Protein and water recovery from tuna defrosting wastewater

The objective of this research was to recover protein and water from tuna defrosting wastewater. Tuna defrosting wastewater (TDW) was concentrated, and salt protein residue (PR) was separated from concentrate TDW (cTDW). Protein in the cTDW was precipitated (PP). Salt was removed from PR and PP by using hot water (60 degrees C). PR and PP were dried at 50 degree celsius before analysis for total protein, amino acid profile and salt content. Salty protein solution (PS) following salt removal from the precipitate was collected and concentrated. Then salt cPS was desalted by Sephadex G-25, and the elution was collected and concentrated. The resulting cPS was analyzed for pH, total protein, salt content, amino acid profile and antioxidant properties. Water from the protein recovery procedure was collected and analyzed for biological qualities (heterotrophic plate count, coliform bacteria, E. coli, Staphylococcus aureus, Salmonella spp. and Clostridium perfringens), physical qualities (apparent color, turbidity, pH) and chemical qualities (total dissolved solids, total hardness and sulfate).The results showed that cTDW contained 11.57 +/- 0.03 % protein and 3.36 +/- 0.03% NaCl. After salt was removed, the dried PR and PP contained 33.10 +/- 0.16% and 6.92 +/- 0.13% protein, respectively, and 0.23 +/- 0.00% and 0.05 +/- 0.00% NaCl, respectively. Dried PR contained 9 essential amino acids at higher concentrations than in PP. Concentrated PS contained 3.15 +/- 0.12% protein and no NaCl. Histidine (254.15 mg/100 g) was the dominant amino acid in cPS. Antioxidant properties are shown by values for DPPH, ABTS and FRAP. The physical, chemical and bacterial parameters of recovered water met the guidelines for drinking water quality. These results indicate that recovery of protein and water is possible in fish processing, which could reduce costs for processors and benefit the environment.