Removal of Soluble Nitrogen From Surimi Wash Water by Protein Recovery Using Lactic Acid for Safe Discharge

In the present study, the effects of pH (2, 3, 4, 5, and 6) and incubation time (0, 10, 20, and 30 min) on the removal of soluble nitrogen from surimi wash water by recovery of protein were investigated. The highest protein removal rate was recorded at pH 4 at 0-10 min (90.43%), was optimized, and further used for the comparison with industrial untreated (raw) surimi water and centrifuged surimi wash water. Acid treated sample showed lower values of protein (0.1%) and fat (0.1%) followed by centrifuged surimi wash water. The significantly (p < 0.05) higher biochemical oxygen demand (BOD) (320 mg/L) and chemical oxygen demand (COD) (800 mg/L) were observed in raw wash water (RWW) and acid treated wash water compared to centrifuged wash water (CWW). The lowest value of ammoniacal nitrogen (24.8 mg/L), total phosphorus (92.8 mg/L), and total suspended solids (4 mg/L) were found in treated surimi wash water. Samples treated with acids (pH 4) (using lactic acid as a green organic acid) notably showed significantly higher values of amino acids compared to RWW. SDS analysis indicated that the treated surimi wash water with acidic condition significantly reduced protein band intensity on SDS-PAGE compared to the other due to higher protein removal and other organic compounds. The lowest microbial loads such as Aerobic plate count (3.6 × 10⁵ CFU/mL), yeast and mould counts (2.1 × 10⁴ CFU/mL) and presence of Lactobacillus (84 CFU/mL) was associated with acid treated surimi wash water. PRACTICAL APPLICATIONS: The outcomes of this study are aligned with zero-waste manufacturing and circular bioeconomy. Production of high-quality protein for food and feed applications in the food and nutritional sector. The study is aligned with low-cost nutritional supplements to ensure nutritional security.