Changes In Volatile Components Research Articles

Preservation strategies for processed grass carp products: Analyzing quality and microbial dynamics during chilled and ice temperature storage

This study investigated the impact of ice temperature storage on quality and bacterial composition of processed fish paste products (PFP). Freezing curve revealed the ice temperature was −1 °C. Electric nose (e-nose) showed significant changes in volatile components within 8 days. Results of total volatile basic nitrogen (TVB-N) showed that PFP stored at 4 °C reached its limit after 2 days, whereas PFP stored at ice temperature remained stable for 6 days. Thiobarbituric acid reactive substances (TBARS) demonstrated delayed oxidation in PFP stored at ice temperature compared to 4 °C. TCA-soluble peptides indicated that the protein degradation was suppressed by ice temperature. Additionally, ice temperature inhibited microbial growth and altered bacterial composition. High-throughput sequencing revealed that Pseudomonas, Brochothrix, Carnobacterium were dominant at 4 °C, while Acinetobacter, Pseudomonas, Janthinobacterium and Brochothrix were dominant at ice temperature. In summary, ice temperature might be a potential method for maintaining the freshness of PFP.

Characterization of flavor substances in cooking and seasoned cooking brown seaweeds by GC-IMS and E-nose

The flavor of algae was one of the key factors for consumer acceptance. The objective of this study was to investigate the characteristic volatile compounds in cooking and seasoned cooking edible brown seaweeds (Undaria pinnatifida and Laminaria japonica). The gas chromatography-ion mobility spectrometry (GC-IMS) and electronic nose (E-nose) analysis showed that baking resulted in significant difference in flavor of brown seaweeds. However, the overall effect of cooking was not as significant as that of the seasoning solution treatment. Additionally, brown seaweeds treated with the seasoning solution were more acceptable. Undaria pinnatifida was found to contain 72 volatile flavor compounds, while Laminaria japonica had a total of 70. This study proved the applicability of GC-IMS combined with E-nose technology to detect the changes of volatile components of brown seaweeds after processing, providing beneficial knowledge and basic theory for the deep processing of brown seaweeds.

Application of pectin hydrolyzing bacteria in tobacco to improve flue-cured tobacco quality.

To study the relationship between the diversity of the surface microbial community and tobacco flavor, and to improve tobacco quality using microorganisms. The microbial community composition and diversity of 14 samples of flue-cured tobacco from tobacco-producing areas in Yunnan with varying grades were analyzed by high-throughput sequencing. PICRUSt was used for predicting microbial functions. A strain of Bacillus amyloliquefaciens W6-2 with the ability to degrade pectin was screened from the surface of flued-cured tobacco leaves from Yunnan reroasted tobacco leave. The enzyme preparation was prepared through fermentation and then applied for treating flue-cured tobacco. The improvement effect was evaluated by measuring the content of macromolecule and the changes in volatile components, combined with sensory evaluations. The bacterial communities on the surface of flue-cured tobacco exhibited functional diversity, consisting primarily of Variovorax, Pseudomonas, Sphingomonas, Burkholderia, and Bacillus. These bacterial strains played a role in the aging process of flue-cured tobacco leaves by participating in amino acid metabolism and carbohydrate metabolism. These metabolic activity converted complex macromolecules into smaller molecular compounds, ultimately influence the smoking quality and burning characteristics of flue-cured tobacco. The pectinase preparation produced through fermentation using W6-2 has been found to enhance the aroma and sweetness of flue-cured tobacco, leading to improved aroma, reduced impurities, and enhanced smoothness. Additionally, the levels of pectin, cellulose, and hemicellulose decreased, while the levels of water-soluble sugar and reducing sugar increased, and the contents of esters, ketones, and aldehydes increased, and the contents of benzoic acid decreased. The study revealed the correlation between surface microorganisms and volatile components of Yunnan tobacco leaves, and the enzyme produced by the pectin-degrading bacteria W6-2 effectively improved the quality of flue-cured tobacco.

