Varietal and crop year effects on lipid composition of walnut (Juglans regia) genotypes

The FA, unsaponifiable, and volatile constituents of oil from three walnut varieties from two consecutive crop years were studied. The walnut oils (WO) were rich in PUFA and low in saturated FA. The tocopherol fraction consisted mainly of γ-tocopherol. High contents of β-sitosterol were found, together with campesterol and Δ⁵-avenasterol in similar amounts. Methylsterols present in WO were identified as cycloartenol, cyclolaudenol, cycloeucalenol, and 24-methylenecycloartanol. The hydrocarbon fraction was characterized by the predominance of C₁₄–C₂₀ n-alkanes. The major volatiles were aldehydes produced through the linoleic acid oxidative pathway. FA, methylsterols, and some hydrocarbons presented statistically significant differences among varieties. Most of this variation was due to the genotype. The Franquette variety was noteworthy by its higher oil and oleic acid contents. In contrast, tocopherols and volatile compounds showed minor differences among varieties; they were strongly influenced by the crop year. Chemical data were subjected to principal component analysis. The parameters that gave the greatest discrimination between the walnut varieties were oleic and linolenic acids, tetradecane, eicosane, tetracosane, cycloartenol, and 24-methylenecycloartanol. These components presented the major varietal influences and could be useful to determine the identity of walnut genotypes.     

Contribution of Compositional Parameters to the Oxidative Stability of Olive and Walnut Oil Blends

Oil blending was conducted to study the effects of changes in fatty acid composition (FAC), tocopherols and total phenol content (TPC) on oxidative stability of virgin olive oil (VOO):walnut oil (WO) blends. The measurement of the antioxidant activity of bioactive components present in the parent oils and blends was achieved by their ability to scavenge the free stable 2,2-diphenyl-1-picrylhydrazyl radical (DPPH·). The highest percentage of DPPH· inhibition was found for pure VOO, and the lowest one for pure WO. EC₅₀ values obtained from the DPPH assay correlated significantly and inversely with TPC. The generation of volatile flavor components in VOO indicated the predominance of C₆ compounds produced through biochemical (enzymatic) pathways, whereas WO showed increased concentrations of medium chain (C₇–C₁₁) aldehydes produced through chemical (oxidative) pathways. The results obtained confirm the importance of VOO phenolics in providing protection against oxidation in VOO and VOO/WO blends. However, considering the impact of FAC and the content of endogenous antioxidant substances mentioned previously on the oxidative stability of the oils analyzed, the effect of an elevated unsaturation level (WO) prevails over a high amount of such bioactive components (VOO).     

Chemical structure of long-chain esters from “sansa” olive oil

The major objective of this study was to determine the chemical structure of long-chain esters present in lower-grade olive oil. The classes of esters composing the hexanediethyl ether (99∶1) extract of the wax fraction from a pomace olive oil were: (i) esters of oleic acid with C₁−C₆ alcohols, (ii) esters of oleic acid with long-chain aliphatic alcohols in the range C₂₂−C₂₈ and (iii) benzyl alcohol esters of the very long-chain saturated fatty acids C₂₆ and C₂₈. The analysis and the structure assignments were carried out by gas chromatography coupled with mass spectrometry and by comparison with synthetic authentic model compounds. This work provided precise data on the chemical nature of the wax esters present in olive oil and should represent a means to detect adulteration of higher-grade olive oil with less expensive pomace olive oil and seed oils.     

