Accelerated Oxidation Conditions Research Articles

Improvement of the oxidative stability of edible oils through enzymatic esterification with hydroxytyrosol‐rich extract

AbstractOxidative degradation is a common issue of commercial edible oils that results in rancidity, downgrading the organoleptic characteristics of food matrices. The aim of this study was the enzymatic modification of common vegetable oils (pomace olive and sunflower oil) with polyphenolic extract to prepare functional oils enriched with bioactive phenolipids. Under that scope, an agro‐industrial effluent, olive mill wastewater, was used as source to recover phenolic compounds. The recovery of hydroxytyrosol and tyrosol reached up to 81.2% ± 0.3% and 98.3% ± 0.2%, respectively. Further, immobilized lipase was used to catalyze the one‐step acylation of these phenolic antioxidants into the oils with the aim of enhancing their stability under accelerated oxidation conditions. The optimum parameters of the bioconversion were found to be 0.1% (w/w) immobilized lipase, 24h of incubation at 50°C under orbital shaking reaching high conversion yields for both phenolic compounds (≥94%). The results also highlighted that the extract‐modified oils presented notable thermooxidative stability at 60°C for 28 days compared to the control and synthetic antioxidant‐enriched oils, as demonstrated by several analytical (conjugated dienes, thiobarbituric reactive substances), chromatographic (solid‐phase microextraction gas chromatography/mass spectroscopy), and spectroscopic (fluorescence, attenuated total reflectance) techniques, giving new insights regarding the preservation of edible oils.Practical Application: Htyr has recently gained much attention as an active ingredient of food matrices for industrial applications due to its high antioxidant/antiradical activity. A major drawback of Htyr exploitation is the high market price and its solubility. Meanwhile, several edible oils are prone to autooxidation during transport, stock management, and household storage. The proposed one‐step biocatalytic process aims to enhance the lipophilicity and bioactivity of Htyr in bulk oil systems, making the use of this potent antioxidant compound feasible. This approach shows promise in extending the shelf life of common oils and highlights the advantages of by‐product management. Moreover, these functional oils can be applied for the preparation of sauces, bakery products, food supplements, and so on, as the bioactive ingredients that are present in them can delay the oxidative cascade reactions and, thus, the spoilage of the products, whereas the whole process meets the requirements of circular economy and green chemistry.

Evaluation the kinetic of peroxide and hexanal formation in ascorbyl palmitate incorporated sunflower oil during accelerated oxidation

The effects of temperature (40-80 °C), time (0-28 days), and different concentrations (0-1000 mg/kg) of ascorbyl palmitate (AP) on peroxide value, conjugated diene, triene acids and hexanal contents in sunflower oil kept under accelerated oxidation conditions have been evaluated. Samples with added AP showed lower peroxide values and hexanal contents than their counterparts without AP. While with increasing temperature, the reaction orders for peroxide formation reduced from first to zero order, those for hexanal formation were found to be first order under different experimental conditions. AP reduced the reaction rate constant for peroxide and hexanal formation. The activation energy required for peroxide and hexanal formation ranged from 14.64-89.40 and 1.62-12.14 kJ/mol K, respectively. 400 mg/kg AP, providing the highest activation energies for peroxide and hexanal formation, was found to be the best concentration to enhance the oxidative stability of sunflower oil under defined conditions.

Antioxidant-efficient indicator determinate by the relationship between β-myrcene/caryophyllene (α, β) on Hop (Humulus lupulus) essential oils under an accelerated oxidation test

The hop essential oil (Humulus lupulus) can be used as a natural additive in food to prevent lipid oxidation, replacing synthetic ones. The aim was to study the antioxidant activity of hop essential oil under accelerated oxidation conditions and determine the relationship between β-myrcene/caryophyllene (α, β) (M/Cs) as an antioxidant-efficient indicator. Sunflower oil was used as a lipid model. Five treatments were carried out (control, BHT, Chinook (CH), Cryo Citra (CYT), and Falconers Flight (F) at 0.02 %). The antioxidant efficacy was measured through free radical-scavenging activity, peroxide value, conjugated dienes, and oxidation volatile compounds. Cryo Citra essential oil showed the highest antioxidant activity, comparable with BHT, and M/Cs of 3.14 and F (0.91) and CH (0.57) showed good performance in the accelerated oxidation test while Chinook showed the best free radical-scavenging activity. The M/Cs relationship can be used as an antioxidant-efficient indicator with values biggest than 0.90.

