APPLICATION OF NMR SPECTROSCOPY TO ASSESS OXIDATIVE STABILITY OF CANOLA AND SOYBEAN OILS

Exploring the lipid oxidation mechanisms during pumpkin seed kernels storage based on lipidomics: From phenomena, substances, and metabolic mechanisms

The study investigated the lipid oxidation of pumpkin seed kernels (PSK) under different storage conditions (room temperature, vacuum-room temperature, refrigeration, and vacuum-refrigeration) using HPLC-MS and GC-MS. Experimental results found the vacuum-refrigeration group showed the lowest PV (0.24 g/100 g), diene (8.68), hexanal (356.64 ± 16.06 ng/g), and nonanal (132.05 ± 8.38 ng/g) after a 9-month storage. A total of 586 lipids, including 6 classes and 27 subclasses, were detected, 46 of which showed significant differences. Refrigeration samples had the highest diacylglycerol content, while room temperature samples demonstrated the highest triacylglycerol and phosphatidylcholine content. Differential lipid metabolite analyses indicated that storage conditions mainly affected glycerolipid metabolism, glycerophospholipid metabolism, and sphingolipid metabolism pathways in PSK, while glycerolipid and glycerophospholipid metabolism were still dominant. It revealed that refrigeration was more effective than vacuum in inhibiting the oxidation of PSK. These findings could offer valuable references for the storage, transportation, preservation, and the development and utilization of PSK.

Characterization of thermo-oxidative behavior of ethylcellulose oleogels

The thermo-oxidative behavior crucial to the applicability of ethylcellulose (EC) oleogels is characterized. Not only did we take into account the composition of the gel network in relation to textural attributes, but also the dynamic chemical changes occurred during formation, heating, and holding of the gels. EC oleogel oxidative stability showed that at 6.0% EC100 concentration in the oleogels the movement of liquid oil trapped in the gel network was hindered by its high viscosity and stable gel network, thus retarding oxidation. Processing temperature ≤ 120 °C for <2 h was recommended when incorporated in food systems to minimize oxidation. As for the measurement of oxidative stability in general, p-AnV was found suitable in depicting oxidation of EC oleogels. Meanwhile, both R_ao and R_ad acquired from ¹H NMR spectra could serve as reliable oxidative indicators to gauge total oxidation of EC oleogels during storage.

Characterization of Hachi (Camelus dromedarius) fat extracted from the hump

In this work, the characteristics of fat from the hump of young camels (Hachi) were evaluated. The physicochemical properties of the fat were as follows: melting point, 45°C; saponification value, 202.3 mg KOH/g oil; refractive index (60°C), 1.468; unsaponifiable matter, 1.37%; free fatty acids (as the percentage of oleic acid), 0.96%; and peroxide value, 3.37 mequiv. O2/kg oil. High-resolution (1)H nuclear magnetic resonance ((1)H NMR) was used for the direct determination of the iodine value of Hachi fat (62.74 g/100 g oil). The Hachi fat was composed primarily of oleic acid (33.35%), followed by palmitic acid (26.16%), stearic acid (10.07%), palmitelaidic acid (9.56%) and myristic acid (8.83%). The thermal properties were assessed by thermogravimetry (TG) and derivative thermogravimetry (DTG). The results of the present analytical study showed that Hachi fat could be used in food products and as an important source of biological materials.

Rapid quantitation of thermal oxidation products in fats and oils by 1H-NMR spectroscopy

This work describes the application of high-resolution proton nuclear magnetic resonance (1H-NMR) spectroscopy to the study of the thermal peroxidation of beef tallow and corn oil under standardized conditions. The approach provides a rapid, quantitative method for determining the degree of oxidation of unsaturated fatty acids in animal and vegetable fats and oils by quantitating the decreasing intensities of 1H-NMR peaks for allylic and olefinic protons in unsaturated fatty acid chains of triglycerides and the increasing peak intensities of hydroperoxide and saturated and alpha, beta-unsaturated aldehydic protons in relation to the less labile protons in the triglyceride molecule. Two-dimensional correlation spectroscopy analysis of highly oxidized beef tallow (180 degrees C for 24 h) suggested that the unsaturated aldehydes that persisted were apparently associated with carboxy groups.