Kinetics of oil uptake during frying of potato slices:: Effect of pre-treatments

Oil uptake in fresh, blanched and, blanched and dried potato slices was studied during frying. Potato slices blanched in hot water (85 °C, 3.5 min) and potato slices blanched (85 °C, 3.5 min) and then dried until to a moisture content of ∼60 g/100 g (wet basis) were deep fried in sunflower oil at 120, 150 and 180 °C. A control treatment consisted of unblanched potato slices without the pre-drying treatment (fresh samples). It was studied applying two empirical kinetic models in order to fit the oil uptake during frying: (i) a first order model; (ii) a proposed model, with a linear time behavior for short times, while time independent for long times. Oil uptake was high even for short frying times at the different temperatures tested suggesting that oil wetting is an important mechanism of oil uptake during frying. For control slices, oil uptake increased approximately by 32% as the frying temperature decreased from 180 to 120 °C at moisture contents ?1 g water/g dry solid. No apparent effect of frying temperature in oil uptake was observed at moisture contents ?0.5 g water/g dry solid in fried slices previously blanched and dried. The two kinetic models studied fitted properly the values of oil uptake during frying, with similar correlation coefficient r².     

Effects of egg yolk powder addition to the flour dough on the lipid oxidation development during frying

Effects of egg yolk powder added to the dough on the oxidation of frying oil and lipid of fried products were studied. Flour dough containing egg yolk at 0, 3.53, 6.73, and 9.66/100 g was fried in 180 °C sunflower oil for 1.5 min, and 55 fryings were performed. Lipid damage was determined by free fatty acids (FFA), conjugated dienoic acids (CDA), and polar compounds contents, and p-anisidine values (PAV). Phospholipid (PL) classes were determined by high performance liquid chromatography. PL was not detected in frying oil and fried products without egg yolk, while the first batch of fried products added with egg yolk at 3.53, 6.73, and 9.66 in 100 g of the dough contained total PL at 3.73, 7.93, and 8.98 mg/g, respectively. Contents of PL classes tended to increase in the products fried in the oil performing more fryings. As the number of fryings of oil increased, FFA, CDA, and polar compounds contents and PAV of frying oil increased. Addition of egg yolk to the dough significantly decreased CDA and polar compounds contents and PAV of frying oil, but it increased FFA values. Lipid of fried products showed the same tendency in CDA contents and PAV. The results clearly indicate that egg yolk powder improved the oxidative stability of frying oil during frying, possibly due to PL.     

Oxidative stability of fried dough from rice flour containing rice bran powder during storage

The aim of this study was to evaluate the efficiency of rice bran powder on lipid peroxidation inhibition of fried dough from rice flour during storage. Rice flour dough containing rice bran powder at 5, 10 and 15 g rice bran powder/100 g mixed rice flour were fried in soybean oil at 160 °C for 1 min and stored in dark at 60 °C for 10 days. Lipid peroxidation of fried dough was determined by change of fatty acid compositions, oxygen absorption in vial headspace, lipid hydroperoxides, TBA values including decreasing tocopherol and gamma-oryzanol contents during storage. Polyunsaturated fatty acid decreased rapidly in fried dough without rice bran powder, while an increase of oxygen absorption in vial headspace, lipid hydroperoxide and TBA values were significantly lower (p?0.05) in fried dough containing rice bran powder. In addition, tocopherol degradation was significantly lower in fried dough containing rice bran powder during storage (p?0.05). However, there was no significant difference in gamma-oryzanol contents among fried dough during storage (p>0.05). These results demonstrated that rice bran powder shows the antioxidative effects on fried dough during storage.     

Effect of hydrocolloid coatings on the heat transfer and oil uptake during frying of potato strips

The effect of the hydrocolloid coatings (gellan gum and guar gum) of a food matrix on the heat transfer during a frying process was investigated and correlated with the oil uptake. While the potato strips coated with the hydrocolloid solutions were fried at 170 °C, the hydrocolloid coatings significantly reduced the heat transfer coefficients as well as oil uptake which became more apparent at higher concentrations. Thus, the oil uptake was found to have a good polynomial correlation (R² > 0.99) with heat transfer coefficients, suggesting that a rapid heat transfer led to an increase in the oil content of the fried samples.     

