Characterizing and decoding the key odor compounds of Spirulina platensis at different processing stages by sensomics.

Processing is an indispensable technology in the preparation of Spirulina platensis (S. platensis). The key odorants in liquids, muds, and powders from S. platensis (NM and GZ) were characterized. A total of 90 odorants were identified and 41 odorants were sniffed with the flavor dilution (FD) factors ranging from 1 to 729. Among them, nonanal, decanal, d-limonene, ß-cyclocitral, and ß-ionone with FD factors ≥1 were detected in S. platensis during the whole processing stages. In addition, heptanal, (E, E)-2,4-nonadienal, trans-4,5-epoxy-(E)-2-decenal, 1-hepten-3-one, isophorone, 3-ethyl-2,5-dimethylpyrazine, and α-ionone exhibited higher odor activity values in powders; ß-myrcene, methional, and S-methyl methanethiosulphonate were key odorants in muds; while trans-3-penten-2-ol was key odorant in liquids. Besides, the GZ-mud presented stronger earthy and fishy odor than NM-mud. S. platensis powders have the stronger grassy odor, roasted odor, and marine odor than S. platensis muds. Overall, drying process promotes the formation of aldehydes, heterocyclic compounds, and terpenoids.

Effect of different starch on masking fishy odor compounds.

Starch is a common ingredient to improve gel property of freshwater fish surimi, but the function of natural starch to mask fishy odor compounds in surimi products has not been investigated systematacially. Therefore, this study aimed to determine which natural starch could effectively mask fishy odor compounds and clarify their interaction by GC-MS, FT-IR spectroscopy, raman spectroscopy, X-ray diffraction, scanning electron microscopy and 13C nuclear magnetic resonance. The results showed that when the concentration, crystal type, amylose content, and dispersion degree of starch was 1 %, type C, 48 % (w/v), and 200 mesh with 0.88 span, the starch had the strongest masking effect on typical fishy odor compounds, namely hexanal, 1-Octen-3-ol, (E,E)-2,4-Heptadienal and (E)-2-Octenal. It indicated that complexation and hydrogen bonding both occurred between the fishy odor compounds and starch.

Research progress of fishy odor in aquatic products: From substance identification, formation mechanism, to elimination pathway.

Fishy odor in aquatic products has a significant impact on the purchasing decisions of consumers. The production of aquatic products is a complex process involving culture, processing, transportation, and storage, which contribute to decreases in flavor and quality. This review systematically summarizes the fishy odor composition, identification methods, generation mechanism, and elimination methods of fishy odor compounds from their origin and formation to their elimination. Fishy odor compounds include aldehydes (hexanal, heptanal, and nonanal), alcohols (1-octen-3-ol), sulfur-containing compounds (dimethyl sulfide), and amines (trimethylamine). The mechanism of action of various factors affecting fishy odor is revealed, including environmental factors, enzymatic reactions, lipid oxidation, protein degradation, and microbial metabolism. Furthermore, the control and removal of fishy odor are briefly summarized and discussed, including masking, elimination, and conversion. This study provides a theoretical basis from source to elimination for achieving targeted regulation of the flavor of aquatic products, promoting industrial innovation and upgrading.

Strategies to reduce fishy odor in aquatic products: Focusing on formation mechanism and mitigation means.

Aquatic products, integral to human diets, often bear a distinct fishy odor that diminishes their appeal. Currently, the formation mechanisms of these odoriferous compounds are not fully understood, complicating their effective control. This review aims to provide a comprehensive overview of key fishy compounds, with a focus on their formation mechanisms and innovative methods for controlling fishy odors. Fishy odors in aquatic products arise not only from the surrounding environment but also from endogenous transformations due to lipid autoxidation, enzymatic reactions, degradation of trimethylamine oxide, and Strecker degradation. Methods such as sensory masking, adsorbent and biomaterial adsorption, nanoliposome encapsulation, heat treatment, vacuum treatment, chemical reactions, and biological metabolic transformations have been developed to control fishy odors. Investigating the formation mechanisms of fishy odors will provide solid foundational knowledge that can inspire creative approaches to controlling these unpleasant odors.

