|DAVIDSON, JOHN - Freshwater Institute|
|RUAN, ERIC - Lacombe Research Centre|
|SWIFT, BRUCE - Tri-Gen Fish Improvement Ltd|
|AALHUS, JENNIFER - Lacombe Research Centre|
|JURAZ, MANUEL - Lacombe Research Centre|
|GOOD, CHRISTOPHER - Freshwater Institute|
|SUMMERFELT, STEVEN - Freshwater Institute|
Submitted to: Aquacultural Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/25/2014
Publication Date: 7/1/2014
Citation: Davidson, J., Schrader, K., Ruan, E., Swift, B., Aalhus, J., Juraz, M., Wolters, W.R., Burr, G.S., Good, C., Summerfelt, S.T. 2014. Evaluation of depuration procedures to mitigate the off-flavor compounds geosmin and 2-methylisoborneol from Atlantic salmon Salmo salar raised to market-size in recirculating aquaculture systems. Aquacultural Engineering. 61:27-34.
Interpretive Summary: Earthy and musty off-flavors present in fish raised in indoor recirculating aquaculture systems result in unpalatable and unmarketable products. Prior to marketing these fish, the off-flavor compounds can be purged from the fish flesh by moving fish to purging systems. Improved strategies for purging these off-flavor compounds from salmon were discovered, and these strategies include utilizing hydrogen peroxide to clean the purging systems and removal of non-essential portions of the system to enhance the cleaning process.
Technical Abstract: Fish cultured within water recirculating aquaculture systems (RAS) can acquire “earthy” or “musty” off-flavors due to bioaccumulation of the compounds geosmin and 2-methylisoborneol (MIB), respectively, which are produced by certain bacterial species present in RAS biosolids and microbial biofilms. Fish cultured in RAS are generally transferred to separate depuration systems that have been cleaned to remove biofilms, in order to purge these unpalatable flavors. Technologies and standard operating practices that optimize purging kinetics for Atlantic salmon Salmo salar and other species cultured in RAS are needed to improve the consistency of depuration. A 2 x 2 factorial trial was conducted to evaluate techniques to mitigate off-flavor from Atlantic salmon cultured to 3-5 kg in a semi-commercial scale freshwater RAS. Key parameters evaluated relative to their effect on off-flavor reduction included: 1) disinfection of depuration systems using 250 mg/L hydrogen peroxide (H2O2) immediately before stocking; and 2) presence/absence of water aeration media within gas transfer columns of depuration systems. Twelve replicated depuration systems (0.5 m3) were divided amongst the following treatments (n=3): 1) H2O2 disinfection and water aeration media present; 2) H2O2 disinfection and water aeration media absent; 3) no H2O2 disinfection and water aeration media present; and 4) no H2O2 disinfection and water aeration media absent. Atlantic salmon were stocked within the depuration systems and kept off feed for 10 days. Six salmon were harvested from the original RAS on Day 0 and filleted for baseline assessment of off-flavor concentrations. Thereafter, fillet samples (n = 3-4) were taken on Days 3, 6, and 10 to evaluate off-flavor kinetics. MIB was significantly lower (p<0.05) within depuration systems that were void of aeration media and pre-treated with H2O2 on Days 6 and 10. Geosmin was significantly lower on Day 6 within depuration systems that were disinfected with H2O2 and on Day 10 in systems that were void of water aeration media within gas transfer columns. The greatest concentrations of MIB and geosmin were measured within salmon from systems that were not disinfected with H2O2 and also contained water aeration media. Conversely, the lowest off-flavor concentrations were generally found within systems that were pre-treated with H2O2 and were void of water aeration media. Overall, the study indicated that: 1) pre-disinfection of depuration systems using 250 mg/L H2O2 is effective in reducing off-flavor from Atlantic salmon fillets; and 2) water aeration media should not be used within depuration systems because of the challenges posed for effective cleaning, disinfection, and inactivation of off-flavor producing bacteria that may be present.