Analysis of changes in flavor characteristics of congou black tea at different fermentation degrees under industrial production conditions using flavor compound weighted network co-expression method

Fermentation is a key process in Congou black tea, but there is limited research on the changes in flavor factors and their interrelationships during different fermentation stages under industrial production. This study applies sensory evaluation and metabolomics techniques to explore the interactions between flavors. Sensory evaluation indicated that the 4-h fermented sample exhibited the best overall performance. The experiment of adding aroma substances further revealed the significant effects of sweet aroma and green odor on taste of sweetness and astringency. Additionally, 532 flavor compounds were identified using high-resolution liquid chromatography-mass spectrometry and gas chromatography-mass spectrometry. Moreover, significant differences were observed in the volatile compounds derived from flavonoids, amino acids, and fatty acids of samples with different fermentation degrees. Furthermore, weighted co-expression network analysis of flavor compounds showed that the oxidation of polyphenols, especially catechins, plays an important regulatory role in content changes of volatile and other non-volatile compounds during fermentation.

Fluorescence Lifetime of Chlorophyll α in Oxidized Edible Vegetable Oil

To promote the application of time-resolved fluorescence in oxidation determination of edible vegetable oil, fluorescence lifetime of chlorophyll α in oxidized edible vegetable oils was recorded and analyzed by simulated microenvironment experiments and spectral methods. It was showed that fluorescence lifetime of chlorophyll α decreased with the increase of polarity in the early stage of oxidation, and increased with the increase of viscosity in the later stage of oxidation. Conjugation effect and hydrogen bonding existed in the microenvironment of oxidized edible vegetable oil were considered to be the factors leading to the increase of fluorescence lifetime. The change mechanism of fluorescence lifetime in oxidized edible vegetable oil was supplied, which was considered to be strong support for the application of time-resolved fluorescence.

Hydroxy fatty acids in the surface Earth system

Lipids are ubiquitous and highly abundant in a wide range of organisms and have been found in various types of environmental media. These molecules play a crucial role as organic tracers by providing a chemical perspective on viewing the material world, as well as offering a wealth of information on metabolic activities. Among the diverse lipid compounds, hydroxy fatty acids (HFAs) with one to multiple hydroxyl groups attached to the carbon chain stand out as important biomarkers for different sources of organic matter. HFAs are widespread in nature and are involved in biotransformation and oxidation processes in living organisms. The unique chemical and physical properties attributed to the hydroxyl group make HFAs ideal biomarkers in biomedicine and environmental toxicology, as well as organic geochemistry. The molecular distribution patterns of HFAs can be unique and diagnostic for a given class of organisms, including animals, plants, and microorganisms. Thus, HFAs can act as a valuable proxy for understanding the ecological relationships between different organisms and their environment. Furthermore, HFAs have numerous industrial applications due to their higher reactivity, viscosity, and solvent miscibility. This review paper integrates the latest research on the sources and chemical analyses of HFAs, as well as their applications in industrial/medicinal production and as biomarkers in environmental studies. This review article also provides insights into the biogeochemical cycles of HFAs in the surface Earth system, highlighting the importance of these compounds in understanding the complex interactions between living organisms and the environment.

Application of Sorbent-Based Extraction Techniques in Food Analysis

This review presents an outline of the application of the most popular sorbent-based methods in food analysis. Solid-phase extraction (SPE) is discussed based on the analyses of lipids, mycotoxins, pesticide residues, processing contaminants and flavor compounds, whereas solid-phase microextraction (SPME) is discussed having volatile and flavor compounds but also processing contaminants in mind. Apart from these two most popular methods, other techniques, such as stir bar sorptive extraction (SBSE), molecularly imprinted polymers (MIPs), high-capacity sorbent extraction (HCSE), and needle-trap devices (NTD), are outlined. Additionally, novel forms of sorbent-based extraction methods such as thin-film solid-phase microextraction (TF-SPME) are presented. The utility and challenges related to these techniques are discussed in this review. Finally, the directions and need for future studies are addressed.

Beyond Autoxidation and Lipoxygenases: Fatty Acid Oxidation Products in Plant Oils

For decades, research on oxidation of linoleic acid (LA, C18:2 n6) and α-linolenic acid (ALA, C18:3 n3) in plant oils has focused on autoxidatively formed and lipoxygenase-derived 9-hydro(pero)xy- and 13-hydro(pero)xy-LA and -ALA. Here, using a non-targeted approach, we show that other hydroxy fatty acids are more abundant in plant oils. Liquid chromatography-mass spectrometry and gas chromatography-mass spectrometry analyses unveiled highly abundant peaks in flaxseed and rapeseed oils. Using authentic reference standards, seven of the peaks were identified as 9-, 10-, 12-, 13-, and 15-HODE as well as 9- and 13-HOTrE. Additionally, six peaks were characterized based on the retention time, the exact mass of the [M-H]- ion, and its fragment ions as 16-OH-C18:3, 18-OH-C18:3, three isomers of 12-OH-C18:2, and one of 15-OH-C18:2. 16-OH-C18:3 and 18-OH-C18:3 were tentatively identified as 16-OH-ALA and 18-OH-ALA, respectively, based on autoxidation and terminal hydroxylation of ALA using CYP4F2. Investigation of formation pathways suggests that fatty acid desaturase 3 is involved in the formation of the 12-OH-C18:2 isomers, 15-HODE, and its isomer. The dominantly occurring 12-OH-C18:2 isomer was identified as 12R,S-OH-9Z,15Z-octadecadienoic acid (densipolic acid) based on a synthetic standard. The characterized oxylipins occurred in cold-pressed flaxseed and rapeseed oils at concentrations of up to 0.1 g/100 g and thus about sixfold higher than the well-known 9-hydro(pero)xy- and 13-hydro(pero)xy-LA and -ALA. Concentrations in sunflower oil were lower but increased when oil was pressed from preheated seeds. Overall, this study provides fundamental new information about the occurrence of oxidized fatty acids in plant oils, having the potential to characterize their quality and authenticity.

