Aromatic Esters Research Articles

A COF template-derived mesoporous CeO2-supported Au nanoparticles catalyst for the oxidative esterification of benzaldehydes and benzyl alcohols.

The direct oxidative esterification of benzaldehydes and benzyl alcohols to high value-added aromatic esters under mild and green reaction conditions is significant in the fine chemical industry. The accurate design of catalysts with high catalytic performance is crucial for this process. Herein, 2,4,6-trimethylpyridine, benzoic anhydride, and terephthalaldehyde were used to prepare a covalent organic framework (COF) material, which was then used as a template to construct a mesoporous CeO2-supported Au nanoparticles catalyst. The obtained Au@CeO2 catalyst was thoroughly characterized, and it possessed a mesoporous structure with a high surface area. Meanwhile, the as-prepared Au@CeO2 exhibited excellent catalytic performance in the oxidative esterification of benzaldehydes and benzyl alcohols with methanol, affording the corresponding aromatic esters under mild and green reaction conditions. Furthermore, the Au@CeO2 catalyst could also be recycled. Therefore, this study provides a green and sustainable pathway for the synthesis of high-value-added esters through a direct oxidative esterification strategy.

Comparison of Biological Activities and Bioactive Components of Seed, Leaf, and Blossom Parts of Camellia sinensis (L.) Kuntze and Commercial Black Tea

In this study, bioactive properties and GC-MS analyses of the Camellia sinensis (seed, leaf, and blossom parts) and commercial black tea extracts were compared. The total phenolic content (TPC) and antioxidant and antimicrobial activities of extracts were determined. The gas Chromatography-Mass Spectrometry (GC-MS) technique was used to identify the major bioactive compounds in extracts. The TPC and antioxidant activity values of the alcohol extract prepared from the leaf part of the C. sinensis are higher than the other extracts. There was a strong correlation between total phenolic content and antioxidant amount among the ethanol extracts of C. sinensis. In antimicrobial evaluation, the ethanol extracts showed more activity; the ethanolic extract of C. sinensis seeds was the most effective. GC-MS results indicated various organic compounds in the C. sinensis extracts, mainly saturated and unsaturated aromatic esters, aromatic alcohols, some cyclic structures, aromatic amine, and boranic esters with different therapeutic activities. The black tea extracts exhibited a more straightforward variety of bio components as aromatic esters and boranic ester. According to the obtained results, C. sinensis and black tea extracts would exert several beneficial effects by their biological activities thanks to the possible synergistic effect of chemical contents detected by GC-MS analysis. However, GC-MS results indicated that the black tea sample had much fewer bioconstituents than fresh C. sinensis plant samples.

Использование элементоорганических соединений некоторых элементов III, V групп и пероксидов в синтезе органических соединений и полимеров. Памяти профессора В.А. Додонова

Professor Viktor Alekseevich Dodonov (11.07.1933 – 27.09.2021) was the Head of the Department of Organic Chemistry of the Chemical Faculty of Lobachevsky State University of Nizhny Novgorod from 1971 to 2016. He was an Honored Scientist of the Russian Federation, full member of the Academy of Engineering Sciences of the Russian Federation, Fulbright Professor, the author of 42 patents, 500 scientific articles, the Head of the Scientific and Pedagogical school “Organic and organoelement chemistry: radical reactions in the liquid phase”. He synthesized new classes of organic and organoelement peroxides based on non-transition elements. He created unique adhesives based on an amine complex with an organoboronic compound, capable of gluing polymers with low surface energy at room temperature (polyethylene, polypropylene, polyvinyl chloride, and especially Teflon). He showed the possibility of oxidation of hydrocarbons and their derivatives (alkanes, alkenes, alkyl-substituted aromatic hydrocarbons, alcohols, ketones, ethers and esters, and sulfides) at room temperature with tert-butylhydroperoxide in the presence of the aluminum and bismuth compounds. He found that under certain conditions the air oxygen became the main participant in the reaction, while peroxide and metal act as catalysts. He used phenyl derivatives of antimony and bismuth under metal complex catalysis by copper and palladium compounds for selective O-, N-, C-phenylation of organic substances including OH, NH, C=C-H groups under mild conditions at 20–50 °C. He studied the processes of gas-phase decomposition of organometallic compounds of chromium and nickel in order to obtain metal-containing (metallic, carbide, oxide) films and coatings.