Flavor components of olive oil—A review

The unique and delicate flavor of olive oil is attributed to a number of volatile components. Aldehydes, alcohols, esters, hydrocarbons, ketones, furans, and other compounds have been quantitated and identified by gas chromatography-mass spectrometry in good-quality olive oil. The presence of flavor compounds in olive oil is closely related to its sensory quality. Hexanal, trans-2-hexenal, 1-hexanol, and 3-methylbutan-1-ol are the major volatile compounds of olive oil. Volatile flavor compounds are formed in the olive fruit through an enzymatic process. Olive cultivar, origin, maturity stage of fruit, storage conditions of fruit, and olive fruit processing influence the flavor components of olive oil and therefore its taste and aroma. The components octanal, nonala, and 2-hexenal, as well as the volatile alcohols propanol, amyl alcohols, 2-hexenol, 2-hexanol, and heptanol, characterize the olive cultivar. There are some slight changes in the flavor components in olive oil obtained from the same oil cultivar grown in different areas. The highest concentration of volatile components appears at the optimal maturity stage of fruit. During storage of olive fruit, volatile flavor components, such as aldehydes and esters, decrease. Phenolic compounds also have a significant effect on olive oil flavor. There is a good correlation between aroma and flavor of olive oil and its polyphenol content. Hydroxytyrosol, tyrosol, caffeic acid, coumaric acid, and p-hydroxybenzoic acid influence mostly the sensory characteristics of olive oil. Hydroxytyrosol is present in good-quality olive oil, while tyrosol and some phenolic acids are found in olive oil of poor quality. Various off-flavor compounds are formed by oxidation, which may be initiated in the olive fruit. Pentanal, hexanal, octanal, and nonanal are the major compounds formed in oxidized olive oil, but 2-pentenal and 2-heptenal are mainly responsible for the off-flavor.     

Use of nitrogen to improve stability of virgin olive oil during storage

Experiments were carried out to study the possibility of improving the stability of extra virgin olive oil by using nitrogen as a conditioner gas during storage. With this aim, virgin olive oil samples, obtained from Leccino and Coratina cultivars, were stored in the dark, in closed bottles conditioned with air or nitrogen at 12–20 and 40°C. Results indicated that the FFA percentage increased over 1% only when oils were stored at 40°C. The PV and the K ₂₃₂ value (light absorbance at 232 nm) of oils increased over the limit value allowed by European Union law when the bottles were only partly filled and air was the conditioner gas. The use of nitrogen as conditioner gas helped to avoid this risk during 24 mon of storage at 12–20°C. The total phenolic content of both cultivars oils decreased during storage because their oxidation protected the oils from autoxidation. The content of total volatile compounds in oils decreased continuously during storage at 12–20°C, whereas it increased over 10 (Coratina cv.) and 15 (Leccino cv.) mon and then diminished when the storage temperature was 40°C. The same behavior, i.e., increase then decrease, was ascertained for trans-2-hexenal. The hexanal content of oils increased continuously during storage because this compound is formed by the decomposition of the 13-hydroperoxide of linoleic acid.     

Wax analysis of vegetable oils using liquid chromatography on a double-adsorbent layer of silica gel and silver nitrate-impregnated silica gel

A chromatographic method is described to measure the crystallizable wax content of crude and refined sunflower oil. It can also be applied to any other vegetable oil. The preparative liquid chromatography step on a glass column containing a silica gel adsorbent superimposed upon a silver nitrate-impregnated silica gel support is used to isolate a wax fraction which is then analyzed by gas chromatography. The recovered wax fraction contains, in addition to the crystallizable waxes, hydrocarbons and other compounds with gas chromatographic retention times corresponding to waxes with chain lengths C₃₄−C₄₂. These compounds are short-chain saturated waxes in fruit oils, such as grapeseed and pomace. In seed oils such as sunflower, soybean or peanut, the compounds initially referred to as “soluble esters” are identified as monounsaturated waxes, esters of long-chain saturated fatty acids, and a monounsaturated alcohol, mainly eicosenoic alcohol. Such waxes are absent from corn or rice bran oils.     

