In the previous trial, the prawns were maintained under the specified background colour conditions for 28 days before being evaluated. The following trial was undertaken to determine just how rapidly the colour changed since this could significantly affect the commercial application of the process. In this trial, prawns were maintained under the specified background conditions for 28 days prior to changed conditions at time 0 h. At this time, prawns from the
white tank had similar (p≥0.05) total astaxanthin contents to those from the black tank(32.1±2.20 μg/g prawn tail and 36.7±2.16 μg/g prawn tail respectively). In order to obtain more accurate data (through increased numbers) on the astaxanthin content of the prawns from these two tanks, all prawns used over 168 h were analysed. Overall values were 35.1±1.096
μg/g prawn tail for prawns moved into the white tanks and 36.7±1.108 μg/g prawn tail for those
moved into the black tanks (see Fig. 6). Although the total pigment content of the two groups of prawns was similar at 0 h, there were large visual differences in the colour of the raw and cooked prawns. When graded by the panellists, cooked prawns from the white tank were significantly (p≤0.001) lighter in colour, having a mean grade score of about 7.0±0.306, compared with 10.8±0.225 for those from the black tank (Fig. 6).