Characterization and finding the origin of off-flavor compounds in Nile tilapia cultured in net cages in hydroelectric reservoirs, São Paulo State, Brazil.

An increasing demand for fish products has led to an intensive aquaculture production in Brazil, and cultivation of fish constituted 860 × 103 tons in 2022, contributing to the 87% of total fish consumption. Nile tilapia constitutes almost half of the aquaculture production, and most tilapia farms use floating net cages. One of the major constraints of intensive fish production is production of off-flavors. Release of nutrients by the fish leads to deterioration of the water quality and stimulates growth of microorganisms, also including off-flavor producing species. The objective of this study was to determine levels of taste and odor compounds (geosmin, 2-MIB and a selection of volatile compounds) and their impact on the flavor quality of Nile tilapia produced in net cages in reservoirs in São Paulo State, Brazil. GC-MS analysis of fish and water from six different farms showed concentrations of geosmin in the water from 1 to 8 ng/L, while geosmin in fish flesh ranged from 40 to 750 ng/kg. The level of 2-MIB in water was 2 to 25 ng/L, and 0 to 800 ng/kg fish. The GC-MS analysis also revealed presence of more than 100 volatile organic compounds in the fish flesh, consisting of aldehydes, alcohols, benzene derivatives, hydrocarbons, ketones and few other compounds. Geosmin and 2-MIB related flavor notes were detected in all fish by a sensory panel, and a high correlation between the chemical and sensory analyses was found. The potential impact of the volatile organic compounds on the fish flavor is discussed. Analysis of the water quality in the reservoirs indicated that levels of geosmin and 2-MIB levels were highly influenced by the nutrient levels in the water.

Risk of Collapse in Water Quality in the Guandu River (Rio de Janeiro, Brazil).

The Guandu River, one of the main rivers in the state of Rio de Janeiro, provides water for more than nine million people in the metropolitan region. However, the Guandu has suffered from massive domestic and industrial pollution for more than two decades, leading to high levels of dissolved total phosphorus, cyanobacteria, and enteric bacteria observed during the summers of 2020 and 2021. The use of Phoslock, a palliative compound, was not effective in mitigating the levels of phosphorus in the Guandu River. Furthermore, potable water driven from the river had levels of 2-MIB/geosmin and a mud smell/taste. With all these problems, several solutions are proposed for improving the Guandu River water quality, including establishment of (i) sewage treatment plants (STPs), (ii) strict water quality monitoring, (iii) environmental recovery (e.g., reforestation), and (iv) permanent protected areas. The objective of this paper is to verify the poor water quality in the Guandu and the ineffectiveness and undesired effects of Phoslock.

Microbial Production of the Off-Flavor Geosmin in Tilapia Production in Brazilian Water Reservoirs: Importance of Bacteria in the Intestine and Other Fish-Associated Environments.

AIM: To determine major sources of microbially produced geosmin in the commercially important aquaculture fish species tilapia. METHODS AND RESULTS: Abundance and composition of geosmin-producing bacteria in water and fish biosphere (intestine, digesta, and fins) of Nile tilapia (Oreachromis niloticus) raised in net cages in Brazilian freshwater farms were examined. By combining qPCR of the geosmin synthase geoA gene and 16S rRNA gene amplicon sequencing to identify potential geosmin-producing organisms, we observed that the proportion and composition of geosmin producers appeared to be rather similar in the water, digesta, intestinal mucous, and on skin, making up about 0.1-0.2% of the total bacterial densities. A high proportion of Cyanobacteria and other putative geosmin producers affiliated to the Actinomycetales were identified in the intestinal mucous layer. The main uptake site for geosmin in fish is traditionally assumed to be through the gill surface, but the present results suggest that uptake by the intestinal tract may represent a major source of geosmin uptake in fish. CONCLUSION: The high abundance of geosmin-producing bacteria in the intestinal mucous layer and digesta may indicate that the digestive system in fish is an important, but hitherto overlooked, source of geosmin and likely other off-flavors in fish. SIGNIFICANCE AND IMPACT OF STUDY: Tainting of fish by microbially produced off-flavors spoils fish quality and lowers consumer preferences for aquaculture-produced freshwater fish. Our results highlight the potential for the application of probiotic microorganisms for management of the intestinal microflora to improve the fish quality. HIGHLIGHTS: -Off-flavor producing bacteria are widely abundant in aquaculture.-Off-flavor producers found on skin surface of fish.-Off-flavor producing bacteria accumulate in the digestive system.-Off-flavor producers might release significant amounts of off-flavor during lysis in the gut.-Off-flavor uptake through the digestive system might be quantitatively significant.

Geosmin induces genomic instability in the mammalian cell microplate-based comet assay.

Geosmin (GEO) (trans-1,10-dimethyl-trans-9-decalol) is a metabolite that renders earthy and musty taste and odor to water. Data of GEO genotoxicity on mammalian cells are scarce in the literature. Thus, the present study assessed the genotoxicity of GEO on Chinese hamster ovary (CHO) cells in the microplate-based comet assay. The percent of tail DNA (tail intensity (TI)), tail moment (TM), and tail length (TL) were used as parameters for DNA damage assessment. The results demonstrated that concentrations of GEO of 30 and 60 µg/mL were genotoxic to CHO cells after 4- and 24-h exposure periods, in all parameters evaluated, such as TI, TM, and TL. Additionally, GEO 15 µg/mL was genotoxic in the three parameters only in the 24-h exposure time. The same was observed for GEO 7.5 µg/mL, which induced significant DNA damage observed as TI in the 24-h treatment. The results present evidence that exposure to GEO may be associated with genomic instability in mammalian cells.