Effects of hot air drying on drying kinetics, quality and flavor changes of Fructus aurantii

This study aimed to evaluate the effect of hot air drying on drying kinetics, quality and flavor changes of Fructus aurantii. The results showed that Midilli model (R 2 = 0.9995, RMSE = 6.16 × 10−9, χ 2 = 7.62 × 10−5) was the best model for hot air drying of Fructus aurantii, and the effective moisture diffusion coefficient (D eff) and activation energy (Ea) of hot air drying process was 2.63 × 10−5 - 6.61 × 10−4 m2/s and 42.36 KJ/moL, respectively. The HS-GC-MS and E-nose techniques were used to evaluate the changes in volatile components and aromatic characteristics. The results of HS-GC-MS showed that linalool content was 6.69%, 5.32% and 5.10% at 50°C, 60°C and 70°C respectively, showing a decreasing trend. Flavor radar fingerprint map showed that sensors S13, S12 and S2 have obviously higher response values, S11 , S5, S4 and S9 have higher response values, but other sensors have no obvious response values. PCA analysis showed that the first principal component (PC1) and the second principal component (PC2) accounted for 57.38% and 22.59% respectively, and the cumulative variance contribution rate was 87.1% (> 85%). The results of flavor radar fingerprint and PCA showed that the drying process obviously changed the aroma characteristics. The overall results showed that hot air drying at 50-60°C could effectively improve the final quality of dried Fructus Aurantii by maintaining flavor characteristics.

Adulteration identification of Hainan camellia (Camellia oleifera Abel.) oil based on comprehensive two‐dimensional gas chromatography and quadrupole time‐of‐flight mass coupled with chemometrics spectrometry

SummaryThe nutritional value of Hainan camellia oil is incomparable to other places, and Hainan camellia oil is expensive, so unscrupulous businessmen often mix other edible oils into them for illegal profit. This study detected the changes of volatile components in Hainan camellia oil adulterated with five edible oils (peanut, soybean, corn, rapeseed, and sunflower oils) using comprehensive two‐dimensional gas chromatography and quadrupole time‐of‐flight mass spectrometry (HS‐SPME‐GC × GC‐Q‐TOFMS). The principal component analysis (PCA) score plot showed that pure Hainan camellia oil (PHCO) and Hainan camellia oil samples were adulterated with other edible oils clearly to identify the adulteration separated from each other. The adulteration of PHCO could be accurately predicted using the developed PCA and OPLS‐DA models for concentrations as low as 5%. More importantly, several potential markers were found to identify the impersonate PHCO. Therefore, the volatile compound determination based on HS‐SPME‐GC × GC‐Q‐TOFMS proved to be an effective method for detecting adulteration of other edible oils in PHCO.

Dynamic changes in volatile components during dark tea wine processing

Tea wine is a beverage that combines the flavors of tea and wine with a variety of health benefits and has thus attracted widespread attention. However, few systematic studies have focused on dark tea wine, particularly on the dynamic changes in dark tea wine aroma. A sensory evaluation was conducted based on process optimization, and headspace solid-phase microextraction combined with gas chromatography-mass spectrometry was used to analyze the volatile components of dark tea wine. The results showed that dark tea wine gradually showed the sensory characteristics of wine as fermentation proceeded, presenting a strong and lasting herbal, spicy and sweet flavor. During fermentation, both the type and content of volatile components increased, especially higher alcohols and esters, which impart green, fruity, and sweet aromas. Aroma formation in dark tea wine occurs mainly during the late stages of fermentation. The monoterpenoid biosynthesis, fatty acid biosynthesis, lipoic acid metabolism, and phenylalanine metabolism pathways play roles in the unique aroma of dark tea wine. These results provide a theoretical basis for studying the aroma formation mechanism of dark tea wine and quality control of fermented dark tea wine in the future.

