Effects on the flavor and oxidative stability of stripped soybean and sunflower oils with added pure tocopherols

Effects of tocopherols on the oxidative stability of stripped vegetable oils were studied by adding pure tocopherols--alpha, beta, gamma, and delta--in their naturally occurring proportions in soybean and sunflower oils to the triacylglycerols (TAG) of soybean and sunflower oils. Soybean and sunflower oils were purified by stripping all minor constituents, leaving the triacylglycerols. Pure tocopherols in the proportion typical of sunflower oil--high alpha, low gamma, and low delta--were added to purified sunflower oil and to purified soybean oil. Pure tocopherols in the proportion typical of soybean oil--low alpha, high gamma, and high delta--were added to the purified oils. Oils were subjected to accelerated autoxidation using oven storage at 60 degrees C in the dark and accelerated photooxidation at 7500 lx light intensity at 30 degrees C. Oxidation levels of aged oils were measured by the formation of both peroxides and volatile compounds and by flavor analysis. Results from substituting the tocopherol profile from one oil type to another varied on the basis of whether they were oxidized in the dark or in the light. For example, during autoxidation in the dark, soybean oil with the typical soybean tocopherol profile had the lowest levels of peroxides and total volatile compounds, whereas sunflower oil with the sunflower tocopherol profile had the highest levels. In flavor analyses of the same oils, sunflower oil with the soybean tocopherol profile was the most stable. Soybean oil with the profile of sunflower tocopherols was the least stable in dark oxidation. In contrast to the data from autoxidation in the dark, addition of tocopherols typical of sunflower oil significantly improved light stability of both oil types compared to the addition of soybean tocopherols to sunflower oil. The tocopherol profile typical of soybean oil was significantly more effective in inhibiting autoxidation in the dark; however, the tocopherol profile typical of sunflower oil inhibited light oxidation significantly more than the soybean tocopherol profile.     

Novel approach to study oxidative stability of extra virgin olive oils: importance of alpha-tocopherol concentration

The stability of extra virgin olive oils is mainly due to their relatively low fatty acids unsaturation and to the antioxidant activity of some of the unsaponifiable components. We studied the activity of alpha-tocopherol in extra virgin olive oil in its natural state, using new and simple oxidizing conditions in "thin layer" and "bulk phase". Oxidation time course was monitored at 37 degrees C or 75 degrees C. A storage test was also performed. Two parameters were evaluated: depletion of alpha-tocopherol and formation of PUFA hydroperoxides, measured as conjugated dienes (CD) and peroxide value. The value of complex polyphenols was also measured. alpha-Tocopherol concentration decreased in function of time and temperature and showed a strong inverse correlation with the increase of CD. When alpha-tocopherol reached a "threshold value" of 60-70 mg/kg, a significant increase of CD formation was observed, together with a good correlation between CD and peroxide value. The initial amount of alpha-tocopherol is one of the components that influences oil oxidative susceptibility.     

Effect of antioxidants on oxidative stability of edible fats and oils: thermogravimetric analysis

Thermogravimetric analysis was used to determine the oxidative stability of various edible oils (olive oil, milkfat) and triacylglycerides (triolein, trilinolein), while the effect of natural (alpha-tocopherol, ascorbic acid) and synthetic antioxidants (butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), and tertiary butyl hydroquinone were evaluated by addition to trilinolein. Oil resistance to oxidation was obtained by measuring the increase in sample weight due to the uptake of molecular oxygen, the temperature at maximum sample weight, and the temperature at the onset of oxidation. When comparing sample weight increase, trilinolein proved to be oxidatively less stable than triolein, olive oil, and milk fat, while triolein was less stable than olive oil and milk fat. Olive oil showed significantly higher stability than milkfat when comparing the temperature at the onset of oxidation. When comparing effectiveness of antioxidants, a combination of 0.01% BHA and 0.01% BHT increased trilinolein stability the most.     