Understanding desaturation/hydroxylation activity of castor stearoyl Δ9-Desaturase through rational mutagenesis

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Rationally designed mutations in the Δ⁹ desaturase promoted hydroxylation activity.

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Proton and electron transfer to the active site is crucial for the Δ⁹D to desaturate

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Detailed analysis of all enzymatic products of the Δ⁹D was carried out

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Insight into the chemo-, and stereoselectivity of non-heme diiron enzymes was obtained

A recently proposed reaction mechanism of soluble Δ⁹ desaturase (Δ⁹D) allowed us to identify auxiliary residues His203, Asp101, Thr206 and Cys222 localized near the di-iron active site that are supposedly involved in the proton transfer (PT) to and from the active site. The PT, along with the electron transfer (ET), seems to be crucial for efficient desaturation. Thus, perturbing the major PT chains is expected to impair the native reaction and (potentially) amplify minor reaction channels, such as the substrate hydroxylation. To verify this hypothesis, we mutated the four residues mentioned above into their counterparts present in a soluble methane monooxygenase (sMMO), and determined the reaction products of mutants. We found that the mutations significantly promote residual monohydroxylation activities on stearoyl-CoA, often at the expense of native desaturation activity. The favored hydroxylation positions are C₉, followed by C₁₀ and C₁₁. Reactions with unsaturated substrate, oleoyl-CoA, yield erythro-9,10-diol, cis-9,10-epoxide and a mixture of allylic alcohols. Additionally, using 9- and 11-hydroxystearoyl-CoA, we showed that the desaturation reaction can proceed only with the hydroxyl group at position C₁₁, whereas the hydroxylation reaction is possible in both cases, i.e. with hydroxyl at position C₉ or C₁₁. Despite the fact that the overall outcome of hydroxylation is rather modest and that it is mostly the desaturation/hydroxylation ratio that is affected, our results broaden understanding of the origin of chemo- and stereoselectivity of the Δ⁹D and provide further insight into the catalytic action of the NHFe₂ enzymes.

Structural Elucidation of Suberin from the Bark of Cultivated Willow (Salix sp.)

Although extractives have been symbolized as major bioactive pharmacological compounds from Salix (Salicaceae) bark, we speculated that these pharmaceutical effects cannot be solely attributed to phenolic components and their derivatives, but the long-chain suberin acids also contribute to their therapeutic effects. Hence, isolation and deconstruction of suberin were conducted, for the first time, to enrich our knowledge about the macromolecular components at the cell wall of willow bark. Saponification was adopted to obtain suberin extracts at a yield of approximately 5 wt % based on the bark of the studied hybrids. Gas chromatography-mass spectrometry allowed qualification and quantification of 23 compounds from the released suberin monomers, from which fatty acids represented majority of the isolated suberin, namely, fatty acid methyl esters (C17-C19); mono-carboxylic acid (C7-C16); alpha, omega-dicarboxylic acid (C7-C16); and omega-hydroxy long-chain fatty acids (C16-C22). Additionally, the lipophilic extractive was dominated by piceol, heptacosane, β-sitosterol, and fatty acids (C16-C28) from the studied hybrids. These findings could boost our integrative approach toward full valorization of willow bark.

Simultaneous quantification of epoxy and hydroxy fatty acids as oxidation products of triacylglycerols in edible oils

Epoxy and hydroxy fatty acids are important intermediates during lipid oxidation; quantification of both structures may help evaluate the extent of competition among various lipid oxidation pathways. This article describes a method to simultaneously determine saturated- and unsaturated- epoxy and hydroxy fatty acids derived from oxidation of vegetable oils. The experimental procedures employed transesterification with sodium methoxide, separation of epoxy and hydroxy fatty acid methyl esters (FAME) using solid-phase extraction (SPE), and trimethylsilyl (TMS) derivatization of hydroxy groups. GC-MS was used to identify the epoxy and hydroxy FAME in two different SPE fractions, while GC-flame ionization detection (GC-FID) was used to determine their quantities. Epoxy-octadecanoate/octadecenoate and hydroxy-octadecanoate/octadecenoate/octadecadienoate were determined as lipid oxidation products generated from oxidation of sunflower and canola oils. An isomer of methyl 13-hydroxyoctadeca-9,11-dienoate (13-HODE) TMS ether co-eluted with methyl 15-hydroxyoctadeca-9,12-dienoate TMS ether, which was only present in canola oil; thus, GC-MS-selected ion monitoring (GC-MS-SIM) was used to determine the concentration of 13-HODE. The proposed method has been successfully applied to monitor epoxy and hydroxy fatty acids in sunflower oil and canola oil oxidized at 40 °C.