Graduate Thesis Or Dissertation

 

Components of bovine plasma that enhance gel strength in Pacific whiting surimi Public Deposited

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  • Proteolysis of myofibrillar proteins in Pacific whiting surimi occurs when the 50- 70°C temperature range is reached during standard cooking procedures (e.g. 90°C for 15 min). This proteolytic activity results in the softening of surimi gels. Bovine plasma protein (BPP) is the most effective of the food-grade inhibitors used to prevent this reaction, and enhance gel strength in PW surimi. The objective of this study was to determine the effective components of bovine plasma that enhance gel strength in PW surimi. Five bovine plasma fractions were evaluated for components that contribute to gel strength enhancement in PW surimi. Fraction I, which consists mostly of fibrinogen and albumin, was found to also contain plasma transglutaminase (PTGase) activity. Part of fraction I gel-enhancing ability may be attributed to an unknown component which inhibited papain independently of Ca²⁺ and inhibited 40% of surimi proteolytic activity. Fibrinogen or albumin did not inhibit papain activity or enhance gel strength of surimi. For fraction I-S, which is a more concentrated PTGase fraction, gel-enhancement of PW surimi was completely dependent on the presence of Ca²⁺. Autolytic inhibitory activity of fraction I-S in surimi was completely eliminated by the presence of Zn²⁺. Fraction II+III (1%) inhibited over 50% of surimi autolytic activity and displayed a small amount of PTGase activity. Fraction II+III (1%) gel enhancing abilities were low when compared to the other fractions and BPP, and only slightly effected by EGTA. Fraction IV (1%), which contains approximately 50% albumin and 15% α₂-macroglobulin, inhibited over 70% of surimi autolytic activity. It enhanced gel strength at a 1% (w/w) concentration when set for 20 hr at 4°C before cooking, and was not affected by EGTA. This fraction displayed no apparent PTGase activity. Fraction IV-1 (1%), which contains approximately 20-30% α₂-macroglobulin, gel strength enhancement surpassed the other fractions and BPP when set for 20 hr at 4°C and 2 hr at 25°C before being cooked at 90°C for 15 min. The gel strength enhancing abilities of fraction IV-1 were significantly affected by EGTA. Fraction IV-1 (1%) inhibited over 80% of surimi proteolytic activity. The gel strength of 1 mM (0.03%) E-64, which is a cysteine protease inhibitor, was equivalent to that of BPP (1%) after setting at 4°C for 20 hrs before cooking. E-64 (1 mM) inhibited 83% of the autolytic activity of PW surimi and BPP (1%) inhibited 78%. These data indicate that a cysteine protease inhibitor can increase gel strength, and suggests that BPP is acting as a cysteine protease inhibitor. Ca²⁺ dependent gel strength enhancement was attributed to transglutaminase (TGase) activity, both added PTGase and endogenous TGase. Gel strength enhancement that was Ca²⁺ independent was attributed to cysteine protease inhibitors, specifically α₂-macroglobulin. Overall, it was determined that gel strength in PW surimi was greatly enhanced by both concentrated PTGase (I and I-S) and concentrated α₂-macroglobulin (IV-1) fractions, with a combination of these fractions being most effective in gel strength enhancement, when the surimi is first set at 4°C or 25°C before cooking at 90°C for 15 min. These data suggest that the mechanisms of gel strength enhancement of BPP are from cysteine protease inhibition, possibly from α₂-macroglobulin, and from crosslinking of myosin in surimi from both added (PTGase) and endogenous TGase activity.
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