Comparison and analysis of fatty acids, sterols, and tocopherols in eight vegetable oils

The similarities and differences of eight vegetable oils produced in China were investigated in terms of their fatty acid, sterol, and tocopherol compositions and subsequent data processing by hierarchical clustering analysis and principal component analysis. The lipid profiles, acquired by analytical techniques tailored to each lipid class, revealed great similarities among the fatty acid profiles of corn and sesame oil as well as few differences in their sterol profiles. It turns out that not only was there great similarity between the fatty acid profiles of corn oil and sesame oil but also there were not too many differences for the sterol profiles. Sunflower and tea-seed oil showed similar sterol compositions, while the tea-seed oil tocopherol was very similar to palm oil. The results demonstrated that the use of only one of these profiles was unreliable for indentifying oil origin and authenticity. In contrast, the use of the sterol or tocopherol profile together with the fatty acid profile more accurately discriminates these oils.     

Quantification of tocopherols and tocotrienols in portuguese olive oils using HPLC with three different detection systems

Three different HPLC detection systems were compared for the determination of tocopherols and tocotrienols in olive oil: fluorescence and diode array connected in series, ultraviolet, and evaporative light scattering. The best results were obtained with the fluorescence detector, which was successfully applied in the quantification of tocopherols and tocotrienols in 18 samples of Portuguese olive oils. To support the validity of the method, the parameters evaluated were linearity, detection limits, repeatability, and recovery. All of the studied samples showed similar qualitative profiles with six identified compounds: alpha-T, beta-T, gamma-T, delta-T, alpha-T3, and gamma-T3. Alpha-tocopherol (alpha-T) was the main vitamin E isomer in all samples ranging from 93 to 260 mg/kg. The total tocopherols and tocotrienols ranged from 100 to 270 mg/kg. Geographic origin did not seem to influence the tocopherol and tocotrienol composition of the olive oils under evaluation.     

Secoiridoids, tocopherols, and antioxidant activity of monovarietal extra virgin olive oils extracted from destoned fruits

The effect of olive stone removal before processing on the degradation level, secoiridoid and tocopherol contents, and antioxidant activity of monovarietal extra virgin olive oils (EVOOs) was studied. EVOOs were extracted from olives of the Leccino, Moraiolo, Frantoio, Pendolino, Taggiasca, and Colombaia varieties both in the presence and in the absence of the stones. The degradation level of EVOOs was evaluated by acidity, peroxide number, and spectroscopic indices K(232) and K(270), according to EU regulation. The secoiridoid compounds typical of EVOO, namely, the oleuropein and ligstroside derivatives, hydroxytyrosol, tyrosol, and tocopherols were analyzed by HPLC. The antioxidant activity was evaluated by the xanthine oxidase/xanthine system, generating superoxide radical and hydrogen peroxide, and by the 2,2-diphenyl-1-(2,4,6-trinitrophenyl)hydrazyl test. Results showed that EVOOs obtained from both stoned and destoned olives had a very low degradation level, which was not affected by destoning. Destoning lowered slightly the alpha-tocopherol content in EVOOs but increased the total secoiridoid content and the antioxidant activity of EVOOs (up to 3.5-fold). However, these effects were variety-dependent and negligible in some conditions. It was concluded that a better knowledge of the reactions occurring during olive processing, and particularly on the involvement of endogenous pulp and stone enzymes, is essential to predict the effect of destoning on EVOO quality.     

High-yield preparation of wax esters via lipase-catalyzed esterification using fatty acids and alcohols from crambe and camelina oils

Fatty acids obtained from seed oils of crambe (Crambe abyssinica) and camelina (Camelina sativa) via alkaline saponification or steam splitting were esterified using lipases as biocatalysts with oleyl alcohol and the alcohols derived from crambe and camelina oils via hydrogenolysis of their methyl esters. Long-chain wax esters were thus obtained in high yields when Novozym 435 (immobilized lipase B from Candida antarctica) and papaya (Carica papaya) latex lipase were used as biocatalysts and vacuum was applied to remove the water formed. The highest conversions to wax esters were obtained with Novozym 435 (> or =95%) after 4-6 h of reaction, whereas with papaya latex lipase such a high degree of conversion was attained after 24 h. Products obtained from stoichiometric amounts of substrates were almost exclusively (>95%) composed of wax esters having compositions approaching that of jojoba (Simmondsia chinensis) oil, especially when crambe fatty acids in combination with camelina alcohols or camelina fatty acids in combination with crambe alcohols were used as substrates.     

