Catfish Fillets Research Articles

Catfish Special Issue: Growth of Non-O157:H7 Shiga-Toxin Producing Escherichia Coli on Catfish Fillets

Shiga-toxin producing Escherichia coli (STECs) are emerging pathogens which have been involved in numerous foodborne illness outbreaks. In this study the ability of a multi-isolate cocktail of STEC serovars O26:H11, O45:H2, O103:H2, O111: NM, O121:H19, and O145:RM to grow on catfish fillets at refrigeration and abuse temperatures was investigated. Catfish fillet samples (10 g) were inoculated with the STEC cocktails to ca. 3 log CFU/g and incubated under aerobic conditions for up to 120 hrs. There was no STEC growth at 4°C, however, the STECs grew at 10, 15, 20 and 30°C in a temperature dependent manner, with higher growth rate being associated with higher temperature. Lag phase ranged from 15 h at 10°C to 1.75 h at 30°C. Exponential phase growth rate ranged from 0.03 log CFU/g/h at 10°C to 0.65 log CFU/g/h at 30°C. Growth curves constructed using ComBase DMfit provided a good statistical fit to the observed data, resulting in a high correlation coefficient (R2) of 0.98. The results of this study provide information to risk assessors regarding the growth potential of the STECs on aquaculture-raised fish using catfish as a model system.

Catfish Special Edition: Thermal Inactivation of Non-O157:H7 Shiga Toxin Producing Escherichia coli (STEC) on Catfish Fillets

Non-O157:H7 shiga toxin-producing Escherichia coli (non-O157 STEC) strains have emerged as food borne pathogens which have been involved in numerous food borne illness outbreaks worldwide. Seafood (fish) consumption has increased in recent years: it could become more common that STEC outbreaks may be associated with the non-O157 serovars. However, there is a lack of data on thermal inactivation of non-O157 STECs in fish muscle (e.g. catfish). Catfish fillets were inoculated with a six-isolate cocktail of non-O157 STEC serovars, i.e. O26:H11, O45:H2, O103:H2, O111:NM, O121H19, and O145:RM (the Big 6), to determine the impact of thermal treatment (heat) on their survival or thermal inactivation kinetics. The inoculated catfish fillet samples (108-9 cfu/g) were subjected to isothermal heating at 55, 60, and 65°C. The D- and z- values were determined by using linear regression of the survival data. The D- values were found to be 712 sec (R2 = 0.88), 38.8 sec (R2 = 0.97) and 3.6 sec (R2 = 0.91) at 55, 60 and 65°C, respectively. The z-value was 4.4°C, consistent with reported values for STECs in other food systems. The results of this study showed that the thermal inactivation effect of non-O157 STECs is not the same as of O157 strains in catfish meat, especially at lower temperature (e.g. 55°C), but becomes similar as temperature increases. The findings will assist risk assessors in providing safer finfish products to consumers.

Evaluation of a Modified pH‐Shift Process to Reduce 2‐Methylisoborneol and Geosmin in Spiked Catfish and Produce a Consumer Acceptable Fried Catfish Nugget‐Like Product

Muddy and/or musty off-flavors in farmed-raised catfish occur as a result of the absorption of geosmin (GEO) and 2-methylisoborneol (MIB), compounds produced by algae. Previous research suggests the acid pH-shift method may be able to reduce off-flavors to produce a consumer acceptable product. The objective of this research was to evaluate application of the acid pH-shift method using a shaker sieve for protein recovery and to evaluate consumer acceptability of a resultant batter-coated fried nugget-like catfish product. Farm-raised catfish were either allowed to depurate (control) or treated with 1 ppb GEO or MIB. Fillets from each replicate were collected and ground and treated by the acid pH-shift process. Samples from all treatments and replicates were evaluated for residual GEO and MIB. In addition, batter-coated fried catfish samples were prepared for a consumer sensory evaluation. Results demonstrated that the pH-shift process decreased moisture, ash, and collagen content of catfish fillet tissue (P < 0.05). Flavor of control samples was preferred (P < 0.05). Texture of catfish samples treated by the pH-shift process was preferred (P < 0.05). Results demonstrate the pH-shift process can be utilized to reduce off-flavors and increase the acceptability of a processed catfish product. Use of a sieve as an economic alternative for the pH-shift process was evaluated for removing off-flavors from catfish. Difficulties were encountered with regard to protein recovery using the sieve and suggestions are made to, perhaps, make the process more applicable for a sieve-based recovery step. The process as described reduced off-flavors, but only 2-fold suggesting the process would work best on catfish near or just over off-flavor thresholds. Results also indicated the pH-shift process could be used to improve texture of a fried catfish product designed to be similar to chicken nuggets.