Investigation of volatiles and quality attributes of indica-japonica hybrid paddy by radio frequency combined hot air drying

The study was aimed at investigating the effects of radiofrequency combined hot air drying (RF-HAD) on volatiles and quality attributes of indica-japonica hybrid paddy. The results indicated that RF-HAD reduced the drying time by 40% compared to hot air drying (HAD). In addition, HA-RF-dried samples showed significantly higher color, vigor, and taste value but less fatty acid value than HA dried-ones. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis revealed that RF-HAD did not affect the protein profile of rice protein. Gas chromatography-ion mobility spectrometry characterized changes in volatile components of paddy before and after drying, results showed that the content of aldehyde and ester aromatic compounds increased after drying and the content of most volatile components in RF-HA-dried paddy was higher than in HA-dried samples. Thus, the inference was that RF-HAD technology may be an innovative alternative to existing drying methods such as microwave, HA, and other drying technologies.

Evolution behavior of volatile components of shiitake mushrooms during infrared-assisted spouted bed drying

The present study aimed to investigate the effect of different drying temperatures and airflow speeds on the number and species of volatile components in infrared-assisted spouted bed dried (IRSBD) Shiitake mushrooms. The dynamics changes in volatile components (determined by HS-SPME-GC-MS) during drying under optimal conditions were also monitored. Results revealed that the maximum number of volatile components (69 species) was observed at a temperature of 55 °C and airflow speed of 8.0 m/s, of which the volatile components in Shiitake mushrooms varied significantly over the drying process at this condition. Fresh Shiitake mushrooms mainly composed of volatile substances such as alcohols, ketones and acids. During the early drying stage (0–40 min), the levels of alcohols and ketones gradually decreased, while the species and levels of aldehydes, esters, and volatile sulfur-containing compounds (VSCs) increased. In the middle stage (40–120 min), levels of alcohols, esters, aldehydes, acids, and alkanes species increased, while the levels of VSCs decreased. For the last stage (120–200 min), the levels of sulfur-containing heterocyclic compounds, aldehydes, esters, acids, pyrazines, and alkanes were all increased. The findings of this study provide insights into the flavor formation mechanism during IRSBD of Shiitake mushrooms and offer a theoretical reference for the production of industrial flavorful dried goods.

Cinnabaris modified with SiO2 nanoparticles stabilized Pickering emulsion to improve the photostability of volatile oil: A Lingzhu San case study

The pharmacological activity of volatile oils (VOs) is significant, but they can generate peroxides under light conditions, reducing the VO content and affecting their stability. This study aims to introduce Pickering emulsion technology to enhance the antioxidant activity of VOs and improve the photostability and efficacy of solid formulations. In this work, Cinnabaris was used as a stabilizer in the formulation of Lingzhu San to prepare Pickering emulsions using high-speed shearing. By controlling the duration of light exposure, the retention rate, degree of oxidation, and changes in volatile components of the volatile oil of Acorus tatarinowii Schott (AT-VO) were compared between the crude oil group and the Pickering emulsion group. Compared with the crude oil group, the Pickering emulsion group significantly improved the retention rate, reduced the degree of oxidation, and mitigated the changes in volatile components. GC–MS analysis of the quantitative and qualitative changes showed that the volatile components of the oil retained by the Pickering emulsion were closer to the untreated AT-VO in the light environment. In addition, the Pickering emulsion with water as the outer phase and oil as the inner phase retarded the formation of peroxides in the VOs and achieved the goal of maintaining the photostability of the VOs.

Correlation between fungi and volatile compounds during different fermentation modes at the industrial scale of Merlot wines

