Stabilisation of sunflower oil and reduction of acrylamide formation of potato with rosemary extract during deep-fat frying

The aim of this study was to evaluate the effects of rosemary extract on the stabilisation of sunflower oil and the reduction of acrylamide formation in potato during deep-fat frying. The synthetic antioxidants butylated hydroxyanisole, tertiary butylhydroquinone, and tocopherols served as positive controls. Thermo-oxidative alterations were measured according to various physical and chemical parameters. Total polar compounds, free fatty acids, conjugated dienes, conjugated trienes, and colour (L*, b*) were evaluated for effectiveness of the antioxidants to stabilise the sunflower oil. The acrylamide concentration was evaluated for effectiveness of the antioxidants to reduce the acrylamide content in the deep-fried potato. Except for the decreased L* value (darkness of oil colour), these parameters all increased with the number of frying cycles. The order of effectiveness for inhibition of sunflower oil degradation and reduction of acrylamide formation in deep-fried potato was: rosemary extract > tocopherols > tertiary butylhydroquinone > butylated hydroxyanisole > control (P < 0.05). Total polar compounds, free fatty acid and acrylamide levels were significantly correlated with frying time (P < 0.05). The acrylamide formation in fried potatoes was significantly correlated with the formation of total polar compounds (P < 0.05) in the frying oil during the frying process.     

Simultaneous monitoring of the conventional qualitative indicators during frying of sunflower oil

Deterioration of sunflower oil during a 32 h frying was studied by monitoring the levels of polar compounds (total content, TPC; triglyceride polymers, TGP; triglyceride dimmers, TGD; oxidised triglyceride monomers, oxTGM; diglycerides, DG; and free fatty acids, FFA), carbonyl value (CV), oil/oxidative stability index (OSI), and conjugated diene value (CDV). The frying process increased the level of TPC in the oil from 2.8% to 28.9%. The TGP, TGD, oxTGM, DG, and FFA increased 186.5, 29.1, 6.1, 5.1, and 5.4 times, respectively. The CV, OSI, and CDV changed from 7.9 μmol/g, 2.7 h, and 10.6 mmol/l to 70.9 μmol/g, 1.2 h, and 61.6 mmol/l, respectively. The TPC or TGDP (TGD + TGP) contents were significantly correlated with the CV, OSI, or CDV. Finally, it was recommended that the sunflower oil should be discarded at 10% TGDP, 20% TPC, or 44 mmol/l CDV.     

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.     

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.     

Quality changes in trans and trans free fats/oils and products during frying

The physico-chemical changes occurring during simulated frying conditions at 180 °C for 24 h in trans free speciality fat, trans rich vanaspati and PUFA rich sunflower oil were evaluated. The samples became darker, the polar components and viscosity increased as the time of heating increased. The oxidative stability as determined by peroxide, anisidine values and TOTOX number, increased, whereas the total unsaturated fatty acids and iodine value decreased with time of heating in all the samples. The trans free speciality fat was as stable as vanaspati showing similar quality parameters, while sunflower oil showed a higher degree of deterioration. The layered fat used for traditional products such as Chiroti dough consisted 14% trans fatty acids (TFA), which was reduced to 4–7%, and correspondingly 18:2 was increased in the product upon frying in sunflower oil. Accordingly, trans fatty acids increased in the medium from 0 to 7.5%. Chiroti when fried in vanaspati with TFA 18%, their content in both products (16%) and in medium (17%) remained similar.     

Use of some agricultural waste hull ashes for the regeneration of fried sunflower oil

The present study was aimed at improving the quality of fried sunflower oil. Synthetic (Magnesol XL), natural (diatomaceous earth) and hull ashes of rice, wheat and barley (agriculture plant wastes) were used to adsorb the oxidation products of fried sunflower oil. The mineral pattern (Si, Mg, Ca, Fe, Al, Mn and Cu) of the aforementioned substances were determined. The physico-chemical properties [refractive index, viscosity, colour, smoke point, acid value, peroxide value, thiobarbituric acid (TBA) value, conjugated dienes and trienes, polar content, polymer content and oxidised fatty acids] of non-fried, fried and fried-treated sunflower oil were determined. The frying process was carried out at 180 °C ± 5 °C for 20 h, 4 h heating cycle per day for five consecutive days. The fried sunflower oil was treated with synthetic, natural and agricultural hull ashes at 105 °C for 15 min. The results indicate that Magnesol XL, diatomaceous earth, rice hull ash, wheat hull ash and barley hull ash contained Si + Mg + Mn, Si + Mn + Ca, Si + Mn, Si +Mn and Mn + Si as the basic metals, respectively. Frying of sunflower oil led to significant increase in refractive index, viscosity, colour, smoke point, acid value, peroxide value, TBA value, conjugated dienes and trienes, polar content, polymer content, and oxidised fatty acids and decrease in iodine value. Treatments of fried sunflower oil with the aforementioned substances greatly improved the quality of fried oil. Under the present experimental conditions all adsorbing substances performed similarly in removing the fried sunflower oil oxidation products.     

