Acrylamide in potato crisp—the effect of raw material and processing

Reducing sugars and free amino acids were analysed in slices from three potato cultivars before and after blanching (0-3 min). The potato crisps were deep fried at 185 °C for different times (3-8.5 min), and analysed for the concentration of acrylamide (AA) and moisture. Potato cultivar and the temperature during processing were important parameters for AA formation in potato crisps. The amount increased with an increase in the processing time. Blanching before deep-frying reduced the concentration of free asparagine and reducing sugar in the raw material. We found no effect of blanching as pretreatment on the concentration of AA in the potato crisps. Any relationship was not detected between the levels of asparagine in the different cultivars, before and after blanching, and the formation of AA in the crisp products. However, it was shown that the content of reducing sugars determined the level of AA after frying.     

The influence of variety, agronomical factors and storage on the potential for acrylamide formation in potatoes grown in Norway

Freeze-dried potato samples were obtained from the varieties Saturna and Peik that had been subjected to different agronomic conditions and storage. Powdered samples originating from the same growth year were mixed with oil and heated simultaneously in a stone oven in order to study the potential for acrylamide (AA) formation in a fixed time and temperature situation. For baked samples originating from unstored potato a linear relationship was found between asparagine (Asn) and reducing sugar (RS) content and AA formation. For these samples the AA content varied linearly with a* except from samples that originally were high or low in Asn. Upon storage the correlation between the quantity of the common precursors, Asn and RS, and AA were smaller. Results of the baking experiments suggest that the AA potential for stored potato cannot be predicted from RSs and Asn alone, and that other factors that might change during storage are of importance. Due to north European conditions the RSs might not always be the limiting substrate for AA formation. Additional information for the precursor content in 2004 and 2005 are included. No systematic effect on precursor contents related to chemical vine killing was observed. Precursor contents varied among and between varieties, different cultivation years and growth sites.     

Reduction of acrylamide formation in potato slices during frying

Reduction of acrylamide formation in potato chips was investigated in relation to frying temperature and three treatments before frying. Potato slices (Tivoli variety, diameter: 37 mm, width: 2.2 mm) were fried at 150°C, 170°C and 190°C until reaching moisture contents of ∼1.7 g water/100 g (total basis). Prior to frying, potato slices were treated in one of the following ways: (i) soaked in distilled water for 0 min (control), 40 min and 90 min; (ii) blanched in hot water at six different time-temperature combinations (50°C for 30 and 70 min; 70°C for 8 and 40 min; 90°C for 2 and 9 min); (iii) immersed in citric acid solutions of different concentrations (10 and 20 g/l) for half an hour. Glucose and asparagine concentration was determined in potato slices before frying, whereas acrylamide content was determined in the resultant fried potato chips. Glucose content decreased in ∼32% in potato slices soaked 90 min in distilled water. Soaked slices showed on average a reduction of acrylamide formation of 27%, 38% and 20% at 150°C, 170°C and 190°C, respectively, when they were compared against the control. Blanching reduced on average 76% and 68% of the glucose and asparagine content compared to the control. Potato slices blanched at 50°C for 70 min surprisingly had a very low acrylamide content (28 μm/kg) even when they were fried at 190°C. Potato immersion in citric acid solutions of 10 and 20 g/l reduced acrylamide formation by almost 70% for slices fried at 150°C. For the three pre-treatments studied, acrylamide formation increased dramatically as the frying temperature increased from 150°C to 190°C.     

Optimization of the blanching process to reduce acrylamide in fried potatoes

A central composite design was used to study the effect of blanching time and temperature on the extraction of reducing sugars from potato strips and slices. After frying, the impact of both factors on the acrylamide content in French fries and potato crisps was evaluated. Acrylamide could be lowered more efficiently in potato crisps compared to French fries, due to a more pronounced extraction of sugars from potato slices upon blanching. In both products, blanching temperature was the main influencing factor for sugar extraction and subsequent acrylamide mitigation. Blanching at temperatures of about 70 °C for a short period of time (about 10 min) was more efficient compared to blanching at lower temperatures, which appeared more time-consuming. However, the extraction efficiency of reducing sugars was over 10% lower when the potato cuts were blanched in water which was previously used for blanching, leading to over 10% less reduction in the final acrylamide content.     

