Effect of salt concentration on the quality and microbial community during pickled peppers fermentation

This work aimed to investigate the effect of salt concentration on the quality and microbial community of pickled peppers during fermentation, and the cross-correlation between microorganisms and quality was also revealed. The results showed that 9 volatile flavor compounds were unique to the low salt concentration group (D group), which also contained higher content of FAA, lactic acid and acetic acid than high salt concentration group (G group). Meanwhile, the samples of D2 group have a better texture properties. Firmicutes, Proteobacteria, Ascomycota, Lactobacillus, Pectobacterium, and Pseudomonas were detected as the main microbial community during the fermentation with different salt concentrations. Furthermore, the correlations analysis results indicated that the salt concentration has a significant effect on the microbial community of pickled peppers (p < 0.001), and Pediococcus, Lactobacillus, Cedecca, Issatchenkia, Pichia, Kazachstania, and Hanseniaspora were significantly correlated with flavors, which played crucial roles in the unique flavor formation of pickled peppers.

Effects of different pickling methods on physicochemical properties and flavor profiles of Tongling white ginger: Dry-salting, brine-pickling, and inoculation-pickling

Tongling white ginger is a Chinese fermented vegetable with unique flavors. However, little is known about its physicochemical properties, flavor characteristics, and sensory evaluation. The study examined the physicochemical (pH, titratable acidity [TA], nitrite, soluble protein, and color) and flavor characteristics (organic acids, free amino acids, and volatiles) of white ginger during fermentation. The results showed that the pH value and soluble protein in the dry-salted, brine-pickled, and inoculation-pickled decreased significantly while the TA value increased significantly, inoculation-pickled can effectively reduce the content of nitrite. After fermentation, inoculation-pickled produced the highest content of organic acids, while dry-salted produced the highest total amount of free amino acids. A total of 70, 68, 70, and 69 volatile compounds were identified in fresh, dry-salted, brine-pickled, and inoculation-pickled white ginger. The total contents of terpenoids of Tongling white ginger by three fermentation methods decreased; the total contents of alcohols and aldehydes were the highest in brine-pickled, and esters and ketones were more abundant in inoculation-pickled. The results showed that inoculation-pickled could shorten the fermentation time of Tongling white ginger, produce a unique flavor, and have the highest sensory score.

The Impact of Different Cooking Methods on the Flavor Profile of Fermented Chinese Spicy Cabbage

Chinese spicy cabbage (CSC) is a common traditional fermented vegetable mainly made of Chinese cabbage. In addition to eating raw, boiling and stir-frying are the most common cooking methods for CSC. To identify the impacts of boiling or stir-frying on the quality of CSC, the physicochemical properties, flavor compounds, and sensory properties of CSC were analyzed. A total of 47 volatile flavor compounds (VFCs) were detected by gas chromatography-mass spectrometry. Sulfide was determined as the main flavor compound of CSC, mainly contributed by cabbage, garlic, and onion odors. The content of sulfide decreased significantly after cooking. Nonanal, geranyl acetate, and linalool were newly generated after boiling with odor activity value (OAV) > 1, and contributed fatty, sweet, fruity, and floral odors to BL-CSC. 1-Octen-3-one, 1-octen-3-ol, octanal, nonanal, and (E)-2-nonenal were newly generated after stir-frying with OAV > 1, and contributed mushroom, fatty, and green odors to SF-CSC. Diallyl trisulfide, nonanal, (E)-β-ionone, β-sesquiphellandrene, and (E)-2-decenal were considered as the potential key aroma compounds (KACs) to distinguish the CSCs after different heat treatment. After cooking, the total titratable acidity of CSC increased and the sensory properties changed significantly. This study provides valuable information and guidance on the sensory and flavor changes of thermal processing fermented vegetables.

