Phytostanol Supplementation Through Frying Dough in Enriched Canola Oil

The objectives of this study were to determine a suitable level of phytostanols for addition to canola oil and to investigate the performance of the supplemented oil during frying. The frying oil was supplemented with 5, 10, 15, 20 % w/w phytostanols and two suitable levels (5 and 10 %) were selected. Dough frying was performed for 5 consecutive days at 180 °C for 5 h/day. The ranges of analytical measurements in the treatment groups were; free acidity (0.12–10.07 %), conjugated dienes (0.47–1.37 %), total polar material with probe (9.00–51.25 %), viscosity (46.27–195.51 cP), turbidity (0.82–1.80 NTU), and smoke point (202.75–274.25 °C). The results indicated that 5 % phytostanol enriched oil was superior in terms of oil stability and sensory quality of the fried dough among all the enriched oils. Samples with 10 % added phytostanols were high in free acidity, conjugated dienes and smoke points. Sterol composition analysis showed that the fried dough absorbed total sterols of 49.9 and 95 g/kg in 5 and 10 % supplemented oils, respectively. Hence, some health benefits could be achieved through consuming products which have been fried in phytostanol supplemented canola oil.     

The Role of Water in Protection Against Thermal Deterioration of Liquid Margarine

The thermal stability of liquid margarine and vegetable oils was investigated by measuring the oxidative stability index (OSI) at temperatures ranging from 90 to 180 °C, whereas total polar compounds (TPC) and tocopherols (vitamin E) were measured during heating at 180 °C in frying trays. Results showed that the OSI of liquid margarine was in the same range as the OSI of vegetable oils at lower temperatures, but at 160 and 180 °C, liquid margarine had significantly higher thermal stability, close to that observed for hard margarine and butter. The increased stability was confirmed by lower levels of TPC and a smaller relative reduction in vitamin E content during heating. Variations between different vegetable oils could partly be explained by differences in degree of saturation and level of vitamin E, with high oleic sunflower oil being the most stable oil at all temperatures. The water in liquid margarine vaporized within 1.5 min at 160 °C, and it is hypothesized that volatile pro‐oxidants are removed with the water, inducing a delay in deterioration. The results indicate a role for water in preventing lipid oxidation and decomposition in fat emulsion products at 160–180 °C, suggesting that liquid margarine, low in saturated fat, may be the healthier and preferable alternative for pan‐frying compared to other liquid vegetable oils.     

Degradation and Nutritional Quality Changes of Oil During Frying

The changes in regular canola oil as affected by frying temperature were studied. French fries were fried intermittently in canola oil that was heated for 7 h daily over seven consecutive days. Thermo-oxidative alterations of the oil heated at 185 ± 5 or 215 ± 5 °C were measured by total polar components (TPC), anisidine value (AV), color components formation, and changes in fatty acid composition and tocopherols. Results showed that TPC, AV, color and trans fatty acid content increased significantly (P < 0.05) as a function of frying temperature and time. The oil polyunsaturated fatty acids (PUFA) decreased in direct proportion to frying temperature and time. After 7 days of frying, the amount of PUFA was reduced by half and the trans isomers contribution increased 2.5 times during frying at 215 °C. Of the parameters assessed, total polar component and color had the highest correlation, with correlation coefficients of 0.9650 and 0.9302 for frying at 215 and 185 °C, respectively. TPC formation correlated inversely with the reduction of tocopherols.     

