The formation mechanism of aroma quality of green and yellow teas based on GC-MS/MS metabolomics

Aroma is a crucial determinant of tea quality. While some studies have examined the aroma of yellow tea, there are no reports of the difference and formation mechanism of aroma quality between yellow and green teas from the same tea tree variety. This study employed gas chromatography-mass spectrometry to investigate the difference and formation mechanism of the aroma of yellow and green tea at the omics level, based on sensory evaluation. The sensory evaluation revealed that green tea has a distinct faint scent and bean aroma, while yellow tea, which was yellowed for 48 h, has a noticeable corn aroma and sweet fragrance. A total of 79 volatile metabolites were detected in the processing of yellow and green tea, covering 11 subclasses and 27 were differential volatile metabolites. Benzoic acid, 2-(methylamino-), methyl ester, terpinen-4-ol ethanone, 1-(1H-pyrrol-2-yl-), 3-penten-2-one, 4-methyl- and benzaldehyde were characteristic components of the difference in aroma quality between green and yellow teas. Eleven volatile metabolites significantly contributed to the aroma quality of green and yellow teas, especially acetic acid, 2-phenylethyl ester, with rose and fruity aromas. KEGG enrichment analysis showed that the arginine and proline metabolism might be the key mechanism of aroma formation during green and yellow teas' processing. These finding provide a theoretical basis way for the aroma formation of green and yellow teas.

Melatonin treatment delays postharvest senescence of broccoli with regulation of carotenoid metabolism

The effect of melatonin treatment on the carotenoid metabolism in broccoli florets during storage was explored. The results indicated that 100 µmol/L of melatonin maintained the sensory quality of broccoli florets, which retarded the increase of the L* value and the decrease of the H value. Melatonin treatment increased the activities of tryptophan decarboxylase (TDC), tryptamine 5-hydroxylase (T5H), serotonin N-acetyltransferase (SNAT) and N-acetylserotonin methyltransferase (ASMT), leading to the enrichment of endogenous melatonin content in broccoli florets. Meanwhile, the treatment inhibited the concentrations of β-carotene, β-cryptoxanthin, zeaxanthin and lutein, which was beneficial in delaying the yellowing of broccoli. In addition, a series of carotenoid biosynthetic genes such as BoPSY, BoPDS, BoZDS, BoLCYβ and BoZEP was also suppressed by melatonin. Further analysis revealed that the lower carotenoid content and the down-regulated BoNCED expression in treated broccoli resulted in less accumulation of abscisic acid precursors, inhibiting abscisic acid production during the yellowing process.

Fingerprints and changes analysis of volatile compounds in fresh-cut yam during yellowing process by using HS-GC-IMS

The purpose of this study was to investigate the dynamic change in volatile components during the yellowing process. The volatile components were analyzed by headspace gas chromatography-ion mobility spectrometry (HS-GC-IMS) and the critical enzyme activities were determined by commercial kits. The results revealed that 29 signal peaks for 20 compounds were identified, which were quantified in all samples: 1 furan, 1 ester, 15 aldehydes, 3 ketones, and 9 alcohols. The contents of most of these compounds increased first and then decreased at 36 h, which were basically consistent with the enzyme activities of LOX, HPL, ADH and AAT. Subsequently, principal component analysis (PCA) results clearly showed that the fresh-cut yams for different yellowing processes were well distinguished by the volatile compounds. These results showed that the potential of HS-GC-IMS-based approaches to evaluate the volatile compound profiles of fresh-cut yam at different stages in the yellowing period.

Efficacy of bioagents against Pythium deliense Meurs associated with yellowing of black pepper

Yellowing and wilting of black pepper vines is a serious concern in many black pepper growing tracts where Pythium deliense was recently emerged as a pathogen from the rhizosphere of affected vines, which is proved to be pathogenic by Koch's postulates. As a measure to manage the symptoms, bioagents were evaluated against infection by P. deliense. Among the seven bioagents tested, Trichoderma harzianum and Streptomyces albulus showed 100% inhibition in vitro followed by one Streptomyces sp. and S. rimosus (75.33%). The potential ones were further evaluated under the hydroponic system in vivo by challenge inoculation. No root infection was noticed with T. harzianum and S. albulus inoculation, instead, the inoculated plants showed root regeneration. This suggests the efficiency of these bioagents on plant growth promotion as well as on disease suppression. Biochemical analysis of the hydroponic medium showed an increase in membrane conductivity in all the treatments except in T. harzianum. The release of phenolic compounds into the medium was lowest with T. harzianum indicating the prevention of pathogen invasion. In planta evaluation under greenhouse condition and field evaluation also showed the protective effect of T. harzianum and S. albulus with a reduction in the intensity of yellowing to an extent of 73.1% and 71.2%, respectively. The study revealed that T. harzianum and the actinomycete S. albulus had the potential to prevent the root rot caused by P. deliense.

