Off-flavor In Fish Research Articles

Quality of Rainbow Trout (Oncorhynchus mykiss) Reared in Recirculating Aquaculture System and during Depuration Based on Chemical and Sensory Analysis

In recirculating aquaculture systems (RAS), off-flavors can accumulate in fish muscle tissue. They are problematic for consumer acceptance and the reputation of farmed fish products. Although off-flavors are not toxic at low concentrations, they often give fish muscle earthy, muddy, or other unwanted flavors. Traditionally, the study of off-flavors in fish focused on muddy and earthy off-flavors caused by geosmin (GSM) and 2-methylisoborneol (MIB), but other unwanted flavors and compounds have also been identified. In this study, the selected off-flavors were chemically quantified in fish from a RAS-rearing rainbow trout (Oncorhynchus mykiss) and in different stages of depuration. A group of trained panelists with experience in sensory evaluation was specifically trained in analyzing rainbow trout samples. The panelists evaluated the fish with a sensory profile of 29 sensory attributes (12 odor, 5 taste, and 12 flavor properties). Overall, the concentrations of all the studied off-flavor compounds decreased, some to below the limit of detection and others (e.g., octanal, octanoic acid, phenylacetaldehyde, and acetoin) to a certain low level. Moldy, earthy, and musty odors and flavors especially decreased during depuration compared to fish in RAS. This study shows the consistency of the chemical analysis and sensory profiling. It also provides important information about the effects of the depuration period in RAS and on the chemical and sensorial quality of rainbow trout.

Off-flavor detection in tilapia reared in cages in tropical lakes

Aquaculture activity in the aquatic ecosystem can intensify the presence of the semi-volatile compounds geosmin (GSM) and 2-methylisoborneol (MIB). These metabolites are the leading cause of off-flavor in fish from aquaculture facilities, even at small concentrations. Thus, this study aimed at evaluating the influence of tilapia production in cages on the availability and production of the metabolites GSM and MIB in water and sediment. Samples were obtained from two Brazilian natural tropical lakes (Palmas and Palminhas) in alternate months, in both dry and rainy periods. The physicochemical parameters of water and sediment samples were measured in situ and in the laboratory. Water samples were collected for quantitative analysis of the phytoplankton community, and fresh tissue samples from ten tilapia (Oreochromis niloticus) to analyze semi-volatile compounds (GSM, MIB, and β-ionone). Samples from fish farms in Palminhas Lake present higher aqueous concentrations of phosphorus and ammonia, a higher abundance of Cyanophyceae, and the presence of GSM and MIB in sediment and fish flesh. Conversely, Palmas Lake presented low nutrients and a higher abundance of Chlorophyceae, with GSM presence and MIB absence. Therefore, eutrophication caused by fish farming in these tropical lakes with long water retention time coupled with inadequate governmental policies leads to negative feedback that leads to off-flavors in fish products.

Developing a robust and sensitive analytical method to detect off-flavor compounds in fish

In recirculating aquaculture systems (RAS), off-flavors that accumulate in fish muscle tissue can be problematic in terms of consumer acceptance and the reputation of farmed fish products. Although off-flavors are not toxic at low concentrations, they often give fish muscle earthy, muddy, or other unwanted flavors. Traditionally, muddy off-flavors caused by geosmin (GSM) and 2-methylisoborneol (MIB) have been detected, but a variety of other compounds and flavors have also been identified. In this study, a method based on solid phase micro extraction (SPME) coupled with gas chromatography and mass spectroscopy was developed to identify and quantify 14 off-flavor–inducing compounds in RAS–farmed fish. The selected off-flavors were quantified in circulating water and in fish from a pilot-scale RAS rearing rainbow trout (Oncorhynchus mykiss). The method showed high accuracy and precision with limits of detection and quantification at a low ng L−1 level. In this study, 13 compounds were found in the fish muscle which decreased in concentrations during the 15-day depuration period. This study showed that off-flavors in fish can also be induced by other compounds besides GSM and MIB. This emphasizes the need for sufficient off-flavor control in the RAS, but also the importance of an accurate and reliable analytical quantitation method.

