The proteolytic enzymes in the muscle fluid of Pacific whiting (Merluccius productus) were studied and compared to those found in muscle fluid of true cod (Gadus macrocephalus). Preliminary studies indicated three pH optima of activity for whiting, pH 3.5-3.9, 4.3-4.6 and 7.1-7.2. Only two pH optima were found for the proteolytic activity of true cod, pH 3.2-3.6 and 7.7-8.0. The sarcoplasmic fluid of whiting and cod muscle was studied in more detail. For both whiting and cod, no hydrolysis of the substrates hippuryl-L-phenylalanine, hippuryl-L-arginine, α-N-benzoyl-D,L-arginine p-nitroanilide (BAPA), or toluene sulfonyl arginine methyl ester (TAMA) at neutral pH's could be detected, indicating the absence of trypsin and carboxypeptidases A and B. Neither whiting nor cod contained elastase and only whiting was shown to have activity similar to that of cathepsin B. True cod was found to contain higher chymotrypsin activity than whiting at pH 7.15 using the substrate glutaryl-L-phenylalanine p-nitroanilide. Hydrolysis of the substrate glutaryl-L-phenylalanine β-naphthylamide (Gly-Phe-2-naphthylamide) from pH 5 to 8 occurred to a greater extent in Pacific whiting than in true cod. Various inhibitors and activators were used to characterize the enzymes in whiting and cod muscle hydrolyzing the substrates GPNA and Gly-Phe-2-naphthylamide. The responses to the chemicals were compared with the effects reported in the literature on the hydrolysis of the substrates by enzymes found in other animal sources. / Graduation date: 1981

The optimum conditions for the proteolytic solubilization of trash fish and processing carcass waste in a simple shell-in-tube heat exchange system was investigated. The nutritional and chemical effects of processing variables were evaluated. An exogenous source of proteolytic enzymes (albacore tuna viscera, Thunnus alalunga) yielded a linear increase in the rate of the proteolytic hydrolysis of ground whole Pacific hake (Merluccius productus) up to 40% in the reaction mixture at 55°C. At 60°C optimum temperature for proteolytic hydrolysis was established with a 20% viscera 80% hake reaction mixture. Acidification of hake with 85% H₃PO₄ greatly accelerated proteolytic hydrolysis yielding an optimum between pH 3.6 and 3.7. The optimum pH for liquification based upon the viscometric properties of reaction mixtures varied from that for hydrolysis and was between 4.3 and 5.1. The chemical characteristics of the proteolytic solubilization of hake at 55°C was determined. The total nitrogen and free amino and tyrosine equivalent content of trichloroacetic acid (TCA), water and sodium dodecylsulfate (SDS) fractions of reactions containing 0, 2 and 4% 85% H₃PO₄ were determined at various times over a two hr period. With accelerated reactions (2 and 4% 85% H₃PO₄) the rate of hydrolysis was greatly reduced after 30 min. Under less than optimum pH conditions (0% 85% H₃PO₄) proteolytic hydrolysis proceeded in a linear fashion throughout the two hr period. The relationship between the quantities of chemical indices in the TCA and water fractions suggested that the majority of the proteolytic action yielded amino acids and short peptides. The total nitrogen content of the SDS soluble fraction inferred that very little of the protein that was not SDS soluble was being solubilized. The protein efficiency ratio of samples of hake reacted at 55°C in the presence of 0, 2 and 4% (wt/wt) 85% H₃PO₄ at 30, 60, and 120 min was determined to assess the nutritional effects of proteolytic solubilization. Proteolytic action reduced protein quality to a degree related directly to the level of acid accelerated proteolytic action. Full reduction in quality was accomplished at the end of 30 min for reaction mixtures containing 0 and 2% acid in comparison to a raw hake control; no reduction was observed between 30 and 120 min. In addition to the initial reduction in quality within the first 30 min of reaction, mixtures containing 4% acid were significantly reduced between 30 and 120 min. Conversion of native protein to nutritionally less utilizable amino acids and peptides probably played the major role in reducing protein quality in reaction mixtures containing 0 and 2% acid. The time dependent reduction in protein quality for the reactions containing 4% supports the destruction of amino acids, probably tryptophan, at this higher level of acidity. / Graduation date: 1977

