Quality improvement of gels made with protein isolate extracted from catfish by-products

Authors: ZHANG, Y - Mississippi State University; CHANG, S - Mississippi State University

Submitted to: Institute of Food Technologists (IFT) Nonthermal Processing Divison
Publication Type: Abstract Only
Publication Acceptance Date: 2/26/2021
Publication Date: N/A
Citation: N/A

Interpretive Summary: In USA, channel catfish farming is an important aquaculture in some southern states including Mississippi, Alabama and Arkansas. However, competition from abroad and increasing feed cost are making this industry waning. After filleting, the by-products accounted for about 65% of total weight and 50% of total protein of the whole fish, but these by-products end up as low-value animal feed, fertilizer or waste which is thrown away. Therefore, it is imperative to properly utilize these underused by-products and improve the profitability of the catfish farming industry as a whole. Our previous research has proved the protein isolate extracted from catfish by-products can be used as a substitute for expensive fish fillet mince (or surimi), but the dark color and lack of elasticity of the gels made from protein isolate need to be addressed. We tested different conditions to wash the by-product mince before protein extraction and found washing mince with 2:1 water-to-mince ratio for 2 min before protein extraction was optimal economically and technically. With this washing protocol, the protein isolate showed comparable color profile with catfish fillet mince. Then we applied different levels of transglutaminase (cross-linking enzymes) to improve the gel textural profile. It was found the elasticity was substantially improved. Solving these problems renders it possible to make various fish meat-based products from protein isolate extracted not only from catfish by-products, but also from other fish species.

Technical Abstract: Introduction: In order to utilize catfish by-products and improve the profitability of catfish farming industry, alkaline protein extraction from catfish by-products including frames and heads was studied and proved economically feasible. However, the gel made from protein isolate was darker and more brittle than the gel made from catfish fillet mince. The study’s objective was to improve the color and texture quality of the gel made from protein isolate. Methods: Catfish by-product mince was washed with different combinations of time (1, 2, 3, 4, 5, 10, 20, 30, and 40 min) and water-to-mince ratio (2, 3, and 4) and the myoglobin and protein washed were determined. With the selected optimal water-to-mine ratio and washing time, other conditions including second washing of mince and protein isolate washing with acidic water were investigated to achieve the best color and protein yield. Finally, different concentrations of transglutaminase from 0.1 to 0.6 unit/g at 0.1 units increment were applied to improve the gel texture profile. Texture profile and rheological property analyses and protein electrophoresis were conducted. Results: Washing mince with 2:1 water-to-mince ratio for 2 min before protein extraction proved to be optimal economically and technically. It could remove 2.92 mg myoglobin per gram of mince and resulted in 11.1% solid recovery and 24.9% protein recovery, respectively. The values of “L”, “a”, and “b” were 74.1, 1.70 and 13.0, which were similar to that of the fillet mince. Hardness, cohesiveness, resilience, elasticity, chewiness, fracturability and deformation of gels increased with the increase of transglutaminase concentrations. With the addition of transglutaminase, deformation was improved from 6.43 up to 11.08 mm. Elasticity was increased from 59.93 to 66.16%, and resilience was increased from 9.04 to 17.09%. Electrophoretic analysis revealed that both cross-linking and disulfide formation played an important role in the gelation. Meanwhile, proteolysis also occurred due to the residual endogenous enzymes. Sol-gel transition by temperature sweep revealed that the endogenous enzymes reached their peak activity at around 50 °C. Significance: This study solved the quality issues of gels made from protein isolate and explored the chemistry during gelation. The techniques can be used to make high quality fish protein gels, such as fish balls and fish cake products, from catfish by-products.