On nitrogen fixation and "residual nitrogen content" in cellulosic pulps

Cellulosic material is capable of permanently retaining nitrogen compounds (mostly having amino functions), which is reflected in a residual nitrogen content (in the low per mille range to the low percent range) of some pulps and certain lab samples. Merely adsorptively bound compounds can be removed by mild acidic washing, but part of the nitrogen seems to be resistant and very tightly bound, and thus not accessible for removal by washing. Tertiary and aromatic amines are not retained in this way, but only primary and secondary amines. There is only a weak correlation between the "firmly bound nitrogen" and the carbonyl content in cellulosics (because of oxidative damage), so that possible aminal, Schiff base and enamine structures can hardly be relevant as major nitrogen sources. However, there is a very good linear correlation between the ISO brightness (chromophore content) in aged pulps and the residual nitrogen content. In particular the concentration of the cellulosic key chromophore 2,5-dihydroxy-[1,4]-benzoquinone (DHBQ) determines the permanent N-binding capacity of the pulp. DHBQ reacts very readily with primary and secondary amines under ambient conditions to 2,5-diamino-substituted [1,4]-benzoquinones, which have very low solubility (because of zwitterionic resonance contributions) and thus remain on/in the pulp. Examples of nitrogen fixation in pulps are the binding of piperidine (a common amine catalyst in derivatization reactions), amine degradation products of the cellulose solvent NMMO, dimethylamine in materials processed from the cellulose solvent DMAc/LiCl, imidazole (a degradation product of 1-alkyl-3-methylimidazolium ionic liquids), and of amino groups in proteins after enzymatic treatment. The nature of the respective DHBQ-amine addition compound has been verified by complete structure determination.

Analysis of secondary metabolites induced by yellowing process for understanding rice yellowing mechanism

The current study applied wide-targeted metabolomics based approach using LC-ESI-MS/MS to characterize the secondary metabolic difference between yellowed and normal rice. The results indicated that the biosynthesis of secondary metabolites including flavonoids, flavonols and phenolic acids was significantly enhanced during the rice yellowing process, which appears to be highly managed by phenylpropanoid metabolism and flavonoid biosynthetic pathways. Furthermore, rice yellowing led to an increased color parameter b* value, and a number of increased secondary metabolites in the yellowed rice such as homoeriodictyol, naringenin chalcone, 4,2',4',6'-tetrahydroxychalcone contributed to the yellow color. These may have application as potential biomarkers for characterizing rice yellowing.

Chlorophyll degradation and carotenoid biosynthetic pathways: Gene expression and pigment content in broccoli during yellowing

Broccoli undergoes yellowing in unfavorable conditions, thereby diminishing the sensory quality and commodity value. This study aimed to investigate systematically cellular and/or biomolecular changes involved in broccoli yellowing by analyzing changes in microstructural integrity, pigment content, and gene expression. On day-5 of storage at 20 °C, the buds turned yellow without blooming and showed structural damage; ultrastructural analysis revealed plastid transformation and abnormal chloroplast development. Genes regulating pigment content and chloroplast structure directly were identified. More specifically, BoCAO and BoNYC1 regulated chlorophyll turnover, affecting chlorophyll a and b contents. Changes in the β-cryptoxanthin content were influenced by the combined action of up- (BoHYD) and downstream (BoZEP) genes. BoZEP and BoVDE were activated after cold-temperature induction. High BoHO1 expression delayed yellowing at low temperature, inducing BoZEP expression. Color intensity correlated significantly with the chlorophyll b, β-cryptoxanthin, and β-carotene contents, which were associated with increased yellowing of plant tissues.

Association of a 'Candidatus Phytoplasma aurantifolia'-related strain with apricot showing European stone fruit yellows symptoms in Iran

During 2012-2015 surveys in some orchards in Faraghe (Iran), a number of apricot trees showed symptoms resembling those associated with the phytoplasma disease known as European stone fruit yellows that are severe leaf roll, yellowing and die back. The presence of an infectious agent was confirmed by graft transmission experiments in which all the previously symptomless GF-677 (peach × almond) trees showed phytoplasma-type symptoms. The phytoplasma presence was confirmed by nested PCR assays using DNA extracted from samples from both field collected and graft-inoculated trees. The sequences of four nested PCR products from symptomatic apricot and experimentally graft-inoculated GF-677 trees were 100% identical to each other. RFLP and phylogenetic analyses carried out on these sequences allowed to cluster the strain infecting apricot trees in Iran with the16SrII-C subgroup phytoplasmas. This is the first report of a 16SrII-C phytoplasma associated with leaf roll and yellowing of the leaves in apricot trees.

