Microwave heating instead of blanching to produce low-fat French fries

Blanching pretreatment is necessary for preparing French fries, but it causes water consumption and nutrient outflow. This work was aimed to investigate the effects of microwave (MW) pretreatment instead of blanching on the quality of fries, evaluated via changes to microstructure and crust characteristics. First, MW pretreatment could inactivate polyphenol oxidase in fresh-cut potato strips to inhibit enzymatic browning. Subsequently, the fries after proper MW pretreatment (60 s) had a golden appearance and better texture. As compared with the blanching process, the oil content of the fries obtained by MW pretreatment was decreased sharply from 41.3% to 18.1%. The results of scanning electron microscopy showed that MW pretreatment significantly altered the crust and internal microstructure of fries. Specially, it was found that the MW pretreatment made the fries form a thicker “protective crust” (1.81 μm), which was crucial to prevent oil adsorption during the frying and improve texture.Industrial relevanceBlanching is a traditional thermal processing technique that was once widely used in French fries around the world. However, blanching has some drawbacks, such as slow heat conduction, long processing time, substantial loss of soluble nutrients, massive water wastage, and even increased oil content of the fries. Meanwhile, MW heating is known for its high efficiency. The fries obtained with proper MW pretreatment are of good quality, but the oil content is drastically reduced compared to conventional blanching pretreatment. So, the above findings may provide helpful information to guide effective strategies for applying MW heating instead of blanching in the preparation of fried potato foods.     

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.     

Effect of Microwave Frying on Acrylamide Generation,Mass Transfer,Color, and Texture in French Fries

The objective of this work was to evaluate the effect of microwave power on acrylamide generation, as well as moisture and oil fluxes and quality attributes of microwave-fried potatoes. Concretely, 25 g of potato strips, in 250 mL of fresh oil (at room temperature), were subjected to three different microwave powers (315, 430, and 600 W) in a conventional microwave oven. Microwave frying resulted in an acrylamide reduction ranged from 37 to 83% compared to deep-oil frying. Microwave-fried French fries presented lower moisture and higher fat content than deep-oil fried potatoes. Concretely, microwave-fried potatoes presented values of moisture and texture more similar to potato chips than French fries, nonetheless with lower fat levels (less than 20 g/100 g wb) and acrylamide content (lower than 100 μg/kg wb) at the reference time. This study presents an alternative way of frying to address the production of healthier potato chips.     

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.     

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.     

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.     

Lipid profile of foods fried in thermally polymerized palm oil

Lipids extracted from foods fried in thermally polymerized palm oil were evaluated in papads, French fries and fish fry (Bombay duck) with moisture content ranging between 10% and 75%, in an attempt to investigate the effect of moisture content on lipid quality indices such as free fatty acids, conjugated dienes, p-anisidine value, viscosity, total polar materials and colour values. The quality of lipids in products with high moisture content (50% or more) was found to be inferior to that of the oil left after frying, as evidenced in Bombay duck and French fries from potatoes with initial moisture content of 52–77%. A reverse trend was observed in papads and French fries prepared from dehydrated potatoes with moisture content of 12% or less. The results indicate the moisture content of food plays a definite role in the distribution of the lipid constituents during frying in thermally polymerized oil.     

油炸马铃薯食品中发现丙烯酰胺的研究近况

对油炸或焙烤马铃薯食品中的丙烯酰胺含量、食品中丙烯酰胺含量的分析方法、丙烯酰胺毒性问题的最新研究结果进行了综述。现有研究结果表明 ,炸薯片、炸薯条中含有较高含量的丙烯酰胺 ,过度油炸会进一步增加薯条中的丙烯酰胺含量 ,而相应的生马铃薯原料与煮熟马铃薯中则不含丙烯酰胺。食品中丙烯酰胺含量的分析方法目前采用气相色谱 -质谱法 (GC MS)与液相色谱 串联质谱联用新技术 (LC/MS/MS) ,但食品中丙烯酰胺含量的分析方法、丙烯酰胺的毒理学研究仍在进一步发展中。     

