Electrical Conductivity of Pacific Whiting Surimi Paste during Ohmic Heating

Electrical conductivities of Pacific whiting surimi paste with various moisture contents (75, 78, 81, and 84%) and added salt (1, 2, 3, and 4%) were measured using ohmic heating at alternating current of 3.3, 6.7, and 13.3 V/cm. Electrical conductivity of surimi increased with temperature and salt content and slightly increased with moisture content. Electrical conductivity correlated linearly with temperature (r²= 0.99). Generally, voltage gradient did not affect conductivity. However, variations of conductivity with voltage gradient observed in surimi containing 3–4% salt, were probably caused by electrochemical reactions at electrode surfaces. The empirical model of electrical conductivity predicted values ± 16% of independent experimental results.     

Surimi Production from Partially Processed and Frozen Pacific Whiting (Merluccius productus)

Pacific whiting surimi was made from stabilized mince (SM), unstabilized mince (UM), and headed and gutted (H&G) fish kept in frozen storage and compared to a surimi control made from fresh fillets. SM was made by mixing fresh mince with 12% w/w sucrose and 0.2% w/w polyphosphates. Surimi was produced from SM, UM, H&G at 1, 30, 90, and 180 days and evaluated by torsion, measuring shear stress, and true strain. After 6 months, there were no differences (p>0.05) between surimi samples prepared from SM stored at - 20° and -50° and the control surimi. UM and H&G fish produced surimi of inferior quality.     

白鲢鱼糜流变特性的研究

本实验利用ARES-RDA流变仪,通过动态振荡测量,研究了不同温度和浓度下的白鲢鱼糜的流变特性、凝胶过程及动态粘弹性的变化规律。结果表明白鲢鱼糜的粘度随剪切速率增大而减小,存在剪切变稀行为;鱼糜的动态剪切模量(包括弹性模量和损耗模量)在5℃和10℃时几乎与动态频率(f)(2～16Hz)无关,其中G’远高于G’’,20℃时,当动态频率(f)>8Hz,糊状鱼糜的动态剪切模量与动态频率有关,随着频率的增加而增加;温度扫描(温度范围:5～70℃)结果表明鱼糜凝胶过程经历了三个阶段:第一段在30℃之前,第二段出现在38～43℃,第三段出现在46℃之后,蛋白开始形成了最终的凝胶。该结果为进一步扩宽白鲢鱼糜的应用范围有一定的借鉴意义。     

Rheological and Textural Properties of Pacific Whiting Surimi Gels As Influenced by Chicken Plasma

Rheological properties of Pacific whiting surimi, in the absence and presence of chicken plasma (CP) at different levels (0.3–3.0%, w/w), were studied by dynamic rheological (small strain) and torsion fracture measurements, respectively. The surimi paste exhibited two major distinctive rheological transitions during heating (1°C/min) from 20 to 90°C with peaks observed at 33 and 56°C. The abrupt loss of G′ upon heating from 47 to 57°C, and the occurrence of small peak of phase angle at the same temperature range were prevented by the addition of CP. Nevertheless, the final G′ of the surimi paste added with CP was lower than that of the control. But shear fracture stress of both kamaboko and modori gels increased as the CP levels increased and shear strain increased with the addition of CP up to 2% (P < 0.05). CP inhibited the degradation of myosin heavy chains (MHC) caused by endogenous proteinases as indicated by more retained MHC and lowered TCA-soluble peptide content. Whiteness of gels decreased somewhat with increasing CP levels. CP, thus, could be a helpful additive for improving gelling properties of Pacific whiting surimi     

USE OF CYSTEINE PROTEINASE INHIBITORS FROM INJURED TOMATO LEAVES IN WHITING SURIMI

Cooking surimi paste from Pacific whiting results in a gel with poor texture due mainly to myosin degradation caused by a cysteine proteinase. Cysteine and serine proteinase inhibitors were isolated from injured and methyl jasmonate treated tomato leaves. Tomato cysteine proteinase inhibitor was stable at 60C but inactivated at 90C, making it suitable for use in surimi. Tomato proteinase inhibitors (TPI), having 7.9 papain inhibitor units, inhibited autolysis about 95% in 10 g of Pacific whiting surimi. Gel strength of Pacific whiting surimi was improved by adding only 0.0 27% of TPI to the surimi formulation. Addition of TPI did not affect the color of whiting surimi gel, while egg white needed to prevent gel weakening caused the gels to have more yellow hue (P<0.05). SDS-PAGE showed that myofibrillar protein degradation was prevented during cooking when 0.027% of TPI was included in the surimi. TPI extracted from tomato plants has potential for use as food grade additive in Pacific whiting surimi.     

