Recovery of cathepsins from marinating brine waste

Summary In the fish industry, brine left after herring marinating is discarded to waste. This study presents laboratory-scale findings regarding recovery of aspartyl (D + E) and cysteine cathepsins (B + L) from waste brine. Ultrafiltration enabled cathepsin recovery from both the soluble and lysosomal fraction of the marinating brine. Retentate 10 kDa had the highest cathepsin activity 140% compared to crude brine. The amount of recovered cathepsins using membranes 30 and 100 kDa was less than 10 kDa, because part of cathepsins passes to permeate. In turn, the salting-out with ammonium sulphate enabled activity recovery of only 80%, but ensured over twofold higher purity of the enzymes than ultrafiltration. The highest precipitation of D + E cathepsins was noted at salt concentration of 40–60%, whereas that of B + L cathepsins at 50–80%. It is recommended to dissolve the salted-out aspartyl cathepsins at pH 4.0 or 8.0, whereas the cysteine ones at pH 5.0. The appropriate selection of parameters enables controlling the aspartyl to cysteine cathepsins ratio in the preparation in the range from 1:2 to 2:1. The new cathepsin preparations showed high activity in a wide range of pH values and ionic strength and can be used in food production.