Activity of Endogenous Muscle Proteases from 4 Australian Underutilized Fish Species as Affected by Ionic Strength,pH, and Temperature

Storage conditions may influence the hydrolytic activity of endogenous muscle enzymes postmortem, rate of autolysis of myofibrillar proteins, and biological properties of hydrolyzed end products. This study investigated the effect of ionic strength, pH, and temperature on the activity of endogenous calpain‐like, cathepsins B and B+L measured in crude extract obtained from deepwater flathead, silver warehou, ribaldo, and ribbonfish muscles. Activity of calpain‐like enzymes in 3 examined species was significantly higher at pH 6.5 than pH 6.0 or 5.5. Raising the reaction temperature increased (P < 0.05) calpain‐like activity in ribaldo. Endogenous activity of cathepsin B in ribbonfish and silver warehou declined significantly with increasing ionic strength at pH 6.5 to 6.0. The obtained results will further expand our understanding of the impact that postmortem storage conditions have on the activity of endogenous fish proteases with respect to quality and bioactivity of fish proteins and potentially diversify utilization of underutilized fish species.     

Fish Myosin Fragments Solubility and ANS-Fluorescence Intensity Affected by n-Butanol

Changes in the solubility and 8-anilino-1-napthalene sulfonate (ANS)-fluorescence intensity of oval filefish, tilapia, and black marlin myo-sins and their fragments by n-butanol were examined in connection with myosin gel-forming abilities. The thermal gel-forming abilities of myosins were greatly enhanced by the addition of 0.3–0.8M n-butanol. KC1 concentration-solubility curves revealed that after n-butanol addition a marked decrease in the solubility was observed for myosins and S-1s, whereas there was a slight decrease for rods. The fluorescence intensity of myosins-ANS in the presence of n-butanol increased markedly by heating at 30° and 35°C. A similar increase in the fluorescence intensity occurred in all S-ls-ANS, but not in rods.     

赖氨酸诱导低离子强度下罗非鱼肌球蛋白增溶及机制

以罗非鱼肉为原料提取肌球蛋白,研究5 mmol/L赖氨酸对低离子强度（1～150 mmol/L KCl）条件下肌球 蛋白（蛋白质量浓度为2.0 mg/mL）体系浊度、溶解度及分子结构和形态的影响,分析赖氨酸诱导肌球蛋白增溶 机理。结果表明,在低离子强度下,肌球蛋白分子聚集成纤丝,溶解度低,赖氨酸的添加能显著降低肌球蛋白体 系的浊度（P＜0.05）,抑制蛋白分子间的聚集,增溶效果明显,增溶后分子的表面疏水性增大,α-螺旋含量减小 （P＜0.05）,且与酸碱处理组比较,在1～40 mmol/L KCl范围内,赖氨酸增溶效果更好。增溶后的肌球蛋白Zeta- 电位的绝对值增大,丝状体解离。     

自由基氧化对猪肌球蛋白-醛类化合物吸附特性的影响

采用FeCl3/抗坏血酸/H2O2羟自由基氧化体系模拟猪肌球蛋白氧化,研究不同H2O2浓度对肌球蛋白巯基总量、活性巯基、二级结构和表面疏水性的影响及与4?种典型醛类风味物质间的相互作用。结果表明：H2O2浓度对蛋白质构象有显著影响,随着H2O2浓度逐渐增加,活性巯基含量显著下降（P＜0.05）,表面疏水性显著增加（P＜0.05）。当H2O2浓度在0～5?mmol/L之间时,巯基总量、α-螺旋相对含量显著下降（P＜0.05）,蛋白质吸附能力显著增强（P＜0.05）;当H2O2浓度在5～10?mmol/L之间时,α-螺旋相对含量显著上升（P＜0.05）,蛋白质吸附能力显著减弱（P＜0.05）;当H2O2浓度在10～20?mmol/L之间时,蛋白质吸附能力显著增强（P＜0.05）。肌球蛋白与醛类化合物间的作用力主要为氢键和疏水相互作用,氢键和（或）疏水相互作用越强,蛋白质对醛类化合物吸附能力越强。     

Ionic Strength Effects on Heat-induced Gelation of Myofibrils and Myosin from Fast- and Slow-twitch Rabbit Muscles

