Effect of microwave pre-thawing of frozen potato strips on acrylamide level and quality of French fries

The objective of this study was to reduce frying time, and hence acrylamide level of French fries by microwave pre-thawing of frozen potato strips. Effect of this pre-treatment on acrylamide content and quality attributes of French fries was determined. Frozen par-fried potato strips (8.5 × 8.5 × 70 mm) were thawed in a microwave oven prior to final frying in sunflower oil at 170, 180, and 190 °C. Potato strips that were final fried without pre-thawing were considered as the control. Acrylamide analysis was performed by liquid chromatography–mass spectrometry (LC–MS) method. Microwave pre-thawing of frozen strips reduced the acrylamide level of French fries by 10% (from 17.7 to 15.9 ng/g), 89% (from 72.1 to 8.0 ng/g), and 64% (from 50.5 to 18.4 ng/g) for frying at 170, 180, and 190 °C, respectively, in comparison to the control samples. Quality attributes (texture, color, and oil content) of pre-treated strips were found to be comparable to those of the control.     

Influence of the frying temperature on acrylamide formation in French fries

It is well established that high oil temperatures during frying strongly increase acrylamide formation in French fries, but it is less clear, which temperature or rather which part of a temperature profile is relevant and if rules or regulatory measures should be established in respect of frying temperature, on which temperature they should refer. In most fryers, the oil temperature strongly drops on adding the potato sticks and may not fully recover up to the end of the frying process (depending on the amount of potato added in relation to the volume of oil and the heating power of the fryer). Since acrylamide is formed towards the end of frying, the temperature during the second half of the process is more important than that regulated by the thermostat. The profile of the frying temperature was optimized regarding product quality (crispness, flavor) and acrylamide formation. An initial temperature of 170–175 °C dropping to 140–145 °C and a virtually isothermal frying at 160 °C resulted in products of similar quality and acrylamide content. At initial temperatures below 160 °C and with main frying temperatures below 140 °C, crispness and the flavor of the French fries suffered: the sticks dried out and became oily. Isothermal frying at 167–170 °C resulted in approximately doubled acrylamide content compared to conditions that were optimal in respect of culinary quality and low acrylamide formation, showing that rules on the initial temperature alone are inadequate to ensure low acrylamide contents. Optimized fryers should program temperature: allowing an initial temperature drop, but then efficiently heating to prevent the temperature dropping below a given limit; after the end of frying, the initial temperature must be restored before frying the next portion.     

Effect of frying time on acrylamide content and quality aspects of French fries

The effect of frying time on quality and acrylamide (AA) content of French fried potatoes, obtained simulating home-cooking practices, was studied in order to investigate the optimal conditions to minimize the amount of produced toxicant together with the maintenance of good culinary quality. French fries were obtained from fresh potatoes using a domestic fryer with static basket; a 4:1 oil:product ratio and a fixed initial oil temperature of 180 °C were used. Several batches were fried at different times (3, 4, 5, 6, 7, 8, 9 min). During frying tests the oil, the sticks surface and core temperatures were measured by thermocouples. Analysis of water removal, oil uptake, colour, texture and AA content were carried out on fried final products. AA content increased exponentially increasing the frying time. In our working conditions after around 4 min of frying, when the temperature of potato surface and the oil bath reached, respectively, 120 and 140 °C, the increase of time became a key factor in terms of the quantity of AA and its formation rate. On the basis of colour, oil content and AA level the best culinary product was obtained after 5 min of frying.     

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.     

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.     

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.     

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.     