Antioxidant Activity of Sesamol in Soybean Oil Under Frying Conditions

Antioxidant activity of sesamol was investigated in soybean oil using a miniaturized frying experiment with potato cubes fried at 180 °C. Oxidation of soybean oil was determined by gel permeation chromatography for polymerized triacylglycerols and by ¹H-NMR spectroscopy for reactions at reactive sites of soybean oil molecules including olefinic, bisallylic and allylic protons during frying. Sesamol showed lower antioxidant activity than 0.02 % (w/w) tert-butylhydroquinone (TBHQ) at the same molar concentration. Higher concentrations of sesamol provided better antioxidant effects indicating that no prooxidant activity occurred. Sesamol in this frying test showed better results than 0.02 % TBHQ when the concentration was as high as 0.66 % by weight. An HPLC experiment showed that the concentration of sesamol decreased sharply during frying. Thermogravimetric analysis indicated that sesamol is highly volatile and easily oxidizes when exposed to air. To overcome this problem, two multiple addition methods were evaluated in which sesamol was added portion by portion every hour. The multiple additions of divided portions of 0.66 % (w/w) sesamol maintained the concentration of sesamol at the minimum of 0.04–0.06 % throughout the frying process and showed improved antioxidant activity compared to one single addition of 0.66 % sesamol at the beginning of frying. One of the multiple addition methods showed 28, 18, 59, and 27 % less polymerized triacylglycerols and losses of olefinic, bisallylic and allylic protons, respectively, than 0.02 % TBHQ after 8-h frying. This study shows that sesamol can be used as an alternative for synthetic antioxidants for frying oil.     

Performance of Regular and Modified Canola and Soybean Oils in Rotational Frying

Canola and soybean oils both regular and with modified fatty acid compositions by genetic modifications and hydrogenation were compared for frying performance. The frying was conducted at 185 ± 5 °C for up to 12 days where French fries, battered chicken and fish sticks were fried in succession. Modified canola oils, with reduced levels of linolenic acid, accumulated significantly lower amounts of polar components compared to the other tested oils. Canola oils generally displayed lower amounts of oligomers in their polar fraction. Higher rates of free fatty acids formation were observed for the hydrogenated oils compared to the other oils, with canola frying shortening showing the highest amount at the end of the frying period. The half-life of tocopherols for both regular and modified soybean oils was 1–2 days compared to 6 days observed for high-oleic low-linolenic canola oil. The highest anisidine values were observed for soybean oil with the maximum reached on the 10th day of frying. Canola and soybean frying shortenings exhibited a faster rate of color formation at any of the frying times. The high-oleic low-linolenic canola oil exhibited the greatest frying stability as assessed by polar components, oligomers and non-volatile carbonyl components formation. Moreover, food fried in the high-oleic low-linolenic canola oil obtained the best scores in the sensory acceptance assessment.     

Chemical Changes of Canola Oil During Frying Under Atmospheric Condition and Combination of Nitrogen and Carbon Dioxide Gases in the Presence of Air

The effects of different frying methods; frying under atmospheric condition and frying in the presence of different ratios of nitrogen and carbon dioxide gases; were investigated on chemical changes of canola oil. The tests were conducted four times per day during four consecutive days. The chemical changes of oil samples were determined by analyzing peroxide value (PV), p-anisidine value (p-AV), totox value (TV) and acid value (AV). Irrespective of the test methods, PV increase was observed on the first day followed by significant (p < 0.05) reduction in the subsequent days. On the first day, the highest p-AV and TV was observed in oil fried under atmospheric condition and the lowest p-AV and TV for those fried under gases. However, from the second day, the p-AV and TV in frying under different ratios of nitrogen and carbon dioxide gases were significantly (p < 0.05) higher than the frying under atmospheric condition. Additionally, hydrolysis and oxidation of oil during frying resulted in continuous AV increase that among them atmospheric frying had the highest AV. In conclusion, atmospheric frying accelerates the rate of oil deterioration and application of nitrogen and carbon dioxide gases in the fryer could reduce the rate of oil disintegration.     

Protecting oil during frying: A comparative study

The effect of carbon dioxide blanketing (CDB) and vacuum frying (VF) on the frying performance of regular canola oil was evaluated. For 7 h daily and for 7 days French fries were fried in regular canola oil at 185 ± 5 °C without and with CDB and in a vacuum fryer. The extent of changes in the oil was assessed by analysis of total polar compounds (TPC), anisidine value (AV), color component formation and changes in composition of fatty acids and tocopherols. Frying under CDB reduced the amount of TPC by 54%, while 76% reduction was observed during VF compared to standard frying conditions (SFC). Similarly, lower oxidative degradation was observed when measured by AV. At the end of the frying period, the reduction in unsaturated fatty acid content was 3.8, 1.9 and 12.7% when frying under CDB, vacuum and SFC, respectively. The rate of tocopherol degradation was three and twelve times slower in VF when compared to CDB and SFC, respectively.     

