Physicochemical Properties Changes of Donuts During Vacuum Frying

Vacuum frying was explored to cook donuts and compared to the conventional atmospheric frying. A temperature of 190°C was used for atmospheric frying. Three vacuum levels (3, 6, and 9 kPa vacuum) with three temperature levels (150, 165, and 180°C) were used for vacuum frying. The effects of initial moisture content (IMC), vacuum level and frying temperature on physicochemical properties, such as moisture loss, oil absorption, and quality were investigated. The properties of fried donuts were significantly affected by IMC. Under vacuum frying, volume and total color changes were affected by frying temperature; and oil uptake was affected by vacuum and frying temperature. Frying temperature and vacuum were not directly related to the final moisture content (MC) of donuts. There was no relationship between MC and fat content of donuts. Donut texture was directly related to the vacuum and frying temperature.     

The influence of oil type and frying temperatures on the texture and oil content of French fries

The purpose of the present study was to determine the effects of the frying medium and temperatures on fat content and texture of French fries. The material taken for the study consisted of seven types of vegetable oil: refined sunflower, rape, soy, olive oil, palm, partially hydrogenated rape oil (modified oil I) and a blend of vegetable oils (modified oil II). The French fries prepared from Asterix potato variety were fried at oils heated to 150, 160, 170, 180 and 190 °C. The length of frying (12, 10, 8, 6.5 and 4.5 min, respectively) depended on oil temperature. Fat content and the texture of French fries were determined. The type of frying medium significantly affects the texture of French fries. Temperature influenced both the fat content and texture of product. The increase of frying temperature decreased fat uptake and hardness of French fries. French fries fried in rape oil exhibited the most delicate texture and the lowest oil absorption when compared with French fries fried in other types of oil under investigation. Copyright © 2005 Society of Chemical Industry     

Comparison of Microwave and Conventional Frying on Quality Attributes and Fat Content of Potatoes

A comparative analysis of quality attributes (moisture, fat, color, and relaxation modulus) of French fries was performed between conventional and microwave frying. Experiments were performed in triplicate for both frying operations at temperatures of 177, 185, and 193 °C for frying times of 60, 90, and 120 s. The real‐time pressure and temperature profiles at above conditions indicated that during microwave frying, gage pressure had greater magnitudes that lasted longer, and the temperature increased to boiling point of water faster in comparison to conventional frying. Lower magnitude of negative pressure during microwave frying is expected to have caused lower fat content in fries obtained using this method (0.08 g/g solids less at 185 °C and 0.07 g/g solids less at 193 °C) than conventional frying. The lightness parameter (L^*) decreased to a lesser extent in microwave frying than in conventional frying. The stress relaxation function of the French fries were significantly different between the 2 frying operations. Consumer test confirmed that reduced fat uptake during microwave frying did not compromise with desirable quality attributes of French fries. X‐ray micro‐computed tomography scanning provided complementary understanding about differences in microstructural properties of fries made using microwave and conventional frying.     

The Effect of Methylcellulose,Temperature, and Microwave Pretreatment on Kinetic of Mass Transfer During Deep Fat Frying of Chicken Nuggets

The aim of this study was to determine the effect of microwave pretreatment, usage of methylcellulose, oil temperature, and frying time on mass transfer during deep fat frying of chicken nuggets. Methylcellulose was used in batter and as a coating on product. Microwave with two power densities namely 3.7 and 7.4 W/g was used for reduction of initial moisture content of samples before frying. Frying was performed at three temperatures (150 °C, 170 °C, and 190 °C) and five intervals (0.5, 1, 2, 3, and 4 min) in the sunflower oil. The least oil content was observed when MC was used as a coating layer on non-precooked samples fried at 190 °C. Oil absorption of samples with MC in batter was partially higher compared to control samples. This could be attributed to the rheology of batters. The first-order kinetic model was fitted to moisture and oil content. For determining the correlation between temperature and moisture diffusivity, Arrhenius equation was used. The constant rate for moisture and oil transfer was in the range of 2.2–5 and 0.023–2.67 s^?1, respectively. Effective moisture diffusivity values were between 1.43?×?10^?8 and 3.24?×?10^?8 m²/s. Activation energy ranged between 0.71 and 1.71 kJ/mol.     

