Effects of Sesame Oil Addition to Soybean Oil During Frying on the Lipid Oxidative Stability and Antioxidants Contents of the Fried Products During Storage in the Dark

ABSTRACT: Effects of sesame oil addition to soybean oil during frying on the lipid oxidative stability and antioxidants contents of fried products during storage in the dark were studied. Flour dough pieces (2 cm × 2 cm × 0.1 cm) were fried at 160 °C for 1 min in sesame oil-added soybean oil. Concentrations of sesame oil in the frying oil were 0%, 10%, and 20% by volume. Fried products were put into a glass bottle, and the bottles were tightly sealed and stored at 60 °C in the dark for 18 d. Lipid oxidation of fried products was determined by fatty acid composition changes and conjugated dienoic acid (CDA) and p -anisidine (PA) values. Tocopherols and lignan compounds in the fried products were determined by high-performance liquid chromatography. Relative content of linolenic acid decreased, and CDA and PA values increased during storage of the fried products in the dark. Fatty acid composition change and CDA and PA values during storage were lower in the products fried in sesame oil-added soybean oil than in the products fried in soybean oil without sesame oil. The results clearly showed that addition of roasted sesame oil to soybean oil at 10% and 20% during frying decreased the lipid oxidation of fried products during storage in the dark for 18 d by extension of induction period and decrease in decomposition of oxidized lipids. Fried products contained 134 to 267 ppm tocopherols and 0 to 148 ppm lignans before storage; however, their contents decreased during storage in the dark. Lignan compounds were more stable than tocopherols, and the rate of tocopherols degradation was lower in the products fried in sesame oil-added soybean oil than in the products fried in soybean oil without sesame oil, which could be because of protection of tocopherols from degradation by lignan compounds.     

Oxidation of corn oil during frying of soy-flour-added flour dough

ABSTRACT:  Oxidation of corn oil during frying of soy–flour-added dough was studied. Flour dough containing soy flour at 0%, 10%, 20%, and 30% was fried in corn oil at 180 °C for 2.5 min, and a total of 60 fryings were performed every 30 min. The oxidation of oil was determined by contents of free fatty acids (FFA), conjugated dienoic acids (CDA), polar compounds, and p -anisidine values (PAV). Tocopherols and phospholipids (PLs) in the oil were determined by HPLC. Tocopherols were present in corn oil at 1000 ppm before frying and increased after the first frying of dough containing soy flour due to tocopherol transfer from soy–flour-added dough to the oil during frying. However, as the oil repeated frying, tocopherol contents decreased and its degradation rate was higher in the oil that fried soy–flour-added dough than in the oil that fried the dough without soy flour. PL was not detected in corn oil before and after frying. As the oil repeated frying, FFA, CDA, and polar compounds contents, and PAV of frying oil increased due to the oil oxidation. The values were higher in the oil which fried soy–flour-added dough than in the oil fried the dough without soy flour, indicating the acceleration of oil oxidation by soy flour added to dough. Increase in the oil oxidation by soy flour added to the dough was highly correlated with fast decomposition of tocopherol in the oil.     

Effects of sesamol, sesamin, and sesamolin extracted from roasted sesame oil on the thermal oxidation of methyl linoleate

This study investigated the effects of lignan compounds extracted from roasted sesame oil, which were sesamol, sesamin, and sesamolin, on oxidation of methyl linoleate (ML) during heating. These compounds were added at 500 or 1000 mg/kg to ML, and α-tocopherol was used as a reference antioxidant. The ML added with lignans or α-tocopherol was heated at 180 °C for 60 min. Thermal oxidation of ML was evaluated by conjugated dienoic acid (CDA) contents, p-anisidine value (PAV), and ML retention. Contents changes of lignan compounds or α-tocopherol in ML during heating were monitored by high-performance liquid chromatography. CDA contents and PAV of samples increased and ML decreased with heating time at 180 °C. Samples added with lignan compounds showed lower CDA contents and PAV but higher ML retention than samples without lignan compounds. The antioxidant activity of sesame oil lignan compounds in ML oxidation during heating tended to be higher than that of α-tocopherol. The contents of lignan compounds in samples decreased with heating time due to their degradation, but the degradation rates were lower than that of α-tocopherol. This study suggested that sesame oil lignan compounds be used as antioxidants in oil at high temperatures for deep-fat frying due to their higher effectiveness and stability than α-tocopherol.     

