Effect of phosphate and bicarbonate replacers on quality changes of raw and cooked Pacific white shrimp as influenced by the repeated freeze–thawing

• Shrimp treated with 0.75% NaOH solution + 3% MSG showed the reduced drip loss after freeze–thawing.
• Treatment with 0.75% NaOH solution + 3% MSG increased redness in raw shrimp but decreased redness in cooked shrimp.
• Both raw and cooked shrimp treated with 0.75% NaOH solution + 3% MSG had the lower shear force.
• The 0.75% NaOH solution + 3% MSG could be used as phosphate replacer for shrimp processing.

The effect of different soaking solutions and varying numbers of freeze–thaw cycles on the quality of raw and cooked Pacific white shrimp was investigated. The soaking solutions included 1) 0.75% NaOH, pH 11.5 (alkaline soaking solution; ASS), 2) ASS with 3% monosodium glutamate (pH 11.5) (ASS + 3% MSG) and 3) 2.5% NaCl containing mixed phosphates (M-P). Higher protein solubility was observed in raw shrimp treated with ASS + 3% MSG, compared with other treatments (P < 0.05), regardless of the number of freeze–thaw cycles. Raw shrimp treated with ASS + 3% MSG or M-P showed the lowest drip loss after 5 freeze–thaw cycles. No α-glucosidase (AG) or β-N-acetyl-glucosaminidase (NAG) activities were found in the raw shrimp treated with ASS + 3% MSG and M-P at all freeze–thaw cycles tested. As more freeze–thaw cycles were applied, the a*-value (redness) of raw shrimp increased (P < 0.05), while the a* value of cooked shrimp treated with ASS containing 3% MSG decreased (P < 0.05). The shear force of both raw and cooked shrimp with all treatments increased when freeze–thaw cycles increase up to 3 cycles (P < 0.05); however, it drastically decreased after 5 freeze–thaw cycles (P < 0.05). Therefore, treatment of shrimp with 0.75% NaOH containing 2.5% NaCl and 3% monosodium glutamate (pH 11.5) could retard the deteriorative change induced by freeze–thawing process.