Elucidation of the relationship between fungal community development and dynamic changes in volatile components during fermentation is of great significance in controlling wine production. However, such studies on an industrial scale are rarely reported. In this study, fungal community succession during spontaneous fermentation (SPF) and inoculation fermentation (INF) of Merlot wine was monitored by a research strategy combining culture-dependent and culture-independent methods. The volatile compounds were monitored during SPF and INF by headspace solid-phase micro-extraction coupled with gas chromatography-mass spectrometry technology. The Spearman correlation coefficient was also used to investigate the interplay between fungal communities and volatile compounds. We found that fungal community diversity in SPF decreased as fermentation progressed but was significantly higher than that of INF. Starmerella and Kazachstania were the dominant non-Saccharomyces genera in Merlot wine during SPF. However, the presence of commercial yeasts and sulphur dioxide led to a sharp decrease or the disappearance of non-Saccharomyces genera during INF. Spearman correlation analysis revealed that all major volatiles were positively correlated with most functional microbiotas except P. fermentans, S. bacillaris, E. necator, and D. exigua in INF. In SPF, most non-Saccharomyces were negatively correlated with core volatiles, whereas K. humilis, M. laxa, P. kluyveri, and A. japonicus were positively correlated with the major volatiles, especially some higher alcohols (isopentol, heptanol) and terpenes (linalool, citronellol). S. cerevisiae was positively correlated with most of the main volatile substances except ethyl isovalerate and isoamyl acetate. These findings provide a reference for comprehending the diverse fermentation methods employed in the wine industry and improving the quality of Merlot wines.

HS-SPEM-GC-MS Analyses of Volatiles and Transcriptome Analysis of Camellia tetracocca in Response to Feeding by Empoasca onukii Matsuda

The tea leafhopper (Empoasca (Matsumurasca) onukii Matsuda, 1952) is the predominant pest infesting tea and causes significant losses in yield. Plants have evolved multiple defense responses to protect themselves from insect herbivores. Camellia tetracocca, a kind of ancient tea with local popularity, is unique to southwest China. This ancient tea is often attacked by the tea leafhopper. However, there are no relevant reports on changes in volatile components and defense signaling pathways after Camellia tetracocca has been attacked by E. onukii. To reveal changes in the responses of the volatile components of C. tetracocca to E. onukii, the headspace sampling technique and GC-MS were adopted to determine and analyze the volatiles. Furthermore, to unveil the defense mechanisms of C. tetracocca in response to E. onukii, transcriptome analysis was applied to damaged tea leaves and healthy leaves. The GC-MS analysis showed significant increases in the linalool and (E)-2-hexenal contents. The transcriptome analysis revealed a set of core pest-responsive genes (3074 upregulated and 5098 downregulated). Most of the enriched pest-responsive genes are mainly involved in plant hormone signal transduction photosynthesis, terpenoid backbone biosynthesis, alpha-linolenic acid metabolism, and the NF-κB signaling pathway. A conjoint analysis of the transcriptome and metabolome indicated that N2-acetylornithine, D-malic acid, theogallin, fucosyllactose, 5-caffeoylquinic acid, fumarprotocetraric acid, and arabinogalactose have a significant correlation with LOC114279735, LOC114317534, LOC114282078, LOC114317768, and LOC114263181. This study lays a foundation for further research on the breeding and cultivation of insect-resistant germplasm resources for C. tetracocca and on the promotion and development of the plant.

Characterization of volatile flavor compounds from fish maw soaked in five different seasonings.

In this study, sensory evaluation, electronic nose, and HS-GC-IMS were used to investigate the effects of different seasonings (deionized water, onion, ginger, Sichuan pepper, and mixed seasonings) on the flavor of fish maw. The results showed that the volatile compounds of fish maw soaked in different seasonings were mainly organic sulfides and aromatic compounds. A total of 95 volatile compounds were identified, including 25 aldehydes, 23 olefins, 19 alcohols, 11 esters, 9 ketones, 3 acids, 2 sulfides, 1 furan, 1 ether and 1 ketoxime. Sichuan pepper group and mixed seasoning group had the most significant changes in volatile components, and had the most effective improvement on the flavor of fish maw compared with other groups. These findings will provide reference for producing high quality fish maw and improving its flavor quality. These findings will provide feasible theoretical support for the pretreatment and exploration of fish maw products in the future.

Gas Chromatographic-Ion Mobility Spectrometry Combined with Chemometrics to Study the Changes in Characteristic Odor Components of Galli gigerii Endothelium Corneum in Different Processing Methods.

