# Off-flavors in Aguacultured Fish: Origins and Implications for Consumers
## 2 Off-Flavor Compounds in the Environment: An Overview  
Climate change and anthropogenic factors, such as nutrient enrichment, pollutant load, increased temperature, and exposure to sunlight, can lead to increased blooms of cyanobacteria and other phytoplankton species [14; 15; 16]. Usually, the blooms occur in summer and early autumn, a period with favorable conditions such as warmth, ample sunlight, and a stable or low water flow. These cyanobacterial blooms are generally responsible for the appearance of undesirable metabolites, are toxic in many cases or non-toxic as off-flavors [17] and are increasing annually worldwide [18; 19]. The main derivatives of alga, fungi, cyanobacteria, and other microorganisms (_Actinomycetes_ and _Myxococcus_) are commonly identified as terpenoids, carotenoid derivatives, fatty acids, and sulfur compounds [20; 21; 22; 23; 24]. These metabolites confer flavors and smell described as \"earthy\", \"muddy\" or \"moldy\" [25]. Studies have described that the main metabolites that impart earthy, moldy and tobacco odor in water and food are the volatile compounds such as 2-methylisobornel (MIB), geosmin (GEO), 2-isopropyl-3-methoxyyrazine (IPMP), 2-isobutyl-3-methoxyyrazine (IBMP), \(\beta\)-Cyclocitral, and \(\beta\)-Ionone [26; 27; 28; 29]. The main physical-chemical properties of these compounds are presented in Table 1. Among the TOCs produced by cyanobacteria and other microorganisms, GEO, and MIB are the TOCs most commonly found in fish and water. They are also the most difficult to remove through oxidation, which is the process applied in water purification [6; 30; 31]. Initially, GEO was isolated and identified as sesquiterpenoid alcohol degraded in cyanobacteria at the gills and skin, and are the main site of GEO and MIB on uptake due to contact with [32], while MIB was isolated as methyl monoterpene in actinomycetes [33]. _Anabaena_ strains produce TOCs, and according to [PERSON] et al. [34], this strain has shown that \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Compound** & **Chemical** & **Chemical** & **Molecular** & **CAS** & **Water** & **Log Kow** & **Water** \\  & **Structure** & **Formula** & **Weight** & **Number** & **Half-Life** & **Log Kow** & **Solubility** \\  & & & & & & & **(mg\(\cdot\)cm\({}^{3}\)) \\ \hline MIB & \(\chi_{\text{m}}\) & C\({}_{11}\)H\({}_{20}\)O & 168.3 & 2371-42-8 & 19.5 days & 3.13 & 0.45 \\ GEO & \(\chi_{\text{m}}\) & C\({}_{12}\)H\({}_{22}\)O & 182.3 & 16423-19-1 & 24.5 days & 3.7 & 0.0512 \\ IPMP & \(\chi_{\text{m}}\) & C\({}_{8}\)H\({}_{12}\)N\({}_{2}\)O & 152.2 & 25773-40-4 & n.a. & 2.41 & 61.4 \\ IBMP & \(\chi_{\text{m}}\) & C\({}_{9}\)H\({}_{14}\)N\({}_{2}\)O & 166.2 & 24683-00-9 & n.a. & 2.72 & 20.9 \\ \(\beta\)-Ionone & \(\chi_{\text{m}}\) & C\({}_{13}\)H\({}_{20}\)O & 192.2 & 14901-07-6 & n.a. & 2.9 & 0.104 \\ \(\beta\)-Cyclocitral & \(\chi_{\text{m}}\) & C\({}_{10}\)H\({}_{16}\)O & 152.2 & 432-25-7 & n.a. & 2.4 & Insoluble \\ \hline \hline \end{tabular} n.a. = not available.  
\end{table} 
Table 1: Physico-chemical properties of main off-flavor TOCs. the lowest MIB production was achieved at lower temperatures (<20 \({}^{\circ}\)C), while a lower production of GEO was achieved at high light intensity (>100 \(\upmu\)mol/m\({}^{2}\)/s) [34]. GEO is a semi-volatile metabolite that remains stored in vacuoles inside cells and its release to ambient water is due to the decomposition of cyanobacteria biomass or cell death [17]. Some researchers have shown that GEO is a residual metabolite that provides an energy benefit to bacteria production since more energy is required for the production of chlorophyll-a (Chl a) than for the production of GEO, and thus when cyanobacteria do not need Chl a, GEO production occurs. Although some studies are being carried out to understand the mechanisms of GEO production, its biological function in the cell has not yet been fully elucidated [35].