芝麻种子中内源性蛋白酶的热稳定性及其运用

近年来,芝麻的深加工偏重于制油,而忽略了对芝麻蛋白的高值利用。为了实现芝麻蛋白与油脂的高值综合利用,该研究将湿法脱皮芝麻进行干燥,经压榨制取芝麻油和压榨粕后,再利用内源性蛋白酶对芝麻压榨粕中的蛋白质进行水解,制取蛋白水解物。在此过程中,考察了干燥温度对湿法脱皮芝麻压榨出油率和内源性蛋白酶活性的影响。结果显示,在80～180 ℃干燥1 h时,脱皮芝麻出油率上升至88.55%～90.98%（带皮芝麻为81.76%）;对于内源性蛋白酶而言,在130 ℃时,仍可保留约57%的活性,表明芝麻种子中内源性蛋白酶具有良好的热稳定性。同时,通过将低变性芝麻粕（干燥条件为50 ℃、4 h）制浆,在pH 值为4.5、50 ℃下孵育6 h,经3 000 g离心5 min后,分离得到透明清液（蛋白水解物）,其清液中蛋白质的分布率为66%,且主要由38%小肽（< 1500 Da）和37%游离氨基酸组成,除此之外,还存在多种生物活性物质。该研究为芝麻内源性蛋白酶的实际应用以及芝麻蛋白新产品的开发提供了一种新思路。     

Contribution of the phenolic fraction to the antioxidant activity and oxidative stability of olive oil

Antioxidant activity of the phenolic fraction of extra virgin olive oil (EVOO) was measured by means of a chemical and an electrochemical method. Both methods were tested in predicting the oxidative spoilage and stability to oxidation of 22 EVOO samples and resulted correlated with peroxide values and oxidative stability measured by Rancimat. The main phenolic compounds of EVOOs were detected by HRGC. To study the contribution of single polyphenols (PPs) to antioxidant activity of phenolic fraction and oxidative stability of EVOOs, multivariate statistical analyses were applied on HRGC data. An isomer of oleuropein aglycon was shown to affect significantly antioxidant activity of phenolic fraction but not oil stability to oxidation. No individual compounds was identified as the main cause of the overall antioxidant activity, and the total polyphenol determination by the Folin reagent was better correlated to antioxidant activity and oxidative stability than each tested PP or PPs groups such as o-diphenols.     

Enhancing quality and oxidative stability of aged fried food with gamma-tocopherol

To determine the effects of gamma-tocopherol on the stability of fried food, potato chips were fried in triolein with 0, 100, or 400 ppm gamma-tocopherol. Potato chips, sampled at 1, 3, and 6 h of frying time, were aged for 0, 2, and 4 days at 60 degrees C and then evaluated for odor attributes by sensory analysis and for volatile compounds by purge-and-trap gas chromatography-mass spectrometry. Oil sampled after 1, 3, and 6 h of frying time from the fryer was evaluated for total polar compounds and retention of gamma-tocopherol. Oil extracted from the potato chips was also analyzed for residual gamma-tocopherol. gamma-Tocopherol disappeared rapidly, with only slight amounts of the original 100 ppm level detectable after the triolein was used for frying. gamma-Tocopherol significantly inhibited polar compound production in the triolein. Results showed that gamma-tocopherol inhibited the oxidation of the fried food even when only very low levels of retained gamma-tocopherol were present in the frying oil or potato chips. Nonanal formation was inhibited by gamma-tocopherol in aged potato chips. Odor analysis of the aged potato chips showed that samples with 0 ppm gamma-tocopherol had a rancid odor after being aged for 4 days. Potato chips with 400 ppm gamma-tocopherol had no rancid odors; however, as the level of gamma-tocopherol decreased in the triolein and in the potato chips, a weak plastic odor characteristic of oxidized triolein was detected.     

Effect of enzymatic randomization on positional distribution and stability of seal blubber and menhaden oils

In an effort to investigate the effect of positional distribution on oxidative stability of menhaden and seal blubber oils, Novozyme 435 was used as a random biocatalyst. Positional distribution of fatty acids was determined using gas chromatography. As some of the α-tocopherol was lost during randomization, its content was adjusted to the level prior to the process to eliminate this effect on oxidative stability of oils tested. Conjugated dienes (CD) and thiobarbituric acid reactive substances (TBARS) were used as indicators of oxidative stability. The results showed that the polyunsaturated fatty acids were distributed predominantly at terminal positions in randomized menhaden oil, whereas they were distributed more evenly among all positions in enzymatically randomized seal blubber oil, compared to their unrandomized counterparts. Results of CD and TBARS values indicated that randomized menhaden oil was more stable than the original oil, whereas randomized seal blubber oil was more vulnerable to oxidation compared to its counterpart. Changes of oxidative stability after randomization were mainly due to positional redistribution of fatty acids, especially those of the polyunsaturated types.     

