Grape Seed Oil Characterization: A Novel Approach for Oil Quality Assessment

The amount of organic pomace, left behind agricultural processes, is continuously rising in accordance with industrial progress. Grape pomace, generated in the wine industry all over the world, represents a raw material for obtaining valuable products. Grape seeds are especially rich in oil containing bioactive compounds that can have various health‐related effects. The aim of the study is to compare the quality of seed oils obtained from six white grapes, including two Serbian autochthonous varieties. Linoleic acid, associated with numerous health benefits, is the major fatty acid in all samples (≈66% of total); α‐tocopherol is the main tocopherol homologue. Total polyphenol content ranges from 73.4 to 104.3 mg of gallic acid equivalents per 100 g. In order to provide comprehensive information about antioxidant capacity of grape seed oil (GSO), three tests are performed (ferric ion reducing antioxidant power; 2,2’‐diphenyl‐1‐picrylhydrazyl, and 2,2’‐azino‐bis(3‐ethylbenzthiazoline‐6‐sulphonic acid) radical scavenging). Antimicrobial activity is investigated against different strains; however, GSO inhibits the growth of Staphylococcus aureus and Candida albicans. Obtained results are used to develop a novel approach for oil quality assessment. Calculated oil quality scores (OQS) reveal no significant difference between international and autochthonous varieties, although Smederevka stands out as the most potent one. Practical applications : Considering the progressive waste increase in the wine industry and keeping in mind all health‐promoting effects of grape seed oil (GSO), it is clearly observed that oil production represents a profitable and sustainable utilization of grape seeds. The results of the present study show that GSO is a rich source of compounds with antioxidant and antimicrobial properties. In addition, this work provides deeper insight into a quality of Serbian autochthonous grape varieties that are still insufficiently explored. Furthermore, the proposed oil quality score could be used as a comprehensive and unbiased method that enables quality assessment of oils. This tool can find practical application in comparing different plant oils regarding their compositional and functional properties. Finally, it would contribute to making some general oil intake recommendations.     

Contents of Carotenoids, Tocopherols and Sterols in Acacia cyanophylla Seed Oils

Seeds from 12 Acacia cyanophylla ecotypes, harvested in Tunisia, were examined for their seed oil contents of carotenoids, tocopherols and phytosterols. The average carotenoid content (lutein and zeaxanthin) was ca. 102 mg kg^?1 of total extracted lipids. Lutein (ca. 97 mg kg^?1 of total extracted lipids) was usually more abundant than zeaxanthin (ca. 5 mg kg^?1 of total extracted lipids). The mean total tocopherol content was ca. 704 mg kg^?1 of total extracted lipids. The main isomer was α‐tocopherol, with more than 75 % of total tocopherols (ca. 528 mg kg^?1 of total extracted lipids), followed by γ‐tocopherol (ca. 168 mg kg^?1 of total extracted lipids) and δ‐tocopherol (ca. 86 mg kg^?1 of total lipids). High levels of phytosterols (ca. 7.8 g kg^?1 of total extracted lipids) were detected, among which β‐sitosterol was the most abundant (47 %). All these results highlight the richness of carotenoids, tocopherols and sterols in A. cyanophylla seed oil, and imply that this species might constitute a potential resource for the development of functional foods.     

Stability of refined olive oil and olive‐pomace oil added by phenolic compounds from olive leaves

