Aquaculture Research, 2011, 42,360^365 doi:10.1111/j.1365-2109.2010.02630.x Geosmin causes off-flavour in arctic charr in recirculating aquaculture systems Ste¤phanie Houle1, Kevin K Schrader2, Nathalie R Le Franc°ois3,4,Yves Comeau5, Mourad Kharoune6, Steven T Summerfelt7, Arianne Savoie3 & Grant W Vandenberg1 1De¤partement des sciences animales, Universite¤Laval, Que¤bec, QC, Canada 2United States Department of Agriculture, Natural Products Utilization Research, Agricultural Research Service, University of Mississippi, University, MS, USA 3Universite¤du Que¤bec aØRimouski, Rimouski, QC, Canada 4BiodoŒ me de Montre¤al, Montre¤al, QC, Canada 5Department of Civil, Geological and Mining Engineering, EŁ cole Polytechnique de Montre¤al, Montre¤al, QC, Canada 6De¤partement de Ge¤nie de la Production Automatise¤e, EŁ cole deTechnologie Supe¤rieure, Montre¤al, QC, Canada 7The Conservation Fund Freshwater Institute, Shepherdstown,WV,USA Correspondence: G W Vandenberg, De¤partement des sciences animales, Universite¤Laval,2425, rue de l’Agriculture, Que¤bec, QC, Canada G1V 0A6. E-mail: [email protected] Abstract Keywords: geosmin, o¡-£avour, arctic charr, recirculating aquaculture systems The ‘earthy’ and ‘muddy’ o¡-£avours in pond-reared ¢sh are due to the presence of geosmin or 2-methyli- soborneol in the £esh of the ¢sh. Similar o¡-£avours Introduction have been reported in ¢sh raised in recirculating aquaculture systems (RAS); however, little informa- ‘O¡-£avour’ in aquacultured products is a problem tion is available regarding the cause of these o¡-£a- that can be costly for the industry and can also lead vours. Our hypothesis was that earthy and muddy to the loss of sales. The problem was ¢rst recognized o¡-£avour compounds, found previously in pond- in farmed ¢sh raised in outdoor ponds but it is now raised ¢sh, are also responsible for o¡-£avours in ¢sh also being observed in ¢sh raised in recirculating raised in RAS. In this preliminary study, we exam- and partial recirculating systems (Schrader & Dennis ined water, bio¢lms in RAS and ¢llets from cultured 2005; Robin, Cravedi, Hillenweck, Deshayes & Vallod arctic charr known to have o¡-£avours and requiring 2006). The o¡-£avours most frequently encountered depuration using instrumental [solid-phase microex- are ‘earthy’ and ‘muddy’. The earthy and muddy £a- traction procedure and gas chromatograph-mass vours in cultured ¢sh are due to the presence of geos- spectrometry (GC-MS)] and human sensory ana- min or 2-methylisoborneol (MIB) in the £esh of the lyses. Geosmin was present in the samples taken from ¢sh (Tucker 2000; Howgate 2004).These compounds the bio¢lter and on the side walls of the tanks. Two- are semivolatiles and, when present in the water, are methylisoborneol was only found in low levels in the absorbed by the ¢sh and stored in lipid-rich tissues. samples. The GC-MS results indicated the presence of Planktonic and benthic cyanobacteria and actinomy- geosmin in the ¢llets (705 ng kg À 1), but lower levels cetes are known producers of MIB and geosmin were found in the water (30.5 ng L À 1). Sensory ana- (Grimm, Lloyd, Zimba & Palmer 1999). The process lyses also detected an earthy £avour (i.e., geosmin of elimination of these compounds by the ¢sh is presence) in the ¢llets, and, therefore, it appears that much longer then the absorption. The elimination geosmin is the main compound responsible for the rate decreases with lower temperature water and is o¡-£avour in RAS. Further studies are being per- slower in ¢sh with more fatty tissues (Tucker 2000). formed to identify the microorganisms responsible In a commercial operation, a depuration time is re- for geosmin production in RAS. quired before the harvesting in order to gradually r 2010 The Authors 360 Aquaculture Research r 2010 Blackwell Publishing Ltd Aquaculture Research, 2011, 42, 360^365 Geosmin is the dominant o¡-£avour compound in RAS SHouleet al. eliminate the earthy-muddy taste produced by geos- Sample collection of water and bio¢lms min and MIB. Most o¡-£avour-related research has Six water samples were taken in each tank; the been performed with channel cat¢sh raised in USA samples were taken from di¡erent places in the (Tucker 2000) and relatively little research has been tank. Six bio¢lm samples were also taken from performed with other types of ¢sh, such as charr, each tank. Individual water samples were placed raised in recirculating systems. This is the ¢rst report in 20 mL glass scintillation vials with foil-lined on the issue of o¡-£avour aimed at Arctic charr caps (Fisher Scienti¢c, Ottawa, ON, Canada).The vials (Salvelinus alpinus) largely raised in recirculating were ¢lled completely so that no air bubbles were ob- aquaculture systems (RAS) as it displays clear adapt- served when the vial was capped and inverted. Indi- ability to crowding, tolerance to disease and