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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.

The production of cold fish marinades is characterized by high seasonality, and therefore producers have problems with providing the sufficient supply of marinades. Besides, after the spawning season, herrings do not ripen properly. Therefore, in the present study, marinated Atlantic and Baltic herring fillets were frozen and stored for 2 days up to 5 months using constant and fluctuating temperatures (recrystallization). The freezing-thawing of marinades improves the hardness, color, and overall sensory evaluation of meat. Temperature fluctuations increase the disintegration of the muscle tissue structure and lysosomal membranes, enhancing the activity of aspartyl endopeptidase responsible for improving the texture of meat and increasing the concentration of protein-hydrolyzing products. The highest thaw drip loss and lipid oxidation were observed after 3 months of frozen storage with temperature fluctuation. Frozen storage had a different effect on fatty and thin herrings. Frozen-thawed marinades stored for up to 5 months were of good microbiology quality. Study results show that the freezing of the semi-marinades may be one of the methods for quality improvement and for extending marinades shelf-life before the seasonally increased demand on the market.