Refined olive oil and olive‐pomace oil were enriched with olive leaf phenolic compounds in order to enhance its quality and bring it closer to virgin olive oil. The changes that occurred in the concentrations of pure oleuropein, oleuropein aglycone, hydroxytyrosol acetyl and α‐tocopherol at 400 µg/kg of oil during the storage of refined olive oil and olive‐pomace oil under accelerated conditions (50 °C) were investigated. In a period of 4 months, α‐tocopherol decomposed by 75% whereas less than 40% of the phenols were lost. During storage, enzymatic olive leaf extract hydrolysate that contains two major compounds, hydroxytyrosol and oleuropein aglycone showed the highest antioxidant activity and the lowest detected stability, followed by oleuropein. The oleuropein in olive leaf extracts exhibited similar degradation profiles, reducing by 60–50% and 80% for the olive oil and olive‐pomace oil in 6 months, respectively. The acetylated extract, however, displayed a loss of 10 and 5% in olive oil and olive‐pomace oil, respectively. In the fatty acid composition, an increase in oleic acid and a decrease in linoleic acid were observed. The antiradical activities of the olive oil and olive‐pomace oil enriched with olive leaf phenolic compounds at 400 ppm showed that enzymatic hydrolysate extract had the highest protective effect against oil oxidation. Based on the Rancimat method, the oils with added leaf enzymatic hydrolysate extract had the lowest peroxide value and the highest stability. After 6 months of storage and at 120 °C, the oxidative resistance of refined olive oil and olive‐pomace oil reached 0.71 and 0.89 h, respectively, whereas that of the non‐enriched samples fell to zero.     

Lipophilic components in black currant seed and pomace extracts

The nature of the fatty acids and other lipophilic components in extracts from black currant seed and pomace (containing seed) were investigated, with a view to highlighting any potential uses. The same non‐hydroxylated fatty acids were the major components in both types of extract, but total levels were less in pomace (75 582 mg 100 g^?1 oil) than in seed alone (90 972 mg 100 g^?1 oil) and there were less unsaturated fatty acids, including GLA (8653 and 12 625 mg 100 g^?1 oil, respectively), but long chain n‐20:0 – n‐30:0 fatty acids (4080 and 437 mg 100 g^?1 oil, respectively) were greatly increased in pomace. Phytosterols (mainly β‐sitosterol), saturated n‐20:0 – n‐30:0 policosanols, ω‐hydroxy fatty acids (mainly 16‐hydroxy 16:0) and 2‐hydroxy fatty acids (mainly 2‐hydroxy 24:0) were present at much greater levels in pomace (2496, 2097, 958 and 46 mg 100 g^?1 oil, respectively) than in seed (553, 108, 161, and 1 mg 100 g^?1 oil, respectively). The pomace extract is a useful source of fatty acids, phytosterols and policosanols with potential functional properties. Practical applications: The study investigated the lipophilic components in isohexane extracts from black currant seed and pomace (containing seed). Only pomace extracts had substantial amounts of phytosterols and policosanols that have potential as cholesterol‐lowering agents, whereas fatty acids such as GLA, that has anti‐inflammatory properties, are mainly in the seed.     

Chemical Characterization of Virgin Almond and Hazelnut Oils and Their By‐Products

Various cultivars of almonds (“Ferragnes,” “Guara,” “Largueta,” and “Marcona”) and hazelnuts (“Negret,” “Pauetet,” and “Tonda”), particularly their virgin oils and by‐products, are evaluated in this study. The almond and hazelnut virgin oils present high contents of oleic acid (59–73% and 76–80%, respectively) and α‐tocopherol (420–542 and 310–378 mg kg^–1, respectively), as compared with other virgin vegetable oils. Aldehydes are the major contributors to their aromatic profile (54–74% almond oil and 30–40% hazelnut oil of total content), especially, benzaldehyde in almond oils (1.35–7.52 mg kg^–1), and hexanal in hazelnut oils (0.99–1.27 mg kg^–1). Statistical differences exist between the virgin almond and hazelnut oils and their varieties, for most of the chemical compounds studied. While all the nut varieties are high in polar phenolic compounds, “Ferragnes” almonds (1262 mg kg^–1) and “Negret” hazelnuts (1720 mg kg^–1) stand out. Accordingly, high antioxidant activity is also observed. Finally, the residual cakes may be considered a good source of polar phenolic compounds (823–2064 mg kg^–1 almond cakes, 2261–4179 mg kg^–1 hazelnut cakes), possessing high antioxidant capacity with potential applications of these by‐products as functional ingredients in food and non‐food formulations. Practical Applications: Virgin nut oils are gaining consumers’ preference due to their unique organoleptic attributes and potential health effects. It is therefore very relevant to establish their specific chemical composition, directly related to their properties, and that are greatly affected by the cultivar.     

