Isoelectric filtration and protein removal from spent brine after fish marination

Brines after herring marination are economic burden and cause environmental pollution. Spent brine filtration is impossible due to high protein content causing filter fouling. Therefore, novel single and double isoelectric solubilization/precipitation (ISP) was investigated for the first time for spent brine filtration. Minimum pH necessary to precipitate proteins and precipitation efficiency for pH 2.0 to 12.5 were determined. Protein precipitation at acidic and alkaline pH differed quantitatively and qualitatively. Brine filtration efficiency increased with greater protein precipitation and number of precipitations and was pH dependent. Filtration of double and single ISP-supernatants (pH 2.0 + 12.0 and 12.0, respectively) was only 4–5 times slower than water filtration (control), whereas filtration of single ISP-supernatant (pH 2.0) and untreated brine was impossible. Cathepsins did not precipitate or inactivated, remaining in the brine, which may increase bioactive peptides. Therefore, protein precipitates lacking cathepsins were biochemically characterized, which suggested their potential for food or feed applications. • Microfiltration of raw spent brine cause fouling due to dissolved proteins. • Isoelectric precipitation (IP) at pH 3.0 or 8.0 is effective. • IP does not precipitate cathepsins and peptides fraction. • Brine filtration efficiency depends on number of IP and pH. • Brine after double IP can be filtrate as fast as water without fouling.