Mechanisms underlying the formation of main volatile odor sulfur compounds in foods during thermal processing.

Volatile sulfur compounds (VSCs) significantly influence food flavor and garner considerable attention in flavor research due to their low sensory thresholds, diverse odor attributes, and high reactivity. Extensive research studies have explored VSC formation through thermal processes such as the Maillard reaction, thermal pyrolysis, oxidation, and enzymatic reactions. However, understanding of the specific reaction mechanisms and processes remains limited. This is due to the dispersed nature of existing studies, the undefined intermediates involved, and the complexity of the matrices and processing conditions. Given these limitations, the authors have shifted their focus from foods to sulfides. The structure, source, and chemical characteristics of common precursors (sulfur-containing amino acids and derivatives, thiamine, thioglucoside, and lentinic acid) and their corresponding reactive intermediates (hydrogen sulfide, thiol, alkyl sulfide, alkyl sulfenic acid, and thial) are provided, and the degradation mechanisms, reaction rules, and matrix conditions are summarized based on their chemical characteristics. Additionally, the VSC formation processes in several typical foods during processing are elucidated, adhering to these identified rules. This article provides a comprehensive overview of VSCs, from precursors and intermediates to end products, and is crucial for understanding the mechanisms behind VSC formation and managing the flavor qualities of processed foods.

Release characteristics and risk assessment of volatile sulfur compounds in municipal wastewater treatment plants.

In recent years, the malodorous gases generated by sewage treatment plants have gradually received widespread attention due to their sensory stimulation and health hazards. The emission concentration, sensory evaluation and health risk assessment of volatile sulfur compounds (VSCs) were all explored in two municipal wastewater treatment plants (WWTPs) with oxidation ditch and anaerobic/oxic treatment process, respectively. The VSCs concentration showed the highest amount in the primary treatment unit in both the two WWTPs (73.3% in Plant A and 93.0% in Plant B), while the H2S took the main role in the composition of VSCs. However, H2S took a larger percentage in Plant A (84.5% âˆ¼ 87.0%) rather than Plant B (61.2% âˆ¼ 83.5%), which may be due to the different operating conditions and sludge properties in different treatment process. Besides, H2S also gained the first rank in the sensory evaluation and health risk assessment, which may cause considerable sensory irritation and health risk to workers and surrounding residents. Furthermore, the influencing factor analyses of VSCs emission showed that the temperature of water and air, ORP of sludge made the greatest effect on VSCs release. This study provides theoretical and data support for the research of VSCs emission control in WWTPs.

Release characteristics and risk assessment of volatile sulfur compounds in a municipal wastewater treatment plant with odor collection device.

Due to the malodorous effects and health risks of volatile sulfur compounds (VSCs) emitted from wastewater treatment plants (WWTPs), odor collection devices have been extensively utilized; however, their effectiveness has rarely been tested. In the present investigation, the characteristics of VSCs released in a WWTP equipped with gas collection hoods are methodically examined by gas chromatography. The obtained results indicate that the concentration of VSCs in the ambient air can be substantially reduced, and the primary treatment unit still achieves the highest concentration of VSCs. Compared to WWTPs without odor collection devices, the concentration of H2S in this WWTP is not dominant, but its sensory effects and health risks are still not negligible. Additionally, research on the emission of VSCs from sludge reveals that the total VSCs emitted from dewatering sludge reaches the highest level. Volatile organic sulfur compounds play a dominant role in the component and sensory effects of VSCs released by sludge. This study provides both data and theoretical support for analyzing the effectiveness of odor collection devices in WWTPs, as well as reducing the source of VSCs. The findings can be effectively employed to optimize these devices and improve their performance.

Enterogenous extra-oral halitosis has a more severe impact on quality of life in females compared to males.