Malaxing temperature affects volatile and phenol composition as well as other analytical features of virgin olive oil

Three Italian olive varieties (Caroleo, Leccino and Dritta) were processed by centrifugation in the oil mill. The olive paste was kneaded at 20, 25, 30 and 35 °C. The results achieved revealed that the oil content in green volatiles from lipoxygenase pathway (including C₅ and C₆ compounds and especially unsaturated C₆ aldehydes) decreased progressively as the kneading temperature increased, dropping markedly at 35 °C. The content of phenols, o‐diphenols and secoiridoids showed an opposite trend, but the temperature of 35 °C was critical also for them, as it was for the majority of the other components, analytical parameters and indices related to quality, typicality and genuineness. In general, an increasing kneading temperatures increased the release of oil constituents from the vegetable tissue. This factor also affected the oil extraction yields. The best overall results were achieved by malaxing the olive paste at 30 °C. In fact, this temperature level led to achieving both pleasant green virgin olive oils and satisfactory oil extraction outputs.     

The volatile composition of samples from the blend of monovarietal olive oils and from the processing of mixtures of olive fruits

The volatile fraction deriving from the lipoxygenase pathway of samples obtained by processing olive fruits of 2 cultivars in known proportions was compared with that of samples deriving from the blending of oils extracted from the same cultivars and in the same proportions. The varieties considered for the mixtures were Coratina and Koroneiki, Coratina and Frantoio, and Dritta and Bosana, respectively. The results confirmed that the accumulation of each volatile compound from the lipoxygenase pathway in the monovarietal oils was different and closely dependent on the genetic store of each variety. The concentrations of the mentioned compounds appeared to change in a way proportional to the percent of each monovarietal oil in the samples obtained by blending 2 monovarietal oils. Instead, the oils obtained by processing mixtures of fruits from the 2 corresponding cultivars showed a striking accumulation of volatile compounds, especially of C₆‐compounds, which reached higher concentration at different percentages depending on the cultivars processed.     

Development of high-performance liquid chromatography criteria for determination of grades of commercial olive oils. Part I. The normal ranges for the triacylglycerols

Criteria for authentic olive oils were developed from isocratic high-performance liquid chromatography analyses of 99 olive oils from the major Mediterranean producers in the 1983–1986 crop years. Authentic olive oils include extra virgin, virgin and pure or refined oils, but exclude all reesterified and adulterated oils. The extra virgin through pure grades will have a combined area for the LOO (C_18:2C_18:1C_18:1), LOP (C_18:2C_18:1C_16:0), OOO (C_18:1C_18:1C_18:1), POO (C_16:0C_18:1C_18:1), POP (C_16:0C_18:1C_18:1), and SOO (C_18:0C_18:1C_18:1) peaks between 82.0 and 92.6% of the total area (L, linoleic; O, oleic; P, palmitic; S, stearic). Authentic oils will have ratios of LOO/LOP and OOO/POO that coincide with a line defined by OOO/POO=0.7844(LOO/LOP)+0.0968; correlation coefficient is 0.885. Authentic oils will not have a trilinolein (LLL) peak over 0.5% in area. Neither triolein (OOO) nor any other single peak suffices to characterize an olive oil sample as one of the authentic grades.     

Hydrocarbons and alcohols of basking shark and pig liver lipids

Four samples of the unsaponifiables of basking shark liver oil were adsorbed on alumina and eluted to yield Fractions 1–5, inclusive. Analyses by temperature programmed GC and by silica gel chromatography showed hydrocarbons in the first four fractions with squalene increasing to Fraction 3 and the pristane level being highest in Fraction 1. Aside from pristane and squalene, other hydrocarbons occurred at levels of 420–750 mg% in the oils on a weight basis, of which about 60% constituted a series of n-paraffins (relative carbon number range: 15.0–38.0) together with smaller amounts of at least one branched chain saturated group. Unsaturated hydrocarbons eluted mainly after squalene. The oils contained up to 460 mg% sterol and 78–270 mg% alcohols of C₁₀ to C₃₀, the ratio of saturated to unsaturated members being about 1.6. The composition of the unsaponifiable lipids of pig liver was quite different from that of the marine oils. It contained 10.6% sterol in addition to 400 mg% alcohols, the latter consisting of 81.8% saturated components (C₁₂ to C₃₁; ratio of saturated: unsaturated members, 4.4). The hydrocarbons comprised 450–700 mg% of the unsaponifiable mixture and squalene, paraffins and additional unsaturated components occurred at levels of 20.6, 24.4 and 11.9 mg%, respectively. The saturated hydrocarbons were high in normal homologs of relative carbon number range, 15 to 36; pristane could not be detected.     

