EFFECT OF GAMMA IRRADIATION ON MICROBIAL AND PHYSICAL PARAMETERS OF POST-HARVEST Penaeus monodon F.

Abstract

Penaeus monodon is the mostly exported shrimp species in Sri Lanka. A 50% of the total export earnings of aquaculture fisheries sector of Sri Lanka depend on P. monodon. Since several microbial contaminations were reported, this study was conducted to evaluate the effect of gamma irradiation on the microbial quality and physical parameters of postharvestP. monodon. Samples were collected from 10 farms from North Western Province, Sri Lanka. Samples were irradiated at 1 kGy, 2 kGy, 3 kGy, 5 kGy and 10 kGy by industrial Co-60 gamma irradiator and a control was maintained. Under microbial parameters, total plate count, yeast and mold count, coliform count and Escherichia coli count were measured. Color, texture, moisture content and water activity were measured as physical parameters. Average total length and total weight of the sample were 12.69 ± 1.42 cm and 15.86 ± 5.70 g respectively. Average total plate count of the control was 3.37 × 104± 5.44×103 CFU g-1 and it was significantly reduced (P < 0.05) at 1 kGy to 8.58 × 102 ± 8.09 × 102 CFU g-1. At 2 kGy and 3 kGy the total plate count was reduced to 3.63 × 102 ± 1.80 × 102 CFU g-1 and 2.47 × 102 ± 96 CFU g-1 respectively. At 5 kGy and 10 kGy the samples became almost sterile. Average yeast and mold count of the control was 9.25 × 104 ± 1.77 × 104 CFU g-1 and it was significantly reduced (p < 0.05) at 1 kGy to 7.42 × 102 ± 17 CFU g-1. At 2 kGy, 3 kGy, 5 kGy and 10 kGy the samples became almost sterile. Coliforms and E.coli were not detected in the control. Hue angle of the peeled shrimps irradiated at 10 kGy was significantly different (p < 0.05) from other samples. But L* , a* , b* ∆ E and chroma of whole shrimp, peeled shrimp and shrimp muscle were not significantly affected (p > 0.05) by irradiation. Hardness, chewiness, adhesiveness, cohesiveness and springiness were not significantly different (p > 0.05) between control and irradiated samples. Moisture content and the water activity were not significantly different (p > 0 .05). Therefore, 1 kGy is appropriate for irradiation of postharvest P. monodon for microbial safety, while preserving the physical attributes.