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.     

Effects of Bleaching on the Properties of Roasted Sesame Oil

ABSTRACT: Improvement in quality of roasted sesame oil was studied. Roasted sesame oil was bleached at 70 °C, 85 °C, or 100 °C for 20 min with acid-activated clay at 0.5%, 1.0%, or 3.0% (w/w) and then centrifuging at 12096 × g at 4 °C for 10 min. The color of the roasted sesame oil became lighter and the viscosity of oil decreased by bleaching. Bleaching caused a significant increase in the smoke point of the oil, from 170 °C to a range of 183 °C to 191 °C. Bleaching increased palmitic acid and decreased linoleic acid contents of roasted sesame oil. Bleaching decreased free fatty acid (FFA) and conjugated dienoic acid (CDA) contents and carbonyl values (CV) of roasted sesame oil. The more the acid clay was used, the lower were the FFA and CDA contents and CV of the oil. Amount of acid clay in bleaching of roasted sesame oil had higher effects on the color, viscosity, smoke point, FFA and CDA contents, and CV of roasted sesame oil than the bleaching temperature. Bleaching did not show a significant effect on tocopherol contents of the sesame oil. Bleaching tended to decrease sesamolin contents and increase sesamol contents in the roasted sesame oil. As the amount of acid clay and the bleaching temperature increased, the contents of sesamin and sesamolin in the oil decreased while sesamol contents increased.     

Extraction of Lignan Compounds from Roasted Sesame Oil and their Effects on the Autoxidation of Methyl Linoleate

ABSTRACT:  Lignan compounds were extracted from roasted sesame oil and their effects on the autoxidation of methyl linoleate (ML) were studied. Lignan compounds extracted from roasted sesame oil, sesamol, sesamin, and sesamolin, were added to ML, which was then oxidized at 60 ^oC for 18 h in the dark. Alpha-tocopherol was separately added to ML for a reference antioxidant. Degree of ML oxidation was monitored by conjugated dienoic acid (CDA) contents and p -anisidine value (PAV) by AOCS methods, and ML retention by gas chromatography. CDA contents and PAV of samples increased with the oxidation time at 60 ^oC in the dark, and ML decreased. Sesamol-, sesamin-, or sesamolin-added samples showed lower CDA contents, PAV, and ML loss than the samples without lignans during oxidation in the dark, which indicated that lignan compounds lowered the ML autoxidation. The antioxidant activity of sesamol was significantly higher ( P < 0.05) than that of sesamin, sesamolin, or α-tocopherol. Lignan compounds added to ML were degraded during the autoxidation of ML, and the degradation rate was higher in sesamol- than in sesamin-, or sesamolin-added ML, but was lower than in tocopherol-added samples. As the lignan compounds concentration in ML increased, the degradation rate of lignans decreased, and the inhibition of the ML autoxidation by lignan compounds increased. The results strongly suggested that the autoxidative stability of ML could be improved by the addition of sesamol, sesamin, or sesamolin extracted from the roasted sesame oil.     

Chemistry of deep-fat frying oils

ABSTRACT:  Deep-fat frying produces desirable or undesirable flavor compounds and changes the flavor stability and quality of the oil by hydrolysis, oxidation, and polymerization. Tocopherols, essential amino acids, and fatty acids in foods are degraded during deep-fat frying. The reactions in deep-fat frying depend on factors such as replenishment of fresh oil, frying conditions, original quality of frying oil, food materials, type of fryer, antioxidants, and oxygen concentration. High frying temperature, the number of fryings, the contents of free fatty acids, polyvalent metals, and unsaturated fatty acids of oil decrease the oxidative stability and flavor quality of oil. Antioxidant decreases the frying oil oxidation, but the effectiveness of antioxidant decreases with high frying temperature. Lignan compounds in sesame oil are effective antioxidants in deep-fat frying.     

