Extraction, fractionation and activity characteristics of proteases from shrimp processing discards

Proteases recovered from Northern pink shrimp (NPS) and Southern rough shrimp (SS) processing discards (heads, shells, tails) were characterized. Shrimp processing discards were extracted with water following homogenization and centrifugation in order to obtain the crude extract which was subsequently fractionated with solid ammonium sulfate. Two fractions sedimenting with 30-50% (designated as NPS-I and SS-I), and 50-70% (designated as NPS-II and SS-II) ammonium sulfate were collected following centrifugation, respectively. Endoprotease activity of the crude extract was 0.02 U/mg for hemoglobin (Hb, pH 3.0), 0.16 U/mg for azocasein (Ac, pH 6.0) and 0.12 U/mg for benzoyl-Arg-beta-naphthylamide (BANA, pH 7.0). The exoprotease activity was 0.11-0.17 U/mg for Arg-beta-naphthylamide (ArgNA, pH 7.0), 0.06-0.11 U/mg for Lys-beta-naphthylamide (LysNA, pH 7.0) and 0.08-0.09 U/mg for Leu-beta-naphthylamide (LeuNA, pH 7.0). Endoprotease activity increased 5-7.4 fold for NPS-I and SS-I, and 1.9-2.7 fold for NPS-II and SS-H against crude extract. Meanwhile, exoprotease activity increased 3.6-4.8 fold for NPS-I and SS-I, and 5.6-72 fold for NPS-II and SS-II. Meat treated with NPS-I and SS-I was tenderized more extensively than that treated with NPS-II and SS-II. The results of this study suggest that proteases recovered from shrimp processing discards may potentially be used as processing aids in formulated foods.