High-performance size-exclusion chromatographic studies on a high-oleic acid sunflower oil during potato frying

The behavior of a high-oleic acid sunflower oil used for 75 repeated deep-fat fryings of potatoes, with a fast turnover of fresh oil during frying, was evaluated by measuring the total polar content isolated by column chromatography. The total polar content increased in the oil from 3.6 ± 0.1 (mean ± SD) mg/100 mg unused oil to 7.6 ± 0.4 mg/100 mg oil after being used in 20 repeated fryings, followed by a tendency to reach a near-steady state throughout the successive fryings. Further, the polar fraction was examined by high-performance size-exclusion chromatography. Triacylglyceride dimers increased continuously from 0.18 ± 0.01 mg/100 mg unused oil to 2.42 ± 0.12 mg/100 mg oil at the 40th frying with no further significant changes. The amount of triacylglyceride polymers increased from 0.03 ± 0.00 mg/100 mg unused oil to 0.70 ± 0.01 mg/100 mg oil at the 60th frying, but did not increase further with continued frying. Oxidized triacylglycerides also significantly increased from 1.13 ± 0.06 mg/100 mg oil to 3.58 ± 0.09 mg/100 mg oil at the 50th frying to reach a near-steady state in successive fryings. Diacylglycerides and free fatty acids levels, related to hydrolytic alteration, did not change from the starting oil after continued fryings. Data from this study indicated that repeated fryings of potatoes in high-oleic sunflower oil with a frequent turnover of fresh oil throughout the frying slightly increased the level of polar material in the fryer oil during the first fryings, followed by minor changes and a tendency to reach a near-steady state in successive fryings.     

Cyclic fatty acids in sunflower oils during frying of frozen foods with oil replenishment

Frying of frozen foods has become popular because it considerably reduces cooking time. Polymers and cyclic fatty acid monomers (CFAM) formed during frying are potentially toxic and therefore their production should be minimized. Twenty discontinuous fryings of different frozen foods were carried out over ten consecutive days, in sunflower oil (SO) and in high‐oleic acid sunflower oil (HOSO), by adding fresh oil after each frying to bring the volume of the fryer oil back to 3 L. CFAM methyl ester derivates were hydrogenated, isolated, concentrated and quantified by HPLC using a reverse‐phase column, followed by gas chromatography. After 20 fryings, significantly higher contents of polar material, polymers and CFAM (all p <0.001) were found in SO than in HOSO. Bicyclic compound formation was four times higher in SO (p <0.001). The fat from the fried potatoes presented a polymer content very similar to that of their corresponding oils. The 100‐g rations of the SO‐fried potatoes from the 20^th frying supply 49 or 15%, respectively, more polymers and CFAM and 1 mg more bicyclic fatty acids than the 100‐g rations of HOSO‐fried potatoes. Because digestion and absorption of polar material, polymers and CFAM occur, the data clearly show the advantageousness and advisability of frying with HOSO rather than SO.     

High-performance size-exclusion chromatographic studies on polar components formed in sunflower oil used for frying

Thermoxidative and hydrolytic alterations of a sunflower oil used in sixty repeated and discontinuous deep-fat fryings of potatoes were evaluated by column and high-performance size-exclusion (HPSE) chromatography. Successive fryings of potatoes in sunflower oil, without turnover of fresh oil during the performance of fryings, increased the level of total polar components in the oil from 3.75% to 27.28% (w/w). Triglyceride polymers, triglyceride dimers, oxidized triglycerides and diglycerides increased after sixty fryings 89.8, 21.8, 4.9 and 1.7 times, respectively. These increases were well correlated with the number of fryings. However, there was not significant correlation between levels of free fatty acids and the number of fryings. Polar compounds were highly (r=0.9691) and significantly (P<0.01) correlated with triglyceride polymers and also highly (r=0.9969 and r=0.9738) and significantly (P<0.01) with triglyceride dimers and oxidized triglycerides, respectively. Nevertheless polar compounds were not significantly correlated with free fatty acids. Data suggest that an intensive thermoxidative rather than a hydrolytic process takes place in experimental deep-fat frying of potatoes.     