Migration of health promoting microconstituents from frying vegetable oils to French fries

Fried foods, especially French fries, are consumed worldwide with sustainable popularity, correlated to their unique sensory properties. During frying the oil is absorbed by the food and becomes part of our diet. Concerns regarding the fried foods quality due to the accumulation of by-products resulting from frying oil deterioration are adequately justified. Given the consumers’ preference it is however worth exploiting the presence of health promoting components in fried foods and worth studying factors that might increase those microconstituents content. French fries contain vitamin E, phytosterols and depending on the oil used, polyphenols, squalene, triterpenes, and carotenoids. Tocopherols and phytosterols content of French fries comply with the respective oil content; polyphenols seem to survive better inside the food tissue than in the oil, thus presenting higher concentrations in the former. The concentrations of these compounds in French fries are mainly affected by the oil type, oil quality, and the frying procedure adopted.     

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.     

Lactic Acid Fermentation Reduces Acrylamide Formation and Other Maillard Reactions in French Fries

ABSTRACT Blanched and nonblanched potato rods (var. Beate) were fermented with Lactobacillus plantarum strain NC8 (10⁹ colony‐forming units [CFU]/mL) at 37 °C for 45 and 120 min. Potato rods were pre‐fried at 170 °C for 3 min, cooled, and subsequently deep‐fried for 2 min 15 s. Potato juice (var. Beate) was fermented with the same strain (108 CFU/mL) at 30 °C for 1 to 5 h. Lactic acid fermentation of nonblanched potato rods for 45 min reduced acrylamide level in French fries with 48%, and with 71% after 120 min. By blanching potato rods before fermentation, reductions in acrylamide after 45 min and 120 min were 79% and 94%, respectively. Blanching, and especially fermentation, reduced visually judged browning of the French fries. Fermentation of potato juice reduced pH from 5.70 to 4.05 after 3 h. Simultaneously, glucose declined from 610.8 mg/100 mL to 7.9 mg/100 mL, fructose from 457.8 mg/100 mL to 0.0 mg/100 mL, and sucrose from 132.0 mg/100 mL to 29.2 mg/100 mL. Asparagine content remained largely unaffected between 0 h (1217.5 μmol/100 mL) and 4 h (1175.6 μmol/100 mL) and increased slightly (1470.3 μmol/100 mL) after 5 h fermentation. Levels of several other amino acids involved in Maillard reactions, that is, alanine, arginine, phenylalanine, and serine, decreased during fermentation. It is concluded that acrylamide formation during production of French fries can be effectively lowered by lactic acid fermentation of potato rods before deep‐frying. The reduction is due to reduced levels of reducing sugars rather than reduction of available asparagine.     

Influence of deep-frying using various commercial oils on acrylamide formation in French fries

This study investigated the effect of different types of commercial oils (rice bran oil, shortening oil, high-oleic rapeseed oil, low-erucic acid rapeseed oil, blend oil A and blend oil B) and frying cycles on acrylamide formation during the preparation of French fries by deep-frying. Frying was carried out in intermittent mode (two batches each for 12 min without any time lag) and repeated for 600 frying cycles. Results indicated that the French fries that were fried in oils having lower heat transfer coefficients contained lower acrylamide concentrations (913 µg kg^–1), whereas those fried with oils having higher heat transfer coefficients contained higher acrylamide concentrations (1219 µg kg^–1). Unlike the peroxide value, acrylamide levels in French fries did not change significantly with an increase in the number of frying cycles when tested for 600 frying cycles for every type of oil. This study clearly indicates that the contribution of frying oils to the formation of acrylamide should not be neglected due to their different heat transfer coefficients. On the other hand, continuous use of frying oil does not lead to a higher acrylamide concentration in French fries.     

