White shrimps (Penaeus vanamei), size 70e80 shrimps per kilogram,were purchased from specified farms sold in a local market at Klong 6, Patumthani province, Thailand. The samples were kept in ice bath with the ratio of shrimp: ice at 1:1 and transported to the laboratory within 30 min. After being washed, deheaded, and peeled, fifteen shrimps per treatment were soaked in the solution of amino acid at 1.0 g/100 ml in combination with 3.0 g/100 ml NaCl at a ratio of shrimp: solution at 1: 1.5 (by weight) for 3 h at 4 ± 1 C.Each amino acid: nonpolar amino acid (phenylalanine, methionine,proline, isoleucine, and glycine), polar uncharged amino acid (threonine), negatively charged amino acid (glutamic acid), and
basic positively charged amino acid (lysine and arginine) were usedin the preliminary study in order to select appropriate amino acids
for the shrimp treatment before freezing. The sample soaked in the
water without any salt or amino acid was set as a control. After
soaking, the shrimps were drained for 5 min, packed in polyethylene
bags and then frozen in an air-blast freezer (Thermoscience
®) at 30 C with air-velocity of 5 m/s until the core
temperature reached 18 C. The core temperatures were recorded
by using thermocouples with a data logger. The frozen samples
were stored in a freezer (18 C) for a week before the analysis.
Soaking and thawing yield were determined after a freeze-thaw
cycle before the shrimps were cooked and sensory tested. All experiments
were carried out in three replications and the results
were averaged.