Activation Mechanisms of Pro-Phenoloxidase on Melanosis Development in Florida Spiny Lobster (Panulirus argus) Cuticle

A biomimetic adhesive with high adhesion strength and toughness comprising soybean meal, chitosan, and condensed tannin-functionalized boron nitride nanosheets

Soybean meal (SM)-based adhesive can solve the issues of formaldehyde emission and over-reliance of aldehyde-based resins but suffers from poor water resistance, weak adhesion strength, and high brittleness. Herein, a high-performance adhesive inspired by lobster cuticular sclerotization was developed using catechol-rich condensed tannin-functionalized boron nitride nanosheets (CT@BNNSs), amino-containing chitosan (CS), and SM (CT@BNNSs/CS/SM). The oxidative crosslinking between the catechol and amino, initiated by oxygen at high temperatures, formed a strengthened and water-resistant interior network. These strong intermolecular interactions induced by phenol-amine synergy accompanied by the reinforcement of uniformly dispersed BNNSs improved the load transfer and energy dissipation capacity, endowing the adhesive with great cohesion strength. Given these synergistic effects, the biomimetic CT@BNNSs/CS/SM adhesive caused noticeable improvements in water tolerance, mechanical strength, and toughness over the neat SM adhesive, e.g., enhanced wet shear strength (1.46 vs. 0.66 MPa, respectively), boiling water shear strength (0.92 vs. 0.43 MPa, respectively), and debonding work (0.368 vs. 0.113 J, respectively). Thus, this study provided a green and low-cost bionic strategy for the preparation of high-performance biomass adhesives.

Distribution and Characteristics of Polyphenoloxidase from Pacific White Shrimp (Litopenaeus vannamei)

Distribution of polyphenoloxidase (PPO) from different anatomical parts of Pacific white shrimp was examined. Among all parts, cephalothorax possessed the maximal PPO activity (P < 0.05), followed by pereopods, telson, pleopods, carapace, cuticle, and muscle, respectively. The higher PPO activity in cephalothorax was in line with the greater melanosis in this part during chilled storage. According to activity-staining toward 3,4-dihydroxy-ʟ-phenylalanine (ʟ-DOPA), PPO exhibited an activity band with a molecular weight (MW) of 210 kDa. When cephalothorax PPO was purified using ammonium sulfate precipitation and a series of chromatographic techniques, involving DEAE-Sepharose anion exchange and Sephadex G-75 gel filtration columns, homogeneity was obtained. Based on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and native-PAGE, the Sephadex G-75 fraction showed a single band. The MW band on SDS-PAGE and gel filtration was estimated as 210 kDa, suggesting a monomeric molecule. For the inhibitor study, cysteine and 4-hexylresorcinol showed competitive inhibition toward PPO, while epigallocatechin gallate and kojic acid demonstrated mixed-type inhibition toward PPO. PRACTICAL APPLICATION: Melanosis (black spot formation) triggered by polyphenoloxidase (PPO) drastically reduces the shelf-life of shrimp. PPO was localized in several anatomical parts of Pacific white shrimp with varying activities. Certain compounds, including cysteine, 4-hexylresorcinol, epigallocatechin gallate, and kojic acid, showed PPO inhibitory activity with different modes of inhibition. The obtained information provided a promising method for manufacturers to keep the prime eating quality of Pacific white shrimp throughout postmortem transportation and storage using selected PPO inhibitors.

Enzymatic characteristics of polyphenoloxidase from shrimp (Penaeus vannamei) and its inhibition by a novel hydroxypyridinone derivative

Melanosis developed in shrimp (Penaeus vannamei) is mainly initiated by polyphenoloxidase (PPO), thus understanding of the characteristics of PPO in shrimp is important for controlling the melanosis of shrimp. The shrimp cephalothorax turns black most rapidly amongst all the tissues during the chilled storage. Crude PPO extracted from this cephalothorax has an optimal pH of 6.0 and an optimal temperature of 50 °C. PPO is relatively stable under neutral and weak alkaline conditions (pH 5.5-9.0) and the temperature range of 25-35 °C. The kinetic parameters K _m and V _max were recorded as 3.02 mM and 54.3 U/mg of protein, respectively, using L-Dopa as a substrate. The molecular weight of PPO was estimated as 200-220 kDa by an activity staining test. A hydroxypyridinone derivative, 5-hydroxy-1-octyl-4-oxo-1,4-dihydropyridine-2-carbaldehyde O-ethyl oxime, was demonstrated to efficiently inhibit the PPO, indicating that this compound might find application as a shrimp preservative.

Phenoloxidase activity in the hemolymph of the spiny lobster Panulirus argus

The prophenoloxidase activating system plays a major role in the defense mechanism of arthropods. In the present study, the phenoloxidase activity and its location in the hemolymph of the spiny lobster Panulirus argus is presented. Phenoloxidase activity was observed in the hemocyte lysate supernatant (HLS) and plasma after their incubation with trypsin. Higher amounts of trypsin were required to activate the HLS prophenoloxidase, due to the presence of a trypsin inhibitor in this fraction. Activation of prophenoloxidase was found when HLS was incubated with calcium, with an optimal pH between 7.5 and 8. This spontaneous activity is due to the prophenoloxidase activating enzyme, a serine proteinase that activates the prophenoloxidase once calcium ions were available. SDS was able to induce phenoloxidase activity in plasma and hemocyte fractions. Prophenoloxidase from HLS occurs as an aggregate of 300kDa. Electrophoretic studies combining SDS-PAGE and native PAGE indicate that different proteins produced the phenoloxidase activity found in HLS and plasma. Thus, as in most crustaceans, Panulirus argus contains a prophenoloxidase activating system in its hemocyte, comprising at least the prophenoloxidase activating enzyme and the prophenoloxidase. Finally, it is suggested that phenoloxidase activity found in plasma is produced by hemocyanin.

Extension of the shelf life of prawns (Penaeus japonicus) by vacuum packaging and high-pressure treatment

The present study has investigated the application of high pressures (200 and 400 MPa) in chilled prawn tails, both conventionally stored (air) and vacuum packaged. Vacuum packaging and high-pressure treatment did extend the shelf life of the prawn samples, although it did affect muscle color very slightly, giving it a whiter appearance. The viable shelf life of 1 week for the air-stored samples was extended to 21 days in the vacuum-packed samples, 28 days in the samples treated at 200 MPa, and 35 days in the samples pressurized at 400 MPa. Vacuum packaging checked the onset of blackening, whereas high-pressure treatment aggravated the problem. From a microbiological point of view, batches conventionally stored reached about 6 log CFU/g or even higher at 14 days. Similar figures were reached in total number of bacteria in vacuum-packed samples and in pressurized at 200-MPa samples at 21 days. When samples were pressurized at 400 MPa, total numbers of bacteria were below 5.5 log CFU/g at 35 days of storage. Consequently, a combination of vacuum packaging and high-pressure treatment would appear to be beneficial in prolonging freshness and preventing spotting.