Headspace Volatiles and Endogenous Extracts of Prunus mume Cultivars with Different Aroma Types

The effects of core microorganism community on flavor compounds and active substances during the aging process of Citri Reticulatae Pericarpium

Citri Reticulatae Pericarpium (CRP) is a traditional herbal and food spice, the flavor and active compounds content of Xinhui CRP improves with aging. To investigate the pattern of microbial community succession during the aging of Xinhui CRP and its correlation with changes in flavor compounds, the high-throughput sequencing, HPLC, and GC-IMS were used to analyze the microbial community, flavonoids, and flavor compounds of five different aging years in this study. The results revealed different dominant microbial communities in Xinhui CRP at different aging time, and unclassified Bacteria were the predominant bacterial genus during 10-15 years of aging. As the aging time increases, the abundance of microbial community decreases and gradually stabilizes. At the fungal genus level, Xeromyces (>99 %) were the dominant genus during the 10-15 years aging time and had a significant correlation with polymethoxyflavones (PMFs), and the concentrations of PMFs increased with the progression of aging years. The GC-IMS results revealed distinctive flavor profiles in Xinhui CRP across different aging years, floral and fruity aromas, such as heptanal, 3-methyl-3-butenol, and 1-butanol, among others, with increasing aging years. A comprehensive correlation analysis further elucidates the close relationship between the core microorganism community and flavor formation in Xinhui CRP (p < 0.05). Notably, Pseudomonas and Escherichia Shigella exhibited significant correlations with beta-pinene and alpha-pinene, whereas Aureobasidium and Sarcopodium were associated with nerol and α-phellandrene (p < 0.05). This study provides new ideas for accelerating the good quality and flavor of Xinhui CRP during the aging process from the perspective of key microorganisms.

Electrohydrodynamic drying of citrus (Citrus sinensis L.) peel: Comparative evaluation on the physiochemical quality and volatile profiles

Based on the concept of circular economy, citrus peel was considered a valuable source of bioactive compounds for high-value foods. Electrohydrodynamic (EHD) drying is a novel technology appropriated for the dehydration of heat-sensitive products such as citrus peel. In current work, EHD drying of citrus peel was performed based on alternating current (AC) or direct current (DC) sources at various voltage levels (9, 18, 27, 36, and 45 kV). The effect of EHD on drying characteristics, water retention capacity, enzyme inactivation, phytochemical contents (phenolic compounds and carotenoids), and volatile compounds of citrus peel were evaluated and compared. Results showed that the drying time in the AC electric field was shorter compared to DC electric field at the same applied voltages due to the polarization layer formed by unipolar charges. The applied voltage determined electric field strength as well as the degree of tissue collapse and cell membrane rupture. EHD elucidated the transformation and degradation of phytochemicals including phenolic compounds, carotenoids, and volatile composition in proportion to the applied voltage. The findings indicate that EHD drying with AC improves drying behaviors, inactivates enzymes, and retains the phytochemical properties of citrus peel.

Determination of Volatile Organic Compounds and Endogenous Extracts and Study of Expression Patterns of TPS and BSMT in the Flowers of Seven Lilium Cultivars

Lily is one of the most important cut flowers in the world, with a rich floral fragrance. To further explore the fragrance emission mechanisms of lily cultivars, headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) and organic solvent extraction-gas chromatography-mass spectrometry (OSE-GC-MS) were used to unveil the volatile organic compounds (VOCs) and endogenous extracts of seven lily cultivars. Furthermore, real-time quantitative PCR (qRT-PCR) was used to determine the expression levels of two key genes (TPS and BSMT) related to the biosynthesis of monoterpenoids and methyl benzoate. The results show that forty-five VOCs were detected in the petals of seven lily cultivars, and the main compounds were monoterpenoids and phenylpropanoids/benzenoids. Dichloromethane was the best solvent for extracting the endogenous extracts of Lilium 'Viviana' petals and eighteen endogenous extracts were detected using dichloromethane to extract the petals of seven lily cultivars. Each compound's emission ratio (natural logarithm of the ratio of VOC content to endogenous extract content) was calculated, and linear regression analyses between emission ratios and boiling points were conducted. Significant linear negative correlations existed between the emission ratios and boiling points of compounds, and the regression equations' coefficients of determination (R2) were all greater than 0.7. TPS was expressed highly in 'Viviana', 'Pink News', and 'Palazzo', and BSMT was expressed highly in 'Pink News' and 'Palazzo'. Correlation analyses between the gene expression levels and the monoterpenoids and methyl benzoate contents found that the TPS expression levels have strong positive correlations with monoterpenoids content, while no correlations were found between the expression levels of BSMT and the contents of methyl benzoate. This study lays the foundation for research on the release patterns of VOCs in the flowers of Lilium, and the breeding of lilies for their floral fragrance.