Influence of process parameters on the physico-chemical and microstructural properties of rice crackers: A case study of novel spray-frying technique

The physico-chemical and microstructural properties of fried rice crackers were studied as a function of spray-frying. Fried rice crackers were produced using the spray- and deep-frying techniques and their moisture content, oil uptake, color, texture (i.e., hardness, expansion ratio, and bulk density), and microstructure were compared. For spray-frying, the heat distribution inside the frying chamber, the effects of spraying rate of oil (0.3, 0.5, and 0.7 L/s), and spinning speed of the frying basket (60, 80, and 100 rpm) were evaluated. Although the average temperature varied at each depth of the fryer, it did not influence overall heat distribution. Results also revealed that higher spraying rate and spinning speed resulted in higher moisture loss, higher oil uptake, darker color, and less crispiness. Compared with deep-frying, the oil uptake of spray-fried samples was lower by 45.4%. The color of the spray-fried crackers was better than that of the deep-fried samples. SEM micrographs showed that the cellular structure and integrity of the cell wall of deep-fried rice crackers were more deformed. They also had larger pore diameter and deeper and larger cavities, leading to higher oil content and crispier texture than spray-fried samples. Rice crackers fried using a spraying rate of 0.7 L/s and spinning speed of 100 rpm resulted in the most desirable physico-chemical qualities. Although the texture properties of the resulting rice crackers could still be improved, spray-frying could be an alternative technique in producing high-quality rice crackers with very low oil content.     

Formation of trans fatty acids in edible oils during the frying and heating process

To assess an impact of heated edible oils on intake of trans fat, the formations of trans fatty acids (TFAs) in cooking conditions was estimated by a frying and heating model system. For the frying model, sliced raw potatoes (10% of the frying oil (w/w)) were fried in commercially available canola oil at 160, 180 and 200 °C, and the 10 frying cycles were performed. The TFAs contained both in fried potatoes and in frying oils were measured by gas chromatography (GC). Lipids content of raw potatoes was about 0.1% (w/w) and TFAs in the raw potatoes were negligible. On the other hand, fried potatoes contained lipids at the level of 8.8%–9.2% and their fatty acid composition was mostly in correspondence with that of the frying oil. The TFAs amount of potatoes fried by the tenth frying operation was at the level of 0.99–1.05 g/100 g lipids. When 100 g potatoes fried in this process were consumed, the TFAs intake was estimated at less than 0.1 g. After 10 frying operations, TFAs content, acid values and peroxide values of the frying oils were measured and compared with those of corresponding heated canola oils without food. The amounts of trans 18:1 FAs contained both in the frying oil and in heated oil were less than the quantitative limit (0.047 g/100 g oil). The increases of trans 18:2 FAs and trans 18:3 FAs of the used frying oil were 0.02 g/100 and 0.05 g/100 g, respectively, compared with those of the fresh oil. trans 18:2 FAs accumulation in the heated oil was slightly less than that in the frying oil. To elucidate TFAs accumulation in various edible oils during cooking, six kinds of commercially available edible vegetable oils were heated to 180 °C in glass test tubes. Small changes in TFAs amounts were observed after four hours heating. These results suggested that an ordinary frying process using unhydrogenated edible oils has little impact on TFAs intake from edible oils.     

Vacuum frying reduces oil uptake and improves the quality parameters of carrot crisps

Recent consumer trends towards healthier and low fat products have had a significant impact on the snack industry. The objective of this study was to examine the most important quality parameters of vacuum and atmospheric fried carrot slices in order to identify the specific advantages of vacuum technology. Said parameters include oil uptake, colour changes, and trans α and β-carotene degradation. Equivalent thermal driving forces were used (ΔT = 60 °C and 80 °C) to compare the processes, maintaining a constant difference in temperature between the oil and the boiling point of water at the working pressure. The results showed that vacuum frying can reduce oil content by nearly 50% (d.b.) and preserve approximately 90% of trans α-carotene and 86% of trans β-carotene. This process also allowed for the raw carrot colour to be preserved, which was reflected by good correlations between a∗ and trans β-carotene content, b∗ and trans α-carotene content, and hue and total carotenoid content.     

