Graduate Thesis Or Dissertation
 

The Incorporation of Novel Water-Soluble Potato Protein Extract in Pacific whiting (Merluccius productus) Fillets Through Brine Injection Technology to Improve Quality

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/tq57p0120

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  • Pacific whiting (Merluccius productus) is one of the most abundant fisheries on the American west coast. However, these fish are historically underutilized due to quality issues resulting from fillet softening that occurs as a result of both endogenous and exogenous (Myxosporidian parasite infection) cathepsin protease action during either storage (cathepsin B or H) or cooking (cathepsin L). As a result, fillets from Pacific whiting have struggled to find a domestic market. Currently, Pacific whiting is either converted into a mince that is utilized to produce surimi or sold as headed and gutted fish in foreign markets. A higher value product that is more common in the US market is the fresh or frozen fillet. As a result, research is needed to understand how to limit protease action in Pacific whiting fillets. Most of the research focused on limiting the proteolytic action of cathepsin proteases in Pacific whiting has been in surimi. Ingredients that have been blended into surimi to prevent protein degradation have included beef plasma protein, whey protein, egg white (EW), and potato extract (PE). The literature on incorporation of protease inhibiting ingredients through marinade (brine) injection directly into a fillet is limited. Previous work, in this laboratory, evaluated benchtop marinade injection of Pacific whiting fillets with 1, 2 or 3% EW or a crude (<20% protein) PE. The base brine (BB) used for the marinade injection contained 3% sodium chloride (NaCl) and 3% sodium tripolyphosphate (STPP). The PE required a suspension aide, 0.1% xanthan gum, in order to be successfully delivered into fillets by injection. Results demonstrated that cooked fillet myosin band integrity, as measured by electrophoresis, was protected by addition of either EW or PE. However, the BB with 0.1% xanthan gum cooked fillet controls were observed to be significantly lower in chewiness, springiness, cohesiveness, resilience, and adhesiveness than BB treated cooked fillets. Despite the antagonistic action of the suspension aide, the PE texture measures were not significantly different from EW. If potato extracts could be utilized without a suspension aide, they should have a significant economic advantage over egg white as a cathepsin inhibitory ingredient for injection marinades due to their lower price. Recently more highly refined (>80% protein) acidified and non-acidified potato protein extracts were developed (Avebe, Veendam, Netherlands). The focus of this project was to determine their potential for use as a cathepsin enzyme inhibitory ingredient for marinade injection of Pacific whiting fillets. A preliminary study was conducted to determine both solubility and cathepsin enzyme inhibitory activity of refined, high protein content (>80%) non-acidified and acidified potato protein extracts. Solubility was evaluated by incorporating non-acidified or acidified extract into BB. Results indicated acidified extract was highly soluble and the non-acidified extract was only partially suspended. The acidified potato protein extract (PPE) was therefore selected for all subsequent evaluations. Cathepsin inhibitory activity was evaluated using Pacific whiting with visible parasitic infection as infected fish have heightened enzymatic levels. For the first experiment PPE, EW, or PE was incorporated into a BB at a concentration of 3%. Treated BB was incorporated into fish mince at a 10% by weight level. Cathepsin L activity was significantly (p<0.05) inhibited by PPE > EW > PE. The experiment was repeated using only PPE at 1.5%, 2.25%, and 3% concentrations. Results indicated no significant differences in the reduction of cathepsin L activity between the concentration levels. As a result, PPE was subsequently evaluated at even lower concentrations of 1%, 0.5% and 0.1%. All inhibitor concentrations showed similar cathepsin L activity reductions. Finally, the experiment was repeated using 0.1% PPE with cathepsin B, H and L activity measurements being obtained. The PPE treatment significantly reduced cathepsin B and L activity, but not cathepsin H. Results suggested that PPE is an alternative to PE for the inhibition of cathepsin proteases in Pacific whiting. The second study evaluated Pacific whiting fillets injected with 0.1% PPE in BB. Fillets injected with BB were utilized as the control treatment. Protein functionality was assessed through 0, 3, 6, and 12 freeze-thaw (F/T) cycles (1 cycle: 48-hour freeze at -18 °C followed by 24-hour thaw at 4 °C) designed to mimic long term storage. Tests applied included, non-cooked/cooked color and cooked fillet texture. Treatment with PPE did not have a significant effect on pH, drip loss, water holding capacity, cook loss, lipid peroxidation, protein solubility, surface hydrophobicity, or sulfhydryl groups. However, drip loss (p value < 0.05), cook loss (p value = 0.00046), lipid peroxidation (p value < 0.05), protein solubility (p value < 0.05), surface hydrophobicity (p value < 0.05), and sulfhydryl groups (p value < 0.05) did vary significantly due to F/T cycle treatment. Some variables did not behave as expected when assessing treatment within F/T groups, including water holding capacity, protein solubility, surface hydrophobicity, and sulfhydryl groups. The stabilization of water holding capacity and lack of change in protein solubility as F/T cycles increased could indicate some cryogenic protection added from phosphate addition in both brine treatments. Sudden decreases in surface hydrophobicity in early F/T cycles could indicate early formation of hydrophobic bonds. Low initial sulfhydryl content in F/T 0 shows evidence of disulfide bond formation masking free sulfhydryl group content. Color change was not visibly different in raw or cooked products between treatments or F/T cycles, but colorimeter measurement found that in cooked products, generally PPE treated fillets had significantly lower L* (p value < 0.05), hue (p value = 0.048), and chroma (p value = 0.026) meaning PPE treated fillets were darker overall. Texture profile analysis found the only variable impacted by brine treatment was hardness (p value = 0.038). The PPE treated fillets showed significantly firmer texture in F/T cycle 0. However, BB treated fillets showed similar firmness to PPE by F/T group 3 likely due to an increase in drip loss. Addition of PPE also resulted in more consistent readings (as indicated by lower standard deviations) for all texture variables throughout F/T cycles. Based on results from tests assessing protein functionality (cook loss, drip loss, WHC, protein solubility, surface hydrophobicity, TBARS, and sulfhydryl groups), there was no evidence to suggest that PPE improved these measures of protein functionality at the 0.1 % level in BB. However, PPE is a good inhibitor of cathepsin L and B at low concentrations and results in more consistent texture measures, minimal color change, and firmer initial texture. Moving forward, it would be interesting to determine whether PPE could work synergistically with ingredients that enhance protein-protein interactions and cooked protein gel formation.
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  • Pending Publication
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  • 2022-01-13 to 2024-02-14

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