Retention and distribution of polyphenols after pan-frying of French fries in oils enriched with olive leaf extract

ABSTRACT:  Palm oil, olive oil, and sunflower oil were supplemented with an extract rich in polyphenols obtained from olive tree ( Olea europaea ) leaves at levels of 120 and 240 mg total polyphenols per kilogram of oil. Pan-frying of potatoes was performed in both the enriched and the nonsupplemented oils under domestic frying conditions. Total polyphenol content was estimated by the Folin–Ciocalteau assay, oleuropein was determined by HPLC analysis, while other individual polyphenols by GC/MS analysis. Fourteen polyphenol species were identified in the olive leaf extract, among which oleuropein predominated (1.25 g/kg olive leaves). All the enriched oils contained oleuropein before and after frying. Oleuropein as well as other polyphenol species were detected in all French fries cooked in enriched oils. Polyphenol intake by consuming French fries pan-fried in the enriched oils was calculated to be 6 to 31 times higher than that in the case of French fries fried in commercial oils, being dependent on the frying oil type.     

Distribution and retention of phytosterols in frying oils and fried potatoes during repeated deep and pan frying

The retention and distribution of phytosterols in fried oils and French-fries during eight successive pan- and deep-frying sessions of pre-fried potatoes in sunflower oil, palm oil, cottonseed oil, virgin olive oil and a vegetable shortening were evaluated. Phytosterols (β-sitosterol, campesterol, stigmasterol, Δ⁵-avenasterol) were determined in the unsaponifiable fraction of frying oils and lipids extracted from French-fries by GC/FID after derivatization to trimethylsilyl ethers. French-fries were enriched with phytosterols due to the absorption of frying oil, with β-sitosterol predominating in both fried oils and potatoes. The amount of phytosterols decreased during frying, their overall retentions reaching 9.5–22.8% and 29.4–51.2% after eight successive pan- and deep-frying sessions, respectively, while their deterioration was found to be affected by frying time, frying technique, being more prolonged during pan-frying, and by the oils’ unsaturation, being more extended in polyunsaturated oils. Phytosterols were more or less uniformly distributed between the fried oil and the fried potatoes. The phytosterols dietary intake by consuming potatoes fried in the oils tested is discussed.     

Pan-frying of French fries in three different edible oils enriched with olive leaf extract: Oxidative stability and fate of microconstituents

Sunflower oil, olive oil, and refined palm oil were enriched with an extract - rich in polyphenols - obtained from olive tree (Olea europaea) leaves at levels of 120 and 240 mg total polyphenols per kg oil. Potatoes were pan-fried in both the enriched and the non-supplemented oils under domestic frying conditions. Total polyphenols were estimated by Folin-Ciocalteu and antioxidant capacity was assessed by the DPPH radical scavenging assay. Tocopherols' content was determined by HPLC analysis, phytosterols and squalene by GC, and oxidative stability by Rancimat. Supplemented frying oils had higher total polyphenols and tocopherols' content, oxidative stability, and antioxidant capacity, while phytosterols and squalene content were not affected by the supplementation. French fries prepared in supplemented oils had higher total polyphenols, tocopherols, phytosterols, and squalene content and exhibited higher antioxidant capacity than those fried in non-supplemented oils. By consuming French fries pan-fried in enriched oils, up to 1.4-, 2.2-, and 1.5-fold increase of tocopherols, phytosterols, and squalene intake could be achieved as compared to those prepared in the non-supplemented oils.     

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     

The influence of oil type and frying temperatures on the texture and oil content of French fries

The purpose of the present study was to determine the effects of the frying medium and temperatures on fat content and texture of French fries. The material taken for the study consisted of seven types of vegetable oil: refined sunflower, rape, soy, olive oil, palm, partially hydrogenated rape oil (modified oil I) and a blend of vegetable oils (modified oil II). The French fries prepared from Asterix potato variety were fried at oils heated to 150, 160, 170, 180 and 190 °C. The length of frying (12, 10, 8, 6.5 and 4.5 min, respectively) depended on oil temperature. Fat content and the texture of French fries were determined. The type of frying medium significantly affects the texture of French fries. Temperature influenced both the fat content and texture of product. The increase of frying temperature decreased fat uptake and hardness of French fries. French fries fried in rape oil exhibited the most delicate texture and the lowest oil absorption when compared with French fries fried in other types of oil under investigation. Copyright © 2005 Society of Chemical Industry     

