Extraction of γ-oryzanol from rice bran using diverse edible oils: enhancement in oxidative stability of oils.

Diverse edible oils including perilla, corn, soybean, canola, sunflower, olive, and grape seed oils were mixed with heat-stabilized rice bran to extract γ-oryzanol from the rice bran. The oxidative stabilities of the oils with or without extraction were compared by analyzing the headspace oxygen content, conjugated dienoic acid (CDA) values, and p-anisidine values (p-AV). Grape seed oil extracted significantly high γ-oryzanol content while canola oil extracted lowest γ-oryzanol content (p < 0.05). All the solvent oils except corn oil possessed enhanced oxidative stability at 100 °C after extracting γ-oryzanol from stabilized rice bran, based on the results of the headspace oxygen depletion and CDA methods. However, all the recovered oils had high p-AV than vegetable oils. Especially, perilla oil had an exceptionally high p-AV, which may be due to its high linolenic acid content.

Oxidative stability of oil-in-water emulsions with α-tocopherol, charged emulsifier, and different oxidative stress.

α-Tocopherol is known to show different activity depending on the concentration and food matrix. Effects of α-tocopherol at the concentrations of 0, 0.1, 0.5, and 1.0 mM were determined in oil-in-water (O/W) emulsions containing anionic, neutral, and cationic emulsifiers under different types of oxidative stress including riboflavin photosensitization, photooxidation, and autoxidation. Headspace oxygen depletion, lipid hydroperoxides, and conjugated dienes were analyzed to determine the oxidative stability of O/W emulsions. α-Tocopherol served as an antioxidant in O/W emulsion with a cationic emulsifier irrespective of oxidative stress. α-Tocopherol acted as an antioxidant in O/W emulsion with a neutral emulsifier at riboflavin photosensitization while a prooxidant at photooxidation. However, in samples with an anionic emulsifier, α-tocopherol activity differed from the concentration and types of oxidative stress. Therefore, cationic transition metals or reactive oxygen species generated from RF photosensitization could play key roles of α-tocopherol in O/W emulsion.

Antioxidant Properties of Astaxanthin in Oil-in-Water Emulsions with Differently-Charged Emulsifiers Under Chlorophyll Photosensitization.

The antioxidative or prooxidative properties of astaxanthin at the concentrations of 0, 10, and 100 µM were determined in oil-in-water (O/W) emulsions containing neutral, anionic, and cationic emulsifiers, which was Tween 20, sodium dodecyl sulfate, cetyltrimethylammonium bromide (CTAB), respectively, under chlorophyll photosensitization. The oxidative parameters and headspace volatiles were analyzed in O/W emulsions. In the 24 h period of visible light irradiation, 100 µM of astaxanthin acted as an antioxidant in O/W emulsions containing neutral and anionic emulsifiers. However, astaxanthin in O/W emulsions with a cationic emulsifier was neither an antioxidant nor a prooxidant. The profiles of volatile compounds showed that astaxanthin served as a singlet oxygen quencher in O/W emulsions containing neutral and anionic emulsifiers. However, in O/W emulsion with a cationic emulsifier, astaxanthin was neither a singlet oxygen quencher nor a free radical scavenger because prooxidant properties of CTAB overwhelmed the antioxidant effects of astaxanthin. Therefore, the antioxidant properties of astaxanthin were influenced by the emulsifier charges in O/W emulsions. PRACTICAL APPLICATION: Astaxanthin is a lipid-soluble pigment and has antioxidant, anticancer, and anti-inflammatory properties and beneficial effects on cardiovascular diseases. Many lipid-based foods are displayed on the shelves in the markets under fluorescent light. The addition of astaxanthin can extend the shelf life of O/W emulsion type foods such as beverage and dressing products under visible light irradiation. Also, oxidative stability in emulsion type foods containing astaxanthin rich natural ingredients can be predicted.

Oxidative Stability in Oil-in-Water Emulsions with Quercetin or Rutin Under Iron Catalysis or Riboflavin Photosensitization.

The effects of quercetin and rutin on the oxidative stability of oil-in-water (O/W) emulsions were tested under riboflavin (RF) photosensitization in the presence or absence of FeCl2 . The degree of oxidation in O/W emulsions was determined by headspace oxygen content, conjugated dienes, and lipid hydroperoxides. Quercetin chelated more metal than did rutin in iron catalyzed O/W emulsions. Generally, 0.1 mM quercetin and rutin was oxidative while 0.5 and 1.0 mM quercetin and rutin was antioxidative in O/W emulsions under RF photosensitization. Depending on the analysis method, the antioxidants had different strengths. The antioxidative or oxidative properties of quercetin and rutin vary in O/W emulsions and depend the quercetin and rutin concentrations and oxidative forces like transition metals, RF photosensitization, or a combination thereof.

Physicochemical properties and oxidative stability of oleogels made of carnauba wax with canola oil or beeswax with grapeseed oil.

