Unraveling the Thermal Oxidation Products and Peroxidation Mechanisms of Different Chemical Structures of Lipids: An Example of Molecules Containing Oleic Acid

Effect of heme proteins on the lipid molecule profile and aroma formation during hot air drying of non-smoked bacon

Heme proteins and their derivatives play important roles in inducing lipid oxidation to produce volatile compounds during bacon drying. This study investigated the effects of heme proteins and their derivatives (hemoglobin, myoglobin, nitrosylmyoglobin, hemin, Fe2+, and Fe3+) on lipid and volatiles profiles in the washed pig muscle (WPM) model. The results of the study indicated that the inducers primarily caused the oxidation of glycerophospholipids. Furthermore, hemoglobin and myoglobin had the most significant impact, and their potential substrates may include PE (O-18:2/20:4), PE (O-18:1/20:4), PC (16:0/18:1), and PE (O-18:2/18:2). Nitrosomyoglobin has limited ability to promote lipid oxidation and may protect ether phospholipids from oxidation. The analysis of the volatiles in the model revealed that heme proteins and their derivatives have the ability to induce the production of key aroma compounds. The descending order of effectiveness in inducing the production of aroma compounds is as follows: hemoglobin, myoglobin, hemin, and nitrosylmyoglobin. The effectiveness of Fe2+ and Fe3+ is similar to that of nitrosylmyoglobin.

Correlations of dynamic changes in lipid and protein of salted large yellow croaker during storage

Protein and lipid are two major components that undergo significant changes during processing of aquatic products. This study focused on the protein oxidation, protein conformational states, lipid oxidation and lipid molecule profiling of salted large yellow croaker during storage, and their correlations were investigated. The degree of oxidation of protein and lipid was time-dependent, leading to an increase in carbonyl content and surface hydrophobicity, a decrease in sulfhydryl groups, and an increase in conjugated diene, peroxide value and thiobarbituric acid reactive substances value. Oxidation caused protein structure denaturation and aggregation during storage. Lipid composition and content changed dynamically, with polyunsaturated phosphatidylcholine (PC) was preferentially oxidized compared to polyunsaturated triacylglycerol. Correlation analysis showed that the degradation of polyunsaturated key differential lipids (PC 18:2_20:5, PC 16:0_22:6, PC 16:0_20:5, etc.) was closely related to the oxidation of protein and lipid. The changes in protein conformation and the peroxidation of polyunsaturated lipids mutually promote each other's oxidation process.

Generation of key aroma compounds in fat and lean portions of non-smoked bacon induced via lipid pyrolysis reaction

This study explored the evolution of key aroma compounds and their lipid precursors in the lean (LN) and fat (FT) portions of non-smoked bacon during hot air drying. The results showed that the LN portion contained most of the aroma compounds in the bacon (>88%). The volatile content of the FT portion increased as the drying time increased, whereas that of the LN portion reached a maximum within 24 h and then decreased. Based on the highest volatile contents (4889.48 ± 202.06 µg/kg) and sensory scores, 24 h was considered the optimal drying time. For key aroma compounds, hexanal and 2,3-octanedione were derived from free fatty acids and polar lipids. Notably, 1-octen-3-ol was generated only from polar lipids in the FT and LN portions. The 2-undecenal and (E, E)-2,4-decadienal were produced by the oxidation of neutral lipids in the FT portion. Dihydro-5-pentyl-2(3H)-furanone was derived from polar lipids in the LN portion. Altogether, these findings provide theoretical insights into improving the aroma of bacon by optimizing raw material selection and processing methods.

Relationship between PAH4 formation and thermal reaction products in model lipids and possible pathways of PAHs formation

Lipids are closely related to the generation of PAHs during food thermal processing. During heating, lipids mainly triglycerides undergo hydrolysis, oxidation and decomposition. The relationship between the various products and the formation of PAHs is still unclear. This paper investigated the effect of different lipid standards on PAH4 production, and explored their thermal stability and reaction products to delve into nature of the differences in PAH4 production. Fatty acids were more prone to generate PAH4 than glycerides. The higher the degree of esterification of glycerides, the higher its thermal stability and the lower the content of PAH4 generated, implying that hydrolysis of glycerides promoted the generation of PAH4. In addition, there was a positive correlation between unsaturation in lipids and the PAH4 production. After heat treatment, hydroperoxides, unsaturated fatty alcohols and aldehydes, alkenes and aromatic substances were abundant in oleic acid and linoleic acid which produced the most PAH4. Thermal decomposition of lipid hydroperoxides was the pathway for the generation of conjugated hydrocarbon radicals, alcohols, aldehydes, and alkenes. The intramolecular cyclization and Diels-Alder reaction acted as ring-forming reactions, with consequent dehydrogenation, decarboxylation, side-chain breaks and radical reorganization, ultimately facilitating the amplification of the aromatic rings and the formation of PAHs.