Tocopherol—An intrinsic component of sunflower seed oil bodies

Oil bodies were removed from mature sunflower through wet grinding followed by filtration then centrifugation and recovered as the buoyant fraction. Washing this fraction with buffer (water-washed oil bodies, WWOB) or 9 M urea (urea-washed oil bodies, UWOB) resulted in the removal of extraneous proteins. SDS-PAGE of the proteins still associated with the oil body fraction after washing indicated that this effect was particularly dramatic with urea washing. Thirty-eight percent of the total seed tocopherol was recovered in WWOB after only one cycle of oil body recovery. The total phenolic content (TPC) of differentially washed sunflower seed oil bodies was used as a marker for the nonspecific association of phenolic compounds to oil bodies. This value decreased with increased removal of proteins from oil bodies, whereas the converse was true for tocopherol values, which increased from 214 mg total tocopherol kg⁻¹ WWOB [dry wt basis (dwb)] to 392 mg total tocopherol kg⁻¹ UWOB (dwb). The ratio of the four tocopherol isomers remained constant in the seed and oil body preparations (α:β:γ:δ approximately 94∶5∶0.5∶0.5). This work provides evidence that an intrinsic population of tocopherol molecules exists in the oil bodies of mature sunflower seeds.     

Chemical Composition and Antioxidant Activity of Seeds of Various Halophytic Grasses

Increasing population has resulted in overexploitation of conventional seeds. The limited supply of water and salinization of agricultural lands are threats to crop production. This creates food insecurity and results in ever‐increasing prices of crops and edible oils. Halophytes that produce high‐quality seeds can serve as sources of oil and edible products. We analyzed the chemical composition and antioxidant activity of seeds from 5 halophytic grasses, i.e., Aeluropus lagopoides, Eragrostis ciliaris, Eragrostis pilosa, Panicum antidotale, and Sporobolus ioclados. These seeds contained crude protein (10–29%), carbohydrates (32–55%), crude fiber (4–21%), minerals (3.8–9.2%), and oil (4–11%), indicating their nutritional potential. Oils of these seeds had suitable fatty‐acid composition with 62–82% unsaturation and only 17–24% saturation. Out of this, 91–94% of the total oil constituted by linoleic, oleic, and palmitic acids. High contents of total phenols (2.8–4.2 mg gallic acid equivalent [GAE] g^?1), flavonoids (0.5–1.3 mg Quercetin equivalent [QE] g^?1), and tannins (0.3–1.3 mg catechin equivalent [CE] g^?1) supported their high antioxidant activity (1,1‐Diphenyl‐2‐picryl‐hydrazyl (DPPH) activity in terms of half maximal inhibitory concentration‐IC₅₀ 1.1–5.86 mg mL^?1; 2,2′‐azino‐bis3‐ethylbenzothiazoline‐6‐sulphonic acid (ABTS) 18.8–72.8 mmol Trolox g^?1; ferric‐reducing antioxidant power 2.0–4.4 mmol Fe⁺² g^?1). The reverse phase‐high‐pressure liquid chromatography analysis identified the presence of bioactive phenolic antioxidants (mainly gallic acid, chlorogenic acid, coumaric acid, ferulic acid, kaempferol, and quercetin). Due to these characteristic composition and salt tolerability, these plants can serve as potential sources of industrial raw materials for food, edible oil, phytochemicals, and oliochemicals.     