Off-Flavors in Aquacultured Fish: Origins and Implications for Consumers

Off-flavors in fish and water are considered a worldwide problem. Several factors, such as the presence of phosphorus, micronutrients, and organic matter, contribute to phytoplankton proliferation and the production of off-flavors. Geosmin and 2-methylisoborneol are the most common off-flavors that confer the smell of earth or mold to water and fish. These metabolites are not considered toxic, but they can be easily transferred from water to living organisms and accumulate in the biota, up the trophic levels and to consumers, including fish species. Numerous processes have been studied to eliminate or reduce the presence of off-flavors in recirculating aquaculture systems. Managing off-flavors must be eco-friendly and consumer-friendly. Strategies against off-flavors must be efficient and low-cost. However, these solutions may be different for each fish production system. We review herein the main compounds produced by cyanobacteria that can accumulate in fish used in aquaculture that can affect the quality of food, as well as production costs and consumer preference.

Off-Flavors in Fish: A Review of Potential Development Mechanisms, Identification and Prevention Methods

Off-Flavors in Fish: A Review of Potential Development Mechanisms, Identification and Prevention Methods

Potential Contribution of Fish Feed and Phytoplankton to the Content of Volatile Terpenes in Cultured Pangasius (Pangasianodon hypophthalmus) and Tilapia (Oreochromis niloticus).

Geosmin and 2-methylisoborneol are the most recognized off-flavors in freshwater fish, but terpenes may also contribute off-flavor in fish. We identified six monoterpenes, 11 sesquiterpenes, and three terpene-related compounds in pangasius and tilapia from aquaculture farms in Bangladesh. The concentrations of most of the volatiles were below published odor thresholds, except for α-pinene, limonene, β-caryophyllene, α-humulene, and β-ionone in tilapia, and limonene and β-ionone in pangasius. To identify sources of the terpenes, terpene profiles of fish feed and phytoplankton in the ponds were analyzed. In feed and mustard cake (feed ingredient), five monoterpenes and two sesquiterpenes were identified, and five of these compounds were also detected in the fish. In phytoplankton, 11 monoterpenes were found and three also occurred in the fish. The higher number of terpenes common to both fish and feed, than to fish and phytoplankton, suggests that feed was a more abundant source of odor-active terpenes in the fish than phytoplankton.

Combined adsorption and degradation of the off-flavor compound 2-methylisoborneol in sludge derived from a recirculating aquaculture system

Off-flavor in fish poses a serious threat for the aquaculture industry. In the present study, removal of 2-methylisoborneol (MIB), an off-flavor causing compound, was found to be mediated by adsorption and bacterial degradation in sludge derived from an aquaculture system. A numerical model was developed which augmented Langmuir equations of kinetics of adsorption/desorption of MIB with first order degradation kinetics. When laboratory-scale reactors, containing sludge from the aquaculture system, were operated in a recirculating mode, MIB in solution was depleted to undetectable levels within 6 days in reactors with untreated sludge, while its depletion was incomplete in reactors with sterilized sludge. When operated in an open flow mode, removal of MIB was significantly faster in reactors with untreated sludge. Efficient MIB removal was evident under various conditions, including ambient MIB levels, flow velocities and sludge loads. When operated in an open flow mode, the model successfully predicted steady MIB removal rates with time. During steady state conditions, most of the MIB removal was found to be due to microbial degradation of the adsorbed MIB. Findings obtained in this study can be used in the design of reactors for removal of off-flavor compounds from recirculating aquaculture systems.