Ethyl ester/acyl hydrazide-based aromatic sulfonamides: facile synthesis, structural characterization, electrochemical measurements and theoretical studies as effective corrosion inhibitors for mild steel in 1.0 M HCl.

In this research paper, aromatic sulfonamide-derived ethyl ester (p-TSAE) and its acyl hydrazide (p-TSAH) were directly synthesized, characterized, and employed for the first time as prospective anticorrosive agents to protect mild steel in 1.0 M HCl conditions. The corrosion efficiency was probed by electrochemical methods including polarization, impedance, and frequency modulation measurements. Optimal efficiencies of 94% and 92% were detected for the hydrazide and ester, respectively, revealing excellent corrosion inhibition. Moreover, both the hydrazide and ester molecules combat the cathodic and anodic reactions correspondingly in a mixed-type manner. The electron transfer (ET) at the inhibitor/metal interface was evaluated using DFT at the B3LYP/6-31g(d,p) level. Natural bond orbital analysis (NBO) and frontier molecular orbital analysis (FMO) calculations showed superior capabilities of the synthesized inhibitors to easily reallocate charge into the metal surface. However, the hydrazide molecules showed slightly better inhibition efficiency than the ester due to the strong interaction between the lone pairs of the nitrogen atoms and the d-orbitals of the metal. The chemical hardness of the hydrazide and ester are 2.507 and 2.511 eV, respectively, in good accordance with the recorded electrochemical inhibition efficiencies for both molecules. Good and straightforward correlations between the experiments and calculations are obtained.

IN VITRO ANTILEUKEMIC ACTIVITY OF EUPHORBIA ECHINUS EXTRACT

Aim. Cancer continues to pose a serious threat to human health. Euphorbia plants are rich in phenolics, aromatic esters, steroids and several bioactive compounds. Studies have shown the presence of a large number of bioactive compounds in E. echinus including flavonoids, phenolics, and proanthocyanins. Method. There it was investigated cytotoxic effects of E. echinus methanolic extract on K562, HL60, Ishikawa, Raji and SH-SY5Y cells. Results. The E. echinus extract was found to be highly cytotoxic against HL60 and K562 (79.78 and 76.44% cytotoxicity, respectively). DNA fragmentation was exclusively observed in K562 cells indicating that the reduction of viable cells following treatment with E. echinus extract is due to apoptosis. Conclusions. Our results suggest that E. echinus extract might have a drug potential against leukemic cells.

Phytochemical Screening, Antifungal, and Anticancer Activities of Medicinal Plants Thymelaea Hirsuta, Urginea Maritima, and Plantago Albicans.