Unexploited Thapsia garganica,Orlaya maritima,and Retama raetam Seeds: Potential Sources of Unsaturated Fatty Acid and Natural Antioxidants

Total lipid contents, fatty acid compositions, phenolic profiles and antioxidants activities of seeds from Thapsia garganica, Orlaya maritima, and Retama raetam were investigated. The oil values were more than 26 %, except seeds of R. raetam (ca. 3 %). Unsaturated fatty acids accounted for the majority of the fatty acids (more than 75 %). Oleic and linoleic acid were the predominant fatty acids. Total phenolic compounds (24–104 mg GAE g^?1 DR), total flavonoids (4–102 mg QE g^?1g DR), total tannins (28–85 mg GAE g^?1 DR) and condensed tannins (0.62–131 mg CE g^?1 DR) were also determined. The antioxidant activities using different assays were evaluated. The predominant detected classes were the phenolic acids (42–85 %) and the flavonoids (11–48 %). The major phenolic acids were caffeic, trans‐4‐hydroxy‐3‐methoxycinnamic, p‐coumaric, and gallic acid. The predominant flavonoids were quercetin, luteolin, naringin, apigenin, and kaempferol. This study brings attention to the medicinal importance of these species as a source of oil and antioxidant molecules.     

Physicochemical Characterization,Fatty Acid And Tocopherol Content of Moringa ovalifolia (African Moringa) Oil From Namibia

Moringa ovalifolia tree is indigenous to Namibia and is a multipurpose tree whose leaves, pods, fruits, and flowers are edible. The tree is well adapted to the harsh climatic conditions of the region and easily cultivated. In this paper, we investigate the physicochemical characteristics of the oil extracted from M. ovalifolia seeds collected from Remhoogte Farm, Khomas region, Namibia. The oil yield was 34.86 ± 2.47%. The oil contained a high level of monounsaturated fatty acids, with oleic acid (18:1) being the dominant one. The oil had high levels of tocopherol, with a total of 44.56 mg 100 g^?1 of oil, comprising α‐tocopherol (33.94 mg 100 g^?1), β‐tocopherol (6.64 mg 100 g^?1), and δ‐tocopherol (3.98 mg 100 g^?1). High levels of stigmasterol (142.41 mg 100 g^?1) and β‐sitosterol (330.70 mg 100 g^?1) were also detected. The seed oil exhibited good‐quality characteristics, making it a useful new seed oil to be considered for food and nonfood applications.     

Polymer processing and characterization of LLDPE films loaded with α‐tocopherol,quercetin, and their cyclodextrin inclusion complexes

Natural antioxidant additives were compounded into linear low‐density polyethylene (LLDPE) using a twin‐screw counter‐rotating mixer and compression molded into films. Manufactured LLDPE films contained 2715 mg kg^?1 α‐tocopherol in its free and β‐cyclodextrin complexed form and 1950 mg kg^?1 quercetin in its free and γ‐cyclodextrin complexed form. Both cyclodextrin complexes were loaded into films at 1.5% by weight. These natural antioxidants were incorporated into LLDPE resins with two different catalyst types, Ziegler‐Natta and metallocene. Films were characterized by optical microscopy, oxidation induction time (OIT), oxygen transmission rate, contact angle analysis, and atomic force microscopy (AFM). All antioxidant additives increased the oxidative stability of LLDPE as measured by increased OIT, particularly quercetin. Natural antioxidants and their cyclodextrin inclusion complexes may provide a dual function in packaging to protect the polymer from oxidative degradation during melt processing and to delay the onset of oxidation of the packaged food during storage. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Chemical Compositions of Walnut (Juglans regia L.) Oils from Different Cultivated Regions in China

