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Wheat germ is rich in lipids with a very complex composition. The lipids in wheat germ are prone to be hydrolyzed and oxidized during processing and storage. In this study, phospholipids and neutral lipids were extracted from wheat germ with different solvents. Then the phospholipids, mono-, di-, and triacylglycerols, as well as fatty acyl group contents were analyzed by nuclear magnetic resonance (NMR) spectroscopy. The results showed that six kinds of phospholipids were detected by 31P NMR in wheat germ, including phosphatidylcholine (PC), phosphatidyl ethanolamine (PE), phosphatidyl inositol (PI), phosphatidylglycerol (PG), phosphatidic acid (PA), and phosphatidylserine (PS). Furthermore. There were also five kinds of lysophospholipids (lysophosphatidylcholine (LPC), lysophosphatidylglycerol (LPG), and lysophosphatidylethanolamine (LPE)) and two non-lipid phosphorus compounds (inorganic phosphate (pi) and phosphatidylcholine glycerol (GPC)). GPC was the hydrolytic product from the removal of fatty acyl groups by two-step hydrolysis of PC. PC had the highest content of phospholipid in the wheat germ. Specifically, the molar concentration of PC was 0.42 μmol/g wheat germ, the molar fraction of PC was 28.50 %, the mass concentration of PC was 0.31 mg/g wheat germ, and the mass fraction of PC was 30.20 %. The signals of PE, PC, LPC, GPC, and choline (Cho) in ¹H NMR spectra were also used to determine the phospholipids in wheat germ. Compared with ¹H NMR, 31P NMR spectra were better resolved and more suitable for qualitative and quantitative analysis of phospholipid components, as 31P NMR only determined the characteristic signal of phosphorus-containing compounds. The composition and content of free fatty acids, mono-, di-, and triacylglycerols were determined in the wheat germ by ¹H NMR. The proportion of free fatty acids was 12.35 % in the wheat germ. The highest content was triacylglyceride (TG), accounting for 77.25 %. The contents of 1,3-diacylglycerol (1,3-DG) and 1, 2-diacylglycerol (1,2-DG) were 5.80 % and 4.41 %, respectively, and the contents of 1-monoacylglycerol (1-MG) and 2-monoacylglycerol (2-MG) were 0.17% and 0.03%, respectively. Moreover, TG was gradually hydrolyzed to produce diglycerol (DG), monoglycerol (MG), free fatty acid (FA) and glycerol in the wheat germ during storage. FA was always produced in the wheat germ throughout the hydrolysis reaction, leading to a higher content, compared with DG and MG. Six kinds of fatty acyl groups were detected by ¹H NMR in triglycerides and phospholipids of wheat germ, including the acyl groups of docosahexaenoic acid (DHA), eicosapentaenoic acid and arachidonic acid (EPA+ARA), linolenic acid (Ln), linoleic acid (L) and oleic acid (O). Linoleic acid was the most abundant unsaturated fatty acyl group in triglycerides and phospholipids. Saturated and modified acyl groups (S+M) were also detected by ¹H NMR. There was significant difference in fatty acid composition between triglyceride and phospholipid in wheat germ. Lysophospholipids and GPC were the hydrolyzed products of phospholipids, while DG and MG were the hydrolyzed products of triglycerides. As such, their contents shared the degree of lipids hydrolysis in the wheat germ. Therefore, NMR can be used to determine the lipid compositions and hydrolysis in the wheat germ. In short, this NMR is a powerful tool for lipids analysis of wheat germ products. [ABSTRACT FROM AUTHOR]

Phospholipids are one of the most important flavor precursors of the meat. Chicken fat is normally derived from fatty and chicken soup aroma. The oxidation of fatty acids, especially the degradation of unsaturated fatty acids, is critical to the formation of chicken characteristics. Phospholipids in the deposit fat of chicken can play a significant role in the characteristic aroma of chicken fat. In this study, phospholipids in chicken fat tissue were extracted by ethanol, and then precipitation of phospholipids using acetone. A Phosphomolybdate Blue Spectrophotometry was selected to determine the contents of phospholipids in chicken fat tissue, de-phospholipids treated chicken fat tissue, and extracted phospholipids. The relative contents of volatile compounds were analyzed by headspace solid-phase microextraction/gas chromatography-mass spectrometry (HS-SPME-GC-MS), and aroma intensities of chicken fat samples were characterized by sensory evaluation of sequencing test. The results showed that the contents of phospholipids in chicken fat tissue, de-phospholipids treated chicken fat tissue, and extracted phospholipids were 56.69±3.89, 28.10±1.18 and 537.19±20.95 mg/g, respectively. Ethanol can be expected to serve as an effective solution in the extracting of phospholipids, where most of the phospholipids were removed from chicken fat tissue. Volatile compounds were identified by GC-MS analysis in de-phospholipids chicken fat, chicken fat, chicken fat with added phospholipids, and phospholipids sample, respectively. The removal of phospholipids showed a markedly different volatile profile, and the quantities of aliphatic aldehydes were considerably reduced, where only traces of unsaturated aldehyde of (E)-2-heptenal, (E)-2-pentenal were found. The chicken fat with added phospholipids sample had a significant increase in most of the lipid-derived compounds, compared with the de-phospholipids chicken fat sample, especially, (E, E)-2,4-decadienal, (E)-2-nonenal, (E)-2-heptenal, 1-octen-3-ol and 1-octen-3-one, where the characteristic odorants of chicken meat increased 4.5, 7.8, 9.4, 5.0 and 10.4 times, respectively. When linoleate residues assembled in a phospholipid, the C9 position can be the most favored position for the formation of hydroperoxides during the radical initiation step of autoxidation. Since the C9 hydroperoxide was the precursor for (E, E)-2, 4-decadienal, the chicken fat with added phospholipids sample was more likely to form (E, E)-2,4-decadienal, indicating a characteristic odor impact compound in chicken. Meanwhile, hexanal was usually used as the index of warmed-over flavor, and the relative contents of hexanal had no significant difference between the chicken fat with added phospholipids sample and chicken fat sample. Besides, methyl ketones and saturated alcohols, which had higher odor thresholds to be produced by oxidative and thermal degradation of saturated fatty acids, also tended to increase in chicken fat with added phospholipids sample. The main reason was that phospholipids were rich in unsaturated fatty acids, thereby to be more prone to oxidative degradation under heating conditions. Moreover, once the lipid oxidation process had been initiated by the more reactive and more unsaturated fatty acids, this reaction can promote the oxidation of the less reactive fatty acids. Sensory analysis of sequencing test showed that the addition of phospholipids can significantly increase the aroma intensity of chicken fat, whereas, the de-phospholipids chicken fat sample had the weakest intensity. This finding can provide a sound evidence that the phospholipids extracted from chicken deposit fat tissue can be used to significantly increase the aroma intensity of chicken fat. It is highly expected for a potential use for the research and development of chicken fat with strong aroma. [ABSTRACT FROM AUTHOR]