Targeted metabolomics reveals the contribution of degradation and oxidation of lipids and proteins mediated by pH to the formation of characteristic volatiles in preserved egg yolk during pickling.

Targeted metabolomics and flavouromics combined with relative odor activity value were performed to explore the effect of degradation and oxidation of matrix mediated by pH on the formation of characteristic volatiles in preserved egg yolk (PEY) during pickling. It was found that the oxidation of proteins and lipids in PEY induced by pH sequentially occurred in early and later periods, and degradation both mainly occurred in early stage. Moreover, 1-octen-3-one, heptanal, trimethylamine, etc., compounds and 5-HETrE, proline, etc., components were confirmed as up-regulated characteristic volatiles and differential metabolites in PEY during pickling. The formation of octanal-M/D and benzeneacetaldehyde-M was attributed to ß-oxidation of hydroxyeicosapentaenoic acid and L-isoleucine catalyzed by strong alkali at early period based on correlation network between them, respectively. Meanwhile, the generation of 1-octen-3-one-M/D mainly depended on L-serine and could be promoted by phosphatidylcholines oxidation. At later stage, the formation of heptanal-M/D was primarily attributed to phosphatidylethanolamines oxidation induced by alkali, and the enrichment of heptanal-M/D and nonanal were both enhanced by oxidized lipids. Lastly, trimethylamine was derived from L-lysine under alkaline conditions and promoted by protein oxidation during the whole process. This manuscript provided insight into the differential contribution of oxidation and degradation from matrix regulated by exogenous factors on the formation pathway for characteristic volatiles in foods.

A new insight into the key matrix components for aftertaste in Ampelopsis grossedentata (vine tea) infusion: From the intensity and duration of taste profiles using non-targeted metabolomics and molecular simulation.

The aftertaste with a prolonged duration in ampelopsis grossedentata infusion (AGTI) is easily perceived, however, its formation mechanism is unclear. Therefore, aftertaste-A and richness were confirmed as the characteristic aftertaste of AGTI through sensory evaluation and electronic tongue. Moreover, 5-KETE, theobromine, etc., metabolites were identified as the differential components between AGTI and green tea infusion. Among them, p-coumaroyl quinic acid, xanthine etc., and proline, dihydromyricetin, etc., components contributed more to the formation of aftertaste-A and richness, respectively. Further, the bonding between characteristic metabolites for aftertaste in AGTI with their receptors were shown to be more stable using molecular docking, compared to metabolites related to typical taste profiles. The aftertaste in AGTI was more easily perceived by saltiness components or in NaCl system by molecular simulation. This study offers novel insight into the interaction mechanism of aftertaste in tea infusion and will contribute to further study on aftertaste for other foods.

Transparent mechanism of salted egg (white) hierarchically and synergistically driven by NaCl, NaOH and thermal treatment: Based on empirical data and molecular simulation.

Currently, it is a challenge that the yolk in salted preserved egg tends to preserved egg yolk due to extreme NaOH treatment. Therefore, NaCl, NaOH and thermal were successfully used to prepare a new translucent salted quail egg (T-SQE), which combined advantages of preserved egg white with transparent appearance and salted egg yolk with unique texture and odour. Moreover, transparency of opaque gel (Transmittance: 0.09 %) subjected to NaCl and thermal was demonstrated to be improved under the synergistic effect of NaOH (8.55 %) via empirical data and molecular simulation. The disordered and dense network in opaque T-SQE induced by NaCl and thermal tended to form an ordered, porous and transparent structure in presence of NaOH, with more immobilized water that was poorly bonded to protein, larger radius of gyration and lower hydrophobic interaction. This research provides new insight into understanding the influence of hierarchy and synergism on transparency of egg products.

Study on the formation pathways of characteristic volatiles in preserved egg yolk caused by lipid species during pickling.

The formation of volatiles in high-fat foods is strongly influenced by the composition and structure of lipids. The relationship between key variable lipid species and characteristic volatiles were performed by lipidomics and flavoromics to resolve the pathways of volatiles in preserved egg yolk (PEY) during pickling. The results showed that the formation of nonanal and benzaldehyde at early stage possibly derived from oleic acid sited at Sn-1 in TG(18:1_18:2_20:4), Sn-2 in PE(22:6_18:1), and linoleic acid bonded at Sn-2 in TG(18:1_18:2_20:4), respectively. 1-octen-3-ol may be formed from linoleic acid located at Sn-2 in TG(18:1_18:2_20:4) and arachidonic acid sited at Sn-3 in TG(18:1_18:2_20:4). Indole was formed through TGs(16:0_16:1_20:1;16:1_18:1_22:1;23:0_18:1_18:1) at the later stage, and acetophenone through TGs(14:0_20:0_20:4;14:0_15:0_18:1; 16:0_16:0_22:6), PCs(24:0_18:1;O-18:1_18:2), PEs(P-18:1_20:4;P-18:1_22:6) and SPH(d18:0) during whole process of pickling. Our study provides a deep and precise insight for the formation pathways of characteristic volatiles in PEY through lipids degradation during pickling at the molecular level.

Multiomics reveals the formation pathway of volatile compounds in preserved egg yolk (PEY) induced by NaCl: Based on the model of PEY and salted egg yolk (SEY) treated with/without NaCl.

The models of preserved egg yolk (PEY) and salted egg yolk both treated with or without NaCl were performed to explore the effect of NaCl on the characteristic volatile compounds (VOCs) in PEY. 1-hexanol, 2-heptanone, isoamyl acetate, etc., compounds were confirmed as the characteristic VOCs in PEY mainly induced by NaCl and the formation of 1-octanol, 2-pentylfuran, ammonia, etc., characteristic VOCs induced by NaCl may depend on the combined effect of Cu2+ and OH-. Among them, 1-hexanol and 2-heptanone were formed from linoleic acid in PS(18:0_18:2) and oleic acid in PG(22:6_18:1), respectively, through multi-omics and correlation analysis. Meanwhile, 1-octanol may originated from ß-oxidation of oleic acid in PS(18:1); 2-pentylfuran and ammonia maybe derived from the derivative of aspartate and the degradation of l-methionine, respectively. Moreover, this study provides a new insight to parse the influence of NaCl with/without other exogenous factors on the formation of VOCs in food products.