Some studies have examined the impact of intra-oral halitosis on quality of life (QOL), but the impact of enterogenous extra-oral halitosis (EOH) on QOL has not been previously studied. We conducted a retrospective analysis of data from 88 patients with enterogenous EOH who visited our online halitosis clinic. A specialized halitosis associated life-quality test (HALT) questionnaire was used to assess QOL of these patients. Spearman correlation analysis was performed to investigate the relationship between HALT score and age. We found that 21 (23.86%) patients were male and 67 (76.14%) patients were female. HALT scores in females were significantly higher than in males (57.6 ± 13.6vs.45.5 ± 11.9,P< 0.001). Additionally, 13 of the 20 items of the HALT questionnaire showed significant differences between the sexes. No correlation was identified between HALT score and age. Therefore, we conclude that: (1) enterogenous EOH has a more severe impact on QOL in females compared to males. (2) More females with EOH visit the offline halitosis clinic compared to males. (3) The QOL of patients with enterogenous EOH does not decline with age.

Characteristics of extra-oral halitosis induced by functional constipation: a prospective cohort study.

Characteristics of extra-oral halitosis induced by functional constipation (FC) have never been revealed. To address this, this prospective cohort was conducted with 100 FC patients, who were divided into a halitosis group and a negative group. Organoleptic score (OLS) ⩾ 2 in nose breath was diagnosed as extra-oral halitosis. Concentration of overall volatile sulfur compounds (VSCs) measured by Halimeter, concentration of hydrogen sulfide (HS), methanethiol (MT), dimethyl sulfide (DMS) and their total amount measured by OralChroma in nose breath was recorded asC-VSC,C-HS,C-MT,C-DMS andC-sum respectively. We found that 82% (82/100) of the FC patients had extra-oral halitosis. However, only 12.5% (3/82) and 1.22% (1/82) of halitosis group were correctly diagnosed with the current diagnostic threshold ofC-VSC ⩾ 110 parts per billion (ppb) and ⩾150 ppb.C-VSC,C-DMS andC-sum were significantly higher in the halitosis group compared to the negative group (allP< 0.001), with ratios of about 2.2 times, 3.1 times and 2.1 times respectively.C-HS andC-MT were low and not significantly different between the groups. Positive correlations were observed among OLS,C-VSC,C-DMS andC-sum. The area under curve of receiver operating characteristics ofC-VSC, C-DMS andC-sum for predicting FC-induced halitosis was 0.909, 0.9073 and 0.962 respectively, with the threshold values of ⩾36 ppb, ⩾52 ppb and ⩾75 ppb respectively. Therefore, we conclude that: (1) DMS is the primary contributor to FC-induced extra-oral halitosis. (2) OLS, Halimeter and OralChroma are consistent in detecting FC-induced extra-oral halitosis. (3) The diagnostic threshold for Halimeter should be adjusted toC-VSC ⩾ 36 ppb and the diagnostic threshold for OralChroma should be set asC-DMS ⩾ 52 ppb for diagnosing FC-induced extra-oral halitosis.

The assessment of halitosis with a new screening tool in medication-related osteonecrosis of the jaw.

OBJECTIVES: This study aimed to identify the levels of halitosis in patients with Medication-related osteonecrosis of the jaw (MRONJ) and osteoporosis and to suggest a new MRONJ screening method using halitosis measurement. MATERIALS AND METHODS: From October 2019 to April 2023, participants aged 19 years or older without periodontal disease were selected. Seventy-five participants, 25 in each group, were divided into an MRONJ group, an osteoporosis group without MRONJ, and a control group without osteoporosis and not taking osteoporosis drugs or antibiotics. Each participant underwent halitosis assessment twice using an exhaled breath analyzer to measure halitosis twice by blowing a straw for 1 min. Measured concentrations of hydrogen, hydrogen sulfide, and methyl mercaptan were compared between groups. RESULTS: Data from 22 patients in the MRONJ group, 25 in the osteoporosis group, and 25 in the control group were analyzed. The concentrations of hydrogen sulfide and methyl mercaptan were significantly higher in the MRONJ group than in the other groups, but the concentrations of hydrogen did not differ between the groups. When comparing the concentrations of hydrogen sulfide and methyl mercaptan in osteoporosis patients and solid cancer patients in the MRONJ group, there was a significant difference in hydrogen sulfide concentration, but there was no significant difference in methyl mercaptan. CONCLUSIONS: Quantifying the level of halitosis can be used to screen for MRONJ in patients taking bisphosphonates, such as patients with osteoporosis, prostate cancer, and breast cancer. CLINICAL RELEVANCE: MRONJ is accompanied by bad breath, and the concentrations of hydrogen sulfide and methyl mercaptan are associated with MRONJ.

