Steam cracking of coal-derived oils and model compounds: 2. Cracking of hydrogenated coal-derived oils

Coal-derived oils of different degrees of hydrogenation and of different boiling ranges as well as a petrol-based gas oil (for comparison) have been thermally cracked at 830 °C with a residence time of 0.14s. Hydrogenated coal-derived middle oil yields less light olefins than gas oil (32 versus 40 wt%) but substantially more BTX aromatics (21 versus 7 wt%). The amount of olefins (42 wt%) from hydrogenated coal-derived light oil is higher and that of BTX aromatics (16 wt%) is slightly less than obtained from middle oil. Perhydrogenated coal-derived middle oil (> 99% saturated compounds) has been cracked within a wide temperature- and residence time range to verify the applicability of two crack severity functions designed to represent the product distribution. The latter are compared with that of t-decalin and naphtha.     

Fractionation of oligomeric triacylglycerides and the relation to rejection limits for used frying oils

Precipitates enriched in oligomeric triacylglycerides were separated from thermally oxidized olive residue oil, conventional and high-oleic sunflower oils, and soybean oil by solvent fractionation in methanol/acetone at 4–5°C for 16 h. Different fractionation conditions were evaluated in an effort to isolate the oligomeric triacylglycerides (OTG). OTG, formed in frying oils upon heating at low concentations, were not detectable with conventional methods to determine polymeric compounds. The best conditions found from the different assays were the following: (i) weight of oil sample-to-solvent volume ratio of 1∶20; and (ii) solvent system methanol/acetone 10∶90 (vol/vol) for monounsaturated oils and 15∶85 (vol/vol) for polyunsaturated oils. Precipitates, enriched in oligomers, were formed when heated oils and used frying oils contained more than 27% polar compounds, a value which is widely accepted as the upper limit for use of frying oils.     

Phenolic profiles of Turkish olives and olive oils

Phenolic compound distribution of Turkish olive cultivars and their matching olive oils together with the influence of growing region were investigated. One hundred and one samples of olives from 18 cultivars were collected during two crop years from west, south and south‐east regions of Turkey. The olives were processed to oils and both olive and olive oil samples were evaluated for their phenolic compound distribution. The results have shown that main phenolics of Turkish olives were tyrosol, oleuropein, p‐coumaric acid, verbascoside, luteolin 7‐O‐glucoside, rutin, trans cinnamic acid, luteolin, apigenin, cyanidin 3‐O‐glucoside and cyanidin 3‐O‐rutinoside. Oleuropein and trans cinnamic acid were present in higher amounts among all phenolics. Principal component analyses showed that the growing region did not have drastic effect on phenolic profile of olives. The major phenolic compounds of olive oils were tyrosol, syringic acid, p‐coumaric acid, luteolin‐7‐O‐glucoside, trans cinnamic acid, luteolin and apigenin. Luteolin is a predominant phenolic compound in almost all oil samples. Total phenol concentrations of Southeast Anatolian oils were found to be lower than those of the other regions.     

Frying quality and oxidative stability of high-oleic corn oils

To determine the frying stability of corn oils that are genetically modified to contain 65% oleic acid, high-oleic corn oil was evaluated in room odor tests and by total polar compound analysis. Flavor characteristics of french-fried potatoes, prepared in the oil, were also evaluated by trained analytical sensory panelists. In comparison to normal corn oil, hydrogenated corn oil and high-oleic (80 and 90%) sunflower oils, high-oleic corn oil had significantly (P<0.05) lower total polar compound levels after 20 h of oil heating and frying at 190°C than the other oils. Fried-food flavor intensity was significantly higher in the normal corn oil during the early portion of the frying schedule than in any of the high-oleic or hydrogenated oils; however, after 17.5 h of frying, the potatoes fried in normal corn oil had the lowest intensity of fried-food flavor. Corn oil also had the highest intensities of off-odors, including acrid and burnt, in room odor tests. High-oleic corn oil also was evaluated as a salad oil for flavor characteristics and oxidative stability. Results showed that dry-milled high-oleic corn oil had good initial flavor quality and was significantly (P<0.05) more stable than dry-milled normal corn oil after oven storage tests at 60°C, as evaluated by flavor scores and peroxide values. Although the high-oleic corn oil had significantly (P<0.05) better flavor and oxidative stability than corn oil after aging at 60°C, even more pronounced effects were found in high-temperature frying tests, suggesting the advantages of high-oleic corn oil compared to normal or hydrogenated corn oils.     

