Proteolytic activity in Pacific shrimp (Pandalus jordani) processing waste; distribution, effects on muscle proteins, and partial characterization Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/02871030t

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  • Proteases present in shrimp processing waste are factors in the technology of shrimp. The distribution of proteolytic activity in shrimp parts was determined using hemoglobin and casein as substrates. The effects of various parameters upon activity of proteases in the inedible portion were determined using muscle protein as a substrate. Low pH active proteases from the hepatopancreas were characterized using column chromatography and inhibitors. A crude homogenate of shrimp processing waste showed maximum proteolytic activity on casein at pH 6.25, although activity was relatively uniform between pH 5.75 and 7.5. Hemoglobin digestion was greatest between pH 3 and 3.65. Specific activity was greatest in the foregut followed by the hepatopancreas and remainder of the inedible portion. Shrimp which contained food in their foreguts had greatest total activity in the foregut followed by the hepatopancreas. The order was reversed for shrimp which had not been feeding. Total activity was lowest in the inedible portion with digestive organs removed. Only negligible activity was detected in the muscle. Autolytic changes in a model system were studied where shrimp processing waste was the major protease source and muscle protein served as the major substrate. Activity data showed a major maximum at pH 3 and a minor broad maximum between pH 7 and 9. Maximum autolytic activity occurred at 50°C for pH 3 and at 55°C for pH 7.4. Incubation of the inedible portion at 65°C for 30 min was sufficient to inactivate the proteases. Proteases were unstable at low pH and 10 min on ice at pH 1.8 were required for inactivation. Autolysis at pH 3 was completely prevented by 10% NaCl while the inhibitory effects were less at pH 7.4. Protein solubility was decreased by NaCl at pH 3 and increased at pH 7.4. Heat-denatured muscle proteins were less susceptible to hydrolysis, possibly through a reduction in solubility. Changes occurred in the electrophoretic profile of soluble proteins (pH 7.4) from a muscle mixture which was incubated at 50°C. Changes also occurred when incubation mixtures contained inedible portion and these changes were more rapid than when inedible portion was absent. Low pH active proteases from the hepatopancreas were studied using hemoglobin as a substrate at pH 3.5. Gel filtration of a preparation from the hepatopancreas on Sephadex G-150 separated hemoglobin digesting activity in two distinct fractions. Chromatography on DEAE-cellulose also separated activity into two fractions and provided further evidence for the existence of at least two enzymes. Fractions from chromatography were unaffected by phenylmethyl sulphonylfluoride, unaffected or slightly activated by KCN, and greatly inactivated by p-chloromercuribenzoate. EDTA greatly activated all fractions. The result indicated that -SH groups are important for enzyme activity. A crude homogenate of the hepatopancreas and the major fraction from ion-exchange chromatography were most active on hemoglobin between pH 3 and 4.
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