Formation of Furan from Linoleic Acid Thermal Oxidation: (E,E)-2,4-Decadienal as a Critical Intermediate Product

The linoleic acid reaction models were set at 150 °C for 120 min, and its oxidation process was monitored by nuclear magnetic resonance (NMR) and gas chromatography-mass spectrometry (GC-MS). Results showed that no furan was formed from linoleic acid without heating, while furan accumulated throughout the heating process. Linoleic acid ran out within 30 min, which indicated that furan was formed mainly from the intermediate oxidation products of linoleic acid after 30 min. It should be noticed that the content of (E,E)-2,4-decadienal reached maximum once the linoleic acid ran out and then decreased with the formation of furan. Multivariate statistical analysis suggested that (E,E)-2,4-decadienal was the most important aldehyde related to furan formation during linoleic acid oxidation. To prove this assumption, the variation of furan from (E,E)-2,4-decadienal reaction models heating at 150 °C for 60 min was also studied. Results showed that the content of furan increased with the oxidation of (E,E)-2,4-decadienal. Furthermore, NMR and GC-MS data proved that (E,E)-2,4-decadienal could be oxidized to 4,5-epoxy-(E)-2-decenal. In conclusion, our results supported (E,E)-2,4-decadienal and trans-4,5-epoxy-(E)-2-decenal as critical intermediate products of furan formation from linoleic acid oxidation.

Effects of Maillard reaction products on myoglobin-mediated lipid oxidation during refrigerated storage of carp

Lipid oxidation is the major cause of quality deterioration in freshwater fish, especially mediated by myoglobin (Mb). This study aimed to investigate the antioxidant mechanism of Maillard reaction products (MRPs) in Mb-mediated lipid oxidation in common carp (Cyprinus carpio). MRPs exhibited promising antioxidant and antimicrobial capacities based on the reduced content of peroxide and thiobarbituric acid-reactive substances and inhibited microbial growth. MRPs inhibited the oxidation of Mb by lowering the transfer from oxymyoglobin to metmyoglobin and improving the stability of heme iron. The correlation analysis showed that MRPs regulated the formation of free radicals by maintaining the reduced structure of Mb and the integrity of heme iron, and also directly inhibited the formation of oxidation products in a chain radical reaction. The texture and electronic nose analysis indicated that MRPs could delay the structural disruption and flavor deterioration of surimi. Therefore, MRPs could effectively inhibit Mb-induced lipid oxidation and further control the resulting changes in the flavor and texture of surimi.

Insights into the effects of steaming on organoleptic quality of salmon (Salmo salar) integrating multi-omics analysis and electronic sensory system

The effect of steaming treatment on salmon quality was explored by different multi-omics and electronic sensory system in this study. A comparison between conventional steaming (CS) and anaerobic steaming (AS) was conducted in organoleptic quality of salmon. Twelve key volatile compounds were identified, which contributed to the flavor difference. The concentrations of hexanal, (E)-2-octen-1-al, and decanal in AS salmon were significantly lower than in CS salmon, which account for 68.9-80.5 % of the latter. During steaming, the fatty acids and diacylglycerols decreased significantly by 37.4 % and 57.9 %, respectively. Anaerobic steaming limited the degradation of some oxidized lipids, further reduced some volatile secondary oxidation products. Nucleotides and derivatives, succinic acid, glutamic acid, hydroxyproline and betaine contributed to the saltness, umami, richness of steamed salmon. Metabolomics data revealed that the higher creatinine, Ala-Ala and Ala-Leu provided more umami and less bitterness to AS salmon.

Unraveling the Formation Mechanism of Egg's Unique Flavor via Flavoromics and Lipidomics

Egg products after thermal treatment possess a unique flavor and are favored by consumers. In this study, the key aroma-active compounds of egg yolk products and their formation mechanism during thermal treatment were investigated. The volatile aroma compounds in egg yolks were monitored using an electronic nose, gas chromatography-mass spectrometry (GC-MS) and gas chromatography-olfactometry-mass spectrometry (GC-O-MS), and the lipid molecular species were explored using ultra-high-performance liquid chromatography- mass spectrometry with a Q-Exactive HF-X Orbitrap (UPLC-Q-Exactive HF-X). A total of 68 volatile compounds were identified. Boiled eggs mainly derived their flavor from hexanal, 2-pentyl-furan, 2-butanone, 3-methyl-butanal and heptane. Meanwhile, fried eggs relied mainly on 14 compounds, the most important of which were 2-ethyl-3-methyl-pyrazine, 3-ethyl-2,5-dimethyl-pyrazine, 2-ethyl-3,5-dimethyl-pyrazine, nonanal and 2,3-diethyl-5-methyl-pyrazine, providing a baked and burnt sugar flavor. A total of 201 lipid molecules, belonging to 21 lipid subclasses, were identified in egg yolks, and 13 oxidized lipids were characterized using a molecular network. Phosphoethanolamines (PEs) containing polyunsaturated fatty acids were the primary flavor precursors contributing to the development of egg yolks' flavor, participating in lipid oxidation reactions and the Maillard reaction and regulating the production of aldehydes and pyrazine compounds. This study provides reference and guidance for the development of egg yolk flavor products.

Introduction of chlorogenic acid into thermal processed starch- oleic acid system controls the ordered structure and inhibits oleic acid oxidation through molecular interactions

In this study, the effects of starch- oleic acid (OA)- chlorogenic acid (CA) molecular interaction on OA oxidation during thermal processing were investigated based on structural analysis, oxidation characteristics and quantum calculations. The results showed that in the ternary system, on the one hand, OA could enter the spiral cavity of starch through hydrophobic forces and form V-type crystalline structure, which delayed its oxidation. On the other hand, CA could further inhibit the oxidation of OA through free radical reaction and did not affect the molecular interactions between OA and starch due to the steric hindrance and hydrophily. Notably, starch-OA-CA interactions could effectively decrease total oxidation value (19.07), prolong the induction time of oxidation (114.6 min) and reduce the abundance of oxidation products through hydrogen atom transfer reactions with active phenolic hydroxyl to protect the α-methylene groups at C=C. Overall, these results provided insights into functional property regulation by the interaction of starch-based multi-component systems.