Effect of Immersion Chilling and Freezing on Muscle Structure of Litopenaeus vannamei during Frozen Storage
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Abstract:
Changes in fiber profile, intercellular gaps, myofilament, sarcomere, and intermyofibrillar space during frozen storage of shrimp, Litopenaeus vannamei was investigated to determine the effects of immersion chilling and freezing (ICF) as well as refrigerator freezing (RF) on shrimp musculature. The results indicated that muscle fiber of ICF shrimp was tighter and the intercellular ice crystals were smaller and well-distributed, whereas that of RF shrimp was loose, and the intercellular ice crystals were larger and wider. The myofibril diameter of ICF shrimp were shorter than that of RF shrimp. As the storage period increased, the ice crystals in the ICF shrimp grew larger, while cell nuclei gradually decreased. After storing for 90 d, cell nuclei could not be found in tissue slices of RF shrimp, myofilament had largely disappeared, the thick and thin filaments were blurred, the length of the sarcomere was severely shortened, and sarcomere structures had disappeared. Moreover, the complete structure of mitochondria in the tissue of RF shrimp could hardly be found. However, the myofilament structures, and the thick and thin filaments still existed in ICF shrimp. The degree of shortening in myofilament lengths was smaller than that in RF shrimp, while some mitochondrial structures remained intact in the tissues of ICF shrimp. In summary, ICF appeared to be more beneficial to maintain the quality of shrimp during frozen storage.
