1a.Objectives (from AD-416)
The objectives of this cooperative agreement are to develop management strategies to manage the common microbial-derived off-flavors in barramundi (Lates calcarifer) including the following:. 1)identify the microorganisms responsible for production of the common off-flavor compounds in recirculating aquaculture system (RAS);. 2)determination of the rates and conditions to enhance depuration of common off-flavor compounds; and. 3)evaluate methods for reducing levels or removal of common off-flavor compounds in RAS water and subsequently RAS-cultured barramundi.
1b.Approach (from AD-416)
In order to identify geosmin and methylisoborneol (MIB)-producing microorganisms, biosolids (organic matter) samples from the RAS will be used to inoculate various types of media that can support the growth of certain types of microorganisms known to be capable of geosmin and/or MIB production. Geosmin and MIB production by microbial isolates producing earthy-musty odors will be confirmed by instrumental methods. Instrumental analytical methods [solid phase microextraction and gas chromatography-mass spectrometry (SPME-GC-MS)] will be used to identify and quantify levels of the common microbial metabolites geosmin and 2-methylisoborneol (MIB) responsible for “earthy” and “musty” off-flavors, respectively, in the following:. 1)microbial isolates identified as producing earthy and/or musty odors;. 2)water and biosolids samples obtained from within the RAS; and. 3)the flesh of barramundi from the RAS. The conditions required to increase depuration rates or enhance removal of common off-flavor compounds from barramundi will be determined through depuration studies that include instrumental analysis of fish fillets. The evaluation of management methods for reducing common off-flavor compounds in RAS will include monitoring the effects of the addition of oxidizing agents (e.g., hydrogen peroxide) on levels of off-flavor compounds in the water and subsequently in the flesh of barramundi.
In 2009-2010, sensory analysis was performed on barramundi fillet samples to confirm results from previous instrumental analyses that identified the main microbial metabolites responsible for the earthy-musty off-flavor in barramundi raised in commercial recirculating aquaculture systems (RAS).
Instrumental analysis of barramundi fillet samples provided by Australis Aquaculture, Ltd., confirmed the reduction of levels of earthy-musty compounds in the fillets during the depuration process in which granular activated carbon (GAC) was utilized to reduce these off-flavor compounds in the RAS water. Sensory analysis performed by flavor testers at Australis Aquaculture, Ltd., confirmed that these depuration management practices resulted in an “on-flavor” product.
Additional details of research can be found in the report for the in-house research project, 6408-41000-009-00D, Management of Off-flavors and Undesirable Bacteria in Aquaculture. Monitoring activities used by the ADODR included telephone calls, email, and a visit to the production facility at Turners Falls, Massachusetts.