Identification of odor-causing compounds in six species of odor-producing microalgae separated from drinking water source with distinct fishy odor: Insight into microalgae growth and odor characteristics.

Fishy odor, as an offensive and unpleasant odor, could occur in drinking water source with poor nutrition, it is usually considered to be associated with odor-producing microalgae. However, the specific relations among fishy odor, fishy odorants and responsible microalgae were not elucidated comprehensively. In this paper, the odor-causing compounds generated from six microalgae with fishy odor characteristic, isolated in drinking water source Tongyu River, were identified simultaneously. The sensory evaluation result indicated that Tongyu River was principally related to fishy odor (odor intensity 6.5-7.6). Correspondingly, seven, nine, seven, six, seven and seven olfactory detection peaks (ODP) were screened by combining data of GC/O/MS and GC/GC/TOFMS in Cyclotella, Cryptomonas ovate, Melosira, Dinobryon sp., Synedra and Ochromonas sp., which were isolated in Tongyu River and cultured in laboratory. Totally twenty odor-causing compounds, including hexanal, 2-hexenal, 3-hexen-1-ol, heptanal, 1-octen-3-one, 2,4-heptadienal, 2-tetradecanone, 3,5-octadien-2-one, octanal, 1-octen-3-ol, 2-octenal, nonanal, 2,4-octadienal, 2-nonenal, decanal, 2,6-nonadienal, 2-decenal, undecanal, 2,4-decadienal and dodecanal, were screened and identified in all isolated microalgae. Additionally, fishy odor intensity for all identified microalgae increased obviously as microalgae cell number increased and microalgae cell ruptured in cultivation cycles through pearson and spearman correlation analysis. For the first time, twenty odor-causing compounds associating with fishy odor were recognized from six isolated microalgae, which would provide more scientific basis and theoretical support for preventing and treating fishy odor episode of drinking water source.

Effects of ethanol pretreatment on osteogenic activity and off-flavors in blue mussel (Mytilus edulis L.) enzymatic hydrolysates.

Aquatic protein hydrolysates have many biological activities, but the off-flavor seriously decreases their commercial acceptability. Therefore, it is important to invest in finding an effective deodorization of aquatic hydrolysates that do not affect activities. In this study, ethanol pretreatment of mussel was applied to establish a new method to deodorize the blue mussel (Mytilus edulis L.) hydrolysates. LC-MS and GC-MS analysis results showed that 87.34% of fatty acids, 83.94% of aldehydes, most volatile flavor compounds including aldehydes, ketones, alcohols, acids, and hydrocarbons were decreased after ethanol pretreatment. Besides, it was found that the enzymatic hydrolysates of mussel with or without ethanol pretreatment showed high osteogenic activity, which induced an increase of 33.65 ± 4.36% and 31.77 ± 5.45% in MC3T3-E1 cell growth. These results suggest that ethanol pretreatment has beneficial potential for improving the flavor aspects of blue mussel peptides which may have the potential to stimulate bone regeneration and formation.

Enrichment of antiplatelet peptides and removal of fishy odor from silver carp skin collagen hydrolysates by macroporous resins: pH value of loading sample affects the peptides separation.

Enrichment of antiplatelet peptides from silver carp skin collagen hydrolysates (CH) was studied using macroporous resins. Static adsorption showed that XAD-16 resin was the suitable resin due to its high adsorption capacity. The dynamic desorption of CH was studied on XAD-16 resin by ethanol gradient elution. Interestingly, pH value of loading sample had a great impact on the peptides separation. Results revealed that the yield and the antiplatelet activity of Ethl-20% fraction were highest at loading sample pH 6.0. The antiplatelet peptides were enriched in the 20% ethanol fraction with IC50 2.03 mg/mL compared to IC50 of CH, 4.7 mg/mL. Besides, the Ethl-20% fraction had a weakest fishy odor. Moreover, a series of peptides containing Hyp-Gly or Pro-Gly were identified from Ethl-20% fraction, which contributed to the antiplatelet activities. This study provided a simple and efficient method for large-scale separation enrichment of antiplatelet peptides as functional foods from CH.

