Frozen stability of fish protein isolate under various storage conditions

A novel process using pH-shift to recover fish proteins has been intensively studied. However, little information of its frozen stability has been revealed. The highest gel texture was found for samples frozen at pH 5.5 (5) and 7.0 (7) with cryoprotectants (C) and without freeze/thaw (F), whereas the lowest gel texture was obtained from frozen/thawed samples without cryoprotectants (NC). 5NC-F and 7NC-F demonstrated the lowest surface hydrophobicity and total sulfhydryl (SH), perhaps suggesting more protein aggregation through hydrophobic interactions and disulfide bonds. A slightly less stability of alkali-treated protein isolates (AKPI) kept at pH 5.5 than at pH 7 was noticed. AKPI, whether kept at pH 5.5 or 7.0, requires cryoprotectants to maintain frozen stability for longer shelf life.