Cyclic FA monomers in high-oleic acid sunflower oil and extra virgin olive oil used in repeated frying of fresh potatoes

The measurement of FA profile, polar material, oligomers, oxidized triacylglycerols (OTG), total polyphenols, and cyclic FA monomers (CFAM) was used to evaluate the alteration of a high-oleic sunflower oil (HOSO) and an extra virgin olive oil (EVOO) used in 75 domestic fryings of fresh potatoes with frequent replenishment (FR) of unused oil. CFAM were absent in the unused EVOO but appeared in small amounts in the unused HOSO. Although polar material, oligomers, OTG, and CTAM contents increased and linoleic acid and polyphenols content decreased in both oils during repeated frying, the changes produced should be considered small and related to the use of very stable oils and FR. Throughout the 75 fryings, the total CFAM concentration was higher in HOSO than in EVOO. OTG increased more quickly in EVOO, whereas oligomers increased more quickly in HOSO. Polar material and oligomer content appear significantly correlated (r=0.9678 and r=0.9739, respectively; for both, P<0.001) with the CFAM content. A 25% polar material and 12% oligomer content would correspond to about 1 mg·kg⁻¹ oil of CFAM. Data suggest that both oils, particularly EVOO, perform very well in frying, with a low production of oligomers, polar materials, and CFAM.     

Cyclic fatty acid monomers and thermoxidative alteration compounds formed during frying of frozen foods in extra virgin olive oil

The measurement of polar content and specific polar compound distribution was used to evaluate the alteration of an extra virgin olive oil (EVO) used 20 times to fry frozen foods employing two methods of frying (with or without oil replenishment during frying). In addition, cyclic fatty acid monomers (CFAM) were quantified and identified throughout the 20 frying operations. Total polar content and specific polar compounds increased in the used oil (with or without replenishment). Nevertheless, frequent replenishment (FR) permits a higher number of fryings because of a dilution effect that helps maintain lower amounts of polar and specific alteration compounds than when null replenishment (NR) was used. CFAM were absent in the unused EVO, but appeared in the oil bath as a consequence of oil heating. The total CFAM concentration was higher when the oil was used with the NR method. Cyclopentyl fatty acids were more abundant than cyclohexyl ones. The data suggested that the FR frying is more appropriate to maintain the quality of the oil during frozen food frying.     

Sunflower oil used for frying: Combination of column,gas and high-performance size-exclusion chromatography for its evaluation

The alterations of a sunflower oil were evaluated by column, gas and high-performance size-exclusion chromatography after being used for deep-fat frying fifteen repeated and discontinuous times. Polar compounds increased significantly (6.2 ± 0.3% to 18.7 ± 0.8% in oil). Linoleic acid decreased (53.8 ± 0.2 to 48.1 ± 0.8 mg/100 mg oil) while oleic acid remained unaltered after 15 fryings. Saturated fatty acids such as palmitic and stearic, also remained unaltered. Triglyceride polymers (0.1 ± 0.0 to 2.4 ± 0.2 mg/100 mg oil), triglyceride dimers (1.0 ± 0.2 to 6.7 ± 0.3 mg/100 mg oil) and oxidized triglycerides (3.4 ± 0.2 to 7.6 ± 0.3 mg/100 mg oil) increased significantly in the oil used 15 times to fry potatoes. These thermoxidative compounds correlated well with the number of fryings (r=0.9864, r=0.9535 and r=0.9758, respectively). Diglyceride compounds remained unaltered, while free fatty acids increased from 0.4 ± 0.0 to 0.6 ± 0.0 mg/100 mg oil. Both of these, which are characteristic of hydrolytic alteration, did not correlate significantly (r=0.5985 and r=0.4261, respectively) with the number of fryings. These data suggest that a thermoxidative process, rather than a hydrolytic one, took place in this study.     