Microwave Frying Compared with Conventional Frying via Numerical Simulation

Microwave heating can be combined with other means of heating to yield a unique heating profile. In the study, microwave frying, a combination of convective and microwave heating, was compared with conventional frying. Frying experiments were performed by inserting a single food sample (chicken breast meat) in the hot oil at 180?±?1°C for both frying methods. Center temperature of the sample and the oil temperature were recorded during both frying methods. Simulations were performed to predict heat transfer coefficients. Processing time was shorter with microwave frying. Simulations revealed a varying convective heat transfer coefficient, which was in the range of 160–490 W/m² K, during conventional frying. Higher convective heat transfer coefficient, 500 W/m² K, compared to conventional frying was observed during microwave frying with the simulations. This is suggested to be due to higher turbulence in microwave frying.     

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.     

On the Possibility of Nonfat Frying using Molten Glucose

Fried products impose a health concerns due to considerable amount of oil they contain. Production of snack foods with minimal oil content and good management of oil during frying to minimize the production of toxic compounds continue to be challenging aims. This paper aims to investigate the possibility of producing a fat‐free food snack by replacing frying oil with a nonfat medium. Glucose was melted and its temperature was then brought to 185 °C and used to fry potato strips, to obtain a product referred here as glucose fries. The resulting product was compared with French fries prepared conventionally under conditions that resulted in similar final moisture content. The resulting products were also examined for crust formation, texture parameters, color development and glucose content. Stereo microscope images showed that similar crusts were formed in the glucose fries and French fries. Texture parameters were found to be similar for both products at 5 and 2 mm penetration depth. The maximum hardness at 2 mm penetration depth was also similar for both products, but different from cooked potato. The color development that characterized French fries was also observed in glucose fries. The glucose content in glucose fries was found to be twice the content of French fries, which is to be expected because glucose absorbed or adhered to the surface. In conclusion, glucose fries, with similar texture and color characteristics to that of French fries, can be prepared by using a nonfat frying medium.     

Effect of the Addition of Basil Essential Oil on the Degradation of Palm Olein during Repeated Deep Frying of French Fries

The potential antioxidant power of basil essential oil under frying conditions was explored. Two concentrations (200 or 500 ppm) were added to palm olein (PO) to evaluate their effect on fat oxidation/degradation during repeated frying of French fries at 180 °C. A higher oxidative stability index was detected for PO with basil essential oil at 200 ppm. Both concentrations showed lower p‐anisidine values than PO without basil essential oil after 5 d of frying. Addition at 500 ppm resulted in the lowest total polar compounds and free fatty acids contents. Thus, the addition of basil essential oil improved the performance of PO during repeated frying of French fries.     

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.     

Effects of Processing Conditions on Qualities of Rice Fries

ABSTRACT Two rice flour mixtures, 2 extruding temperatures, and 2 insert sizes were used to develop rice fries. The extruded material was cut into pieces 7 to 8‐cm long, prefried in rice oil at 180°C for 20 s, and kept frozen until final frying for another 70 s. The rice fries were evaluated 5 min and 10 min after final frying for their lipid, moisture, and instrumental texture characteristics. Extruding temperature, rice cultivar, and insert size were significantly related to fat content, moisture, hardness, and fracturability values. A mixture consisting of 80:20 (waxy:long‐grain), and extruded at 70 °C using a 6 mm insert, 5 min after frying, gave a texture profile analysis value for hardness, cohesive‐ness, and gumminess values comparable to commercial potato French fries. The rice fries made by the process also had less than 50% fat than potato fries.     

