ALBERT

Notes: A standardized descriptive language for evaluating the flavor of pond-raised channel catfish has been developed. These terms should help researchers determine the causes of off-flavors in catfish and evaluate potential solutions to the problem. The fish processing industry should also be able to apply these terms in quality control and new product development.

Notes: The impact of 2-methylisoborneol (MIB) (earthy/musty), on the flavor evaluation of farm-raised catfish was assessed by a descriptive analysis panel, who are trained to evaluate flavor intensity using universal scales. Ideally, panelists should give the same intensity ratings for all attributes within a sample. Realistically, individual panelists perceive flavor intensity differently, because of variations in detection thresholds, adaptation, fatigue and enhancement or suppression. Experiments were designed to investigate problems associated with evaluating catfish flavor. Samples “spiked” with MIB had lower chickeny flavor than unspiked. Intensities of MIB in spiked samples that followed an equally spiked sample were lower. Problems can occur when catfish are presented at intervals less than 7 min. Panelists experienced difficulty in determining intensity differences of MIB flavor between sessions, but could determine differences in intensity of MIB within a session. These influences must be accounted for in experimental designs to assess catfish flavors.

Notes: A lexicon of terms to describe desirable as well as undesirable flavors in peanuts has been developed. The lexicon and an intensity rating scale was developed by a 13 member panel of flavor and peanut specialists representing industry and the USDA-Agricultural Research Service. This system is intended to provide definitive, common terminology for use in communicating differences in peanut flavor variables among all phases of peanut research and industry.

Notes: A descriptive analysis panel was trained to use a refined lexicon of flavor descriptors to evaluate farm-raised catfish flavor using a referenced intensity rating scale. To reduce variance due to within sample variability, a procedure using Blended Individual Fish Samples (BIFS) was developed. The reproducibility of the panel performance, utility of the BIFS and the sensitivity of the method to discriminate differences in fish flavor was demonstrated in three experiments.

Notes: The microbial metabolite 2-methylisoborneol (MIB) imparts a muddy off-flavor to channel catfish Ictalurus punctatus. Uptake and depuration of MIB from fish are important considerations in the design and implementation of systems to remove off-flavors from fish prior to processing. The kinetics of MIB uptake by channel catfish were determined by placing fish in 6.5, 14.0, 25.0, and 34.0 C water containing approximately 1.0 μg/L chemically-synthesized MIB. Fish were sacrificed following 0, 2, 4, 8, and 24 h exposure to MIB. Fillet tissue samples were subjected to gas chromatographic and fat content analysis. The model for MIB uptake was:MIB in fillet tissue (μg/kg) =−0.61 ± 4.2 [log(h± 1)] ± 0.0076(T) (h) ± 0.089(T),where h is the duration of exposure to MIB in hours and T is the water temperature in degrees C. The model accounted for 74% of the total variation observed in the tissue MIB concentrations and indicated that the fillet fat content was not strongly correlated with MIB uptake. To investigate the depuration of off-flavors, exposure to MIB was halted. Tissue samples were obtained 4, 8, 24, 48, and 72 h from fish held at 6.5, 14.0, 25.0, and 34.0 C. These data yielded the model:MIB in fillet tissue (μg/kg) = 3.6 ± 0.176(T) – 2.06 [log(h± 1)] – 0.00296(T) (h) ± 0.197 (% fat),where h is the duration of exposure to MIB in hours, T is the water temperature in degrees C, and % fat is the % fat in the fillet tissue. The model accounted for 67% of the total observed variation in tissue MIB concentrations. Reducing the fat content of fish and optimizing water temperatures may augment MIB removal from fish tissues prior to processing.

Notes: Abstract 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.