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.     

Legal limit for reducing sugars in prefabricates targeting 50 μg/kg acrylamide in French fries

A legal limit for the reducing sugars in the prefabricates for French fries is a simple and efficient measure to reduce the exposure to acrylamide from the predominant source for many consumers. The acrylamide content of French fries of comparable crispiness is approximately proportional to the concentration of the reducing sugars glucose and fructose in the potato sticks. On average, optimally prepared French fries from prefabricates with a (moderately low) sugar content of 0.3 g/kg contained 32 g/kg acrylamide. With 0.15 g/kg reducing sugar even severe overfrying at 170 °C only resulted in 90 g/kg acrylamide, i.e. a low sugar content keeps acrylamide low even under inappropriate frying conditions. In the prefabricates, the sugar content is about 10% lower than in the raw potato (resulting from the effects of blanching and prefrying). It is similar to that in the finished French fries, which enables one to distinguish whether a high acrylamide content in French fries results from high sugars in the raw material or unsuitable frying conditions. An average concentration of 50 g/kg acrylamide in French fries could be targeted by limiting the reducing sugars in the prefabricates to 0.7 g/kg and the frying temperature to 170 °C. Even considerable overfrying in terms of duration can be tolerated then.     

Important factors to consider for acrylamide mitigation in potato crisps using pulsed electric fields

This preliminary study aimed to compare the application of pulsed electric field (PEF) with a traditional blanching as pre-treatments before frying for the mitigation of acrylamide content in potato crisps.Measuring the degree of cell disintegration index (p_o) and the changes in water electrical conductivity during washing of potato slices, PEF protocol and sample preparation scheme were optimized. Peeled potato slices (thickness 1.5 ± 0.2 mm) were subjected to PEF (1.5 kV/cm, pulse duration 10 μs, total treatment time 10 ms, pulse frequency 100 Hz) and to blanching (85 °C for 3.5 min) pre-treatments and then to washing in water, evaluating the reduction of acrylamide precursors (reducing sugars and free asparagine). After frying (175 °C, 3 min), product quality, in terms of colour, texture and acrylamide content were evaluated. Results showed that PEF promoted acrylamide precursors leaching followed by a reduction of the final acrylamide content of around 30%, significantly higher if compared to the reduction obtained with blanching, with only slight modifications of the final quality of the product, in terms of colour and texture.Industrial relevanceThe Commission Regulation (EU) 2017/2158 of 20 November 2017 has introduced new benchmark levels and mitigation strategies for the reduction of the presence of acrylamide in foods, directing food businesses to the research of measures to lower the acrylamide formation in foods. The actual industrial production process of fried potato crisps involves the use of many mitigation strategies, such as a blanching of raw potatoes. However, the traditional blanching treatment presents several practical drawbacks and leads to undesirable changes of the product quality. The application of PEF as a pre-treatment could reduce the acrylamide content in deep-fat fried potato crisps. This preliminary study gives important indications regarding the possibility of combining a PEF pre-treatment on raw potato slices with subsequent industrial processing steps for the production of potato crisps with low acrylamide concentration.     

French fries with less than 100 μg/kg acrylamide. A collaboration between cooks and analysts

In collaboration with cooking experts, the preparation of French fries in oil and in ovens was optimized, aiming at optimum culinary quality combined with a minimum acrylamide content. French fries with 40–70 g/kg acrylamide were consistently produced, i.e. with 5–10 times less acrylamide than currently normal. The raw potato should contain little reducing sugars, i.e. be of a suitable cultivar, and storage at temperatures below about 10 °C must be avoided. After cutting and elimination of the fines, the potato is immersed in standing cold or boiler-warm water for some 15 min in order to extract asparagine and sugars from the surface without washing out the starch. Pre-frying in oil (ca. 140 °C for 2.5 min) improves crispiness. Frying should occur at an initial oil temperature of about 170 °C, adding some 100 g potato/l oil. Since acrylamide formation increases exponentially towards the end of the process, the most important factor to keep acrylamide contents low is the determination of the proper end point of the frying process. French fries should be crispy with slight browning of the tips to achieve the typical flavor, but without general browning. Preparation in the oven, starting from frozen prefabricates, requires temperatures of around 190 °C or 220 °C, depending on whether or not the air is circulated. The proper determination of the end point is again the most critical step.     