Impact of the reducing sugars on the relationship between acrylamide and Maillard browning in French fries

The relationship between acrylamide content and Maillard browning in French fries was studied as a function of different glucose/fructose ratios in the raw product using several colour measurement methods. An exponential correlation was found between acrylamide formation and surface colour, as evaluated by the parameters a*, delta E and Agtron. As a consequence, small differences in product colour could result in more pronounced differences in acrylamide contamination. This relationship however appeared to be dependant upon the glucose/fructose ratio of the raw material. An excess of fructose compared to glucose stimulated acrylamide formation to a higher extent than Maillard browning. The opposite effect was established with an excess of glucose. In addition, a linear relationship was found between the absorbance of aqueous French fries extracts and acrylamide content, which moreover appeared to be less affected by the addition of extra reducing sugars prior to frying. To predict acrylamide formation, sugar analysis however remains an important instrument and is complementary to surface colour measurement.     

Effect of natural extracts on the formation of acrylamide in fried potatoes

The objective of the present work was to evaluate the effect of natural extracts on the formation of acrylamide in fried potatoes. The aqueous extracts used were obtained from wild oregano (Origanum vulgare), thyme (Thymus vulgaris), cinnamon (Cinnamomum verum), bougainvillea (Bougainvillea spp) and green tea (Camellia sinensis), which presented a high percentage of free radical inhibition (DPPH) (48–99%) and content of total phenolic compounds (205–547 μg EAG/μg of d.w.). Potatoes were submerged in the antioxidant extracts at a concentration of 1 g/L for 1 min, before being fried and their acrylamide concentration quantified by GC–MS. The extracts from green tea, cinnamon and oregano reduced the acrylamide level by 62%, 39% and 17%, respectively. The potatoes submerged in cinnamon and bougainvillea extracts showed differences in the color parameters compared to the control potatoes (P < 0.05); however, no significant differences (P > 0.05) were found in the texture and the peroxide values. The sensorial evaluation showed that the acceptance of the potatoes was not affected by the treatment applied. Thus, we can conclude that pre-treating potatoes with antioxidants before frying produces beneficial effects such as a reduction in acrylamide content, without any significant changes in their physicochemical, sensorial and textural properties.     

A methodology for evaluating the formation and human exposure to acrylamide through fried potato crisps

Potato crisps are a popular snack food which have been implicated as a potential source of acrylamide. This study develops a farm-to-fork human exposure assessment model for acrylamide in fried potato crisps for Irish consumers. The model used Monte Carlo simulation techniques to model the various stages from on farm production of potatoes, storage, processing, crisp production and final human consumption of potato crisps. A baseline model is created and a number of scenarios are subsequently created to look at the impact of different model assumptions and input parameters. The baseline model found that the mean level of acrylamide in potato crisps in Ireland was 720 μg/kg. Irish consumer exposure to acrylamide in potato crisps was estimated to be 0.052 and 0.064 μg/kg bw/day for males and females, respectively. A sensitivity analysis revealed the important parameters influencing the model predictions. The initial level of reducing sugars was found to be the most important parameter (correlation coefficient 0.58 and 0.57 for glucose and fructose, respectively), highlighting the importance of selecting cultivars with low reducing sugar levels for crisp production. The cooking regime had a significant impact on model predictions, highlighting the need for further research into the impact of different time and temperature combinations. Blanching and soaking of potatoes were also identified as important risk reduction processes.     

Effects of sulphur nutrition during potato cultivation on the formation of acrylamide and aroma compounds during cooking

Lack of sulphur nutrition during potato cultivation has been shown to have profound effects on tuber composition, affecting in particular the concentrations of free asparagine, other amino acids and sugars. This is important because free asparagine and sugars react at high temperatures to form acrylamide, a suspect carcinogen. Free amino acids and sugars also form a variety of other compounds associated with colour and flavour. In this study the volatile aroma compounds formed in potato flour heated at 180 °C for 20 min were compared for three varieties of potato grown, with and without sulphur fertiliser. Approximately 50 compounds were quantified in the headspace extracts of the heated flour, of which over 40 were affected by sulphur fertilisation and/or variety. Many of the 41 compounds found at higher concentrations in the sulphur-deficient flour were Strecker aldehydes and compounds formed from their condensation, whereas only one compound, benzaldehyde, behaved in the same way as did acrylamide and was found at higher concentrations in the sulphur-sufficient flour. The reasons for these effects are discussed.     