Investigation of oxidative characteristics, fatty acid composition and bioactive compounds content in cold pressed oils of sunflower grown in Serbia and Argentina

BackgroundIn this work, the chemical composition analysis was performed for cold pressed oils obtained from the 15 sunflower hybrids grown in Serbia and Argentina, as well as the determination of their oxidative quality. The fatty acid composition and bioactive compounds including total tocopherols, phenols, carotenoids, and chlorophyll contents were investigated. The oxidation products were monitored through the peroxide value (PV), anisidine value (AnV), conjugated dienes (CD) and conjugated trienes (CT) content, and total oxidation index (TOTOX) under accelerated oxidation conditions by the oven method. ResultsLinoleic acid was the most abundant fatty acid in investigated oil samples, followed by oleic and palmitic acids. The mean contents of total tocopherols, phenols, carotenoids, and chlorophyll were 518.24, 9.42, 7.54 and 0.99 mg/kg, respectively. In order to obtain an overview of sample variations according to the tested parameters Principal Component Analysis (PCA) was applied. ConclusionPCA indicated that phenols, chlorophyll, linoleic and oleic acid were the most effective variables for the differentiation of sunflower hybrids grown in Serbia and Argentina. Furthermore, based on the fatty acid composition and bioactive compounds content in the oils, a new Artificial Neural Network (ANN) model was developed to predict the oxidative stability parameters of cold pressed sunflower oil.

The Oxidative Stability of Chia Seed Oil Enriched with Oregano (Origanum vulgare L.) and Yarrow (Achillea millefolium) Extracts

Oxidative stability of chia seed oil enriched with oregano (Origanum vulgare L.) and yarrow (Achillea millefolium) extracts at different concentrations (600, 1200, and 1800 ppm) was evaluated under accelerated oxidation conditions for 5 days. The total phenolic compounds and antioxidant activity of oregano extract were higher than the yarrow extract. With decreasing concentrations of extracts and increasing time, the oxidative stability of chia seed oil decreased significantly ( p < 0.05 ). At the first day, the acid value of chia seed oil did not show a significant difference, and the highest acid value was related to the control sample at the end of the storage period. The oil containing 1200 and 1800 ppm of oregano extract had the lowest acid, peroxide, anisidine, and Totox values. In the rancimat, the highest oxidative stability index (OSI) was shown in the sample containing 1800 ppm oregano extract, followed by yarrow extract. Our findings showed the potential of oregano and yarrow extracts by improving the oxidative stability of chia seed oil, especially at 1200 and 1800 ppm. At similar concentrations, oregano extract was more successful than yarrow extract in reducing the oxidation rate.

Evaluation of the Efficacy and Synergistic Effect of α- and δ-Tocopherol as Natural Antioxidants in the Stabilization of Sunflower Oil and Olive Pomace Oil during Storage Conditions.

Tocopherols are natural bioactive compounds with several health benefits. This study evaluated the effect of different ratios of α- and δ- tocopherol homologs to protect sunflower oil (SO) and olive pomace oil (OPO) against oxidation. A synergistic effect was recorded when the two tocopherols were combined at a ratio of 7:1 (α-T/δ-T). The oil samples were exposed to accelerated oxidation conditions using a Rancimat (90 °C and airflow of 15 L/h for 24 h) and protection from tocopherols was compared with that from butylated hydroxytoluene (BHT). Assessment of oil stability was examined using well-known parameters such as peroxide value (PV), thiobarbituric acid reactive substances (TBARS), p-anisidine value (p-AV), conjugated dienes (CD) and trienes (CT), and total oxidation (Totox) value, which were all significantly reduced when tocopherols were added at a ratio of 7:1 α-T/δ-T. Primary oxidative compounds measured according to PV were only reduced in SO samples (6.11%). Off-flavor compounds measured via TBARS assay in SO samples were reduced by above 20%, while p-AV was also reduced. CDvalue was correlated with PV in SO samples, while the 7:1 mixture was more effective than BHT for CTvalue. Total oxidation values in SO samples and OPO samples were reduced by 6.02% and 12.62%, respectively. These values in SO samples also provided a remarkable correlation (R2 > 0.95) with incubation time. Moreover, the synergistic effect was not only effective in reducing the oxidation values of oil samples, but also in lowering the degradation rate of tocopherols. Protective effects from tocopherols were mainly observed in SO samples, as OPO samples were more resistant to oxidation processes. This effect was even observed in fatty acid analysis, where the 7:1 mixture provided better results than BHT-spiked samples. Thus, it is suggested that tocopherol mixtures might be used as a natural preservative in the food industry to restrain lipid oxidation processes.