Changes in Volatile Compounds of Black Cumin Oil and Hazelnut Oil by Microwave Heating Process

Black cumin and hazelnut oils were subjected to a heating process in a microwave oven for a duration of 2, 4, 6 and 8 min at a constant frequency of 2450 MHz and a power of 0.45 kW. The ultraviolet absorption and volatile products of the oils were investigated in detail during the processes. The experimental evidences obtained show that K₂₃₂ and K₂₇₀ parameters reach values of 4.69 and 1.30 for black cumin oil, 3.22 and 1.75 for hazelnut oil, respectively with the increment of heating time. The headspace SPME method was used to analyze volatile compounds extracted from black cumin and hazelnut oils being exposed to the microwave heating process. The SPME–GC/MS method allowed the detection of 17 identified volatile compounds (hexanal, α‐thujene, α‐pinene, sabinene, β‐pinene, 2‐heptenal, α‐terpinene, limonene, p‐cymene, γ‐terpinene, E‐2‐octenal, nonanal, 4‐terpineol, thymoquinone, E,E‐2,4‐decadienal, α‐longipinene and isolongifolene) in black cumin oils. Of the products, hexanal, 2‐heptenal, E‐2‐octenal, nonanal and E,E‐2,4‐decadienal were determined to be the predominant volatile oxidation products. In fact, the hexanal was found as a major volatile oxidation compound and reached a local maximum point of 7.41 × 10⁶ AU at the end of heating. On the other hand, only 8 volatile oxidation products (hexanal, heptanal, 2‐heptenal, nonanal, E‐2‐decenal, E,Z‐2,4‐decadienal, E,E‐2,4‐decadienal and E‐2‐tridecenal) were identified in hazelnut oils as a consequence of the heating process. Based on the experimental evidence observed, it is reasonable to conclude that the nonanal content dramatically increased at the end of heating and reached a value of 9.22 × 10⁶ AU.     

Chemical Composition of Turkish Olive Oil––Ayvalik

Although large amounts of olive oil are produced in Turkey, not much information on its chemical composition is available in the literature to date. The aim of this study was to evaluate the chemical composition of commercial olive oils produced from the Ayvalik olive cultivar in Canakkale, Turkey. Five different samples corresponding to the olive oil categories of extra virgin (conventional, extra virgin olive oil (EVOO), and organic extra virgin olive oil (OGOO) production), virgin olive oil (OO-1), ordinary virgin olive oil (OO-2) and refined olive oil (RFOO) were evaluated. Olive oils were collected from two consecutive production years. According to the free fatty acids, the absorbance values (K₂₃₂ and K₂₇₀), and peroxide values of all the samples conformed to the European standards for olive oil. The level of oleic acid was in the range of 68–73%; while the linoleic acid content was significantly lower in the refined olive oils. The tocopherol and polyphenol content was in the lower range of some European olive oils. However, pinoresinol was a major phenolic compound (5–77 mg/kg depending on the oil category). Its content was markedly higher than in many other oils, which would be a useful finding for olive oil authentication purposes.     

Volatile compounds in oils after deep frying or stir frying and subsequent storage

Soybean oil (900 g) was heated by deep frying at 200°C for 1 h with the addition of 0, 50, 100, 150 and 200 mL water, and then stored at 55°C for 26 weeks. Soybean oil, corn oil and lard were heated by stir frying and then stored at 55°C for 30 weeks. The volatiles and peroxide values of these samples were monitored. All samples contained aldehydes as major volatiles. During heating and storage, total volatiles increased 260-1100-fold. However, aldehyde content decreased from 62–87% to 47–67%, while volatile acid content increased from 1–6% to 12–33%; especially hexanoic acid which increased to 26–350 ppm in the oils after the storage period was completed. Water addition to the oils heated by deep frying tended to retard the formation of volatile compounds. The total amount of volatile constituents of lard heated by stir frying increased more during storage than that of corn oil or soybean oil. Peroxide values did not reflect the changes of volatile content in the samples.     