Effect of Ultrasound-Assisted Osmotic Dehydration as a Pretreatment on Deep Fat Frying of Potatoes

The objective of this study was to investigate the possibility of using ultrasound-assisted osmotic dehydration (UAOD) as a pretreatment prior to frying and to study its effects on the quality of fried potatoes. The quality parameters, moisture content, oil uptake, color, texture, and microstructure of fried potatoes, were chosen. Quality of fried potatoes treated with UAOD was also compared with the ones treated with osmotic dehydration (OD). Potato slabs (40 × 40 × 7 mm) were pretreated with different osmotic solutions (15 % sodium chloride and 15 % sodium chloride/50 % sucrose solutions) at different temperatures (25, 45, and 65 °C) with and without ultrasonic waves for different treatment times. The pretreatment conditions which are OD for 90 min and UAOD for 30 min using 15 % sodium chloride/50 % sucrose solution were applied prior to frying at 170 °C for 2, 4, and 6 min. UAOD reduced the oil content of fried potatoes by 12.5 % (db) as compared to untreated fried potatoes at the end of frying. There was no significant difference between OD and UAOD in reduction of oil uptake in fried potatoes. However, UAOD was found to have the advantage of improving the color of French fries. In addition, it shortened the pretreatment time of OD by about 67 %. Cell structure of fried potato was damaged in the presence of pretreatments of OD and UAOD.     

Crust morphology and crispness development during deep-fat frying of potato

Crust formation is an important factor in determining the crispness of French fries. This study aimed at unravelling detailed structural and textural properties of the crust in relation to crispness during frying as a function of the process temperature and time. X-ray tomography showed a larger overall pore volume at higher frying times, while a lower final moisture content mainly resulted in an increase in the amount of large pores. Texture analysis revealed that the increase in porosity, due to the increased formation of pores, results in a more crispy behaviour after frying with oil of up to 180 °C. At temperatures above 180 °C crispness is actually found to decrease again, which is explained by the increased plastic behaviour of the crust. This may be related to the reduced glass transition temperature of the crust because of increased sugar degradation at a very high temperature.     

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.     

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.     

Provenance of the oil in par-fried French fries after finish frying

Frozen par-fried French fries are finish-fried either by using the same type of oil used for par frying, or a different type. The nutritive quality of the final oil contained in the product depends on the relative amounts and the fatty acid (FA) composition of the oils used for par frying and finish frying. With the aim of understanding the provenance of the oil in the final product, par-fried French fries-either purchased ready or prepared in the laboratory-were finish fried in oils different from the ones used for par frying. The moisture content, oil content, and FA compositions of the par-fried and finish-fried products were experimentally determined, and the relative amounts of each of the oils present in the final product were calculated using the FAs as markers and undertaking a mass balance on each component FA. The results demonstrate that 89% to 93% of the total oil in the final product originates from the finish-frying step. The study also shows that a significant proportion of the oil absorbed during par frying is expelled from the product during finish frying. Further, the expulsion of par-frying oil was found to occur in the early stages of the finish-frying step. Experiments involving different combinations of par-frying and finish-frying oils showed that the relative proportions of the 2 oils did not depend on the individual fatty acid profiles. This study concludes that any positive health benefits of using an oil having a favorable FA profile for par frying, can potentially be lost, if the oil used for finish frying has a less favorable composition. PRACTICAL APPLICATION: This paper estimates the relative amounts of oil in French fries that have been fried in 2 stages-a par-frying step and a finish-frying step-which is commonly practiced in food service establishments as well as homes. The 2 key conclusions are: (1) nearly 90% of the oil content of the final product is the one used for finish frying; that is, a processor may use very good oil for par frying but if the oil used for finish frying is inferior, its effect will dominate. (2) The paper also shows that a significant proportion of the oil used by the processor gets expelled during finish frying.     