This study is a comprehensive report on the quality of Chinese walnut oil, which enriches the research of oil resources. A total of 16 walnut samples from China were selected, and walnut oils were obtained using the pressing process. The lipid compositions and micronutrient contents were analyzed. The fatty acids corresponded to palmitic acid (3.05–8.25%), oleic acid (12.56–26.03%), linoleic acid (51.21–68.97%), and linolenic acid (6.83–15.01%), and the main triacylglycerols were trilinolein (27.87–39.47%), followed by oleoyl‐linoleoyl‐linolenoyl‐glycerol (17.07–24.18%), dilinoleoyl‐oleoyl‐glycerol (9.65–15.46%), palmitoyl‐dilinoleoyl‐glycerol (5.96–14.98%), and dilinoleoyl‐linolenoyl‐glycerol (6.42–12.43%). In addition, high amounts of micronutrients, including phytosterol, squalene, tocopherol, and total phenolic content, were found in walnut oils ranging from 540 to 1594, 17 to 131, 345 to 1280, and 1.04 to 20.39 mg kg^?1 among different samples, respectively. The differences in the geographical location and climate caused different regions of cultivation, which resulted in the differences in the chemical composition of walnut oil. Further multiple linear regression analyses between oxidative stability indices, fatty‐acid compositions, and micronutrients revealed that linoleic acid (R = ?0.891; P < 0.05), α‐tocopherol (R = 0.713; P < 0.05), and total phenolic content (R = 0.369; P < 0.05) were the main factors that affect the oxidative stability of the walnut oil.     

Seed Oils of Five Black Tartary Buckwheat Cultivars with Biochemical Characterization and Antioxidant Properties

Black tartary buckwheat oils (BTBOs) were extracted from five major industrial tartary buckwheat cultivars grown under similar agronomical activities and environmental conditions. These oils were characterized for the bioactive compounds containing fatty acids, β‐carotene, lutein, α‐, β‐, δ‐ and γ‐tocopherol, and for their antioxidant properties. The total tocopherol contents that were obtained ranged from 704.66 to 1156.19 mg/kg, with γ‐tocopherol (588.98–977.91 mg/kg) as the main component. The concentration of lutein ranged from 253.14 to 429.63 mg/kg, which was almost ten times higher than that of β‐carotenoid (46.71–69.2 mg/kg), indicating that black tartary buckwheat seed oils were a good source of lutein. The predominant fatty acids were unsaturated oleic acid (C18:1) (35.27–40.61 %) and linoleic acid (C18:2) (38.25–42.90 %). Excellent values of 2,2‐diphenyl‐1‐picrylhydrazyl radical (DPPH), diammonium salt (ABTS) radical scavenging activities were obtained and the highest oxygen radical absorbance capacity (ORAC) value of 13.89 mmol Trolox equiv/g oil was detected in the variety of Chuanqiao No. 1, which was clearly separated by principal component analysis (PCA) on the basis of the highest content of tocopherols and carotenoids. Moreover, the correlation analysis showed that tocopherols and carotenoids were the major contributors to the antioxidant activities of the BTBOs. This study demonstrates that lipophilic extraction in the tartary buckwheat seed contains many interesting bioactive compounds, which are beneficial for human health.     

Physicochemical,Antioxidative, and Sensory Properties of Refined Rapeseed Oils

Physicochemical characteristics, antioxidant capacity (AC), and sensory quality of rapeseed oils available on the Polish market were analyzed and compared. The fatty acid composition (saturated fatty acids = 6.91–7.58%, monounsaturated fatty acids = 64.14–66.14%, and polyunsaturated fatty acids = 27.22–30.17%), color (T420 = 54.5–83.8%), amounts of free fatty acids (0.02–0.07%), primary (PV = 0.04–2.04 meq O₂ kg⁻¹) and secondary (AV = 1.02–3.21) oxidation products, phosphorus (0.38–1.62 mg kg⁻¹), chlorophyll (0.002–0.068 mg kg⁻¹), and polycyclic aromatic hydrocarbons (Σ4PAH = 0.00–2.50 μg kg⁻¹) in the commercial rapeseed oils meet the requirements of the European Food Regulation and Codex Alimentarius standards. Moreover, total phenolic content (TPC = 40.3–467.9 mg SA kg⁻¹) in the studied oils significantly differs from each other. However, the AC of rapeseed oils was analyzed using the novel iron oxide nanoparticle-based (IONP = 5552.1 − 18,510.2 μmol TE/100 g) method and the modified ferric reducing antioxidant power (FRAP = 55.7–280.3 μmol TE/100 g), cupric reducing AC (CUPRAC = 79.6–784.0 μmol TE/100 g), 2,2-diphenyl-1-picrylhydrazyl (DPPH = 185.7–516.7 μmol TE/100 g), and 2,2′-azinobis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS = 465.6–2142.6 μmol TE/100 g) assays. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) were applied for discrimination of the refined rapeseed oils based on fatty acid composition, physicochemical parameters, AC, and sensory properties.     