The Chemical Properties and Volatile Compounds of Virgin Olive Oil from Oueslati Variety: Influence of Maturity Stages in Olives

The aim of the present work was to investigate the influence of fruit ripening on oil quality and volatile compounds in an attempt to establish an optimum harvesting time for Oueslati olives, the minor olive variety cultivated in Tunisia. Our results showed that many analytical parameters, i.e., peroxide value, UV absorbance at 232–270 nm, chlorophyll pigments, carotenoids and oleic acid contents decreased during ripening, whilst linolenic acid increased. Free acidity remained practically stable with a very slight rise at the highest maturity index. The volatile compounds emitted by the Oueslati olive oil were characterized and quantified by HS‐SPME‐GC‐EIMS. Twenty‐three volatile compounds were identified, mainly aldehydes, sesquiterpenes and esters. The results show variations in the volatile fractions and quality parameters of Oueslati extra virgin olive oil obtained at different olive‐ripening stages. Fifteen sesquiterpenes were identified for the first time in this cultivar, mainly hydrocarbon derivatives, but also oxygenated ones. On the basis of the quality parameters and volatile fractions studied, the best stage of Oueslati olive fruits for oil processing seems to be at ripeness index about 3.0. Indeed, these results suggested the possibility of using sesquiterpenes for olive authenticity and traceability and demonstrated that the volatile fractions can be used as indicators of the degree of ripening of the olives used to obtain the corresponding virgin olive oils.     

Wax composition of sunflower seed oils

Waxes are natural components of sunflower oils, consisting mainly of esters of FA with fatty alcohols, that are partially removed in the winterization process during oil refining. The wax composition of sunflower seed as well as the influence of processing on the oil wax concentration was studied using capillary GLC. Sunflower oils obtained by solvent extraction from whole seed, dehulled seed, and seed hulls were analyzed and compared with commercial crude and refined oils. The main components of crude sunflower oil waxes were esters having carbon atom numbers between 36 and 48, with a high concentration in the C₄₀−C₄₂ fraction. Extracted oils showed higher concentrations of waxes than those obtained by pressing, especially in the higher M.W. fraction, but the wax content was not affected significantly by water degumming. The hull contribution to the sunflower oil wax content was higher than 40 wt%, resulting in 75 wt % in the crystallized fraction. The oil wax content could be reduced appreciably by hexane washing or partial dehulling of the seed. Waxes in dewaxed and refined sunflower oils were mainly constituted by esters containing fewer than 42 carbon atoms, indicating that these were mostly soluble and remained in the oil after processing.     

Oxidative Evolution of Virgin and Flavored Olive Oils Under Thermo-oxidation Processes

Changes in the oxidative status of Chétoui olive oil were monitored to attest the efficiency of some bioactive compounds from aromatic plants to improve the stability of olive oils after a maceration process at different concentrations. Aromatized olive oils were prepared by addition of lemon and thyme extracts at four different concentrations (20–80 g kg⁻¹ of oils) to virgin olive oils. The following parameters were monitored: free fatty acids, peroxide value, ultra violet absorption characteristics at 232 and 270 nm, fatty acid composition and aromatic profiles. After thermo-oxidation processes, the oleic/linoleic acid ratio remained stable (4.5). Oxidative stability slightly decreased during thermo-oxidation processes. The heating of the oils changed their volatile profile and led to the formation of new volatile compounds, such as the two isomers of 2,4-heptadienal after heating at 100 °C or (E,Z)-2,4-decadienal and (E,E)-2,4-decadienal after thermo-oxidation at 200 °C. The use of lemon and thyme extracts modified the aromatic and the nutritional value of the olive oil by the transfer of some bioactive compounds, such as limonene and carvacrol. In contrast, the oxidative stability of the product did not change. Furthermore, the aromatized oils may be employed in seasoning and cooking of some foods.     