[Comparison of odor and quality of Galli Gigerii Endothelium Corneum derived from domestic chickens and broilers].

Galli Gigerii Endothelium Corneum(GGEC) is commonly used for the clinical treatment of indigestion, vomiting, diarrhea, and infantile malnutrition with accumulation. In recent decades, omnivorous domestic chickens, the original source of GGEC, has been replaced by broilers, which may lead to significant changes in the quality of the yielding GGEC. Through subjective and objective sensory evaluation, biological evaluation, and chemical analysis, this study compared the odor and quality between GGEC derived from domestic chickens and that from broilers. The odor intensity between them was compared by odor profile analysis and it was found that the fishy odor of GGEC derived from domestic chickens was significantly weaker than that of GGEC from broilers. Headspace-solid phase microextraction-gas chromatography-triple quadrupole tandem mass spectrometry(HS-SPME/GC-QQQ-MS/MS) suggested that the overall odor-causing chemicals were consistent with the fishy odor-causing chemicals. According to the odor activity va-lue and the orthogonal partial least squares discriminant analysis(OPLS-DA) result, dimethyl trisulfide, 2-methoxy-3-isobutylpyrazine, and 2-methylisoborneol were responsible for the fishy odor(OAV≥1) and the content of fishy odor-causing chemicals in GGEC derived from broilers was 1.12-2.13 folds that in GGEC from domestic chickens. The average pepsin potency in GGEC derived from broilers was 15.679 U·mg~(-1), and the corresponding figure for the medicinal from domestic chickens was 26.529 U·mg~(-1). The results of pre-column derivatization reverse-phase high-performance liquid chromatography(RP-HPLC) assay showed that the content of total amino acids and digestion-promoting amino acids in domestic chickens-derived GGEC was 1.12 times and 1.15 times that in GGEC from broilers, and the bitter amino acid content was 1.21 times folds that of the latter. In conclusion, GGEC derived from domestic chickens had weaker fishy odor, stronger enzyme activity, higher content of digestion-promoting amino acids, and stronger bitter taste than GGEC from broilers. This study lays a scientific basis for studying the quality variation of GGEC and provides a method for identifying high-quality GGEC. Therefore, it is of great significance for the development and cultivation of GGEC as both food and medicine and breeding of corresponding varieties.

Promotion of fishy odor release by phenolic compounds through interactions with myofibrillar protein.

Phenolic compounds are effective means of promoting the release of fishy odor compounds, thereby significantly decreasing the fishy odor of fish products. In this study, the mechanisms underlying the promotion of fishy odor release by three phenolic compounds, rosmarinic acid (RA), carnosic acid (CA), and carnosol (CS), through interactions with the myofibrillar protein (MP) of silver carp were investigated. The addition of phenolic compounds (5, 25 and 125 µmol/g protein) was found to significantly alter the conformation of MP and decrease the fishy odor compound binding sites through the formation of phenolic compound-protein complexes. Of note, both sensory evaluation and gas chromatography analysis revealed a significant facilitation of fishy odor compound release by phenolic compounds in the presence of MP. In MP treated with 125 µmol/g protein of RA, the contents of fishy odor compounds increased from 30% to- 37%, with an increase of fishy odor score of 58%, compared to the un-treated control. Similar changes were observed when treating MP with CA or CS. These changes were likely due to the enhancement of protein-protein interactions caused by phenolic compounds and competition between fishy odor and phenolic compounds for hydrophobic binding sites in MP. The release of fishy odor compounds increased as the amount of phenolic compounds utilized increased with RA being the strongest promoter of fishy odor compounds, followed by CA and CS.