MODELING WATER LOSS DURING FRYING OF POTATO STRIPS: EFFECT OF SOLUTE IMPREGNATION

ABSTRACT

The effect of solute impregnation on water loss and oil uptake during potato strip frying was studied. Blanched potato strips were impregnated at 25°C by soaking in a solution of sucrose–NaCl–water, 20–5–75% by weight. After rinsing and air drying, strips were deep fried in sunflower oil at 160, 170 and 180°C. A control treatment, consisting of potato strips blanched but not soaked and later air dried was also conducted. Solute impregnation provided a decrease of the oil uptake. Two models, based on Fick's law were used to describe water loss during frying. The first one is the classic model with an effective moisture diffusion coefficient assumed a constant value. The second model considers that diffusion coefficient varies during the frying process. For a given frying temperature, constant diffusion coefficient for control potatoes resulted in lower values than the impregnated ones. The variable diffusivity model showed a two-stage behavior: during the first stage of frying, diffusion coefficient increased with frying temperatures, but from a given time on an inverse behavior began. This last fact was found to be related to an increase of the measured peak force needed to penetrate the potato crust.     

Formation of Alkylbenzenes and Tocochromanols Degradation in Sunflower Oil and in Fried Potatoes during Deep‐Frying and Pan‐Frying

Formation of toxic alkylbenzenes, total polar compounds (%TPC) and degradation of tocochromanol are monitored. Analyses of the oil extracted from fried potatoes confirm the trend observed in the frying oil. The fresh oil has a TPC content of 3%, which increases with the frying time, exceeding the acceptable value (25%) after about 25 h for deep‐frying and 1.5 h for pan‐frying. During deep‐frying, total tocochromanol decreases to about half (25 mg per 100 g) of the initial value, pan‐frying shows faster, degradation (complete after 1.5 h). Toluene concentration increases with the frying time reaching a maximum, and afterwards gradually decreases. Except for butylbenzene during pan‐frying, pentylbenzene and butylbenzene concentration, increase with the frying time, but remain much lower than toluene. Practical Applications: This is the first systematic work comparing alkylbenzenes evolution under different frying conditions. Different from previous works, frying experiments are carried out following the indication of many European countries that recommend using temperature lower than 180 °C. The amount of alkylbenzenes assumed through a standard portion of fried potatoes (200 g) is assessed, which is relevant for evaluating dietary exposure to these contaminants.     

Pore Development and Moisture Transfer in Chicken Meat during Deep-Fat Frying

Abstract

Changes in the structure of food products play important role in the various mass transfer processes during deep-fat frying. The relationship between moisture loss and pore formation were investigated at frying oil temperatures of 170, 180, and 190°C and frying times up to 900 s. Porosity and pore structure were characterized by using mercury intrusion porosimetry and helium displacement pycnometer. Moisture transfer in the samples was modeled using Fick's law and effective moisture diffusivity was computed from experimental data. Pore formation changes significantly (P < 0.01) in time as modulated by frying oil temperature. A peak pore fraction of 0.283 (after 360 s of frying), 0.238 and 0.220 (after 900 s of frying) at frying temperatures 190, 180 and 170°C, respectively was observed. Effective moisture diffusivity of 5.4 to 6.9 × 10^?9 m² s^?1 and activation energy of 20 kJ/mol was obtained for the frying oil temperatures. Changes in pore structure influenced moisture diffusivity and oil uptake. Eighty-four percent of the pores are capillary pores, hence moisture transfer increased.     

