No Evidence Found for Diels–Alder Reaction Products in Soybean Oil Oxidized at the Frying Temperature by NMR Study

It has been generally accepted that the Diels–Alder reaction mechanism is one of the major reaction mechanisms to produce dimers and polymers during heating process of vegetable oil. Soybean oil oxidized at 180 °C for 24 h with 1.45 surface area-to-volume ratio showed 36 % polymer peak area in gel permeation chromatogram. However, the NMR DEPT (Distortionless Enhancement by Polarization Transfer) 135 spectrum did not show any signals of possible Diels–Alder products. A fraction separated from the oxidized soybean oil by column chromatography contained 98 % polymers, but again, showed no signals of proposed Diels–Alder products in the DEPT 135 spectrum. Methyl oleate and triolein without a diene required for the Diels–Alder reaction produced 27 and 63 % of total polymers, respectively, under the same condition. This indicates that the polymers must be produced by reactions other than the Diels–Alder reaction for these oils. This study shows that the Diels–Alder reaction is not the major reaction to produce polymers during oxidation of soybean oil, within the DEPT 135 spectroscopy sensitivity level, about 5 mol %.     

Thermal Oxidation Rate of Oleic Acid Increased Dramatically at 140 °C Studied using Electron Spin Resonance and GC–MS/MS

Thermal oxidation of oleic acid at high temperatures was studied using combination of electron spin resonance (ESR) spin-trapping technique and solid phase microextraction (SPME)-Gas chromatography-mass spectrometry-mass spectrometry (GC–MS/MS). Dimethyl pyridine N-oxide (DMPO) was applied as the spin trap. Alkyl, alkoxyl, and oxidized DMPO adducts were identified in the experimental spectra. At 140 °C, the alkyl radical adduct was the major component, accounting for 63.89% of the total radical adducts. However, the alkoxyl radical adduct was the main radical adduct in the temperature range of 120 to 135 °C. The total amount of spins, a parameter to indicate radical concentrations, detected at 140 °C was nearly three times higher than that at 135 °C. And, the total amount of alkyl radical adducts was higher than that of alkoxyl radical adducts at 140 °C, which indicated a higher alkyl radical formation rate. Besides, a larger amount (10.30%) of oleic acid degraded at 140 °C than that at 135 °C with the detection of GC. More (E)-2-Decenal (plastic) and (E)-2-undecenal (herbaceous) formed affect the flavor of frying.     

Linolenic Acid as the Main Source of Acrolein Formed During Heating of Vegetable Oils

Acrolein, which is an irritating and off-flavor compound formed during heating of vegetable oils, was estimated by the gas–liquid chromatography (GLC). Several vegetable oils such as high-oleic sunflower, perilla, rapeseed, rice bran, and soybean oils were heated at 180 °C for 480 min and then the concentration of acrolein in the head space gas was determined by GLC. The formation of acrolein was greatest in perilla oil among the tested oils, while it was much lower in rice bran oil and high-oleic sunflower oil. There was a good correlation between the level of acrolein and linolenate (18:3n-3) in the vegetable oils. To investigate the formation of acrolein from linolenate, methyl oleate, methyl linoleate, and methyl linolenate were also heated at 180 °C, and the amounts of acrolein formed from them were determined by GLC. The level of acrolein was the greatest in methyl linolenate. Acrolein was also formed from methyl linoleate, but not from methyl oleate. Acrolein in vegetable oils may be formed from polyunsaturated fatty acids, especially linolenic acid but not from glycerol backbone in triacylglycerols.     

Highly accurate photopyroelectric measurement of thermal diffusivity of vegetable oils

High‐accuracy photopyroelectric measurements, in the thermal‐wave‐resonator‐cavity configuration, were performed in order to measure the thermal diffusivity of some vegetable oils. The high resolution (relative error ±0.5%) of the above method allows for the detection of small changes in the values of this dynamic thermal parameter. The accuracy of the results is mainly due to the possibility to precisely control the variation (30‐nm step) of sample thickness, a proper selection of the range of the thickness scan (2 µ_m < L_m < 4 µ_m ? 5 µ_m), and an iterative procedure of data analysis. A correlation between thermal diffusivity and the fatty acid composition (obtained via gas chromatography) is suggested for some fresh (sunflower, hemp, flax, and soybean) oils and for hemp oil exposed to a microwave field: Thermal diffusivity appears to be determined by the overall content of polyunsaturated fatty acids.     