Comparison between atmospheric and vacuum frying of apple slices

Vacuum deep-fat frying is a new technology that can be used to improve quality attributes of fried food because of the low temperatures employed and minimal exposure to oxygen. In this paper atmospheric and vacuum frying of apple slices were compared, in terms of oil uptake, moisture loss and color development. In addition, some apple slices were pre-dried (up to 64% w.b.) before vacuum frying to determine the overall effect. To carry out appropriate comparisons between both technologies equivalent thermal driving forces were used in both processes (ΔT = 40, 50, 60 °C), keeping a constant difference between the oil temperature and the boiling point of water at the working pressure. Vacuum frying was shown to be a promising technique that can be used to reduce oil content in fried apple slices while preserving the color of the product. Particularly, drying prior to vacuum frying was shown to give the best results. For instance, when using a driving force of ΔT = 60 °C, pre-dried vacuum fried slices absorbed less than 50% of the oil absorbed by atmospheric fried ones. Interestingly, a strong relationship between water loss and oil content was observed in both technologies, allowing the extension of observations that have been made for atmospheric frying.     

Quality changes in chicken nuggets fried in oils with different degrees of hydrogenatation

Quality changes in chicken nuggets fried in different mixtures of hydrogenated and non-hydrogenated canola oils were studied. Colour, texture, oil and moisture contents of the chicken nugget samples fried at 190 °C for 30, 60, 90, 120, 180, 240 and 300 s were investigated. The proportions of hydrogenated to non-hydrogenated frying oils used in the study were 0%, 20%, 40%, 60%, 80% and 100%.Results indicate that increase in frying time resulted in decreased product lightness (L*) whereas redness (a*) and yellowness (b*) increased. The maximum load to puncture increased with increasing frying time. In addition, oil content increased slowly with frying time, and moisture content decreased as expected. Both frying times and oil types have significant effects on the quality parameters investigated. First-order kinetic equation was used to describe colour changes as well as oil and moisture contents of the samples. Oil and moisture contents had negative correlation relationship. With increasing degree of oil hydrogenation, the surface colour of the fried chicken nuggets samples were lighter, texture increased, oil and moisture contents decreased.     

Physical and thermal properties of potato chips during vacuum frying

Vacuum frying (1.33 kPa), with the aid of a de-oiling mechanism, was used to produce low-fat potato chips.The kinetics of oil absorption and oil distribution in the potato chips was studied so that effectiveness of the de-oiling system could be established. Non-linear regression was used to fit the experimental data to the models used to describe oil absorption in potato chips with time.Moisture content, oil content, microstructure, diameter and thickness expansion, bulk density, true density, and porosity of chips fried at different temperatures (120, 130, and 140 °C) was performed to evaluate the effect of process temperature on the product. The convective heat transfer coefficient at the oil-chip interface was determined for the same temperature range.The final oil content of the potato chips was 0.072 ± 0.004, 0.062 ± 0.003, and 0.059 ± 0.003 g/g solid for frying temperatures of 120, 130, and 140 °C, respectively. These values are lower (80-87% less) than those found in the not de-oiled potato chips, which indicates that the de-oiling mechanism is crucial in vacuum frying processing. A significant difference (P < 0.05) was observed in oil content and oil distribution within temperatures. The rate of change in product quality attributes was greatly affected by temperature; however, the final values of moisture content, bulk density, true density, porosity, diameter shrinkage, and thickness expansion were not affected by temperature.During vacuum frying, the convective heat transfer coefficient changed considerably as frying progressed; moreover, it increased with temperature reaching a maximum between 2200 and 2650 W/m² K depending on frying temperature.     