Physicochemical properties and oxidative stability of frying oils during repeated frying of potato chips

Physicochemical properties and oxidative stability of refined coconut oil (RCO), refined soybean oil (SBO), pure olive oil (POO), and vegetable shortening (VST) during repeated frying of potato chips were determined. Polyunsaturated fatty acids of all the oils significantly decreased after frying. Tocopherols in SBO, POO and VST, and DPPH radical scavenging activities of POO and VST significantly decreased after frying. L* values of the oils significantly decreased, and a* and b* values significantly increased after 80 times repeated frying. Conjugated dienes and p-anisidine value of SBO after 80 times repeated frying were 21.8 mmol/L and 47.7, respectively, the highest among the oils. Levels of total polar compounds of all the oils after 80 times repeated frying were between 8.1 and 9.5%, not exceeding rejection limit after frying. Compositions and contents of alkanals, 2-alkenals, and 2,4-alkadienals in the oils during frying were largely affected by their fatty acid compositions.     

Stability of tocopherols and lutein in oil extracted from roasted or unroasted mustard seeds during the oil oxidation in the dark

This study compared stabilities of tocopherols and lutein in oil extracted from roasted mustard seeds (RMSO) with those in oil from unroasted seeds (URMSO) during oil oxidation at 60°C in the dark for 12 days. Tocopherols and lutein were determined by high performance liquid chromatography, and the oil oxidation was monitored with conjugated dienoic acid (CDA) content and fatty acid composition by gas chromatography. The rate of CDA increase was lower in RMSO (0.038%/day) than in URMSO (0.047%/day) during 12-day oxidation in the dark, with little change in fatty acid composition in both oils. Tocopherols and lutein were more abundant in RMSO, initially 465.38 and 100.55 μg/g, respectively, than in URMSO, and their stability was higher in RMSO (−4.63 and −5.94%/day of degradation in tocopherols and lutein, respectively) than in URMSO during 12-day oxidation of oil, both of which contributed to higher autoxidative stability of RMSO than URMSO.     

The recovery of used sunflower seed oil utilized in repeated deep-fat frying process

In this study, 50 consecutive deep-fat fryings were done by frying potato samples, each weighing 100 g, in sunflower seed oil at 170 °C. Significant chemical and physical changes in sunflower seed oil were observed during frying. A number of official methods were used to evaluate its adsorption abilities including free fatty acids (FFA), peroxide value (PV), conjugated dienes at 232 nm, secondary oxidation products at 270 nm and specific heat value determination. These parameters were determined in oil samples taken after each of the ten fryings before and after adsorbent treatment. A mixture of 2% pekmez earth, 3% bentonite, and 3% magnesium silicate was used as the adsorbent mixture. The FFA content of oil increased from 0.17 to 0.29% during frying. The use of adsorbents reduced FFA content of the used oil to 0.13%, i.e., a value below the FFA content of fresh oil (0.17%). Peroxide values decreased during frying because of decomposition of peroxides at high temperatures. A significant reduction was obtained in peroxide and conjugated diene values (K₂₃₂ value) due to the adsorbent treatment. However, the treatment increased the amount of secondary oxidation products (K₂₇₀ value). The specific heats of untreated used oil were higher than specific heats of adsorbent treated used oil over the entire frying process.     

EFFECTS OF SESAME LIGNAN EXTRACT ON LINOLEIC ACID, LIPID OXIDATION, COLOR AND TEXTURAL PROPERTIES OF GROUND PORK, AND SAUSAGE PRODUCTS

Sesame lignan extract was prepared from roasted sesame oil and added at 0.02, 0.05, 0.10 and 0.20% (w/w) to linoleic acid and ground pork products. Cooked ground pork containing more than 0.02% of lignan extract showed TBA values lower than those containing butylated hydroxyanisole (BHA) during storage. Sausages containing 0.05% of lignan extract had lower thiobarbituric acid (TBA) values when stored at 4C for 14 days; they also showed higher CIE color values than the control meat sample (P < 0.05). There were no differences in textural properties such as hardness, cohesiveness and chewiness between the control and the sausages containing lignan extract when determined by Instron Testing Machine. Thus, lignan extract prepared from roasted sesame oils was highly antioxidative when used in cooked ground pork at > 0.02% or in sausages at > 0.05%.     