The determination of frying oil quality using Fourier transform infrared attenuated total reflectance

The possibility of using the whole spectra (wave numbers between 4000 and 850 cm⁻¹) from Fourier transform infrared attenuated total reflectance spectroscopy (FTIR-ATR) to differentiate between good, marginal and unacceptable oils with regard to various intensities of oil rancidity was investigated. Fresh, used, and discarded oils were collected from several fast food restaurants from each frying cycle for 4 weeks. Dielectric constant, peroxide value, free fatty acid content, and density of oil samples significantly (P<0.01) increased with frying time. The correlation (r) between FTIR absorbance at 3300 cm⁻¹ and free fatty acid content was from 0.84 to 0.94 for oils from the three restaurants. Similarly, the correlation between FTIR absorbance at 3471 cm⁻¹ and peroxide value was from 0.90 to 0.97. The results of principal component analysis using the whole spectra (4000-850 cm⁻¹) showed good discrimination and stability for identification between acceptable, marginal and unacceptable frying oils.     

A chromametric method for the rapid assessment of deep frying oil quality

A rapid chromametric method was developed for the assessment of deep frying oil quality based on the strong correlation between colour index and total polar compounds in deep frying oil. Colour indices of frying oil samples, measured by chromameter, decreased significantly during frying and were strongly correlated with frying time (r ≥ 0.95, p < 0.001). Colour indices of a set of oil samples taken from 0 to 80 h of deep frying were also significantly correlated with total polar compounds of the same samples determined using the official method of the American Oil Chemists' Society (r = 0.96, p < 0.001). The equation for conversion of the colour index (x) to the content of total polar compounds (y) in an oil sample is y = 0.0174x² ? 2.9506x + 124.34. In addition, colour indices of 10 different types of frying oils were strongly correlated with the corresponding contents of total polar compounds in the oils with samples taken from 0 to 80 h of deep frying in duplicate (r = 0.95, p < 0.001, n = 220). The results of colour index analyses agreed well with the results of chemical and sensory analyses of the frying oils tested. This chromametric method is rapid, convenient and reliable. Copyright © 2003 Society of Chemical Industry     

Polar compounds distribution of sunflower oil as affected by unsaponifiable matters of Bene hull oil (BHO) and tertiary-butylhydroquinone (TBHQ) during deep-frying

Total polar compounds (TPC) contents of the sunflower oil (SFO) increased linearly (R² > 0.99) with frying time. At the same concentration (100 ppm), the increase rate of the TPC content for the SFO containing the unsaponifiable matters (USM) of the Bene hull oil (BHO) was lower than that for the SFO containing the tertiary-butylhydroquinone (TBHQ). The TPC analysis by high-performance size-exclusion chromatography allowed the separation and quantification of triglyceride polymers (TGP), triglyceride dimers (TGD), oxidised triglyceride monomers (oxTGM), diglycerides (DG), and free fatty acids (FFA) during frying. The ability of the USM to resist the TGP formation was higher than that of the TBHQ. The USM and TBHQ showed lower influences on the changes in TGD and oxTGM contents, as well as there was an effectiveness better for the USM than for the TBHQ. The increase rate of DG and FFA contents more effectively decreased by the USM rather than by the TBHQ.     

Antioxidative properties of Pandanus amaryllifolius leaf extracts in accelerated oxidation and deep frying studies

The potential uses of Pandanus amaryllifolius leaf extract as a natural antioxidant were evaluated in refined, bleached and deodorized (RBD) palm olein, using accelerated oxidation and deep frying studies at 180 °C from 0 to 40 h. The extracts (optimum concentration 0.2%) significantly retarded oil oxidation and deterioration (P < 0.05), comparably to 0.02% BHT in tests such as peroxide value, anisidine value, iodine value, free fatty acid, oxidative stability index (OSI), polar and polymer compound contents. In sensory evaluation studies, different batches of French fries were not significantly different (P < 0.05) from one another for oiliness, crispiness, taste and overall acceptability when the same oil was used for up to the 40th hour of frying. P. amaryllifolius leaf extract, which had a polyphenol content of 102 mg/g, exhibited an excellent heat-stable antioxidant property and may be a good natural alternative to existing synthetic antioxidants in the food industry.     