Microbial Quality and Safety of X‐Ray Irradiated Fresh Catfish (Ictalurus punctatus) Fillets Stored under CO2 Atmosphere

The effect of low-dose X-ray irradiation (0, 2, and 3 kGy) on pathogens, spoilage bacteria (psychrotrophic, anaerobic, and lactic acid bacteria), and physicochemical parameters of iced catfish fillets stored under carbon dioxide (CO(2) ) atmosphere were studied. Irradiation of 2 or 3 kGy eliminated all Listeria monocytogenes (4.8 log CFU/g) and Salmonella Typhimurium (4.7 log CFU/g) while CO(2) atmosphere alone showed less than 1 log reduction on Salmonella Typhimurium. There was no recovery of either pathogen for the experimental period. Regardless of dose, irradiation showed 2 log reduction on psychrotrophic, anaerobic, and lactic acid bacteria for 24 d. Further post-irradiation reductions of spoilage bacteria were observed. Spoilage bacteria on catfish fillets treated with 2 kGy irradiation regained their growth after 16 d of storage. However, catfish fillets exposed to 3 kGy did not show growth of spoilage bacteria throughout the experimental period (24 d). Irradiation (2 or 3 kGy) increased pH and TBARS, and decreased Hunter "b" values but produced no effect on water holding capacity and texture. Shelf life of catfish fillets exposed to 2 or 3 kGy irradiation could be extended by more than 24 d at 2 to 4 °C, with the added safety of possibly eliminating pathogens.

Reduction of Listeria monocytogenes in Raw Catfish Fillets by Essential Oils and Phenolic Constituent Carvacrol

The antimicrobial activity of various essential oils and carvacrol was determined on fresh raw catfish fillets against a 4-strain Listeria monocytogenes mixture representing serotypes 1/2b, 3b, 4b, and 4c that were predominantly isolated from catfish processing environments. Thyme oil, oregano oil and carvacrol exhibited concentration and time dependent responses in broth against L. monocytogenes; for example 0.5% concentrations resulted in 4 log CFU/mL reduction within 30 min whereas 0.1% concentrations required more than 24 h for the same level of reduction. Lemon, orange, and tangerine oils, at 0.5% showed listeriostatic effect in which 4 log CFU/mL of the initial L. monocytogenes load was unchanged at 4 °C in 10 d whereas 1% concentrations were listericidal in a time dependent manner. Apart from carvacrol, efficacy of tested essential oils in reducing L. monocytogenes and total microbial load from catfish fillet was very limited. Dipping treatment of catfish fillets in 2% carvacrol solution for 30 min at 4 °C reduced L. monocytogenes to an undetectable level from their initial load of 5 log CFU/g and reduced total microbial load from catfish fillets by approximately 5 log CFU/g. In sensory analysis trained panelist preferred control samples over 2% carvacrol treated samples implying potential limitation in applicability of carvacrol for fillet treatments.