Deodorizing effects of rosemary extract on silver carp (Hypophthalmichthys molitrix) and determination of its deodorizing components.

Fishy odor in fish products severely influences both eating quality and commercial acceptability, and natural plant extracts, particularly spices, have recently become popular for the removal of fishy odor. This study aimed to explore the potential of rosemary extract for the deodorization of silver carp (Hypophthalmichthys molitrix), as well as to identify the deodorizing components in rosemary extract. Results showed that all of the spice extracts used in this study (ginger, garlic, angelica dahurica, fennel, rosemary, nutmeg, white cardamom, cinnamon, star anise, and bay leaf) significantly reduced the fishy odor value of silver carp, among which rosemary extract was most effective, decreasing the fishy odor value by about 58%. Gas chromatography-mass spectrometry analysis and sensory evaluation showed that the fishy odor value and concentrations of the fishy odor-active compounds were significantly reduced by the application of rosemary extract. However, the lower the total phenolic content of rosemary extract, the poorer the deodorizing effects against silver carp, suggesting that the deodorizing effect was primarily driven by polyphenols. Fourteen phenolic compounds were measured in rosemary extract, and three individual phenolic compounds (rosmarinic acid [RA], carnosic acid [CA], and carnosol [CS]) were chosen for deodorizing experiment. Sensory detection results and changes of contents of volatile showed that these three phenolic compounds are effective at removing the fishy odor. These results suggest that polyphenols are the main deodorizing components, and RA, CA, and CS are the main deodorizing active compounds in rosemary extract. PRACTICAL APPLICATION: The results of this study may provide a new way to determine the deodorizing components of spice extracts. Moreover, it can provide guidance for further research in investigating the deodorizing mechanism of sipce extracts.

Bromhidrosis por trimetilaminuria. Dificultades en su diagnóstico y tratamiento / Bromhidrosis caused by trimethylaminuria. Difficulties in its diagnosis and treatment

La trimetilaminuria es una causa de bromhidrosis, que hay que tener en cuenta en niños prepúberes con un desarrollo normal. Su relación con la ingesta, sobre todo de pescado marino, nos hará sospechar su existencia, que deberemos confirmar mediante el análisis de la excreción urinaria de trimetilamina y el estudio genético. Presentamos cuatro casos de trimetilaminuria donde se analizan y discuten las fórmulas más empleadas para valorar una excreción urinaria aumentada de trimetilamina, su correlación con la gravedad del cuadro y con el rendimiento de las pruebas genéticas. Por último, se describen los tratamientos empleados y se realiza una propuesta de tratamiento, basada en las recomendaciones dietéticas y en el asesoramiento a los padres para un mejor conocimiento y manejo de la enfermedad (AU)

Trimethylaminuria is a cause of bromhidrosis to be considered in pre-pubertal children, with normal development. Its relation with the ingestion, especially of marine fish, will make us suspect its existence that we will have to confirm by means of the analysis of the urinary excretion of trimetilamine and the genetic study. We present four cases of trimethylaminuria where the most used formulas to assess increased urinary excretion of trimethylamine are analysed and discussed, as well as their correlation with the severity of the disease and with the performance of genetic tests. Finally, the used treatments are described, and a treatment proposal is made, based on dietary recommendations and advices to parents for a better understanding and management of the disease (AU)

Effect of Microbial Fermentation on the Fishy-Odor Compounds in Kelp (Laminaria japonica).

