Effect of Pressure Treatment on Actomyosin ATPases from Flying Fish and Sardine Muscles

The effect of pressure treatment (1 atm ～ 5000 atm) on flying fish and sardine actomyosin ATPases was studied from the standpoint of interaction between myosin and actin. The activities of actomyosin Mg-ATPases markedly decreased and those of the EDTA-ATPases rapidly increased with prolonged pressure treatment at 3000 atm and 5000 atm. Changes in activities of F-actin plus pressure-treated myosin Ca-ATPases showed results similar to those of pressure-treated actomyosin Ca-ATPases, while myosin plus pressure-treated F-actin resulted in decreased Mg-ATPase activity and increased EDTA-ATPase activity.     

Temperature-Dependency of Rigor-Mortis of Fish Muscle: Myofibrillar Mg2+-ATPase Activity and Ca2+ Uptake by Sarcoplasmic Reticulum

Myofibrillar Mg²⁺-ATPase activity of plaice and red sea bream increased with increase in reaction temperature and Ca²⁺ concentration. However, temperature decrease tended to lower Ca²⁺ sensitivity of Mg²⁺-ATPase activity. While it was assumed that spiked fish muscle was relaxed and the myofibrillar Ca²⁺ concentration was low, the progress rate of rigor-mortis correlated well with Mg²⁺-ATPase activity in the presence of a few micromolar Ca²⁺ at 0°C. Correspondingly, it was found that Ca²⁺ uptake by plaice sarcoplasmic reticulum decreased with the decrease in reaction temperature. These results strongly suggest the acceleration of fish rigor-mortis at 0°C is due to the increase of Ca²⁺ concentration in myofibrils during storage at this temperature.     

Thermal Transitions of Myosins/Subfragments from Black Marlin (Makaira mazara) Ordinary and Dark Muscles

Thermal transitions were studied by means of differential scanning calorimetry (DSC) and a spectrophotometric method. Three endothermic peaks (40, 43, 50°C: ordinary muscle; 46, 54, 62°C: dark muscle) were observed in DSC thermograms of both myosins. Thermograms of S-l fragments showed one peak (41°C: ordinary muscle, 43°C: dark muscle). But ordinary and dark muscle rod fragments gave two peaks (41, 62°C) and one peak (58°C), respectively. The spectrophotometric results also showed two thermal transitions for both myosins and one transition for their S-1 fragments. However, the rod from ordinary muscle myosin had two transitions, whereas that from dark muscle myosin had one transition.     

Mg2+ Selectively Isolates Gellan Gum from Dairy Products

Gellan gum was precipitated from the papain digest of dairy products by 5% MgSO₄. The precipitate was collected by centrifugation and washed with 2.5% MgSO₄ until the washings were negative to the phenol H_aSO₄ test. It was dispersed with hot 50% H₂SO₄ and the amount in the dispersion determined by the H₂SO₄-thiourea-cyste-ine-HCl reagent. Recovery from chocolate milk, yogurt, evaporated milk, ice cream, cream cheese, process cheese spread, flan and blue cheese (no oil) dressing ranged from 76–95%. Prior removal of fat and starch was unnecessary. Carrageenan, xanthan gum, alginate, pectin and other hydrocolloids did not interfere.     

Thermal Activation of Actomyosin Mg-ATPases from Ordinary and Dark Muscles of Tuna and Sardine

Changes in activities of actomyosin, acto-heavy meromyosin (acto-HMM), and acto-subfragment-I (acto-S-I) ATPases from tuna and sardine due to heat treatment (20°, 25°, 30°, 35°, 40°C) were compared for ordinary muscle and dark muscle. Activation of ordinary muscle actomyosin Mg-ATPases was more than doubled for tuna and tripled for sardine by heating at 35°C, while activation of dark muscle actomyosin was not observed at any temperature. The occurrence of thermal activation corresponded to a rapid loss of the EDTA-ATPase activity. Activation of hybrid actomyosins from dark and ordinary muscles was dependent upon myosin. For acto-HMM and acto-S-I thermal activation was not observed. The role of myosin tail fragments in thermal activation is discussed.     

