The potential of Pacific hake (Merluccius productus), which occur in Pacific north east waters, for human consumption is of interest because the biomass of the fish is known to be of significant size. However, this resource has not been fully exploited by the local fishing industry. The presence of Myxosporean parasite spores in the fish muscle is thought to cause a soft cooked fish texture, thus giving rise to problems in processing and affecting the marketability of the fish product. Studies were conducted on the textural properties of Pacific hake from two different fishing areas with different postharvest handling treatments. Fish samples from the Strait of Georgia and from offshore waters west of Vancouver Island were obtained from commercial sources. The west coast offshore hake samples were obtained in frozen form. They were thawed, filleted, vacuum-packed in barrier bags and refrozen for storage at -29°C. Two batches of fish chilled in refrigerated sea water were available from Georgia Strait. One of these batches was frozen immediately when received and subsequently processed similar to the west coast samples, whereas the other batch was chilled in ice for 1-3 days after landing while the fish were progressively processed into fillets for frozen storage at -29°C. The presence and types of species of Myxosporean parasite spores in fish fillets were determined by light and scanning electron microscopy. The fillets were grouped according to the level of infection in terms of the numbers of parasite spores determined by wet mount microscopic examination. The potential of Pacific hake (Merluccius productus), which occur in Pacific north east waters, for human consumption is of interest because the biomass of the fish is known to be of significant size. However, this resource has not been fully exploited by the local fishing industry. The presence of Myxosporean parasite spores in the fish muscle is thought to cause a soft cooked fish texture, thus giving rise to problems in processing and affecting the marketability of the fish product. Studies were conducted on the textural properties of Pacific hake from two different fishing areas with different postharvest handling treatments. Fish samples from the Strait of Georgia and from offshore waters west of Vancouver Island were obtained from commercial sources. The west coast offshore hake samples were obtained in frozen form. They were thawed, filleted, vacuum-packed in barrier bags and refrozen for storage at -29°C. Two batches of fish chilled in refrigerated sea water were available from Georgia Strait. One of these batches was frozen immediately when received and subsequently processed similar to the west coast samples, whereas the other batch was chilled in ice for 1-3 days after landing while the fish were progressively processed into fillets for frozen storage at -29°C. The presence and types of species of Myxosporean parasite spores in fish fillets were determined by light and scanning electron microscopy. The fillets were grouped according to the level of infection in terms of the numbers of parasite spores determined by wet mount microscopic examination. / Land and Food Systems, Faculty of / Graduate

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

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

Cryoprotection in stabilized mince from Pacific whiting (Merluccius productus) was investigated by monitoring changes in physical and chemical properties during 32 weeks of frozen storage. The effects of 4 different cryoprotectants were evaluated by torsion test, color analysis, extractability of salt soluble proteins, and formation of dimethylamine (DMA) and 2-thiobarbituric acid (TBA). The quality of the stabilized mince was significantly higher than the control (mince without cryoprotectants) when compared by shear strain, salt soluble proteins, and DMA. The results show that the functionality of the proteins in the mince can be protected by using cryoprotectants with Polydextrose® being the most effective of the 4 tested. The effect of food-grade protease inhibitors on the gel-forming characteristics of Pacific whiting mince was also investigated. Four levels (1, 2, 3, and 4%) of different protease inhibitors (beef plasma protein, whey protein concentrate, egg white liquid, and egg white powder) were added to the stabilized mince before heating and effects on texture and color were evaluated. Shear strain was significantly increased by increasing the level of inhibitors. Beef plasma protein was most effective and presented significantly higher strain than the other inhibitors tested. Due to higher concentration of proteolytic enzymes in the mince, an increased amount of protease inhibitors is needed compared to surimi to prevent proteolysis during heating. / Graduation date: 1995

Graduation date: 1993

Means of reducing the quantity of water required for the washing unit operation in surimi processing were evaluated. The yield of flesh mechanically dewatered with a screw press and the degree of reduction in trimethylamine oxide (TMAO) content were used as indices of washing efficiency. Variations in water:minced flesh ratio, multiple exchanges and washing conditions near the mean isoelectric point of flesh proteins were techniques evaluated to optimize the yield and quality of washed minced flesh. Single exchanges in potable water produced solids and protein recoveries superior to those observed for multiple exchanges utilizing the same total amount of water. A single exchange of a water:minced flesh ratio of 3.0 produced the highest recoveries (73.32 and 74.07 % of flesh solids and protein, respectively) with the composition characteristics desired. Multiple potable water exchanges (water:minced flesh ratio = 1.0/exchange) at equal total water volume produced desired composition characteristics, but pressed flesh yield was reduced (65.9 and 68.5 % of flesh solids and protein, respectively). Washing (water:minced flesh = 1.0) under acidic conditions near the isoelectric point (pH 4.9-5.3) of the minced flesh protein followed by a potable water wash (water:minced flesh = 1.0) produced recoveries (73.02 and 76.20 % of flesh solids and protein, respectively) superior or equal to all of the wash regimes of equal total water volume. These recoveries were observed even with considerable loss during screening between exchanges and at a water usage 66 % of the single exchange (water:minced flesh ratio = 3.0) of potable water. The moisture content of pressed flesh was increased by both the total potable water:minced flesh ratio and by the number of exchanges to which minced flesh was exposed. Moisture contents mediated by the number of exchanges were a function of water volume and exposure time. Washing conducted in an acidic water:minced flesh mixture at pH 4.9-5.3 (near the mean isoelectric point of flesh proteins) produced pressed flesh with a moisture content 10.09-15.09 percentage points lower than minced flesh wash in an identical (total water:minced flesh ratio; means of separation between exchanges) potable water regime. Washing under acidic conditions produced the most efficient reductions in TMA0 and lipid content (91.4 and 31.1 % of flesh TMA0 and lipid, respectively). Superior reductions were accomplished through pH conditions favoring the extraction of amines and by the greater pressures produced during screw pressing by the altered physical characteristics of the flesh. Pressing between multiple potable water exchanges also showed better reductions than single exchanges involving only one pressing operation. "Folding test" evaluation of heat-set gels (kamaboko) produced from a standard surimi formulation (containing 4 % each of the cryoprotectants sucrose and sorbitol and 0.5 % condensed phosphate) with the addition of 5 % each of potato starch and dried egg white revealed a difference between potable water and acid-washed flesh. Potable water-washed flesh (one exchange; water:minced flesh ratio = 3.0) graded SA (the highest possible grade for the "folding test used by Japanese processors to test the gel strength of surimi". An A-B grade (second and third grade on a five point scale) was assigned gels produced from acid washed flesh. Texture profile analysis of gels revealed acid washed flesh to yield significantly lower gel elasticity (P [greater than or equal to] .007) and cohesiveness (P [greater than or equal to] .0223) than those prepared from potable water washed flesh. The gels were equal in hardness (P [greater than or equal to] .05). The two washing regimes produced gels with comparable (P [greater than or equal to] .05) expressible water contents. Low potable water (a single exchange; waterrminced flesh ratio = 3.0) and acidic (two exchanges; water:minced flesh ratio = 1.0/exchange; exchanges = first pH 5.0-5.3, second potable water) washing regimes improved surimi yield by 26 % and 34 %, respectively, over yields reported for the conventional shore-based processing operations. This was accomplished at water use levels conservatively estimated to be 20 % of those reported for these processes. / Graduation date: 1987

No description available.

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