Antioxidant capacity of extra-virgin olive oils

In this study, the oxygen radical absorbance capacity (ORAC) of vegetable oils was investigated using a spectrofluorometric method, which measures the protection of the phenolic substances of the oil on the β-phycoerythrin fluorescence decay in comparison with Trolox. More than 97% of the phenolic substances was extracted from the oil using methanol, and the methanolic extract was then used for the ORAC and the total phenolics assay. We found a significant correlation between ORAC values of different olive oils and the total amount of phenolics. For extra-virgin olive oils, maximal ORAC values reached 6.20±0.31 μmol Trolox equivalent/g, while refined and seed oils showed values in the 1–1.5 μmol Trolox equivalent/g range. Our method is useful to assess the quality of olive oils and to predict, in combination with the rancidity tests, their stability against oxidation.     

Membrane processing of used frying oils

Studies were conducted with used frying oils in a flat membrane batch cell using five different types of polymeric membranes to decrease the soluble degradation products. During membrane processing, triglycerides permeated preferentially compared to the majority of the polar compounds including oxidation products, polymers, and color compounds. Two of the composite membranes, NTGS-AX and NTGS-2200, selectively rejected polar compounds and oxidation products to the extent of 25–48% and 24–44% respectively. The reduction in Lovibond color values (5R+Y) was in the range of 83–93%. The viscosity of the used frying oil was reduced to the extent of 22%. The composite membranes were effective in reducing the soluble impurities, as well as insoluble particulates, without causing any undesirable changes to the oil. The membrane process appears to improve the life of used frying oils and does not have the disadvantages associated with the active filtration systems, however, for commercial application the permeate flux needs to be improved considerably.     

The use of vegetable oils to recover compounds from aqueous solutions

Corn oil, canola oil, olive oil, sunflower oil, peanut oil and soyabean oil were tested as extractants for the recovery of organic compounds from aqueous solution. Short chain aliphatic alcohols and acids were poorly recovered (K_d < 1.0) while most esters, aldehydes and aromatic compounds tested were satisfactorily recovered (K_d > 2.0) from aqueous solution by vegetable oils. K_d is defined as the ratio of the concentration of the dissolved substance in the extractant to that in the aqueous phase. The exception was caffeine which was poorly extracted from water. The type of oil used appeared to have limited effect on K_d. Increasing the reaction temperature resulted in increased K_d for most readily extractable compounds. Acidulated fatty acid was also tested as an extractant. Although it generally resulted in a greater K_d than the oils or hexane control, acidulated fatty acid was less desirable as an extractant because it tended to create an emulsion with the aqueous phase under the test conditions.     

Steam cracking of coal-derived oils and model compounds: 1. Cracking of tetralin and t-decalin

Cracking of tetralin and t-decalin has been investigated in the temperature range between 700 and 850 °C and with residence times between 0.08 and 0.4 s. Most of the tetralin is dehydrogenated to yield 1,2-dihydronaphthalene and naphthalene. Other main products are indene and styrene, whereas t-decalin is predominantly cracked into ethylene and BTX aromatics. The kinetics of decalin decomposition can be described by a first-order irreversible reaction, whereas the behaviour of tetralin has to be expressed in terms of a reversible reaction. The overall activation energies are determined.     

Phenolic composition and antioxidant activity of Southern Italian monovarietal virgin olive oils

The phenolic composition and antioxidant activity of several monovarietal extra virgin olive oils used as blenders for the production of Collina di Brindisi protected designation of origin (PDO) oil, produced between December 2008 and January 2009 using two‐phases or three‐phases extraction system, were evaluated and compared with other manufacturer products designated as PDO. Oils were taken from the most representative ones industrial oil mills in the PDO geographical area. The parameters assessed were free acidity, peroxide value, K₂₃₂ and K₂₇₀ indices, organoleptic characteristics, total phenolic content (TPC), phenolic profile, and antioxidant activity coefficient (AAC). The phenolic contents and profiles of the monovarietal oils showed remarkable differences with respect to PDO oils. The variables that exerted a major influence on phenols concentration were the maturity degree of olives (December>January), followed by the extraction system (two‐phase>three‐phase), and place of growing. The Pearson r correlation index showed that AAC was positively correlated with TPC, p‐coumarate, and 3,4‐DHPEA‐EA, and negatively correlated with peroxide value. Practical applications: The results provide detailed information about: (i) the phenolic composition and the AAC of several monovarietal extra virgin olive oils used as blenders for the production of a PDO oil; (ii) the impact of genetic variability, place of growing, olive maturity degree, and extraction technology on oil phenol compounds; and (iii) the relationships among each phenolic compound and AAC, and their potential utilization as analytical index of antioxidant activity. It is important to study the phenolic compounds and antioxidant activity of monovarietal extra virgin olive oils used to produce PDO oil and to compare with the relative PDO samples in order to define a possible analytical tool able to verify what is stated in the label for consumer information and protection.     