Anti-Rancidity Effects of Sesame and Rice Bran Oils on Canola Oil During Deep Frying

In this study, the effect of sesame oil (SEO) and rice bran oil (RBO) on the rancidity of canola oil (CAO) during the process of frying potato pieces at 180 °C was investigated. The SEO and RBO were added to the CAO at levels of 3 and 6%. Frying stability of the oil samples during the frying process was measured on the basis of total polar compounds (TPC) content, conjugated diene value (CDV), acid value (AV), and carbonyl value (CV). In general, frying stability of the CAO significantly (P < 0.05) improved in the presence of the SEO and RBO. The positive effect of the SEO on the stability of the CAO was more than that of the RBO. Increasing the amounts of SEO and RBO from 3 to 6% led to decreases in the TPC and AV, and increases in the CDV and CV of the CAO during the frying process. The best frying performance for the CAO was obtained by use of 3% of both SEO and RBO together (CAO/SEO/RBO, 94:3:3 w/w/w).     

Antioxidative properties of phenolic acids and interaction with endogenous minor components during frying

The ability of selected phenolic acids to improve the frying performance of canola oil was evaluated in a frying test. The frying performance of the oil was assessed by analysis of total polar components (TPC), level of 4‐hydroxynonenal (HNE), and the rate of formation of volatile carbonyl compounds (VCC). All the tested phenolic acids; ferulic acid (FA), caffeic acid (CA), dihydrocaffeic acid (HCA), gallic acid (GA), and vanillic acid (VA) significantly increased the frying performance of canola oil triacylglycerols (CTG). At the end of the frying test, the amount of TPC in CTG was 22.9 ± 1.0% compared to a maximum of 18.8 ± 0.8% in CTG fortified with the phenolic acids. Similarly, the level of HNE was reduced by up to 45% when it was supplemented with phenolic acids. The results showed that ethyl ferulate (EF) was a better antioxidant than FA under frying conditions; HCA offered a slightly better protection than CA; and the cinnamic acid derivative, FA was better than VA, its benzoic acid analogue. A significant synergy was observed between phenolic acids and the sterol fraction isolated from canola oil. The observed synergy was attributed to the possible formation of steryl phenolates during the frying test. Practical applications: The poor thermal stability of polyunsaturated oils limits their application for prolonged frying. PUFA offer important health benefits and can improve nutritional value of fried foods. Contrary to the commonly applied synthetic antioxidants, the phenolic acids tested in this study often are part of endogenous oil components present in oilseeds and also in some oils, and are known for their positive health benefits. Thus, the simple phenolic acids, especially the cinnamic acid derivatives may be applied as potent antioxidants to protect oils during thermal processes used for food production.     

Review of stability measurements for frying oils and fried food flavor

Measurements of degradation in frying oils based on oil physical properties and volatile and nonvolatile decomposition products were reviewed. Rapid methods by means of test kits were also considered. Factors that affect the analysis of total polar components (TPC) in frying oils were examined. Relationships between TPC, free fatty acid (FFA) content, Food Oil Sensor readings (FOS), color change (ΔE), oil fry life and fried-food flavor were evaluated. Flavor scores for codfish, fried in fresh and discarded commercial frying oil blends, were dependent upon individuals in the consumer panel (n=77). Part (n=29) of the panel preferred the flavor of fresh fat; others (n=24) didn't; the rest (n=24) had no preference. FFA, FOS and TPC were analyzed in two soybean oils and in palm olein during a four-day period in which french fries were fried. Flavor score and volatiles of potatoes fried on days 1 and 4 in each oil were also determined. TPC, FFA and FOS significantly increased (P<0.05) in all oils during the frying period. TPC and FFA were highest in the used palm olein, and flavor of potatoes fried in palm olein on day 1 was less desirable than those fried in the soybean oils. Potatoes fried in day-1 oils had significantly higher concentrations (P<0.10) of several pyrazines and aldehydes than those fried in day-4 oils. Presented at the 84th Annual Meeting of the American Oil Chemists' Society, Anaheim, California, April 25–29, 1993.     