Survival of Listeria monocytogenes, Escherichia coli O157:H7, and Salmonella spp. on Catfish Fillets Exposed to Microwave Heating in a Continuous Mode

Microwave (MW) heating using continuous power output with feedback control and a modified ingredient formulation may provide better and consistent cooking of foods. Currently, household units with build-in inverter power supply units are available. These new generation MW ovens provide continuous, adjustable output and cooking, in contrast to the traditional rectifier-based ovens that rely on the on-off mechanism for control. This study attempted to apply a feedback power control (termed as modified or "smart" MW oven) and phosphate treatment to further improve heating uniformity and enhance food quality and safety. Listeria monocytogenes (Lm, 4-strain cocktail), Escherichia coli O157:H7 (Ec, 5-strain cocktail), and Salmonella spp. (Sal, 6-strain cocktail), surface inoculated onto catfish fillets (75 × 100 × 15 mm; weight 110 g), were heated using the modified MW oven to study the inactivation of the pathogens. The sensitivity of these 3 bacteria to MW heating was in the order of Ec (most), Lm, and Sal (least). Greater than 4 to 5 log CFU reductions of Ec, Lm, or Sal counts on catfish fillet surfaces were inactivated within 2 min of 1250 W MW heating, where the fillet surface temperature increased from 10 to 20 °C to 80 to 90 °C. MW heating caused degradation of catfish fillet texture, which was noticeable as early as 10 to 15 s after the heating started, as evidenced by bumping sounds. Bumping can be significantly reduced by soaking fillets in phosphate solution. However, the results may need verification if applied in different MW ovens and/or with foods positioned away the geometric oven center. This study successfully demonstrated the feasibility of applying MW energy to eliminate foodborne pathogens on fish fillets. The results demonstrated in this report with the "smart" microwave oven design may enhance microwaveable food safety and quality, and therefore promote the microwaveable food business.

Effects of Potassium Lactate and Acetate on Listeria monocytogenes Inhibition, Physicochemical and Sensory Properties of Smoked Catfish Fillets

The objective of this study was to evaluate the effects of liquid and wood smoking with a potassium lactate (PL) and acetate (PA) combination on the quality and inhibition of L. monocytogenes growth in ready-to-eat (RTE) smoked catfish fillets. Catfish fillets were tumbled with PL and PA, and treated with no smoke (NS), wood smoke (WS), liquid smoke 1 (LS1), and liquid smoke 2 (LS2). Wood smoke with antimicrobials (WSWA) showed greater inhibition (p < 0.05) of L. monocytogenes growth than other treatments with the exception of the LS1 treatment with antimicrobials. Consumers preferred (p < 0.05) smoked catfish fillets treated with WS to LS1 with respect to appearance, odor, flavor, texture, and overall acceptability. In conclusion, the use of PL and PA did not have a negative impact on the quality and sensory properties of smoked catfish fillets but had a synergistic effect with wood smoke constituents that inhibited the growth of L. monocytogenes.

Effects of Tea Polyphenols Dip Treatment on the Quality of Catfish Fillets during Partial Freezing Storage

The effects of tea polyphenols(TP) dip treatment on the quality changes of catfish fillets during partial freezing storage for 25 days were investigated. The catfish were filleted, after being gutted and cleaned, and given a dip treatment in 0.15% TP solution for 30min at room temperature. And then, they were packed in plastic bags, stored at -3°C. The sensory scores, total bacterial count(TVC), pH values, Total Volatile Basic Nitrogen(TVB-N) and TBARS values were used to evaluate the catfish quality. The results showed that TVC, pH, TVB-N and TBARS values of catfish, which was processed with TP, could be significantly restrained, and sensory scores decreased slowly as well. So it can be concluded that tea polyphenols have great effects on the inhibitions of bacteria growth and anti-oxidation of fat, and thus significantly delay the spoilage of partial-frozen catfish.

Evaluation of Off‐Flavor in Pond‐Raised Channel Catfish following Partial Crop Harvest