煎炸油中极性物质与酸价之间的相关性研究

本实验以油茶籽油、橄榄油和棕榈油为研究对象,研究经过180℃下油炸薯条后三种油的酸价与极性物质的相关性以及主要脂肪酸的变化。发现,三种油随着油炸时间的增加酸价(p<0.05)显著增大。油茶籽油、橄榄油和棕榈油的最终酸价分别为0.32、0.66、0.58mg/g。经过20次油炸,三种油的总极性物质(TPC)显著增加,油茶籽油、橄榄油和棕榈油总极性物质分别为16.01%、20.91%和17.66%。随着油炸时间的增加,三种煎炸油的饱和脂肪酸含量显著增加。不饱和脂肪酸的含量变化较大,C18∶2和C18∶3显著下降,而C18∶1逐渐下降。      

COMPARISON OF THE FRYING STABILITY OF REGULAR AND LOW-LINOLENIC ACID SOYBEAN OILS

The frying stability of a regular soybean oil (RSO) was compared with a modified low linolenic-acid soybean oil (LLSO). The rate of free fatty acid (FFA) formation was similar for both oils during 72 h of frying. Despite a reduction in polyunsaturated fatty acids, however, the rate of formation of total polar compounds (TPC) in LLSO was greater than RSO. The higher production of TPCs in LLSO was explained, in part, by a lower level of tocopherols and a more rapid rate of degradation of the main isomers, γ- and δ tocopherols. This study points to the limitations of predicting frying stability based solely on fatty acid composition.     

Estimating the time of frying oils have been used for French fries based on profile changes of fatty acids derived from heated oil model systems

Time of use for frying oils recovered from French fries was estimated based on ratios of fatty acids and values of conjugated dienoic acid (CDA) and/or p-anisidine (p-AV) derived from oxidation data of oils heated to 180°C in model systems. Changes in CDA and p-AV values in oils occurred faster than changes in ratios of fatty acids (oleic to linoleic acids, O/L) and saturated to unsaturated fatty acids (SFAs/UFAs). Oil use times estimated by O/L SFAs/UFAs ratios, and on CDA and p-AV values in oil recovered from French fries were 1.38, 1.42, 0.36, and 0.22 h, respectively. The actual oil use time was 1.5 h. Although oxidation parameters from heated oil models may not accurately reflect changes in oils during deep-fat frying of French fries, ratios of fatty acids in oils may be more useful for predicting the use time of frying oils than CDA and p-AV values.     

Lipid oxidation-related characteristics of gim bugak (Korean fried cuisine with <Emphasis Type="Italic">Porphyra</Emphasis>) affected by frying oil

The effect of frying oil on the lipid oxidation, antioxidants, and in vitro antioxidant activity of gim bugak was studied. Bugak was prepared by pan-frying at 180 °C in unroasted sesame, soybean, extra virgin olive, or palm oil. The degree of lipid oxidation based on conjugated dienoic acid and p-anisidine values was higher in the bugak fried in soybean or sesame oil with high contents of polyunsaturated fatty acids and tocopherols. However, the oil oxidation was lower in olive and palm oils, which showed higher degradation of tocopherols and polyphenols than in sesame or soybean oil during frying. Although the bugak fried in palm oil contained less antioxidants than that fried in soybean or sesame oil, the in vitro antioxidant activity was not different (p > 0.05). Results suggest that palm oil can replace unroasted sesame oil for the preparation of gim bugak with improved lipid oxidative stability and health functionality.     