Electrical conductivity and physical properties of surimi-potato starch under ohmic heating

ABSTRACT:  Electrical conductivities of Alaska pollock surimi mixed with native and pregelled potato starch at different concentrations (0%, 3%, and 9%) were measured at different moisture contents (75% and 81%) using a multifrequency ohmic heating system. Surimi-starch paste was tested up to 80 °C at frequencies from 55 Hz to 20 KHz and at alternating currents of 4.3 and 15.5 V/cm voltage gradient. Electrical conductivity increased when moisture content, applied frequency, and applied voltage increased, but decreased when starch concentration increased. Electrical conductivity was correlated linearly with temperature ( R ²≈ 0.99). Electrical conductivity pattern (magnitude) changed when temperature increased, which was clearly seen after 55 °C in the native potato starch system, especially at high concentration. This confirms that starch gelatinization that occurred during heating affects the electrical conductivity. Whiteness and texture properties decreased with an increase of starch concentration and a decrease of moisture content.     

Degradation Kinetics of Myosin Heavy Chain of Pacific Whiting Surimi

Pacific whiting surimi paste was ohmically heated to investigate degradation of myosin heavy chain (MHC) caused by endogenous proteinase over a range of 40–85°C and 0.5–35 min. Degradation was best described with an apparent reaction order of 1.4. Changes of degradation rate increased with temperature and reached a maximum at 57°C. Then, rate of MHC degradation decreased with higher temperature and reached a minimum at 75°C. E_a values of activation and inactivation zone were 142.3 and 83.1 kJ/mol, respectively. Generally, failure shear stress and shear strain increased linearly with MHC content. Proteolytic degradation of actin exhibited the same trend as that of MHC but at a slower rate. The synergistic effect of actin in the gelation of whiting surimi was predominant at ≥75°C.     

Characterization of Thermorheological Behavior of Alaska Pollock and Pacific Whiting Surimi

ABSTRACT: Thermorheological behavior of Alaska pollock (AP) and Pacific whiting (PW) surimi was evaluated during gelation at different moisture contents (80% to 95%). The temperature sweep data (storage modulus, G', compared with temperature) for both surimi clearly indicated G' minima. Unlike for the PW surimi, the minimum values of the AP surimi was moisture-content dependent and there was a linear relationship between logarithm of concentration and reciprocal absolute temperature at gelation. The activation energy ( Ea ) for aggregation after gelation temperature at each moisture content was calculated by a nonisothermal kinetic model for both AP and PW Surimi. The Ea values increased with moisture content of the system and ranged from 172.8 to 232.9 kJ/mol. Based on the assumption that melting temperature for a thermo-reversible gel may be considered equivalent to gelation temperature for thermo-irreversible gels, an Arrhenius-type model was used to estimate the enthalpy of cross-links formation for AP surimi to be 300.3 kJ/mol.     

Protease Inhibitor Effects on Torsion Measurements and Autolysis of Pacific Whiting Surimi

Beef plasma protein (BPP), egg white and potato extract were tested for their ability to inhibit proteolysis in fish mince and surimi made from Pacific whiting (Merluccius productus). Strong inhibition resulted from all three compounds in fish mince when measured by autolysis. However, when tested in surimi significant differences occurred among the compounds. BPP showed strongest inhibition of proteolytic effect followed by egg white and potato extract when measured by autolysis, gel electrophoresis and torsion. BPP was an effective inhibitor in surimi at a concentration as low as 1%.     

Elucidating Factors Affecting Floatation of Fish Ball

ABSTRACT:  Factors affecting floatation of fish ball in water were investigated. The density of threadfin bream (TB) surimi paste significantly decreased ( P < 0.05) as moisture content, temperature, or salt concentration increased. The ability of surimi paste to float or sink in water was observed according to changes in density. In gel texture measurement, when surimi was thawed for 1 h before chopping at 5 °C with 2% salt, the highest breaking force and deformation values were obtained. Apparent viscosity of surimi paste decreased as moisture content increased or salt concentration increased, and chopping temperature decreased. Setting gels in salt solution (5 or 10%) significantly reduced ( P < 0.05) stickiness, which is the tendency to stick to one another.     

