Changes in Biochemical Properties and Activity of Trypsin-like Protease (Litopenaeus vannamei) Treated by Atmospheric Cold Plasma (ACP).

The changes in the functional properties of trypsin from shrimps (Litopenaeus vannamei) after, Atmospheric Cold Plasma (ACP) treatments, have been evaluated in terms of enzyme inactivation, surface hydrophobicity, secondary structure, fluorescence intensity, and particle size distribution. Different exposure voltages of 10, 20, 30, 40, and 50 kV at various treatment times (1, 2, 3, and 4 min) have been employed, in a separate assay. The results showed that trypsin-like protease activity decreased (by about 50%), and the kinetic constants Km value increased, while the kcat value decreased. Surface hydrophobicity and fluorescence intensity revealed a significant increase compared to the control sample. A high degree of protein degradation has been noticed by SDS-PAGE analysis. In addition, circular dichroism indicated that random coil and α-helix contents declined while ß-turn and ß-sheet contents have raised. A sharp drop in the particle size was observed with increasing the treatment voltage from 0 to 40 kV for 4 min, and the corresponding peak reached the minimum of 531.2 nm. Summing up the results, it can be concluded that the ACP technique effectively affects the activity of trypsin-like protease, which in terms enhances the quality of dietary protein.

Understanding the role of atmospheric cold plasma (ACP) in maintaining the quality of hairtail (Trichiurus Lepturus).

Impacts of atmospheric cold plasma (ACP) on the properties of muscle protein and performance of extracted crude enzyme of hairtail (Trichiurus Lepturus) fish have been evaluated. A decrease in extracted crude enzyme activity with increasing the ACP treatment time has been found, and the highest reduction (p < 0.05) value of 0.035 units/mg proteins was obtained after 240 s. A considerable increase in the carbonyl content in the treated sample for about three times higher than the control sample was found, and a decrease of total sulfhydryl content to 0.34 nmol/mg protein. Texture profile analysis, water holding capacity, and the color properties of the muscle protein improved significantly in the samples treated with ACP. SDS-PAGE pattern showed an increase in the band intensity of cross-linked myosin heavy chains and actin proteins. Based on these outcomes, ACP could play a significant role as a promising non-thermal method to prolong the shelf-life of hairtail fish.

Effects of cold atmospheric plasma on squid proteases and gel properties of protein concentrate from squid (Argentinus ilex) mantle.

The effect of cold atmospheric plasma (CAP) on protein concentrate from squid (Argentinus ilex) mantle has been evaluated in terms of gel properties, protease inhibition, texture profile, color attributes, and water holding capacity. Different exposure time (15, 60, 120, 180, 240 and 300 s) at 60 kV have been employed. Our results indicated that protease activity decreases with increasing treatment time. The highest reduction (p < 0.05) in protease activity (64%) was observed after 240 s of CAP treatment. Texture profile analysis, color properties and water holding capacity of the treated squid gel revealed a significant increase. Protein carbonyl and sulfhydryl group contents findings' showed a significant increase in carbonyl content (about three times of the original content), while the total sulfhydryl group decreased (up to about 40%) in the crude extract. Microstructure and SDS-PAGE analysis revealed a high degree of protein aggregation in the squid gel treated with CAP.

Physicochemical changes of myofibrillar proteins of squid (Argentinus ilex) induced by hydroxyl radical generating system.

The effect of a hydroxyl radical generating system (HRGS), which contained FeCl3, sodium ascorbate, and different concentrations of H2O2, on the physiochemical properties of myofibrillar protein (MP) from squid mantles, has been investigated. The effect of different exposure times to HRGS was also considered. Compared to non-oxidized MP, a significant (p < 0.05) increase in carbonyl content (more than 50% of its original content) and protein solubility, as well as in surface hydrophobicity, was observed in the oxidative MP. With different treatment times, a sharp decrease (p < 0.05) in sulfhydryl content was detected. In addition, hydroxyl radical treatment significantly reduced the MP gel's texture properties, whiteness and water holding capacity, especially at higher concentrations of H2O2. This observation could be attributed to extensive disorderly and less compact structure of MP gels. The results demonstrate the negative effect of HRGS on the structural and functional properties of MP from squid mantles.