Kelp (Laminaria japonica) is an important marine resource with low cost and rich nutrition. However, its fishy odor has compromised consumer acceptance. In this study, the effects of fermentation with Lactobacillus plantarum FSB7, Pediococcus pentosaceus CICC 21862 and Saccharomyces cerevisiae SK1.008 on fishy notes in kelp was studied using gas chromatography-mass spectrometry (GC-MS), gas chromatography-ion mobility spectrometry (GC-IMS) and odor activity values (OAVs). Forty-four volatile organic compounds (VOCs) were identified in unfermented kelp, most of which were aldehydes, followed by alkanes, alcohols and ketones. Among them were 19 volatile compounds with OAV greater than one. Substances containing α,ß-unsaturated carbonyl structure (1-Octen-3-one, (E,Z)-2,6-nonadienal, (E,E)-2,4-decadienal, etc.) are the main contributors to kelp fishy odor. The number of VOCs in kelp samples fermented by L. plantarum, P. pentosaceus and S. cerevisiae were decreased to 22, 24 and 34, respectively. GC-IMS shows that the fingerprint of the S. cerevisiae fermented sample had the most obvious changes. The disappearance of 1-octen-3-one and a 91% decrease in unsaturated aldehydes indicate that S. cerevisiae was the most effective, while L. plantarum and P. pentosaceus only reached 43-55%. The decrease in kelp fishy notes was related to the decrease in α,ß-unsaturated carbonyl groups. The experimental results show that odor reduction with fermentation is feasible.

Development of Hydrolysis and Defatting Processes for Production of Lowered Fishy Odor Hydrolyzed Collagen from Fatty Skin of Sockeye Salmon (Oncorhynchus nerka).

Lipid oxidation has a negative impact on application and stability of hydrolyzed collagen (HC) powder from fatty fish skin. This study aimed to produce fat-free HC powder from salmon skin via optimization of one-step hydrolysis using mixed proteases (papain and Alcalase) at different levels. Fat removal processes using disk stack centrifugal separator (DSCS) for various cycles and subsequent defatting of HC powder using isopropanol for different cycles were also investigated. One-step hydrolysis by mixed proteases (3% papain and 4% Alcalase) at pH 8 and 60 °C for 240 min provided HC with highest degree of hydrolysis. HC powder having fat removal with DSCS for 9 cycles showed the decreased fat content. HC powder subsequently defatted with isopropanol for 2 cycles (HC-C9/ISP2) had no fat content with lowest fishy odor intensity, peroxide value, and thiobarbituric acid reactive substances than those without defatting and with 1-cycle defatting. HC-C9/ISP2 had high L*-value (84.52) and high protein (94.72%). It contained peptides having molecular weight less than 3 kDa. Glycine and imino acids were dominant amino acid. HC-C9/ISP2 had Na, Ca, P, and lowered odorous constituents. Combined processes including hydrolysis and defatting could therefore render HC powder free of fat and negligible fishy odor.

Establishment and Application of Identification Method for Fishy Odor of Cordyceps Based on HS-SPME/GC-QQQ-MS/MS / 中国实验方剂学杂志