Removal of the off-flavor compounds geosmin and 2-methylisoborneol from recirculating aquaculture system water by ultrasonically induced cavitation

With its high economic impact, off-flavor in fish is still one of the most serious problems in the aquaculture industry worldwide. Until now, the highly cost- and time-intensive, as well as capacity demanding depuration procedure by moving the fish to clean and odor-free water for a certain time prior to harvest is the only reliable way to counteract off-flavors in aquaculture. Alternative strategies and processes for efficient off-flavor prevention are still lacking. Hence, the aim of this study was to investigate the potential of ultrasonic water treatment to decrease the concentration of the relevant off-flavor compounds geosmin (GSM) and 2-methylisoborneol (2-MIB) in aquaculture water. Therefore, different water matrices, varying in their organic and inorganic load and composition (tap water, RAS fresh water, RAS sea water), were spiked with 2-MIB and GSM standard and subsamples of 250mL were subsequently treated for 15min using a lab-scale ultrasound transducer at 850kHz. For verification samples from commercial RAS containing biogenic 2-MIB and GSM were treated equally. The effects of ultrasound frequency and salinity on the removability of 2-MIB and GSM via ultrasonic treatment were investigated by comparing the removal efficiency of high (850kHz) vs. low (20kHz) frequency ultrasound and by adding artificial sea salt (10ppt) to different freshwater samples prior to ultrasound treatment, respectively.Results have demonstrated that ultrasonically induced cavitation significantly reduces the tested off-flavor compounds GSM and 2-MIB in all tested water types, seemingly irrespective of the (in)organic load. In general, the reduction of GSM was slightly higher compared to that of 2-MIB. Furthermore, the reduction of tested off-flavor compounds was significantly enhanced at high frequency ultrasound (850kHz) compared to low-frequency ultrasound (20kHz). The addition of artificial sea salt to fresh water samples caused an additional improvement in removability of both off-flavor compounds.Our results evidence high frequency ultrasound as a potential treatment process for significant removal of the relevant off-flavor compounds 2-MIB and GSM from RAS process water. In particular, the seemingly low dependency of the ultrasound-induced removal of GSM and 2-MIB on the organic and inorganic process water load predestines ultrasonically induced cavitation as a potential strategy for off-flavor prevention in RAS compared to alternative strategies such as advanced oxidation processes or adsorption processes.

Removal of off-flavors and isolation of fatty acids from boiled anchovies using supercritical carbon dioxide

Herein, we extracted boiled anchovies with supercritical carbon dioxide (SCO2) at various temperatures (40 to 50°C) and pressures (7.7 to 35 MPa), which successfully removed trimethylamine and dimethyl disulfide, the main odorous compounds that produce off-flavors in fish. We extracted the following fatty acids from boiled anchovies: myristic acid, palmitic acid, stearic acid, palmitoleic acid, EPA (eicosapentaenoic acid), and DHA (docosahexaenoic acid). In addition, we observed a higher concentration of polyunsaturated fatty acids (PUFAs), such as EPA and DHA, in SCO2-extracted anchovy oil than in organic solvent-extracted oil.

Effects of Selected Water Quality Variables on the Persistence of Tannic Acid and Related Compounds under Simulated Aquaculture Conditions

Tannins have potential commercial applications in aquaculture for the prevention of piscine diseases and off-flavor in fish. Selected water quality variables, such as temperature, pH, dissolved oxygen, light intensity, total hardness and total alkalinity, and available nutrients found in fish ponds were examined for their influence on the fate of gallic acid, methyl gallate, propyl gallate, and tannic acid. It was determined that total hardness and alkalinity were the most effective factors in the dissipation of tannin compounds. High levels of selected water quality variables were significantly different from low levels in their ability to transform tannin compounds. It was also found that natural suspended solids were effective in precipitating 60% of the methyl gallate and 81.3% of the propyl gallate per week from solution. Abiotic processes, such as physical transportation and chemical transformation, affected the fate of tannin compounds in a simulated fish pond. This study may guide the use of tannins as a feed additive or disease treatment in the management of fish-farming problems.