Dielectric Properties of Mashed Potatoes Relevant to Microwave and Radio-frequency Pasteurization and Sterilization Processes

ABSTRACT: Dielectric properties of mashed potatoes relevant to microwave and radio-frequency (RF) pasteurization and sterilization processes were measured over 1 to 1800 MHz and 20 °C to 120 °C. Effects of moisture content (81.6% to 87.8%, wb) and salt content (0.8% to 2.8%, wb) were investigated. Dielectric loss factors and constants decreased with frequency. Dielectric loss factors increased with temperature and salt content, but dielectric constants were not significantly affected. Ionic conductivity played a dominant role at low frequencies. Power penetration depth increased with moisture content and decreased with temperature, frequency, and salt content. Regression equations were developed to relate the dielectric properties to temperature, moisture, and salt contents.     

Cathepsin Degradation of Pacific Whiting Surimi Proteins

Cathepsin B was the most active cysteine protease in Pacific whiting fish fillets; cathepsin L was predominant in surimi. Cathepsin L showed highest activity at 55°C in both fish fillets and surimi, indicating its function in myosin degradation during conventional heating of fillets and surimi, gels. Washing during surimi processing removed cathepsin B and H but not cathepsin L. Myosin heavy chain was the primary substrate during autolysis of surimi paste and actin and myosin light chain showed limited hydrolysis during 2 hr incubation. Purified Pacific whiting cathepsin L hydrolyzed myofibrils, myosin and native and heat-denatured collagen. The degradation pattern of myofibrils by the protease was the same as the autolytic pattern of surimi.     

CAPILLARY EXTRUSION VISCOMETER FOR THE VISCOSITY MEASUREMENT OF FISH PROTEIN PASTE

To overcome various limitations of conventional viscometers in measuring salted or unsalted surimi paste, a capillary extrusion viscometer was developed. The viscosity of surimi paste was measured as a function of moisture content (MC) (75–80%), salt content (2–4%) and liquid egg white (LEW) content (2–4%). As moisture, salt and LEW contents increased, viscosity gradually decreased. The viscosity values, as affected by MCs, showed a highly negative relationship with fracture properties of surimi gel, especially shear stress from the torsion test, indicating that MC is linearly correlated to the strength of gels at fracture. This easy and quick viscosity measurement can effectively facilitate the production control of comminuted muscle foods, including surimi paste.

PRACTICAL APPLICATIONS

There had been a difficulty to measure the exact viscosity of comminuted muscle food pastes when conventional viscometers were used. This was due to the non-linearity between dilution rates and viscosity of muscle paste, or limited range of shear rate during viscosity measurement. New developed small capillary extrusion viscometer can measure a wide range of comminuted muscle paste viscosity. When using this capillary viscometer, flow behavior of non-Newtonian surimi paste and other comminuted muscle paste can be well defined.     

Rheological Behavior and Potential Cross-Linking of Pacific Whiting (Merluccius productus) Surimi Gel

Gelation behavior and potential cross-linking of Pacific whiting (Merluccius productus) surimi were affected by setting temperatures and an enzyme inhibitor. Gels of Pacific whiting surimi with salt and beef plasma protein were compared with those containing guanidine hydrochloride, sodium dodecyl sulfate, and β-mercaptoethanol. The strongest gels were formed at 25°C setting followed by 90°C heating. Hydrogen and hydrophobic bonds appeared to strongly influence gel formation, while the influence of disulfide bonds was moderate. Viscosity scanning during setting at different temperatures was also useful to estimate effects of enzymes and inhibitors.     

Dielectric properties of ground almond shells in the development of radio frequency and microwave pasteurization

To develop pasteurization treatments based on radio frequency (RF) or microwave energy, dielectric properties of almond shells were determined using an open-ended coaxial-probe with an impedance analyzer over a frequency range of 10–1800 MHz. Both the dielectric constant and loss factor of almond shells decreased with increasing frequency, but increased with increasing temperature and moisture content. The absolute value of the slopes of log–log plots between loss factor and frequency increased with increasing temperature at low frequencies, especially at high temperatures and moisture contents. The effective electrical conductivity of shell samples was close to zero at the lowest moisture content (6% w.b.) and 3–9 times larger at 90 °C than 20 °C for the highest moisture content (36% w.b.). A good linear relationship was observed between permittivity and density at 1800 MHz. The power penetration depths at RF range (27 and 40 MHz) were about 6–24 times as deep as those for microwave frequencies (915 and 1800 MHz) at each corresponding temperature and moisture content. It is likely that RF energy may provide uniform heating and high throughput treatments for controlling Salmonella in in-shell almonds after washing.     

