Plasma Activated Water and Computer Vision System application to control and evaluate melanosis in crustaceans

Aim of work: The aim of this work was to find a new, environmentally friendly and consumer-oriented alternative to control melanosis in crustaceans, different from the commonly applied chemical treatments based on sodium bisulphite and 4-hexylresorcinol. From a methodological point of view, melanosis was evaluated using an optimized Computerized Vision System (CVS) to overcome sensory evaluation problems. Methodology: Innovative Plasma Activated Water (PAW) treatment was used since its composition in reactive species can chemically interact with browning enzymes and/or substrates. All treatment solutions (distilled water (control); sodium bisulphite 3%; 4-hexylresorcinol 0.1% (conventional chemical treatments) and PAW (15kV, 5kHz, 1min)) were prepared and applied to two crustaceans species, caramote prawn (Melicertus kerathurus) and deep-water pink shrimp (Parapenaeus longirostris) using vacuum impregnation at 200 mbar for 10 min. Melanosis has been monitored for 9 days (at 4°C) using CVS. Images were obtained in a standardized environment and processed to identify browned areas and color changes of the carapace. Results/Discussion: Image analysis showed that all samples developed some browned areas during shelf-life, except for the samples treated with 4-hexylresorcinol, which showed a reddening phenomenon, which was also measured and quantified. Tests on M. keathurus showed a protective effect of PAW against browning during the first 5 days of storage, while no significant differences (p <0.05) were observed in deep-water pink shrimps compared with the samples treated only with water. The same observation was confirmed by a principal component analysis using the modes obtained from the histograms of the mains channels of each image. Conclusion: Under the conditions used, PAW showed the ability to delay melanosis in some species, resulting in a longer shelf-life. However, the mechanism behind this is still unclear, so further research is needed to find the optimal treatment conditions. The application of CVS showed promising potentialities; it has been possible to identify the parameters that can describe both the phenomenon of browning due to melanosis, and the secondary reddening of the samples treated with 4-hexylresorcinol. However, to validate the model presented here, the results of the image analysis must be compared with the sensory evaluation carried out by trained panelists.