AbstractPonds used to raise channel catfish Ictalurus punctatus in the southeastern United States often contain more food‐sized catfish than processors can accept at one time. Fish remaining after initial harvest are returned to the pond and harvested again as soon as possible based upon processor demands. Some catfish farmers report that catfish crops initially declared “on‐flavor” appear to develop off‐flavors soon after the first harvest, which postpones harvest of the remaining population and delays subsequent production. We conducted a 9‐month study on a commercial catfish farm in northwest Mississippi to determine whether fish systematically develop off‐flavors after partial fish harvest and, if so, the type and origin of the flavor. Channel catfish and water samples were obtained from 12 ponds before initial harvest and then at intervals for 2 weeks after harvest. Water and catfish fillet samples were analyzed for geosmin and 2‐methylisoborneol (MIB). Phytoplankton were identified and counted microscopically. Catfish fillets were also used in sensory analysis to determine quality and intensity of off‐flavor. In most ponds, MIB levels decreased or remained unchanged in pond water after the first seining while geosmin levels remained very low (&lt;10 ng/L) in all ponds. Analysis indicated that mean MIB concentrations in catfish fillets either decreased or were unchanged after the initial harvest. Similar results were found for geosmin concentrations in catfish fillets. There was also no systematic change in fillet flavor quality as determined by sensory analysis. The MIB‐producing cyanobacterium Planktothrix perornata was found in only three ponds, and the abundance of P. perornata decreased in two ponds after initial harvest and transiently increased in the third pond. Overall, we found no systematic changes in fish flavor quality after partial fish harvest and no indication that harvest activities changed ecological conditions that would cause an increase in odor‐producing cyanobacteria.

Reduction in Listeria monocytogenes and spoilage bacteria on smoked catfish using X-ray treatments

To determine the efficacy of X-ray processes in inactivating L. monocytogenes levels in smoked catfish during storage at 5°C and to determine the effects of X-ray doses on controlling the growth of spoilage bacteria on smoked catfish during storage at 5°C for up to 5 weeks. Smoked catfish fillets inoculated with L. monocytogenes were treated with 0.0-2.0 kGy X-ray and stored at 5°C for 5 weeks. The negative controls (uninoculated/untreated) and uninoculated samples treated with the lowest (0.1 kGy) and highest (2.0 kGy) doses were stored at 5°C and tested for psychrotrophs count during the 5 weeks of storage. The initial L. monocytogenes population on smoked catfish was significantly (P < 0.05) reduced to undetectable level by a treatment of 1.0 kGy or higher. The initial psychrotrophs count on smoked catfish was significantly reduced from 4.7 CFU g(-1) to below the detectable level by a treatment with 2.0 kGy. Smoked catfish treated with 2.0 kGy X-ray had no detectable L. monocytogenes throughout 35 days of storage at 5°C. A treatment with 2.0 kGy X-ray also kept the levels of psychrotrophs in the smoked catfish within the acceptable level until 35 days. The results of this investigation indicate that X-ray at 2.0 kGy can eliminate L. monocytogenes and extend the shelf life of smoked catfish stored at refrigeration temperature.

Effect of anolyte on background microflora, Salmonella, and Listeria monocytogenes on catfish fillets.

Near-neutral electrolyzed water (anolyte), having a pH of 6.0 to 6.5 ± 0.02, oxidation reduction potential of greater than 700 mV, and a residual chlorine level of 10 to 200 ppm, was reported to have a potential use to decontaminate food surfaces. An electrolyzing cell was developed that is capable of producing neutral electrolyzed water containing a chlorine level of greater than 700 ppm in the form of hypochlorous acid (anolyte). Anolyte with a chlorine level of 300 ppm was used to determine its effect on Salmonella and Listeria monocytogenes cells after a 3-min contact. Transmission electron micrograph results showed disruption of the outer cellular membrane for both bacteria. The anolyte (300 ppm) was used as a washing solution to decontaminate catfish fillets inoculated with either Salmonella or L. monocytogenes. After a 3-min contact time with the anolyte, there was a 1-log reduction for Salmonella, and after 8 days of refrigerated storage (4°C), this bacterial reduction was maintained. There was no reduction of L. monocytogenes on the catfish fillet surfaces. The anolyte was an effective wash solution for Salmonella reduction on the catfish fillet surfaces.