Effect of lactoferrin on oxidative stability of corn oil emulsions and liposomes

Interest in using lactoferrin in foods for its antimicrobial activity inspired the present study of its antioxidant activity. Natural bovine lactoferrin inhibited oxidation in buffered corn oil emulsions and lecithin liposome systems at pH 6.6 and 50 degrees C. The antioxidant activity increased with lactoferrin concentration in both phosphate- and Tris-buffered emulsions, but not in both buffered liposome systems. A mixture of 1 microM lactoferrin and 0.5 microM ferrous ions was a significantly better antioxidant than 1 microM lactoferrin alone in Tris-buffered emulsions and in phosphate-buffered liposomes. Lactoferrin was a prooxidant at 1 microM in phosphate-buffered liposomes and at 15 and 20 microM in Tris-buffered liposomes. Copper was a stronger prooxidant than iron in both buffered emulsions. Lactoferrin decreased the prooxidant effect of iron, but not of copper, in emulsions. The antioxidant or prooxidant activities of lactoferrin depended on the lipid system, buffer, its concentration, the presence of metal ions, and oxidation time.     

复合纳米材料修饰丝网印刷电极检测土壤中铅和镉

为了快速、准确、低成本检测土壤中痕量Pb(Ⅱ)和Cd(Ⅱ),该研究应用电化学还原和滴涂方法制备了一种铋膜/Nafion/还原氧化石墨烯/离子液体复合纳米材料修饰的丝网印刷电极(Bi/Nafion/rGO/IL/SPE).通过扫描电子显微镜、循环伏安法和能量色散谱手段表征了修饰电极的电化学分析性能,结果显示修饰材料增大了...     

Effects of roasting on pyrazine contents and oxidative stability of red pepper seed oil prior to its extraction

Red pepper seeds were roasted with constant stirring for 6, 9, 10, and 12 min at 210 degrees C, and oils were extracted from the roasted red pepper seeds using an expeller. The iodine values and fatty acid compositions of red pepper seed oils did not change with roasting time. The fatty acid composition of the oil obtained from the red pepper seeds roasted for 6 min was 0.24% myristic acid, 13. 42% palmitic acid, 0.33% palmitoleic acid, 2.07% stearic acid, 10. 18% oleic acid, 73.89% linoleic acid, and 0.37% linolenic acid, showing a fatty acid composition similar to that of high-linoleate safflower oil. Thirteen alkylpyrazines were identified in the roasted red pepper seed oils: 2-methylpyrazine, 2,5-dimethylpyrazine, 2,6-dimethylpyrazine, 2-ethylpyrazine, 2-ethyl-6-methylpyrazine, 2-ethyl-5-methylpyrazine, trimethylpyrazine, 2,6-diethylpyrazine, 2-ethyl-3,5-dimethylpyrazine, tetramethylpyrazine, 2, 3-diethyl-5-methylpyrazine, 2-isobutyl-3-methylpyrazine, and 3, 5-diethyl 2-methylpyrazine. The pyrazine content increased markedly as the roasting time increased, showing 2.63, 5.01, 8.48, and 13.10 mg of total pyrazine/100 g of oils from the red pepper seeds roasted for 6, 8, 10, and 12 min, respectively, at 210 degrees C. 2, 5-Dimethylpyrazine in the roasted red pepper seed oil seemed to be the component most responsible for the pleasant nutty aroma of the oils. The oxidative stabilities of oils increased greatly as the roasting time increased.     