Galli gigerii endothelium corneum (GGEC) is a traditional Chinese medicine commonly used in clinical practice to treat various conditions such as indigestion, vomiting, spermatorrhea, and enuresis. In this study, the volatile components of different concoctions of GGEC were examined by gas chromatography-ion mobility spectrometry (GC-IMS), and the changes of the components were compared by fingerprinting, combined with principal component analysis (PCA) and orthogonal partial least squares-discriminant analysis (OPLS-DA) to analyze the main volatile components and find out the different markers that can distinguish the different concoctions of GGEC. In the result, the GC-IMS fingerprints of GGEC and its different concoctions showed differences in their volatile components, of which 49 volatiles were clearly characterized, with some components including monomers and dimers. The characteristic volatile components of raw GGEC (SP) were n-nonanal, (E)-2-octenal, beta-ocimene, 2-ethyl-1-hexanol, etc. The characteristic volatile components of stir-fried GGEC (QC) are heptanal, 2-octanol, (E)-2-heptenal, etc. The characteristic volatile components of sand ironing GGEC (ST) are isoamyl acetate, decanal, cyclohexanone, 2-ethyl pyrazine, etc. The characteristic volatile components of stir-fried GGEC with vinegar (CZ) are thiazole, linalool, 2,3,5-trimethylpyrazine, etc. The characteristic volatile components of stir-fried GGEC with milk (FH) are 2-methylbutanoic acid, ethyl acetate, ethyl 2-hydroxypropanoate, butyl acetate, etc. By chemometric analysis, components such as n-nonanal, (E)-2-octenal, 2-pentyl-furan, butanal, 1,4-dioxane, and 2-methylpropanoic acid could be used as difference markers to distinguish different concoction products of GGEC. Furthermore, by analyzing different volatile compounds, we can examine the changes in volatile components during processing of GGEC, which can provide experimental data for the identification and establishment of quality standards.

Effects of different heat treatments on Maillard reaction products and volatile substances of camel milk.

Camel milk has unique compositional, functional and therapeutic properties compared to cow's milk and also contains many protective proteins with anti-cancer, anti-diabetic and anti-bacterial properties. In this experiment, fresh camel milk was heat-treated at different temperatures and times, and the changes in Millard reaction products were analyzed. Meanwhile, headspace-gas chromatography-ion migration spectrometry (HS-GC-IMS), electronic nose and electronic tongue were used to analyze the changes of volatile components in camel milk after different heat treatments. The results showed that the Maillard reaction was more severe with the increase of heat treatment, and the contents of furosine and 5-hydroxymethylfurfural increased significantly when the heat treatment temperature was higher than 120°C. HS-GC-IMS results showed that the contents of aldehydes and ketones increased obviously with the increase of heat treatment degree. The study clarifies the effects of different heat treatment degrees on Maillard reaction degree and flavor of camel milk, which has practical production guidance significance for the research and industrialization of liquid camel milk products.

Determining the changes in metabolites of Dendrobium officinale juice fermented with starter cultures containing Saccharomycopsis fibuligera FBKL2.8DCJS1 and Lactobacillus paracasei FBKL1.3028 through untargeted metabolomics

BackgroundThe present study aimed to investigate the changes in volatile components and metabolites of Dendrobium officinale (D. officinale) juice fermented with starter cultures containing Saccharomycopsis fibuligera and Lactobacillus paracasei at 28 ℃ for 15 days and post-ripened at 4 ℃ for 30 days using untargeted metabolomics of liquid chromatography-mass spectrometry (LC–MS) and headspace solid-phase microextraction-gas chromatography (HS–SPME–GC–MS) before and after fermentation.ResultsThe results showed that the alcohol contents in the S. fibuligera group before fermentation and after fermentation were 444.806 ± 10.310 μg/mL and 510.999 ± 38.431 μg/mL, respectively. Furthermore, the alcohol content in the fermentation broth group inoculated with the co-culture of L. paracasei + S. fibuligera was 504.758 ± 77.914 μg/mL, containing a significant amount of 3-Methyl-1-butanol, Linalool, Phenylethyl alcohol, and 2-Methyl-1-propanol. Moreover, the Ethyl L (-)-lactate content was higher in the co-culture of L. paracasei + S. fibuligera group (7.718 ± 6.668 μg/mL) than in the L. paracasei (2.798 ± 0.443 μg/mL) and S. fibuligera monoculture groups (0 μg/mL). The co-culture of L. paracasei + S. fibuligera significantly promoted the metabolic production of ethyl L (-)-lactate in D. officinale juice. The differential metabolites screened after fermentation mainly included alcohols, organic acids, amino acids, nucleic acids, and their derivatives. Twenty-three metabolites, including 11 types of acids, were significantly up-regulated in the ten key metabolic pathways of the co-culture group. Furthermore, the metabolic pathways, such as pentose and glucuronate interconversions, the biosynthesis of alkaloids derived from terpenoid and polyketide, and aminobenzoate degradation were significantly up-regulated in the co-culture group. These three metabolic pathways facilitate the synthesis of bioactive substances, such as terpenoids, polyketides, and phenols, and enrich the flavor composition of D. officinale juice.ConclusionsThese results demonstrate that the co-culture of L. paracasei + S. fibuligera can promote the flavor harmonization of fermented products. Therefore, this study provides a theoretical basis for analyzing the flavor of D. officinale juice and the functional investigation of fermentation metabolites.