Tetracycline residue alters profile of lactic acid bacterial communities and metabolites of ginger pickle during spontaneous fermentation

Antibiotic residue, an emerging contaminant, has been an increasing concern worldwide in vegetables. However, the focus is still limited to its accumulation in vegetables and its adverse health effect on humans, with little mention of its impact on the vegetable process. Fermentation is an important method of the vegetable process. Tetracycline (TC) is the most widely used antibiotic, and its residue is often higher than other antibiotics in ginger. Therefore, current research was to characterize how the TC residue affected the lacticacidbacterial (LAB) communities and metabolites during the salted fermentation of ginger. The TC residue, organic acids, volatile compounds and LABs were analyzed during the fermentation, and the correlations between the LABs and compounds were also revealed. The results suggested that the hetero-lactic fermentation did not happen under the TC residue although the TC residue decreased from 4 mg/kg to 2.56 mg/kg in salt brine of ginger fermentation. Meanwhile, TC residue affected the occurrence, propagation and succession of LABs. The LAB biomarkers shifted to Lab. parafarraginis, Lab. buchneri and Lab. kisonensis under TC residue. Responded to LAB communities, the organic acids and volatile compounds were also markedly changed under the TC residue. And the important volatile compound variables shifted to citronellol, allylsenevol, geranyl acetate, vinylstearylether, isothiocyanic acid phenethyl, 3-octanol, geraniol, bingpian, citral and camphor. The transformation of LAB biomarkers induced by TC residue was the main cause of the change of important volatile compound variables, but interestingly, not all of them had significant positive or negative correlations. These results indicated that the antibiotic residue has an adverse ecological effect on the vegetable fermentation process.Therefore, the antibiotic residue should be listed as a quality control index in fermented vegetable raw materials.

Identification of Olfactory Nuisance of Floor Products Containing Bitumens with the TD-GC-MS/O Method

The adopted TD-GC-MS/O method helps determine the correlation between the odour signals and compounds separated on the chromatographic column, from the analysed gas mixture. It is possible to compare the retention times at which the odour signals were identified with the retention time of eluting compounds, when the test system and matrix are known. The presented study describes the details of representative samples obtained from (1) indoor air samples from a room where floor materials containing bitumen are present, (2) wooden floor staves placed in an emission chamber, and (3) fragments (chips) of the materials mentioned above, placed in glass tubes, exposed to an elevated desorption temperature. The results, presented in the paper, describe the identified odours and their intensity and assign chemical compounds to each odour, indicating their likely source of origin. The results presented in the manuscript are intended to show what methodology can be adopted to obtain intense odours from the tested samples, without losing the sensitivity derived from GC-MS. The manuscript presents representative results-case studies. The results for various types of samples were not very reproducible, related to the complex matrix of bituminous products. The enormity of compounds present in tar adhesives makes it possible to indicate only the groups of compounds that emit from these systems. They include, primarily, aliphatic, aromatic and heteroaromatic hydrocarbons, particularly Naphthalene and Phenol derivatives.

Characterization of aroma and bacteria profiles of Sichuan industrial paocai by HS-SPME-GC-O-MS and 16S rRNA amplicon sequencing