MODELING WATER LOSS DURING FRYING OF POTATO STRIPS: EFFECT OF SOLUTE IMPREGNATION

The effect of solute impregnation on water loss and oil uptake during potato strip frying was studied. Blanched potato strips were impregnated at 25°C by soaking in a solution of sucrose-NaCl-water, 20-5-75% by weight. After rinsing and air drying, strips were deep fried in sunflower oil at 160, 170 and 180°C. A control treatment, consisting of potato strips blanched but not soaked and later air dried was also conducted. Solute impregnation provided a decrease of the oil uptake. Two models, based on Fick's law were used to describe water loss during frying. The first one is the classic model with an effective moisture diffusion coefficient assumed a constant value. The second model considers that diffusion coefficient varies during the frying process. For a given frying temperature, constant diffusion coefficient for control potatoes resulted in lower values than the impregnated ones. The variable diffusivity model showed a two-stage behavior: during the first stage of frying, diffusion coefficient increased with frying temperatures, but from a given time on an inverse behavior began. This last fact was found to be related to an increase of the measured peak force needed to penetrate the potato crust.     

Frying of Potatoes: Physical,Chemical, and Microstructural Changes

Frying is one of the oldest unit operations and is used not only in industry but also at home. The most commonly fried vegetable is potato, for important commercial products such as potato chips, par-fried potatoes, and french fries. Quality parameters of interest for fried potatoes include physical and chemical properties such as color, mechanical properties (e.g., crispness, hardness, etc.), structural properties (e.g., porosity and roughness), oil content, and water content, among others. Some chemical contaminants such as acrylamide and furan are heat-generated during the frying of potato slices or strips, leading to final fried pieces with considerable amounts of these contaminants. The controllable variables in industrial frying processes are generally potato variety, oil type, frying time, and frying temperature. Therefore, the study of the quality changes during frying is critical because knowledge regarding kinetics parameters will enable prediction of the final quality in fried potatoes and improvements in the final product value by selecting properly the processing conditions. Finally, modern techniques such as computer vision provide valuable tools to quantify and predict physical and chemical properties of potato pieces during frying in a fast and noninvasive way. In addition, computer vision can allow us to classify fried potatoes in different quality classes previously determined by sensorial panels.     

Optimising the baking and frying process using oil‐improving agents

Despite slimness mania and acrylamide scare, the market of fried products is still growing. Frying is an extremely effective way to cook food. A fried product tastes good, has a good flavour and is prepared within a few minutes. Every effort has been made to optimise the frying process. With regard to the quality of the fried food, the quality of the frying oil is very important. In the past, important characteristics of industrial frying oils were oxidative stability, high smoke point and low foaming. Nowadays, new frying fats with various additives, with a healthier fatty acid profile and higher heat stability are emerging. Emulsifiers, anti‐polymerising agents, and natural and synthetic antioxidants improve the performance during frying. Sesamol, rosemary and other natural extracts display strong stabilising effects during the frying operations. Filtration and the use of heat‐stabilising additives help to retard fat degradation and give the producer a larger time‐window for optimum frying. The effectiveness of the treatment with filter aids or mineral adsorbents and the stabilising effects of synthetic and natural agents were compared by using the Rancimat test for testing oxidative stability and the OSET (oxidative stability at elevated temperature) test to determine the stability at the frying temperature.     

Effectiveness of modified zeolites as adsorbent materials for frying oils

Natural zeolite was modified by four different techniques namely using Tween80, β‐cyclodextrine and olive mill waste water at RT and hydrochloric acid at 110°C, and then modified zeolites were used as adsorbent materials in six consecutive days dough frying with refined hazelnut oil. Some parameters in the oil samples of control and experimental groups were measured and the ranges were determined as following; total polar materials (TPM)‐chromatography (4.09–70.22%), free acidity (0.16–1.19%), smoke point (221.50–184.00°C), conjugated dienoic acids (0.36–2.19%), L value (35.65–52.15), a* value (?0.18–5.98), b* value (?3.73–10.40), turbidity (0.70–10.40 NTU), viscosity (67.67–825.50 cP), and oil absorbed by the dough (5.10–8.85%). The results of this study have shown that both natural zeolite and modified zeolites have different level of activities as frying oil adsorbent materials. The best results were achieved with Tween80 modified zeolite for the TPMs, free acidity, instrumental color values, smoke point, and conjugated dienoic acid measurements. Similarly better result for turbidity was with olive mill waste water modified zeolite and for viscosity was with hydrochloric acid modified zeolite. It was determined that adsorbent treatment did not affect fat absorption level of fried dough. Practical applications : The results of this study have shown that natural zeolite modification with different techniques can improve its adsorption capacity significantly. In this respect, utilization of modified zeolite for frying oil recovery applications can be an industrially sound practice since natural zeolite is a very cheap and easily found material.     

