Pilot plant scale production of protein from catfish treated by acid solubilization/isoelectric precipitation.
Catfish fillets were minced and acid (pH 3.0) solubilized in dilute conditions (1:9). Insolubles were removed by centrifugal force (3000 xg) and the soluble protein was recovered by isoelectric precipitation (pI approximately 5.4). Moisture and NaCl of the batters were equilibrated to 78% and 2%, respectively. Samples were stuffed into casings, cooked, and chilled. Proximate composition, color, cook yield, water holding ability (WHA), and texture profile analysis (TPA) were determined. Treatment of catfish protein by the solubilization process removed 74% of the fat. In addition, gels from treated protein were less red (-1.61 compared with -1.06) and yellow (6.58 compared with 7.09). There was no difference in whiteness (72.0 compared with 71.8) of gels or in percent cook yield (94.6% compared with 95.0%) between treated protein and the control, respectively. The WHA of gels made from control protein was 0.73 g/g protein higher than treated. The texture analysis indicated that treated proteins had significantly higher hardness (1193 g compared with 1046 g), springiness (0.919 compared with 0.897), chewiness (0.701 compared with 0.584), and cohesiveness (0.637 mJ compared with 0.619 mJ). The resilience was equivalent for both treated and control gels. The results indicated the protein solubilization process produced a low fat protein product with good gel strength properties.
Channel catfish (Ictalurus punctatus) muscle protein isolate performance processed under different acid and alkali pH values.
Channel catfish (Ictalurus punctatus) muscle was subjected to 6 protein extraction and precipitation techniques using acid solubilization (pH 2.0, 2.5, and 3.0) or alkaline solubilization (pH 10.5, 11.0, 11.5) followed by precipitation at pH 5.5. The catfish protein isolate was compared with ground defatted white muscle. Alkali-processed catfish showed increased gel rigidity, gel strength, and gel flexibility compared to acid-processed catfish, which exhibited inconsistent functional performance, increasing and decreasing gel rigidity, gel strength, and gel flexibility. The gel rigidity (G') at pH 3.0 in the absence of salt had the highest G' of the acid treatments and was not significantly different from the alkaline-treated catfish muscle (P>0.05). However in the presence of added salt pH treatment it had the lowest G' and was different from alkaline treatments (P<0.05) during break force testing. These results show that pH-shift processing of channel catfish muscle provides highly functional isolates with a potentially broad range of applications. This range of applications is possible due to the modification of the textural properties of catfish muscle protein produced using different acidic or alkaline pH solubility treatments.
Initial Fish State and Mixing Time Effects on Textural Characteristics of a Restructured Catfish Product
A restructured catfish product similar to a corn dog was developed using tumbled catfish from low cost fillets. The product when made from fresh fillets, was more tender but had tougher skin than when made from frozen fillets. Mixing more than 5 min resulted in a more rubbery and tougher product as demonstrated by higher Instron peak load and longer relaxation time.