Sichuan industrial paocai and traditional home-made paocai have different aroma profiles due to different manufacturing techniques, but detailed information about the aroma profiles and aroma-producing microorganism of Sichuan industrial paocai remain largely elusive. For this reason, we established and validated an external standard method of headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS) combined with gas chromatography-olfactometry (GC-O) for identification and accurate quantitation of aroma-active compounds in Sichuan industrial paocai. This method was combined with 16S rRNA amplicon sequencing to comprehensively analyze the aroma and bacteria profiles of Sichuan industrial paocai. A total of 121 volatile compounds were identified, among which 36 odorants were identified as aroma-active compounds with aroma intensities (AIs) ranging from 0.67 to 5.00 by GC-O. The types of aroma-active compounds in Sichuan industrial paocai were variety-specific to some extent, but the aroma-active compounds shared by different varieties of Sichuan industrial paocai (i.e., skeleton aroma-active compounds) were phenylethyl alcohol, acetic acid, butanoic acid, 2-methylbutanoic acid, ethyl hexanoate, 4-ethylphenol and 4-ethylguaiacol. Moreover, 17 key aroma-active compounds of AI > 1 in radish paocai were quantitated by external standard method, and their odor activity values (OAVs) were calculated based on the odor thresholds. Further, 12 aroma-active compounds with OAV ≥ 1 in one of the radish paocai were selected to construct the recombination model, which revealed good agreement with the original sample. Furthermore, Lactobacillus, Pediococcus, Pseudomonas and Sphingomonas were the dominant bacteria in Sichuan industrial paocai. Correlation analysis between 16 dominant bacteria and 36 aroma-active compounds showed that Pediococcus, Arcobacter and Lactobacillus could be the core aroma-producing bacteria of Sichuan industrial paocai.

Insights into the major aroma-active compounds in clear red raspberry juice (Rubus idaeus L. cv. Heritage) by molecular sensory science approaches

The major aroma-active compounds in clear red raspberry juice were identified by molecular sensory science approaches. Thirty-one aroma-active compounds were identified using detection frequency analysis and aroma extract dilution analysis. Among them, 18 volatiles with aroma activity in red raspberry were identified for the first time, while 14 volatiles with odor activity values (OAVs) ≥ 1 were confirmed as the major aroma-active compounds. Three C6 aldehydes showed the highest detection frequencies of 8, and β-ionone exhibited the highest OAV of 9507 and flavor dilution factor of 512, which indicated that the floral and grassy note could be dominant in overall aroma. Quantitative descriptive analysis suggested that the grassy, floral, woody, and caramel-like notes can be simulated using aroma recombination model 1. Electronic nose analysis also demonstrated that model 1 had closer similarity to the original juice than others. The combination strategy used here would help improve the knowledge of red raspberry aroma.

Physicochemical, microbial, and aroma characteristics of Chinese pickled red peppers (Capsicum annuum) with and without biofilm

Biofilm formation in the production of fermented vegetable might impact its quality and safety. In this study, physicochemical and microbial properties, volatile and aroma-active compounds between PRPs without biofilm (NPRP) and with biofilm (FPRP) were investigated by gas chromatography-mass spectrometry, gas chromatography-olfactometry, aroma extract dilution analysis, and spiking tests. The pH and titratable acidity were 3.66 ± 0.00 and 0.47 ± 0.08 g/100 g lactic acid in NPRP and 3.48 ± 0.01 and 0.87 ± 0.10 g/100 g lactic acid in FPRP, respectively. The nitrite level of the two PRPs was 1.87–1.92 mg kg⁻¹, which was below the limited value (20 mg kg⁻¹) of fermented vegetables regulated by the GB2760-2017. FPRP had relatively higher microbial and yeast numbers than NPRP, three common pathogens, namely, Salmonella spp., Staphylococcus aureus, and Shigella spp. were not detected. A total of 70 and 151 aroma compounds were detected in NPRP and FPRP, respectively, including 13 classes of compounds. The dominant aroma attributes of FPRP were sour, floral, mushroom-like, green, and smoky, while NPRP exhibits a mushroom-like flavor. Acetic acid, ethanol, α-terpineol, (E)-2-nonenal, 2-heptanol, phenylethyl alcohol, and linalool were potent key aroma-active compounds in NPRP and FPRP. Results of spiking tests showed that the addition of each substance not only increased its own odour, but also had significant effects on other smells. FPRP displayed richer varieties and contents of aroma profile than NPRP. However, some compounds, such as 4-ethylguaiacol and 4-vinylguaiacol, which were only detected in FPRP, had negative roles on the aroma attributes.

The aroma profile of PRPs was evaluated by GC-MS, GC-O, AEDA, OVA and spiking test. Biofilm can improve the variety and contents of aroma.