Treatment of Catfish Fillets with Citric Acid Causes Reduction of 2-Methylisoborneol, but not Musty Flavor

Comparative quality and volatilomic characterisation of unwashed mince, surimi, and pH-shift-processed protein isolates from farm-raised hybrid catfish (Clarias macrocephalus × Clarias gariepinus)

Earthy off-odour in farm-raised freshwater fish is considered a quality defect. This study aimed to investigate the potential of pH-shift processing to remove off-odours from farm-raised hybrid catfish while at the same time documenting de-novo formation of other volatile compounds. In comparison with crude mince and conventional surimi, the alkali pH-shift process gave larger reductions in geosmin, 2-methylisoborneol, undesirable volatile compounds (e.g. hexanal, (E)-2-nonenal, (E)-2-heptenal, 2-butanone, and hexadecane), lipids, myoglobin, total volatile basic nitrogen, and TCA-soluble peptides (p < 0.05). The acid-produced protein isolate showed the highest TBARS and processing-induced evolution of the following volatiles: octanal, nonanal, decanal, 2-butyl-2-octenal, pentadecanal, 1-hexanol, 1-octanol, 1-octen-3-ol, and 2,3-octanediol (p < 0.05). Alkali-aided process provided better overall gelling characteristics (i.e. breaking force, deformation, and texture profile) and gave lower fishy, earthy, and rancid off-odour scores (p < 0.05). Thus, alkali pH-shift process can be used to isolate gel-forming proteins from hybrid catfish while minimizing the accumulation of undesirable volatile compounds.

Increased thermal sensitivity of Listeria monocytogenes in sous-vide salmon by oregano essential oil and citric acid

Inadequate cooking during sous-vide processing may cause foodborne diseases in case the food is contaminated with pathogens such as Listeria monocytogenes. In this study, thermal inactivation of L. monocytogenes in sous-vide processed salmon was investigated. Oregano oil and citric acid were used alone or in combination to determine the probability of increasing the efficiency of heat treatment. Control (C); 0.5% citric acid added (S); 1% oregano essential oil added (O); and citric acid and oregano essential oil combined (OS) groups were prepared. Samples were inoculated with L. monocytogenes, vacuum packed, then sous-vide cooked at 55, 57.5, 60, or 62.5 °C for predetermined times. The D-values of all treated samples were significantly lower than control. The use of oregano oil (O), citric acid (S) and their combination (OS) significantly reduced the time required to inactivate L. monocytogenes. The z-values of L. monocytogenes in C, O, S and OS groups were 5.50, 5.62, 6.54, and 6.92 °C, respectively. It was determined that effective results could be achieved by adding natural antimicrobials to provide safety in sous-vide fish.

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.

PRACTICAL APPLICATION

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.

Potassium acetate and potassium lactate enhance the microbiological and physical properties of marinated catfish fillets

Sodium or potassium salts such as lactate and acetate can be used to inhibit the growth of spoilage bacteria and food-borne pathogens, and thereby prolong the shelf-life of refrigerated seafood. However, minimal information is available regarding the combined effects of potassium salts (acetate and lactate) with an agglomerated phosphate blend on the quality and safety of refrigerated catfish fillets. The objective of this study was to determine the microbiological and quality characteristics of marinated catfish fillets treated with organic acid salts. Catfish fillets were vacuum-tumbled with a brine solution with and without the added organic acid salts, at 10% over initial, raw weight prior to tray-packing and storage at 4 °C for 14 d. Fillets were evaluated for yields, color, pH, tenderness, consumer acceptability, and shelf-life. No differences (P > 0.05) existed among the treated and untreated fillets with regards to solution pick-up and pH, but all treated fillets increased (P < 0.05) cooking yields and Intl. Commission on Illumination (CIE) a* values, and decreased (P < 0.05) CIE L* and b* values in the catfish fillets when compared to the untreated fillets. The fillets treated with a combination of potassium acetate and potassium lactate had lower (P < 0.05) psychrotrophic plate counts and lower spoilage scores than the control treatments on days 7, 10, and 14. In addition, consumers preferred (P < 0.05) treated catfish fillets (fried) with respect to appearance, flavor, and overall acceptability over the negative control. In conclusion, the combination of potassium acetate and potassium lactate enhanced sensory quality and extended the shelf-life of refrigerated catfish fillets.