辽河焦化蜡油脱碱氮工艺研究

为降低焦化蜡油中碱性氮化物含量,采用糠醛溶剂精制和TTS络合脱氮两种方法对辽河焦化蜡油开展了脱碱氮工艺研究。研究发现,采用糠醛二级抽提的方法可使焦化蜡油中的碱氮脱除率达到81.3%,但糠醛对碱性氮化物的选择性较低,精制油收率不高;采用TTS络合脱氮的方法可使精制油收率达到95%,碱性氮化物的脱除率达到73.3%,TTS脱氮剂对焦化蜡油中的碱性氮化物有较好的选择性,脱碱氮效果较好。     

Effect of refining on the phenolic composition of crude olive oils

By definition, virgin olive oil is consumed unrefined, although a great proportion of the olive oil produced has to be refined to render it edible. Phenolic compounds are among the substances eliminated during the refining process; in the present work these were characterized by HPLC, and their evolution during the different refining steps was studied. The complete refining process removed most polyphenols from oils, but the behavior of individual compounds at each step also was observed. o-Diphenols (hydroxytyrosol, catechol, and hydroxytyrosol acetate) and flavonoids (luteolin and apigenin) were eliminated first during the alkaline treatment. Tyrosol and 4-ethylphenol remained in the oil until the deodorization step. A large amount of phenolic compounds was discovered in the refining by-products such as soapstocks and deodorization distillates. In the latter streams, the concentrations of tyrosol and 4-ethylphenol reached up to 149 and 3720 mg/kg by-product, respectively. This high level of 4-ethylphenol and its well-known strong off-odor can interfere during further processing of the deodorization distillates, and this must be taken into account when deciding what is to become of them. Similarly, the results of this work open the possibility of recovering phenolic compounds from the “second centrifugation olive oils” by adding a new washing step prior to the refining process. By including this new step, the most polar polyphenols, hydroxytyrosol and tyrosol, will diffuse from oil to water and a concentration of up to 1400 mg/L of hydroxytyrosol may be achieved.     

Oxidative stabilities of soybean oils that lack lipoxygenases

Lipoxygenase (LOX)-null soybean lines that lack LOX 2, or LOX 2 and 3, and contain normal (8.0–8.6%) or low (2.0–2.8%) linolenate (18∶3) amounts were evaluated for their oil qualities and storage stabilities. Soybean oils of six genotypes were extracted by both laboratory-scale and pilot-plant systems and were refined, bleached, and deodorized in the laboratory. Citric acid was added to oils during the cool-down stage of deodorization. Two replications, separated at the point of conditioning, were evaluated for each genotype. Under storage conditions of 55–60°C in the dark, soybean oils with low 18∶3 contents were significantly (P<-0.05) more stable as measured by peroxide values than were oils with normal 18∶3 contents, regardless of the LOX content of the beans. The volatile analysis showed few differences between oils with low and high 18∶3 contents or among oils from beans that lack different LOX enzymes. After 16 d of storage, the amount of 1-octen-3-ol was significantly greater in oils with low 18∶3 content, and soybean oils from beans with normal LOX content had a significantly (P<-0.05) lower amount of 1-octen-3-ol than did the oils that lacked LOX enzymes. Storage at 35°C under light showed no differences in volatile amounts or sensory evaluations after 14 d of storage. During storage, peroxide values tended to be lower in oils from beans with normal 18∶3 content and in oils from beans with normal LOX content. Generally, the abscence of LOX 2 or LOX 2 and 3, although having a small effect on lipid oxidation, was not as important to oil quality as was the 18∶3 content.     

Effect of evening primrose extracts on oxidative stability of sunflower and rapeseed oils

Antioxidative activities of evening primrose seed meal extracts in sunflower and rapeseed oils were compared with that of commercially used antioxidants, namely butylated hydroxytoluene (BHT), ascorbylpalmitate as well as Grindox‐118. The study was carried out under Schaal oven conditions at 60 °C and the weight gain was followed up by p‐anisidine value measurement following the oxidation. An Oxidograph apparatus monitored the oxidation of oils at 110 °C. Among the examined extracts, the ethyl acetate extract (0.2%), containing only 87 mg/g of total phenolics, exhibited a stronger antioxidant activity than BHT (0.01%) and effectively stabilised both oils. A strong antioxidative effect was also noted for the ethanol‐ethyl acetate extract (168 mg/g of total phenolics). The study showed that addition of ethyl acetate and ethanol‐ethyl acetate extracts could extend the sunflower and rapeseed oils shelf‐life by protecting oils from further decomposition that naturally occurs during thermal treatments.     

