Protein extraction from catfish by-products and physicochemical properties of the protein isolates

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

Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/19/2021
Publication Date: N/A
Citation: N/A

Interpretive Summary: In the USA, channel catfish (Ictalurus punctatus) 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. However, no standard protein extraction protocol is available for fish by-products. In this study, the effects of extraction factors, including particle size, mince-to-water ratio, alkalinity, and extraction time were optimized in terms of protein recovery and solid mass yield. The protein products extracted by various combinations of the extraction conditions were studied for their physicochemical properties , including color, solubility, secondary structure and gel properties. It was found protein properties were greatly affected by alkalinity used for protein extraction and the gels made from protein isolates showed different rheological and textural properties. In general, the protein extraction protocol devised was effective and economically feasible. This study proved that utilization the extracted protein for making surimi-like gels is possible and promising. In addition, this work provided guidance for the industry to select optimal processing parameters to economically obtain value-added proteins.

Technical Abstract: In order to optimize protein recovery from catfish by-products by alkaline extraction, the effects of different factors, including particle size, mince-to-water ratio, pH, and extraction time were investigated. It was found that a protein recovery of about 30% could be achieved. Increases in pH (pH 10.5, 11 and 11.5) improved protein recovery, but also increased protein denaturation as evidenced by decreased solubility, decreased a-helix, increased ß-sheet and increased random coil structures. The color and texture of gels made from protein isolate were greatly affected by the pH values used for protein extraction. For the gels made from fillet mince, and protein isolates extracted at pH 10.5, pH 11 and pH 11.5, the “L” values were 78.96, 60.38, 57.74 and 54.39, the breaking forces were 205, 492, 585 and 458 grams, and deformation values were 10.59, 8.07, 6.73, and 5.04 millimeters, respectively. Electrophoresis revealed protein degradation during alkali-aided extraction with myosin heavy chain (MHC), the most predominant band, showing about 50% decrease in comparison with fillet mince. It also demonstrated that gelation not only caused cross-linking, but also autolysis with 53, 56, 59 and 81% decrease in MHC intensity for fillet mince, protein isolates extracted at pH 10.5, 11 and 11.5, respectively. Fillet mince and protein isolates exhibited different storage modulus patterns during temperature sweep, implying different gelation mechanisms. The current study proved the protein extracted from catfish by-products was potential to be utilized as edible food components especially in gel making.