Development and characterization of the freeze-thaw and oxidative stability of edible rice bran wax-gelatin biphasic gels

Edible biphasic gels with high lipid fractions (>50%) were developed and characterized for their freeze-thaw and lipid oxidation stability. Gels consisted of gelatin in aqueous buffer (hydrogel; HG), and rice bran wax (RBW) in high-oleic soybean oil (oleogel; OG). Freeze-thaw stability was studied by rheology, liquid loss measurement, and microstructural characterization of the gels before and after one freeze-thaw cycle. Biphasic gels were stored for 6 months under accelerated oxidation conditions to assess oxidative stability through peroxide value (PV) analysis. Biphasic gels led to superior systems compared to control OG and HG. The storage modulus (G′) increased with increasing OG. Yield stress (σ*) for biphasic gels were greater than for OG alone, and σ*increased as the proportion of HG increased. Micrographs of biphasic gels showed OG-in-HG matrix for all gels, including those of >50% OG. After one freeze-thaw cycle, biphasic gels had less total liquid loss by approximately 50% compared to the controls and showed an increase in G′. No samples were rancid after the storage period, as demonstrated by the low PV (<3 meq/kg). Changing the ratio of OG:HG for this biphasic gel demonstrates the potential to design semi-solid fat replacers of desired properties with good overall physico-chemical stability.

Enhancing the Oxidative Stability of Linoleic Acid by Esterification with Hydroxytyrosol

This work aimed to evaluate the effect of covalent binding of an antioxidant, hydroxytyrosol, on the oxidative stability of linoleic acid. Hydroxytyrosol was bound to linoleic acid through an ester bond to produce hydroxytyrosol linoleate. The results of 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging activity and ferric reducing antioxidant power (FRAP) assays indicated that hydroxytyrosol linoleate retained the main antioxidant activity of hydroxytyrosol. Linoleic acid, hydroxytyrosol linoleate, and linoleic acid with 0.2 mg/g 2,6-di-tert-butyl-4-methylphenol (BHT) were stored under accelerated oxidation conditions (37 °C or illumination) for 9 days. Adding BHT only inhibited the oxidation of linoleic acid for 5 days. In contrast, hydroxytyrosol linoleate inhibited oxidation for 9 days. After 9 days, the peroxide, conjugated diene, thiobarbituric acid reaction substance values, and degradation rate of hydroxytyrosol linoleate were less than 26% of those of linoleic acid. The findings indicate that esterification with hydroxytyrosol can significantly improve the oxidative stability of linoleic acid.

NMR Analysis of Lipid Oxidation in Flaxseed Oil-in-Water Emulsions.