The supramolecular chemistry of lipid oxidation and antioxidation in bulk oils

The microenvironment formed by surface active compounds is being recognized as the active site of lipid oxidation. Trace amounts of water occupy the core of micro micelles and several amphiphilic minor components (e.g., phospholipids, monoacylglycerols, free fatty acids, etc.) act as surfactants and affect lipid oxidation in a complex fashion dependent on the structure and stability of the microemulsions in a continuous lipid phase such as bulk oil. The structures of the triacylglycerols and other lipid‐soluble molecules affect their organization and play important roles during the course of the oxidation reactions. Antioxidant head groups, variably located near the water‐oil colloidal interfaces, trap and scavenge radicals according to their location and concentration. According to this scenario, antioxidants inhibit lipid oxidation not only by scavenging radicals via hydrogen donation but also by physically stabilizing the micelles at the microenvironments of the reaction sites. There is a cut‐off effect (optimum value) governing the inhibitory effects of antioxidants depending inter alias on their hydrophilic/lipophilic balance and their concentrations. These complex effects, previously considered as paradoxes in antioxidants research, are now better explained by the supramolecular chemistry of lipid oxidation and antioxidants, which is discussed in this review. The evolution of micellar size and number during and after the induction period of lipid oxidation. Amphiphilic compounds, including lipid hydroperoxides, contribute to micelle formation and act as prooxidants. Antioxidants and retarders stabilize micelles and prevent their breakdown.     

煤炭直接液化油中酚类化合物的分离与利用

酚类化合物是煤炭直接液化产物中具有较高附加值的主要含氧化合物,也是煤液化油酸性物质的主要成分。它不仅对油品的提质加工的技术路线有影响,而且也对煤炭直接液化的经济性具有较大的影响。由于该方面的研究工作尚属起步阶段,借鉴煤焦油和石油系产品中酚类化合物的有关分离与利用情况,结合笔者的研究实践和认识,提出了在煤直接液化油中酚类的分离与利用方面应开展的工作和研究方向。     

Phenolic composition of virgin olive oils from cross breeding segregating populations

The evaluation and characterization of segregating populations is a critical step in olive breeding programs. In this work, phenolic profiles of virgin olive oils (VOOs) from segregating populations obtained by cross breeding in Cordoba (Spain) have been evaluated. Genotypes obtained from open pollination of the cultivar Manzanilla de Sevilla, and from crosses between the cultivars Arbequina × Arbosana, Picual × Koroneiki and Sikitita × Arbosana were tested. The phenolic composition was determined after liquid–liquid extraction with 60:40 v/v methanol–water and subsequent chromatographic analysis with ultraviolet (UV) detection of both absorption and fluorescence in a sequential configuration. Results for all studied compounds showed high degree of variability between genotypes, with a higher range of variation than the observed for the genitors. Most of the observed variability was attributable to differences in genotypes within crosses rather than among crosses. Some issues related to breeding strategies are discussed. Practical applications: Phenolic compounds are considered to be of paramount importance for the assessment of virgin olive oil quality due to their contribution to the nutraceutical and sensory profile of this natural food. This study focuses on the evaluation of the content of phenolic compounds in olive oils originated from cross breeding in an olive breeding program (Cordoba, Spain). This step is crucial to determine the range of variation of phenolic compounds and the selection of interesting genotypes with higher composition in total phenols or in an individual phenol targeted at a breeding program.     

Effect of fatty acid composition of oils on flavor and stability of fried foods

Effects of fatty acid composition of frying oils on intensities of fried-food flavor and off-flavors in potato chips and french-fried potatoes were determined. Commercially processed cottonseed oil (CSO) and high-oleic sunflower oil (HOSUN) were blended to produce oils with 12 to 55% linoleic acid and 16 to 78% oleic acid. Analytical sensory panels evaluated french-fried potatoes and pilot plant-processed potato chips. Initially, both foods prepared in CSO (16% oleic/55% linoleic acid) had the highest intensities of fried-food flavor; however, this positive flavor decreased with decreasing levels of linoleic acid. 2,4-Decadienal in potato chips also decreased with decreasing linoleic acid in the oils. Frying oil stability, measured by total polar compounds (TPC), and oxidative stability of potato chips, measured by volatile compounds, showed that HOSUN (78% oleic acid) produced the lowest levels of TPC and the lowest levels of hexanal and pentanal, indicating greater frying oil stability and oxidative stability of the food. However, fresh potato chips fried in HOSUN had the lowest intensities of fried-food flavor and lowest overall flavor quality. Fried-food flavor intensity was the best indicator of overall flavor quality in fresh potato chips. Volatile compounds, TPC, and oxidative stability index directly varied with increasing oleic acid, and were therefore not directly indicative of flavor quality. No oil analysis predicted flavor stability of aged potato chips. Compositions of 16 to 42% oleic acid and 37 to 55% linoleic acid produced fresh fried-food with moderate fried food flavor intensity, good overall flavor quality, and low to moderate TPC levels (chips only). However, in aged food or food fried in deteriorated oil, compositions of 42 to 63% oleic and 23 to 37% linoleic provided the best flavor stability.     

