Freshness determination of cultured shrimp (Litopenaeus vannamei) using physical and mechanical properties

In this study, freshness and quality of cultured shrimp (Litopenaeus vannamei) were studied by using some mechanical properties (under shear and compression) during four storage stages (0, 3, 6 and 9 days) with generally used conditions (at temperature of 0 oC, in ice). For this purpose, two shearing loading rates of 48 and 144 mm/min were examined. Shear properties including stiffness modulus, yield energy, maximum energy, maximum shear force and total energy and the compression properties including total strain energy, recycle energy, stiffness, hardness, resilience, hysteresis, maximum adherence of exerted force and springiness were evaluated. The parameters of weight with and without skin, volume with and without skin, specific weight with and without skin, and length were considered as some physical properties of the shrimp samples. A factorial statistical design with completely randomized block design was used for data analysis and Duncans’ test was exploited for mean comparisons. Based on the results, effects of the independent variables (storage day, modulus of stiffness) were significant at 1% probability level. Also, hysteresis and total strain energy for storage day showed marked difference at 5 % level. It can be concluded that mechanical properties of the shrimp could be used to determine shrimp freshness and use of compression method with modulus of stiffness and shrimp tissue stiffness is the most appropriate approach for this aim. Resilience energy, springiness and stiffness of shrimp tissue continuously reduced by sixth day of storage afterward the parameters tend to increase. This finding demonstrates that the tenderness of the tissue is gradually diminished after harvest.