The effects of ionic strength on myofibrils and myosin from rabbit fast-twitch Psoas major (PM) and slow-twitch Semimembranosus proprius (SMp) muscles before and after heating were studied by electron microscopy and thermal scanning rheometry. The direct suspension of proteins in low ionic strength (0.2M KCl; pH 6.0) led to very weak gels, whereas a gradual lowering of the ionic strength (by dialysis against 0.2M KCl; pH 6.0) of 0.6M KCl protein solutions induced strand-type networks at low temperature and strong heat-induced gels. As shown by transmission and scanning electron micrographs, in low ionic strength, SMp myosins formed shorter filaments before heating and thinner and shorter structures in heat-induced gels, as well as a lower gel porosity than PM myosins.     

Moisture Retention and Textural Properties of Ground Chicken Meat as Affected by Sodium Tripolyphosphate, Ionic Strength and pH

Batches of ground chicken meat were mixed with 10% solutions containing 0.0–5.0% sodium tripolyphosphate and sufficient NaCl to adjust the ionic strength (IS) of the solutions from <0.7 to 6.0 at pH 6.5 to 9.5 in a 6 × 4 × 7 factorial experimental design. Patties prepared from the mixtures were evaluated for pH, cooking loss, and objective texture characteristics. Most effects of STPP were attributable to the direct effect of STPP on IS. However the ability of the phosphate to alter textural properties was greater at a pH value near the pK_a of the phosphate.     

Fish Myosin Aggregation as Affected by Freezing and Initial Physical State

ABSTRACT: Fish myosin obtained from Tilapia nilotica was solubilized in 20 mM Tris-HCl, pH 7.0, with 0.6 M KCl (solution model system), or suspended without salt (suspension model system). Changes in % soluble protein, Ca²⁺-ATPase activity, and total and reactive -SH groups during frozen storage were evaluated. Frozen induced aggregation of fish myosin showed different behavior depending upon its initial physicochemical state. When myosin was solubilized prior to frozen storage, head-to-head interactions seemed to be more involved in protein aggregation with a strong participation of disulfide bonds. On the contrary, a preferentially side-to-side mechanism might be involved in the aggregation of myosin upon suspension, with a minor interaction of -SH groups.     

Headspace Volatiles of Sockeye and Pink Salmon as Affected by Retort Process

Sockeye and pink salmon were canned according to constant and variable temperature retort processes. A total of 102 volatile constituents were detected by gas chromatography-mass spectrometry. Based on principal component analysis (PRIN) applied to the different classes of volatiles, PRIN1 explained 72.2% of variation and was significant (P < 0.0001) for species differentiation. PRIN2 and PRIN4 extracted smaller variations (14.5% and 3.1%, respectively) but were significant (P < 0.05 and P < 0.01, respectively) for differences in retort regimes. However, sensory panelists did not find flavor differences between retort modes. Olfactometry revealed that aldehydes, sulfurs, and ketones constituted the major volatile classes of aroma-impact constituents in canned sockeye salmon.     

Age of Farmed Atlantic Salmon at Seawater Transfer Affects Muscle Collagen Content and Solubility at Harvest

Salmon released to seawater as different smolt types differed significantly in the total collagen content and the solubility of the collagen present. A 11/2 smolt contained more total collagen than 1/2 and 1 smolt types. Less insoluble collagen and more of the pepsin soluble collagen was generally present in 11/2 smolt type as compared with both 1/2 and 1 types, with the exception of prerigor type 1 salmon. No differences between smolt types in acetic soluble collagen were present. Fish with the higher amount of collagen also had the lowest end pH. Although the bled body weight differed, no correlation between body weight and collagen content or its solubility was found. Fish with higher end pH had lower total collagen and pepsin soluble collagen (r = ‐0.77, P = 0.0001 and r = ‐0.51, P = 0.04, respectively, and more insoluble collagen (r = 0.72, P = 0.002).     