Graduation date: 1974

Feasibility of ohmic heating to overcome gel-weakening in Pacific whiting surimi was investigated. An ohmic heating apparatus was developed using two rhodium-coated stainless steel electrodes inside a polyvinyl chloride (PVC) tube, a variable transformer, and voltage and current transducers. Rapid heating associated with the ohmic process quickly inactivated endogenous proteinase(s), resulting in significantly high shear stress and shear strain of surimi gels (78% moisture content, 2% NaCl). Degradation of myosin heavy chain (MHC) and actin examined by SDS-PAGE were significantly reduced and continuous gel structure were shown by scanning electron microscopy. Whiting surimi heated in a 90°C water bath for 15 min exhibited poor gel quality and disordered microstructure due to proteolysis of MHC. Electrical conductivity, a critical parameter influencing rate of heat generation during ohmic heating, was elucidated. Electrical conductivities of whiting surimi pastes with four moisture contents (75, 78, 81, and 84% wet basis) and added NaCl (1, 2, 3, and 4%) were measured from 10 to 90°C using ohmic heating at voltage gradient of 3.3, 6.7, and 13.3 V/cm. Electrical conductivity significantly increased with temperature and salt content and slightly increased with moisture content. The effect of the voltage gradient was evident at combinations of high moisture (81, 84%) and NaCl content (3, 4%), due to electrochemical reactions at the electrodes. The empirical model of electrical conductivity as a function of temperature and compositional characteristics predicted values with an error range of 0-15.6%. Finally, kinetic models of textural degradation of whiting surimi were developed using two different approaches: isothermal and nonisothermal procedure over a range of temperature (40-85°C) and time (0.5-35 min). The effect of thermal lag was accounted for using the models derived from the Arrhenius equation. Textural degradation obtained from both methods followed first order kinetic. Degradation of MHC derived from nonisothermal procedure was best described by apparent reaction order of 1.4. Degradation rate of gel texture and MHC increased with temperature and reached the highest rate at 55 and 57°C, respectively. Then they decreased to minimum rate at 70 and 75°C, respectively. The kinetic model for the loss of MHC satisfactorily estimated MHC content of the controls with an averaged error of 10.8%. Relationship between degradation of MHC and gel texture are discussed. / Graduation date: 1996

Kinetic properties of the two proteases, causing textural degradation of Pacific whiting (Merluccius productus) during heating, were compared and characterized with the synthetic substrate, Z-Phe-Arg-NMec. Pacific whiting P-I and P-II showed the highest specificity on Z-Phe-Arg-NMec, specific substrate for cathepsin L. The K [subscript m] of preactivated P-I and P-II were 62.98 and 76.02 (μM), and k [subscript cat], 2.38 and 1.34 (s⁻¹) against Z-Phe-Arg-NMec at pH 7.0 and 30°C, respectively. Optimum pH stability for preactivated P-I and P-II is between 4.5 and 5.5. Both enzymes showed similar pH-induced preactivation profiles at 30°C. The maximal activity for both enzymes was obtained by preactivating the enzyme at a range of pH 5.5 to 7.5. The highest activation rate for both enzymes was determined at pH 7.5. At pH 5.5, the rate to reach the maximal activity was the slowest, but the activity was stable up to 1 hr. P-I and P-II shared similar temperature profiles at pH 5.5 and pH 7.0 studied. Optimum temperatures at pH 5.5 and 7.0 for both proteases on the same substrate were 55°C. Significant thermal inactivation for both enzymes was shown at 75°C. Preactivated P-I and P-II displayed a similar first order thermal inactivation profile at pH 7.0. At 30 and 90°C, half lives, t [subscript 1/2], for Pacific whiting P-I were 49.50 and 0.20 min and for P-II, 32.54 and 0.18 min, respectively. The rate constant of inactivation for both proteases increased about 200-fold between two limits, 30 and 90°C. Half lives at 55°C, optimum temperature, for P-I and P-II were also determined to be 5.29 and 6.75 min. The increase in thermal inactivation rate constants independent of substrates corresponded to an activation energy for heat denaturation of 21.18 kcal/mol for P-I and 19.97 kcal/mol for P-II by Arrhenius plot. These similar kinetic properties, i.e., kinetic parameters, pH profile and thermal inactivation rate constant, suggested that Pacific whiting P-I and P-II are the same enzyme. / Graduation date: 1994

The effect of salt (0, 0.9, 1.7, 2.5%) and pH (range 4 to 10) on surimi gels made from Pacific Whiting (Merluccius productus) was investigated. Gel-forming ability was measured by the torsion test. In general, surimi gels increased in gel strength with increased pH. Breaking shear stress increased to a greater degree than breaking shear strain above pH 7.0. The increase in gel strength was greater at higher pHs for gels made without salt than those made with salt. At neutral pH, the salted surimi showed greater gel forming abilities than the unsalted whiting surimi. Poor gels were formed at low pH (pH 4 to 6) for both the salted and no-salt surimi. These results demonstrated that pH and salt concentration had an interactive effect on the gel-forming ability of the Pacific whiting surimi and that improved gel strength at low salt levels might be obtained by increasing the pH. / Graduation date: 1993