Ethyl acetate, ethanol, and acetone extracts of the medicinal plants Thymelaea hirsuta L., Urginea maritima L., and Plantago albicans L. (aerial parts) were evaluated for their phytochemical compositions, antimycotic activity against dermatophytes, and antiproliferative activity against different human cancer cell lines. Among them, the ethanolic extracts showed the highest phytochemical contents along with hyperactivities and were then selected for gas chromatography-mass spectrometry and Fourier-transform infrared spectroscopy analysis. The Fourier-transform infrared spectroscopy analysis confirmed the presence of different characteristic peak values with various functional chemical groups of the active components. However, U. maritima extracts through Fourier-transform infrared spectroscopy analysis showed distinctive peaks related to phenolic, amines, amides, aromatic, alkanes, alkyne, cyclopentanone, conjugated aldehyde, nitro, methoxy, uronic acids, aromatic esters, tertiary alcohol or ester, secondary and primary alcohols, aliphatic ether, sulfoxide, vinylidene, and halo compounds. Many bioactive main compounds with reported biological activities were detected by GC/MS (%) in the ethanolic extract of T. hirsuta, U. maritima, and P. albicans. All studied dermatophytes included a diverse set of virulence factors, including phospholipase, protease, keratinase, hemolysis, and melanoid production, all of which play vital roles in dermatophytic infection. Ethanolic extract of P. albicans inhibited the growth of Trichophyton soudanense totally and Trichophyton erinacei in addition to all Microsporum species. In contrast, the ethanolic extract of Trichophyton hirsuta at concentrations of 25 g/mL totally prevented the growth of all Trichophyton species. EtOH extract of U. maritima completely prevented the growth (100% inhibition) of all dermatophytic strains under study at the lowest concentration of 12.5 μg/mL. Scanning electron microscope analysis revealed considerable morphological modifications and structural alterations in dermatophyte species exposed to ethanolic extract of these plants. The viability of HCT-116, HepG-2, MCF-7, and HeLa cell lines was reduced after treatment with the ethanolic extracts of T. hirsuta, U. maritima, and P. albicans individually with IC50 values (10.0, 9.97, 48.5, and 56.24 μg/mL), (26.98, 25.0, 17.11, and 9.52 μg/mL), and (9.32, 7.46, 12.50, and 16.32 μg/mL), respectively. Our work revealed the significance of these traditional ethnomedical plants as potent sources for biologically active pharmaceuticals with potential applicability for the treatment of fungal and cancer diseases.

Chemical Structure and Antifungal Activity of Agean Region of Propolis in Türkiye

The chemical composition of propolis from Aegean Uşak (Balcıdamı and Kaşbelen), Afyon ( Emirdağ and Dinar), Manisa (Salihli and Kula), Denizli (Merkez and Çivril), Muğla (Milas and Merkez), İzmir (Kemalpaşa and Menemen), Aydın (Söke and Kuşadası) and Kütahya (Hisarcık and Tavşanlı) was studied in order to determine the major compounds by using GC-MS. In this study, 8 % ethanol extract of propolis prepared by mixing 920 ml of 70 % ethanol and 80 g of propolis was used. Chemical analysis of propolis extracts indicated that the propolis samples had high concentrations of the aromatic acids, esters and other derivatives which are responsible for the antibacterial, antifungal, antiviral, anti-inflammatory and anti-cancer properties of propolis such as benzyl cinnamate, methyl cinnamate, caffeic acid, cinnamyl cinnamate and cinnamoylglcine besides the most common compounds as fatty acid, terpenoids, esters, alcohols hydrocarbons and aromatic acids. Also, in this research the antifungal effects of 7 concentrations (6.25, 12.5, 25, 50 ppm) of propolis ethanol extract (PEE) against Fusarium oxysporum was investigated in vitro conditions. Propolis was mixed alone or in combination with potato dextrose agar (PDA) medium at various concentrations. The results indicated that the mycelial growth of the tested fungi decreased with each increase in PEE concentrations. Propolis extract collected from Muğla province showed 77.81% antifungal effect against Fusarium oxysporum at the highest concentration (50 ppm). The lowest antifungal effect (64.52%) against the pathogen was detected in the propolis extract collected from Denizli province.

Changes in Key Aroma Compounds and Esterase Activity of Monascus-Fermented Cheese across a 30-Day Ripening Period.

