Effects of Multiple Freeze-Thaw Cycles on Biochemical and Physical Quality Changes of White Shrimp (Penaeus vannamei) Treated with Lysine and Sodium Bicarbonate.

Freezing and thawing occur during storage, transportation, and retail display, leading to deterioration of frozen shrimp. The objective of this research was to investigate the change in quality of frozen white shrimp treated by lysine and NaHCO after multiple freeze-thaw cycles. Shrimp were soaked in lysine and lysine/NaHCO each at 1% (w/v) frozen in an air-blast freezer at -30 °C, and kept in a chest freezer (-18 ± 2 °C) for a week before they were thawed using tap water before the analysis (freeze-thaw cycle 1). The samples were subjected to five freeze-thaw cycles, which were repeated every week. Qualities of the samples were determined for thawing loss, cutting force, and total volatile basic nitrogen (TVB-N), as well as oxidation stability by using Rancimat. The use of lysine/NaHCO could significantly reduce thawing loss at all freeze-thaw cycles compared to the control and lysine treatment (P < 0.05). Similar results were found with TVB-N and the oxidation stability of the samples. A difference in cutting forces of the shrimp between lysine and lysine/NaHCO treatment was found when the frequency of freeze-thawing was increased to three cycles; it was lower than that in the control at all cycles. Histological study showed that the treatment with lysine/NaHCO led to the swelling of muscle fibers and fewer fragments at five freeze-thaw cycles. The results showed that lysine/NaHCO could effectively retard the quality loss from repeated freeze-thawing during frozen storage. PRACTICAL APPLICATION: Repeated freezing and thawing usually occur during storage, transportation, retail display or in restaurants, and in consumers' kitchens. The temperature at the manufacturing site and during transportation in a tropical country like Thailand is relatively high, and frozen food producers come across quality deterioration resulting from multiple freeze-thaw cycles occurring during transportation and storage. Frozen shrimp producers require research to improve product quality by adding nonphosphate food additives or, if possible, by using natural food ingredients instead of polyphosphate or sodium bicarbonate.