Changes of bacterial communities and volatile compounds developed from the spoilage of white Hypsizygus marmoreus under different storage conditions

The succession of bacterial communities and changes of volatile components throughout the storage of white Hypsizygus marmoreus (white H.marmoreus) were investigated. The results showed that the microbial communities were mainly composed of Proteobacteria and Firmicutes at 4 °C and 25 °C, with Serratia, Pediococcus, Enterococcus, Pseudomonas and Stenotrophomonas as the dominant genera. Serratia could be detected during the whole period of storage, and the relative abundance increased with increasing time. It indicated that Serratia might be one of the main spoilage bacteria for white H.marmoreus spoilage. Pseudomonas and Stenotrophomonas had a sharp increasing trend during the late storage period, indicating they might be a potential factor for spoilage. The volatile components of white H.marmoreus were mainly composed of ketones, aldehydes, alcohols and esters, among which 3-octanone was the main component. Correlation analysis showed that Serratia was negatively correlated with 16 volatile compounds, and also suggested that Serratia might play an important role in inhibiting the production of 16 volatile compounds. The results would provide a theoretical basis for studying the microbial dynamics and the changes of volatile compounds of white H.marmoreus during storage to control the spoilage of edible fungi.

Changes of volatile substance composition during processing of nine-processed tangerine peel (Jiuzhi Chenpi) determined by gas chromatography-ion mobility spectrometry.

Nine-processed tangerine peel (Jiuzhi Chenpi in Chinese) is a famous Chinese traditional snack. The composition and contents of volatile substances during its processing is unclear. Gas chromatography combined with ion mobility spectrometry (GC-IMS) was applied to determine the characteristic changes of volatile components throughout the production process. Four stages such as untreated dry tangerine peel (raw material), debittered tangerine peel, pickled tangerine peel, and final product were examined. A total of 110 flavor compounds including terpenes, alcohols, aldehydes, ketones, esters, acids, and two others were successfully detected in tangerine peel samples across the various production stages. There were abundant amounts of terpenes contributing to the flavor, including limonene, gamma-terpinene, alpha-pinene, myrcene, beta-pinene, and alpha-thujene which were reduced at the later stage of production. Large amounts of esters and alcohols such as methyl acetate, furfuryl acetate, ethyl acetate, benzyl propionate, 2-hexanol, linalool, and isopulegol, were diminished at the early stage of processing, i.e., soaking for debittering. One the other hand, the final product contained increased amount of aldehydes and ketones including pentanal, hexanal, 2-hexenal, 2-heptenal (E), 2-pentenal (E), 1-penten-3-one, 6-methyl-5-hepten-2-one, 2-methyl-2-propenal, and 2-cyclohexen-1-one, and very high level of acetic acid. Present findings help to understand the formation of the unique flavor of nine-processed tangerine peel and provide a scientific basis for the optimization of processing methods and quality control.