Monascus-fermented cheese (MC) is a new type of mold-ripened cheese that combines a traditional Chinese fermentation fungus, Monascus purpureus M1, with Western cheese fermentation techniques. In this study, the compositions of the volatile aroma compounds in MC were analyzed during a 30-day ripening period using SPME-Arrow and GC-O-MS. The activity of esterase in MC, which is a key enzyme catalyzing esterification reaction, was determined and compared with the control group (CC). Next, sensory analysis was conducted via quantitative descriptive analysis followed by Pearson correlation analysis between esterase activity and the key flavor compounds. A total of 76 compounds were detected. Thirty-three of these compounds could be smelled at the sniffing port and were identified as the key aroma compounds. The esterase activity in MC was found to be 1.24~1.33 times that of the CC. Moreover, the key odor features of ripened MC were alcohol and fruity flavors, considerably deviating from the sour and cheesy features found for the ripened CC. Furthermore, correlation analysis showed that esterase activity was strongly correlated (|r|> 0.75, p < 0.05) with various acids such as pentanoic and nonanoic acids and several aromatic esters, namely, octanoic acid ethyl ester and decanoic acid ethyl ester, revealing the key role that esterases play in developing the typical aroma of ripened MC.

A broad specificity β-propeller enzyme from Rhodopseudomonas palustris that hydrolyzes many lactones including γ-valerolactone

Lactones are prevalent in biological and industrial settings, yet there is a lack of information regarding enzymes used to metabolize these compounds. One compound, γ-valerolactone (GVL), is used as a solvent to dissolve plant cell walls into sugars and aromatic molecules for subsequent microbial conversion to fuels and chemicals. Despite the promise of GVL as a renewable solvent for biomass deconstruction, residual GVL can be toxic to microbial fermentation. Here, we identified a Ca2+-dependent enzyme from Rhodopseudomonas palustris (Rpa3624) and showed that it can hydrolyze aliphatic and aromatic lactones and esters, including GVL. Maximum-likelihood phylogenetic analysis of other related lactonases with experimentally determined substrate preferences shows that Rpa3624 separates by sequence motifs into a subclade with preference for hydrophobic substrates. Additionally, we solved crystal structures of this β-propeller enzyme separately with either phosphate, an inhibitor, or a mixture of GVL and products to define an active site where calcium-bound water and calcium-bound aspartic and glutamic acid residues make close contact with substrate and product. Our kinetic characterization of WT and mutant enzymes combined with structural insights inform a reaction mechanism that centers around activation of a calcium-bound water molecule promoted by general base catalysis and close contacts with substrate and a potential intermediate. Similarity of Rpa3624 with other β-propeller lactonases suggests this mechanism may be relevant for other members of this emerging class of versatile catalysts.

Co-pyrolysis of waste polyester enameled wires and polyvinyl chloride: Evolved products and pyrolysis mechanism analysis

Waste enameled copper wire is an important secondary source of copper and often recovered by removing their organic paint layer through pyrolysis. This research focused on studying co-pyrolysis behaviors of poly(ethylene terephthalate) (PET) paint of waste enameled wires, mixed with a small amount of polyvinyl chloride (PVC) which is part of electric wires or cables. The results indicated that mixing PVC with a mass fraction of 10% into enameled PET wire paint (EPET) would significantly affect pyrolysis products, especially the chlorinated compounds, as well as increase energy consumption of the pyrolysis process. TG-FTIR and Py-GC/MS analyses showed that the chlorinated organics were mainly generated in the second stage of pyrolysis. Chloroesters such as terephthalic acid, di(2-chloroethyl) ester were dominant over other chloroorganic compounds, and their formations were attributed to the addition reaction of aromatic vinyl esters with HCl which formed from PVC pyrolysis. It is also worth mentioning that the chemically active acid chlorides including propanoyl chloride and benzoyl chloride were detected in the products, and they were proposed to be formed from the HCl acidolysis of esters that produced from pyrolytic EPET. Besides pyrolysis products, energy consumption of pyrolysis process also was closely correlated to the interactions between pyrolytic PVC and EPET. The average co-pyrolysis activation energy was calculated by Kissinger-Akahira-Sunose (KAS) method and was about 15 kJ/mol higher than that of EPET. These should be consequences of reactions between HCl and EPET. Since PVC is the minority component in the pyrolysis mixture that HCl eliminated from the few PVC was mostly consumed by EPET to form chloroorganic compounds, which negatively influences EPET degradation.

