanching water from the surfaces of the potato slices, and to the inac-tivation of lipoxygenase at the surfaces which prevented further oxidation during the subsequent chilling period. The hexanal formation indicates that lipid oxidation occurs during the process. The formation of other volatile compounds also is discussed.