Electronic Nose and Head Space GC-IMS Provide Insights into the Dynamic Changes and Regularity of Volatile Compounds in Zangju (Citrus reticulata cv. Manau Gan) Peel at Different Maturation Stages

Zangju (Citrus reticulata cv. Manau Gan) is the main citrus cultivar in Derong County, China, with unique aroma and flavour characteristics, but the use of Zangju peel (CRZP) is limited due to a lack of research on its peel. In this study, electronic nose, headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS), and partial least squares-discriminant analysis (PLS-DA) methods were used to rapidly and comprehensively evaluate the volatile compounds of dried CRZP and to analyse the role of dynamic changes at different maturation stages. The results showed that seventy-eight volatile compounds, mainly aldehydes (25.27%) and monoterpenes (55.88%), were found in the samples at four maturity stages. The contents of alcohols and aldehydes that produce unripe fruit aromas are relatively high in the immature stage (October to November), while the contents of monoterpenoids, ketones and esters in ripe fruit aromas are relatively high in the full ripening stage (January to February). The PLS-DA model results showed that the samples collected at different maturity stages could be effectively discriminated. The VIP method identified 12 key volatile compounds that could be used as flavour markers for CRZP samples collected at different maturity stages. Specifically, the relative volatile organic compounds (VOCs) content of CRZP harvested in October is the highest. This study provides a basis for a comprehensive understanding of the flavour characteristics of CRZP in the ripening process, the application of CRZP as a byproduct in industrial production (food, cosmetics, flavour and fragrance), and a reference for similar research on other C. reticulata varieties.

Novel application of HS-GC-IMS for characteristic fingerprints and flavor compound variations in Citrus reticulatae pericarpium during storage with different Aspergillus niger fermentation

Citrus reticulatae pericarpium (CRP) is regarded as a valuable functional food in many countries due to its pharmacological activities and unique aroma. In this study, CRP was treated by different A. niger to accelerate aging. Headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS) fingerprinting was adopted to rapidly and comprehensively evaluate the flavor compounds of CRP and to identify their dynamic changes at different storage time. Results revealed that the hesperidin content of DOL groups reduced more clearly than other groups during storage. A total of 134 volatile flavor compounds were identified. The volatile organic compounds (VOCs) showed that the lemon, sweet with the musk aroma of CRP, changed to apple, pineapple, and coffee odors during storage. The principal component analysis (PCA) and fingerprint similarity analysis (FSA) results showed that the CRP was clearly distinguished at different storage time. DOL-3 and DOS-6 differ the most from the DOW-3,6, respectively. This work provided helpful information for accelerating the aging of CRP and has great potential for industrial application.

Evaluation of Dynamic Changes and Regularity of Volatile Flavor Compounds for Different Green Plum (Prunus mume Sieb. et Zucc) Varieties during the Ripening Process by HS-GC-IMS with PLS-DA

Headspace gas chromatography-ion mobility spectrometry and partial-least-squares discriminant analysis (PLS-DA) were adopted to analyze the rule of change in flavor substances for different varieties of green plums at different levels of maturity (S1-immature, S2-commercially mature, and S3-fully mature). The results showed that 68 kinds of volatile flavor substances were identified in all green plum samples. The types and contents of such volatile substances experienced a V-shaped trend with an increasing degree of green plum maturity. During the S1 and S2 stages, aldehydes, ketones, and a small amount of alcohols were the main volatile flavor substances in the green plum samples. During the S3 stage, esters and alcohols were the most important volatile flavor components in the green plum pulp samples, followed by terpenes and ketones. YS had the most types and highest contents of volatile flavor substances in three stages, followed by GC and DZ. By using the PLS-DA method, this study revealed the differences in flavor of the different varieties of green plums at different maturity stages, and it identified eight common characteristic volatile flavor substances, such as ethyl acetate, 3-methylbutan-1-ol, and 2-propanone, produced by the different green plum samples during the ripening process, as well as the characteristic flavor substances of green plums at each maturity stage (S1-S3).

Volatile Metabolome and Aroma Differences of Six Cultivars of Prunus mume Blossoms

Prunus mume is a traditional Chinese plant with high ornamental and application values due to its very early blooming and unique fragrance. Long-term breeding and cultivation have resulted in a variety of P. mume blossoms and have made their exploitation more possible. Existing studies on the volatile metabolome and aroma of P. mume blossoms are limited. In this study, six extensively planted cultivars of P. mume blossoms, including Gulihong (GLH), Yudie (YD), LvE (LE), Dongfang Zhusha (DFZS), Jiangmei (JM), and Gongfen (GF), were investigated for their differences in terms of volatile metabolome, as well as their aroma characteristics based on the strategies and methods of metabolomics. The volatile metabolites were analyzed using HS-SPME-GC-MS technique. A total of eighty-nine compounds were detected and sixty-five of them were tentatively identified, including thirty-seven phenylpropanoids/benzenes, seventeen fatty acid derivatives, ten terpenoids, and one other compound. YD contains the most volatile metabolites in terms of number and amounts, which impart more abundant aromas to this cultivar. Fifteen differential compounds were screened through the untargeted metabolic analysis of twenty-nine samples by principal component analysis (PCA) and partial least squares-discriminant analysis (PLS-DA), while nine compounds were screened based on the odor activity value (OAV) analysis of the sixty-five identified compounds. GLH and GF, JM and LE were found to be more similar to each other based on chemometrics analysis of both volatile contents and OAVs, while YD and DFZS were markedly different from other cultivars. Six main metabolites, including benzaldehyde, methyl benzoate, benzyl acetate, eugenol, (E)-cinnamic alcohol, and 4-allylphenol, together with 2-nonenal, 3,4-dimethoxytoluene, and trans-β-Ionone were screened as differential compounds, owing to their higher contents and/or lower olfactory threshold, which endow an almond, cherry, phenolic, wintergreen, cananga odorata, floral, jasmine, hyacinth, cinnamon, clove, woody, medicinal, and violet fragrance to each variety, and greatly contribute to the aroma differences of six cultivars of P. mume blossom.