Oxidative stability of potato chips: effect of frying oil type,temperature and antioxidants

The effect of type of frying oil and temperature on the oxidative stability of potato chips during storage was studied. Cottonseed oil, soybean oil, olive kernel oil and palmolein were used as frying media. The chips were packaged in metallized cellophane bags and incubated at 63 °C. At definite time intervals the absorbed oil was extracted and analyzed for peroxide value, Totox number and conjugated diene content. Olive kernel oil and palmolein absorbed into the chips showed better stability, whereas soybean oil presented the higher oxidation rate. Frying temperature (170, 180 or 190 °C) did not affect the oxidation rate during storage, with the exception of conjugated diene formation which was greater for chips fried at 190 °C. Ground oregano or oregano extract, obtained by petroleum ether extraction, were added to the chips as antioxidants. Both retarded significantly the oxidation rate of the oil absorbed into the chips, with results comparable to tertiary butylhydroquinone (TBHQ) during storage at 63 °C for 7 days; however TBHQ proved significantly more effective after that time. © 1999 Society of Chemical Industry     

Anti‐radical power gives insight into early lipid oxidation events during frying

The aim of this research was to use anti‐radical power (ARP) to study early lipid oxidation events during frying. The 2,2‐diphenyl‐1‐picrylhydrazyl radical (DPPH?) test was used to determine the ARP. As oil does not dissolve completely in methanol, which is generally used for the DPPH? test, butanol was used instead. Changing the solvent did not influence the value of the ARP. The decrease of the ARP highly correlated with the increase of the peroxide value for soybean oil heated at 110 °C (R² = 0.99). Sensory analysis showed that rancidity of soybean oil and frying oil, heated at 180 °C, was perceived before the ARP decreased. Once the oil was perceived as rancid, the intensity of rancidity did not change significantly upon further heating. The ARP of soybean oil was found to decrease faster at 110 °C than at 180 °C, suggesting different mechanisms of radical formation. The total polar compounds of frying oil in which French fries were fried did not differ significantly from frying oil that was heated alone. However, frying of French fries caused more hydrolysis of the oil, while the ARP decreased faster when the oil was heated alone. Copyright © 2006 Society of Chemical Industry     

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.     

A Kinetic Study of Furan Formation in Wheat Flour‐Based Model Systems during Frying

Furan is a possible human carcinogen, which is formed in worldwide highly consumed fried starchy foods. In order to elucidate the mechanisms responsible for its occurrence in this food category and propose techniques for its mitigation, the kinetics of furan formation, oil absorption, lipid oxidation, and color change were studied in wheat flour‐based model systems during frying at 160, 170, 180, and 190 °C up to 13 min and data were fitted to mathematical models. Additionally, an Arrhenius‐type dependency with temperature was evaluated for all studied responses. More drastic frying conditions increased significantly (P ≤ 0.05) the furan content of fried samples. Furan formation followed a sigmoid trend with frying time only for frying temperature of 190 °C (RMS_190°C: 7.6%). At lower temperatures, furan generation did not reach the asymptotic concentration level. Color change, lipid oxidation, and oil absorption increased with frying temperature and followed asymptotic relationships with frying time. For all evaluated temperatures, color change (RMS: 4.4% to 12.5%) and polar compound generation (RMS: 2.6% to 7.4%) presented good fit to a first‐order kinetic model. Oil absorption was successfully fit to a mass balance‐based model (RMS: 10.0% to 19.8%). Under the experimental conditions studied, only color change (E_A: 15.47 kJ/mol), lipid oxidation (E_A: 6.67 kJ/mol), and oil absorption (E_A: 76.98 kJ/mol) presented good fit (RMS: 0.7% to 6.3%) to an Arrhenius‐type equation. Based on our results, the keeping of frying temperature below 180 °C and the reduction of the frying time would contribute to reduce not only the final furan occurrence in fried foods but also their oil content.