Purification and characterization of a proteinase inhibitor from white croaker skeletal muscle (Micropogon opercularis)

Proteolysis and Its Control Using Protease Inhibitors in Fish and Fish Products: A Review

Texture is one of the food quality attributes affecting the consumer's acceptability and the market value. Fish and shellfish undergo weakening or softening of muscle, particularly during extended storage under inappropriate conditions. The phenomenon is governed by endogenous proteases, both digestive and muscle proteases. Proteases present in the gastrointestinal tract that leach out to muscle tissue can induce proteolysis of myofibrillar and collagenous proteins. Furthermore, the muscle proteins present in gels fabricated from fish or shellfish meat also encounter degradation during thermal processing. Endogenous heat-activated proteases strongly bind to muscle proteins and are activated during heating, thereby degrading myofibrillar proteins, which are abundant in muscle tissue. This deterioration of the proteins directly leads to a weakened gel with poor water-holding capacity. Both cysteine and serine proteases are responsible for the degradation of myofibrillar proteins in several aquatic animals. Effective pretreatment of fish and shellfish, as well as the use of food-grade protease inhibitors (PIs), have been implemented to inactivate endogenous muscle and digestive proteases. For this review, proteolysis of muscle proteins and its control by food-grade PIs are revisited. Improved and effective lowering of proteolysis should be gained, thereby maintaining the quality of fish and their products.

Identification by GeLC-MS/MS of trypsin inhibitor in sarcoplasmic proteins of three tropical fish and characterization of their inhibitory properties

Sarcoplasmic proteins from 3 fish species were fractionated by 50% to 70% ammonium sulfate precipitation. Lyophilized fractionated sarcoplasmic proteins of threadfin bream (TB-SP), bigeye snapper (BS-SP), and yellow croaker (YC-SP) showed 80% to 92% trypsin inhibitory activity. Trypsin inhibitory activity staining gel electrophoresis revealed bands at 32, 33, 37, 45, 48, and 50 kDa for the 3 species, and a band at 95 kDa was observed for TB-SP and YC-SP. Alpha-1-antitrypsin with molecular mass of 45 to 50 kDa was identified in YC-SP by gel-based liquid chromatography-tandem mass spectrometry (GeLC-MS/MS). Other major protein bands appeared on trypsin activity staining included phosphorylase, glyceraldehyde-3-phosphate dehydrogenase, and creatine kinase with molecular mass of 95 and 35 to 40 kDa, respectively. But, these 3 proteins did not show true trypsin inhibitory activity. Trypsin inhibitory activity of fractionated sarcoplasmic proteins showed good stability, with >80% activity retained at 60 °C and up to 0.6 M NaCl. TB-SP showed the highest inhibitory activity against autolysis of washed threadfin bream mince at 65 °C. Addition of 0.5% or 1% TB-SP improved textural properties of threadfin bream surimi gels preincubated at 37 or 65 °C followed by heating at 90 °C. Therefore, TB-SP could be a promising protein ingredient for enhancing surimi gel texture.

PRACTICAL APPLICATION

Threadfin bream, bigeye snapper, and yellow croaker are the main species used as raw material for tropical surimi production. Sarcoplasmic proteins from 3 species contain trypsin inhibitor(s) that can minimize proteolytic activity and improve gel texture of proteinase-laden fish muscle. Therefore, sarcoplasmic proteins that are byproducts from surimi processing of these species could be recovered, fractionated, and utilized as a functional protein ingredient.

Enhanced anti-proteases inLabeo rohita fed with diet containing herbal ingredients

Aqueous root extract ofAchyranthes aspera was incorporated in the experimental diet ofLabeo rohita (rohu). Control diet was prepared without root extract. Feeding of fishes with experimental diet has significantly (p<0.05) enhanced the serum anti-proteases level than fishes fed with control diet.