Physical and oxidative stability of fish oil-in-water emulsions stabilized with beta-lactoglobulin and pectin

The oxidation of fatty acids can be inhibited by engineering the surface of oil-in-water emulsion droplets to decrease interactions between aqueous phase prooxidants and lipids. The objective of this research was to evaluate whether emulsions stabilized by a multilayer emulsifier systems consisting of beta-lactoglobulin and citrus or sugar beet pectin could produce fish oil-in-water emulsions that had good physical and oxidative stability. Sugar beet pectin was compared to citrus pectin because the sugar beet pectin contains the known antioxidant, ferulic acid. A primary Menhaden oil-in-water emulsion was prepared with beta-lactoglobulin upon which the pectins were electrostatically deposited at pH 3.5. Emulsions prepared with 1% oil, 0.05% beta-lactoglobulin, and 0.06% pectins were physically stable for up to 16 days. As determined by monitoring lipid hydroperoxide and headspace propanal formation, emulsions prepared with the multilayer system of beta-lactoglobulin and citrus pectin were more stable than emulsions stabilized with beta-lactoglobulin alone. Emulsions prepared with the multilayer system of beta-lactoglobulin and sugar beet pectin were less stable than emulsions stabilized with beta-lactoglobulin alone despite the presence of ferulic acid in the sugar beet pectin. The lower oxidative stability of the emulsions with the sugar beet pectin could be due to its higher iron and copper concentrations which would produce oxidative stress that would overcome the antioxidant capacity of ferulic acid. These data suggest that the oxidative stability of oil-in-water emulsions containing omega-3 fatty acids could be improved by the use of multilayer emulsion systems containing pectins with low metal concentrations.     

Facile immobilization of evolved agrobacterium radiobacter carbamoylase with high thermal and oxidative stability

Optically pure amino acids have been widely used as intermediates in the synthesis of antibiotics, antifungal agents, pesticides, and sweeteners. Of particular importance, d- p-hydroxyphenylglycine (D-HPG) can be produced from d, l-hydroxyphenly hydantoin (D,L-HPH) in a two-step reaction mediated by d-hydantoinase and N-carbamoyl- d-amino acid amidohydrolase (or carbamoylase). To make this production more industrially appealing, the carbamoylase gene from Agrobacterium radiobacter NRRL B11291 cloned in an Escherichia coli strain was intensively mutated to improve the thermal stability of carbamoylase by three rounds of DNA shuffling. After an extensive screening of the mutant library, the mutant E. coli strain M303 was obtained to produce variant carbamoylase, CBL303, with three critical mutated residues, including V40A, G75S, and V237A. Further characterization showed that in comparison with the wild-type counterpart the evolved carbamoylase exhibited more than 20-fold tolerance to heat and, in addition, hydrogen peroxide as a result of the synergistic effect caused by the three mutations. Moreover, with the fusion of the chitin-binding domain (ChBD) of Chitinase A1, the evolved carbamoylase CBL303 was specifically adsorbed on chitin beads. Subsequent analysis indicated that the linkage between the enzyme and the affinity matrix was substantially stable. The half-life of the immobilized carbamolyase CBL303 could reach 210 h at 45 degrees C, whereas its free form had that of 17 h. In particular, when applied to D-HPG production, the immobilized enzyme could be recycled 16 times with the achievement of 100% conversion yield. Along with the previous illustration of d-hydantoinase immobilization, the success achieved by immobilization of the evolved carbamoylase in this work apparently offers a promising way for the efficient production of D-HPG from D,L-HPH.     

Hydrogenation and interesterification effects on the oxidative stability and melting point of soybean oil

Soybean oil with an iodine value of 136 was hydrogenated to have iodine values of 126 and 117. The soybean oils with iodine values of 136, 126, and 117 were randomly interesterified using sodium methoxide. The oxidative stabilities of the hydrogenated and/or interesterified soybean oils were evaluated by measuring the headspace oxygen content by gas chromatography, and the induction time was measured using Rancimat. The melting points of the oils were evaluated by differential scanning calorimetry. Duncan's multiple range test of the headspace oxygen and induction time showed that hydrogenation increased the headspace oxygen content and induction time at alpha = 0.05. Interesterification decreased the headspace oxygen and the induction time for the soybean oils with iodine values of 136, 126, and 117 at alpha = 0.05. Hydrogenation increased the melting points as the iodine value decreased from 136 and 126 to 117 at alpha = 0.05. The random interesterification increased the melting points of soybean oils with iodine values of 136, 126, and 117 at alpha = 0.05. The combined effects of hydrogenation and interesterification increased the oxidative stability of soybean oil at alpha = 0.05 and the melting point at alpha = 0.01. The optimum combination of hydrogenation and random interesterification can improve the oxidative stability and increase the melting point to expand the application of soybean oil in foods.     