蛋白质浓度、pH、离子强度对鲢鱼肌原纤维蛋白粘度的影响

利用二次回归正交旋转试验设计 ,研究了蛋白质浓度、pH、离子强度对鲢鱼肌原纤维蛋白粘度的影响 ,建立相应的回归方程 ,分析比较了它们间的相互作用关系 ,确定了取得最优粘度时 ,各因素的组合     

Solubility of Proteins from Quail (Coturnix coturnix japonica) Egg White as Affected by Agitation Time,pH, and Salt Concentration

The solubility of proteins from quail egg white subjected to different agitation times, pH, and NaCl at 25°C was evaluated in this study. The greatest solubility achieved was obtained in the 0.05 mol/L of NaCl, pH 10.0, and under agitation for 1 h. The lowest solubility was found in the NaCl 1.0 mol/L, pH 3.0, and agitated for 2 h. Under the test conditions, aqueous solutions of NaCl 1.0 mol/L, pH 3.0, and agitated for 2 h may provide the greatest extraction index of proteins from quail egg white because these conditions promoted the protein precipitation in a large extension.     

Carrageenans in Beaker Sausage as Affected by pH and Sodium Tripolyphosphate

We investigated effects of meat pH or sodium tripolyphosphate (STPP) on performance of carageenans (kappa, iota or lambda) in low-fat beaker sausage model systems. Adding STPP or using high-pH meat affected performance of the meat batter in similar ways. High-pH meat batters or those containing STPP had lower force values when extruded, lower cooking losses, and were firmer when cooked. The addition of lambda-carrageenan produced the softest texture. Kappa- and iota-carrrageenan improved water retention of low-pH meat batters. After staining, light microscopy revealed different structural effects of the carrageenans.     

Myofibrillar Protein Solubility of Model Beef Batters as Affected by Low Levels of Calcium, Magnesium and Zinc Chloride

Preblended composites of semimembranosus and adductor muscles were stored 12h at 4°C with 2.0% NaCl, 0 or 0.05% CaCl₂, MgCl₂, or ZnCl₂ and 0 or 0.4% sodium tripolyphosphate (STPP). Model systems were formulated to contain 30% fat (high fat; HF) or 10% fat (low fat; LF). Divalent salts lowered extract pH and ZnCl₂ elicited the greatest reduction. At both fat levels, CaCl₂ increased and ZnCl₂ decreased protein solubility, compared to the control (p<0.05). Myosin was not detected in ZnCl₂-treated HF and LF batters without STPP and in the presence of STPP, MgCl₂ and ZnCl₂ increased myosin concentration at both fat levels (p<0.05). Zinc chloride increased actin concentration in HF batters; whereas, MgCl₂ decreased soluble actin in LF batters (p<0.05). Magnesium chloride (0.05%) increased soluble proteins in LF batters containing 0.4% STPP by increasing myosin extractability.     

Role of Reduced Ionic Strength and Low pH in Gelation of Chicken Breast Muscle Protein

ABSTRACT: Elastic gels with a high moisture content of 88% were prepared at an acidic pH and low ionic strength. The relationship among pH, ionic strength, water-holding capacity, and fold score of gels was investigated. A decrease of pH from 4.1 to 3.7 or below increased gel elasticity and significantly decreased water loss under pressure ( P < 0.05). In the presence of sodium chloride, gels made at pH 3.5 to 3.7 had decreased elasticity and increased water loss under pressure. Prior freezing increased the water loss of gels under pressure. Gels made with phosphoric acid and hydrochloric acid lost less water under pressure than those made with citric acid. The percentage loss of water from cylindrical gels was inversely related to the height of the cylinders, suggesting that surface effects were involved. These results suggest that net positive charges on the protein molecules at low pH produced electrostatic repulsion, which was a major driving force for water uptake in the low-salt gels.     

Rigor Contractions in "Rested" and "Partially Exercised" Chinook Salmon White Muscle as Affected by Temperature

Time lapse video was used to determine the effects of temperature and fatigue on the development of rigor contractions in chinooksalmon ( Oncorhynchus tshawytscha ) white muscle. Minimal handling and chemical anaesthesia (AQUI-STM) produced rested fish. After removal of one fillet from the rested fish, post-mortem electrical stimulation of the carcass was used to partially exercise the remaining muscle. Specific strips of rested and partially exercised muscle were held in physiological saline at 0,4,6,8 and 12°C. Contraction onset and end were delayed by decreasing temperature in the rested treatment, but were unaffected in the partially exercised treatment. The final contracted length was affected by fatigue state and temperature.     