Halitosis: etiology, prevention, and the role of microbiota.

OBJECTIVES: This study aims to review halitosis research, discuss its various causes, and propose effective interventions based on the underlying etiologies and mechanisms. The main research question is to identify the primary factors contributing to halitosis and appropriate strategies to address them. MATERIALS AND METHODS: A comprehensive literature review was conducted on halitosis and its associated causes, including oral pathological factors, oral microbial influences, microbial metabolic pathways, gastrointestinal diseases, and gut microbiota dysbiosis. RESULTS: Unhealthy eating habits and an imbalance of microorganisms in the oral cavity and gastrointestinal tract were identified as primary causes of halitosis. Dental caries, periodontal disease, xerostomia, and digestive disorders like gastritis and irritable bowel syndrome were also found to be related to the development of halitosis. Due to poor oral hygiene or antibiotic use, disruption of microbial communities can result in dysbiosis, inflammation, and halitosis. CONCLUSIONS: Halitosis is a multifactorial condition with various underlying causes, including oral and systemic diseases. Effective interventions should be tailored based on the specific etiologies and mechanisms involved. CLINICAL RELEVANCE: Understanding the factors contributing to halitosis is crucial for developing appropriate treatment strategies. Enhancing oral hygiene habits, using antimicrobial drugs, or administering probiotics may help regulate oral or intestinal flora, thereby improving halitosis and overall oral health.

Oral microbiome as a co-mediator of halitosis and periodontitis: a narrative review.

Objective: Halitosis or oral malodor is an unpleasant odor from the oral cavity. However, although patients with periodontitis often complain of halitosis, their relationship has not been fully elucidated. We reviewed previous literature based on the hypothesis that the relationship between halitosis and periodontitis is mediated by the oral microbiome. Materials and methods: This narrative review sought to provide insight into the causative role of the oral microbiome in influencing halitosis and periodontitis. In addition, we tried to deepen knowledge related to the relationship between halitosis and periodontitis generated by the oral microbiome accumulated over the past 40 years. Results: From 1984 to 2023, a total of 106 papers that carefully and scientifically dealt with halitosis and periodontitis were included in this narrative review. Based on previous results, halitosis and periodontitis were closely related. For decades, researchers have taken an intriguing approach to the question of whether there is a relationship between halitosis and periodontitis. Central factors in the relationship between halitosis and periodontitis include volatile sulfur compounds (VSCs), the oral microbiota that produce VSCs, and the inflammatory response. Conclusions: Taken together, the more severe periodontitis, the higher the level of VSC in halitosis, which may be mediated by oral microbiome. However, the relationship between the occurrence, maintenance, and exacerbation of periodontitis and halitosis is not a necessary and sufficient condition for each other because they are complex interplay even in one individual.

Factors influencing on the formation of dimethyl disulfide and dimethyl trisulfide in model systems.

The generations of dimethyl disulfide (DMDS) and dimethyl trisulfide (DMTS) in a binary or ternary model system including lipids, free amino acids and Maillard reaction products (MRPs) were studied. Various factors affecting the formation of DMDS and DMTS indicated that cysteine (Cys) and Cys MRPs could effectively decrease not only the concentrations of methionine (Met), DMDS and DMTS, but also the pH level. Rapid drops in pH limited the formation of DMDS and DMTS during Met thermal degradation. Quantitative analyses of DMDS and DMTS at acidic aqueous solutions revealed that the mixtures of MRPs derived from Cys and xylose (Xyl) had the best inhibition effect on the formation of DMDS and DMTS. The low level of DMDS and DMTS and the increasing level of furfuryl methyl sulfide and 2-thiophenecarboxaldehyde during storage indicated that MRPs derived from Cys and Xyl could effectively not only decrease the concertation of DMDS and DMTS, but also promote the development of thiophene and sulfur substituted furan. Thus, this study implied that MRPs derived from Cys/Xyl could be applied as effective substances to control the formation of DMDS and DMTS and improve the production of volatile compounds with meat-like aroma.