The formation of linolenic (Ln) and linoleic (L) acyl oxidation products during storage of flaxseed oil (FO)-in-water emulsions was monitored using proton nuclear magnetic resonance (1H NMR) spectroscopy, as well as chemical analytical methods and gas chromatography. Emulsions containing 10% FO and 1% Tween 60 were prepared by homogenization and then stored at 37 °C in the dark for 21 days under accelerated oxidation conditions (500 μmol ferrous sulfate). The induction time of the emulsions, after which rapid lipid oxidation was first observed, was 5-7 days, as shown by increases in peroxide values and hydroperoxide concentrations determined by NMR spectroscopy. Analysis of the hexanal and propanal concentrations during storage by HS-SPME-GC indicated that the oxidation of Ln and L acyls in the emulsions occurred simultaneously. The oxidation products originating from the Ln and L acyls were monitored using 1H NMR spectroscopy throughout the oxidation process. These results also showed that the Ln and L acyls oxidized simultaneously, and isomers of hydroperoxy-cyclic hydroperoxides (HCPs), Z,E-conjugated dienic hydroperoxides (ZECDHPs), and E,E-conjugated dienic hydroperoxides (EECDHPs) were the major primary oxidation products. Aldehydes were observed after 7 days, which was taken to be the start of the propagation stage, with the formation of a significant amount of oxygenated α, β-unsaturated aldehydes (OαβUAs). Based on the concentrations of hydroperoxides originating from the Ln and L acyls, our results suggested that the loss rate of L acyls was parallel to that of Ln acyls. This result was consistent with Ln acyls adopting a tighter packing at the oil-water interface in the emulsions than L acyls. This hypothesis was supported by the NMR relaxation time data. A good correlation between the isomer concentrations of ZECDHPs and HCPs in Ln acyls and between ZECDHPs and EECDHPs in L acyls was shown, with the mole ratios between them being 1.2 and 1.1, respectively. Droplet size and microstructure analyses showed that droplet aggregation occurred from 11 days onwards, which was attributed to polar oxidation products located at the oil droplet surfaces promoting coalescence. Zeta-potential measurements indicated that the droplets became more negative during storage, which was attributed to the accumulation of anionic reaction products at the droplet surfaces.

Characterization and oxidation stability of spray-dried emulsions with omega-3 oil and buttermilk processed by ultra-high-pressure homogenization (UHPH).

Integrating functional ingredients, such as buttermilk and omega-3 rich oils, in spray-dried emulsions (SDE) is a suitable way to incorporate these ingredients in dairy products to substitute dairy fat and increase their added value. Ultra-high-pressure homogenization (UHPH) processing of liquid emulsions considerably improves stability compared to the conventional homogenization (CH) process. With this premise, SDE were produced while comparing CH (30 MPa) and UHPH (100 or 200 MPa) processing of feeding emulsions. Emulsions were formulated with (50:50 chia:sunflower) oil, whole commercial buttermilk (BM), and maltodextrin (MD) as wall materials. Further spray drying of emulsions was then conducted. Obtained SDE were characterized in terms of water content, Aw (water activity), flowing properties, water solubility, encapsulation efficiency (EE), color, and microstructure. Oxidation stability of SDE was analyzed in accelerated oxidation conditions at 50 °C for one month for primary and secondary oxidation analysis evolution on days 1, 7, 14, and 31 of storage. Results showed better ability of BM as encapsulating agent in UHPH-processed emulsions with 7% of BM. This improvement was especially observed in the flowing properties and encapsulating efficiency. Seven percent BM UHPH-treated SDE showed the best primary oxidation stability during storage, while the 4% BM-UHPH-treated SDE exhibited better secondary oxidative stability.

Complexed Biopolymer of Whey Protein and Carboxymethyl Cellulose to Enhance the Chemical Stability of Lemon Oil-in-Water Emulsions

Lemon oil (LO) has been used as a flavoring food additive and its encapsulation in emulsions has facilitated its incorporation in food and pharmaceutical products. d-Limonene, the main ingredient in LO, and citral, the compound responsible for the aromatic profile, are easily oxidized and a new emulsion interfacial structure is needed to protect these compounds. This paper studies the physical and chemical stabilities of LO-in-water emulsions produced by membrane emulsification as a function of the oil droplets’ surface electric charge and interfacial thickness. For that purpose, the different stabilizers used were whey protein (pH: 3.8 and 6.8), and, for the first time in lemon oil encapsulation, an electrostatic whey protein–carboxymethyl cellulose (WP-CMC) complex (pH: 3.8). Although this complex did not improve emulsions’ physical stability when it comes to droplet size, it has contributed to maintaining the emulsions’ original color. As for chemical stability, the WP-CMC complex decreased the production of off-flavors resulting from the deterioration of d-limonene and citral under accelerated oxidation conditions.

