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.
Research has identified the presence of the “earthy” compound geosmin and the “musty” compound 2-methylisoborneol (MIB) in the flesh of off-flavor barramundi raised in commercial recirculating aquaculture systems (RAS). This report is the first to confirm the presence of geosmin and MIB in off-flavor barramundi produced in RAS. Activities are being monitored by regular conference calls.