Shrimps treated with proline at 0.5 and 1.0 g/100 ml could increase soaking yield and thawing yield better than the samples treated with NaCl alone but no significant improvement of cooking yield was bserved. Treating with lysine at 2.0 g/100 ml and arginine at all concentration used exhibited significant improvement of WHC during freezing, and cooking (p < 0.05). Comparatively high water-holding improvement was observed for the use of lysine and
arginine. Maximum WHC was expressed in shrimp soaked with arginine at 1.0 g/100 ml and its cooking yield (97.59 g/100 g fresh shrimp) was not significantly different (p > 0.5) to shrimp treated with STPP at 4.0 g/100 ml.Considering from thawing yield and cooking yield, the results indicated the synergistic effect of lysine/arginine with NaCl to
enhance WHC of frozen shrimps. This might be because of the effects
on pH, ionic strength and also specific interactions between
amino acid side chain, polar group, nonpolar group with myofibrillar
protein. The presence of NaCl could increase the electrostatic
repulsive force (Offer & Knight, 1988) and facilitated the incorporation
of amino acid inside the myofibril protein.
Generally, myosin exhibits a negative charged molecule at pH of
living tissue which is about 7.1 (Chantarasataporn et al., 2013). The
effectiveness of amino acids on water holding properties of shrimp
depended on type of amino acids. However, the effect was not
concentration-dependent in our study. Arginine and lysine have
functional groups, COOH, eNH2 with positively charged group,
NH3
þ. These groups are prone to form hydrogen bonding with water
molecules and reduce drip loss from the shrimp samples. The polar
group of the side chains of lysine or arginine supposed to bind
water molecules on their surfaces by van der walls forces (Hamm,
1972). Both amino acids caused the increase in pH and the deviation
from the average isoelectric point of meat protein, pH 5.0. The