Comparative study of physical and sensory properties of pre-treated potato slices during vacuum and atmospheric frying

The objective of this research was to study the effect of different processing conditions on physical and sensory properties of potato chips. Potato slices of Desirée and Panda varieties (diameter: 30 mm; thickness: 3 mm) were pre-treated in the following ways: (i) control or unblanched slices without pre-drying; (ii) blanched slices in hot water at 85 °C for 3.5 min and air-dried at 60 °C until a final moisture content of ∼0.6 kg water/kg dry solid; (iii) control slices soaked in a 3.5 kg/m³ sodium metabisulphite solution at 20 °C for 3 min and pH adjusted to 3. Pre-treated slices were fried at 120 and 140 °C under vacuum conditions (5.37 kPa, absolute pressure) and under atmospheric pressure until they reached a final moisture content of ∼1.8 kg water/100 kg (wet basis). An experimental design (3 × 2³) was used to analyze the effect of pre-treatment, potato variety, type of frying and frying temperature over the following responses: oil content, instrumental color and texture and sensory evaluation. Vacuum frying increased significantly (p < 0.05) oil content and decreased instrumental color and textural parameters. Sensory attributes, flavor quality and overall quality, were significantly improved using vacuum frying. The higher frying temperature (140 °C) increased ΔE, maximum breaking force, hardness and crispness and decreased L^* and b^* values. On the other hand, Panda potato variety improved the color of the product. A great improvement on color parameters was obtained using sulphited potato slices instead of the other pre-treatments. Although, the better flavor was obtained for control potato chips, no significant differences were found for overall quality between control and sulphited potato chips. Significant correlations (p < 0.01) between sensory and instrumental responses were found.     

The bioavailability of iron fortified in whole grain parboiled rice

The present study was to evaluate the bioavailability of iron (Fe) fortified in parboiled rice grain, expressed as Fe uptake by Caco-2 cells after in vitro digestion. The bioavailability of Fe-fortified in the rice grain was closely and positively correlated with increasing concentrations of Fe in the grains of the three cultivars (r = 0.96∗∗). The uptakes of the Fe-fortified in parboiled rice milled for 120 s (34.2, 47.7 and 107 ng ferritin mg protein⁻¹ in three cultivars, respectively) were well above those of the unfortified raw (6.1, 4.9 and 5.7 ng ferritin mg protein⁻¹) or parboiled rice (4.7, 3.6 and 4.4 ng ferritin mg protein⁻¹), the high Fe rice line IR68144-2B-3-2-2 (4.0 ng ferritin mg protein⁻¹) and popular Jasmine rice cultivar KDML 105 (3.9 ng ferritin mg protein⁻¹). Increasing milling time and rinsing the Fe-fortified parboiled rice decreased Fe bioavailability, due to their negative effects on total Fe concentrations in the parboiled rice grains, but uptakes were still well above that of their unfortified raw or parboiled rice grains. Rinsing or washing the Fe-fortified and milled rice grains decreased the bioavailability to 85 ng ferritin mg protein⁻¹ in the YRF cultivar, compared to about 100 ng ferritin mg protein⁻¹ in its non-rinsed grains. Dilute acid-extractable (DAE) Fe was linearly, positively correlated with the uptake of Fe assessed by the in vitro digestion/Caco-2 cell technique (r = 0.90∗∗), which can be used as a rapid method for optimizing levels of bioavailable Fe to be fortified in the parboiled rice by parboiled-rice mills if this Fe-fortification technique should be adopted in south and southeast Asia.     

Modeling water loss and oil uptake during vacuum frying of pre-treated potato slices

The objective of this research was to determine the kinetics of water loss and oil uptake during frying of pre-treated potato slices under vacuum and atmospheric pressure. Potato slices (diameter: 30 mm; width: 3 mm) were pre-treated in the following ways: (i) raw potato slices “control”; (ii) control slices were blanched in hot water at 85 °C for 3.5 min; (iii) blanched slices were dried in hot air until reaching a moisture content of ∼0.6 g water/g dry basis. The slices were fried under vacuum (5.37 kPa, absolute pressure, at 120, 130 and 140 °C) and atmospheric conditions (at 180 °C). Two models based on the Fick's law were used to describe water loss: (i) with a constant effective diffusive coefficient; and (ii) with a variable effective diffusive coefficient. Oil uptake data were fitted to an empirical model, with a linear behavior for short times whereas the model was time independent for long times. The variable diffusivity model better fitted experimental water loss, giving values of effective diffusivity between 4.73 × 10⁻⁹ and 1.80 × 10⁻⁸ m²/s. The proposed model for the study of the kinetics of oil uptake fitted the experimental data properly. Control and blanched vacuum fried potato chips increased their final oil contents to 57.1% and 75.4% respectively, when compared with those fried at atmospheric pressure. However, the oil absorption of dried vacuum fried potato chips diminished by ∼30%.     