Effects of Ca++, Mg++ and Na+ on Heat Aggregation of Whey Protein Concentrates

Effect of Ca⁺⁺ on the heat aggregation of whey protein concentrates (WPC) was compared with that of Na⁺ and Mg⁺⁺. On the alkaline side of the isoelectric zone, aggregation of WPC was increased by the addition of CaCl₂, MgCl₂ or NaCl, among which CaCl₂ showed the greatest effect. The denaturation temperature of WPC determined by differential scanning calorimetry significantly decreased in the presence of CaCl₂ or MgCl₂, but increased slightly in the presence of NaCl. In the electrophoretic patterns of heated WPC, the most sensitive protein to Ca⁺⁺ was β-lactoglobulin.     

热处理对扇贝闭壳肌肌动球蛋白生化性质的影响

肌动球蛋白是扇贝闭壳肌中的主要功能蛋白质,对贝类制品的品质起关键的作用。文中以虾夷扇贝(Patinopecten yessoensis)闭壳肌为原料,提取其肌动球蛋白,并考察了热处理温度和时间对肌动球蛋白的α-螺旋含量、表面疏水性、活性-SH含量和浊度的影响。结果表明:在热处理过程中,扇贝闭壳肌肌动球蛋白的α-螺旋发生解旋,肽链展开,疏水性氨基酸残基暴露,蛋白表面疏水性增强;同时热处理使活性-SH氧化生成二硫键,蛋白聚集,使得扇贝闭壳肌肌动球蛋白的浊度增加。加热温度越高,这些指标变化越快。由此推断,扇贝闭壳肌肌动球蛋白在热处理过程中伴随着肽链的解旋和蛋白的无规则聚集。     

5 种淡水鱼肌肉热特性比较研究

为研究不同品种名优淡水鱼冷藏保鲜及热加工的特性,采用差示扫描量热法研究武昌鱼、草鱼、黄颡鱼、鲈鱼和鳜鱼5 种新鲜淡水鱼鱼肉的水分含量、冰点、变性温度、变性热焓和比热容并进行品种间的比较。结果发现：5 种淡水鱼冰点分布在－0.57～－0.1 ℃之间;50 ℃附近热吸收峰起始温度分布在37～41.57 ℃之间,终止温度分布在60.47～62.33 ℃之间;变性热焓在1.680 0～2.499 7 J/g之间;70 ℃附近热吸收峰的起始温度分布在66.33～71.13 ℃之间,终止温度分布在73.60～82.20 ℃之间,变性热焓在0.418 0～0.512 2 J/g之间;鱼肉的比热容在1.658 0～3.862 3 J/（g·K）之间。结果表明：在5 种新鲜淡水鱼中,武昌鱼水分含量和冰点相对较低;草鱼肌球蛋白和鳜鱼肌动蛋白变性温度和变性热焓相对较高,蛋白质稳定性更高;新鲜鱼肉的比热容高于冻结鱼肉,加工后鱼肉的比热容高于未加工鱼肉。     