Effects of combined pulsed electric field and blanching pretreatment on the physiochemical properties of French fries

The aim of this work was to explore the effect of combining pulsed electric field (PEF) with blanching pretreatment on the physiochemical properties of French fries. The effects of PEF plus blanching pretreatment on the color parameters, texture, content and spatial distribution of moisture and oil, microstructure, colony count and acrylamide content of French fries were investigated. Results showed that the pretreated French fries were brighter (L value was 60.44) and golden yellow, with lower hardness (312.27 g), higher springiness (0.81) and higher chewiness (119.71). In addition, moisture and oil contents of the fries were reduced, with more uniform distributions. The cross-section microstructure of these French fries also showed near-complete gelatinization of starch particles, and the internal structure of fries was fluffy. Finally, French fries obtained by the combined pretreatment had an improved food safety profile, with a lower colony count (13 CFU/g) and acrylamide content (1533.75 ng/g).Industrial relevanceBlanching is a traditional thermal processing technology widely used in the field of fried potatoes. However, blanching has some disadvantages such as slow heat conduction, long processing time, substantial loss of soluble nutrients, and huge water wastage. PEF is an emerging technology in the 21st century that can maintain the original flavor, color, taste, and nutritional value of foods treated by it. The French fries obtained by combining PEF and blanching pretreatment were brighter and golden yellow, and were also softer, and more springy and chewy – an overall net improvement in aesthetic appeal and organoleptic profile. The above findings may provide useful information to guide effective strategies for the practical application of PEF combined with blanching in the preparation of fried potato foods.     

Is lowering reducing sugars concentration in French fries an effective measure to reduce acrylamide concentration in food service establishments?

The objective of this study was to obtain insight into the actual effectiveness of lowering reducing sugars concentration in par-fried potato strips on the concentration and variation of acrylamide in French fries prepared in real-life situations in food service establishments. Acrylamide, frying time, frying temperature, and reducing sugars were measured and characteristics of fryers were recorded. Data showed that the use of par-fried potato strips with lower concentrations of reducing sugars than the commonly used potato strips was an effective measure to reduce acrylamide concentrations in French fries prepared under standardised frying conditions. However, there was still large variation in the acrylamide concentrations in French fries, although the variation in reducing sugars concentrations in low and normal types of par-fried potato strips was very small and the frying conditions were similar. Factors that could affect the temperature-time profile of frying oil were discussed, such as setting a lower frying temperature at the end than at the start of frying, product/oil ratio and thawing practice. These need to be controlled in daily practice to reduce variation in acrylamide.     

油炸马铃薯片中丙烯酰胺形成的影响因素的研究

丙烯酰胺是富含碳水化合物和氨基酸的食品经高温加热发生美拉德反应而产生的,但有关影响丙烯酰胺形成因素的研究却较少。探讨了油炸温度、原料中还原糖和氨基酸含量、鲜薯切片浸泡液的柠檬酸浓度、油炸前薯片的水分含量及抗氧化剂和油的使用时间对丙烯酰胺形成的影响。结果表明:原料中还原糖和氨基酸含量越高,产品中生成的丙烯酰胺就越多;油炸温度越高,产品中丙烯酰胺含量也相应越高;浸泡液柠檬酸浓度越大,产品中丙烯酰胺含量越低;而随着半成品中含水量的降低,产品中的丙烯酰胺含量也逐渐减少;在油中添加不同浓度的BHT和TBHQ以及采用使用时间不同的油,对加工出来的薯片之间丙烯酰胺含量没有显著的影响。     

Effective quality control of incoming potatoes as an acrylamide mitigation strategy for the French fries industry

The correlation between sugar levels in raw material (potatoes), brown colouring and formation of acrylamide in French fries was investigated. The objective was to identify incoming potatoes (raw material) with a high potential for acrylamide formation. Ten different potato varieties commonly used in the Western European French fries industry were stored at 8°C and samples were taken throughout the storage time. The current quality control used in the French fries industry for incoming potatoes is poorly correlated with acrylamide in the final product (r = 0.74). Changing the quality control parameter from colour to reducing sugars in raw material did not improve the correlation (r = 0.72). The best correlation was obtained with the Agtron colour measurement after blanching and a two-stage frying (r = ?0.88). It was concluded that alternative entrance control measurements could provide better mitigation of the acrylamide issue in French fries from the start of production. These alternatives, however, are less cost-effective and more difficult to implement.     

