Industry’s approaches to reduce acrylamide formation in French fries

In 2002, The Swedish National Food Administration reported relevant amounts of acrylamide in several carbohydrate rich foods when baked at high temperatures (> 120°C) upon frying, baking and roasting. Toxicological studies demonstrated the carcinogenicity of acrylamide in animals and thus indicated potential health risks for humans. Consequently, in 1994, the IARC evaluated acrylamide as probably carcinogenic to humans (Group 2A)1 (IARC, 1994). Even though the risks associated with the carcinogenicity of acrylamide intake in humans still present some uncertainties2, this contaminant is present at quite high levels in many food products consumed daily. Because of this, it is essential to evaluate the ‘margin of exposure’ (MOE) for acrylamide, which represents the ratio between a particular point on the dose–response curve leading to tumours in experimental animals and the human intake.

The value of MOE gives an indication about the possible extent of the risk. The higher the MOE, the lower the risk of exposure to the component concerned. In this respect, MOE values reported for acrylamide range from 50 to 2,000, indicating that acrylamide is a much more ‘severe’ process contaminant compared to others (e.g. benzo(a)pyrene with MOE values ranging from 10,000 to 25,000).

The discovery of acrylamide in foods was immediately confirmed by other research groups, and together with stakeholders, efforts were carried out to build greater understanding of acrylamide concerning the mechanism of its formation in foods, the risks associated for consumers and possible strategies to lower acrylamide levels in foodstuffs. The Confederation of the European Food and Drink Industries (CIAA) established a Technical Acrylamide Expert Group in 2003 and created the ‘Acrylamide Toolbox’. This toolbox represents a regularly updated and robust medium for the categorisation and summarisation of formation and mitigation of acrylamide in various foods3.

Fried potato products have always been important in the acrylamide issue because they are rich in the main precursors necessary for its formation. Moreover, this food commodity is accountable for an important part of the dietary exposure to acrylamide4. The free amino acid asparagine and the reducing sugars fructose and glucose have been identified as the main precursors for its formation during the Maillard reaction. Since generally the amount of free asparagine largely exceeds the amount of reducing sugars in potato tubers, it is the latter which determines the degree of acrylamide formation and Maillard browning upon frying.

Several strategies may be considered with respect to the mitigation of acrylamide formation in French fries. For instance, various factors have an impact on the reducing sugar content of the raw material and therefore affect acrylamide formation upon subsequent frying. In addition, the Maillard reaction may be ‘prevented’ either by treating potato strips with additives/processing aids or by manipulating final frying conditions. Up to now, research has demonstrated the necessity of an approach from farm to fork in order to reduce acrylamide in fried potato products. For example, cultivar selection, fertilisation and climatological conditions may have an impact on reducing sugar contents of the raw material. Long-term potato storage may also influence the levels of reducing sugars due to senescent sweetening. It is known that storage temperatures below 8°C may induce low temperature sweetening. On the other hand, during the winter season, potato storage at optimal temperatures may be difficult. These factors lead to great variability in the raw material between different seasons and even within the same storage season. Therefore, a more effective entrance control of the raw potato tubers in order to identify batches of potatoes prone to acrylamide formation is necessary. This would tackle the acrylamide issue at the start of the production process in a more efficient way. The current quality control at the reception point of the potatoes is usually done based on colour evaluation with a USDA (US Department of Agriculture) / Munsell colour chart (after a short frying test, typically 180°C for three minutes). This quality control measure relates raw material to colour specifications of final product (customer demand) and either the raw material is rejected for processing or appropriate adjustments are taken accordingly (e.g. optimised blanching conditions).

A recent study performed at Ghent University during two consecutive potato storage seasons, in collaboration with the potato processing industry (Belgapom and EUPPA, European Potato Processors’ Association) and the Flemish government (Flanders’ Food), has shown that a more effective entrance control for incoming potatoes was indeed possible5. Even though differences were observed in reducing sugar contents in raw material for both seasons, similar trends were observed between the acrylamide content of the final product, colour formation upon final frying and reducing sugars in the raw material. Using the relationships between acrylamide and colour formation (measured by the Agtron methodology) and reducing sugar content, batches of potatoes more prone to acrylamide formation could be identified, thus potentially enabling the industry to imply preventive measures in order to minimise the acrylamide risk in their products.