Fractionating Soybean Storage Proteins Using Ca2+ and NaHSO3

ABSTRACT:  Individual soybean storage proteins have been identified as having nutraceutical properties, especially β-conglycinin. Several methods to fractionate soy proteins on industrial scales have been published, but there are no commercial products of fractionated soy proteins. The present study addresses this problem by using calcium salts to achieve glycinin-rich and β-conglycinin-rich fractions in high yields and purities. A well-known 3-step fractionation procedure that uses SO_2, NaCl, and pH adjustments was evaluated with CaCl₂ as a substitute for NaCl. Calcium was effective in precipitating residual glycinin, after precipitating a glycinin-rich fraction, into an intermediate fraction at 5 to 10 mM CaCl₂ and pH 6.4, eliminating the contaminant glycinin from the β-conglycinin-rich fraction. Purities of 100%β-conglycinin with unique subunit compositions were obtained after prior precipitation of the glycinin-rich and intermediate fractions. The use of 5 mM SO₂ in combination with 5 mM CaCl₂ in a 2-step fractionation procedure produced the highest purities in the glycinin-rich (85.2%) and β-conglycinin-rich (80.9%) fractions. The glycinin in the glycinin-rich fraction had a unique acidic (62.6%) to basic (37.4%) subunit distribution. The β-conglycinin-rich fraction was approximately evenly distributed among the β-conglycinin subunits (30.9%, 35.8%, and 33.3%, for α', α, and β subunits, respectively). Solids yields and protein yields, as well as purities and subunit compositions, were highly affected by pH and SO₂ and CaCl₂ concentrations.     

Acceleration of Postmortem Tenderization in Ovine Carcasses Through Activation of Ca2+ -Dependent Proteases

Infusion of lamb carcasses with 0.3M CaCl₂ resulted in acceleration of postmortem tenderization process. Control and treated animals had similar cathepsin B, H, and L activities. Various control groups had similar CDP-I, -II and inhibitor activities, whereas these were all decreased in CaCl₂ infused animals. Hence, it was concluded that the activation of Ca²⁺ -dependent proteases was responsible for the observed postmortem proteolysis and tenderization and, it seems unlikely that activity of these cathepsins is related to postmortem tenderization under conditions used in this experiment.     

KCI, CaCI2, Na+ Binding, and Salt Taste of Gum Systems

Aqueous nonionic (0.3% w/v) and ionic (0.1% and 0.3% w/v) gum systems containing NaCl, or equal weights of NaCl plus KCl, or NaCl plus CaCl, were examined. At equivalent molar concentrations of added ions, ²³Na NMR transverse relaxation rates (R₂, set^?1) showed an increase in average Na⁺ mobility with the addition of K⁺ or Ca²⁺ to ionic gum systems. Correspondingly, salt taste increased with addition of KCl as determined by Decision Boundary modeling of subject identification data. Viscosity did not affect saltiness. Na⁺ was free to induce salt taste when K⁺ was bound to the gum. Enhancement of salt taste by KCl is due, in part, to competitive binding of Na⁺ and K⁺ in a system.     

Thermal Denaturation and Aggregation of Actomyosin from Atlantic Croaker

The denaturation of croaker actomyosin was studied with respect to the important role of coagulation and gelation phenomena in the manufacture of gel-type meat and fish products. Measurements of turbidity (A₆₀₀), viscosity, calcium ATPase activity, total sulfhydryl groups and protein coagulation of croaker actomyosin solutions during heating at a constant temperature increase of 1°C/min revealed no loss of enzymic activity nor evidence of protein aggregation prior to reaching a temperature of 37–40°C, at which point the protein coagulated with corresponding loss of ATPase activity and sulfhydryl groups and an increase in turbidity. The degree of protein coagulation was highly dependent on the protein concentration. An observed increase in the apparent viscosity over the 30–35°C temperature range was postulated to result from interaction of protein molecules due to noncovalent forces.     

α;2-Macroglobulin Inhibition of Endogenous Proteases in Fish Muscle

Kinetic parameters for α;₂-macroglobulin inhibition of selected proteases (collagenase, cathepsin D, trypsin and chymotrypsin) were determined along with the extent of inhibition of the corresponding fish muscle proteases. Protease inhibition by α;₂-macroglobulin occurred in the presence of large macromolecular substrates but not in the presence of synthetic substrates. The inhibitor remained active at refrigerated temperatures (4–7°C). The α;₂-macroglobulin did not have any inhibitory effects on proteases in intact fish muscle tissue possibly due to lack of penetration of the tissues, but showed various levels of inhibition of proteases in tissue homogenates. Inhibitor concentration of 0.1% per weight of tissue homogenate resulted in about 17% loss of proteolytic activity while 0.4% inhibitor concentration caused complete loss of protease activity.     