Modification of ascorbic acid using transglycosylation activity of Bacillus stearothermophilus maltogenic amylase to enhance its oxidative stability

Ascorbic acid (1), a natural antioxidant, was modified by employing transglycosylation activity of Bacillus stearothermophilus maltogenic amylase with maltotriose and acarbose as donor molecules to enhance its oxidative stability. The transglycosylation reaction with maltotriose as donor created mono- and di-glycosyl transfer products with an alpha-(1,6)-glycosidic linkage. In addition, two acarviosine-glucosyl transfer products were generated when transglycosylation was performed with acarbose as a donor. All transfer products were observed by TLC and HPLC, and purified by Q-sepharose anion exchange and Biogel P-2 gel permeation chromatographies. LC/MS and (13)C NMR analyses revealed that the structures of the transfer products were 6-O-alpha-D-glucosyl- (2) and 6-O-alpha-D-maltosyl-ascorbic acids (3) in the reaction of maltotriose, and 6-O-alpha-acarviosine-D-glucosyl- (4) and 2-O-alpha-acarviosine-D-glucosyl ascorbic acids (5) in the reaction of acarbose. The stability of the transglycosylated ascorbic acid derivatives was greatly enhanced against oxidation by Cu(2+) ion and ascorbate oxidase. Among them, compound 3 proved to be the most stable against in vitro oxidation. The antioxidant effects of glycosyl-derivatives of ascorbic acid on the lipid oxidation in cooked chicken breast meat patties indicated that they had antioxidant activities similar to that of ascorbic acid. It is suggested that the transglycosylated ascorbic acids can possibly be applied as effective antioxidants with improved stability in food, cosmetic, and other applications.     

Selectivity of Candida antarctica B lipase toward fatty acid and (Iso)propanol substrates in esterification reactions in organic media

Fatty acid (FA) selectivity of immobilized Candida antarctica B lipase was assessed as influenced by various cosubstrate systems for ester synthesis. Reaction mixtures contained a homologous series of even-chain n-acyl donor (C(4)(-)(16)) substrates (FA or their methyl esters, FAME) and a single alcohol cosubstrate (propanol, 2-propanol, or their acetate derivatives) in hexane. Multiple FA optima were often observed, with preferences for C(6) (or C(4)) followed by C(14) and sometimes C(10). The degree of selectivity among acyl donors was modest (up to 1.28-2.60, based on ratios of selectivity constants) and was dependent on the choice of cosubstrate system. Acyl group selectivity ranged up to 1.31-1.36 for [FA + alcohol], 1. 48-2.60 for [FAME + alcohol], 1.30-1.72 for [FA + alcohol acetate], and 1.28-1.88 [FAME + alcohol acetate] reaction systems. General shifts in selectivity were observed between short-chain (C(4)(-)(8)) and long-chain (C(10)(-)(16)) FA as groups with propanol cosubstrate, whereas shifts in reaction selectivity were observed toward specific FA(s) for 2-propanol cosubstrate. Selectivity among a series of alcohol cosubstrates ranged up to 13-fold in esterification reactions with C(6) FA.     

Bioaccessibility and antioxidant activity stability of phenolic compounds from extra-virgin olive oils during in vitro digestion

The impact of an in vitro procedure that mimics the physiochemical changes occurring in gastric and small intestinal digestion on the bioaccessibility and antioxidant activity of phenols from 10 extra-virgin olive oil samples was assessed. Extra-virgin olive oil phenols were totally extracted in the aqueous phase, which reproduces gastric fluids during the digestion procedure. A linear bioaccessibility model, based on tyrosol behavior in model oil samples, was used to estimate the bioaccessibility index (BI%) of extra-virgin olive oil phenols. The BI% varied amongst samples from a maximum of 90% to a minimum of 37%, thus indicating that only a fraction of phenols can be considered bioaccessible. The specific antioxidant activity of olive oil phenols proved to be negatively affected by the digestion procedure. By computing a principal component analysis, it was possible to show that differences in the potential bioactive effect of extra-virgin olive oil samples were related to different phenolic profiles.