减少高温加工食品中丙烯酰胺含量的几种方法

原料中还原糖、天冬酰胺含量及加工温度是影响食品中丙烯酰胺形成的主要因素。减少原料中的还原糖或天冬酰胺含量及降低加工温度能显著降低食品中丙烯酰胺的含量。本文概述了几种减少高温加工食品中丙烯酰胺含量方法的研究进展。     

Interaction effects of fermentation time and added asparagine and glycine on acrylamide content in yeast-leavened bread

The interaction effects of fermentation time and added asparagine and glycine on acrylamide precursors (asparagine and reducing sugars) in dough and content of acrylamide in yeast-leavened wheat bread were studied. Two experiments, with low and high levels of added asparagine (0–0.044 and 0.071–0.476 g/100 g flour, respectively), were performed. Glycine was added (0.042–0.380 g/100 g flour) only in the high asparagine addition experiment. The fermentation time, which was varied between 13 and 164 min, showed a reducing effect on acrylamide precursors in the dough in both experiments (p < 0.001). These effects of fermentation were more pronounced in the experiment with low asparagine levels, which resembled levels in ingredients. In contrast, fermentation time did not affect the content of glycine in the dough. Added asparagine increased the levels of asparagine in dough and of acrylamide in bread (p < 0.001). A strong correlation was found between the contents of asparagine in the fermented dough and acrylamide in breads at all levels of asparagine. Glycine significantly increased the colour intensity and reduced the acrylamide in bread (p < 0.001) with the latter effect being dependent on the level of asparagine.     

Use of unusual storage temperatures to improve the amino acid profile of potatoes for novel flavoring applications

To investigate the potential of potato culls as a source of novel flavorings, free amino acid profiles of juice from tubers stored at 0°C, 12°C or 24°C were analysed by gas chromatography/mass spectrometry after separation on cation exchange resin and derivatization with N-methyl-t-butyl-dimethyl-silyl-trifluoroacetamide. Juices were also incubated for 42 h with or without a commercial protease for comparison. Storage at all three temperatures increased glutamine concentration. The relative percentages of asparagine and glutamine decreased while several other amino acids increased in the juice of potatoes stored at 0°C and 24°C. Small shifts in free amino acid profile, increasing alanine, valine, aspartic acid, asparagine and arginine levels, were obtained by incubating juice from potatoes stored at 0°C without added protease while the protease produced substantial increases but with emphasis on leucine and isoleucine and phenylalanine, which increased bitterness. Since storage alone increased the concentration of single amino acids such as alanine, methionine and phenylalanine by several fold, it may be the preferred means of improving potato culls for novel flavor applications where bitterness must be minimized.     

Kinetic modelling: A tool to predict the formation of acrylamide in potato crisps

Three empirical models were used to fit the formation of acrylamide in crisps of three different cold-sweetened potato genotypes, fried under the same experimental conditions. Statistical methods were used to compare the performance of the models, with the “Logistic-Exponential” model performing the best. The obtained model parameters for the formation of acrylamide showed improvement in precision compared to an earlier study, the precision of the parameter estimates for the degradation of acrylamide was still problematic. Nevertheless, the predictive capacity of the “Logistic-Exponential” model was tested, as this model showed a strong correlation between parameter a and the reducing sugar content of the raw potato. The predictions from this model for the formation of acrylamide in potato crisps were close to earlier reported experimental values. Therefore, the use of the “Logistic-Exponential” model as a tool to predict acrylamide in potato crisps seems promising and should be developed further.     

Evaluation of acrylamide formation in potatoes during deep-frying: The effect of operation and configuration

It is nowadays well known that heating, which is carried out to improve the hygienic, sensory and nutritional properties of foods, can be also responsible for the development of acrylamide. Acrylamide levels between a few ppb and in excess of 1000 ppb have been found in many heated foods. As acrylamide is classified as a probable human carcinogen, the knowledge of critical processing variables leading to its formation is needed to ensure safety requirements.     