Antioxidant capacity of rapeseed meal and rapeseed oils enriched with meal extract

Response surface methodology (RSM) was used to evaluate the quantitative effects of two independent variables: solvent polarity and temperature of the extraction process on the antioxidant capacity (AC) and total phenolics content (TPC) in meal rapeseed extracts. The mean AC and TPC results for meal ranged between 1181–9974 µmol TE/100 g and 73.8–814 mg sinapic acid/100 g of meal. The experimental results of AC and TPC were close to the predicted values calculated from the polynomial response surface models equations (R² = 0.9758 and 0.9603, respectively). The effect of solvent polarity on AC and TPC in the examined extracts was about 3.6 and 2.6 times greater, respectively, than the effect of processing temperature. The predicted optimum solvent polarity of ε = 78.3 and 63.8, and temperature of 89.4 and 74.2°C resulted in an AC of 10 014 µmol TE/100 g and TPC of 863 mg SAE/100 g meal, respectively. The phenolic profile of rapeseed meal was determined by an HPLC method. The main phenolics in rapeseed meal were sinapine and sinapic acid. Refined rapeseed oils were fortified with an extract – rich in polyphenols – obtained from rapeseed meal. The supplemented rapeseed oil had higher AC and TPC than the refined oil without addition of meal extracts. However, AC and TPC in the enriched oils decreased during storage. The TPC in the studied meal extracts and rapeseed oils correlated significantly (p<0.0000001) positively with their AC (R² = 0.9387). Practical applications: Many bioactive compounds extracted from rapeseed meal provide health benefits and have antioxidative properties. Therefore, it seems worth to consider the application of antioxidants extracted from the rapeseed meal for the production of rapeseed oils with potent AC. Moreover, antioxidants extracted from the rapeseed meal were added to refined rapeseed oil in order to enhance its AC. AC was then tested by FRAP assay. FRAP method is based on the reduction of the ferric tripyridyltriazine (Fe³⁺‐TPTZ) complex to the ferrous tripyridyltriazine (Fe²⁺‐TPTZ), and it is simple, fast, low cost, and robust method. FRAP method does not require specialized equipment and can be performed using automated, semi‐automatic, or manual methods. Therefore the proposed FRAP method can be employed by the fat industry laboratories to asses the AC of rapeseed oils and meal.     

Characterisation of virgin olive oils from European olive cultivars introduced in Tunisia

The behaviour of three European olive varieties, Ascolana Tenera, Koroneiki and Picholine, cultivated in the north of Tunisia, was compared to an autochthonous variety, Chétoui. Most of the quality indices and the fatty acid composition showed significant variations between the olive oils. Among the introduced varieties, the Picholine cultivar had the highest value of oleic acid (61%) whereas the Ascolana Tenera cultivar was noteworthy for its lowest content of phenolic compounds (175 mg/kg) and presented the highest level of palmitic acid. The Chétoui variety presented a high content of oleic and linoleic acids. But all samples, both the autochthonous Chétoui and the introduced cultivars, have similar levels of antioxidant compounds, with the exception of phenols. The aroma composition showed significant differences between the oils from the foreign cultivars. The major volatile component was the C‐6 aldehyde fraction whose content varied greatly between the different varieties studied: The E‐2‐hexenal content ranged from 1.6 mg/kg of oil in the Ascolana Tenera variety to >5 mg/kg for the Picholine and Koroneiki cultivars, whereas the Chétoui variety had the lowest levels of volatile compounds, with the exception of the hexanal level which was tenfold higher than in the foreign cultivars. Therefore, our results showed that two of the introduced varieties, Koroneiki and Picholine, showed good adaptation to the Tunisian cultivation conditions. So far, we claim the possibility to develop the successful cultivation of these latter imported varieties in the country.