Objective:To establish and apply a new practical analytical method for identifying the fishy odor of Cordyceps based on headspace-solid phase microextraction-gas chromatography-triple quadrupole mass spectrometry （HS-SPME/GC-QQQ-MS/MS） technique. Method:The InertCap Pure-WAX capillary column （0.25 mm×30 m， 0.25 μm） was used for chromatographic separation. The injection port temperature was set at 250 ℃. The injection mode was split injection with a ratio of 5∶1. High purity helium was used as the carrier gas and control mode was set to constant pressure. The column flow rate was 1.43 mL∙min^-1， the linear velocity was 43.3 cm∙s^-1， and the purge flow rate was 3.0 mL∙min^-1. The chromatographic column temperature program as follows：maintained the initial temperature at 50 ℃ for 5 min， and increased the temperature at a rate of 10 ℃∙min^-1 to 250 ℃， held for 10 min. The column equilibrium time was 2.0 min. The ion source of mass spectrographic analysis was electron ionization with ion source temperature of 200 ℃， and the monitoring mode was set to multiple reaction monitoring. Result:Seven batches of Cordyceps samples were collected， including 3 batches from Sichuan， 3 batches from Qinghai and 1 batch from Tibet. There were six batches of counterfeits， including 3 batches from Sichuan， 2 batches from Guizhou and 1 batch in Xinjiang. A total of 81 volatile compounds were screened out in Cordyceps， which could be divided into 13 types （esters， ketones， aldehydes and others） according to the compound structure， indicating that the fishy odor of Cordyceps was a complex odor. There was no significant difference in the types of volatile compounds of Cordyceps from different regions， which suggested that these volatile compounds in Cordyceps produced in Tibet （Naqu）， Qinghai （Yushu and Guoluo） and Sichuan （Litang， Rangtang and Seda） were relatively consistent. However， the contents of some volatile compounds in Cordyceps produced in different regions were quite different， and 16 volatile compounds with significant difference were screened out， including 1-methoxy-2-propyl acetate， <italic>γ</italic>-octalactone， hexyl acetate and others， those compounds maybe could been used as the quality markers for identification of regions of Cordyceps. There was a large difference in volatile compounds between Cordyceps and its counterfeits， and 34 volatile compounds were screened out， including ethyl acetate， acetophenone， 2-ethyl-1-hexanol and others， those compounds maybe could been used as the quality markers for authenticity identification of Cordyceps. Conclusion:In summary， the established method for identifying the fishy odor of Cordyceps in this paper has the characteristics of high sensitivity， accuracy and simplicity， which can provide reference for the analysis of volatile compounds in other Chinese herbal medicines.

Hydrolyzed collagen from porcine lipase-defatted seabass skin: Antioxidant, fibroblast cell proliferation, and collagen production activities.

Defatting of seabass skins using porcine pancreas lipase (PPL) at 25 or 50 units/g dry matter) for 1-3 hr at 30ºC was investigated. Treatment of seabass skin with PPL (25 unit/g dry matter) for 3 hr removed 83.81% lipids when compared to 57.27% using isopropanol. Hydrolysis of PPL-treated skin by papain (0.3 unit/g dry matter) (PPL-papain-3 process) at 40ºC for 90 min provided hydrolyzed collagen (HC) with higher yield, α-amino group content, ferric-reducing antioxidant power, and metal chelating activity than other treatments (p < 0.05). There was no difference in fishy odor between HC from PPL-papain-2 and PPL-papain-3 processes (p > 0.05). All the HC (50-250 µg/ml) samples stimulated L929 fibroblast cell proliferation and also induced collagen production in a dose-dependent manner. Also, all HC contained peptides with molecular weight of 406-11,860 Da. Gly and imino acids were dominant amino acids in HC prepared with PPL-papain-3 process. PRACTICAL APPLICATIONS: Seabass skin is a potential raw material for the production of hydrolyzed collagen (HC). However, seabass skin contains a large amount of lipids, including polyunsaturated fatty acids. These unsaturated lipids are oxidized during processing, particularly during hydrolysis at high temperature. This leads to the development of undesirable odor, especially fishy odor. Therefore, seabass skin defatting is an important step for improving the quality of the resulting HC. The use of lipase is an alternative method that can be used to remove lipids in skins without using solvents. HC from defatted skins will contain bioactive peptides and therefore, can be used as a food supplement or for skin nourishment.

Effect of Pulsed Electric Field-Assisted Process in Combination with Porcine Lipase on Defatting of Seabass Skin.