Evaluation and improvement of the oxidative stability of leather fatliquors

Fatliquor oxidation may give leather unpleasant odor, and excessive amounts of Cr(VI) and volatile organic compounds. The accurate evaluation and improvement of the oxidative stability of fatliquors are of great significance to high-quality leather manufacturing. We proposed a set of practical methods for evaluating the oxidative stability of fatliquors on the basis of oxidation induction time, change in iodine value (∆ IV), and change in acid value (∆ AV) under accelerated oxidation conditions (at 100 °C with 10 L/h of air). Oxidation induction time is a highly sensitive marker for quantifying the oxidative stability of fatliquors, and ∆ IV and ∆ AV that are low cost and easy to operate are useful in evaluating the oxidative stability of fatliquors when the oxidation induction time is less than 22 h. The number of double bonds in fatliquors is an important factor affecting oxidative stability. The sulfation modification of fatliquors that greatly reduces double bonds and the addition of antioxidants, especially butylated hydroxyanisole and butylated hydroxytoluene, markedly improve oxidative stability of fatliquors.

Comparative study of accelerated assays for determination of equivalent days in the shelf life of roasted high oleic peanuts: Chemical and volatile oxidation indicators in accelerated and room temperature conditions

Lipids present in peanuts are susceptible to oxidation, which affects food quality and safety, for this reason shelf-life studies are carried out. The objective was to determine the relation between accelerated oxidation conditions and room temperature storage for roasted peanuts. Lipid oxidation indicators and roasted flavour volatiles were measured. There was a negative correlation between roasted and oxidation volatiles. In this research, 2,5-dimethylpyrazine and 2-ethyl-3,6-dimethylpyrazine were good indicators of the storage conditions of roasted peanuts, and the peroxide value (PV) was the most important oxidation indicator. For the comparision of equivalent days, it was used the peroxide value which reached 7.90, 2.47 and 0.89 Meq.O2/kg after 21 days at 25, 45 and 60 °C, respectively. The accelerated storage condition of 60 °C is optimal for estimation of the shelf life at 25 °C wherein 1 day at 60 °C is equal to 8.79 days at 25 °C.

Peanut skin phenolics obtained by green solvent extraction: characterization and antioxidant activity in pure chia oil and chia oil in water (O/W) emulsion.

The peanut skin (PS) is considered as an industrial waste with undervalued applications. Although several studies report potent antioxidant capacities of PS phenolics, the effectiveness in highly unsaturated lipid systems has not yet been evaluated. The objectives of the present study were two-fold: (i) to characterize a PS phenolic extract (PSE) obtained by means of a green technology and (ii) to evaluate its antioxidant efficacy on pure chia oil and chia oil in water (O/W) acid emulsion. PSE was composed mainly of monomeric and condensed flavonoids (procyanidin and proanthocyanidin oligomers). PSE displayed strong antioxidant properties as measured by different reducing power and radical scavenging capacities [IC50 =0.36 μg dry extract (DE) mL-1 for ferric reducing antioxidant power; IC50 =4.96 μg DE mL-1 for 2,2-diphenyl-1-picrylhydrazyl (DPPH)• ; IC50 =6.01 μg DE mL-1 for 2,2'-azinobis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS)•+ ; IC50 =2.62 μg DE mL-1 for HO• ]. It also showed high antioxidant efficacy when tested in pure chia oil under accelerated oxidation conditions (Rancimat, 100 °C). When added to the O/W emulsions maintained at 40 °C for 15 days, the PSE was more effective than a synthetic antioxidant (tert-butylhydroquinone) with respect to minimizing the formation and degradation of lipid hydroperoxides. The antioxidant efficacy of PSE was primarily attributed to the abundance of compounds with a high number of phenolic-OH groups. Because they were found to cover a relatively wide range of partition coefficients, the antioxidant properties could be also enhanced by effect of both interfacial and solubility phenomena. All of these features allow the potential use of PSE as a natural antioxidant in different types of foods, including acid emulsion systems. © 2021 Society of Chemical Industry.

