MFSc

With a view to standardizing the technology of cold –anesthetization and live storage of adult penaeus monodon in chilled saw dust, three cooling rates of 1.38 + 160C/h within 8 hours (slow cooling rate) 2.76 + 0.320C /h within 4 hours (moderate cooling rate), and 5.52 + 0.640C/h within 2 hours (fast cooling rate) were tested to cold – anesthetize farm raised P.monodon (22.25g) at 15ppt salinity, from 250C to 14+ 10C (fixed on the basis of a pilot study) in plastic net boxes kept in a refrigerated chilling tank of 40 litre capacity, provided with aeration. The cold-anaesthetized shrimps at each cooling rate were packed separately in between two layers (about 3cm thick) of saw dust with 10% moisture and chilled previously at 2-30C, in specially prepared card board boxes (33x22x9cm) lined inside with 12 mm thick Styrofoam sheet. The boxes were kept inside a chilled storage cabinet and maintained at 14 + 10C for a duration of 16-36 hours, and the survival of the shrimps observed at four hourly intervals. The temperature was monitored using a six channel, digital, continuous freezer temperature monitor with a precision of 0.10C.

The shrimps cold-anaesthetized at each cooling rate and live stored for each duration were revitalized in aerated circular fibre glass tanks of 80 litre capacity, half-filled with brackish water of salinity 15ppt, and temperature 200 C, which was raised @ 2.70C/h to the ambient temperature of 280C, within 3 hours. The shrimps which showed abnormal behavioural patterns by rolling over into their sides, and remained immobilized upon cold anaesthetization, recovered to active movements after revitalization.

Although 100% survival of the packed shrimps was obtained for maximum durations of 24, 20 and 16 hours at the slow, moderate and fast cooling rates respectively, the corresponding statistically valid safe durations for obtaining 100% survival were computed to be 22.9 + 1.09, 19.1 + 0.4 and 14.62 + 1.13 hours, using probit analysis. However, for practical purposes, the durations for obtaining 95% survival were determined as 28.18 + 0.54, 25.7 + 0.54 and 21.88 + 0.71 hours for the slow, moderate and fast cooling rates respectively. Analysis of variance of the percentage survival showed significant difference (P<0.005) among the three cooling rates tested, while pairwise comparison revealed that the slow and moderate cooling rates were identical. This suggested that the moderate cooling rate which took only half the time for cold –anaesthetization of shrimp compared to the slow cooling rate can be considered the optimum, though the choice of the different cooling rates depends on the duration of storage desired.

The difference in weight before cold anaesthetization and after revitalization of the live shrimp was studied at 12 and 24 hours of live storage at the three cooling rates, separately which indicated a loss of weight (1.49-8.83%) varying with the cooling rates and durations . However, this was not found to be statistically significant among the cooling rates and durations tested.

Sensory evaluation of the cold – treated shrimps was conducted to study the effect of cold-anesthitization and live storage on their appearance and meat quality, at the three cooling rates after 12 and 24 hours of live storage, talking untreated shrimp as control. The body colour of the shrimps turned dark brown and the tips and margins of the pleopods and peraeopods became reddish. There was significant difference (P<0.05) in general appearance, and the colour and flavor of the meat between cold treated and untreated shrimps. However, the texture and odour /aroma of the raw/ cooked meat remained unaffected by cold – treatment. The effect of different cooling rates and the durations tested on the sensory quality of shrimp meat was not significant.