Using hydrocolloids to decrease oil absorption in banana chips

The aim of this research was to investigate the influence of hydrocolloids (alginate, CMC and pectin) on the oil absorption in fried banana chips. The control banana chips (no hydrocolloid treatment) had oil content as high as 40 g/100 g sample, whereas the sample blanched in 0.5 g CaCl₂/100 ml water and following with immersion in 1 g alginate/100 ml water exhibited a small decrease of oil uptake (p ≤ 0.05) to 38 g/100 g sample. The others which treated with 0.5 g CaCl₂/100 ml and 1 g pectin/100 ml water, and with 0.25 g CaCl₂/100 ml water and 1 g CMC/100 ml water absorbed much less oil (p ≤ 0.05), approximately 23 g/100 g sample. Besides, pectin-treated chips had higher sensory scores in all attributed than CMC-treated sample. These resulted showed that pectin was the most effective hydrocolloid for low fat fried banana chip production. Scanning electron microscope photographs indicted that coating banana chips with pectin was effective in protecting the cellular structure of the banana tissue from damage during deep-fat frying.     

Vacuum frying of high-quality fruit and vegetable-based snacks

Sweet potato, green beans, Tommy Atkins mango, and blue potato were fried in a vacuum frying process at a temperature of 120-130 ± 1°C. Before frying, green beans and mango slices were soaked in a 50% maltodextrine 0.15% citric acid solution. The products were also fried in a traditional (atmospheric pressure) fryer at 160-165 ± 1°C for 4 min. A 30-member consumer panel rated the sensory quality of both types of fried snacks using a 1-9 hedonic scale. Compared with traditional frying, oil content of vacuum-fried sweet-potato chips and green beans was 24% and 16% lower, respectively. Blue potato and mango chips had 6% and 5% more oil, respectively, than the traditional-fried samples. Anthocyanin (mg/100 g d.b.) of vacuum-fried blue potato chips was 60% higher. Final total carotenoids (mg/g d.b.) were higher by 18% for green beans, 19% for mango chips, and by 51% for sweet-potato chips. Sensory panelists overwhelmingly preferred (p < 0.05) the vacuum-fried products for color, texture, taste, and overall quality. Most of the products retained or accentuated their original colors when fried under vacuum. The traditional-fried products showed excessive darkening and scorching. These results support the applicability of vacuum frying technology to provide high-quality fruit and vegetable snacks.     

Effect of fish (Catla catla) frying on the quality characteristics of sunflower oil

The quality of sunflower oil, as affected by fish (Catla catla) frying at 180 °C for 14 h was investigated. The purpose of the study was to find out the quality deterioration of sunflower oil with respect to time as affected by fish frying and to generate equations that can be used for predicting the quality parameters. The physico-chemical characteristics of sunflower oil were evaluated by drawing out the oil samples (75 ml) from the fryer at an interval of 2 h. The parameters evaluated were refractive index, colour, total polar material, free fatty acids, iodine value and peroxide value. There was a gradual increase in refractive index and colour with time of frying which was found to be significant (P < 0.05) in the latter. Iodine value decreased significantly (P < 0.05) with time of frying. Peroxide value first increased up to 12 h of frying and then decreased. After 10 h of frying, the total polar materials were 26.9%, indicating the need for replenishment or refinement of sunflower oil. Total polar material correlated well (r > 0.97) with colour, free fatty acids, peroxide value and time of frying. Free fatty acids correlated well (r > 0.96) with colour, total polar material and duration of frying. Fit of the equations was determined for total polar material and free fatty acids as a function of the respective correlated parameters.     