ORGANOLEPTIC AND HALITOMETRIC ASSESSMENTS DO NOT CORRELATE WELL IN INTRA-ORAL HALITOSIS: A SYSTEMATIC REVIEW AND META-ANALYSIS.

BACKGROUND: The gold standard method for diagnosing oral halitosis is the subjective organoleptic measurement. Device-supported methods are also widespread worldwide. The challenges and safety concerns around performing organoleptic measurements during pandemics and the diversity of measuring device alternatives raised our clinical question: which halitometer is the most suitable for diagnosing halitosis? METHODS: This systematic review was registered in PROSPERO (ID CRD42022320024). The search was performed on March 23, 2022 in the following electronic databases: MEDLINE, Embase, Scopus, Web of Science, and CENTRAL. Adult populations with or without halitosis were included, and patients with systemic diseases were excluded. Organoleptic (subjective) measurement and the device-supported (objective) methods were compared; the primary outcome was the correlation coefficient, and the secondary was the specificity and sensitivity of the devices. QUADAS-2 and QUADAS-C were used to evaluate the risk of bias in the studies. Random-effects meta analyses were performed on the outcomes, and the secondary outcomes were plotted on a common ROC plot. RESULTS: A total of 1231 records were found in the 5 databases. After the selection process, 76 articles were eligible for the systematic review, and 14,635 patients were involved in the qualitative analysis. The pooled Spearman's correlation coefficient (c.c.) for sulfide monitors was 0.65; 95% CIs: [0.53-0.74]; I2 = 95%, P < .01. The pooled Spearman's c.c. for portable gas chromatographs was 0.69; 95% CIs: [0.63-0.74]; I2 = 12%, P < .01. The pooled Spearman's c.c. for gas chromatographs was 0.76; 95% CIs: [0.67-0.83]; I2 = 0%, P < .01. DISCUSSION: None of the most commonly used halitometers proved to be significantly superior to the others. Halimeter and OralChroma measurements did not correlate well with the organoleptic level of oral halitosis in adults. Therefore, better halitometers need to be developed as an alternative to organoleptic measurements.

Volatile Sulfur Compounds Produced by the Anaerobic Bacteria Porphyromonas spp. Isolated from the Oral Cavities of Dogs.

Porphyromonas spp. are oral anaerobic Gram-negative bacteria that form black-pigmented colonies on blood agar and produce volatile sulfur compounds (VSCs), such as hydrogen sulfide (H2S), methyl mercaptan (CH3SH), and dimethyl sulfide ((CH3)2S), which cause halitosis and the destruction of periodontal tissues. P. gulae is considered the main pathogen involved in periodontal disease in dogs. However, the characteristics of the VSCs produced by P. gulae are unknown. In the present study, VSCs were measured in 26 isolates of P. gulae and some isolates of the other Porphyromonas spp. obtained from the oral cavities of dogs with periodontal disease using an in vitro assay with an Oral ChromaTM gas chromatograph. The results demonstrated that P. gulae was able to produce large amounts of H2S and CH3SH, and the dominant product was CH3SH (CH3SH/H2S was approximately 2.2). Other Porphyromonas spp. that were also obtained from the oral cavities of dogs with periodontal disease indicated similar levels of production of H2S and CH3SH to those of P. gulae. It is strongly suggested that the high levels of H2S and CH3SH produced by P. gulae and other Porphyromonas spp. contribute to halitosis and the destruction of periodontal tissues during the progression of periodontal disease in dogs.

Multi-dimension analysis of volatile sulfur compound emissions from an urban wastewater treatment plant.

Long-term monitoring of volatile sulfur compounds (VSCs) released at the water-air interface from different treatment units of an anaerobic/oxic (A/O) wastewater treatment plant (WWTP) was carried out to assess the temporal and spatial emission characteristics of VSCs, to explore relationships between wastewater quality and VSC release. The VSC from non-aerated and aerated units were collected using dynamic and static chambers, respectively, and determined using gas chromatography. The VSC emission fluxes diminished in the order of primary sedimentation tank (PST) > anaerobic areas (ANA) > oxic section 1 (OX1). VSCs were not detected in the oxic section 2 (OX2), the oxic areas section 3 (OX3), and the final setting basin (FSB). Release capacities of VSCs descended in the order of summer > fall > spring > winter, with July, August, and September being the months with the highest VSC release capacities. VSC emission fluxes correlated well with wastewater temperatures, sulfate concentrations, and COD. VSC emission flux empirical equations based on wastewater temperature, sulfate concentrations, and COD were established. Based on the established VSC emission empirical equation, a control strategy to reduce the operating costs of deodorization facilities was proposed. This strategy is economically efficient and reduces the consumption of electrical energy.