Ca2+-Induced Gelation of Pre-heated Whey Protein Isolate

Addition of CaCl₂ to pre-heated whey protein isolate (WPI) suspensions caused an increase in turbidity when pre-heating temperatures were ≥ 64°C. Pre-heating to ≥ 70°C was required for gelation. WPI suspensions which contained CaCl₂ became turbid at 45°C and formed thermally induced gels at 66°C. Thermally and Ca²⁺-induced gels showed significant time/temperature effects but the penetration force values in the Ca²⁺-induced gels were always lower. However, Ca²⁺-induced gels were higher in shear stress at fracture. The Ca²⁺-induced gels had a fine-stranded protein matrix that was more transparent than the thermally induced gels, which showed a particulate microstructure.     

Oxidation of Tryptophan by H2O2 in Model Systems

Degradation reactions of tryptophan (trp) and the dipeptides alanyltryptophan (ala-trp) and phenylalanyltryptophan (phe-trp), induced by H₂O₂, were investigated under different conditions in aqueous systems. Decreases in the content of trp as well as the formation of soluble degradation products were determined. Highest losses of trp were obtained after H₂O₂ treatment at 100°C for 2 hr at pH 8.5. Lowest losses occurred at pH 4.0, 25°C, for 30 min. The destruction of trp in ala-trp was similar, while losses of trp in phe-trp under the same reaction conditions were lower. This was indicative of a negative induction effect of the phenyl ring. The quantity of degradation products showed extensive variations, dependent upon the radical mechanism of the oxidation reaction.     

Dynamic Changes of Headspace Gases in CO2 and N2 Packaged Fresh Beef

Two independent experiments were conducted to examine the effects of initial packaging/product conditions and storage conditions on in-package headspace pressure changes for modified atmosphere packaged beef during 12 hr storage. Headspace-to-meat volume ratio 1.8 to 5.9, surface area 200--800 cm², sample volume 0.22–0.75L, storage at 3–13°C and initial gas composition 20–100% CO₂ balanced with N₂ were studied. Headspace-to-meat volume ratio was the most important packaging parameter, but surface area and meat volume also affected headspace CO₂ changes. Decreased storage temperature reduced CO₂ concentration remaining in headspace. Higher initial CO₂ concentration resulted in greater concentration changes.     

Effects of pH, CaCl2 and Soy Protein on [Ca2+] in Reconstituted Nonfat Dry Milk and on Rennet-Induced Coagulum Properties

Increasing CaCl₂ and lowering pH caused a significant increase in [Ca²⁺] in reconstituted nonfat dry milk (RNDM), while the addition of soy protein caused a significant reduction in [Ca²⁺]. Lowering pH greatly increased rennet-induced coagulum firmness in RNDM and slightly increased it in RNDM-soy protein mixtures. Added CaCl₂ increased coagulum textural parameters and syneresis in both systems. The extent to which these properties were increased was higher in RNDM than in the coagulum containing soy protein depending on the time after rennet addition and the amount of CaCl₂ added. The first increment of CaCl₂ added had the highest effect in improving textural properties and increasing syneresis.     

Conversion of Provitamin D3 to Vitamin D3 by Monochromatic Ultraviolet Rays in Fish Dark Muscle Mince

To determine whether the photochemical conversion of provitamin D₃ is possible in fish meat, the dark muscle of skipjack was irradiated with monochromatic ultraviolet rays (peak, 305 nm; range, 280–360 nm) under various conditions of both time of exposure and strength of light. The vitamin D₃ and provitamin D₃ content were analyzed by HPLC. The vitamin D₃ content increased, and the provitamin D₃ content decreased with 20W light at a distance of 50 cm. The conversion was at a maximum 15 hr after the start of irradiation and about 20% of the provitamin D₃ changed to vitamin D₃