Properties, composition, and analysis of grain sorghum wax

Grain sorghum wax has been judged to be a potential source of natural wax with properties similar to carnauba wax. Approximately 0.16–0.3% (w/w) wax can be extracted from grain sorghum depending on the efficiency of the organic solvents. Although the melting points of carnauba wax and sorghum wax are similar, i.e., 78–86 and 77–85°C, respectively, they differ in acid values, i.e., 2–10 and 10–16, respectively, and saponification numbers, i.e., 77–95 and 16–49, respectively. Improved knowledge of the properties, composition, and analysis of grain sorghum wax would assist in efforts for industrial application of this product. Major components of sorghum wax are hydrocarbons, wax esters, aldehydes, free fatty alcohols, and FFA. The hydrocarbons consist mainly of C₂₇ and C₂₉, and the aldehydes, alcohols, and acids are mainly C₂₈ and C₃₀. The wax esters are mostly esters of C₂₈ and C₃₀ alcohols and acids.     

A high-field1H nuclear magnetic resonance study of the minor components in virgin olive oils

High-field (600 MHz) nuclear magnetic resonance (NMR) spectroscopy was applied to the direct analysis of virgin olive oil. Minor components were studied to assess oil quality and genuineness. Unsaturated and saturated aldehyde resonances, as well as those related to other volatile compounds, were identified in the low-field region of the spectrum by two-dimensional techniques. Unsaturated aldehydes can be related to the sensory quality of oils. Other unidentified peaks are due to volatile components, because they disappear after nitrogen fluxing. The statistical analysis performed on the intensity of these peaks in several oil samples, obtained from different olive varieties, allows clustering and identification of oils arising from the same olive variety. Diacylglycerols, linolenic acid, other volatile components, water, acetic acid, phenols, and sterols can be detected simulteneously, suggesting a useful application of high-field NMR in the authentication and quality assessment of virgin olive oil.     

Sterol fractions in hazelnut and virgin olive oils and 4,4′-dimethylsterols as possible markers for detection of adulteration of virgin olive oil

Reports on the methylsterol fractions of hazelnut oils are scarce. The objectives of this study were to characterize methylsterols in hazelnut and virgin olive oils and to study the possibility of detection of adulteration of virgin olive oils. In hazelnut oils, 4-desmethylsterols were present in higher proportions (86 to 91%) than in virgin olive oils where this fraction was ca. 50% of the total sterol. In the 4-monomethylsterol fraction, citrostadienol was the major component in both kinds of oils followed by cycloeucalenol and obtusifoliol in virgin olive oils, and obtusifoliol in hazelnut oils. 24-Methylenecycloartanol was predominant in both kinds of oils in the 4,4′-dimethylsterols. For the first time, δ-amyrin was tentatively identified by comparing published mass spectral data in the analyzed samples of both kinds of oils. An unknown compound X (containing a lupane skeleton) and lupeol were detected only in the 4,4′-dimethylsterols fraction of hazelnut oils at a level of 2–8 and 6–10%, respectively. GC-MS analysis showed that adulteration of virgin olive oil by hazelnut oil could be detected at a level less than 4% by using these two compounds as possible potential markers.     

Low molecular weight polypeptides in virgin and refined olive oils

Twenty-eight virgin olive oils—from different regions of Spain and prepared from olive drupes of different varieties—and six refined olive oils were analyzed to determine the presence of proteins in these oils. All oils studied showed the presence of proteins in the range of 7–51 μ/100 g of oil. There were no significant differences in protein content in oils from different varieties or between virgin or refined oils. In addition, all oils exhibited analogous amino acid patterns, suggesting a similarity among protein fractions obtained from different oils. A polypeptide with an apparent M.W. of 4600 Da was common to the isolated protein fractions. These results suggest that this polypeptide is a previously unknown minor component in olive oils. No clear influence of this component on oil stability was observed when oil stabilities were estimated as a function of phenol, tocopherol, phosphorus, and protein contents of the oils.