The Effect of Food Type (Fish Nuggets or French Fries) on Oil Blend Degradation during Repeated Frying

Abstract: Oil that is reused multiple times for deep frying goes through changes in chemical composition and physical characteristics, affecting the quality of the fried foods. In this study, the effect of the food type (fish nuggets or French fries) on the degradation of an oil blend during the deep‐fat frying of each food at 180°C during 12 days was determined, and the characteristics of the fried products were evaluated. The degradation of oil during repeated use was relatively faster when fish nuggets were fried than when French fries were fried, as higher values of total polar compounds were obtained. Practical Application: The results are useful for producers of French fries and fish nuggets, such as restaurants or fast foods sellers, providing them with practical guidelines within the permitted values established by the regulatory authorities. The studied foods have high economic importance and are different in their composition. Under the studied conditions, the tested oil blend may be used during 4 d (4 h per day) with a daily replenishment, without discarding the oil when frying fish nuggets, and must be discarded after 8 d when French fries are processed. This suggestion allows preparing safe fried foods for consumers.     

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.     

热烫预处理降低鲜切油炸薯片中丙烯酰胺的工艺优化研究

研究热烫预处理对鲜切油炸薯片中丙烯酰胺的影响和薯片油炸工艺优化。在相同条件下,分别对原料进行热烫和非热烫处理,在不同油炸温度和时间条件下进行油炸试验,采用DNS法测还原糖,液质联用法检测薯片中丙烯酰胺含量。结果表明,通过对切片的马铃薯进行热烫处理,即75℃热烫150s,能明显降低还原糖含量,160℃油炸120s,可降低丙烯酰胺含量至67.18μg/kg。     

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.     

Changes of pectic substances concentration in potatoes and French fries and the effect of these substances on the texture of the final product

The texture of fried potato products depends on the building elements present in the cell walls, which play the structure-forming function, as well as on physical and biochemical changes of those elements which take place in the potato tissue, when it is exposed to blanching or frying. For the research the tubers of four potato varieties (Ekra, Orlik, Sumak, and Bryza) were used, which served as material for the production of French fries. In the samples of potato tubers before and after peeling, as well as in French fries blanched in the solutions of 0.4% CaCl2 and 0.4% MgCl2 salts the contents of pectic substances and their effect on the texture of the final product were determined. The process of peeling potato tubers contributed to the decrease of the content of the pectic substances. On the average 20% of the content of water-soluble pectins and about 5% of protopectins was decreased. Water blanching and frying contributed to a further decrease of the pectic substances in French fries in relation to their content in the raw material. However, potato strips blanching in the solutions of calcium and magnesium salts prevents further loss of those substances in the final product. The presence of calcium and magnesium ions in the solution of the blanching salts caused their partial binding by the pectin substances present in the potato tissue, which resulted in the improvement of the texture of French fries, especially obtained from early potato varieties.     

The effects of low‐temperature potato storage and washing and soaking pre‐treatments on the acrylamide content of French fries

BACKGROUND: Since the discovery in 2002 of acrylamide in a wide range of foods, there has been much work done to explore mechanisms of formation and to reduce acrylamide in commercial products. This study aimed to investigate simple measures which could be used to reduce acrylamide formation in home‐cooked French fries, using potatoes from three cultivars stored under controlled conditions and sampled at three time points. RESULTS: The reducing sugar content for all three cultivars increased during storage, which led to increased acrylamide levels in the French fries. Washing and soaking (30 min or 2 h) raw French fries before cooking led to reductions in acrylamide of up to 23, 38 and 48% respectively. Pre‐treated fries were lighter in colour after cooking than the corresponding controls. CONCLUSION: Pre‐treatments such as soaking or washing raw French fries in water reduce acrylamide and colour formation in the final product when cooking is stopped at a texture‐determined endpoint. Copyright © 2008 Society of Chemical Industry     

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.     

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