Variation in Channel Catfish Ictalurus punctatus Flavor Quality and its Quality Control Implications

Producers may capture two to three channel catfish Ictalurus punctatus L. for flavor analysis from ponds scheduled for harvest. If off‐flavors are not present in several consecutive fish samples, the population may be considered acceptable for harvest. However, instrumental analysis of the muddy/earthy off‐flavor metabolites 2‐methylisoborneol (1‐R‐exo‐1,2,7,7‐tetramethyl‐bicyclo‐[2,2,1]‐heptan‐2‐ol) (MIB) and geosmin (lα, 10β‐dimethyl‐9α‐decalol) concentrations in approximately 80 catfish from each of three commercial ponds found both acceptable (on‐flavor) and unacceptable (off‐flavor) individuals within a single pond (i.e., mixed‐flavor populations). Ascertaining the frequency of mixed‐flavor populations by instrumentally determining the off‐flavor metabolite concentration in muscle tissues from a large number of fish sampled from many ponds at several locations over time is not currently feasible. However, analysis of 12,725 commercial processor flavor assessments collected in 1994 and 1995 indicated 120 instances of individual ponds yielding off‐flavor fish followed by on‐flavor fish in one day or less. Reports indicate that fish require approximately four days to depurate off‐flavors fully, suggesting that a proportion of these rapidly changing flavor assessments may reflect the stochastic selection of fish from mixed‐flavor populations rather than a complete and rapid conversion of the flavor quality of entire populations. Factors that contribute to the occurrence of mixed‐flavor‐populations have not been identified fully. However, increased proportion of fat in catfish fillet tissues has been reported to be correlated with a greater retention of MIB by fish. In this investigation, fish fat contents ranged from 4.45% to 30.45%, and were positively correlated (P < 0.0001) with MIB concentrations. Additionally, the spatial distributions of algal populations within certain commercial catfish ponds were not uniform, and the sensory analysis of the flavor intensity of MIB and geosmin in catfish was more variable than the assessment of the intensity of chickeny and nutty flavors. Probability analysis indicated that in certain mixed‐flavor populations there was a 10 to 25% probability of a shipment of fish being rejected due to the random collection of only on‐flavor fish prior to harvest followed by the post harvest capture of at least one off‐flavor fish. In addition, a chance of no off‐flavor fish being sampled from a population containing a proportion of unacceptable fish was indicated. At current sample sizes, replacing sensory analysis with instrumental analysis would not completely avoid problems associated with sampling mixed‐flavor‐populations. Until effective means to reduce/avoid off‐flavor metabolite accumulations in fish are widely available, careful attention to proper sensory evaluation protocols, an enhanced attention to pond conditions that affect flavor quality, the production of leaner more uniform populations of fish, and optimizations of sampling strategies offer the most practical near‐term augmentations of current practice.