Microbially Derived Off-Flavor from Geosmin and 2-Methylisoborneol: Sources and Remediation - Reviews of Environmental Contamination and Toxicology - page 11

The minimum period required for fish to regain flavor quality is the cause of
concern for aquaculturists (Dionigi et al. 2000). Lazur (2004) observed that holding
fish in raceways with flow-through well water can purge geosmin and MIB off-
flavors from fish; however, this process involves additional costs from harvesting
and handling, tank facility overhead, water pumping, requirement of large amount
of water (Johnsen and Dionigi 1993) and fish weight loss and mortality. Purging
recirculating systems may be more practical but biological filters and other compo-
nents of systems may become off-flavor sources (Johnsen and Dionigi 1993). van
Breeman et al. (1991) reported an effective and environmentally friendly technique
for the control T/O problems caused by algal activity in a reservoir, where sediment
surface was disturbed with a harrow pulled by a boat.
Uptake and depuration of MIB from fish are important considerations in the
design and implementation of systems to remove off-flavors from fish before
processing (Johnsen et al. 1996). Flavor can be evaluated by tasting and assigning
grades when fish is cooked in a microwave; flavor from a distinct to slight off-flavor
is indicative of clearing of flavor, and the fish may soon be marketable (Lazur 2004).
Song and O'Shea (2007) reported degradation of geosmin and MIB through ultra-
sonic irradiation, which may have potential applications in the removal of T/O com-
pounds from potable water supplies and fish farms.

B Chemical Methods

Blue-green algae can be eliminated to some extent by chemical use in ponds (Wagner
et al. 1999). One of the management practices to prevent or kill the growth of
unwanted cyanobacteria includes the application of algicides to fish ponds (Tucker
and van der Ploeg 1999; Lazur 2004). Copper sulfate, chelated-copper compounds,
and diuron (3-[3,4-dichlorophenyl]-1,1-dimethylurea) are the USEPA-approved com-
pounds for use in catfish production ponds as algicides (Schrader et al. 1998a,b,
2003; Schrader and Harries 2001; Tucker and Leard 1999). Most of the cyanobacteria
are sensitive to 1-2 mg/L cupric ion, and some of them are affected even at 5 g/L

(Horne and Goldman 1974). An Oscillatoria species isolated in India was damaged
at 1 mg/L copper sulfate after 8 d and failed to grow when transferred to growth
medium (Arora and Gupta 1983). Studies conducted by Schrader and Blevins (2001)
on the testing of trace elements revealed that copper had the most inhibitory effect on
biomass and geosmin production at a concentration as low as 10.7

µ

M, and it was
concluded that copper applied in the form of copper sulfate to the sediments of
drained fish ponds might help prevent future off-flavor occurrences.
Prolonged use of copper sulfate can result in accumulation in the sediments, as
shown in the Fairmont Lakes in Minnesota (Hanson and Stefan 1984) and Lake
Monona, Wisconsin (Nichols et al. 1946). Large quantities of gesomin and MIB are
retained in the blue-green cells, which may rupture on copper sulfate application
with the result of rapid release of these intracellular odorous compounds (Negoro
et al. 1988; Wu and Juttner 1988; Bowmer et al. 1992; Martin et al. 1991; Rosen
et al. 1992; Utkilen and Frøshaug 1992). In Live Oak reservoir, Southern California,

µ