Defatting of seabass skins using pulsed electric field (PEF)-assisted process at different electric field strengths (16 and 24 kV/cm) and times (36, 72, and 108 ms) in combination with porcine pancreas lipase (PPL) at 25 U/g dry matter was investigated. PEF-treated skin at 24 kV/cm for 72 ms followed by PPL treatment removed 86.93% lipids. PEF-treated skin was further optimized for lipid reduction by response surface methodology. Central composite design was adopted to establish treatments based on two independent variables, involving PPL concentration (30 to 55 U/g dry matter) and hydrolysis time (60 to 180 min). Second-order polynomial model was used for predicting the response. The highest lipid removal (91.96 ± 1.70%) was attained when the optimal condition (42.36 PPL units/g dry skin matter for 139.78 min) was used. The experiment value was in accordance with the predicted value. PEF-PPL-treated skin had lower monounsaturated and polyunsaturated fatty acids than the solvent-extracted skin (P < 0.05). When PEF-PPL-treated skin was hydrolyzed using papain at 0.30 U/g dry matter, lower fishy odor/flavor of resulting hydrolyzed collagen (PEF-PPL-HC) was found than other samples (P < 0.05). Lower total volatile compounds were also obtained in PEF-PPL-HC sample. Thus, the use of PEF pretreatment along with PPL before papain hydrolysis effectively prevented the formation of fishy odor/flavor in hydrolyzed collagen from seabass skin. PRACTICAL APPLICATION: Fishy odor/flavor caused by lipid oxidation of fish skin hydrolysates limits their applications in foods. Defatting process is the significant step for skin pretreatment. Although several methods could remove lipids from fish skins, either by lipase or solvent extraction, fishy odor/flavor is still detected in hydrolysate. Pulsed electric field-assisted process in combination with porcine lipase is another approach that can be used to enhance efficiency via electroporation, causing the loosened skin matrix and facilitating the migration of lipase into the skin. Consequently, the resulting hydrolysate might have the lowered fishy odor/flavor and could be used in foods, especially for fortification.

Analysis of fishy taint in duck eggs reveals the causative constituent of the fishy odor and factors affecting the perception ability of this odor.

Fresh duck eggs normally have an unpleasant fishy odor when compared with eggs from other poultry. However, the cause of this unpleasant smell remains unknown. Besides, we have limited knowledge regarding the perception ability of this odor. Therefore, we aimed to identify the causative substances responsible for the fishy odor in duck eggs, and further evaluate the factors affecting the perception ability of this odor. We detected and quantified the volatile substances in the yolks of Jingjiang duck and Beijing duck eggs using headspace gas chromatography, and evaluated the fishy odor rating scores. We performed association studies on the relationship between the relative content of volatile substances and fishy odor rating scores. The fishy odor of egg yolks from different species/breeds was also characterized. Furthermore, we assessed the species/breeds of poultry eggs and the effects of gender and region of the evaluators on the fishy odor rating score by using an ordinal logistic regression model. Results showed that trimethylamine (TMA) is responsible for the fishy odor of duck eggs, which was confirmed with subsequent verification (P < 0.001). The fishy odor of duck eggs was stronger than that of chicken eggs; the fishy odor of Jingjiang duck eggs was the strongest. Results also indicated that the fishy odor perception ability was affected by the gender and region of the evaluators (P < 0.001). Overall, these data clarified that TMA imparted the fishy odor to duck eggs; factors such as gender and region may affect the fishy odor perception ability.

Identification of fishy odor causing compounds produced by Ochromonas sp. and Cryptomonas ovate with gas chromatography-olfactometry and comprehensive two-dimensional gas chromatography.

Disgusting fishy odor problems have become a major concern in drinking water quality, and are commonly related to algal proliferation in source water. Unlike the typical musty/earthy odorants 2-methylisoborneol (MIB) and geosmin, identification of the corresponding fishy odorants is still a big challenge. In this study, two species of fishy-odor-producing algae, Ochromonas sp. and Cryptomonas ovate, were cultured to explore the odor production characteristics and typical odorants. When algae were ruptured in the stationary and decline phases, fishy odor intensities of 4 to 8 characterized by FPA were produced. However, some frequently reported aldehydes that could cause fishy odor, including n-hexanal, 2-octenal, heptanal, 2,4-heptanal and 2,4-decadienal, were not detected in either of the cultured algae. The possible fishy odor-causing compounds were further identified by combining gas chromatography-olfactometry (GC-O/MS) and comprehensive two-dimensional gas chromatography (GC × GC-TOFMS) using retention indices (RIs). From GC-O/MS analysis, twelve and six olfactometry peaks with various odor characteristics were identified in Ochromonas sp. and Cryptomonas ovate, respectively, of which three and two olfactometry peaks showed fishy odor characteristics. 2-Nonenal, 2,4-octadienal, fluorene and 2-tetradecanone were identified as fishy odorants in Ochromonas sp., and 1-octen-3-ol, 6-methyl-5-hepten-2-one, 1-octen-3-one, 2-nonenal and 2,4-octadienal were identified in Cryptomonas ovate. Other identified compounds, including butyl butanoate (fragrant odor), ionone (fragrant odor), bis (2-chloroisopropyl) ether (chemical odor) etc., did not show fishy features. Therefore, the fishy odor might be a synthetic and comprehensive odor, which resulted from the combination of different odorants and their synergistic effects. The results of this study will be helpful for understanding fishy odor problems, which will provide support for fishy odor management and control in the drinking water industry.