Thermoxidative and hydrolytic changes in sunflower oil used in fryings with a fast turnover of fresh oil

The modification of a sunflower oil used for 75 repeated deep-fat fryings of potatoes, with a fast turnover of fresh oil during frying, was evaluated by measuring the total polar components isolated by column chromatography. The total polar components increased rapidly during the first 20 fryings from 5.09±0.21 (mean±SD) mg/100 mg unused oil to 15.99±0.40, followed by minor but also significant changes until the thirtieth frying (17.99±0.41 mg/100 mg oil). The level did not increase further with continued frying. Further, the polar fraction was examined by high-performance size-exclusion chromatography. Triglyceride polymers increased from 0.10±0.01 mg/100 mg unused oil to 1.65±0.13 and 3.44±0.17 mg/100 mg oil at the twentieth and seventy-fifth fryings, respectively. Triglyceride dimers also increased significantly from 0.75±0.12 mg/100 mg unused oil to 6.25±0.28 (mg/100 mg oil) at the twentieth frying and to 7.09±0.31 mg/100 mg oil at the thirtieth frying, with no further significant changes. Oxidized triglycerides also significantly increased, but at the twentieth frying reached a near-steady state of 6.26 mg/100 mg oil. Diglycerides and free fatty acid levels, related to hydrolytic alteration, did not increase with continued fryings. The results indicate that during deep-fat frying of potatoes with fast turnover of fresh sunflower oil, more thermoxidative than hydrolytic processes take place. A dramatic leap of total polar content and a change of compounds related to thermoxidative alteration of the oil were found during the first twenty fryings, followed by minor changes and by a tendency to reach a near-steady state throughout the successive fryings.     

Comparison of the frying stability of regular and high-oleic acid sunflower oils

The frying stability of a regular sunflower oil (RSFO) was compared with that of a high-oleic acid sunflower oil (HOSFO). The rate of FFA formation was greater for HOSFO than RSFO during 72 h of frying. The content of tocopherols was much higher in RSFO and their degradation was markedly slower than that observed for HOSFO. The formation of total polar compounds, however, was similar for both oils despite the dramatic differences in FA composition. This study further confirms the limitations in predicting frying stability based solely on the FA composition and is consistent with earlier studies conducted in our laboratory.     

Iron accumulation in oil during the deep-fat frying of meat

Iron accumulation in oil is a potential problem when frying food containing substantial amounts of iron. Selected meat products (skinless chicken breast, beef liver, and lean beef) were ground and fried (ca. 2-cm spheres, ca. 10 g/sphere) in partially hydrogenated soybean oil (PHSBO). Samples (450 g) of ground meat were fried 3 times/h for 8 h/d for 3 d. Oil samples were collected for analysis for iron (every 8 h) and oil degradation (every 4 h) and replaced with fresh oil. The iron contents of oil samples after 3 d of frying were approximately 0.11, 0.48, and 4.01 mg of iron/kg of PHSBO for the oil used to fry chicken, beef, and liver, respectively. There was a notable darkening in color and an increased tendency to foam for the beef liver oil sample compared with the other samples. After frying, the acid values were 0.9, 1.1, and 1.4 for the oil samples for chicken, beef, and liver, respectively. After frying, the p-anisidine values were 11.5, 12.8, and 32.6 for the oil samples for chicken, beef, and liver, respectively; the food oil sensor values were 0.96, 0.96, and 0.83 for the oil samples for chicken, beef, and liver, respectively.     

Oxidation of sunflower oil during storage

Effects of temperature and oxygen concentration on oxidative deterioration during storage of crude sunflower oils, obtained by pressing and solvent extraction, were studied. Oxidation was monitored through several analytical and chromatographic methods that determine chemical and physical changes or analyze specific oxidation compounds at different stages of the process: peroxide value, p-anisidine value, free fatty acids, weight gain, total content and distribution of polar compounds, and composition of fatty acids. Extracted oil showed a higher oxidative stability than pressed oil. Oxidative deterioration was strongly dependent on temperature, oxygen availability, and the ratio of exposed surface to sample volume. A kinetic model of two series reactions was developed to represent oxidation rate in terms of peroxide value, the reaction rate constants and their temperature dependence being evaluated by nonlinear regression. Finally, good correlations between the percentage of polar compounds or oxidized triglyceride monomers and the peroxide value were found.     