Possible causes of variation in acrylamide concentration in French fries prepared in food service establishments: An observational study

Acrylamide is a probable human carcinogen, and its presence in a range of fried and oven-cooked foods has raised considerable health concern world-wide. Dietary intake studies observed significant variations in acrylamide concentrations, which complicate risk assessment and the establishment of effective control measures. The objective of this study was to obtain an insight into the actual variation in acrylamide concentrations in French fries prepared under typical conditions in a food service establishment (FSE). Besides acrylamide, frying time, frying temperature, and reducing sugars were measured and the actual practices at receiving, thawing and frying during French fries preparation were observed and recorded. The variation in the actual frying temperature contributed most to the variation in acrylamide concentrations, followed by the variation in actual frying time; no obvious effect of reducing sugars was found. The lack of standardised control of frying temperature and frying time (due to inadequate frying equipment) and the variable practices of food handlers seem to contribute most to the large variation and high acrylamide concentrations in French fries prepared in a restaurant type of FSE as compared to chain fast-food services, and institutional caterers. The obtained insights in this study can be used to develop dedicated control measures in FSE, which may contribute to a sustainable reduction in the acrylamide intake.     

Modelling the effect of asparaginase in reducing acrylamide formation in biscuits

The influence of asparaginase on acrylamide formation, as well as colour development, in short dough biscuits was studied. In particular, asparaginase concentration, incubation time and temperature were changed according to an experimental design. As acrylamide formation was found to vary significantly between biscuits obtained by using the same ingredients and process, a mixed effect model was used to model variation of acrylamide concentration. By contrast a fixed effect model was used for colour polynomial analysis. Within the range of study, the overall results allowed the best conditions for minimising acrylamide formation to be found. It can be suggested that acrylamide development was at a minimum at intermediate asparaginase concentrations, as well as at the lowest time and temperature of incubation. Asparaginase addition did not significantly affect the colour of the final product, although the quadratic term of the incubation temperature did slightly.     

Reduction of acrylamide formation in French fries by microwave pre‐cooking of potato strips

In this study, the effect of microwave pre‐cooking of potato strips on the resultant acrylamide levels in French fries was investigated. Control and microwaved (10, 20, and 30 s at 850 W) samples were fried at 150, 170 and 190 °C for predetermined times. Surface and core temperatures of potato strips were acquired during frying, and acrylamide content in the surface and the core regions were determined separately. The results showed that microwave application prior to frying resulted in a marked reduction of acrylamide level in the surface region, whereas a slight increase was noted for the core region. When the potato strips were subjected to frying after a microwave pre‐cooking step, acrylamide content in the whole potato strip was reduced by 36%, 41%, and 60% for frying at 150, 170, and 190 °C, respectively, in comparison to the control. Copyright © 2006 Society of Chemical Industry     

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.     

Effect of pre-drying and par-frying conditions on the crispness of French fries

An experimental design was used to study the effect of pre-drying (to 10, 15 and 20% weight loss) and par-frying conditions (160, 170 and 180 °C) on the crispness of French fries. Par-frying time was adjusted with a software program to obtain equal moisture content and internal texture for all samples. Crispness was evaluated with a sensory panel. Furthermore, samples were analysed with a texture analyser and with confocal scanning laser microscopy (CSLM). Par-frying at 180 °C resulted in a crispier product than at 160 and 170 °C. Pre-drying to 20% weight loss lead to blisters and reduced crispness in comparison with pre-drying to 10 and 15% weight loss. Instrumental texture measurements showed a good correlation with sensory crispness. Large differences in cell structure, such as blisters, could be observed with CSLM. CSLM was useful to explain results from the instrumental and sensory texture evaluation.     

The effects of enzymes on fat content and texture of French fries

The purpose of the present investigation was to study the changes in the microstructure of potato cells during French fries processing with the use of enzymes and to find the impact of the enzymes on fat content and texture of French fries. The samples for laboratory studies were of potato strips and French fries, collected from five locations of the technological line.     