Enrichment of frying oils with plant phenolic extracts to extend the usage life

The aim of this research was to evaluate the efficacy of extracts prepared from olive leaf (OLVL), hazelnut leaf (HAZL), and hazelnut green leafy cover (HGLC) in frying conditions. The extracts were added into canola oil at 200 ppm phenolic equivalence level and fried for seven consecutive days and analyzed. Generally, the lowest phenolic content and antioxidant capacity value were measured in HGLC extract, although, the best performance during frying was with HGLC extract. There were significant differences among the free acidity, conjugated dienoic acids, and total polar materials (TPM). The oil enriched with HGLC extract did not exceed the limit TPM value at the end of seventh day. Also the remaining antioxidant capacities in the frying oil samples were highest in HGLC enriched samples. The viscosity and turbidity values of the oils enriched with OLVL and HAZL extract were a little higher than a control sample. Generally trans‐fatty acid formation was lower in the enriched oil samples. Also significant decreases in the level of unsaturated fatty acids during frying period were observed. This study shows that enriching oils with easily found and cheap natural plant extracts can extend their usage life. Practical applications: The results of this study have shown that liquid frying oils can successfully be enriched with plant phenolic extract to enhance thermo‐oxidative stability. Addition of phenolic extract up to 200 ppm level have not created any problem in sensory quality of either the oil or fried dough. The HGLC and OLVL extract were found very suitable for this purpose. These materials are common agro‐food by‐products and can be produced very easily with low cost. Also, this type of enrichment may aid consumers to get some beneficial phenolic compounds through fried food consumption. In addition, these types of applications may open another area for marketing the named plant extracts.     

Monitoring of Changes in Composition of Soybean Oil During Deep-Fat Frying with Different Food Types

Changes in the composition of soybean oil during deep‐fat frying with wheat dough (WD) and chicken breast meat (CBM) were comparatively investigated using gas chromatography–mass spectrometry and Fourier transform infrared spectroscopy (FTIR). The amounts of saturated fatty acids (FAs) and short‐chain FAs were increased. The amount of unsaturated FAs was decreased as the processing time increased. An increase in the amount of tetradecanoic acid and 9‐cis‐hexadecanoic acid was observed during the CBM frying only. The FTIR spectrum of frying oil was analyzed by extracting the entire information as the area ratios based on vibration absorptions of the specific functional groups. Changes in content of functional groups, namely cis C=C, trans C=C, C=O, C–O, O–H, and C–H, were studied by the FTIR‐based method. Based on the changes in the content of FAs and functional groups, soybean oil fried with CBM degraded more quickly than that fried with WD. Moreover, good linear correlations between the change in contents of functional groups and the mass percentages of FAs were also observed. The FTIR‐based method could be used in real time to monitor the quality of frying oil during the deep‐fat frying.     

Specific Heat Capacity Measurements of Frying Oil Using Modulated Differential Scanning Calorimetry

The specific heat capacity (c_p) of frying oils is of practical importance in engineering work associated with refining operations and the thermal resistance during application. The objective of this study was to use modulated differential scanning calorimetry (MDSC) to measure the specific heat capacity of frying oil. Samples were exposed to a cyclic heating profile that was generated by a linear heating rate while simultaneously superimposing a sinusoidally varying time–temperature wave. The c_p variation of three commercial frying oils during frying was tested over a temperature range between 0 and 250 °C, and the correlation of c_p with triacylglycerol (TAG) polymer contents, total polar compounds (TPC), and polar fractions was studied. Results indicated that the specific heat capacity of frying oils increased linearly as temperature increased. During frying, c_p had a positive relation with TAG polymers and TPC at the beginning, but finally decreased when frying ended. This was possibly associated with the variation of polar fractions as frying continued. The large molecular compounds and small molecular compounds of polar fractions were considered to contribute oppositely to c_p, which led to its final decrease.