Performance of sunflower oil with high levels of oleic and palmitic acids during industrial frying of almonds,peanuts, and sunflower seeds

High-oleic, high-palmitic sunflower oil (HOHPSO) is a seed oil from a new mutant sunflower line characterized by increased levels of both oleic acid (>50%) and palmitic acid (>25%) and a high oxidative stability. In this study, its performance at frying temperature was compared with that of palm olein in thermoxidative assays (4 h, 180°C). Also, industrial discontinuous frying of almonds, peanuts, and sunflower seeds (200 kg of each product) was carried out to define both the performance of HOHPSO and the main changes undergone by the foods. The evaluation of polar compounds and their distribution in the main groups, i.e., polymers, oxidized monomers, and DAG, as well as changes in tocopherols and oxidative stability, demonstrated the excellent behavior of HOHPSO during thermoxidation and frying. The increase in polar compounds and the loss of tocopherols and stability were much lower for HOHPSO than for palm olein under identical heating conditions. Only 1.3% polar compounds were formed during industrial discontiuous frying for 4 h and the oil stability increased, probably due to the formation of antioxidant compounds. As for the foods, the FA composition of the surface oil was clearly different from that corresponding to the internal oil, the former denoting the presence of HOHPSO in high concentration, particularly in fried sunflower seeds. Changes in oil stability of the foods attributable to the frying process clearly demonstrate the interest in using a highly stable oil such as HOHPSO to protect the surface against oxidation during food storage.     

氢化葵花油脂肪酸蔗糖酯的合成

以氢化葵花油为原料 ,采用两步法合成了氢化葵花油脂肪酸蔗糖酯。探讨了反应温度、时间、压力、催化剂用量、助熔剂等对蔗糖酯收率的影响规律。结果表明 :当助熔剂和催化剂分别为 30 %和 2 .1%时 ,在 15 0℃下反应 6h ,产物收率达 4 5 %以上。     

Effect of fatty acid composition of oils on flavor and stability of fried foods

Effects of fatty acid composition of frying oils on intensities of fried-food flavor and off-flavors in potato chips and french-fried potatoes were determined. Commercially processed cottonseed oil (CSO) and high-oleic sunflower oil (HOSUN) were blended to produce oils with 12 to 55% linoleic acid and 16 to 78% oleic acid. Analytical sensory panels evaluated french-fried potatoes and pilot plant-processed potato chips. Initially, both foods prepared in CSO (16% oleic/55% linoleic acid) had the highest intensities of fried-food flavor; however, this positive flavor decreased with decreasing levels of linoleic acid. 2,4-Decadienal in potato chips also decreased with decreasing linoleic acid in the oils. Frying oil stability, measured by total polar compounds (TPC), and oxidative stability of potato chips, measured by volatile compounds, showed that HOSUN (78% oleic acid) produced the lowest levels of TPC and the lowest levels of hexanal and pentanal, indicating greater frying oil stability and oxidative stability of the food. However, fresh potato chips fried in HOSUN had the lowest intensities of fried-food flavor and lowest overall flavor quality. Fried-food flavor intensity was the best indicator of overall flavor quality in fresh potato chips. Volatile compounds, TPC, and oxidative stability index directly varied with increasing oleic acid, and were therefore not directly indicative of flavor quality. No oil analysis predicted flavor stability of aged potato chips. Compositions of 16 to 42% oleic acid and 37 to 55% linoleic acid produced fresh fried-food with moderate fried food flavor intensity, good overall flavor quality, and low to moderate TPC levels (chips only). However, in aged food or food fried in deteriorated oil, compositions of 42 to 63% oleic and 23 to 37% linoleic provided the best flavor stability.     