Reduction of acrylamide formation by vanadium salt in potato French fries and chips

The effects of vanadyl sulphate on the formation of acrylamide have been studied in fried potato products, such as French fries and chips. Acrylamide formation was inhibited by 30.3%, 53.3% and 89.3% when the sliced potato strips were soaked in 0.001, 0.01 and 0.1 M vanadyl sulphate (VOSO₄) solutions, respectively, for 60 min before frying. Moreover, 57.7%, 71.4% and 92.5% inhibition of acrylamide formation was observed when chips were soaked in the respective vanadyl sulphate solution before frying. In a separate model reaction, a solution containing an equimolar concentration of l-asparagine and d-glucose showed a significant inhibition of acrylamide formation when heated at 150 °C for 30 min in the presence of vanadyl sulphate (VOSO₄). The results indicate that the binding of VO²⁺ to asparagine and the decrease in the pH of the potato samples resulted in a significant reduction of acrylamide formation in fried potato products.     

Impact of chemical pre-treatments on the acrylamide formation and sensorial quality of potato crisps

Several components were added to the blanching water of potato crisps. Calcium ions, sodium acid pyrophosphate, citric, acetic and l-lactic acid significantly reduced the final acrylamide content, as well as free glycine and l-lysine. The acids, NaCl and calcium-containing additives also lowered the oil absorption, which may have led to a reduced heat transfer and acrylamide contamination in the final product. Textural and compositional product changes may thus also influence acrylamide formation. By means of sensory analyses of these crisps, a successful combination was demonstrated between acrylamide mitigating treatments and crisps of acceptable or even superior product quality, compared to control crisps blanched in water. However, the applied components and concentration levels should be well chosen in order not to generate product-foreign flavours or undesired product colour.     

Impact of additives to lower the formation of acrylamide in a potato model system through pH reduction and other mechanisms

The impact on acrylamide formation of several additives was investigated as well as the mechanisms behind it. In a potato powder model system, sodium acid pyrophosphate, citric, acetic and l-lactic acid significantly reduced the final acrylamide content, merely due to the lowering of the pH. Free glycine, l-lysine and l-cysteine also lowered acrylamide, while keeping the pH at its original level. l-glutamine increased the formation of acrylamide. A synergistic acrylamide lowering effect was observed, adding citric acid and glycine or l-lysine to the model system. Yet, a combination of these amino acids with acetic acid appeared to induce a restricted antagonistic acrylamide lowering effect. Calcium and magnesium ions induced a supplementary acrylamide reduction in addition to a lower pH of the food matrix. No lowering effect was however observed upon NaCl addition to the model system.     

Acrylamide content in fried chips prepared from irradiated and non-irradiated stored potatoes

The content of reducing sugars and asparagine, responsible for the formation of acrylamide, was determined in eight Indian potato varieties. Among these, Kufri chipsona-2 and Kufri lavkar showed the lowest level of reducing sugar (680.68 ± 56.50 mg/kg) and asparagine (2074.36 ± 122.27 mg/kg), respectively. The acrylamide content in potato chips prepared from Kufri chipsona-2, the variety that is used commercially in India for making potato chips was also the lowest. Irradiation of this variety of potatoes at the sprout inhibition dose of 60 Gy and subsequent storage for six months showed a 10.7% lower content of reducing sugars at both 14 and 4 °C. The acrylamide content was 8.41% and 6.95% lower in chips from irradiated potatoes stored at 14 and 4 °C than the corresponding non-irradiated controls. The colour of the chips was also better in irradiated potatoes as judged from the L∗ and a∗ values.     

The effect of asparaginase on acrylamide formation in French fries

Acrylamide formation in French fries was investigated in relation to blanching and asparaginase soaking treatments before final frying. Par-fried potatoes of Bintje variety were prepared by cutting strips (0.8 × 0.8 × 5 cm) which were blanched at 75 °C for 10 min. Unblanched strips were used as the control. Control or blanched strips were then dried at 85 °C for 10 min and immediately partially fried at 175 °C for 1 min. Finally, frozen par-fried potatoes were fried at 175 °C for 3 min to obtain French fries. Pre-drying of raw or blanched potato strips did not generate acrylamide formation as expected. Partial frying of pre-dried control potato strips generated 370 μg/kg of acrylamide and the final frying determined French fries with 2075 μg/kg of acrylamide. When control potato strips were treated with a 10000 ASNU/l asparaginase solution at 40 °C for 20 min, the acrylamide formation in French fries was reduced by 30%. When blanched potato strips were treated in the same way, the produced French fries have 60% less acrylamide content than blanched strips without the enzyme treatment. Soaking of blanched potato strips (75 °C, 10 min) in an 10000 ASNU/l asparaginase solution at 40 °C for 20 min is an effective way to reduce acrylamide formation after frying by reducing the amount of one of its important precursors such as asparagine.