Machine learning workflow for the oil uptake prediction of rice flour in a batter-coated fried system

Machine learning algorithms were applied to predict the oil uptake of rice flour in batter-coated fried foods, depending on its physicochemical features before frying (amylose content, pasting parameters, and batter viscosity). Low coefficients of Pearson correlation (0.29–0.61) were observed between the oil uptake of rice frying batters and other physicochemical parameters. Based on an exhaustive search method by the regsubsets function, the four experimental features (amylose content, peak time, peak temperature, and final viscosity) were selected as the best subset to affect the oil uptake of rice batters after frying, and then subjected to two machine learning algorithms – multivariable linear regression and multilayer perceptron neural network. Based on K-fold cross-validation, the experimental results were divided into 5 datasets consisting of each 80% training and 20% testing dataset. Compared to the multivariable linear regression (R² = 0.6204–0.7219), the iterative application of the multilayer perceptron model made a relatively higher prediction (R² = 0.7388–0.7781) of the oil uptake of rice flour frying batter. Thus, the multilayer perception model with a hidden layer outperformed the multivariable linear regression by showing higher R² and lower relative error.     

Occurrence of heterocyclic amines in cooked meat products

Heterocyclic amines (HCAs), potent mutagens and a risk factor for human cancers, are produced in meats cooked at high temperature. The aim of this study was to determine the HCA content in cooked meat products (beef, chicken, pork, fish) prepared by various cooking methods (pan frying, oven broiling, and oven baking at 170 to 230 °C) that are preferred by U.S. meat consumers. The primary HCAs in these samples were PhIP (2-amino-1-methyl-6-phenylimidazo [4,5-b]pyridine) (1.49-10.89 ng/g), MeIQx (2-amino-3,8-dimethylimidazo [4,5-f]quinoxaline) (not detected-4.0 ng/g), and DiMeIQx (2-amino-3,4,8-trimethyl-imidazo [4,5-f]quinoxaline) (not detected-3.57 ng/g). Type and content of HCAs in cooked meat samples were highly dependent on cooking conditions. The total HCA content in well-done meat was 3.5 times higher than that of medium-rare meat. Fried pork (13.91 ng/g) had higher levels of total HCAs than fried beef (8.92 ng/g) and fried chicken (7.00 ng/g). Among the samples, fried bacon contained the highest total HCA content (17.59 ng/g).     

Producing lower-calorie deep fat fried French fries using infrared dry-blanching as pretreatment

The main objectives of this work were to study the suitability of using infrared (IR) heating as a dry-blanching pretreatment prior to frying and to investigate its potential to reduce the oil uptake in French fry production. It was observed that by using IR heat complete inactivation of polyphenol oxidase enzyme could be achieved in 3 min with 4.7% moisture loss for 9 mm French fries. Following IR dry-blanching, the samples were fried at 146, 160, and 174 °C for 1, 3, 5, and 7 min. At the end of 7 min frying, compared to unblanched samples, dry-blanched samples had 37.5%, 32% and 30% less total oil at the frying temperatures of 146, 160 and 174 °C, respectively. The final moisture contents of unblanched and dry-blanched samples were between 50% and 60% after 7 min frying. The L*a*b* colour values of both unblanched and dry-blanched samples decreased initially and then increased as the frying progressed. The sensory evaluation revealed that panelists mostly favored the IR dry-blanched French fries in terms of taste, texture, colour and appearance.     

Antioxidant capacity and inhibitory effect of grape seed and rosemary extract in marinades on the formation of heterocyclic amines in fried beef patties

The effect of oil-based marinades containing grape seed extract (Vitis vinifera L.; 0.2, 0.4, 0.6 and 0.8 g/100 g) formulated in a water/oil emulsion or rosemary extract (Rosmarinus officinalis; 0.12, 0.2, 0.6, 1.0 and 1.5 g/100 g) in oil on the formation of heterocyclic amines (HAs) in fried beef patties was examined. After application of marinades and frying, four HAs MeIQx (2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline), PhIP (2-amino-1-methyl-6-phenylimidazo[4,5b]pyridine), Norharman, and Harman were found at low levels in all fried patties, MeIQx (0.3–1.0 ng/g), and PhIP (0.02–0.3 ng/g). The content of MeIQx and PhIP were significantly reduced by approx. 57% and 90% (p < 0.05), respectively, after use of marinades containing the highest extract concentration. The antioxidant capacity of grape seed was about two-times greater than that of rosemary extract. A correlation between inhibition of HAs and Trolox-equivalents (MeIQx, R² = 0.85, p < 0.001; PhIP, R² = 0.83, p < 0.001) was found. Sensory tests showed a high acceptance of flavour and colour for controls and samples.