Production of Proteolytic Enzymes by a Keratin-Degrading Aspergillus niger

A fungal isolate with capability to grow in keratinous substrate as only source of carbon and nitrogen was identified as Aspergillus niger using the sequencing of the ITS region of the rDNA. This strain produced a slightly acid keratinase and an acid protease during cultivation in feather meal. The peak of keratinolytic activity occurred in 48 h and the maximum proteolytic activity in 96 h. These enzymes were partly characterized as serine protease and aspartic protease, respectively. The effects of feather meal concentration and initial pH on enzyme production were evaluated using a central composite design combined with response surface methodology. The optimal conditions were determined as pH 5.0 for protease and 7.8 for keratinase and 20 g/L of feather meal, showing that both models were predictive. Production of keratinases by A. niger is a less-exploited field that might represent a novel and promising biotechnological application for this microorganism.

Proteinase inhibitory activity of sarcoplasmic proteins from threadfin bream (Nemipterus spp.)

BACKGROUND

Thailand is the second largest surimi producer in the world and 50% of surimi is produced from threadfin bream. During surimi processing, sarcoplasmic proteins are removed through water washing and discarded in the waste stream. This study was aimed at investigating the proteinase inhibitory activity of sarcoplasmic proteins.

RESULTS

Sarcoplasmic proteins from threadfin bream (TBSP) exhibited inhibitory activity toward trypsin but did not inhibit papain and chymotrypsin. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis under non-reducing condition stained by trypsin inhibitory activity revealed three protein bands of molecular mass of 95, 41 and 37 kDa. Inhibitory activity of TBSP reached a maximum when subjected to 45 degrees C and completely disappeared at 60 degrees C. The breaking force and deformation of lizardfish surimi gel with added TBSP and pre-incubated at 37 degrees for 20 min increased with additional levels of TBSP (P < 0.05). Trichloroacetic acid-oligopeptide content of lizardfish surimi gel with added TBSP decreased with the addition of 4 g kg(-1) TBSP (P < 0.05). Retention of myosin heavy chain (MHC) increased when TBSP concentration was increased. TBSP effectively protected MHC from proteolysis at 37 degrees C to a similar extent as egg white powder, but efficacy of TBSP was not observed at 65 degrees C.

CONCLUSION

TBSP could be applied to reduce proteolytic degradation of lizardfish surimi or other surimi associated with trypsin-like proteinase, rendering an improvement in surimi gelation set at 37-40 degrees C.

A novel serine protease complexed with α2-macroglobulin from skeletal muscle of lizard fish (Saurida undosquamis)

A novel fish muscle serine protease named muscle soluble serine protease (MSSP) was purified from the soluble fraction of lizard fish (Saurida undosquamis: Synodontidae) muscle by ammonium sulfate fractionation followed by four steps of column chromatographies. In native-PAGE, the purified enzyme appeared as a single band with an estimated mol. mass of approximately 380 kDa by gel filtration. In SDS-PAGE under reducing conditions, the purified enzyme migrated as two protein bands at 110 and 100 kDa, named subunits A and B, respectively. The 20 residues of N-terminal amino acid sequence of subunit B showed 70% of homology to beta-chain of carp alpha(2)-macroglobulin-1. Moreover, both subunits A and B showed immunoreactivity with anti carp alpha(2)-macroglobulin antibody. Purified MSSP was inactivated by Pefabloc SC, aprotinin, benzamidine and TLCK, but not by alpha(1)-antitrypsin. After acid treatment (pH 2, 24 h), however, the enzyme activity eluted at 14 kDa from Sephacryl S-200 carried out under acidic conditions was inhibited by alpha(1)-antitrypsin. Lizard fish MSSP most rapidly hydrolyzed Boc-Val-Pro-Arg-MCA and Boc-Gln-Arg-Arg-MCA, but did not hydrolyzed Suc-Leu-Leu-Val-Tyr-MCA and Suc-Ala-Ala-Pro-Phe-MCA, and was not suppressed either by E-64, pepstatin A and ethylenediaminetetraacetic acid (EDTA). These results indicate that the purified MSSP is a serine protease complexed with alpha(2)-macroglobulin, and the entrapped protease was dissociated by the acid treatment. Purified and free MSSPs were most active at pH 10.0 and 9.0, respectively. Purified MSSP degraded myofibrillar proteins and casein but time courses of degradation of these substrates by the enzyme differed.