Channel Catfish Polyculture with Fathead Minnows or Threadfin Shad: Effects on Pond Plankton Communities and Catfish Fillet Flavor, Color, and Fatty Acid Composition

Threadfin shad, Dorosoma petenense, or fathead minnows, Pimephales promelas, were co‐cultured with channel catfish, Ictalurus punctatus, in earthen ponds to determine the effects of planktivory on plankton community dynamics and catfish fillet quality. Fathead minnows had no effect on the plankton community structure or catfish fillet flavor, color, and fatty acid composition. Fillet color was also unaffected by the presence of threadfin shad. Small differences were found in fillet fatty acid composition for catfish from ponds with shad, but these differences probably have no biological significance. Threadfin shad did, however, have important impacts on the plankton community structure and catfish flavor. Size‐selective filter‐feeding by shad reduced cyanobacterial abundance relative to ponds with catfish‐only and fathead minnows. Relative abundance of smaller phytoplankton in the groups Chlorophyta, Cryptophyta, Bacillariophyceae, and Euglenophyta increased in ponds with shad. Relative abundance of small zooplankton (rotifers) also increased in shad ponds. Reduced abundance of large, colonial cyanobacteria that are known to produce odorous metabolites caused a corresponding reduction in off‐flavor prevalence and intensity in catfish from ponds with threadfin shad when sampled in September. Although threadfin shad dramatically reduced catfish off‐flavor prevalence during the warm season, they apparently caused a high prevalence of “fishy” off‐flavors in the February sample. This undesirable flavor appeared to be caused by catfish foraging on shad killed during a preceding period of exceptionally cold water temperatures. Use of threadfin shad for phytoplankton biomanipulation therefore presents a dilemma: catfish–shad polyculture reduces prevalence of cyanobacteria‐related off‐flavors in warm months but may cause undesirable forage‐related off‐flavors in the colder months. Catfish farmers must consider these benefits and risks when deciding to use threadfin shad as a management tool.

Extraction, identification and quantitation of carotenoids in discolored channel catfish (Ictalurus punctatus) fillets

Yellow discoloration of channel catfish fillets is a major quality concern to the catfish industry. This discoloration is thought to be caused mainly by dietary carotenoids, which are deposited as yellow regions within the fillet. In the present work, yellowish fillets were extracted and quantitatively analyzed for their carotenoid contents using an improved extraction procedure. The pigments found in discolored fillets were lutein, zeaxanthin, alloxanthin, and diatoxanthin. The identification of carotenoids was confirmed based on their accurate mass measurement, high-performance liquid chromatography (HPLC) retention time, and UV–vis spectrum. The carotenoid content in catfish fillets ranged from 58ng/g for slightly yellow fillets to approximately 215ng/g for the enhanced yellow fillets. Alloxanthin was identified as a principle carotenoid in channel catfish for the first time.

Antimicrobial Activity of Vinegar on Bacterial Species Isolated from Retail and Local Channel Catfish (Ictalurus punctatus)

The use of vinegar was studied to reduce the growing number of illnesses caused by spoilage bacteria. The antimicrobial activity of organic vinegar was studied on various bacterial species isolated from domestic channel catfish fillets (Ictalurus punctatus). The effectiveness of the vinegar on the bacteria was measured. Bacteria isolated from catfish fillets with the largest inhibition zone were identified through 16S rDNA sequencing to better understand the spoilage bacteria that could be inhibited by vinegar to increase the quality of fishery products. Microbial changes of catfish fillets were evaluated following treatments of vinegar marinades during storage at 4°C and sensory evaluation was performed with baked catfish fillets to evaluate consumer sensory acceptability. Fish and chip vinegar was the most effective on Shewanella putrefaciens isolated from catfish fillets from the market and the pond. Microbial changes were evaluated and sensory evaluation was performed on different acetic acid dilutions of vinegar. Results showed that vinegar diluted to 0.5% acetic acid on catfish fillets would be suitable for prolonging shelf life and appealing to consumers. Vinegar as a natural antimicrobial product can improve the shelf life and safety of food products providing acceptable sensory quality at an affordable price and reducing economic lost due to spoiled catfish and other food products.

Effect of Trisodium Phosphate or Water Dip on the Survival of Salmonella and Listeria monocytogenes Inoculated Catfish Before and After Freezing

Salmonella and Listeria monocytogenes (LM) are occasional contaminants on raw fish. Catfish fillets were artificially contaminated with LM and Salmonella, dipped in a 1.5 % (30 min) trisodium phosphate solution (TSP), and cryogenically frozen. After 3 months frozen storage, Salmonella (2 log), but not LM, was inactivated on the fillets treated with the dip. This indicates that TSP dip followed by cryogenic freezing can be used to control Salmonella, but not LM, on catfish fillets.