Two types of oleogels-made of carnauba wax with canola oil or beeswax with grapeseed oil-were prepared at concentrations from 0 to 15% (w/w) of wax. Physical characterization was done and oxidative stability of the oleogels were evaluated. As the proportion of wax increased from 5 to 15%, the enthalpy of crystallization and melting increased in both oleogels. The carnauba wax-based oleogel (CWO) required greater enthalpy than the beeswax-based oleogel (BWO). Differences in L*, a*, and b* values between control oils and the oleogels significantly decreased as the concentration of wax increased in the oleogels (5-15%; p<0.05). Oil-binding capacity of the BWO was higher than that of the CWO. Solid-fat content of the CWO did not change significantly from 10 to 60oC, whereas that of the BWO decreased. In general, oxidative stability of the CWO was better at 60 and 180oC heat treatment in comparison with control oils (p<0.05). However, the BWO did not provide high oxidative stability than the control oils.

Evaluation of Antioxidant or Prooxidant Properties of Selected Amino Acids Using In Vitro Assays and in Oil-in-Water Emulsions Under Riboflavin Sensitization.

The antioxidant properties of selected amino acids were tested using in vitro assays and oil-in-water (O/W) emulsions under riboflavin (RF) photosensitization. Headspace oxygen content, lipid hydroperoxides, and conjugated dienes were determined for the degree of oxidation. Riboflavin photosensitization was adapted as the oxidation driving force. In vitro assays showed that cysteine had the highest antioxidant properties followed by tryptophan and tyrosine. However, in O/W emulsions under RF photosensitization, tyrosine inhibited lipid oxidation whereas tryptophan acted as a prooxidant. Tryptophan accelerated the rates of oxidation in O/W emulsion without RF. The antioxidant properties of amino acids differed depending on the antioxidant determination methods, oxidation driving forces, and food matrices.

Effects of emulsifier charges on the oxidative stability in oil-in-water emulsions under riboflavin photosensitization.

The oxidative stability in oil-in-water (O/W) emulsions containing different emulsifier charges was tested under riboflavin photosensitization by analysis of headspace oxygen content and lipid hydroperoxides. Sodium dodecyl sulfate (SDS), Tween 20, and cetyltrimethylammonium bromide (CTAB) were selected as anionic, neutral, and cationic emulsifiers, respectively. The O/W emulsions containing CTAB had lower oxidative stability than those with SDS and Tween 20. The addition of ethylenediaminetetraacetic acid, a well-known metal chelator, increased the oxidative stability in O/W emulsions, irrespective of emulsifier charges. Oxidative stability in Tween 20-stabilized emulsions decreased in FeCl3 and FeCl2 concentration-dependent manner. However, oxidative stability in samples containing CTAB increased up to 0.5mM of FeCl3 and FeCl2 and then decreased, which implies that CTAB act differently during lipid oxidation compared to SDS and Tween 20.

Analysis of Trans Fat in Edible Oils with Cooking Process.

Trans fat is a unsaturated fatty acid with trans configuration and separated double bonds. Analytical methods have been introduced to analyze trans fat content in foods including infrared (IR) spectroscopy, gas chromatography (GC), Fourier transform-infrared (FT-IR) spectroscopy, reverses-phase silver ion high performance liquid chromatography, and silver nitrate thin layer chromatography. Currently, FT-IR spectroscopy and GC are mostly used methods. Trans fat content in 6 vegetable oils were analyzed and processing effects including baking, stir-frying, pan-frying, and frying on the formation of trans fat in corn oil was evaluated by GC. Among tested vegetable oils, corn oil has 0.25 g trans fat/100 g, whereas other oils including rapeseed, soybean, olive, perilla, and sesame oils did not have detectable amount of trans fat content. Among cooking methods, stir-frying increased trans fat in corn oil whereas baking, pan-frying, and frying procedures did not make changes in trans fat content compared to untreated corn oils. However, the trans fat content was so low and food label can be declared as '0' trans based on the regulation of Ministry of Food ad Drug Safety (MFDS) (< 2 g/100 g edible oil).

Antioxidant properties of ascorbic acid in bulk oils at different relative humidity.

The effects of relative humidity (RH) on the antioxidant properties of ascorbic acid (10, 20, 42, and 84ppm) were investigated in stripped corn oils stored at 60°C. The degree of oxidation in oils was determined by analysing headspace oxygen content and conjugated dienoic acids. The oxidative stability of bulk oils without addition of ascorbic acid was significantly different depending on the RH. As the concentration of ascorbic acid increased from 10 to 84ppm, oxidative stability increased significantly irrespective of RH (p<0.05). Generally, oils containing ascorbic acid at low RH had higher oxidative stability after storage at 60°C than those at high RH. The antioxidant properties of ascorbic acid were greatly influenced by both the moisture content in the oil and the ascorbic acid concentration.

Effects of relative humidity on the antioxidant properties of α-tocopherol in stripped corn oil.

The effects of relative humidity (RH) on the antioxidant properties of α-tocopherol (10, 20, 42, and 84 ppm) were determined in stripped corn oil oxidised at 60°C. The degree of oxidation in oils was determined by analysing headspace oxygen content and conjugated dienoic acids (CDAs). Changes in moisture and α-tocopherol content were also monitored. The oxidative stability of stripped corn oil and stability of α-tocopherol differed significantly depending on the RH. As the concentration of α-tocopherol increased from 10 to 84 ppm, oxidative stability decreased significantly irrespective of RH. The remaining α-tocopherol content decreased as RH increased, suggesting an important role for moisture content in the stability of α-tocopherol. Antioxidant properties of α-tocopherol were greatly influenced by both moisture content in oil and α-tocopherol concentration.