Regarding the industrial process of French fries production, blanching is an important unit operation, since it influences final product specifications, such as colour, fat content and texture. In addition, during this step, acrylamide precursors are leached out, resulting in the reduction of acrylamide content in the final product6. Therefore modifying blanching conditions (time and temperature) relates to the extraction of reducing sugars. In general, potato processors increase the intensity of blanching conditions towards the end of the potato season due to senescent sweetening. These conditions needed to be kept constant. However, reducing sugars resultant from senescent sweetening are not always easily leachable and moreover, due to textural issues, blanching can only be adapted within certain limitations.

Besides the impact of reducing sugars on acrylamide formation, the use of certain additives/processing aids in the French fries production process may equally affect acrylamide formation. For example, disodium diphosphate or sodium acid pyrophosphate (E450), which is used in French fry production (subsequent to the blanching step) to reduce the darkening of the blanched potato cuts, reduces the pH and therefore limits acrylamide formation. Several lab experiments with potato model systems and potatoes have demonstrated that the addition of organic acids (e.g. acetic, lactic and citric acid)7-9, salts such as Na+, Ca2+ or Mg2+10,11 and the enzyme asparaginase12 may reduce acrylamide formation in potato products. However, these treatments have never been tested on the industrial production process of French fries and their effects on the overall quality of the final product is not yet known.

Within the same collaborative study mentioned above, pre-treatments of the potatoes with various food-grade additives or processing aids were evaluated on the industrial production of French fries in 2009, based on their potential to prevent acrylamide formation and other quality parameters13. First, preliminary lab experiments with fifteen additives (including acids, salts, amino acids and asparaginase), demonstrated that asparaginase, acetic and citric acid were the most successful treatments regarding their effect on sensorial attributes and their acrylamide reducing capabilities in French fries. These and calcium lactate were tested on an industrial production line of French fries. Despite some of the compounds seeming to significantly reduce the acrylamide content of the final product during preliminary laboratory experiments, their application on industrial scale did not result in further acrylamide reductions in pre-frozen French fries, except if very strong acidification was applied, but this resulted in sensorial defects. Regarding asparaginase, at pH values above the pH of standard production (e.g. pH 6.0), the enzyme indeed proved to lower acrylamide formation significantly (up to 39 per cent). However, lowering the process pH towards the normal pH used in industry (pH 4.7), acrylamide formation was already reduced without the application of the enzyme to a similar extent. Moreover, additional application of the enzyme did not result in a further acrylamide reduction, probably due to lower enzyme activity at this more acidic pH. Another important aspect demonstrated with these trials was the negative impact of all pre-treatments tested on the sensorial properties of the final product. Overall results suggest that current industrial practices in the pre-frozen French fries sector, such as selection of potato varieties with low reducing sugars contents, potato storage temperature at 8°C, blanching conditions and the acidifying effect of added disodium diphosphate, already considerably reduces the acrylamide formation in French fries.

The application of asparaginase was additionally extended to chilled French fries (not par-fried). Since for this product a longer period of time is allowed for enzyme-substrate contact, the enzyme treatment resulted in French fries with acrylamide levels below the limit of detection. These significant acrylamide reductions were obtained without affecting the shelf life of the product and sensorial properties of the French fries. However, the application of the enzyme on chilled French fries implies the presence of residual enzyme activity on the product before frying. This is in disagreement with the definition of processing aid, and therefore the regulatory status regarding the use of the enzyme under these circumstances still needs clarification. Another important aspect to consider is that the implementation of such treatment requires modifications on the industrial lines and therefore additional investments besides the cost of the enzyme.

Finally but no less important, baking conditions may dramatically affect acrylamide levels of the products as they are eaten. It has been demonstrated that the correlation between Maillard browning and acrylamide formation14, and consequently, a more intensive frying operation (temperature and time) produces more acrylamide15. On the other hand, frying at lower temperatures (below 140°C) results in increased frying time and may enhance fat uptake.

In conclusion, ‘lab scale studies’ in acrylamide mitigation research should be interpreted with utmost care when considering acrylamide mitigation in French fries. Because so many factors are involved in the formation of this process contaminant, a big variability in acrylamide occurrence may be observed even within a same batch of processed potatoes and this may affect the implementation of a determined mitigation strategy. Therefore, factors such as seasonal variability of the raw material, raw material characteristics (before and after blanching), the complexity of the blanching step (1, 2 or 3 blanchers), dip tank parameters (temperature, pH and duration) and other variables should be considered when implementing an acrylamide mitigation strategy on industrial level while maintaining the expected product quality for the consumer. Other considerations such as feasibility, legislation, cost, effluent treatment, safety and comfort of the employees, ability to control dosage, etc. are equally relevant when considering the implementation of any change to an industrial process. Ultimately, the success of any acrylamide mitigation strategy implemented by industry is strongly dependent upon the final baking conditions adopted by the household consumers or caterers. For lower acrylamide contents, frying temperature of 160- 170°C and to fry until the French fries have a light-yellow colour is suggested.