Computer vision-based image analysis for the estimation of acrylamide concentrations of potato chips and french fries

In this study, digital colour images of fried potato chips and french fries were analyzed to estimate acrylamide levels based on the correlation with analyses using liquid chromatography-mass spectrometry. In fried potato images, bright yellow (Region 1), yellowish brown (Region 2) and darker brown (Region 3) regions were clearly visible, having different kinds of image pixels with characteristic mean values of red, green and blue components. Pixels of the fried potato image were classified into three sets (Set 1, Set 2 and Set 3) by means of semi-automatic and automatic segmentation. There was a strong correlation between acrylamide concentration and NA2 value, which is defined as the number of pixels in Set 2 divided by the total number of pixels of the entire fried potato image. To verify the applicability of this approach, a linear regression equation was used to estimate the acrylamide concentrations of a number of commercial potato chips and home-made french fries. Mean differences between the measured and predicted acrylamide concentrations were found to be +4 ± 14% and −14 ± 24% for commercial potato chips and home-made french fries, respectively.     

The influence of frying medium degradation on fat uptake and texture of French fries

The purpose of the present investigation was to study the influence of the degree of degradation of different kinds of oils used as a frying medium on fat uptake and texture of frozen pre‐fried French fries. As has been found, the degradation degree of the frying medium depends on the kind of oil and processing time. Liquid hydrogenated rapeseed oil exhibited the best thermo‐oxidative stability among the oils under investigation. The kind of oil influenced fat uptake and the texture of French fries. The lowest fat uptake was observed with French fries fried in solid oil. Some correlations between fat uptake and changes in fatty acid content were found in the frying medium during frying. Fat absorption increased with increasing unsaturated fatty acids and decreasing saturated fatty acid content. The texture of French fries fried in hydrogenated oils was harder than that exhibited by French fries fried in liquid rapeseed oil. The hardness of French fries fried in liquid oils decreased during frying while the hardness of French fries fried in solid oil increased. Some correlations between the texture of French fries and iodine value and fatty acids content of frying media were found. The hardness of French fries increased with increasing content of saturated fatty acids and decreasing unsaturated fatty acids and trans isomer fatty acid content. Copyright © 2005 Society of Chemical Industry     

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.     

Growth of Bacillus cereus on Oil-blanched Potato Strips for "Home-style" French Fries

Fresh cut, oil blanched strips from whole potatoes stored at 7 or 13 °C were inoculated with approximately 3 or 5 log CFU/g Bacillus cereus and incubated at 21 or 26.7 °C for up to 9 h to model handling of "home-style" French fries. Whole potato storage at 13 °C and incubation at 26.7 °C resulted in faster growth than 7 or 21 °C. Frying (2 to 3.5 min at 185 °C) inactivated up to 5.1 log B. cereus spores. Oil blanched potato strips for "home-style" French fries should be stored at £ 21 °C or finish fried or discarded within 3 to 4 h.     

煎炸薯条条件对高油酸葵花籽油中饱和型甘油酯核心醛生成的影响

为对煎炸过程中甘油酯核心醛(GCAs)的调控提供指导,以高油酸葵花籽油煎炸薯条实验为例,探讨煎炸方式、频次、温度以及油料比对煎炸过程中9-氧代壬酸酰基甘油三酯(9-oxo)、8-氧代辛酸酰基甘油三酯(8-oxo)两种饱和型GCAs生成的影响。结果表明：间歇煎炸较连续煎炸更易导致GCAs的生成;每小时煎炸1批次薯条所产生的饱和型GCAs低于每小时煎炸2批次和4批次的;随着煎炸温度的降低,两种饱和型GCAs含量均减少;油料比为10∶1时,两种饱和型GCAs含量整体较低。综上,为控制饱和型GCAs的生成,需采用连续煎炸方式,尽量降低煎炸温度和煎炸频次,控制油料比为10∶1。     

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.     

Changes of polysaccharide content and texture of potato during French fries production

The purpose of the present study was to determine the changes in non-starch polysaccharide and lignin contents of potato during French fries production and also the relationship between the texture of the finished product and half-products, as a result of processing at each stage under investigation. The samples for laboratory studies were taken from potato tubers, strips and French fries collected from nine locations of a technological line. The greatest changes in non-starch polysaccharide content and texture of potatoes resulted from blanching and frying. The texture of French fries was mainly affected by pectin and cellulose. The texture of French fries can be predicted from the measurements of the texture of potato strips after blanching.