A preliminary study on platelet aggregation in postmenopausal women consuming extra-virgin olive oil and high-oleic acid sunflower oil

The purpose of the present study was to examine the effects of two monounsaturated fatty acid-rich oils, extravirgin olive oil (EVOO) and high-oleic sunflower oil (HOSO), on platelet aggregation in 14 postmenopausal women (aged 62.9 ± 1.8 yr) with high-fat dietary habits. Both oils contained oleic acid as the major compound (≈76% of total fatty acids), but the content of palmitic and linoleic acids and many minor compounds was significantly different. These oils were used as the only culinary fats during two 28-d periods, and represented ≈62% of the total lipid intake (≈46% of total energy consumption). Other dietary components were matched. The daily energy contribution of saturated, monounsaturated, and polyunsaturated fatty acids to the total energy consumption was 11.8, 28.5, and 2.8%, respectively, during the EVOO dietary period and 10.3, 27.8, and 4.6%, respectively, with HOSO. Aggregation in platelet-rich plasma was measured after addition of ADP. Platelet aggregation (expressed as cm/5 min) was significantly lower after the EVOO diet than after HOSO (2.1 ± 1.1 and 3.0 ± 1.4, respectively; P<0.05). Although maximal aggregation time was 40.2% higher in HOSO than in EVOO, the difference was not significant. Independent of serum cholesterol level, platelet aggregation tended to be different on the EVOO diet when women were classified according to cholesterol levels: <220 mg/dL or ≥220 mg/dL. Results suggest that other compounds present in the oils aside from the fatty acids may play an important role in modulating platelet aggregation in these postmenopausal women.     

Effect of tocopherols on the frying stability of regular and modified canola oils

A study was conducted to compare the relationship between frying stability and levels and degradation rates of tocopherols in regular and three modified canola oils. Oils were heated at 175 ± 2°C for a total of 72 h, with french fries fried intermittently. Frying stability was compared based on the rates of formation of free fatty acids (FFA) and total polar compounds (TPC). Significant differences (P<0.05) were identified between oils using analysis of covariance and t-tests for multiple comparisons. No significant differences were observed in the rates of FFA formation among the canola oils during frying. Nevertheless, regular canola (RCO) and high-oleic, low-linolenic acid canola (HOLLCO) oils produced less FFA compared to higholeic LLCO and HOCO both had significantly (P<0.05) faster rates of TPC formation compared to HOLLCO or RCO. HOLLCO with the highest level of tocopherols (893 mg/kg) exhibited a slow rate of degradation which accounted for a halflife of 48–60 h of frying. RCO, with a lower level of tocopherols (565 mg/kg), however, had the slowest degradation rate with a half-liofe of >72 h. In contrast, HOCO and LLCO with 601 and 468 mg/kg tocopherols, respectively, both exhibited a half-life for tocopherols of 3–6 h of frying. An inverse relatioship was observed between TPC formation and the reduction of tocopherol. Thus, the greater frying stability of RCO and HOLLCO appears to be affected far more by the rate of tocopherol degradation than by any changes in fatty acid composition.     

A kinetic study of oil deterioration during frying and a comparison with heating

The thermooxidative alterations of cottonseed oil during frying of potato chips without oil turnover, in a temperature range of 155–195°C, were studied. The results showed that the content of polar compounds, conjugated dienes, conjugated trienes, and p-anisidine value (p-AV) increased linearly with the time of frying at a rate depending on temperature. The rate constants showed a significant but low increase with temperature, except for the rate constant of conjugated trienes that was not correlated to frying temperature. The alterations induced by heating the oil were also measured and compared with those observed in frying at the same temperature. The major difference observed between frying and heating was related to the p-AV increase, which presented a considerably higher rate during heating. The FA content, as a function of process time during frying at 185°C, showed a significant increase in palmitic acid (C16∶0) and a significant decrease in linoleic acid (C18∶2). Oleic acid (C18∶1) also showed a small but significant decrease. The same results were obtained for the oil heated at 185°C. Examination of p-AV or conjugated dienes with polar compounds showed that both p-AV and conjugated dienes had a linear relationship with total polar compounds, with correlation coefficients of 0.946 and 0.862, respectively.     

