ARS | Publication request: DETECTION OF OFF-FLAVOUR IN CHANNEL CATFISH (ICTALURUS PUNCTATUS RAFINESQUE) FILLETS BY TRAINED DOGS

Submitted to: Aquaculture Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 21, 2005
Publication Date: November 28, 2005
Citation: Shelby, R.A., Myers, L.J., Schrader, K.K., Klesius, P.H. 2005. Detection of off-flavour in channel catfish (Ictalurus punctatus Rafinesque) fillets by trained dogs. Aquaculture Research 2005, 37, 299-301.

Interpretive Summary: This paper describes the training and testing procedure we used to train dogs to detect “musty-earthy” compounds in catfish fillets. The industry refers to this problem as “off-flavor” and causes a 23 million dollar loss to the catfish aquaculture annually. In summer months, as ponds become warm, blue-green algae proliferate in catfish ponds. These microscopic organisms produce the odors which are absorbed by the catfish. While not toxic, the compounds give the fish an unpleasant taste which can negatively affect consumer perception of the product. In previous research, we trained dogs to detect two compounds responsible for the problem, methylisoborneol (MIB) and geosmin (GSM), using water samples and naturally contaminated pond water. We wanted to see if these dogs could also be used to discriminate between on-flavor and off-flavor fillets from naturally occurring off-flavor ponds. Fillet samples from production ponds were quantitatively analyzed by gas chromatography, and the fillet samples then were presented to four dogs in a series of “blind” tests with decreasing amounts of the off-flavor compounds. All of the dogs in the present study were able to distinguish off-flavor fillet samples from “on-flavor” samples, which had no detectable GSM or MIB. The enhanced sensitivity of dogs may be utilized to protect the consumer from objectionable tastes and odors in processed catfish.

Technical Abstract: “Off-flavors” are a persistent problem in various food industries when consumers perceive that a food product may be contaminated or spoiled, even though the product may be completely safe. Commercial production of channel catfish is particularly plagued by this problem due to the presence of “earthy-musty”compounds in the pond water which accumulate in the flesh of the catfish. In a previous study, we developed a protocol which used trained dogs to detect and distinguish between low levels of geosmin (GSM) and 2-methylisoborneol (MIB) in 1-mL pond water. In this study, we used the same dogs and identical protocol to detect these off-flavor compounds in catfish fillets. Fillet samples from production ponds were quantitatively analyzed by SPME-GC-MS for GSM and MIB, and the fillet samples then were presented to four dogs in a series of “blind” tests with decreasing amounts of the off-flavor compounds. All of the dogs in the present study were able to distinguish off-flavor fillet samples from “on-flavor” samples, which had no detectable GSM or MIB. In a final series of tests, we were surprised to find that all of the dogs could distinguish between two different on-flavor samples from different ponds. This result raises concerns about the efficacy of field tests designed to interdict off-flavor before processing.