Effect of salt treatments on survival and consumer acceptability of freshwater prawn, Macrobranchium rosenbergii

Post harvest acclimation of live freshwater prawns to a mixture of water and marine salt increases the consumer acceptability of the finished product. However, the high cost of marine salts prohibits their use in commercial practice. Therefore, the identification of successful, cost effective salt alternatives to replace acclimation with marine salt could potentially lead to an economically practical method to add value to prawns. This study was conducted to evaluate the consumer acceptability of freshwater prawns that were harvested and either held and acclimated with different salt treatments or marinated with salt. Post-harvest freshwater prawns were transferred to 250-l tanks containing one of five salt treatments (10 ppt): Instant Ocean (IO; marine salt), solar salt (SS-NaCl), solar salt supplemented with KCl and CaCl2 (SS +), fresh water (FW), and fresh water marinated postmortem (marinated). Salts were increased by increments of 5 ppt every 2 h until 30 ppt was achieved. Prawns were harvested after 18 h of salt acclimation. Survival was recorded and prawns were then chill killed, de-headed and frozen. Freshwater control samples were divided into non-marinated controls and samples that were marinated in 5% NaCl for 18 h at 2-3 °C with either shells on or off prior to freezing. Three consumer panels (n = 60) were conducted to assess the acceptability of prawns on a 9-point hedonic scale. Survival was 67% in the SS treatment with the highest survival in the FW (95%) followed by IO (85%) and SS + (73%). Consumer acceptability studies indicated that prawns marinated post-mortem without the shell were more acceptable (P < 0.05) than those from other treatments with respect to flavor, texture and overall acceptability. In addition, prawns marinated in the shell and from all salt acclimation treatments were preferred (P < 0.05) over the freshwater prawns. Panelists were clustered into 5 consumer groups of which 94.2% of consumers rated the post-mortem marinated prawns without the shell as like slightly or greater. These data suggest that post-mortem marination or salt acclimation significantly improves the acceptability of the freshwater prawns. Live acclimation to salt enhances flavor due to significantly higher concentrations of glutamic acid in the tail muscle of prawns in comparison to that found in prawns from the FW and marinated treatments.