Prevention of quality loss and melanosis of Pacific white shrimp by cashew leaf extracts

Inhibition of Pacific white shrimp polyphenoloxidase (PPO) by the selected Thai indigenous leaf extracts (Liang, Mun-poo, cashew and lead) was comparatively studied. Cashew leaf extract (CE) showed the highest PPO inhibitory activity and copper chelating activity at all concentrations (0.025-0.5%) tested (P < 0.05). Inhibitory activity was in a dose dependent manner. Epifisetinidol-4alpha-ol and hinokiflavone were identified as the most dominant polyphenols in CE using LC-DAD-ESI-MS/MS. Quality changes and melanosis of raw Pacific white shrimps treated with CE solution at various concentrations (0.1-1%) were monitored during refrigerated storage at 4 °C for 12 days. Microbiological analyses showed that shrimps treated with CE solution exhibited the lower total viable count, psychrophilic bacteria, Pseudomonas spp., H2S-producing bacteria and Enterobacteriaceae counts than the control throughout 12 days of storage (P < 0.05). Lower total volatile base content and thiobarbituric acid reactive substances were observed in shrimps treated with CE solution, compared to the control. Efficacy in quality maintenance of CE generally increased with increasing concentrations used. Shrimps treated with 1% CE solution and those treated with 1.25% sodium metabisulfite had the lowest melanosis scores throughout the storage (P < 0.05). Moreover, shrimps treated with 1% CE had the higher color and overall likeness scores, compared to the others, after the storage of 12 days at 4 °C. Therefore, soaking of raw shrimps in 1% CE solution for 30 min could be a promising method to prevent deterioration and melanosis during the extended refrigerated storage.