Optimization of Ultrasound-Assisted Extraction of Bioactive Compounds from Pelvetia canaliculata to Sunflower Oil

In this study, Pelvetia canaliculata L. macroalga, collected from the Atlantic Portuguese coast, was used as a source of bioactive compounds, mostly antioxidants, to incorporate them in sunflower oil with the aim of increasing its biological value and oxidative stability. The lyophilized alga was added to the oil, and ultrasound-assisted extraction (UAE) was performed. Algae concentration and UAE time varied following a central composite rotatable design (CCRD) to optimize extraction conditions. The following parameters were analyzed in the oils: oxidation products, acidity, color, chlorophyll pigments, carotenoids, flavonoids, total phenolic content, antioxidant activity by DPPH (2,2-diphenyl-1-picrylhydrazyl) and FRAP (ferric reducing antioxidant power) assays, and sensory analysis. Extraction conditions did not affect the acidity and the amount of oxidation products in the oil. Chlorophylls and carotenoid contents increased with algae concentration, while flavonoid extraction did not depend on algae content or UAE time. Total phenolics in the oil were highly related only to FRAP antioxidant activity. Storage experiments of supplemented oil (12.5% algae; 20 min UAE) were carried out under accelerated oxidation conditions at 60 °C/12 days. Antioxidant activity (FRAP) of supplemented oil was 6-fold higher than the value of non-supplemented oil. Final samples retained 40% of their initial antioxidant activity. The presence of algae extracts contributed to the increased oxidative stability of sunflower oil.

Effect of Adding Curcumin on the Properties of Linseed Oil Organogels Used as Fat Replacers in Pâtés.

Beeswax-based organogels were formulated with linseed oil and curcumin according to a statistical design to increase the oxidative stability of spreadable meat products (pâté) where these organogels (OGCur) were incorporated as fat substitutes. The organogels obtained under optimal conditions (9.12% beeswax, 0.54% curcumin) showed a mechanical strength similar to pork backfat determined by back extrusion and high oil binding capacity (OBC; over 90%). The incorporation of curcumin at this concentration did not lead to any change in the arrangement of the crystal network, OBC, and mechanical, thermal, or rheological properties of the organogels. Beeswax organogels with and without curcumin, with a β’ orthorhombic subcell structure, showed a predominant elastic behavior and a melting event wider and shifted to lower temperatures than pure beeswax, suggesting a plasticizer effect of the oil in the wax crystals. The oxidative stability of the organogels under accelerated oxidation conditions increased due to the incorporation of curcumin. A decrease in the curcumin content was found from day 4 at 60 °C, together with a significantly lower formation of both peroxides and malonaldehyde. When pork backfat was partially or totally replaced by OGCur in pâtés, a noticeable protective effect of curcumin against lipid oxidation was found during chilled storage

Comparative antioxidant capacity of plant leaves and herbs with their antioxidative potential in meat system under accelerated oxidation conditions

This study evaluated the comparative antioxidant effects of nine leaves extracts (pomegranate, PL; citrus, CL; kinnow, KL; mango, ML; guava, GL; peppermint, PM; oregano, OL; rosemary, RM; thyme, TL) in the meat system (MS) formulated with a healthier oil consisted of high level of polyunsaturated fatty acids. Total phenolic content of the extracts varied from 10.1 ± 1.44 to 98.8 ± 2.15 mg TAE/g; whereas, total flavonoid content varied from 1.6 ± 0.16 to 64.8 ± 0.41 mg CE/g. The DPPH scavenging activity of the extracts varied from 29.8 ± 0.87 to 58.5 ± 1.57% while BHT showed 77.1 ± 1.57% scavenging activity. Total antioxidant activity of extracts varied from 0.91 ± 0.14 to 3.90 ± 0.16 while the activity of BHT was 3.06 ± 0.14. The descending order for the antioxidant potential of the extracts (prepared at 70 °C) in the meat system was MS-GL70 = MS-PL70 = MS-BHT > MS-ML70 > MS-RM70 = MS-TL70 > MS-KL70 = MS-PM70 > MS-control. The addition of KL extract exerted negative effects (P < 0.05) on the color attributes. The addition of ML extracts increased in the emulsion stability (total expressible fluid % and expressible fat %). Hence, GL, PL, and ML can be considered as a good source of natural antioxidants for enhancing the oxidative stability of meat systems without affecting other technological properties.

Pomegranate peel methanolic-extract improves the shelf-life of edible-oils under accelerated oxidation conditions.

