³¹P nuclear magnetic resonance (NMR) spectroscopy was used to compare the composition of egg yolk phospholipids before and after enzymatic oxidation. ¹H NMR spectroscopy was used to monitor and compare the changes in the molar percentage of fatty acyl groups and the concentrations of primary and secondary oxidation compounds between the unoxidized control, lipoxygenase-catalyzed oxidation and thermal oxidation (in water bath at 95 ℃) groups. The results showed that phosphatidylcholine and phosphatidylethanolamine were the major components of egg yolk phospholipids. After oxidation of egg yolk phospholipids, the contents of phosphatidylcholine and phosphatidylethanolamine decreased, while the content of hemolytic phospholipids increased. The molar percentage of total unsaturated fatty acids in both oxidized samples decreased, while the molar percentage of saturated fatty acids increased. The degradation rate of linoleic acid was the fastest with the enzyme at pH 6, and more hydroperoxide was formed from the enzymatic oxidation of egg yolk phospholipids. (Z,E)-2,4-dienal was mainly produced after heating. At pH 9, hydroperoxide was produced and rapidly degraded and more n-alkaldehyde was generated after heating. Therefore, lipoxygenase can be used to catalyze the oxidation of egg yolk phospholipids at pH 6 to produce more flavor compounds such as 2,4-diene aldehydes.

In order to gain an in-depth understanding of the mechanism for the changes in the major ingredients and volatile compounds of cream during heating treatment, nuclear magnetic resonance (NMR) spectroscopy was used to analyze quantitatively the polar and apolar components of cream, and gas chromatography-mass spectrometry (GC-MS) was used to identify the volatile compounds of cream before and after heating treatment. NMR analysis revealed lactose as a major polar component, as well as lesser amounts of free amino acids, free fatty acids and organic acids; and triglycerides as major apolar components, as well as lesser amounts of diglycerides and monoglycerides. After heating treatment, the content of polar components, mainly including lactose and free amino acids, was reduced greatly, while the content of apolar components was reduced less. GC-MS analysis showed that the contents of short-chain fatty acids and aldehydes were increased less, whereas the contents of methyl ketones, lactones and Maillard reaction products were increased signifciantly, among which methional, maltol and furaneol were only detected in heated cream. The results showed that the formation of the Maillard reaction products and the growth of lipid-derived compounds during thermal treatment resulted in a reduction of polar components and fatty acids in cream, respectively, which provides a new idea for further research on cream falvor and products.

In order to investigate the nonvolatile taste-active components in crayfish, free amino acids, nucleotides, organic acids, soluble sugars and alkaloids in cooked crayfish muscle were qualitatively and quantitatively analyzed by ¹H nuclear magnetic resonance (¹H NMR). Their taste activity values (TAVs) and equivalent umami concentration (EUC) were calculated to evaluate the key taste-active compounds and umami attributes, respectively. The results suggested that a total of 33 taste-active compounds were detected, among which arginine, histidine, glutamic acid, alanine, lysine, glycine, adenosine 5’-monophosphate (AMP), inosine 5’-mononucleotide (IMP), succinic acid and lactic acid were the key taste-active compounds with TAVs greater than 1.0, and they played an important role in the taste of crayfish. The EUC of crayfish was 9.1 g monosodium glutamate (MSG)/100 g, indicating very intense umami taste.

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.