Composition, stability and acceptability of different vegetable oils used for frying peanuts

The purpose of this work was to determine the chemical stability of vegetable oils in the frying process and the consumer acceptance of fried-salted peanuts prepared in different vegetable oils. Fatty acids composition was determined in sunflower, corn, soybean, peanut and olive oils. A chemical study (free fatty acid and p-anisidine values) of these oils at frying temperature (170 °C) was developed during 96 h. Consumer test of fresh products was performed on fried-salted peanuts prepared in the different oils. Peanut oil and virgin olive oil presented oleic acid as predominant fatty acid (44.8% and 64.2%, respectively), making it more resistant to lipid oxidation at frying temperature than the other refined vegetable oils (sunflower, corn and soybean oils). Virgin olive and peanut oils showed less increment of free fatty acids and p-anisidine value than the other oils along the heating essay. In addition, fried-salted peanuts prepared with refined peanut oil showed higher consumer acceptance than those prepared with other vegetable oils such as sunflower, corn, soybean and olive oils. Peanut oil could be used to fry peanuts obtaining products with higher consumer acceptance and shelf-life, thus preventing loss of their sensory and nutritional quality.     

Lipid profile of foods fried in thermally polymerized palm oil

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

Quality characteristics of sesame seeds and by-products

The chemical composition, of raw sesame seed (RS); Sesame coats 1 (SC1) and sesame coats 2 (SC2) obtained as a by-product respectively after dehulling and roasting processes during preparation of sesame paste (tehineh) for the manufacturing of Halaweh (sweetened tehineh), was determined along with the physicochemical characteristics of the oil fraction. Compared to RS, SC1 and SC2 showed higher amounts of dietary fibre, ash and polyphenol and lower amounts of oil and protein. Oil from SC1 and SC2, had a higher content of free fatty acids, chlorophylls, polyphenols and sesamol than RS oil. SC2 oil showed more intense colour, more absorbance in UV-A, UV-B and UV-C ranges and a significant higher viscosity (P < 0.05). No differences (P > 0.05) were observed for refractive index, iodine value and fatty acids composition. This latter was essentially dominated by oleic and linoleic acids. Oxidative stability of oil was investigated using a Rancimat system and in an oven test at 65 °C over 60 days. RS oil was more resistant to the thermal treatment during a long period than SC1 and SC2 oils.     

Oxidative and thermal stabilities of genetically modified high oleic sunflower oil

The oxidative and thermal stabilities of genetically modified high oleic sunflower oil (87% oleic acid) were compared with those of regular sunflower (17% oleic acid), soybean, corn, and peanut oils during storage at 55 °C and simulated deep fat frying at 185 °C. Oxidative stability was evaluated by measuring the oxygen content and volatile compounds in the sample bottle headspace and peroxide value. The coefficient variations (CVs) for volatile compound, headspace oxygen, and peroxide value analyses were 2.02%, 1.41%, and 3.18%, respectively. The oxidative stability of high oleic sunflower oil was greater than those of regular sunflower and soybean oil (P < 0.05) and as good as those of corn and peanut oils (P > 0.05). The thermal stabilities of oils during deep fat frying were evaluated by measuring the infrared absorption at 2.9 μm and conjugated diene content. The CV of conjugated diene content was 1.07%. Infrared and conjugated diene results showed that the high oleic sunflower oil had greater thermal stability than had regular sunflower, soybean, corn, and peanut oils (P < 0.05). The genetically modified high oleic sunflower oil, with 5.5% linoleic acid, had better oxidative and thermal stabilities than had the regular sunflower oil with 71.6% linoleic acid.     

Production and refinement of oil from carp (Cyprinus carpio) viscera

Carp viscera oil can be obtained by both ensilage and fishmeal processes. This study examined the refinement of carp (Cyprinus carpio) oils obtained by both processes, and compared crude, neutralised, bleached, winterised and deodorised oils’ characteristics and lipid profiles. Refined oils obtained by the two processes did not present significant difference (p > 0.05) for Lovibond colour, free fatty acids, and thiobarbituric acid values. The major fatty acids identified in the carp crude, bleached and refined oils were oleic, palmitic, palmitoleic, linoleic and linolenic, constituting approximately 69.6% of the total fatty acids of the oils. The n − 3/n − 6 ratio was approximately 1.05 for refined oil. Therefore, carp viscera refined oil can be considered a rich source of essential fatty acids of the n − 3 and n − 6 series.     

