The Effect of Oil Type on the Formation of Acrylamide in French Fries

Introduction: Acrylamide, also known as acrylic amide and prop-2-enamide, is a white, odorless, crystalline, water-soluble solid, with the chemical formula C3H5NO and relative molecular mass of 71.08. Acrylamide is classified by the International Agency for Research on Cancer (IARC) as a probable human carcinogen. Acrylamide is formed in some foods such as potato chips, French fries, and toast due to heating. French fries are one of the most popular products in the world; their texture characteristics and special taste are attractive to customers. The sensory attributes of French fries depend both on the raw material and technological parameters used for French fries production. A factor affecting the flavor and texture of French fries is the frying (temperature, time, and type of frying oil). They are widely consumed among teenagers and young people in the community, which makes this age group more exposed to the dangers of acrylamide. The major pathway leading to acrylamide formation in foods is a part of the Maillard reaction with free amino acid (Asparagine) and reducing sugars through the decarboxylation of the Schiff base in a Strecker-type reaction. Although the formation of acrylamide in foods has its major routes through asparagine and reducing sugars, several other formation routes are suggested via Acrolein and ammonia. Oil is one of the most important components in the preparation of French fries due to its heat transfer and effects on taste. Due to the use of oil at high temperatures for a long time, the deteriorative chemical processes of hydrolysis, oxidation, and polymerization occur. Finally, various compounds such as aldehydes, epoxides, hydroxy ketones, and decarboxylated compounds are formed; these compounds can be reacting with amino acids. Therefore, these compounds may react with the asparagine in potatoes and increase the concentration of acrylamide in fried potato products.
Materials and methods: 15 kg of Agria potatoes were prepared from the (SPI) Institute. Four kinds of oil (Sunflower oil, frying oil, and canola oil) were purchased from a chain store and soybean oil prepared from Korosh food industries. 1.5 liters of oil were poured into the fryer, the temperature reached 180°C and, stabilized. After 1 hour, 200 g of sliced potatoes (2×2×2 cm) was poured into the hot oil. Frying time was 5 min. Heated oil and fried potatoes were sampled for testing. The fryer remained on at 180°C. After 3 hours, the second sample of raw potatoes was fried for 5 min. The third and fourth samples were prepared 3 hours apart. GC-ECD method was used for acrylamide measurement. 2 g of sample and 20 ml of distilled water were poured into the Falcon tube. Then 3 ml of Carrez I, II solution was added to the solution and centrifuged at 5000 rpm. The water layer was discarded. Then 2 ml of hexane was added. The solution was centrifuged again. The hexane layer was discarded. 10 ml of the remaining solution was extracted with potassium bromide, bromic acid, and bromine water and injected into the GC. The fatty acid profile test was performed by ISIRI 13126 2 & 4 methods. ISIRI 4093 was used as a method for Peroxide value measurement. Anisidine and totox values are determined by methods defined in ISIRI 4093 was calculated by the ISIRI 4093 method. Data were verified by ANOVA variance analysis.
Results and discussion: According to the obtained results, values of total monounsaturated fatty acids are canola oil (%65.74), frying oil (%39.32), sunflower oil (%23.11), and soybean oil (%22.00). Also total polyunsaturated fatty were determined 65.41, 61.04, 26.21 and 43.99% for sunflower, soybean, canola and frying oils respectively. Oils containing polyunsaturated fatty acids (PUFAs) have less resistant to oxidation than monounsaturated fatty acids (MUFAs). Oxidative stability decreases with increasing number of double bonds. Accordingly, oleic acid has the highest thermal stability among unsaturated fatty acids, followed by linoleic acid and the lowest stability of linolenic acid. The results of peroxide, anisidine, and totox values determination showed that changes in these factors are affected by time (P<0.05). At most heating times, the highest values of peroxide were observed in soybean oil, and the lowest values were observed in frying oil (P<0.05). In all treatments by increasing of heating time, the amounts of anisidine and totox values increased significantly (P<0.05). The results of statistical analysis of different treatments indicated that in most heating times, the highest levels of anisidine and totox values and the lowest values were observed in soybean oil and canola oil respectively. Increased Peroxide value indicates that the level of the primary lipid oxidation products increased, which resulted in the formation of hydroperoxides. Peroxide and anisidine values indicate the rate of oxidation reactions at the beginning and the end of the process. In fact, the totox values simultaneously measures the amount of peroxides and their degraded products and provides a better estimate of the progress of oxidative degradation of oils and fats. Based on the results obtained from calculate of the totox value, the oxidation ratio of the studied oils was as follows:
Soybean oil > Sunflower oil > Frying oil > Canola oil.
According to the results, by increasing of heating time, the amounts of acrylamide in all treatments increased significantly (P<0.05). Therefore, the highest amounts of acrylamide were obtained in soybean oil and the lowest values were observed in canola oil (P<0.05). The correlation coefficient between totox value and acrylamide at different heating time was as follows: In the first hour of heating (R2 = 0.967), in the fourth hour of heating (R2 = 0.95), after 7 hours (R2 = 0.646) and in the tenth hour of heating was equal (R2 = 0.98), respectively. It shows that the levels of totox and acrylamide had a high correlation with each other and in fact the values of totox had a direct effect on the values of acrylamide.
Conclusion: The amounts of unsaturated fatty acids are effective in the oxidation of oils, and this effect is mostly due to double bonds. Oxidation of oils produces primary oxidation (hydroperoxides) that are degraded and secondary oxidation products such as aldehydes, ketones, and other might be produced. Secondary oxidation products in oil might be converted to acrylamide precursors in food without the presence of sugars, and by increasing the production of these products, more acrylamide might be formed. The results of this study showed that there is a high correlation between acrylamide in fried potato samples with the totox values in the oils. Therefore, the type of oil and heating duration influenced on formation of acrylamide in French fries.