In surimi manufacturing, less than 25% of the total weight of the fish is utilized. This research focused on meat recovery from fish frames, the residual portion of the fish after filleting headed and gutted fish. A new technology, the water jet deboning (WJD) system, was tested. The WJD system uses oscillating high pressure water jet nozzles to recover edible flesh from the frames without breaking the kidney located under the backbone. To evaluate the function of added salt on dewatering and process recovery, the WJD was operated without NaCl (WJD1) and with 0.2% NaCl added to the discharge slurry (WJD2). In conventional mechanical deboning process (MD), which was the other deboning system applied in the study, no salt was used. The recovered frame meat was further processed to surimi and then stored at -18��C. Meat recovery and surimi processing yields were compared between the three meat recovery processes. Functional properties of gels (texture and color) were evaluated after 1 and 6 mo frozen storage and compared to commercially manufactured surimi, which served as a control. As a result of manual trimming, the maximally recoverable meat from the frames was 42.8% of frame weight. MD showed the highest mince yield (mince prior to cryoprotectant addition), 24% of frame weight, while the two WJD methods resulted in only 5% yield. Color and shear strain for gels from WJD1, MD surimi and mixtures of those and control (10-20% frame mince surimi/80-90% control), were comparable to control. Gels from WJD2 showed significantly lower lightness (L*) but did not differ otherwise. Shear stress values of all frame meat surimi gels and the gels from mixtures of those and the control were significantly lower than the control. This low shear stress is probably due to a difference in processing equipment and processing conditions between the lab scale and the commercial scale. Due to the promising processing yield for the MD system an additional study was performed where effects of kidney and kidney blood contamination in the frame mince were investigated. Pacific whiting frames were mechanically deboned with/without kidney and the frame mince further processed into surimi. Functional properties of gels (texture and color) were evaluated after 1 and 6 mo frozen storage and compared to commercially manufactured surimi, which served as a control. At 1, 2, 4, and 6 mo, salt extractable proteins (SEP) concentration, dimethylamine (DMA) formation and pH were measured to monitor protein denaturation. Removing the kidney and washing the frames prior to MD resulted in higher gel strength after 1 and 6 mo frozen storage. / Graduation date: 2000

The major portion of Pacific whiting (PW) is commercialized in the form of frozen surimi. Alternative products for PW were investigated focusing on fresh surimi and texturized meat from PW mince. Fresh surimi is made without additives and kept refrigerated instead of frozen. Texturized meat is a meat-like product made from PW mince through freeze-texturization. Fresh surimi was stored at 5°C and analyzed for its total aerobic plate count (APC), shear stress, shear strain, and color during 7 days storage. Frozen surimi from PW was prepared with 0, 3, 6, and 9% cryoprotectants and was compared with fresh surimi for its gel forming ability. Fresh surimi had a shelf life of 5 days and the gel forming ability remained unchanged throughout storage time. Shear strain of fresh surimi was not different from frozen surimi with 9% cryoprotectants but shear stress was almost 3 times higher than the frozen one. Texturized meat from PW mince was prepared from unwashed or 1-washed mince kept frozen for 6-8 mo with or without the addition of 6% cryoprotectants. The minces were comminuted into a protein slurry, formed into patties, and frozen at -7, -18, and -50°C. The evaluations of ice formation (by microscopic study), hardness, cook loss, color, and water holding capacity were carried out during 20 days storage. The results showed that texturized meat with parallel layers was made from 1-washed PW mince. Unwashed PW mince created a sponge-like texture and had rapid quality deterioration, thus it is not recommended for this product. Cryoprotectants did not significantly affect the texture formation of the product and are not required to store mince as raw material for the texturized meat. The optimum freeze-texturized temperature for this product was -18°C or lower because it minimized quality changes during storage depending on the desirable texture. The lower the temperature (higher freezing rate), the finer the layers created. / Graduation date: 1996

The abundance and low fat content of Pacific whiting support Its use for the production of surimi. The degradation of muscle proteins by myxosporidian secreted proteinase(s) has been associated with its soft texture. High residual activity is retained through the washing process used in the production of surimi and precludes the formation of a strong heat-set gel by surimi sols. Physical, chemical and SDS-PAGE analysis defined the reinforced oxidation of free sulfhydryl groups on myofibrillar proteins to disulfide bonds by potassium bromate. SDS-PAGE demonstrated myosin degradation during heat-setting and the protection of myosin from protelnase attack by bromate. A level of 0.075% bromate Inactivated 89.87% of the total proteinase activity in sols. It was assumed that cysteine proteinases were Inactivated and residual activity was associated with proteinases with a serine active site. Major iraprovement in gel coheslveness and elasticity was observed at bromate levels [less than or equal to] 0.075% with only a slight improvement at higher levels. Maximum hardness was observed at 0.150% with no (P>0.050) increase at higher levels. Brittleness was improved (P>0.050) by bromate levels [greater than or equal to] 0.100%; no maximum degree of brittleness was observed within the range ([less than or equal to] 0.250%) of concentrations investigated. An optimum folding test grade of AA was achieved by a minimum of 0.150% Potassium bromate improved gelling characteristics of sols of Pacific whiting surimi through proteinase inactivation and reinforced disulfide formation during heat-setting. Improvement in cohesiveness and elasticity was primarily a function of proteinase inactivation. Maximum hardness and brittleness required additional oxidative capacity which was not fully required for an optimum folding test grade. / Graduation date: 1989

Thesis (M.S.)--Oregon State University, 2001. / Typescript (photocopy). Includes bibliographical references. Also available online.