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Acrylamide in food is normally measured as “free water-soluble acrylamide”. However, it is shown that certain extraction techniques, like extraction as for dietary fibre or at high pH can affect the result. This has to be accounted for, particularly in exposure assessment and in studies of bioavailability and, in the long run, the health risk assessment.

Since the first discovery of the presence of acrylamide in a variety of food products in April 2002, numerous methods have been developed to determine the acrylamide monomer in heat-treated carbohydrate-rich food. These detection methods are mainly MS-based, coupled with a chromatographic step using LC or GC. The Food Chemistry Institute (LCI) of the Association of the German Confectionery Industry (BDSI) therefore established a detection method by means of aqueous extraction plus a cleaning step and LC-MS/MS detection, making great efforts to ensure internal and external validation. Citing potato crisps as an example, we will in the following show how the German manufacturing companies have gone to great pains to reduce acrylamide levels in their products.

A system to monitor the formation of acrylamide in model systems and from real food products under controlled conditions of temperature, time and moisture content has been developed. By humidifying the gas that flows through the sample, some control over moisture content can be affected. Results are presented to show the validity and reproducibility of the technique and its ability to deliver quantitative data. The effects of different processing conditions on acrylamide formation and on the development of color, due to the Maillard reaction, are evaluated.

Our finding that acrylamide is formed during heating of food initiated a range of studies on the formation of acrylamide. The present paper summarizes our follow-up studies on the characterization of parameters that influence the formation and degradation of acrylamide in heated foods. The system designed and used for studies of the influence of added factors was primarily homogenized potato heated in an oven. The net content of acrylamide after heating was examined with regard to the following parameters: heating temperature, duration of heating, pH and concentrations of various components. Higher temperature (200°C) combined with prolonged heating led to reduced levels of acrylamide, due to elimination/degradation processes. At certain concentrations, the presence of asparagine or monosaccharides (in particular fructose, glucose and glyceraldehyde) was found to increase the net content of acrylamide. Addition of other free amino acids or a protein-rich food component strongly reduced the acrylamide content, probably by promoting competing reactions and/or covalently binding of formed acrylamide. The pH-dependence of acrylamide formation exhibited a maximum around pH 8; lower pH enhanced elimination and decelerated formation of acrylamide. In contrast, the effects of additions of antioxidants or peroxides on acrylamide content were not significant. The acrylamide content of heated foods is the net result of complex reactions leading to both the formation and elimination/degradation of this molecule.

Simulated food pieces constructed from fiberglass pads (models for French fries and chips) were used as carriers for defined aqueous solutions, dispersions of test substances and ingredients to evaluate acrylamide formation. The pads were loaded with a solution containing asparagine and glucose (10 mM each) plus selected reaction modulators before deep fat frying and analysis for acrylamide. Data from fiberglass models along with companion sliced potato samples were used in developing hypotheses for the mechanisms involved in the suppression of acrylamide formation by polyvalent cations, polyanionic compounds, pH, and altered food polymer states in fried potato products.

We previously reported that in potato chip and French fry models, the formation of acrylamide can be reduced by controlling pH during processing steps, either by organic (acidulants) or inorganic acids. Use of phytate, a naturally occurring chelator, with or without Ca^++ (or divalent ions), can reduce acrylamide formation in both models. However, since phytate itself is acidic, the question remains as to whether the effect of phytate is due to pH alone or to additional effects. In the French fry model, the effects on acrylamide formation of pH, phytate, and/or Ca^++ in various combinations were tested in either blanching or soaking (after blanching) steps. All treatments significantly reduced acrylamide levels compared to control. Among variables tested, pH may be the single most important factor for reducing acrylamide levels, while there were independent effects of phytate and/or Ca^++ in this French fry model. We also developed a mathematical formula to estimate the final concentration of acrylamide in a potato chip model, using variables that can affect acrylamide formation: glucose and asparagine concentrations, cut potato surface area and shape, cooking temperature and time, and other processing conditions.

An integrated approach is described with respect to acrylamide minimization in heated foodstuffs. All relevant variables have to be considered and the main focus is on maintaining the expected product quality. The role of the processes at the interface between product and heating medium during processing is characterized for the case of frying operations. Examples of parameters influencing these processes with respect to minimizing acrylamide and maintaining product quality (e.g. brown color) are described. First, the local distribution of acrylamide in a French fries type model food was investigated. Lowering water activity at the surface of French fries before frying contributes to a reduction of acrylamide without lowering product quality. Both pre-drying of the potato sticks before frying and an increasing of salt concentration at the product surface by coating with a salt solution showed positive effects. Additionally, it was demonstrated by simulation that combined effects of these measurements may enable a reduction of up to 80% in the acrylamide content.

The discovery of acrylamide in processed potato products has brought increased interest in the controlling Maillard reaction precursors (reducing sugars and amino acids) in potato tubers. Because of their effects on nonenzymatic browning of fried potato products, reducing sugars and amino acids have been the focus of many potato research and breeding programs. This study focused on changes in sugars and amino acids in diploid potatoes selected for their storage qualities and their effect on acrylamide formation in the fried product. In addition, a second study was performed using cultivated lines that evaluated the effect of nitrogen fertilization on amino acid levels in tubers. Glucose, fructose, sucrose, and asparagine concentrations in tubers increased upon storage at 2°C. Glucose and fructose concentrations in the tubers were significantly and positively correlated with subsequent acrylamide formation in the products. Tuber sucrose and asparagine concentrations did not have an effect on acrylamide levels. Acrylamide levels in the products were significantly reduced if tubers were preconditioned before being placed in storage at 2°C. Higher rates of nitrogen fertilization resulted in increased amino acid concentrations in the tubers.

The discovery of the formation of acrylamide in fried and baked foods containing high levels of starch and the amino acid asparagine, prompted widespread concern. Both processed and home cooked foods are affected and this has led to the increased study of variations in cooking and processing conditions to minimize formation. While changes in cooking protocols have been in part successful, particularly when lower frying and baking temperatures are used, pretreatments to reduce levels of acrylamide by prevention of formation or acceleration of destruction have been investigated. In this study, a range of pretreatments of grilled potato were investigated and compared with surface washing to remove asparagine and reducing sugars. Synergies were observed between different treatments, and reductions of up to 40% were achieved in a non-optimized system.

Prototype processes were developed for the substantial suppression of acrylamide formation (40–95% compared to untreated controls) in cut surface fried potato products using potato chips (crisps) as the primary model. The most efficacious procedures employed sequentially both surface preparation and subsequent acrylamide precursor complexation and/or competitive inhibition processing steps. Surface preparation processing involved either various low-temperature (50–75°C) aqueous (5–30 min) or ca. 80% ethanol blanch solutions for various times (1–5 min) combined with aqueous leaching steps (1–10 min) to reduce concentration of acrylamide precursors in the critical frying zone of cut potato surfaces. Acrylamide precursor complexation and/or competitive inhibition processing strategies included immersion exposure of prepared cut potato surfaces to solutions or dispersions of various combinations of either calcium chloride, phytic acid, chitosan, sodium acid pyrophosphate, or N-acetylcysteine.