Acrylamide in Potato Crisps - A Three-year Study on Swedish-grown Potatoes

Abstract: Acrylamide, a probable human carcinogen, has been found at mg/kg levels, in heat-treated carbohydrate-rich foods. Acrylamide is formed via the Maillard reaction as a result of the reaction between the amino acid asparagine and reducing sugars (glucose and fructose). Potatoes contain relatively high levels of both asparagine and reducing sugars and therefore potato products such as crisps, French fries and roasted potatoes can contain high levels of acrylamide. However, the concentration of precursors can differ considerably not only between potato varieties but also with storage conditions. Acrylamide is formed in a number of foods, and until more is known about its role in human health, it is prudent to find means to prevent the formation of acrylamide in food with the aim of reducing its intake. The work described in this thesis has been focused on different potato varieties and their potential for acrylamide formation in crisps produced in a laboratory set-up intended to reproduce industrial full-scale production. Swedish-grown potatoes, Saturna, Hulda, SW (breeding clone SW91 102 from Svalöf Weibull, Sweden), Lady Rosetta and Bintje, from three years of harvest (2004-2006) were chosen for the experiments. The tubers were stored for up to 8 months at 4, 6 or 8°C. The potatoes covered a wide range of precursor concentrations: asparagine ranged from 2.1 to 15.3 mg/g dry matter and reducing sugars from 0.9 to 23.7 mg/g dry matter. Acrylamide was formed at temperatures above 100°C, when crust formation starts on the dry surface. The yield of acrylamide was small, below 0.4% on a molar basis. The acrylamide content in the crisps increased with frying time, however, prolonged heating reduced the acrylamide content, but those crisps were not edible. The acrylamide content varied significantly between crisps made from the different potato varieties, from 300 µg/kg up to more than 10,000 µg/kg. Crisp colour was measured and related to the acrylamide content; the darker the crisps the more acrylamide. Kinetic modelling was used to predict acrylamide content in the crisps; different parameters were needed for different potato varieties. Seasonal growing conditions affected the concentrations of precursors and consequently the acrylamide content. The contents of reducing sugars varied during storage and were significantly higher in potatoes stored at 4°C than at 8°C. The content of acrylamide in crisps made from 4°C was therefore higher. The content of asparagine varied somewhat during storage and was generally highest in potatoes stored at 4°C. Asparagine influenced the acrylamide formation to a higher degree than has been shown earlier: low contents of asparagine resulted in lower levels of acrylamide in the crisps at similar contents of reducing sugars. The correlation between acrylamide and reducing sugars was r=0.75-0.86, while the correlation between acrylamide and the product of reducing sugars and asparagine was r=0.90-0.95. Blanching the potato slices before frying decreased the levels of precursors. Blanching was an efficient way of reducing the acrylamide content; blanched crisps contained 51-73% less acrylamide. Blanching resulted in similar acrylamide levels in crisps from potatoes stored 4°C to those in crisps from un-blanched potatoes stored at 8°C. The results of the present study indicate several factors that are important in minimising the content of acrylamide in crisps, such as choice of potato variety, storage conditions, and control of precursor content and frying time. The results can be used for the design of processing techniques and equipment, but also as a basis for recommendations to retailers, catering business and home-cooking. More investigations are, however, needed to increase our knowledge concerning the transport of precursors to the surface, the reaction activity of the precursors and their capacity to form acrylamide to further reduce acrylamide formation. Such studies are motivated by both food quality and food safety aspects.