Effects of frying oil composition on potato chip stability

Potato chips were fried in six canola (low-erucic acid rape-seed) oils under pilot-plant process settings that represented commercial conditions. Oil samples included an unmodified canola oil and oils with fatty acid compositions modified by mutation breeding or hydrogenation. Chips were fried for a 2-d, 18-h cycle for each oil. Chips and oil were sampled periodically for sensory, gas-chromatographic volatiles and chemical analyses. Unmodified canola oil produced chips with lower flavor stability and oxidative stability than the other oils. The hydrogenated oil imparted a typical hydrogenation flavor to the chips that slightly affected overall quality. the modified canola oil (IMC 129) with the highest oleic acid level (78%) had the lowest content of total polar compounds and the lowest total volatile compounds at most of the storage times; however, the sensory quality of the potato chip was only fair. The potato chip with the best flavor stability was fried in a modified/blended oil (IMC 01-4.5/129) with 68% oleic acid, 20% linoleic acid and 3% linolenic acid.     

The effect of oxygen concentration on oxidative deterioration in heated high-oleic safflower oil

High-oleic safflower oil was heated at 180°C in atmospheres with four levels of oxygen concentration (2, 4, 10, and 20%) modified with nitrogen gas, to assess the effects of atmospheric oxygen concentration on the oxidative deterioration of deep-frying oils. Acid value, carbonyl value, polar materials, linoleic acid, tocopherol contents, and oxidative stability were measured to evaluate the quality of heated oils. These values were found to be correlated with both heating time and oxygen concentration. Acid and carbonyl values and polar material content of oils heated at oxygen concentrations of 2 and 4% were lower than those at 10 or 20%. On the other hand, linoleic acid and tocopherols were hardly reduced in oils after heating for 30 h at 2% O₂, whereas they were decomposed according to the oxygen concentration and heating time. Oxidative stability was well maintained in oils heated at 2 and 4% O₂. These results suggest that the oxidative deterioration of heated higholeic safflower oil depends on oxygen concentration.     

Impact of frying on key fatty acid ratios of canola oil

The study was carried out to investigate the changes in saturated (SFA), monoene (MUFA), trans (TFA), and polyunsaturated (PUFA) fatty acids and the key fatty acid ratios (SFA/UFA, cis PUFA/SFA, C18:2/C16:0 and C18:3/C16:0) during potato chips frying in canola oil using single bounce attenuated total reflectance FTIR (SB‐ATR‐FTIR) spectroscopy. The data obtained from GC‐FID were used as reference. The calibration of main fat groups and their key fatty acid ratios were developed by partial least square (PLS) regression coefficients using 4000 to 650 cm^?1 spectral range. FTIR PLS regression for the predicted SFA, MUFA, TFA, and PUFA were found 0.999, 0.998, 0.998, and 0.999, respectively, whereas for SFA/UFA, cis PUFA/SFA, C18:2/C16:0 and C18:3/C16:0 the regression coefficients were 0.991, 0.997, 0.996, and 0.994, respectively. We conclude that FTIR‐PLS could be used for rapid and accurate assessment of changes in the main fat groups and their key fatty acid ratios ratio during the frying process. Practical applications: FTIR‐ATR method is very simple, rapid, and environmentally friendly. No sample preparation is required and one drop of oil is enough for FTIR analysis. The proposed method could be applied for quick determination of key fatty acid ratios in the food processing industry.     

Changes in the characteristics and composition of oils during deep-fat frying

Refined, bleached, and deodorized soybean oil and vanaspati (partially hydrogenated vegetable oil blend consisting of peanut, cottonseed, nigerseed, palm, rapeseed, mustard, rice bran, soybean, sunflower, corn, safflower, sesame oil, etc., in varying proportions) were used for deep-fat frying potato chips at 170, 180, and 190°C. Refractive index, specific gravity, color, viscosity, saponification value, and free fatty acids of soybean oil increased with frying temperature, whereas the iodine value decreased. The same trend was observed in vanaspati, but less markedly than in soybean oil, indicating a lesser degree of deterioration. Iodine values of soybean oil and vanaspati decreased from their initial values of 129.8 and 74.7 to 96.2 and 59.6, respectively, after 70 h of frying. Polyunsaturated fatty acids decreased in direct proportion to frying time and temperature. Losses were highest in soybean oil with a 79% decrease in trienoic acids and a 60% decrease in dienoic acids. Levels of nonurea adduct-forming esters were proportional to the losses of unsaturated fatty acids. Butylated hydroxyanisole and tertiary butylhydroquinone did not affect deterioration of soybean oil at frying temperatures.