The effect of different thawing methods on chemical properties of frozen pink shrimp (Penaeus duorarum)

BACKGROUND: Freezing is a common way and one of the best methods of seafood preservation for long periods of time; however, the freeze thawing process may influence the quality of food. OBJECTIVES: Oxidation and denaturation of proteins, sublimation and recrystallization of ice crystals can cause changes in the quality of the frozen products. This study was aimed to evaluate the effect of three different thawing methods including microwave, refrigerator, and water thawing on the quality of pink shrimp (Penaeus duorarum). METHODS: For this purpose, the pink shrimps were hunted from Persian Gulf. Then, 200 g of peeled undeveined shrimps were frozen in vacuum-packed polyethylene bags at -40°C. The samples were transferred to Kerman Veterinary School and were kept at -18°C freezer. After four days, the shrimp were defrosted by three mentioned methods. Three cycles of freezing and defrosting with four days intervals were performed. Percentage of thawing loss (%TL), thiobarbituric acid (TBA), total volatile base (TVB), and salt-soluble protein (SSP) were detected at each freeze-thaw cycle. RESULTS: An increase in the freeze-thaw cycles increased TBA and TVB value slightly and significantly decreased the SPP value (p<0.05). Microwave thawing method gave the samples with the highest thawing loss in comparison to the other methods in each freeze-thaw cycle (p<0.05). A significant increase was seen in TBA value in water and microwave thawing methods in comparison to refrigerator thawing method (p<0.05). Refrigerator thawing method had higher SSP value in comparison to the other thawing methods (p<0.05). Likewise, there was no significant difference between three mentioned methods in TVB value (p>0.05). CONCLUSIONS: The obtained results showed that refrigerator thawing method had lower effect in decreasing chemical quality of the pink shrimp than two other methods, and multiple freeze-thawing processes caused some deleterious effects on the quality of the frozen shrimps.