Geosmin-producing species of Streptomyces and Lyngbya from aquaculture ponds

Water and sediment samples collected monthly from six aquaculture ponds in east-central Alabama were analyzed for the presence of actinomycetes and cyanobacteria capable of producing geosmin and (or) 2-methylisoborneol, which cause earthy–musty off-flavors in fish. Six actinomycetous isolates were identified as geosmin producers, five of which were capable of producing 2-methylisoborneol. The one actinomycetous isolate producing geosmin but not 2-methylisoborneol was identified as Streptomyces halstedii. Only one of several cyanobacterial isolates was found to produce geosmin. This isolate was identified as Lyngbya cf. subtilis and was prevalent throughout the sampling period in a pond with a history of off-flavor problems. None of the cyanobacterial isolates produced 2-methylisoborneol in laboratory culture.Key words: geosmin, Streptomyces, Lyngbya, off-flavor, aquaculture.

Evaluation of potassium ricinoleate as a selective blue-green algicide in channel catfish ponds

The effectiveness of potassium ricinoleate as a selective blue-green algicide was investigated in experimental channel catfish, Ictalurus punctatus, culture ponds. Five ponds were treated with 0.8 mg/l potassium ricinoleate three times per week from May through October and five ponds served as controls. Treatment did not affect concentrations of chlorophyll- a, total and un-ionized ammonia-nitrogen, or dissolved oxygen; nor did it affect average hours of supplemental aeration or net fish production. The mean nitrite-nitrogen concentration in control ponds was higher ( P<0.05) than that in treated ponds, but concentrations of nitrite never reached levels considered detrimental to the health of the fish. Treatment did not reduce the incidence or percentage of blue-green algae in phytoplankton communities and did not prevent severe episodes of off-flavor in fish from treated ponds.

Environmental Factors Affecting Flavor of Channel Catfish from Production Ponds

Abstract Environmental variables and the flavor of channel catfish (Ictalurus punctatus) were monitored at 3-4-week intervals during 1982 and 1983 in 11 ponds at Browns, Alabama, and during 1983 in five production ponds near Auburn, Alabama. Off-flavor in fish flesh was most severe in late summer when algal and actinomycete activity in ponds was greatest in response to high water temperatures and large daily applications of fish feed. However, some fish from all ponds were not off-flavor. For example, in August 1982, flavor scores for fish from 11 ponds at Browns ranged from 1.6 to 9.5 (a score above 9 indicates no off-flavor). The earthy-musty flavor of geosmin was the most common and intense off-flavor in fish. Regression analyses between environmental variables and flavor scores failed to yield strong or consistent correlations. Blue-green algae and actinomycetes, which are known to produce geosmin and other odorous compounds, were abundant in ponds with off-flavor fish; however, these microorganisms also were abundant in ponds where fish were not off-flavor. Off-flavor was equally common in fish from ponds with acidic muds and low alkalinity waters and from ponds with alkaline muds and high alkalinity waters, but the lowest flavor scores were recorded in the more alkaline environments.

Off-Flavors in Pond-Cultured Channel Catfish

A serious problem in pond culture of fish is the absorption of compounds from the aquatic environment which impart disagreeable flavor in the fish. “Musty” or “muddy” off-flavor is caused by geosmin (trans, 1, 10,-dimethyl-trans-9- decalol) and 2-methylisoborneol. These compounds can be produced by various species of algae and actinomycetes. Aquarium studies with mono-species cultures of geosmin-producing algae indicate that channel catfish can absorb off-flavor compounds exclusive of the digestive tract. Geosmin was absorbed at sensorily detectable levels within 24 hours. Off-flavor can be purged from catfish relatively quickly by holding in clean water for 4-10 days. Temperature influences rate of flavor removal and also rate of weight loss by the fish. Although the “musty-muddy” flavor has been regarded as the predominant pond-related off-flavor in fish, a recent study in which catfish from 220 commercial ponds was sensorily evaluated showed that it accounted for only 17% of the off-flavor. “Sewage” was the dominant flavor in 25% of the off-flavor samples. “Stale”, “rancid”, “metallic”, “moldy”, “petroleum”, and “weedy” were other off-flavors described. Geosmin was chemically identified in the fish with the “musty-muddy” flavor; the other compounds have not been identified.