17E-26 |
|
S. THAWORNCHINSOMBUT and J. W. Park. Dept. of Food Science & Technology, Oregon State Univ., OSU Seafood Research Lab., 2001 Marine Dr., Rm. 253, Astoria, OR 97103-3420 Several studies have been recently conducted to maximize yield and improve protein functionalities using pH shift. This new method denatures fish proteins by altering pH to maximize solubility, whereas the conventional surimi process needs to avoid denaturation. This leads to the notion that the pH-shift process, where proteins are already chemically denatured, may not require cryoprotectants to prevent denaturation during frozen storage. Our objective was to characterize the stability of fish proteins during frozen storage as affected by cryoprotectants and pH with regards to the gelation properties of the alkali-treated Pacific whiting (PW) proteins. Alkali-treated proteins were prepared from fresh PW fish. Proteins were solubilized at pH 11 and subsequently recovered at pH 5.5. A half portion of the pellet was adjusted to pH 7.0. The pellet at both pH levels were subdivided into 2 sets. They were mixed with 0% and 8% cryoprotectants (sucrose:sorbitol=1:1), respectively. All 4 treatments were subjected to 3 freeze-thaw cycles at -18°C and 4°C. One set of samples containing cryoprotectants was stored at –80°C without freeze/thaw. All samples were adjusted to maintain equal pH (7) and cryoprotectants before measurements. Gels were prepared with 1.5 % beef plasma protein at 78% moisture content without salt. To evaluate gelation properties, surface hydrophobicity (So), fracture analysis, and scanning electron microscope (SEM) were performed. No significant difference in texture was observed between samples stored at pH 5.5 and 7.0 during frozen storage. Highest texture was found for samples frozen at pH 5.5 and 7 with cryoprotectants and without freeze/thaw, while lowest texture was obtained from frozen/thawed samples without cryoprotectants. Samples frozen/thawed without cryoprotectants at both pH demonstrated the lowest So, probably suggesting that proteins were more aggregated as evidenced by SEM images. Alkali-treated proteins, whether kept at pH 5.5 or 7.0, require cryoprotectants to maintain frozen stability.
Session 17E, Food Chemistry: Proteins
|