|TUCKER, CRAIG - Mississippi State University|
Submitted to: Global Aquaculture Advocate
Publication Type: Trade Journal
Publication Acceptance Date: 6/17/2011
Publication Date: 7/1/2011
Citation: Schrader, K., Tucker, C.S. 2011. Evaluation of common off-flavors in pond-raised channel catfish Ictalurus punctatus following partial crop harvest. Global Aquaculture Advocate. 14(40):46,48-49.
Technical Abstract: Channel catfish (Ictalurus punctatus) ponds often contain larger standing crops of food-sized catfish than processors can accept at one time. Large fish populations with acceptable flavor quality are partially harvested and remaining fish are returned to the pond and harvested again as soon as possible based upon processor demands. In some instances, catfish populations declared “on-flavor” appear to develop off-flavors soon after the initial harvest, which postpones harvest of the remaining population and delays subsequent production. In this study, samples of water and catfish were collected from 12 catfish production ponds prior to the initial harvest and afterwards at approximately 2-week periods until the next harvest to determine the occurrence and types of off-flavors. The following were monitored: 1) levels of the odorous compounds geosmin and 2-methylisoborneol (MIB) in pond water and catfish fillets; 2) phytoplankton identification and enumeration in pond water using; and 3) sensory analysis of catfish fillets. In most sampled ponds, MIB levels decreased or remained relatively unchanged in pond water after the first seining while geosmin levels remained very low in all ponds (< 10 ng/L). Statistical analysis of variance of mean MIB levels in catfish fillets revealed either a decrease or remained unchanged following the first seining, although several catfish sampled after the first harvest had significantly higher MIB levels (i.e., greather than or equal to 200 ng/kg, a level attributed as the sensory detection threshold for the average trained flavor checker). Similar results were found for geosmin levels in catfish fillets. Flavor sensory analysis identified musty to be the most prevalent type of off-flavor during the summer months while “rancid,” “decay,” “grassy,” and “stale” types of off-flavor were detected in catfish fillets obtained during the winter months. Microscopic analyses of water samples revealed the MIB-producing cyanobacterium Planktothrix perornata in water from only three ponds during the study, and the abundance of P. perornata decreased in two of these ponds while increasing in the third pond during the sampling periods. Overall, results indicate that seining the ponds did not result in ecological conditions leading to an increase in the abundance of P. perornata or MIB and geosmin levels in water and catfish fillet samples. Most likely, detection of off-flavored catfish by processing plant flavor checkers after crop partial harvests is related to large within-population variation in fish flavor quality.