Phytosterols in frying oils: evaluation of their absorption in pre-fried potatoes and determination of their destruction kinetics after repeated deep and pan frying

The levels of β-sitosterol and total phytosterols were monitored in pre-fried potatoes during eight successive pan- and deep-frying sessions in five different commercial frying oils (virgin olive oil, sunflower oil, palm oil, cottonseed oil and vegetable shortening oil). The amount of these constituents that were transferred from the frying oils to the potatoes at the end of each frying session was determined prior and after frying by GC/FID. Except for the potato enrichment with phytosterols, the kinetics of the destruction of β-sitosterol and total phytosterols, mainly due to thermal oxidation of the oils, were evaluated for each of the five different types of oil. The experiments showed that in most cases the destruction of both β-sitosterols and total phytosterols followed first order kinetics with quite good correlation coefficients (R>0.92) and the reaction constant k was found to be at the range of 0.004 - 0.028 min^-1. Concerning the absorption of the two types of phytosterols in the fried potatoes during frying, they were found to be at the range (average) of 0.4-27% of their initial content in the oil at the beginning of each frying process (eight frying processes/session), depending on the type of oil and the constituent.     

Calcium Absorption in Rats Consuming Olive Oil or Sunflower Oil Unused or Used in Frying

Olive and sunflower oils were used in repeated potato‐frying operations without turnover until the oils reached the 25% polar compound limit allowed by law. During a 28‐d period, 5 groups of rats were fed diets containing 8% of unused olive oil, olive oil used in 48 and 69 potato‐frying operations, unused sunflower oil, and sunflower oil used to fry potatoes 48 times. No significant differences in food intake, body weight, and food efficiency was observed. The 2 sunflower oil diets increased calcium absorption efficiency without modifying calcium balance, urinary calcium, blood‐serum calcium, and calcium in the carcasses. Intake of oils used in frying did not induce any significant changes. Sunflower oil enhanced calcium bioavailiability slightly, but oil used for frying did not produce any additional effect.     

Use of hydrogenated rapeseed oil for French frying in household fryers

Both solid and liquid partially hydrogenated rapeseed oils were tested for deep intermittent French frying in a household fryer. The frying time could be estimated on the basis of viscosity or trichromatic colour changes, or of the content of polar compounds in frying oil. Still better results were obtained by combining several variables and their combinations in one expression. The frying time could be determined by means of an expression based on sensory profiles of French fries. The regressions were different for different oils used for frying.     

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.     

Provenance of the oil in par-fried French fries after finish frying

Frozen par-fried French fries are finish-fried either by using the same type of oil used for par frying, or a different type. The nutritive quality of the final oil contained in the product depends on the relative amounts and the fatty acid (FA) composition of the oils used for par frying and finish frying. With the aim of understanding the provenance of the oil in the final product, par-fried French fries-either purchased ready or prepared in the laboratory-were finish fried in oils different from the ones used for par frying. The moisture content, oil content, and FA compositions of the par-fried and finish-fried products were experimentally determined, and the relative amounts of each of the oils present in the final product were calculated using the FAs as markers and undertaking a mass balance on each component FA. The results demonstrate that 89% to 93% of the total oil in the final product originates from the finish-frying step. The study also shows that a significant proportion of the oil absorbed during par frying is expelled from the product during finish frying. Further, the expulsion of par-frying oil was found to occur in the early stages of the finish-frying step. Experiments involving different combinations of par-frying and finish-frying oils showed that the relative proportions of the 2 oils did not depend on the individual fatty acid profiles. This study concludes that any positive health benefits of using an oil having a favorable FA profile for par frying, can potentially be lost, if the oil used for finish frying has a less favorable composition. PRACTICAL APPLICATION: This paper estimates the relative amounts of oil in French fries that have been fried in 2 stages-a par-frying step and a finish-frying step-which is commonly practiced in food service establishments as well as homes. The 2 key conclusions are: (1) nearly 90% of the oil content of the final product is the one used for finish frying; that is, a processor may use very good oil for par frying but if the oil used for finish frying is inferior, its effect will dominate. (2) The paper also shows that a significant proportion of the oil used by the processor gets expelled during finish frying.     