Selenium-binding protein 1 (SELENBP1) is a copper-dependent thiol oxidase.

Selenium-binding protein 1 (SELENBP1) was reported to act as a methanethiol oxidase (MTO) in humans, catalyzing the conversion of methanethiol to hydrogen peroxide, hydrogen sulfide and formaldehyde. Here, we identify copper ions as essential to this novel MTO activity. Site-directed mutagenesis of putative copper-binding sites in human SELENBP1 produced as recombinant protein in E. coli resulted in loss of its enzymatic function. On the other hand, the eponymous binding of selenium (as selenite) was no requirement for MTO activity and only moderately increased SELENBP1-catalyzed oxidation of methanethiol. Furthermore, SEMO-1, the SELENBP1 ortholog recently identified in the nematode C. elegans, also requires copper ions, and MTO activity was enhanced or abrogated, respectively, if worms were grown in the presence of cupric chloride or of a Cu chelator. In addition to methanethiol, we identified novel substrates of SELENBP1 from the group of volatile sulfur compounds, ranging from ethanethiol to 1-pentanethiol as well as 2-propene-1-thiol. Gut microbiome-derived methanethiol as well as food-derived volatile sulfur compounds (VSCs) account for malodors that may contribute to extraoral halitosis in humans, if not metabolized properly. As SELENBP1 is particularly abundant in tissues exposed to VSCs, such as colon, liver, and lung, it appears to contribute to copper-dependent VSC degradation.

Hydrogen sulfide production during early yeast fermentation correlates with volatile sulfur compound biogenesis but not thiol release.

Yeasts undergo intensive metabolic changes during the early stages of fermentation. Previous reports suggest the early production of hydrogen sulfide (H2S) is associated with the release of a range of volatile sulfur compounds (VSCs), as well as the production of varietal thiol compounds 3-sulfanylhexan-1-ol (3SH) and 3-sulfanylhexyl acetate (3SHA) from six-carbon precursors, including (E)-hex-2-enal. In this study, we investigated the early H2S potential, VSCs/thiol output, and precursor metabolism of 11 commonly used laboratory and commercial Saccharomyces cerevisiae strains in chemically defined synthetic grape medium (SGM) within 12 h after inoculation. Considerable variability in early H2S potential was observed among the strains surveyed. Chemical profiling suggested that early H2S production correlates with the production of dimethyl disulfide, 2-mercaptoethanol, and diethyl sulfide, but not with 3SH or 3SHA. All strains were capable of metabolizing (E)-hex-2-enal, while the F15 strain showed significantly higher residue at 12 h. Early production of 3SH, but not 3SHA, can be detected in the presence of exogenous (E)-hex-2-enal and H2S. Therefore, the natural variability of early yeast H2S production contributes to the early output of selected VSCs, but the threshold of which is likely not high enough to contribute substantially to free varietal thiols in SGM.

Eutrophication levels increase sulfur biotransformation and emissions from sediments of Lake Taihu.

Eutrophication can stimulate the emissions of volatile sulfur compounds (VSCs) accompanied by variations in environmental variables in lakes. However, the effects of eutrophication on VSC emissions from lake sediments as well as the underlying mechanisms remain unclear. In this study, depth gradient sediments at different eutrophication levels and seasons were collected from Lake Taihu to investigate the response of sulfur biotransformation in the sediments to eutrophication based on the analysis of environmental variables, microbial activity, abundance and community structure. H2S and CS2 were the main VSCs produced from the lake sediments, with the production rates of 2.3-7.9 and 1.2-3.9 ng g-1 h-1 in August, respectively, which were higher than those in March, mainly due to the increasing activity and abundance of sulfate-reducing bacteria (SRB) at high temperatures. The VSC production rates from the sediments increased with lake eutrophication level. Higher VSC production rates were detected in surface sediments in eutrophic regions but in deep sediments in oligotrophic regions. Sulfuricurvum, Thiobacillus and Sulfuricella were the main sulfur-oxidizing bacteria (SOB) in the sediments, while Desulfatiglans and Desulfobacca were the predominant SRB. Organic matter, Fe3+, NO3--N and total sulfur had significant influences on the microbial communities in the sediments. Partial least squares path modelling showed that the trophic level index could stimulate VSC emissions from lake sediments by influencing the activities and abundances of SOB and SRB. These findings indicated that sediments contributed substantially to VSC emissions from eutrophic lakes, especially surface sediments, and sediment dredging might be an effective way to mitigate VSC emissions from eutrophic lakes.