Rapid Detection and Quantification by GC–MS of Camellia Seed Oil Adulterated with Soybean Oil

Camellia seed oil with high nutritional value is widely used in southern China and southeastern Asia for cooking. Due to the high price of camellia seed oil, fraudulent traders blended the oil with inexpensive oils to increase profits. In this paper, a new method was introduced to detect the adulteration of camellia seed oil with soybean oil by GC–MS with consideration of a parameter which was defined by the total content of oleic and linoleic acid, the oleic to linoleic acid ratio and the content of linolenic acid. Oils samples were prepared by blending pure camellia seed oil with pure soybean oil at levels from 1 to 50 %. Fatty acids esterified by TMSH and TBME in seconds were separated and identified by GC–MS. The detection limit of adulteration was as low as 5 %, and even much lower than 5 % for most kinds of camellia seed oil, which was lower than those measured by other methods. All the results indicated that this simple, accurate and rapid method can also be recommended for the authentication of olive oil with some modification.     

Continuous Gradient Temperature Raman Spectroscopy of Oleic and Linoleic Acids from −100 to 50 °C

We analyzed the unsaturated fatty acids oleic (OA, 18:1n‐9) and linoleic (LA, 18:2n‐3), and a 3:1 LA:OA mixture from ?100 to 50 °C with continuous gradient temperature Raman spectroscopy (GTRS). The 20 Mb three‐dimensional data arrays with 0.2 °C increments and first/second derivatives allowed rapid, complete assignment of solid, liquid, and transition state vibrational modes. For OA, large spectral and line width changes occurred in the solid state γ to α transition near ?4 °C, and the melt (13 °C) over a range of only 1 °C. For LA, major intensity reductions from 200 to 1750 cm^?1 and some peak shifts marked one solid state phase transition at ?50 °C. A second solid state transition (?33 °C) had minor spectral changes. Large spectral and line width changes occurred at the melt transition (?7 °C) over a narrow temperature range. For both molecules, melting initiates at the diene structure, then progresses towards the ends. In the 3:1 LA:OA mixture, some less intense and lower frequencies present in the individual lipids are weaker or absent. For example, modes assignable to C8 rocking, C9H–C10H wagging, C10H–C11H wagging, and CH3 rocking are present in OA but absent in LA:OA. Our data quantify the concept of lipid premelting and identify the flexible structures within OA and LA, which have characteristic vibrational modes beginning at cryogenic temperatures.     

Fingerprinting Krill Oil by 31P, 1H and 13C NMR Spectroscopies

The detailed analysis of krill oil is of importance to be able to differentiate other oils, identify adulterated products, and provide the highest quality associated with its beneficial health effects. The objective of this study was to demonstrate the usefulness of the combination of ³¹P, ¹H and ¹³C nuclear magnetic resonance (NMR) spectroscopies to characterize the krill oil profile. It was found that in contrast to fish oil, where eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) fatty acids are found in triacylglycerol, krill oil is characterized by a more asymmetric fatty acid distribution with a higher polyunsaturated fatty acids PUFA content in the sn‐2 position of phospholipids and lower amounts in triacylglycerol. Besides the typical asymmetric fatty acid composition, several other markers were investigated for krill oil origin test. The validation of the ³¹P NMR spectroscopic method regarding major phospholipid species was performed according to the Good Laboratory Practice (GLP) and International Council for Harmonisation (ICH) guidelines. The method was characterized by high sensitivity, accuracy, and reproducibility. Interlaboratory testing showed satisfactory robustness regardless of the type of NMR equipment used by different laboratories. High‐resolution NMR spectroscopy has proven to be a convenient and exact method for providing a characteristic fingerprint of krill oil. By this technique, clear distinctions to other oils can be made through qualitative and quantitative analysis of krill oil.     

Soy fatty acid oxidation with sodium hypochlorite monitored by nuclear magnetic resonance spectroscopy

The oxidation process of soy fatty acids by sodium hypochlorite with ruthenium trichloride catalyst was examined at different temperatures and active chlorine:fatty acid molar ratios. ¹H and ¹³C distortionless enhancement by polarized transfer nuclear magnetic resonance (NMR) spectroscopy techniques were used to monitor oxidation of the double bonds in unsaturated lipids by measuring the peak integration ratio of double-bond peaks:methylene-methyl peaks. This NMR monitoring technique proved to be an excellent means to quantify double-bond reactions. Gas chromatography-mass spectrometry was used to identify mono- and diacid products, separated by hexane/methylene chloride extraction, as well as other oxidation products. While the presence of ruthenium catalyst increased the initial rate of oxidation, it also catalyzed the decomposition of hypochlorite, decreasing the available reactive chlorine, resulting in a delay in complete oxidation. A 9:1 molar ratio of active chlorine to fatty acids completely oxidized all double bonds of soy fatty acids. However, the yield of low-molecular-weight monoacid oxidation products was only 17%, indicating the probable formation of hydroxy fatty acids.     