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.     

Acrylamide monitoring in Switzerland, 2007–2009: results and conclusions

Parallel to the European Union acrylamide monitoring for the years 2007–2009, Switzerland performed its own monitoring, covering the whole range of products that significantly contain acrylamide (almost 300 samples per year), but focusing on those products that may result in high exposure. As reducing sugars are critical for potato products, these were included. No significant change, particularly improvement, was noticed, especially regarding those products for which substantial potential for improvement is known. ‘Western-style’ French fries continued to contain some four times more reducing sugars than ‘traditional’ fries, with correspondingly higher acrylamide in the finished product. The supply of raw potatoes low in reducing sugars by retail shops needs improvement, but there seemed to be insufficient willingness on a voluntary basis. A foreign producer was successful in penetrating the Swiss market with special potato chips containing up to 7000 µg kg^?1 acrylamide and only harsh measures could stop this. Three of about 61 products in the group of bakery ware showed a marked improvement. But there was also a store brand cracker that competed with a leading brand which contained 15 times more acrylamide (845 µg kg^?1). Cereals contained 1080 µg kg^?1 acrylamide and even a warning did not prompt the producer to sell substantially better products one year later. It seems that only measures by the authorities will achieve improvements. The following seem promising: a limit for reducing sugars in prefabricates for French fries; the improved supply of raw potatoes low in sugars for roasting and frying; a legal limit for acrylamide content in potato chips; a general provision that products must not contain substantially more acrylamide than achievable by good manufacturing practice; and fryers with a temperature profile from an initial high to a lower final value.     

Effects of potato strip size and pre-drying method on french fries quality

Potato strips of 8 mm × 8 mm and 10 mm × 10 mm after blanching were pre-dried using two methods: convective and vacuum-microwave (VM). A two-stage frying in rapeseed oil was applied to prepare French fries from pre-dried potato strips. The quality of French fries in terms of texture, oil content and color was analyzed based on the results from instrumental tests and sensory evaluation. Using vacuum-microwave instead of hot air resulted in substantial shortening of the potato strips’ pre-drying time and decreasing the fat content in French fries. Pre-drying of potato strips, particularly by VM method, improved color and increased maximum cutting force as well as maximum cutting work estimated for French fries. French fries prepared from potato strips of 10 mm × 10 mm exhibited lower lightness, higher fat content and higher cutting strength compared with those made from potato strips of 8 mm × 8 mm. Based on the sensory results, it was found that the best French fries were those from pre-dried potato strips of 8 mm × 8 mm, independently of the pre-drying method used, and the worse were those from potato strips of 10 mm × 10 mm pre-dried with the convective method. SEM images confirmed structural changes occurred in potato tissue during pre-drying and frying.     

Higher acrylamide contents in French fries prepared from “fresh” prefabricates

A recent campaign indicated that French fries prepared from fresh prefabricates stored at about 4 °C had a double acrylamide content compared to those from frozen products. During storage at 4 °C, reducing sugars were liberated which enhance acrylamide formation. Even with boiling water, blanching did not completely inactivate the alpha amylase. Pre-frying was more effective, but conditions of 170 °C/60 s, as often applied, were still only at the borderline of suppressing liberation of reducing sugar. It is concluded that processing conditions of fresh prefabricates for potato products like French fries and roasted or baked products should be revisited to prevent liberation of reducing sugar during storage and enhanced acrylamide formation.     