Pushing the limits: Quantification of chromophores in real-world paper samples by GC-ECD and EI-GC-MS

Widening the methodology of chromophore analysis in pulp and paper science, a sensitive gas-chromatographic approach with electron-capture detection is presented and applied to model samples and real-world historic paper material. Trifluoroacetic anhydride was used for derivatization of the chromophore target compounds. The derivative formation was confirmed by NMR and accurate mass analysis. The method successfully detects and quantifies hydroxyquinones which are key chromophores in cellulosic matrices. The analytical figures of merit appeared to be in an acceptable range with an LOD down to approx. 60ng/g for each key chromophore, which allows for their successful detection in historic sample material.

Generation of hydroxyl radicals and effective whitening of cotton fabrics by H2O2 under UVB irradiation

Chemically crosslinked cotton fabrics may show yellowish appearance, especially citric acid (CA) crosslinked ones. Hydrogen peroxide (H₂O₂) bleaching under alkaline condition could improve the whiteness of the CA-crosslinked cotton fabrics but sacrificing certain crosslinking performance of the products due to alkaline hydrolysis of ester connections. Regular H₂O₂ and UV irradiation (H₂O₂/UV) system can destroy color but also damage fibers due to the use of very short wavelength of UVC such as 254nm or shorter. Now, it was found that longer wavelength UV such as 312nm performed better in H₂O₂/UV systems on CA-crosslinked cotton fabrics. The reaction mechanism and potential product of the oxidation reaction on CA-crosslinked cotton were proposed and demonstrated. UV-vis spectrophotometer and Fourier transform infrared spectroscopy provided key evidence. Whiteness, wrinkle recovery angle and tensile strength of the fabrics were evaluated, and the results support the mechanism. The process is environmentally friendly and highly efficient.

Pepo aphid-borne yellows virus: a new species in the genus Polerovirus

Pepo aphid-borne yellows virus (PABYV) has been proposed as a putative representative of a new species in the genus Polerovirus in the family Luteoviridae. The genomes of two South African (SA) isolates of cucurbit-infecting PABYV were described in this record. Total RNA, extracted from a pattypan (Cucurbita pepo L.) and a baby marrow (C. pepo L.) leaf samples, was subjected to next-generation sequencing (NGS) on the HiSeq Illumina platform. Sanger sequencing was subsequently used to authenticate the integrity of PABYV's genome generated from de novo assembly of the NGS data. PABYV genome of SA isolates consists of 5813 nucleotides and displays an organisation typical of poleroviruses. Genome sequence comparisons of the SA PABYV isolates to other poleroviruses support the classification of PABYV as a new species in the genus Polerovirus. Recombination analyses showed that PABYV and Cucurbit aphid-borne yellows virus (CABYV) shared the same ancestor for the genome part situated between breaking points. Phylogenetic analyses of the RNA-dependent RNA polymerase and the coat protein genes showed that SA PABYV isolates shared distant relationship with CABYV and Suakwa aphid-borne yellows virus. Based on our results, we propose that PABYV is a distinct species in the genus Polerovirus.

Virulence determination and molecular features of peach latent mosaic viroid isolates derived from phenotypically different peach leaves: a nucleotide polymorphism in L11 contributes to symptom alteration

Symptoms of chlorosis along leaf edges (chlorosis-edge), along leaf veins (chlorosis-vein) and yellowing on peach leaves have been observed for a long history in the field, while the pathological factor(s) responsible for these symptoms remained unknown. Peach latent mosaic viroid (PLMVd) was detected in the leaves collected from three unique phenotypic peach trees showing above mentioned symptoms. The obtained PLMVd isolates were subjected to population structure analyses and biological assays to evaluate their pathogenicity on peach seedlings in an effort to elucidate the relationship between the PLMVd and the symptoms observed on peach trees in China. In addition, molecular features of PLMVd isolates were analyzed to obtain some insight into the structure-function relationships of this viroid. The results revealed that the symptoms of chlorosis-edge and yellowing were indeed incited by PLMVd, and a direct link between the nucleotide polymorphisms and the symptoms of yellowing and chlorosis-edge was established, i.e. residue U338 responsible for the yellowish symptom and C338 responsible for the chlorosis-edge symptom. This study provides an additional proof to endorse a previous proposal that PLMVd pathogenicity determinants reside in L11. The illustrative etiology of the disease, visualization of the symptoms progression and identification of the unique single nucleotide polymorphism possibly involved in the symptom induction will significantly increase understanding of the pathogenic mechanisms of PLMVd and will help in designing control strategies for the resulting disease.