Effects of thyme on halitosis in gingivitis patients: Can thyme mouthwash prevent halitosis-A randomized trial.

OBJECTIVES: Bad breath is a condition that negatively affects people's social interactions and quality of life. The aim of this study was to evaluate the effect of thyme mouthwash on intraoral halitosis, gingival index (GI) and plaque index (PI) in patients with gingivitis. METHODS: In this retrospective study, 60 gingivitis patients (30 women/30 men) received initial periodontal treatment followed by oral hygiene instructions (OHI) and then were divided into four groups: The control group (C) received only OHI, while chlorhexidine (CHX) mouthwash was prescribed to the CHX group, Zinc acetate and CHX diacetate mouthwash was prescribed to the zinc acetate and CHX diacetate (ZnA) group, and the thyme (T) group was instructed to use thyme mouthwash. GI, PI and volatile sulfur compound (VSC) values were recorded at baseline and at the first week of treatment. RESULTS: The initial values of the recorded parameters did not differ significantly between the groups. In all groups, VSCs, GI and PI decreased after treatment (p = 0.001). There was no significant difference between the PI values of the groups after treatment (p = 0.188). On the contrary, the GI and VSC values after treatment were significantly different between the groups (p = 0.001). GI values were highest in the control group and lowest in the CHX group. In terms of VSCs, a significant difference was found between groups T and C, and between groups T and ZnA (p = 0.001). CONCLUSION: This study showed that the use of thyme mouthwash after periodontal treatment was effective in improving bad breath and gingivitis in gingivitis patients.

Effect of face masks on salivary parameters and halitosis: Randomized controlled crossover trial.

BACKGROUND: Face masking is associated with self-perceived dry mouth and halitosis. Aim of the study was to measure the effect of different face masks on salivary parameters and halitosis. METHODS: The randomized controlled crossover clinical trial with four periods included 40 oral healthy participants using different face masks (cloth mask, surgical mask, filtering facepiece 2 [FFP2] mask) or no mask (control) for 4 h in random order. Unstimulated salivary flow rate (primary outcome) and stimulated salivary flow rate, salivary pH and buffer capacity of stimulated and unstimulated saliva (secondary outcomes, blinded), and volatile sulfur compounds (secondary outcome) were measured before and after the 4-h periods. Statistical analysis was performed by repeated measures ANOVA (p < 0.05). RESULTS: Of 40 randomized participants, 39 completed the study. Unstimulated salivary flow rate prior to face masking amounted to 0.6 ± 0.3 ml/min. Face masking had no significant effect on unstimulated salivary flow (p = 0.550). Face masking had also no significant effect on the other salivary parameters (p ≥ 0.518). The concentration of volatile sulfur compounds (VSC) prior to face masking amounted to 157.3 ± 59.7 ppb. After face masking, the concentration of VSC increased slightly, but not significantly (p = 0.055): 168.1 ± 76.3 ppb (control), 199.3 ± 132.7 ppb (cloth masks), 188.5 ± 101.1 ppb (surgical masks), and 189.7 ± 90.1 ppb (FFP2 masks). CONCLUSION: Four hours of face masking did not change the salivary flow rate, pH, and buffer capacity, and had no significant effect on VSC's levels. Wearing face masks does not seem to result in measurable side-effects on salivary parameters such as a reduced salivary flow rate or VSC's levels. CLINICAL TRIAL REGISTRATION: The protocol was prospectively registered at ClinicalTrials.gov (NCT04914208) on June 4, 2021.

