Microbially Derived Off-Flavor from Geosmin and 2-Methylisoborneol: Sources and Remediation - Reviews of Environmental Contamination and Toxicology - page 4

(Cees et al. 1974; Tyler et al. 1978; Persson 1979; Polak and Provasi 1992; Veijanen
et al. 1988, 1992; Watson et al. 2000). A Lab test conducted by Jung et al. (2004)
revealed that threshold odor levels for MIB and geosmin appeared to be 30 ng/L,
which can create consumer complaints. However, concentrations as low as 10 ng/L
can impart off-flavors to a variety of food and water sources (Krasner et al. 1985;
Dionigi et al. 1993). Concentrations as low as 10 ng/L in water and 0.7 µ g/kg in fish

can be detected (Zimmerman et al. 2002).
Occurrence of geosmin and MIB are common in aquaculture as bioaccumulation
of these sesquiterpenoids in fish and shellfish causes off-flavors in farmed and wild
stocks (Persson 1981; Lovell and Broce 1985; Hsieh et al. 1988; Dionigi et al.
1998; Farmer et al. 1995; Lazur 2004). During summer months with higher feeding
rates, conditions are conducive to the growth of certain species of algae and bacte-
ria, causing off-flavor in fish and shellfish and making them unmarketable (Kajino
and Sakamoto 1995; Eynard et al. 2000). Tellez et al. (2001a) concluded that
besides MIB several volatile compounds may cause off-flavor problems in catfish
aquaculture; however, off-flavor due to MIB may mask the odors of dimethyl
disulfide/trisulfide. Nakajima et al. (1996) and Gagne et al. (1999) reported toxici-
ties levels of geosmin and MIB for sea urchin embryos ( Hemicentrotus pulcher-
rimus Agassiz) and rainbow trout ( Oncorhynchus mykiss Walbaum) (see Table 1).

III Geosmin- and MIB-Producing Species

Geosmin, an earthy-smelling substance, was isolated in 1964 by Gerber and
Lechevalier (1965). MIB, a musty- or camphorous-smelling compound, was
reported in 1969 by Medsker et al. (1969) and Gerber (1969), and independently by
Rosen et al. (1970) in 1970. Geosmin and MIB were first identified in actinomycetes
(Gerber 1968, 1969, 1979, 1983; Blevins 1980; Yagi et al. 1981, 1983; Bentley and
Meganathan 1981; Schrader and Blevins 1993), then later in cyanobacteria
(Izaguirre et al. 1982; Wu and Jüttner 1988; Martin et al. 1991; Matsumuto and
Tsuchiya 1988; Tsuchiya et al. 1981; Tsuchiya and Matsumoto 1988; Schrader and
Blevins 1993; Tabachek and Yurkowski 1976) and fungi (Kikuchi et al. 1981) that
inhabit aquatic and soil environments (Tables 2-4).
Siegmund and Pollinger-Zierler (2006) reported for the first time the presence
of Streptomyces sp. as the spoilage bacteria of apple juice. Initially, only certain
actinomycetes were reported to produce MIB; later, various cyanobacterial species
from the genera Anabaena, Oscillatoria, Lyngbya, and Phormidium have been
reported to produce musty and earthy flavors in cultured catfish (Tucker 2000).
MIB-producing Lyngbya species was reported from Manitoba fish farming
(Tabachek and Yurkowski 1976; Yurkowski and Tabachek 1980). In catfish ponds,
MIB is usually produced by the blue-green alga Oscillatoria perornata ( Planktothrix
perornata ) (Tucker 2000). Martin et al. (1988) were the first to report MIB-related
off-flavor in commercial farm-raised channel catfish and later attributed it to a
planktonic Oscillatoria sp. (Martin et al. 1991). Tellez et al. (2001a) reported major