Ultrasonic-assisted leaching of glucose and fructose as an alternative mitigation technology of acrylamide and 5- hydroxymethylfurfural in potato chips

The effect of ultrasound (480 W, 40 kHz) on the leaching of reducing sugars during the water soaking of potatoes slices (60, 70 and 80 °C- 1, 8 and 15 min) was investigated to reduce the formation of acrylamide (AA) and 5-hydroxymethylfurfural (5-HMF) in potato chips.Ultrasound (US) influenced abruptly the reducing sugar leaching during the first 15 min, significantly increasing their extraction rate (glucose: 60%, fructose: 30%) at all evaluated temperatures. When potato slices were treated with US, the formation of AA (~95%) and 5-HMF (~96%) were reduced significantly after frying. Although AA content did not correlate with glucose and fructose concentrations, 5-HMF did (r²: 0.80 and 0.83, respectively), probably because reducing sugars are their main precursors. The AA and 5-HMF concentrations of potato chips presented good correlation coefficient (r²:0.76), suggesting the use of 5-hydroxymethylfurfural as an acrylamide indicator for potato chips.     

Acrylamide reduction in potato chips by using commercial asparaginase in combination with conventional blanching

In this research acrylamide reduction in potato chips was investigated in relation to blanching and asparaginase immersion treatments before final frying. Potatoes slices (Verdi variety, diameter: 40 mm, thickness: 2.0 mm) were fried at 170 °C for 5 min (final moisture content of ∼2.0 g/100 g). Prior to frying, potato slices were treated in one of the following ways: (i) Rinsing in distilled water (control I); (ii) Rinsing in distilled water plus blanching in hot water at 85 °C for 3.5 min; (iii) Rinsing in distilled water plus immersion in an asparaginase solution (10000 ASNU/L) at 50 °C for 20 min; (iv) Rinsing in distilled water plus blanching in hot water at 85 °C for 3.5 min plus immersion in an asparaginase solution (10000 ASNU/L) at 50 °C for 20 min; (v) Rinsing in distilled water plus blanching in hot water at 85 °C for 3.5 min plus immersion in distilled water at 50 °C for 20 min (control II). Blanching in hot water (ii) was almost as effective as asparaginase potato immersion (iii) in order to diminish acrylamide formation in potato chips (acrylamide reduction was ∼17% of the initial acrylamide concentration). When potato slices were blanched before asparaginase immersion, the acrylamide content of the resultant potato chips was reduced considerably by almost 90%. We have demonstrated that blanching of potato slices plus asparaginase treatment is an effective combination for acrylamide mitigation during frying. It seems to be that blanching provokes changes in the microstructure of potato tissue leading to an easier and more effective diffusion of asparaginase.     

Structural changes and shrinkage of potato during frying

Summary Light microscopy was used to study changes in cell size, blister formation and crust evolution during potato frying. Frying experiments with both French fries and crisps of different thickness (1–5 mm) were performed at temperatures of 140 and 180 °C. Thickness, volume and density changes were also measured. The formation of crust in French fries starts after the potato surface reached approximately 103 °C, and then the crust thickness increased linearly with the square root of frying time, this increase being faster at 180 °C. The potato volume decreased during frying, although in the late stages the volume may increase because of oil uptake and cell separation caused by entrapped water vapour. Shrinkage was adequately described by the Weibull model with a residual value, with shrinkage rate increasing with temperature and decreasing with potato thickness. The residual volume was not affected by temperature (65% for French fries and 59–30 for crisps, depending on thickness). Volume appeared to decrease mainly as the result of water loss, except for very low water content, and thus potato density changes were very small.     

Reduction of acrylamide formation by selected agents in fried potato crisps on industrial scale

Great interest and rapid research efforts on acrylamide in foods followed an announcement in April 2002 by the Swedish National Food Authority and the University of Stockholm. Reduction of acrylamide in high-temperature processing foods, including selection of the raw material and variation of processing parameters, etc. were extensive reported. In this research, effect of some agents on acrylamide formation was investigated. A glucose-asparagines reaction model system was used to test the effect of ferulic acid, catechin, CaCl₂, NaHSO₃, and l-cysteine on inhibition of acrylamide formation and three efficient inhibitors, NaHSO₃, CaCl₂ and l-cysteine were screened. The results showed that immersing of the fresh potato chips using different concentration of the agents greatly inhibited acrylamide formation in fried potato crisps, and the efficiency increased as their concentrations increased; among them, l-cysteine is the most efficient agent but CaCl₂ is most potential. Effects of these food additives on the texture of fried potato crisps were also studied. It was found that l-cysteine showed little effect on the texture of the crisps and CaCl₂ is regarded as the suitable choice because of its low price and the acceptable mouth feel of fried crisps treated by CaCl₂, although it increased the brittleness. Moreover, the application of CaCl₂ in industrial production of fried potato crisps was also studied. In the blanching process (deactivation process of enzymes at 85 °C), a computerized electrical conductivity detector was used to keep the concentration of CaCl₂ at constant and the result showed that immersion of potato slices in CaCl₂ solution at 5 g/L reduced acrylamide formation by more than 85% in fried crisps.Industrial relevanceThis research presents a technology to inhibit acrylamide formation in fried potato chips by immersion of fresh potato chips with some food additives. The approach suggested that cysteine and calcium chloride significantly decreased the content of acrylamide in fried potato chips and their concentrations could be kept constant by using a conductor as a detector.     