Analysis of the changes of volatile flavor compounds in a traditional Chinese shrimp paste during fermentation based on electronic nose, SPME-GC-MS and HS-GC-IMS

Traditionally fermented shrimp paste has a long fermentation period and is susceptible of external factors, which leads to unstable quality and limits its development and application. Therefore, the purpose of this study is to analyze the flavor changes in the shrimp paste fermentation process and screen out the key volatile aroma components in the shrimp paste to control the flavor quality of the shrimp paste products. The overall odor profile was detected by the electronic nose. A total of 106 volatile flavor compounds in the shrimp paste samples at different fermentation stages were identified by solid-phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS) and headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS). The main aroma components alcohols, aldehydes, pyrazines and other substances in the fermentation process showed an overall upward trend. A total of 17 key volatile aroma components in shrimp paste at different fermentation stages were identified by the relative aroma activity value (ROAV) method. The combination of electronic nose, SPME-GC-MS and HS-GC-IMS could comprehensively reflect the changes of volatile components in shrimp paste at different fermentation stages, which helps to further understand the mechanism of shrimp paste flavor formation and provides a basis for the regulation of the flavor quality of shrimp paste products.

A Correlation Between Pericarpium Citri Reticulatae Volatile Components and the Change of the Coexisting Microbial Population Structure Caused by Environmental Factors During Aging.

Pericarpium Citri Reticulatae (PCR) is a natural citrus by-product with beneficial health and nutritive properties that is used widely in food and is an ingredient in traditional Chinese medicine. PCR improves gradually with aging. However, the present research has not yet revealed the reasons for this. Some data prove the important role of microorganisms in the quality of tobacco and fermented tea with the time of the aging of these foods. Our studies further proved that the coexisting Aspergillus niger plays an important role in the change of flavonoids and volatile oil in PCR during this process. Therefore, we put forward that longer storage is better for PCR and is highly correlated with the change of the coexisting microbial population structure caused by environmental factors. Samples of PCR aged in Beijing, Sichuan, Guangdong, and Yunnan were collected at different time points. Using GC/MS and high throughput 16S rDNA and ITS sequencing techniques, massive changes in volatile profile and microbial communities were observed during aging. Spearman correlation analysis indicated that Exobasidium, Xeromyces, Pseudocercospora, Russula, Aspergillus, Herbaspirillum, Sphingomonas, and Streptococcus, which are the dominant microbial genera in Sichuan and Guangdong showed strong connections with volatile components of chemical markers. It was preliminarily verified that the changes of volatile components for PCR are highly correlated with the change of the coexisting microbial population structure caused by environmental factors, providing a new idea for the research on the aging mechanism of PCR and key influencing factors of aging quality.

Flavor and compositional analysis of macadamia nuts during long‐term storage

The production of unpleasant flavor of macadamia nuts during long-term storage is a very common phenomenon in nut industry. Changes in volatile components were monitored by HS-SPME/GC–MS throughout a 9-month storage period to expound the unpleasant flavor of macadamia nuts. Aldehydes (primarily hexanal, heptanal, octanal, (E)-2-octenal, (2E)-2-nonenal, trans-2-decenal, nonanal, decanal, (E)-2-heptenal, and pentanal), and acids (mainly hexanoic and acetic acid) composed the main unpleasant flavor of macadamia nuts based on their concentrations, olfactory characteristics, and thresholds. Compositional analysis showed total lipid, fatty acids, and amino acids decreased by 6.35 g/100 g, 137, and 4.165 mg/g, respectively, after 9 months of storage. Besides, there was no kernel discoloration, while the AV and PV increased by 1.89 mg/g and 8.13 meqO2/kgOil, respectively. The flavor deterioration was induced by lipid oxidation and had little correlation with protein oxidation. Moreover, results of correlation and PLSR analysis demonstrated protein oxidation in macadamia nuts during storage were related to lipid oxidation. Novelty impact statement Unpleasant flavor composition was first identified based on sensory analysis and ROAVs of volatiles. Lipid oxidation of macadamia nuts induced flavor deterioration during storage. Changes in amino acids were closely related to lipid oxidation in macadamia nuts.