Histamine Production by Morganella morganii in Mackerel, Albacore, Mahi-mahi, and Salmon at Various Storage Temperatures

Morganella morganii was studied for its growth and histamine formation in mackerel, albacore, mahi‐mahi, and salmon stored at various temperatures from ‐30 °C to 37 °C. The optimal temperature for histamine formation was 25 °C. Mackerel, albacore, and mahi‐mahi were shown as good substrates for histidine decarboxylation by M. morganii at elevated temperatures (> 15 °C). M. morganii inoculated in all fish species including salmon formed histamine above the FDA guideline. Their growth was controlled by cold storage of the fish at 4 °C or below, but histamine formation was controlled only by frozen storage. Although histamine was not detected in any frozen samples, it accumulated rapidly in the previously frozen fish stored at 25 °C.     

Influence of pH and Salts on Egg White Gelation

ABSTRACT: Egg white is used in food products for various functional properties. These are strongly influenced by pH, ionic strength, type and concentration of salts. Through an experimental design strategy, the aim of this study was to quantify the influence of pH, cations, and anions naturally present in egg white, and of citrate on egg white gelation. Results showed that pH and Fe³⁺ modified the coagulation temperature of egg white and consequently, the gel characteristics. High concentrations of NaCl decreased the water-holding capacity and the microstructure of egg white gels. At pH 7, viscoelastic properties and microstructure of egg white gels were altered by Ca²⁺ and Mg²⁺ addition.     

Nutrients in Salmon and Red Grouper Fillets as Affected by Chlorine Dioxide (ClO2) Treatment

The effect of chlorine dioxide (ClO₂) treatment on nutrients of seafood was studied using Atlantic salmon (Salmo salar) and red grouper (Epinephelus morio) with five volumes (1:5, w/v) of aqueous ClO₂ at 20, 40,100, and 200 ppm ClO₂ in 3.5% brine for 5 min. Compared to nontreated controls, treatment of salmon and red grouper with ClO₂ solutions in brine did not significantly change the contents of protein, fat, moisture, niacin, calcium, iron, phosphorus, or potassium. However, such treatment with brine or ClO₂ solutions in brine caused a significant reduction in thiamin content in both species, but only riboflavin was reduced significantly in red grouper, possibly due to the solubilization effect of salt on the vitamins.     

Role of pH and Ionic Strength on Water Relationships in Washed Minced Chicken-breast Muscle Gels

ABSTRACT The relationship between pH, ionic strength, and water balance of chicken-breast muscle gels was investigated. An increase in gel pH (pH 6.4 to 7.4) without added NaCl led to dramatic increases in water-holding capacity and water uptake (P < 0.05). Gels at 150 mM NaCl exhibited less ability to adsorb water than salt-free gels (P < 0.05 at pH 6.8 to 7.4) and had lower water-holding capacities (P < 0.05) and fold scores at and below pH 7. Varying salt concentration of the gel-bathing solutions had dramatic effect on the water uptake of the gels. The results show that strong water-absorbing gels can be produced at low ionic strengths and suggest that the negative charge of the muscle proteins is the driving force for water uptake and retention.     

Ca2+ Affects Physicochemical and Conformational Changes of Threadfin Bream Myosin and Actin in a Setting Model

The effect of Ca²⁺ on physicochemical and conformational changes of threadfin bream (TB) myosin and actin during setting at 25 and 40°C was investigated. Ca²⁺ ion at 10 to 100 mM induced the unfolding of myosin and actin as evident by an increase of surface hydrophobicity (S_o ANS) at 40 °C. Total SH groups also decreased with an increased Ca²⁺ concentration, suggesting that Ca²⁺ promoted the formation of disulfide bonds during setting at 40 °C. Both hydrophobic interactions and disulfide linkages were involved in formation of myosin aggregates at 40 °C and were enhanced by addition of 10 to 100 mM Ca²⁺. Myosin Ca‐ATPase activity decreased when Ca²⁺ was greater than 50 mM, indicating conformational changes of myosin head. Circular dichroism spectra demonstrated that Ca²⁺ reduced the α‐helical content of myosin and actin incubated at either 25 or 40 °C. Ca²⁺ induced conformational changes of TB myosin and actin incubated at 40 °C to a greater extent than at 25 °C.