## 3 Results and Discussion
### Activity of Digestive Proteases and Cathepsins
Therefore, it is likely that the lowest cathepsin D activity in Danish marinades was due to the inhibitory effect of salt and the lack of activating acetic acid during the first two days of brining [32]. Cathepsin D activity is important for the ripening of marinated meat, because this endoprotease prepares substrates for the other cathepsin [33]. Figure 5: Effect of marinating method (G—German, D—Denmark) and degree of primary processing of Baltic herring (whole, headed, fillets) on activity of (**A**) trypsin esterase, (**B**) trypsin amidase, (**C**) chymotrypsin and (**D**) carboxopeptidase-A during marinating. \({}^{\text{a,b,c}}\) Results marked with the same lower case letter do not statistically differ by the influence of marinating time; \({}^{\text{A,B,C}}\) Results marked with the same capital letter do not statistically differ by the influence of the marinating method. For a better presentation of the results, a break (\(\approx\)) in the Y axis was used. Cathepsin L activity, after 2 days of marinating the fillets, increased twice to 612-683 U, after which it decreased to 170-380 U (Figure 6B). In marinades from headed herring, cathepsin L activity increased 6.5 times after 2 days by the German method (1679 U) or after 7 days by the Danish method (1692 U). In marinades from whole herring, cathepsin L activity increased as much as 8 and 9 times after 4 days in the Danish (2000 U) and German (2260 U) methods, respectively, and then decreased, reaching 1400-1499 U after 14 days of marinating. Cathepsin L, like cathepsin D, is also an acidic endopeptidase, but requires the presence of salt and a higher pH for optimal activity [2]. Therefore, cathepsin L activity positively correlated with the pH value in only G-fillets (0.593), G-headed (0.964) and G-whole (0.736) marinades. In turn, salt concentration significantly correlated with cathepsin L activity for all marinades, except G-fillets. In the case of cathepsin B, the activity of this endopeptidase decreased 20-40 times after 2-7 days of marinating; the fastest in G-fillets marinades and the slowest in D-whole marinades (Figure 5C). The cause was the strong inactivation of cathepsin B by salt and acetic acid [2]. Thus, the results showed that the activity of digestive proteases and cathepsin was higher in marinades made from whole and headed herring than from fillets, especially after 2-7 days of marinating. The higher cathepsin activity in marinades from ungutted herring was possibly related to (i) the release of cathepsin from lysosomes by digestive proteases [6; 34], (ii) the reduction of cathepsin loss from meat to brine by the  
Figure 6: Effect of marinating method (G—German, D—Denmark) and degree of primary processing of Baltic herring (whole, headed, fillet) on activity of (**A**) cathepsin D, (**B**) cathepsin L and (**C**) cathepsin B during marinating. \({}^{\text{a,b,c}}\) Results marked with the same lower case letter do not statistically differ by the influence of marinating time; \({}^{\text{A,B,C}}\) Results marked with the same capital letter do not statistically differ by the influence of the marinating method. For a better presentation of the results, a break (\(\approx\)) in the Y axis was used. herring skin [2] and (iii) the slower diffusion of acetic acid into meat [32], which inhibits the activity of alkaline digestive proteases. Moreover, higher cathepsin D activity may have promoted the release of intracellular proteases [35].