Off-flavor by geosmine and 2-methylisoborneol in aquaculture / Off-flavor por geosmina e 2-Metilisoborneol na aquicultura

The aquaculture has reached a new age, in which traditional extensive systems are being substituted by technology-intensive aquaculture systems. In order to achieve higher yields, aspects of fish quality have been neglected, a fact that causes or aggravates hitherto tolerable problems, such as off-flavor. The main purpose of this review is to clarify, briefly, the problem of off-flavor in aquaculture, as well as put forward present solutions and future perspectives.

A aquicultura entra numa nova era nas últimas décadas, em que os sistemas extensivos tradicionais estão sendo substituídos por criações intensivas e tecnificadas. No intuito de auferir maior lucratividade, a qualidade do pescado tem sido relegada a segundo plano, fato que gera ou agrava problemas antes toleráveis, a exemplo do off-flavor. Assim, a presente revisão tem por objetivo esclarecer, de forma sucinta, o problema do off-flavor na aquicultura, bem como apontar as soluções atuais e as perspectivas futuras para reverter a situação que se apresenta.

Off-flavor by geosmine and 2-methylisoborneol in aquaculture / Off-flavor por geosmina e 2-Metilisoborneol na aquicultura

The aquaculture has reached a new age, in which traditional extensive systems are being substituted by technology-intensive aquaculture systems. In order to achieve higher yields, aspects of fish quality have been neglected, a fact that causes or aggravates hitherto tolerable problems, such as off-flavor. The main purpose of this review is to clarify, briefly, the problem of off-flavor in aquaculture, as well as put forward present solutions and future perspectives.

A aquicultura entra numa nova era nas últimas décadas, em que os sistemas extensivos tradicionais estão sendo substituídos por criações intensivas e tecnificadas. No intuito de auferir maior lucratividade, a qualidade do pescado tem sido relegada a segundo plano, fato que gera ou agrava problemas antes toleráveis, a exemplo do off-flavor. Assim, a presente revisão tem por objetivo esclarecer, de forma sucinta, o problema do off-flavor na aquicultura, bem como apontar as soluções atuais e as perspectivas futuras para reverter a situação que se apresenta.

Off-flavor by geosmine and 2-methylisoborneol in aquaculture / Off-flavor por geosmina e 2-Metilisoborneol na aquicultura

The aquaculture has reached a new age, in which traditional extensive systems are being substituted by technology-intensive aquaculture systems. In order to achieve higher yields, aspects of fish quality have been neglected, a fact that causes or aggravates hitherto tolerable problems, such as off-flavor. The main purpose of this review is to clarify, briefly, the problem of off-flavor in aquaculture, as well as put forward present solutions and future perspectives.

A aquicultura entra numa nova era nas últimas décadas, em que os sistemas extensivos tradicionais estão sendo substituídos por criações intensivas e tecnificadas. No intuito de auferir maior lucratividade, a qualidade do pescado tem sido relegada a segundo plano, fato que gera ou agrava problemas antes toleráveis, a exemplo do off-flavor. Assim, a presente revisão tem por objetivo esclarecer, de forma sucinta, o problema do off-flavor na aquicultura, bem como apontar as soluções atuais e as perspectivas futuras para reverter a situação que se apresenta.

Remoção dos compostos odoríferos geosmina e 2-metilisoborneol de águas de abastecimento através de processos de aeração em cascata, dessorção por ar e nanofiltração / Removal of the odoriferous compounds geosmin and 2-methylisoborneol from drinking water by the processes of cascade aeration, air strippingand nanofiltration

Atividades humanas aceleram o processo natural de eutrofização das águas, favorecendo a floração de algas e cianobactérias. Estes organismos emitem os compostos 2-metilisoborneol (MIB) e geosmina, que conferem gosto e odor de mofo e terra à água. A presença destes compostos se estende à água potável uma vez que os processos convencionais de tratamento são insuficientes para removê-los. Esta pesquisa foi realizada com o objetivo de avaliar alternativas de processos de tratamento para a remoção de MIB e geosmina da água. Os processos estudados foram aeração em cascata, dessorção por ar e nanofiltração. Os resultados sugerem a possibilidade de remoção quase total de MIB e geosmina da água através do sistema de nanofiltração, enquanto que os processos baseados em aeração e dessorção foram relativamente ineficientes.

Human activities accelerate the natural process of eutrophication, favouring the occurrence of algae and cyanobacterial blooms. These organisms emit the compounds 2-methylisoborneol (MIB) and geosmin, which confer earthy and moldy taste and odor to water. The presence of MIB and geosmin is extended to drinking water inasmuch they are not completely removed by the processes used in conventional treatment. This research was conducted to evaluate the capability of alternative treatment processes to remove MIB and geosmin from water. The processes studied were cascade aeration, air stripping, and nanofiltration. The results suggested that MIB and geosmin can be almost completely removed by nanofiltration, while the processes based on aeration and stripping were relatively inefficient.