For all these reasons, mitigating acrylamide formation in French fries remains quite challenging with respect to lowering the formation of acrylamide, while safeguarding product quality for the consumer.

References

1. IARC, 1994, Acrylamide. International Agency for Research on Cancer, Lyon, France

2. EFSA. EFSA Scientific Colloquium N° 11 – Acrylamide Carcinogenicity, New Evidence in Relation to Dietary Exposure. May 2008. 1-30

3. CIAA, 2009, Rev. 12: The CIAA acrylamide toolbox

4. Claeys, W., K. Baert, F. Mestdagh, J. Vercammen, P. Daenens, B. De Meulenaer, G. Maghuin-Rogister, and A. Huyghebaert, 2010, Assessment of the acrylamide intake of the Belgian population and the effect of mitigation strategies: Food Additives and Contaminants Part A-Chemistry Analysis Control Exposure & Risk Assessment, v. 27, no. 9, p. 1199-1207

5. Medeiros Vinci, R., F. Mestdagh, N. De Muer, C. Van Peteghem, and B. De Meulenaer, 2010, Effective quality control of incoming potatoes as an acrylamide mitigation strategy for the French fries industry: Food Additives and Contaminants Part A-Chemistry Analysis Control Exposure & Risk Assessment, v. 27, no. 4, p. 417-425

6. Mestdagh, F., T. De Wilde, S. Fraselle, Y. Govaert, W. Ooghe, J. M. Degroodt, R. Verhe, C. Van Peteghem, and B. De Meulenaer, 2008c, Optimization of the blanching process to reduce acrylamide in fried potatoes: Lwt- Food Science and Technology, v. 41, no. 9, p. 1648-1654

7. Kita, A., E. Brathen, S. H. Knutsen, and T. Wicklund, 2004, Effective ways of decreasing acrylamide content in potato crisps during processing: Journal of Agricultural and Food Chemistry, v. 52, no. 23, p. 7011-7016

8. Mestdagh, F., J. Maertens, T. Cucu, K. Delporte, C. Van Peteghem, and B. De Meulenaer, 2008d, Impact of additives to lower the formation of acrylamide in a potato model system through pH reduction and other mechanisms: Food Chemistry, v. 107, no. 1, p. 26-31

9. Pedreschi, F., K. Kaack, K. Granby, and E. Troncoso, 2007, Acrylamide reduction under different pre-treatments in French fries: Journal of Food Engineering, v. 79, no. 4, p. 1287-1294

10. Gökmen, V., and H. Z. Senyuva, 2007, Acrylamide formation is prevented by divalent cations during the Maillard reaction: Food Chemistry, v. 103, no. 1, p. 196-203

11. Mestdagh, F., T. De Wilde, K. Delporte, C. Van Peteghem, and B. De Meulenaer, 2008b, Impact of chemical pretreatments on the acrylamide formation and sensorial quality of potato crisps: Food Chemistry, v. 106, no. 3, p. 914-922

12. Hendriksen, H. V., B. A. Kornbrust, P. R. Ostergaard, and M. A. Stringer, 2009, Evaluating the Potential for Enzymatic Acrylamide Mitigation in a Range of Food Products Using an Asparaginase from Aspergillus oryzae: Journal of Agricultural and Food Chemistry, v. 57, no. 10, p. 4168-4176

13. Medeiros Vinci, R., F. Mestdagh, C. Van Poucke, B. Kerkaert, N. De Muer, Q. Denon, C. Van Peteghem, and B. De Meulenaer, 2011, Implementation of acrylamide mitigation strategies on industrial production of French fries: Challenges and pitfalls: Journal of Agricultural and Food Chemistry, v. In press

14. Viklund, G., F. Mendoza, I. Sjöholm, and K. Skog, 2007, An experimental set-up for studying acrylamide formation in potato crisps: LWT – Food Science and Technology, v. 40, no. 6, p. 1066-107

15. Mestdagh, F., T. De Wilde, P. Castelein, O. Németh, C. Van Peteghem, and B. De Meulenaer, 2008a, Impact of the reducing sugars on the relationship between acrylamide and Maillard browning in French fries: European Food Research and Technology, v. 227, no. 1, p. 69-76