915MHz和2450MHz频率下温度和盐溶液浸渍对青鱼介电特性的影响

采用同轴探针法测定了频率915、2450MHz,温度范围10～90℃下,经浓度1%、2%、3%、4%食盐溶液浸渍的生鲜青鱼鱼片和预加热青鱼鱼片的介电特性值,并应用DSC测定了样品肌动蛋白和肌球蛋白的热变性温度。考察了温度、频率、水分含量、食盐溶液浸渍和蛋白质热变性对样品介电常数、介电损失率和穿透深度的影响。结果显示,浸渍盐溶液的渗透使得样品介电行为在一定程度上接近于相应盐浓度的浸渍溶液。浸渍对样品介电常数影响较小,而对介电损失率变化较大。随温度的上升,因加热过程中蛋白质的热变性引起样品水分的流失,导致生鲜样品的介电常数值的减小趋势明显大于预加热样品。而经浸渍的生鲜样品的介电损失率增大趋势明显大于预加热样品,并随浸渍溶液含盐量增大而增大。应用二项式方程得出介电特性的回归预测方程。      

Functional Properties and Shelf Life of Fresh Surimi from Pacific Whiting

Total aerobic plate count (APC), shear stress, shear strain, and color of fresh Pacific whiting surimi stored at 5°C were determined at day 0, 1, 3, 5, and 7. Frozen surimi was prepared with four levels of cryoprotectams (0, 3, 6, and 9%) and was compared with fresh surimi for gelforming ability. Fresh Pacific whiting surimi had a shelf life of 5 days. The gel functionality remained unchanged throughout the storage time. Strain values of fresh surimi were not different from those of frozen surimi with 9% cryoprotectants, but stress values of fresh surimi were almost three times higher than those of frozen surimi.     

Gelation of Surimi by High Hydrostatic Pressure

The effects of high hydrostatic pressure (HHP) on gel strength of Pacific whiting and Alaska pollock surimi were determined by torsion. Pacific whiting gels were made with and without 1% beef plasma protein (BPP) as protease inhibitor. HHP treated whiting (1% BPP added) and pollock gels showed greatly increased strain values at all pressure/temperature combinations compared with heat-set controls. Stress values for the same samples were variable depending on treatment and species. A three-fold increase in strain and stress was found for HHP treated whiting gels made without inhibitor.     

Comparison of the Thermostability of Red Hake and Alaska Pollock Surimi during Processing

Thermostability of red hake (Vrophycis chuss) mince and its temperature-dependent gel-forming properties were determined while using Alaska pollock (Theragra chalcogrumma) for comparison. Fish mince and surimi were subjected to various washwater, chopping and setting/ cooking temperatures, cooking times at varying salt concentrations and moisture levels. The optimal temperatures for washing and chopping were 15°C and 12°C for red hake and 10°C and 4°C for pollock, respectively. All treatments significantly affected gel properties. For red hake gels, 77% moisture, 2.0% salt, and a 40°C preheat-setting temperature produced the most cohesive gel. Gels of both red hake and pollock gradually became less cohesive with extended cooking time. The results suggest that red hake is more thermally stable than pollock.     

EFFECT OF PACIFIC WHITING WASH WATER PROTEINS ON ALASKA POLLACK SURIMI GELS

The objective of this work was to evaluate the effect of adding insoluble proteins recovered from Pacific whiting surimi wash water (SWW) on the mechanical and functional properties of Alaska pollack surimi gels. Insoluble proteins from Pacific whiting SWW were added at 0 (control), 10, 30 or 50 g/kg into Alaska pollack grade FA surimi. Changes on mechanical properties, expressible water ( EW ) and color attributes were evaluated in pastes and gels. Results obtained showed that texture profile analysis, puncture test and EW parameters increased significantly by increasing the amount of insoluble proteins added. Although slight changes in color attributes were detected, all surimi gels remained in the same color zone. The results obtained suggest that insoluble proteins from Pacific whiting SWW could be used to improve the mechanical properties of Alaska pollack grade FA surimi gels with a minimum effect on color.

PRACTICAL APPLICATIONS

Insoluble proteins recovered from surimi wash water (SWW) of Pacific whiting added at 10–50 g/kg to Alaska pollack surimi showed no adverse effects on their textural properties (hardness, fracturability, springiness and chewiness) and slight changes on color attributes. The results obtained suggest that it is feasible the use of insoluble proteins recovered from SWW of Pacific whiting in Alaska pollack surimi. Therefore, a double target is obtained: the preservation of environment and an increase in the yield of surimi processing without negative effects on texture.