Evaluation of oenological tannins for preventing the light-struck taste.

The light-struck taste (LST) is a fault occurring in white and rosé wines associated to the formation of volatile sulfur compounds (VSCs) due to the reactions between riboflavin (RF) and methionine (Met). We investigated the possible preventing effect of 15 commercial tannins of different origin in model wine added with RF and Met, under oxic and anoxic conditions, and submitted to standardized light-exposure. All the tannins limited the degradation of Met in comparison to the tannin-free samples. Lower concentrations of VSCs were found in presence of tannins even under anoxia, condition favouring their formation. The sniffing trials evidenced the minor perception of cooked cabbage note with added tannins. The multivariate analysis showed the presence of flavan-3-ols was related to the formation of DMDS and DMTS, while tannic acid was related to MeSH, both the behaviors occurring under oxic condition. The study highlighted the ability of tannins to prevent the LST.

Estimation of sulfur fate and contribution to VSC emissions from lakes during algae decay.

Algae decay is an important process influencing environmental variables and emissions of volatile sulfur compounds (VSCs) in eutrophic lakes. However, effects of algae decay on VSC emissions from eutrophic lakes as well as fate of algae-derived sulfur remain poorly understood. In this study, simulated algae-sediment systems were used to explore the flow and distribution of sulfur during algae decay. VSCs including hydrogen sulfide (H2S), methanethiol (CH3SH), carbon disulfide (CS2) and dimethyl sulfide ((CH3)2S) were detected during algae decay, which increased with algae biomass and eutrophic levels in lakes. During algae decay, the highest H2S, CH3SH and (CH3)2S emission rates of 10.45, 21.82 and 43.26 µg d-1 occurred in the first 1-2 days, respectively, while the highest CS2 emission rates were observed between days 8 and 11. The maximum emissions of H2S and CS2 from algae decay were estimated at 0.51 and 0.35 mg m-2 d-1 in Lake Taihu, accounting for 1.57% and 0.69% of the total H2S and CS2 emissions of in situ, respectively. Algae decay could significantly increase the contents of total sulfur and total carbon in sediments by 2.90%-21.11% and 4.23%-45.05%, respectively. The VSC emissions during algae decay could be predicted using the multiple regression models with the contents of total carbon, total nitrogen and sulfur-containing compounds in sediments. Partial least squares path modelling demonstrated that algae decay had a low direct effect on VSC emissions with a strength of 0.06, while it had a significant influence on environmental variables with a strength of 0.63, which could affect VSC emissions with a strength of 0.85, indicating VSC emissions from eutrophic lakes were affected by the environmental variables rather than the direct influence of algae decay. These findings illustrated the mechanisms of VSC emissions during algae decay and provided insights into VSC control and mitigation for eutrophic lakes.

Effect of lemon essential oil on halitosis.

OBJECTIVES: To evaluate the effect of lemon essential oil (LEO) on salivary bacteria and volatile sulfur compound (VSC) production of patients with halitosis. MATERIALS AND METHODS: Saliva of five patients with halitosis was collected, after adding different concentrations (0.563-9 mg/ml) of LEO, detecting the growth of salivary bacteria, the formation of biofilm, and VSC production, and compare the difference of different concentrations of LEO on bacterial growth and VSC production. 48 volunteers were randomly divided into 4 groups. After gargling with LEO, cetylpyridinium chloride (CPC), chlorhexidine (CHX), and hydrogen peroxide (H2 O2 ) separately measure changes of VSC production and pH values at 30, 45, 60, 90, and 120 min and then compare the differences at different time points within group. RESULTS: Compared with the negative control group, under subinhibitory concentrations of LEO (0.563-2.25 mg/ml), the biofilm formation and VSC production of salivary bacteria in LEO group were significantly inhibited (p < 0.05). Compared with the baseline, the VSC production of subjects decreased after rinsing with the LEO in 60 min (p < 0.05). After gargling with LEO, the pH value rose significantly in 30 min and reverted to the baseline level at 120 min (p < 0.05). CONCLUSIONS: Lemon essential oil can inhibit the growth of salivary bacteria and reduce VSC production of patients with halitosis.