Inactivation of Francisella tularensis Utah-112 on Food and Food Contact Surfaces by Ultraviolet Light

Francisella tularensis is the causative agent of tularemia, a plague-like illness that affects animals and humans, and has caused large illness pandemics in the last century. It has also been used as a biological warfare agent, and tularemia can be contracted through consumption of contaminated food and water. In this study the use of a U.S. Food and Drug Administration approved technology, 254 nm ultraviolet light (UV-C), to inactivate F. tularensis Utah-112 (a rodent pathogen) on food and food contact surfaces was investigated. The D10 value, the UV-C dose needed to inactivate one log of microorganism, was approximately 0.71 mJ/cm2 on agar plates using a low UV-C intensity of 100μW/cm2/s. When a commercial UV-C conveyor was used (5 mW/cm2/s) 0.5 J/cm2 inactivated >7 log CFU of F. tularensis Utah 121 on agar plates. At 0.5 J/cm2 UV-C inactivated >4 log CFU of Utah-112 in beef, chicken, catfish, frankfurter, and bratwurst exudates inoculated onto stainless steel coupons, and >7 log CFU was eliminated at 1 J/cm2 UV-C. Similar results were obtained when the exudates were inoculated onto high density polypropylene. Approximately 0.5 log CFU was inactivated on chicken breast, beef steak, and catfish fillets, and approximately 1.9 log CFU on frankfurters and bratwurst at a UV-C dose of 1 J/cm2. These results indicate routine use of UV-C during food processing would provide workers and consumers some protection against F. tularensis.

Yetiştiriciliğin Balık Eti Besin Kompozisyonu ve Balıkların Verimliliği Üzerine Etkisi

Summary Productivity and meat quality of carp (Cyprinus carpio L.), silver carp (Hypophthalmichthys molitrix), grass carp (Ctenopharyngodon idella), catfish (Silurus glanis), zander (Stizostedion lucioperca) and tench (Tinca tinca), which were grown in policulture on natural food in pond fertilised with livestock manure, were compared. The amount of protein ranged from 15.74% (tench) to 19.26% (zander). Lipid contens (%) in the fillets of zander, tench, catfish, carp, silver carp and grass carp was 0.38; 0.79; 2.19; 2.42; 3.82 and 5.24, respectively. The total cholesterol content was the highest in the silver carp fillets (62.32 mg/100 g) and the lowest in catfish (34.34 mg/100 g). The total amount of saturated fatty acids was the highest in silver carp (33.05%) and the lowest in catfish (24.97%). The total polyunsaturated fatty acids was however the highest in tench (44.50%) and the lowest percentage of PUFA was in silver carp (29.95%) and the lowest ratio n-3/n-6 was in common carp (0.92). The chemical composition and quantity of n-3 fatty acids varied largely by the fish species. In summary, rearing fish in polyculture on natural food with the use of agricultural limestone and livestock manure is feasible and productivity and nutrient content varies by the fish species.

FLAVOR OF COOKED CATFISH (PANGASIUS HYPOPHTHALMUS) FILLETS AS PREDICTION FROM RAW FRESH AND FROZEN‐TO‐THAWED

ABSTRACTThis study aimed to develop a lexicon of sensory descriptors for Vietnamese catfish (Pangasius hypophthalmus) fillet products, and to investigate the use of sensory characteristics of raw and frozen fillets to predict the flavor of cooked catfish fillets. Descriptive Analysis (DA) was applied by a panel of 11 trained panelists to samples of raw fresh fillets and frozen fillets at three stages: frozen, thawing and thawed. Samples were also cooked at 200C for 25 min to evaluate their flavor. A lexicon of sensory attributes was generated for three types of samples: raw fresh, frozen‐to‐thawed and cooked. The validity of this lexicon has been discussed. Raw fresh and frozen‐to‐thawed samples were shown to be predictors for sensory characteristics of cooked samples. Sensory quality of catfish fillets was indicated by textural properties and flavors more than appearances and colors.PRACTICAL APPLICATIONSThis study provides Pangasius processors with sensory lexicons of Pangasius fillets to support the development of their quality control plans. The study also provides producers and purchasers with methodological guidelines for making prediction of flavor of Pangasius products at different phases of the processing: raw fresh, frozen, thawed and cooked.

