EFFECT OF NaCl ON GELATION CHARACTERISTICS OF ACID- AND ALKALI-TREATED PACIFIC WHITING FISH PROTEIN ISOLATES

Abstract

The physicochemical properties of gels prepared from Pacific whiting protein isolated at pH 3 and 11 with three concentrations of NaCl were characterized after a pH readjustment to 7.0. The strongest gels were obtained from fish protein isolate (FPI) prepared at pH 11/150‐mM NaCl and conventional surimi. The protein solubilities of FPI treatments did not contribute significantly to their gel properties. Surface hydrophobicity and differential scanning calorimetry demonstrated that, in addition to adjusting the pH to 3 or 11, salt addition during protein solubilization and subsequent recovery at the isoelectric point (pI) led to protein denaturation. Rheological study indicated that gelation mechanisms of FPI were identical with the same NaCl concentration regardless of pH. The FPI prepared at pH 3 or 11 with NaCl could be partly refolded at pH 7. Nevertheless, some myosin fragments and actin did not refold. PRACTICAL APPLICATIONS Fish protein isolate (FPI) processing is a new concept for protein recovery using a pH shift. While conventional surimi processing is performed by avoiding protein denaturation, this FPI process is performed chemically by unfolding proteins and subsequent refolding. Since FPI is made with the inclusion of sarcoplasmic proteins, which are removed at the conventional surimi process, it guarantees a significant yield increase. This study revealed that the strongest gels were made from conventional surimi and FPI prepared at pH 11 and 15‐mM NaCl. It also confirmed that protein solubility does not support thegelation properties of FPI. Refolding of FPI prepared at extreme pHs (3 or 11) was noted, but in a full scale.

Effect of pH on the gel properties and secondary structure of fish myosin

“…However, when NaCl was added, the chloride ion preferentially binds with the positively charged amino acids to a stronger degree than the sodium ion. The system required more H + ion reach the approximately zero net charge needed to precipitate proteins (Thawornchinsombut & Park, 2007). Thus, the pI of myosin in 0.5 M NaCl was lower than pH 5.5.…”

The Acid and Alkaline Solubilization Process for the Isolation of Muscle Proteins: State of the Art

“…Therefore, the SH groups available for disulfide formation and/or other interchanges were more limited during gelation of the acidtreated sample than of the alkali-treated sample. Thawornchinsombut and Park (2007) investigated the interactive effect of pH and ionic strength during protein solubilization on gelation properties of acid-and alkaliprocessed protein isolates from Pacific whiting. Results were compared to conventional surimi processing.…”

Preparation and thermo-reversible gelling properties of protein isolate from defatted Antarctic krill (Euphausia superba) byproducts

“…Protein aggregation includes reversible (Arakawa, Bhat, & Timasheff, 1990) and irreversible aggregate formation (Kendrick et al, 1998). Protein gels in the presence of salt were shown to undergo heat-induced irreversible gelation (Thawornchinsombut & Park, 2007). Conversely, gels formed with native protein isolate without adding salt or other additives showed thermo-reversible properties (Brenner et al, 2009).…”

“…The process of heat-gelation involves an initial unfolding upon heating and subsequent aggregation of protein molecules. The heating usually has to be carried out at protein isoelectric point or at high ionic strength (Thawornchinsombut & Park, 2007), and often in the presence of different additives (Chen & Jaczynski, 2007). Various studies have reported the gelation of fish muscle protein without adding salt or other additives at neutral pH (Brenner, Nicolai, & Johannsson, 2009).…”