Production and fate of fishy odorants produced by two freshwater chrysophyte species under different temperature and light conditions.

Fishy odor has become one of the most often encountered aesthetic water quality problems in drinking water. While fresh water algae living in colder water can produce offensive fishy odors, their environmental behaviors remain poorly understood. In this study, two chrysophyte species (Synura uvella and Ochromonas sp.), which are often associated with fishy odor events, were selected to investigate the effect of temperature (8, 16, and 24 °C) and light intensity (10, 41, and 185 µmol photons m-2 s-1) on algal growth and odorant production. Five polyunsaturated aldehyde derivatives, including 2,4-heptadienal, 2-octenal, 2,4-octadienal, 2,4-decadienal, and 2,4,7-dectridienal, were identified as fishy/cod liver oil/fatty/rancid descriptors in the cultures of the two algae based on gas chromatography-olfactometry-mass spectrometry and comprehensive two-dimensional gas chromatography mass spectrometry. While biomass yield increased with the increase in temperature for both species, significantly higher odorant yields (production of odorants per cell) were obtained at 8 °C. The total odorant production and cell yield of the odorants decreased with the increase in light intensity from 10 to 185 µmol photons m-2 s-1. The biodegradation half-lives for the released odorants were 6-10 h at 8 °C and 2-4 h at 24 °C, whereas the volatilization half-lives were 36-97 d at 8 °C and 6-17 d at 24 °C, suggesting that temperature-dependent biodegradation was an important factor controlling the fate of fishy compounds in aquatic environments. The results of this study will help clarify why most fishy odor events occur in cooler seasons, and provide knowledge related to cold water persistence for the management of fishy odor problems associated with algae.

Lignin and holocellulose from coir pith involved in trimethylamine (fishy odor) adsorption.

Coir pith is a highly potential adsorbent for adsorbing trimethylamine (TMA). It harbors a higher adsorption capacity for TMA compared to commercial activated carbon (CAC). It was found that lignin and holocellulose extracted from coir pith played an important role in TMA adsorption. Lignin itself had the highest TMA adsorption capacity (269.01 mg/g) followed by holocellulose (75.43 mg/g), coir pith (14.3 mg/g) and CAC (10.26 mg/g), respectively. The pseudo-first- and second orders were applied to the kinetic data. For the adsorption of TMA by coir pith, the best fit was achieved by the pseudo-second order. Thermodynamic studies showed an endothermic and physico-chemical adsorption process between TMA and the coir pith. TMA desorption study suggested that only 14%-47% of TMA was desorbed with distilled water. In addition, Fourier transform-infrared (FT-IR) spectra showed that C-H bond (methyl group), C-O bond from phenolic alcohol and C-O bond from tertiary alcohol in lignin and holocellulose were involved in TMA adsorption. Coir pith-based filter showed high TMA adsorption efficiency (98%) and kept constant for more than 48 days in a continuous system. Pilot scale experiment, coir pith beads filter could be succesfully applied as a packing material for TMA removal. Therefore, coir pith can be used as a promising packing material for TMA treatment at contaminated site.