The management of undesirable cyanobacteria blooms in channel catfish ponds using a constructed wetland: Contribution to the control of off-flavor occurrences

An exploratory study on the management of undesirable cyanobacteria blooms with respect to off-flavor problems using an integrated vertical-flow constructed wetland (CW) was performed at a small commercial-scale channel catfish farm from 2004 to 2007. The results of the three-year experiment indicated that water treatment by the CW could reduce the possibility of dominance by undesirable cyanobacteria species that often cause off-flavor problems. A detailed investigation in 2007, showed that the concentrations of geosmin, MIB (2-methylisoborneol), and β-cyclocitral in the water of the recirculating pond (4.3 ng L −1, U.D. (undetected) and 0.2 ng L −1, respectively) treated by the CW were significantly lower than those in the control pond (152.6 ng L −1, 63.3 ng L −1 and 254.8 ng L −1, respectively). In addition, the relationships among the cyanobacteria species, the off-flavor compounds and ten environmental variables were explored by canonical correspondence analysis (CCA). The results showed that Oscillatoria sp., Oscillatoria kawamurae and Microcystis aeruginosa were the main sources of off-flavor compounds in the catfish ponds. The successful manipulation of undesirable cyanobacteria species potentially resulted in lower concentrations of odorous compounds in the water of the recirculating pond. An investigation of the concentrations of geosmin and MIB in catfish fillets showed that the levels of odorous compounds were below the OTC (odor threshold concentration) values in the recirculating pond but were above the OTC values from July to October in the control pond. Water recycling by the CW could potentially be one of the best management practices to control off-flavor occurrences in aquaculture.

COMPARISON STUDY OF THE EFFECTS OF DIFFERENT CRUDE GREEN TEA POLYPHENOLS ON THE QUALITY OF DRIED CATFISH DURING AMBIENT STORAGE

ABSTRACT The comparative antioxidant effect of adding different crude green tea polyphenols (GTP) and vitamin C (VC) on the susceptibility of dried catfish (Clarias gariepinus) quality changes during ambient storage was investigated. Catfish fillet was treated with different concentrations of GTP: 1% NaCl plus 0.01% GTP, 1% NaCl plus 0.03% GTP and 1% NaCl plus 0.01% of VC before drying process. Control muscle sample (CK) was treated only with 1% of NaCl solution (without GTP extract) contained only 1% NaCl, but not GTP. Samples were oven‐dried for 5 days at 45C. The quality change was evaluated over a course of 4 weeks for pH, volatile basis nitrogen, peroxide value, thiobarbituric acid reactive substances and free fatty acid. The results indicated that the most effective antioxidant was GTP and there was no significant differences (P &lt; 0.01) between laboratory‐extracted crude green tea polyphenol and commercial crude green tea polyphenol. This study pointed out that GTP is a good natural antioxidant in comparison with VC and CK, so, it could be easily used in food industry to improve quality and shelf life of food products.PRACTICAL APPLICATIONSFish is a very important foodstuff because of its high protein content and nutritional value. It is also a greatly perishable product, especially in hot climates and tropical areas where cold preservation techniques are often missing and quality losses can occur very rapidly after catch. Addition of antioxidants during drying process can be used to inhibit lipid oxidation and microbial and insect infestation. However, questions regarding the safety of synthetic antioxidants together with consumer's preference have led to increased interest and research on natural antioxidants. Consumers favor natural antioxidants, which may have a positive effect on human health. Green tea polyphenol (GTP) as a natural antioxidant has lower toxicity than synthetic antioxidants like butylated hydroxyanisole and butylated hydroxytoluene, and more effectiveness than VC. It can be used as an alternative to VC to extend the quality of fish and fish products during storage.