Determination of Physicochemical Properties,Fatty Acid,Tocopherol, Sterol,and Phenolic Profiles of Expeller–Pressed Poppy Seed Oils from Turkey

In this study, the aim was to characterize the physicochemical properties and some bioactive compounds of expeller-pressed oils of five registered poppy seed varieties (TMO–1, Ofis–8, Ofis–96, Ofis–95, Ofis–3) grown in Turkey. The amounts of total carotenoids, chlorophylls, phenols, and antioxidant activities of oils ranged between 0.08–0.24 mg 100 g⁻¹, 0.03–9.04 mg pheophytin a kg⁻¹, 3.41–8.57 mg gallic acid equivalent 100 g⁻¹, and 5.60–7.33 mM Trolox equivalent 100 g⁻¹, respectively. The most abundant fatty acid in poppy seed oils was linoleic acid (69.85–74.02%), followed by oleic acid (13.98–16.99%), and palmitic acid (8.51–9.75%). In addition, poppy seed oils were rich in β–sitosterol (133.47–153.42 mg 100 g⁻¹), campesterol (45.36–58.60 mg 100 g⁻¹), and δ–5–avenasterol (28.21–39.40 mg 100 g⁻¹). High amounts of γ–tocopherol and α–tocopherol were detected. This research is the first study, which identified and quantified the polyphenol, β–carotene, and lutein compounds of expeller–pressed poppy seed oils by HPLC. Tyrosol, apigenin, syringic acid, 3–hydroxytyrosol, luteolin, p–coumaric acid, quercetin, ferulic acid, sinapic acid, and veratric acid were detected in expeller-pressed poppy seed oils.     

Formation of 4‐Hydroxy‐2‐Trans‐Nonenal,a Toxic Aldehyde,in Thermally Treated Olive and Sunflower Oils

4‐Hydroxy‐2‐trans‐nonenal (HNE) is a toxic aldehyde produced mostly in oils containing polyunsaturated fatty acid due to heat‐induced lipid peroxidation. The present study examined the effects of the heating time, the degree of unsaturation, and the antioxidant potential on the formation of HNE in two light olive oils (LOO) and two sunflower oils (one high oleic and one regular) at frying temperature. HNE concentrations in these oil samples heated for 0, 1, 3, and 5 hours at 185 °C were measured using high‐performance liquid chromatography. The fatty‐acid distribution and the antioxidant capacity of these four oils were also analyzed. The results showed that all oils had very low HNE concentrations (<0.5 μg g^?1 oil) before heating. After 5 hours of heating at 185 °C, HNE concentrations were increased to 17.98, 25.00, 12.51, and 40.00 μg g^?1 in the two LOO, high‐oleic sunflower oil (HOSO), and regular sunflower oil (RSO), respectively. Extending the heating time increased HNE formation in all oils tested. It is related to their fatty‐acid distributions and antioxidant capacities. RSO, which contained high levels of linoleic acid (59.60%), a precursor for HNE, was more susceptible to degradation and HNE formation than HOSO and LOO, which contained only 6–8% linoleic acid.     