Synergetic Effect of Metschnikowia pulcherrima and Lachancea thermotolerans in Acidification and Aroma Compounds in Airén Wines.

On the one hand, the species Lachancea thermotolerans is known for its high genetic diversity, allowing for the existence of strains that produce high concentrations of lactic acid. In contrast, the species Metschnikowia pulcherrima is renowned for its high enzymatic activity capable of producing aromatic esters during fermentation. By enhancing acidity and boosting the concentration of aromatic compounds, both species are currently used to enhance the organoleptic profile of wines. In this regard, ternary fermentations with M. pulcherrima and L. thermotolerans were carried out and the wines produced were further analysed with GC-FID, FTIR, and UV-Vis spectrophotometry. The outcomes showed that the species M. pulcherrima favored an increase in ethyl lactate (between 37 and 41 mg/L) along with an increased concentration of 2-phenylethyl alcohol (between 30 and 35 mg/L), whereas the species L. thermotolerans was able to produce 1 g/L of lactic acid in ternary fermentations. Additionally, pH levels were slightly lower in these fermentations and the color of the white wines produced showed less chemical oxidation as hue values were lower than the control. Finally, the ternary fermentations of L. thermotolerans and M. pulcherrima had higher overall rating in the tasting. In conclusion, ternary fermentations involving these two non-Saccharomyces species are suggested as a substitute for spontaneous fermentations in the production of wines from neutral varieties to express freshness more vividly. This biotechnology may be further favored by the possibility of applying emerging technologies for the removal of microorganisms in grapes and musts.

A facile, alternative and sustainable feedstock for transparent polyurethane elastomers from chemical recycling waste PET in high-efficient way

Polymers with excellent optical and mechanical performance fabricated from renewable resources, have been paid an increasing attention in recent years. Here, high-performing polyurethane elastomers with significant mechanical properties, crystallinity, excellent stretchability and good transparency are prepared by a synergistic molecular design in the soft and hard segments. Using the liquid glycolysis degradation product (LGOP) as a chain extender, polyurethane elastomer is synthesized from polyethylene terephthalate (PET) waste bottles. The results suggest that the degradation products from waste PET can be directly used as feedstock for preparing polyurethane elastomers with significant performance. The polyurethanes exhibited excellent optical transparency of near 90%, and can be stretched up to 670% without any treatment to return to original size. It is assumed that the symmetrical hard domain composed of aromatic rings and ester groups in LGOP creates sufficient chain fluidity for the dynamic exchange of hydrogen bonds and urethane. This paper has devoted to achieve a complete and mature system from waste PET to polyurethane products, to create a closed loop of waste PET plastic recycling and regeneration, and to realize the polyurethane industrial chain of raw material self-supply.

Enhanced MOF-immobilized lipase CAL-A with polyethylene glycol for efficient stereoselective hydrolysis of aromatic acid esters

Enzyme immobilization is promising in the development of a lipase-catalyzed process for industrial application. The covalent linkage can effectively enhance the interaction between the enzymes and the supports. However, the covalent linkage may reduce the activity of the enzyme. In this work, lipase A from Candida antarctica (CAL-A) was immobilized on a series of MOFs-supports via covalent linkage. The polyethylene glycol (PEG) was surrounded with the CAL-A by the supramolecular interaction for protecting the enzyme activity during the immobilization process thus enhancing the catalytic performance. The optimal immobilized CAL-A was characterized and the catalytic performance was further investigated in lipase catalyzed kinetic resolution of chiral aromatic acids. Benefitting from the stable interaction between the CAL-A and MOF supports and the excellent protection of PEG, the PEG-CAL-A@UiO-66 exhibited enhanced catalytic activity, stability and reusability. The PEG-CAL-A@UiO-66 was applied to stereoselective hydrolysis of 2-phenylbutyric acid isobutyl ester, where yield (YS) and enantiomeric excess (eep) of (S)− 2-PBA reached 91.71% and ＞99.0%, respectively. The loss of enzyme activity after three cycles of reuse was negligible and 47.16% of the initial activity was retained after five cycles of reuse. We believe this effective technique is meaningful for constructing heterogeneous biocatalysts for industrial applications.