Structural investigations of perlite and expanded perlite using 1H, 27Al and 29Si solid-state NMR

Industrial grade perlite and expanded perlite systems were investigated by multifield and multinuclear Solid State Nuclear Magnetic Resonance (SSNMR), Fourier Transform Infra-Red (FTIR) spectroscopies and Scanning Electron Microscopy (SEM). The SSNMR studies focussed on the ¹H, ²⁹Si and ²⁷Al nuclei using single pulse excitation (SPE) and ¹H, ²⁹Si cross-polarization Magic-Angle-Spinning (CP-MAS) conditions, with ²⁷Al Triple Quantum Magic-Angle-Spinning (3QMAS) measurements also being implemented. The resonances at ~ 52 ppm detected in the ²⁷Al MAS NMR spectra of the industrial grade and expanded systems are tentatively assigned to tetrahedrally coordinated aluminium, while the resonance at ~ 5 ppm, which was only observed in the industrial grade perlite spectrum, is attributed to octahedrally coordinated aluminium. In neither case could the pentahedrally coordinated positions be identified using ²⁷Al MAS and 3QMAS techniques. ²⁷Al data suggests that tetrahedrally coordinated aluminium atoms do not have a significant role in the grain expansion process. The broad resonance envelopes found in the ²⁹Si MAS NMR and FTIR data of both perlites were analyzed by the second-order derivative. The analyses confirmed complex Qⁿ configurations for the perlitic structure suggesting the prevalence of Q³ and Q⁴ species. ¹H-²⁹Si CP-MAS spectra support the presence of Q² units suggested by FTIR and SPE data. SEM micrographs revealed the honeycomb morphology of expanded domains in perlite after heat treatment.     

Dynamic Mechanical Properties and Adhesive Joint Strengths of Emulsion Polymers Produced by Power Feed Technique. II. Chemical Structure of Grafted Power Feed Polymer

Power feed copolymers were synthesized using styrene and n-butyl acrylate through a non-uniform feeding emulsion polymerization. Poly(vinyl alcohol) (PVA) was used as a protective colloid, onto which vinyl monomers were grafted. With the increase of PVA, grafting was also increased. Feeding method did not affect grafting nor grafting efficiency to a great extent. However, the amount of initiator had a negative correlation against grafting or grafting efficiency. From NMR spectroscopy, it was known that n-butyl acrylate monomer grafted onto PVA rather than copolymerized with styrene monomer. In order to increase the cohesive strengths of each phase, grafting was introduced to the power feed polymerization. In these cases, the chemical structure of grafted power feed polymer was investigated.     

Synthesis of Carbonated Cotton Seed Oil and Its Application as Lubricating Base Oil

Epoxidized cotton seed oil (ECSO) was conveniently synthesized from cotton seed oil (CSO) in the presence of hydrogen peroxide, formic acid, and phosphoric acid. Then the ECSO was converted into carbonated cotton seed oil (CCSO) by reacting with CO₂ using tetrabutylammonium bromide as a catalyst. The reaction conditions including reaction temperature, pressure, reaction time and the amount of catalyst were examined. In addition, the final product (CCSO) from cyclic addition reaction was characterized by FT-IR, ¹H NMR and TGA. Compared with CSO and ECSO, CCSO showed excellent thermal and oxidation stability. Additionally, the CCSO’s properties of extreme pressure, anti-wear and friction reduction were tested and analyzed. The results indicated that it could be used as potential lubricating base oil.     

Dynamic Mechanical Properties and Adhesive Joint Strengths of Emulsion Polymers Produced by Power Feed Technique. II. Chemical Structure of Grafted Power Feed Polymer

Power feed copolymers were synthesized using styrene and n-butyl acrylate through a non-uniform feeding emulsion polymerization. Poly(vinyl alcohol) (PVA) was used as a protective colloid, onto which vinyl monomers were grafted. With the increase of PVA, grafting was also increased. Feeding method did not affect grafting nor grafting efficiency to a great extent. However, the amount of initiator had a negative correlation against grafting or grafting efficiency. From NMR spectroscopy, it was known that n-butyl acrylate monomer grafted onto PVA rather than copolymerized with styrene monomer. In order to increase the cohesive strengths of each phase, grafting was introduced to the power feed polymerization. In these cases, the chemical structure of grafted power feed polymer was investigated.