Mass Transfer and Volume Changes in French Fries During Air Frying

The production of healthier fried foods requires the adaptation of industrial processes. In this context, air frying is an alternative to deep oil frying to obtain French fries with lower fat content. Kinetic analysis of compositional changes and main fluxes involved in air frying were carried out, and the results were compared to those obtained for deep oil frying. The influence of the type of sample (unpretreated, frozen, or blanched potatoes) was also analyzed. The results showed that oil uptake is much lower in air frying although a much longer processing time is required. Also, water loss and thus the loss of volume were much higher in air frying compared to the conventional process.     

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.     

Sunflower oil versus olive oil and iron metabolism in rats. Influence of a frying process

Olive oil and sunflower oil were used in repeated potato‐frying operations without turnover until the oils reached the limit of 25% polar compounds allowed by law. Over a 28 day period, five groups of rats were fed diets containing 8% unused olive oil, olive oil used in 48 and 69 potato frying operations, unused sunflower oil and sunflower oil used to fry potatoes 48 times. In the final week, faeces and urine were collected and, on day 28, animals were sacrificed. The type of oil, unused or used in frying, did not modify food intake, body weight, faecal iron and its apparent absorption or retention, but consumption of oils used in frying tended to increase urinary iron excretion. No differences were found in serum iron, total iron‐binding capacity and haemoglobin values. Iron contents and concentrations in liver, spleen and skin did not vary between groups. Iron concentrations in erythrocytes were significantly higher in rats fed sunflower oil, either unused or used in frying. It was concluded that the consumption of sunflower oil compared to olive oil could affect intra‐ and extracellular haematic distribution of iron, probably associated with changes in membrane permeability, and that some alteration products of the oils originated during frying tend to increase urinary iron losses without repercussions on iron metabolism. © 2000 Society of Chemical Industry     

Influence of deep-frying using various commercial oils on acrylamide formation in French fries

This study investigated the effect of different types of commercial oils (rice bran oil, shortening oil, high-oleic rapeseed oil, low-erucic acid rapeseed oil, blend oil A and blend oil B) and frying cycles on acrylamide formation during the preparation of French fries by deep-frying. Frying was carried out in intermittent mode (two batches each for 12 min without any time lag) and repeated for 600 frying cycles. Results indicated that the French fries that were fried in oils having lower heat transfer coefficients contained lower acrylamide concentrations (913 µg kg^–1), whereas those fried with oils having higher heat transfer coefficients contained higher acrylamide concentrations (1219 µg kg^–1). Unlike the peroxide value, acrylamide levels in French fries did not change significantly with an increase in the number of frying cycles when tested for 600 frying cycles for every type of oil. This study clearly indicates that the contribution of frying oils to the formation of acrylamide should not be neglected due to their different heat transfer coefficients. On the other hand, continuous use of frying oil does not lead to a higher acrylamide concentration in French fries.     

INCREASES IN THE DIELECTRIC CONSTANTS OF SOYBEAN AND SUNFLOWER OILS AND PRODUCT QUALITY CHANGES OF POTATOES DURING INTERRUPTED DEEP FAT FRYING1

During a 32 h interrupted period of heat processing French fries, the rate of change in the dielectric constants of soybean and sunflower oils was determined. Selected quality parameters (moisture, yield, texture, food energy) were also measured during this period. Heat processing conditions simulated good operational practices for deep fat frying within a commercial setting. The dielectric constant of sunflower increased at a significantly greater rate than soybean oil, indicating increased rates of oil deterioration. Moisture content and yield of the French fries did not differ throughout the 32 h period. Mean texture values (force) were 661 and 643 g for soybean and sunflower oil, respectively. Significant linear interactions among oil and time were found for texture. The food energy content (Kcal/g; dry basis) of French fries heat processed in sunflower oil was significantly lower than those, in soybean oil.     

Frying Oil Deterioration and Vitamin Loss During Foodservice Operation

Oxidation and vitamin E loss in four frying oils (two partially hydrogenated soybean oils, one with methyl silicone, the other with tertiary butyl hydroquinone, citric acid and dimethyl siloxane added; a semi-solid hydrogenated soybean and palm oil shortening with mono and diglycerides added; and 100% corn oil) were studied under experimental and ‘actual’ operational conditions. Vitamin E loss in the frying oil increased significantly with increasing fatty acid oxidation. Added antioxidants, vitamin E and hydrogenation of fat decreased the rate of vitamin E loss. No significant change in vitamin E of the French fries occurred during 4 days of commercial frying; a significant increase in French fry fat uptake improved the 40% reduction in vitamin E of the frying oil. Vitamin C in the French fries (a major source of the vitamin in fast food meals) decreased significantly as the vitamin E content of the oils was reduced.     