A survey of acrylamide precursors in Irish ware potatoes and acrylamide levels in French fries

Reducing sugars (glucose and fructose) and asparagine levels in three varieties of Irish ware potatoes (Rooster, Record and Oilean) on sale in a local supermarket were monitored over an 11-month period. Samples were processed into French fries using conditions similar to those used for home preparation of fries and acrylamide levels in a selection of samples were measured. A wide range of total reducing sugar levels (fructose+glucose) were observed over the course of the study with values ranging from 152-12,286, 301-8812 and 279-7881 μg/g FW for the Rooster, Record and Oilean varieties, respectively. This resulted in high levels of acrylamide in some samples (up to 2970 μg/kg). In comparison to reducing sugars, asparagine contents were relatively constant for the three varieties and no particular trend in asparagine levels was noted. Both fructose and glucose contents of the tubers were positively correlated with acrylamide content (r=0.809, 0.776, respectively, P<0.001). A negative relationship between Hunter L values and acrylamide content of the French fries was observed (r=−0.712, P<0.001) indicating that L values could serve as a convenient and reliable indicator of acrylamide levels in French fries.     

Development and experimental validation of a frying model to estimate acrylamide levels in French fries

ABSTRACT:  In this study, a numerical model was developed to simulate frying of potato strips and estimate acrylamide levels in French fries. Heat and mass transfer parameters determined during frying of potato strips and the formation and degradation kinetic parameters of acrylamide obtained with a sugar–asparagine model system were incorporated within the model. The effect of reducing sugar content (0.3 to 2.15 g/100 g dry matter), strip thickness (8.5 × 8.5 mm and 10 × 10 mm), and frying time (3, 4, 5, and 6 min) and temperature (150, 170, and 190 °C) on resultant acrylamide level in French fries was investigated both numerically and experimentally. The model appeared to closely estimate the acrylamide contents, and thereby may potentially save considerable time, money, and effort during the stages of process design and optimization.     

Acrylamide Mitigation in Potato Chips by Using NaCl

In April 2002, Swedish researchers shocked the world when they presented preliminary findings on the presence of acrylamide in fried and baked foods, most notably potato chips and French fries, at levels of 30–2,300 ppb. The objective of this research was to study the effect of immersing potato slices in a NaCl solution over the acrylamide formation in the resultant potato chips. Potato slices (Verdi variety, diameter 40 mm, width 2.0 mm) were fried at 170 °C for 5 min (final moisture content of ∼2.0%). Prior to frying, the potato slices were treated in one of the following ways: (1) control slices (unblanched or raw potato slices); (2) slices blanched at 90 °C for 5 min in water; (3) slices blanched at 90 °C for 5 min plus immersed in a 1 g/100 g NaCl solution at 25 °C for 5 min; (4) slices blanched at 90 °C for 5 min plus immersed in a 3 g/100 g NaCl solution at 25 °C for 5 min; (5) slices blanched at 90 °C for 5 min plus immersed in distilled water at 25 °C for 5 min; and (6) slices blanched at 90 °C for 5 min in a 3 g/100 g NaCl solution. Blanching followed by the immersion of potato slices in 1 g/100 g NaCl solution was effective in reducing acrylamide content in ∼62%; however, almost half of this percentage (∼27%) could be attributed to the effect of NaCl and 35% to the effect of the slight heating treatment during salt immersion step (25 °C for 5 min). Blanching seems to make the NaCl diffusion in potato tissue easier leading to a significant acrylamide reduction in the potato slices after frying.