A Photochemical Macrocyclization Route to Asymmetric Strained [3.2] Paracyclophanes.

The intricate frameworks of paracyclophanes are an important target for synthesis since they are found in various chiral auxiliaries, solar cells, high-performance plastics, pharmaceuticals, and molecular machines. Whereas numerous methods exist for the preparation of symmetric paracyclophanes, protocols for the efficient synthesis of strained asymmetric scaffolds are limited. Here we report a remarkably simple photochemical route to strained [3.2]paracyclophanes starting from readily available educts. By way of NMR and X-ray analyses, we discovered that UV-irradiation of an aromatic carboxylic ester tethered to a toluene moiety leads to the intramolecular formation of a new C-C bond, with loss of an alcohol. A systematic evaluation of the reaction conditions and substituents, as well as radical starter and triplet quenching experiments, point to a reaction mechanism involving an excited triplet state and hydrogen atom transfer. The new method proved to be robust and versatile enabling the synthesis of a range of cyclophanes with different substitutions, including an unusual diastereoisomer with two planar chiral centers, and thus proved to be a valuable addition to the synthetic toolbox.

Insights into the evolution of chemical structures in hydrochars from hydrothermal carbonization of PVC

Hydrothermal carbonization (HTC) treatment can induce the comprehensive evolution of PVC structure, which broadens the horizons for the development and optimization of hydrochars derived from PVC. However, there is a lack of understanding of the evolution of chemical structure in hydrochars during the HTC reactions. In this work, the dynamic evolution of the chemical structure of hydrochars during HTC at 220–260 °C within 60 min was comprehensively studied by ultimate analysis, XPS and FTIR. The results showed that hydrothermal temperature had a significant effect on the chemical structure of hydrochars. Raising the hydrothermal temperature facilitated the conversion of C–Cl and C–C/C–H of PVC to C–O, CO, OC–O and CC/C-(C, H), respectively. Under the combined action of hydrolysis, oxidation, aromatization, polymerization and esterification reactions, the hydrochar presented an alicyclic and aromatic structure with different degrees of condensation as its backbone structure. The main oxygen-containing functional groups of the hydrochar were aromatic ethers (C–O), hydroxyl groups (-OH), carboxylic acids (-COOH), and ester groups (-COOR). The maturity of hydrochar was close to that of lignite. Overall, this study provides helpful information for the preparation of diverse value-added products, and also for developing a molecular model of hydrochar for in-depth investigation of the HTC mechanism of PVC.

Multicomponent Reaction: Palladium-Catalyzed Carbonylation of Aryl Halides and Alkyl Halides to Aromatic Esters.

A convenient four-component reaction has been developed that allows for the direct transformation of aryl iodides with alkyl halides into the corresponding aromatic esters and diesters via palladium-catalyzed carbonylation with water as solvent. Various esters and diesters were isolated in moderate to good yields with broad functional group tolerance.

Advanced Molecular Tweezers with Lipid Anchors against SARS-CoV-2 and Other Respiratory Viruses.