Natural antioxidants extracted from agri‐waste resources have gained increased economic, sustainable, and health attention due to their sustainability, safer food‐applications, and beneficial components. Pomegranate peel extracts (Punica Granatum L.) have natural phytochemicals with superior protective effects stabilizing a variety of the most common vegetable oils consumed globally. Among five different pomegranate peel extracts, methanolic extract has maximum total phenolic content of 18.89%, a total flavonoid content of 13.95 mg QE kg−1, and a relative antioxidant activity of 93% when compared to other pomegranate peel extracts. Additionally, the HPLC analysis of pomegranate peel methanolic extract exhibited the maximum number of phenolic and flavonoid fractions. HPLC fractions showed that pyrogallol and ellagic acids were the most abundant phenolic compounds with 453 and 126 mg kg−1, respectively. In terms of flavonoid fractions, hesperidine and quercetrin were the highest detected‐flavonoids with about 50 and 35 mg kg−1, respectively, from HPLC flavonoids fractions. Therefore, pomegranate peel methanolic extract was selected at different concentrations (100, 200, 400, and 600 ppm) for the stabilizing experiment of Egyptian freshly refined edible oils (sunflower, soybean, and corn oils) in comparison with synthetic antioxidant (tert‐butyl hydroquinone TBHQ‐200 ppm) during accelerated storage at 70°C for 10 days. The results from the accelerated storage experiment indicated that pomegranate peel methanolic extract (at different concentrations: 200, 400, and 600 ppm) exhibited stronger antioxidant capability in all tested oils rather than negative controls (without antioxidant) and synthetic antioxidant TBHQ‐200. Under accelerated oxidation conditions, pomegranate peel methanolic extract have the potential capability to improve the shelf life of edible oils in comparison with the most powerful synthetic antioxidant (TBHQ‐200 ppm).

Studies on the anti-oxidative ability of quinones in natural ester based insulating liquids for transformers

Due to the unsaturated olefinic structure of natural esters, their antioxidation ability is generally poorer than that of the mineral oils, thus certain antioxidants were commonly added as the additives to improve the oxidative stability of natural ester for their service as transformer oils. The present study reported the influences of adding quinones as additives on the oxidative stability of versatile natural esters. It was found that, under the accelerated oxidation conditions, added quinones could improve the oxidative stability of these tested natural esters through decreasing their acidic values, viscosity increase and dielectric losses to certain extent, thus providing a new category of antioxidants to improve the oxidative stability of natural ester based transformer oils.

Antioxidant capacity of the extracts from flowers of Erica australis L.: Comparison between microwave hydrodiffusion and gravity (MHG) and distillation extraction techniques - Formulation of sunscreen creams

Microwave hydrodiffusion and gravity (MHG) extraction of Erica australis flowers was optimized evaluating different microwave irradiation powers (25−200 W). Collected extracts were compared with the liquid phase obtained by conventional distillation. Their total phenolic content, antioxidant capacity and color features were evaluated. Microscopical properties of the flower tissues allowed assessing the distinct effects of the extraction processes. The cosmetic application of the collected bioactive extracts in the formulation of sunscreen creams with waters from three different thermal spring waters and the corresponding characterization (e.g. chemical, bioactive and rheological features) and sensory analysis were also made. For cosmetic comparative purposes, extracts from Ulex europaeus flowers obtained by MHG procedure was also analyzed. The stability of these oil-in-water model emulsions was tested during accelerated oxidation conditions. Results indicated that MHG at 50 W for 130 min was the most adequate work conditions for the extraction of antioxidant compounds from these wild flowers (around 0.27 mg Trolox eq/g flower dry weight and 0.01 mg ascorbic acid/g flower dry weight or 0.04 mg FeSO4 * 7H2O/g flower dry weight). This procedure also led a drop of energy consumption environmental impact (about 8 times less) in comparison with distillation method. Small total color differences were detected between the gathered extracts. The incorporation of flower extracts produced similar effects when compared with added commercial antioxidants except for viscous behavior. Sensorially, E. australis extract incorporated with thermal waters displayed a positive effect on the skin cream application of the formulated cosmetic, mainly with thermal water 3.