2-Methylisoborneol (MIB) is an irregular
monoterpene derived from the universal monoterpene precursor
geranyl pyrophosphate. MIB and the irregular
sesquiterpenegeosmin together account for the majority of biologically-caused taste and odor outbreaks in drinking water worldwide.[1] MIB has a distinct earthy or musty odor, which most people can easily smell. The
odor detection threshold of MIB is very low, ranging from 0.002 to 0.02 micrograms per liter in water.[2] MIB is also a factor in
cork taint in
winemaking.
MIB is produced by various blue-green algae (cyanobacteria) and filamentous bacteria in the class
Actinomycetia, and also some other prokaryotes and eukaryotes. The main genera in the cyanobacteria that have been shown to produce MIB include Oscillatoria, Phormidium, and Planktothrix, while the main genus in the Actinomycetia that produces MIB is Streptomyces.[3][4] They give a musty or earthy odor that can be quite strong if an
algal bloom is present. Subsequent death of the microorganisms will release MIB that is trapped in the cells. Along with geosmin, the off flavors that result are issues in the seafood industry. This chemical is the major cause of "muddy" or "dirt" flavors in
catfish and
crawfish.[5]
^Lin, Tsair-Fuh; Watson, Susan; Dietrich, Andrea M.; (Mel) Suffet, I. H. (15 March 2018). Taste and Odour in Source and Drinking Water: Causes, Controls, and Consequences. IWA.
ISBN978-1-78040-665-7.
^Lloyd, Steven W; Grimm, Casey C (1999). "Analysis of 2-Methylisoborneol and Geosmin in Catfish by Microwave Distillation−Solid-Phase Microextraction". Journal of Agricultural and Food Chemistry. 47 (1): 164–169.
doi:
10.1021/jf980419x.
PMID10563866.