11种煎炸油煎炸薯条挥发性成分的组成北大核心CSCD

利用顶空固相微萃取与气质联用相结合的方法测定了11种煎炸油煎炸薯条的挥发性物质组成,并对薯条进行感官评定。结果表明:11种煎炸油煎炸薯条共鉴定出包括醛类、含氧杂环类、含氮杂环类、酮类、醇类、酸类、烃类、含硫化合物和酯类化合物共80种挥发性物质,其中醛类化合物是煎炸薯条中主要的挥发性物质。棕榈油煎炸薯条鉴定出的挥发性物质种类最多,亚麻籽油煎炸薯条的最少,且通过分析11种煎炸油煎炸薯条的醛类物质发现,葵花籽油和棉籽油煎炸薯条中多不饱和醛含量较高,其中(E,E)-2,4-癸二烯醛含量最高,是薯条呈现油脂香的主要物质;高油酸菜籽油和高油酸葵花籽油煎炸薯条中单不饱和醛含量较高,其中高油酸葵花籽油煎炸薯条中2-十一烯醛含量最高;亚麻籽油煎炸薯条中(E,E)-2,4-庚二烯醛含量最高,呈现出消费者不期望的脂肪味和油腻味。感官评定结果显示,棕榈油煎炸薯条品质最好,猪油煎炸薯条品质最差。     

Comparison of the stability of palm olein and a palm olein/canola oil blend during deep‐fat frying of chicken nuggets and French fries

Stability of palm olein (PO) and a blend 50% palm olein/50% canola oil (POC) during deep‐fat frying at 180 °C of French fries (FF) or chicken nuggets (CN) was studied through the determination of physical and chemical parameters in the fresh and used oils. Degradation at the end of the study resulted in total polar compounds of 12–13.5% for PO and 11.5–14.5% for POC and viscosity of 65–123.3 cP for PO and 63–72.8 cP for POC. Lower peroxide values (5.33–6.32) were obtained for the blend (PO had 5.21–8.55). Food type affected colour parameters and p‐anisidine value of the oils. For CN, the lowest fat content and higher hardness were obtained when they were fried in PO. CN caused a faster deterioration in the oils, in comparison with FF, especially in POC. Gas chromatography allowed to observe differences in fatty acids composition for both used oils.     

Quality assessment of refined oil blends during repeated deep frying monitored by SPME–GC–EIMS,GC and chemometrics

The aim of this study was to investigate the effect of the refined palm oil addition (20%) on the fatty acid and sterol compositions of refined olive oil or refined soya bean oil and also to investigate the formation of total polar compounds and volatile compounds in these oil blends during fifty successive deep‐frying sessions of potato fries at 180 °C. The blend of refined olive oil and refined palm oil exhibited a higher chemical stability during the frying process than that of refined soya bean oil and refined palm oil. Indeed, the total polar compounds and volatile compounds formed, especially 2,4‐decadienal, were found to be relatively increased in the refined soya bean oil/refined palm oil blend reaching 36.50% and 46.70%, respectively, after fifty deep‐frying sessions. Moreover, the degradation of linoleic acid and β‐sitosterol was significantly (P < 0.05) observed for the refined soya bean oil/refined palm oil blend. The results have proven that the proper blending of monounsaturated refined olive oil with refined palm oil increases its stability and hence improves the quality of such olive oil during frying process.     

Effect of Microwave Frying on Acrylamide Generation,Mass Transfer,Color, and Texture in French Fries

The objective of this work was to evaluate the effect of microwave power on acrylamide generation, as well as moisture and oil fluxes and quality attributes of microwave-fried potatoes. Concretely, 25 g of potato strips, in 250 mL of fresh oil (at room temperature), were subjected to three different microwave powers (315, 430, and 600 W) in a conventional microwave oven. Microwave frying resulted in an acrylamide reduction ranged from 37 to 83% compared to deep-oil frying. Microwave-fried French fries presented lower moisture and higher fat content than deep-oil fried potatoes. Concretely, microwave-fried potatoes presented values of moisture and texture more similar to potato chips than French fries, nonetheless with lower fat levels (less than 20 g/100 g wb) and acrylamide content (lower than 100 μg/kg wb) at the reference time. This study presents an alternative way of frying to address the production of healthier potato chips.