Process efficiency and long‐term performance of α‐tocopherol in film‐blown linear low‐density polyethylene

α‐Tocopherol was compared with a commercial phenolic antioxidant (Irganox 1076) as a long‐term and process antioxidant in film‐blown and compression‐molded linear low‐density polyethylene. The antioxidant function of α‐tocopherol was high in the film‐blown material, especially in the processing, according to oxygen induction time measurements with differential scanning calorimetry. The residual content of α‐tocopherol after processing, determined with chromatographic techniques, was less than that of the commercial phenolic antioxidant in both the film‐blown and compression‐molded materials. The process stabilizing efficiency was nevertheless higher for the material containing α‐tocopherol. During the long‐term stabilization, the efficiency of α‐tocopherol was less than that of the commercial phenolic stabilizer Irganox 1076 in the thin films, according to chemiluminescence and infrared measurements. The long‐term efficiency in the compression‐molded samples stabilized with α‐tocopherol or Irganox 1076 was equally good because of the low loss of both α‐tocopherol and Irganox 1076 from the thicker films. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2427–2439, 2005     

Antioxidant effect of mono‐ and dihydroxyphenols in sunflower oil with different levels of naturally present tocopherols

Antioxidant properties of mono‐ and dihydroxyphenolic acids and their alkyl esters were examined, with emphasis on the relationship between their molecular structure and antioxidant activity. Test media with different tocopherol level were used for determining the oxidative stability: original refined sunflower oil (total tocopherols 149.0 mg/kg), partially tocopherol‐stripped sunflower oil (total tocopherols 8.7 mg/kg) and distilled fatty acid methyl esters (FAME) as a tocopherol‐free medium. The chemical reaction of tocopherols with diazomethane tested for the purpose to eliminate their antioxidant activity failed due to the negligible degree of methylation of hydroxyl group in the tocopherol molecule. Caffeic acid and protocatechuic acid (3,4‐dihydroxyphenolic acids) and their alkyl esters were found to be more active antioxidants than monohydroxyphenolic acid (p‐hydroxybenzoic acid), 2,5‐dihydroxyphenolic acid (gentisic acid), 3‐methoxy‐4‐hydroxyphenolic acids (vanillic and ferulic acids) and their corresponding alkyl esters. Naturally present tocopherols in refined sunflower oil proved to have a synergistic effect on gentisic acid but not on its alkyl esters. In contrast, tocopherols showed an antagonistic effect on alkyl esters of caffeic acid, because their protection factors decreased with increasing level of tocopherols in the test medium. Moreover, the antioxidant activity of these alkyl esters decreased with increasing length of their alkyl chain in conformity with the polar paradox hypothesis. Practical applications: Tocopherols as naturally present antioxidants influence considerably the antioxidant activity of other antioxidants added to plant oils used as a test medium. Distilled fatty acid methyl esters prepared from refined sunflower oil may serve as an optimal tocopherol‐free test medium. Some alkyl esters of phenolic acids were evaluated to be applicable as natural more lipophilic antioxidants in comparison with phenolic acids.     

Oxidative Stability of α‐Linolenic Acid in Corn Chips Enriched with Linseed Oil Pro/Antioxidative Activity of Tocopherol

Extruded products, particularly those which are corn‐based, are widely consumed salty or sweet snacks; moreover, they very often provide a basis for breakfast for people around the world. Extruded products are characterised by a low nutritional value, and a particularly low content of polyunsaturated fatty acids of the n‐3 group. An attempt was made to enrich extruded corn crisps with α‐linolenic acid (ALA) through the addition of refined linseed oil at an amount of 5 %. Corn crisps were produced with the addition of the oil concerned so that the concentration of ALA in the finished product was at least 2 g 100 g^?1 (in a portion). With such a content of ALA, the crisps may be classified as ‘functional food’ in accordance with Commission Regulation (EU) No 432/2012 of May 2012. The following were tested: oxidative stability, and changes to the content of ALA during 6‐month storage of crisps with the addition of linseed oil and various concentrations of δ‐tocopherol and ascorbic acid. The crisps were packed in polyamide/polyethylene barrier film packages (30/70 µm), using either atmospheric air of argon for the packaging process. The study showed that with each applied concentration of δ‐tocopherol added to the linseed oil (200–800 mg 100 g^?1), it had a strong pro‐oxidant effect. Packaging in argon atmosphere play very protective role in ALA stabilisation in functional corn crisp.     