fetches a vidual bio¢lm samples were also placed in 20 mL high market price (Le Franc°ois, Lemieux & Blier glass scintillation vials. Bio¢lm material was scraped 2002). Our hypothesis was that the compounds in- from the side of the tanks and the bio¢lm was then volved in the production o¡-£avours in pond-raised placed into the vials. The samples were refrigerated ¢sh are responsible for o¡-£avours encountered in (4 1C) until shipping to the United States Department RAS. In this primary study, we analysed ¢llets from of Agriculture, Agricultural Research Service, cultured Arctic charr that were o¡-£avour and sub- NPURU at theThad Cochran Research Center in Uni- sequently required depuration before they could be versity,Mississippi. sold to processors. Instrumental and human sensory analyses were used to identify the types of o¡-£avour and the compound(s) responsible for the earthy o¡- £avour in the ¢llets. Analysis of ¢llets by microwave distillation and solid-phase microextraction-gas chromatograph-mass spectrometer Materials and methods (SPME-GC-MS) Sample collection and ¢llet preparation The method of Schrader, Dhammika Nanayakkara, Tucker, Rimando, Ganzera and Schaneberg (2003) Arctic charr were from a commercial farm operated in as modi¢ed from the method of Lloyd, Lea, Zimba Man, WV, USA. The charr were cultured indoor in and Grimm (1998) was used to analyse geosmin and 3 dual-drain ¢breglass circular tanks (640 m ) under MIB from ¢llets. For each ¢llet of Arctic charr, dim light. The water temperature was maintained at 20 Æ 0.5 g of ¢sh were weighed into a glass distilla- 12.6^13.0 1C. The Arctic charr densities in the grow- tion £ask. The £ask was then heated in the micro- À 3 out tanks were between 120 and 140 kg m .The wave (General Electric, New York, NY, USA; model production system was a water-recirculation unit JES1036WF0001) for 5 min at power level ‘3’ while (95% water exchange) that included bio¢ltration and À 1 purging with 80 mL L of N2 gas. The collected dis- pure oxygen injection. Fish were fed industrial manu- tillate was cooled in a water and antifreeze bath factured pellets from Zeigler (Gardners, PA, USA), (Fisher Scienti¢c, model Isotemp 3006) and the vo- using an automatic feeder for16h a day at10^12-min lume was adjusted to 20 mL using nanopure water. intervals and contained 45% protein and 20% fat. Ten From each 20 mL of sample, aliquots of 600 mLwere ¢sh were collected from four tanks (10 ¢sh  four placed into 2 mL glass vials containing 0.3 g of NaCl. tanks): two grow-out tanks and two depuration tanks, Each vial was sealed with a crimp cap. These vials 3 and 7 days of depuration. The depuration system in- were stored at 4 1C until ready for analysis by SPME- cluded a sand ¢ltration and aeration. Collected ¢sh GC-MS using the same method as that described for were euthanized by farm personnel with a sharp blow the analysis of water samples. to the head immediately ¢lleted and the skin was also removed. Two ¢llets per ¢sh were obtained and placed in separate plastic (Ziploc, SC Johnson Canada, Brant- Sensory determination of ¢llet taste and ford, ON, Canada) bags. The ¢llets were then frozen aroma until they were shipped overnight for the o¡-£avour analysis to the United States Department of Agricul- The ¢llets (40 in total) were sent to the Garrison Sen- ture, Agricultural Research Service, Natural Pro- sory Evaluation Laboratory at Mississippi State Uni- ducts Utilization Research Unit (NPURU) at the Thad versity (Starkville, MS, USA) for sensory analysis by a Cochran Research Center in University,Mississippi. trained panel. The samples were removed from the r 2010 The Authors Aquaculture Research r 2010 Blackwell Publishing Ltd, Aquaculture Research, 42,360^365 361 Geosmin is the dominant o¡-£avour compound in RAS SHouleet al. Aquaculture Research, 2011, 42,360^365 freezer and immediately wrapped and sealed in an Isolation of microorganisms in bio¢lm aluminium foil. The samples were prepared and samples cooked using AOAC method 976.16 for baking in foil. The analyses were performed at the NPURU,Thad Co- They were speci¢cally baked at 190.56 1Cinapre- chran Research Center in University,Mississippi. Bio- heated oven to an internal temperature of 71.11 1C. ¢lm samples were inoculated into di¡erent media After the samples were cooked, a small amount of (ASM, BG-11, Allen, BG-11and J) contained in 6 well the ¢llet was placed in a Te£onTM (Dupont,Wilming- plates and incubated for 2 weeks at 28 1C under cool- ton, DE, USA) sni¡ bottle. The remainder of the ¢llet white £uorescent lights. After 2 weeks, a sample from was left in the aluminium foil. The samples were pre- each well was centrifuged to concentrate the algae at sented to a group of six panellists, and the aroma and the bottom of the centrifuge tube and observed under taste were recorded on a10cm hedonic scale.