Physicochemical properties and bioactive compounds of selected seed oils

The physicochemical properties and chemical composition of oil extracted from five varieties of plant seeds (bittermelon, Kalahari melon, kenaf, pumpkin and roselle seeds) were examined by established methods. The thermal properties of extracted oils by differential scanning calorimetry were also evaluated. Sensorial profiles of these seed oils were defined through the CieLab (L*, a*, b*) colour. Most of the quality indices and fatty acid compositions showed significant (P < 0.05) variations among the extracted oils. Physicochemical properties of the oils extracted were iodine value, 86.0-125.0 g I₂/100 g oil; saponification value, 171.0-190.7 mg of KOH/g of oil; acid value, 1.1-12.9 mg of KOH/g of oil, free fatty acid, 0.6-6.5 g/100 g of oil, and peroxide value 1.5-6.5 meq of O₂/kg of oil. Palmitic, oleic and linoleic acids were the major fatty acids in all of the extracted seed oils except for bittermelon, where eleostearic acid was the major fatty acid. Gallic, protocatechuic, p-hydroxybenzoic, vanillic, caffeic, syringic, p-coumaric and ferulic acids were identified in the extracted plant oils. Among these, vanillic acid was predominant in all extracted oils. The oils were rich in tocopherols with γ-tocopherol as the major components in all oil samples. Among the phytosterols, sitosterol was the major phytosterol extracted from the five plant seed oils. The seeds of these plants contain a great number of valuable minor compounds, which have a potential high value as food and for production of non-food products.     

Frying stability of high oleic sunflower oils as affected by composition of tocopherol isomers and linoleic acid content

The influence of linoleic acid content and tocopherol isomeric composition on the frying performance of high oleic sunflower oil was evaluated during a 14-day restaurant style frying operation. At equal linoleic acid content, no significant difference was observed between high oleic sunflower oil containing only α-tocopherol and the sample containing a mixture of α-, γ-, and δ-isomers as measured by the amount of total polar components, oligomers, anisidine value, and free fatty acids. On the contrary, at similar tocopherol isomeric composition, high oleic sunflower oil containing lower amount of linoleic acid showed superior frying stability compared to the sample with a higher content of linoleic acid, suggesting that the frying performance of high oleic sunflower oil is dictated primarily by the level of linoleic acid, with the tocopherol isomeric composition of the oil having no significant influence. In all oil samples, the loss of γ-tocopherol was higher than the corresponding loss of α-tocopherol.     

Short-Chain Fatty Acid Formation during Thermoxidation and Frying

Formation and evolution of the short-chain fatty acids originated by oxidation and remaining bound to the parent triglyceride, specifically heptanoate and octanoate, were studied during thermoxidation of palm olein, conventional sunflower oil and high-oleic sunflower oil at 180°C, as well as in real used frying oils of unknown history collected by Food Inspection Services. Fatty acids were quantified by gas–liquid chromatography following transesterification of samples and using methyl nonanoate and methyl heptadecanoate as internal standards. Alteration level was determined through analyses of polar compounds and polar fatty acids. Results showed high correlation coefficients between short-chain fatty acids and polar compounds or polar fatty acids, thus suggesting that quantification of short-chain fatty acids is a good indication of the total alteration level in used frying oils.     

亚麻籽油在煎炸过程中的品质变化

本文研究了常规煎炸条件下,经过不同煎炸时间的亚麻籽油营养成分、理化指标及有害物质含量,并通过主成分分析对其煎炸性能进行了综合评价。结果表明:未经煎炸的亚麻籽油不饱和度达81.77%,其α-亚麻酸的含量为47.50%,是一种富含多不饱和脂肪酸、高营养价值的食用油。亚麻籽油在170 ℃连续煎炸60 h（5 d）过程中,亚麻籽油的色泽、酸价、过氧化值、折光指数、羰基价、极性组分、生育酚含量、脂肪酸组成均有显著（P<0.05） 变化,煎炸全程没有产生苯并（α）芘;5种主要脂肪酸（α-亚麻酸、油酸、亚油酸、棕榈酸、硬脂酸）含量均呈下降趋势,C17:0以下的五种饱和脂肪酸（辛酸、癸酸、月桂酸、肉豆蔻酸、棕榈酸）含量均呈逐渐升高的趋势,其余脂肪酸呈下降趋势。通过煎炸性能分析,煎炸35 h后的亚麻籽油的酸价超过国家限量,其他项目均在国家限量范围以内,经综合评估30 h基本到达亚麻籽的煎炸使用极限,在30 h的煎炸时间内是一种健康良好的煎炸用油。     

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.