Improving the Frying Performance and Oxidative Stability of Refined Soybean Oil by Tocotrienol‐Rich Unsaponifiable Matters of Kolkhoung (Pistacia khinjuk) Hull Oil

Increasing consumer awareness for all natural products has quickly led to growing research on new resources of potent and profitable natural antioxidants. In this context, for the first time, the Kolkhoung hull oil (KHO) (Pistacia khinjuk)‐unsaponifiable matters (USM) (UHO) (100, 200, and 400 mg kg^?1) were incorporated into refined soybean oil (RSO) and the oxidative stability of prepared oils was measured during 32 hours of frying. Then, the obtained results (oxidative stability) were compared to the samples containing tert‐butyl hydroquinone (TBHQ) (100 mg kg^?1) as a common synthetic antioxidant. According to the results of oxidative stability assays of acid values, conjugated diene values and carbonyl values, and total polar compounds, the incorporation of UHO, particularly at a concentration of 200 mg kg^?1, was more efficient in improving the oxidative stability compared to TBHQ. The tocol content of KHO (2043.4 mg kg^?1) was higher than the reported amounts of other conventional edible oils. Furthermore, by incorporation of UHO into RSO, as compared with TBHQ, a better protection of naturally occurring antioxidants (tocopherols and sterols) was found after adding UHO to RSO. This fact was mainly attributed to the UHO's tocotrienol fraction. Hence, the USM of KHO can be used as a potent antioxidant to improve the oxidative stability of frying oils.     

High‐Purity Tocored Improves the Stability of Stripped Corn Oil Under Accelerated Conditions

γ‐Tocopherol‐5,6‐quinone (tocored) is of importance among the γ‐tocopherol (γ‐T) oxidant products and found in corn germ oil. Investigation on tocored is impeded in part by the difficulty to access high purity tocored. In this present study, high‐purity tocored is successfully prepared, and its antioxidant activity, together with γ‐T and TBHQ (positive control) in increasing concentrations in stripped corn germ oil is evaluated by Rancimat and Schaal oven tests. The stabilization factor in the Rancimat tests increases significantly (p < 0.05) along with an increase in the levels of antioxidants. Furthermore, tocored exhibits higher stabilization than γ‐T in the Schaal oven tests, although its efficacy gradually increases up to 100 mg kg^–1 and decreases significantly at higher levels (from 100 to 500 mg kg^–1), drawn from the comprehensive parameter A (considering both efficiency and strength) changes (5.06–11.21). In addition, the curves illustrating the residual contents of tocored and γ‐T run in different ways when the four levels are taken into consideration, further bearing the above results. Tocored tends to be a potent natural antioxidant for edible corn germ oil preservation. Practical Application: The present work provides more clear procedures for high‐purity tocored synthesis. Furthermore, tocored may be a potential natural antioxidant that is especially suitable for lipid base food substrates. The results of the present work contribute to the deeper understanding of the antioxidant activity of γ‐tocopherol. The antioxidant activity of tocored is higher than γ‐tocopherol in Schaal oven test. Tocored is a bright orange‐red substance that affects the appearance of the edible oil. Meanwhile, γ‐tocopherol is well known for its valuable health benefits, and appropriate measures should be adopted to store oils (corn oil, soybean oil, and so on) rich in γ‐tocopherol to control transformation in order to keep stability optimal. To some degree, the practical applications of the present results are also related to the processing and storage of edible oils.