The COVID-19 pandemic caused by SARS-CoV-2 presents a global health emergency. Therapeutic options against SARS-CoV-2 are still very limited but urgently required. Molecular tweezers are supramolecular agents that destabilize the envelope of viruses resulting in a loss of viral infectivity. Here, we show that first-generation tweezers, CLR01 and CLR05, disrupt the SARS-CoV-2 envelope and abrogate viral infectivity. To increase the antiviral activity, a series of 34 advanced molecular tweezers were synthesized by insertion of aliphatic or aromatic ester groups on the phosphate moieties of the parent molecule CLR01. A structure-activity relationship study enabled the identification of tweezers with a markedly enhanced ability to destroy lipid bilayers and to suppress SARS-CoV-2 infection. Selected tweezer derivatives retain activity in airway mucus and inactivate the SARS-CoV-2 wildtype and variants of concern as well as respiratory syncytial, influenza, and measles viruses. Moreover, inhibitory activity of advanced tweezers against respiratory syncytial virus and SARS-CoV-2 was confirmed in mice. Thus, potentiated tweezers are broad-spectrum antiviral agents with great prospects for clinical development to combat highly pathogenic viruses.

DABCO-mediated synthesis of aromatic esters from phenols, naphthols or 3-hydroxypyridines and aryl acyl peroxides at room temperature

DABCO-mediated synthesis of aromatic esters from phenols, naphthols or 3-hydroxypyridines and aryl acyl peroxides at room temperature

Co-inoculations of Lachancea thermotolerans with different Hanseniaspora spp.: Acidification, aroma, biocompatibility, and effects of nutrients in wine

The use of non-Saccharomyces yeast in the winemaking industry and even more their co-inoculations to maximize their growth and to express phenotypic characteristic is gaining more and more relevance. This study aimed to shed light on the biocompatibilities between Lachancea thermotolerans and Hanseniaspora spp., using different types of nutrients and considering the effect on Yeast Assimilable Nitrogen (YAN), at low temperature (16 °C) and medium SO2 (50 mg/L), in white must. L. thermotolerans has been used for its positive effect on pH reduction and Hanseniaspora spp. for improving the sensory profile. The behaviour of these yeasts was evaluated in co-inoculation, always finishing the fermentation with the sequential inoculation of S. cerevisiae. Significant results were obtained on the population count (CFU/mL) in CHROMagar™, with higher populations of Hanseniaspora spp. with respect to L. thermotolerans. Fermentations with L. thermotolerans/H. vineae, showed inhibition of acidification, generating up to 0.41 g/L of lactic acid. On the contrary, a synergistic effect when L. thermotolerans/H. opuntiae was used, achieved 2.44 g/L of lactic acid and a pH reduction of up to 0.16 and always more significant with Nutrient Vit BlancTM. At the same time ethanol concentration decreased by 3.4 % and volatile acidity never exceeded 0.5 g/L. Aromatic composition was analysed and it was found that all fermentations retained more aromatic esters and that on day 7 the amount of 2-phenylethyl acetate was at least 3 times higher in all fermentations compared to the control (Sc + Nutrient Vit BlancTM) which had 5.96 mg/L. Less yellow intensity (-17.3 %) typical of oxidation were observed in all fermentations in which Nutrient Vit BlancTM had been used and in the sensory analysis the co-inoculations with H. vineae generated better scores.

Comparative analysis of sugar, acid, and volatile compounds in CPPU-treated and honeybee-pollinated melon fruits during different developmental stages

Plant growth regulator N-(2-chloro-4-pyridyl)-N′-phenylurea (CPPU) is widely used in fruit production. However, the mechanism in which CPPU affects melon fruit quality, especially aroma compound, remains unclear. Here, gas chromatography–mass spectrometry was performed to detect the sugar, citric acid, and aroma content in CPPU-treated and pollinated melon fruit. Results showed that the application of CPPU decreased the sugar and aroma content in melon fruit. The relative content of several important esters, including isobutyl acetate, ethyl acetate, 2-methylbutyl acetate, methyl acetate, benzyl acetate, and phenethyl acetate, in CPPU-treated fruits was significantly lower than that in honeybee-pollinated fruits. The content of many amino acids (isoleucine, leucine, valine, methionine, and l-phenylalanine), which could be metabolized into aroma compounds, in CPPU-treated fruits was significantly higher than that in honeybee-pollinated fruits. In conclusion, CPPU application interferes with amino-acid metabolism and affects the production of aromatic esters in melon fruit.