Autodigestion and Peptidase Activity in Low Quality Baltic Sprat (Sprattus sprattus balticus Schneider, 1908)

This study was conducted on fresh and frozen-thawed sprat of the lowest utility, which is not used for consumption. The peptidase activity was measured (i) against acid- and base-hemoglobin (GPA) and as (ii) autodigestion with an effect of NaCl concentration in the range of 5–30% and a pH effect in the range of 3.5–8.0. The activity has been shown to be divided into endo and exopeptidases. The optimum endopeptidase activity in whole fresh fish was observed at pH 8.0, whereas for exopeptidases it was observed at 5.0. Under acidic conditions, the activity of endopeptidases from intestines was the same as that from carcasses, but under basic conditions, it was over 130 times higher. After freezing the sprat, the GPA was higher than in fresh spat. The increase in GPA was significant especially for endopeptidases. Freezing also affected the activity of endo and exopeptidases. The addition of 5% salt to the whole fresh sprat caused an increase in endopeptidase activity, but higher NaCl concentrations decreased it. At 20% concentration, the endopeptidase activity was almost 20 times lower than that at 5% salt. The salt concentration did not significantly affect the sprat exopeptidase activity. Sprat with the lowest utility has high peptidase activity and can produce hydrolysates used in food technology.