Geosmin off-flavour in pond-raised fish in southern Bangladesh and occurrence of potential off-flavour producing organisms

Abstract

Pangas Pangasianodon hypophthalmus and tilapia Oreochromis niloticus were cultivated for 6 mo in earthen ponds in Bangladesh to examine occurrence of the off-flavour geosmin in water and fish and to test procedures for reduction of off-flavour. In the ponds (~1 m depth and area of 400 m 2 ), the average geosmin concentration was 3.9 ng l −1 (range 0.2 to 20 ng l ) for tilapia. Water treatment reduced the geosmin content by 56 to 74% in pangas, but no effect was found in tilapia. Likewise, depuration for ≥12 h in groundwater lowered the geosmin content in pangas (by 65 to 90%) but not in tilapia. Sensory analysis indicated a positive effect of both water treatment and depuration, and the fish were graded 'no or mild flavour' after such treatment, compared to 'strong off-flavour' in controls. Abundance analyses of known offflavour producing microorganisms (streptomycete bacteria and cyanobacteria) showed a high density of streptomycetes (0.5 to 13% of the bacterial population), while cyanobacteria made up a maximum of 9.3% of the phytoplankton biomass or were absent. This first study on off-flavours in pangas and tilapia in Bangladeshi ponds indicates that geosmin was not a major off-flavour in the fish, but improvement of sensory quality by water treatment and depuration suggests that other, unidentified off-flavours were present in the fish.

Microbial Production of the Off-Flavor Geosmin in Tilapia Production in Brazilian Water Reservoirs: Importance of Bacteria in the Intestine and Other Fish-Associated Environments

“…Concentrations of geosmin in the water (1.2–4.9 ng⋅L –1 ) were comparable to concentrations measured in combined pangasius-tilapia ponds in Bangladesh (Petersen et al, 2014), but were significantly lower than concentrations in tilapia ponds in Thailand (0.41–2.33 μg⋅L –1 ; Gutierrez et al, 2013). Despite the relatively low levels of geosmin found in the Brazilian farms, the content of geosmin in the fish flesh (mean of 284 ng⋅kg –1 , but up to 751 ng⋅kg –1 was measured) was probably above the human threshold for detection of geosmin, at least when compared to the threshold observed for rainbow trout flesh (250 ng⋅kg –1 ) (Petersen et al, 2011).…”

“…For determination of geosmin in fish flesh, a dynamic headspace analysis was employed (Petersen et al, 2014). Briefly, 10 g of fish flesh in 30 mL of water was homogenized in a 250 mL gas washing bottle, using an Ultra Turrax homogenizer (Ika).…”

“…For quantification of geosmin, fish meat samples were spiked with geosmin at 100, 250, 500, and 1000 ng⋅kg –1 prior to homogenization. Following the extraction, both twisters and Tenax traps were analyzed by GC-MS at conditions as described elsewhere (Petersen et al, 2014).…”

Oxidative deterioration of pork during superchilling storage

“…Formation of hexanal in pork samples was monitored by dynamic headspace coupled to gas chromatography/mass spectrometry (GC/MS) . A 10 g sample of minced pork was weighed into a 500 mL glass flask and mixed with 110 g of water and 100 µL of internal standard (IS) solution (5 mg L −1 4‐methyl‐1‐pentanol).…”

Reducing geosmin off-flavor compounds and waste outputs through dietary phosphorus management in rainbow trout aquaculture

“…To provide adequate conditions for depuration of off-flavors, either the fish could be moved to clean odor-free water or the geosmin could be removed from the culture water in situ (Robertson et al 2005, Burr et al 2012); e.g. rainbow trout depuration periods of ~1 wk are typically practiced (Petersen et al 2011(Petersen et al , 2014.…”