Quality changes in mixtures of hydrogenated and non‐hydrogenated oils during frying

BACKGROUND: There is a need for frying oils with reduced trans fatty acid content and increased oxidative stability. This study was conducted to measure and compare frying oil quality parameters, namely colour, viscosity, free fatty acid (FFA) content and dielectric property, and to investigate changes in properties of mixtures of fully hydrogenated and non‐hydrogenated canola oils during deep‐fat frying of chicken nuggets. Proportions of hydrogenated oil to non‐hydrogenated oil used in the study were 0, 20, 40, 60, 80 and 100%. Chicken nuggets were fried at 190 °C. The relationships among quality parameters, frying time and oil type were investigated. RESULTS: Frying time and oil type had significant effects on all properties. First‐order kinetic equations were used to represent changes in colour, viscosity and FFA content. The rates of change of viscosity and FFA content were higher in non‐hydrogenated oil, whereas the rates of change of colour were similar in the different oils. Increasing the level of hydrogenated oil in the mixture resulted in only slight changes in quality parameters. CONCLUSION: Quality parameters, namely colour, viscosity, FFA content and dielectric property, of frying oil are significantly affected by frying time and hydrogenation level. Frying oil quality and stability can be adjusted by mixing hydrogenated and non‐hydrogenated oils. Copyright © 2008 Society of Chemical Industry     

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     

Effect of a novel induction food‐processing device in improving frying oil quality

Producing quality fried snacks involves monitoring the chemical processes that occur during frying to control oil degradation. Our objective was to evaluate the effects of a Novel Induction Food‐Processing Device (NIFPD) on the quality indices of frying oil. Under standard frying conditions, vegetable oil samples (corn and canola) were collected during a standardised frying cycle to test oxidative stability. Fourier transform infrared spectroscopy was used to evaluate and classify samples during the frying time, and standard reference methods used to monitor the oil stability included p‐anisidine value, free fatty acid content and CIELAB colour. The induction technology decreased the rate of free fatty acid and aldehyde formation. Tests also showed a marked effect on total colour difference between control and treatment (NIFPD), reducing colour degradation. Overall, our results showed that a patented induction device slows the rate of lipid degradation, resulting 7–20% reduction in formation rate of key quality parameters and significantly longer utilisation of frying oil.     

以棉籽油为基料油的煎炸专用调和油煎炸品质的研究

以棉籽油为基料油,添加大豆油、菜籽油、棕榈油进行调配,制成煎炸专用的植物调和油。用制得的煎炸调和油进行不间断地煎炸薯条试验,考察煎炸油在煎炸过程中油脂色泽、理化指标及品质的变化情况。结果表明:煎炸调和油的脂肪酸组成合理,满足单不饱和脂肪酸/多不饱和脂肪酸=4.0:0.6的最佳摄入比例。煎炸过程中色泽变化较慢,极性组分超过27%限量的时间为67 h,酸价由(0.18±0.05) mg/g增加至(3.53±0.10) mg/g,羰基价由(9.42±0.12) meq/kg增加至(36.0±0.14) meq/kg,过氧化值和苯并(α)芘没有明显的变化趋势,丙烯酰胺未检出;与河北地区常用于煎炸的三级棉籽油46 h的煎炸寿命和较高的羰基价、过氧化值和苯并(α)芘相比,配制的煎炸调和油的煎炸寿命延长了18 h,稳定性提高了37%,煎炸薯条的平均含油率为18%煎炸感官效果好,可以作为一种新型煎炸调和油。     

Physico-chemical changes occurring in oil when atmospheric frying is combined with post-frying vacuum application

The aim of this study was to investigate the effect of atmospheric frying followed by drainage under vacuum on the stability of oil, compared to similar frying with drainage at atmospheric pressure. Changes in the oil were assessed by the free fatty acid (FFA) content, p-anisidine value (AnV), colour, viscosity, fatty acid profile and concentration of tocols. The rate of FFA formation in the case of vacuum drainage was found to be about half that of atmospheric drainage. Oil deterioration by oxidation and polymerisation was also reduced by the use of vacuum drainage. The AnV of the oil after vacuum drainage was lower by about 12%, the total colour difference was improved by 14% and viscosity was slightly reduced after 5 days of frying, compared to the values for oil that had been drained at atmospheric pressure. There was a reduction in the loss of polyunsaturated fatty acids in the case of vacuum drainage after 5 days of frying but differences in retention of tocols were only evident in the first two days of frying.