Conformational Change in Actomyosin from Post-spawned Hake Stored on Ice

The changes that lead to a decrease in the viscosity of actomyosin of post-spawned hake stored on ice were investigated. Surface hydro-phobicity of actomyosin from hake increased significantly in the first 3 days of storage. Compared with that stored 3 days, the viscosity of actomyosin from day 0 was greater and its changes suggested greater hydrophylic surface area. Electron microscopy showed changes in the filamentous structure of actomyosin during ice storage. Actomyosin from hake stored in ice is hypothesized to undergo conformational changes including exposure of hydrophobic groups resulting in drastic changes in hydrodynamic properties and a loss of the characteristic arrowhead structure of fresh acotmysin.     

Biochemical and Physicochemical Properties of Actomyosin from Pre- and Post-spawned Hake (Merluccius hubbsi) Stored on Ice

Biochemical and physicochemical properties of natural actomyosin (NAM) from pre- and post-spawned hake stored on ice were studied. At the beginning of storage both reduced viscosity and ATPases activities of NAM from post-spawned hake were about 3 times higher than those of the pre-spawned ones, except for the Mg²⁺-(Ca²⁺)-ATPase. Higher loss of functional components during pre-spawned hake NAM purification was found compared to NAM from post-spawned fish. Reduced viscosity and Mg²⁺-(EGTA)-ATPase activity of NAM from both pre- and post-spawned hake decreased following ice storage. SDS-PAGE patterns of NAM from pre-spawned hake showed an absence of the myosin heavy chain and the presence of a 160 kDa component at zero time of storage. No proteolysis occurred in ice-stored fish caught in both gonadal stages.     

Proteolytic Activity of Muscle in Pre- and Post-Spawning Hake (Merluccius hubbsi Marini) After Frozen Storage

The proteolytic activity of fillets from fresh fish and after frozen storage of hake muscle from pre- and post-spawned fish was investigated. The autolytic activity of fresh muscle extracts from pre-spawned muscle extracts was significantly higher than that of post-spawned, except for pH 3.4 and incubation temperature of 60 °C where no significant difference was found. In both gonadal conditions, the freezing of hake fillets affected the proteolytic activity of crude muscle extracts. After 50 d of frozen storage, the proteolytic activity values of crude muscle extracts remained higher than the fresh values, except for pre-spawned extracts incubated at 37 °C. At longer storage period (110 d), the proteolytic activity continued with similar or higher values compared with those observed for fresh muscle extracts. Densitometric analysis of crude muscle extracts indicated degradation of MHC in fresh and frozen storage at both gonadal conditions under incubation conditions of pH 6.2 and temperatures 37 and 60 °C, pH 8.5 and temperatures 37 and 60 °C, pH 3.4 and temperature 4 °C.     

Biochemical Properties of Natural Actomyosin Extracted from Normal and Pale, Soft, and Exudative Pork Loin After Frozen Storage

ABSTRACT: The studies of natural actomyosin (NAM) extracted from normal and pale, soft, and exudative (PSE) pork longissimus muscle stored at -20°C for up to 6 mo, revealed that the surface hydrophobicity (S₀-ANS) of NAM from PSE pork was significantly ( P < 0.05) higher than that from normal pork indicating greater conformational changes in proteins from PSE meat that resulted in the exposure of hydrophobic aromatic amino acid residues on the surface. Also, the S₀-ANS of NAM was a function of storage time. The equations were as follows: S₀-ANS = 16.9 × storage mo + 123 for normal and S₀-ANS = 17.5 × storage mo + 164 for PSE. NAM from frozen normal pork had lower α-helical content than comparable fresh pork. With extended frozen storage, viscosity of NAM from PSE meat was lower than that from normal pork. The sulfhydryl and disulfide contents were unchanged. Electrophoresis revealed an extra 95 to 100 kDa band from PSE meat NAM, possibly from α-actinin or myosin degradation. Water-binding capacity (WBC) of normal and PSE meat decreased with increasing storage time; however, there were only minor changes in thaw loss. The decrease of WBC of pork meat partially can be explained by the increase of S₀-ANS observed for the NAM. These results suggest that proteins from PSE pork are more susceptible to denaturation and degradation in fresh meat and following frozen storage.     

Structural Properties of Aggregates from Frozen Stored Hake Muscle Proteins

ABSTRACT: Raman spectroscopy and electron microscopy were used to examine the structural properties of sodium dodecyl sulfate-mercaptoethanol-unextractable aggregates formed during the frozen storage of hake muscle. Our results showed that: (a) the unextractable residue consisted of thick filaments, which appeared connected and aggregated, forming a network; (b) the protein backbone adopted a conformational structure rich in β-sheets; and (c) Raman spectroscopy revealed for the 1st time the presence of symmetrical stretching v CH₂ bands, whose frequencies are consistent with the presence of lysine-arginine and/or lysine-glutamine/asparagine bridges in the aggregates.     

Physicochemical Properties of Frozen Red Hake (Urophycis chuss) Mince as Affected by Cryoprotective Ingredients

ABSTRACT: Effects of alginate, iota-carrageenan, soy protein concentrate (SPC), sodium tripolyphosphate (STPP), and sorbitol on physicochemical and sensory properties of red hake mince stored at −20 °C for 17 wk were investigated. The addition of 0.4% alginate, 4% sorbitol, and 0.3% STPP kept the mince from hardening and improved its dispersibility during mixing. This is believed to be a result of reduced protein denaturation as evidenced by higher levels of water, salt, SDS-soluble proteins, and higher free sulfhydryl contents than the untreated control mince, which hardened with compact texture and exhibited considerable syneresis. Alginate appears to be responsible for preventing muscle fiber interaction through electrostatic repulsion and chelating Ca²⁺, thus improving dispersibility. Sorbitol and STPP with or without SPC and iota-carrageenan did not improve the dispersibility.     

冷冻保藏对海鳗肌动球蛋白的影响

采用差示量热扫描(DSC)、傅立叶转换- 红外(FT-TR)等手段研究冷冻保藏(－ 18℃)对海鳗肌动球蛋白(AM)的影响。结果表明,随着冻藏时间的延长,肌动球蛋白发生了聚集而变性。表面疏水性随着冻藏时间的延长而增加,Ca2+-ATP 酶活性下降、巯基和盐溶性蛋白质含量等逐渐降低。冻藏引起了蛋白质的变性。     

Hake Muscle Altered by Frozen Storage as Affected by Added Ingredients

The effect of three ingredients (triphosphate, lecithin and sucrose ester) on functionality and extractability of hake muscle proteins that had been intensely aggregated by frozen storage was investigated. Muscle proteins were extracted in 0.6M NaCl, 2% sodium dodecyl sulfate (SDS) and 2% SDS+5% (β-mercaptoethanol (ME). Treatment with the added ingredients increased the amount of protein extracted when secondary interactions were broken with SDS. The same effect, although less pronounced, was found in the lots treated with triphosphate and sucrose ester when electrostatic bonds were broken with NaCl. The amphipathic ingredients (lecithin and sucrose ester) increased the amount of protein linked by nondisulfide covalent bonds.     

Frozen Hake Fillets Quality as Related to Texture and Viscosity By Mechanical Methods

This work aimed to develop a textural quality classification function for frozen hake fillets using instrumental measurements. Frozen hake fillets were stored to provide a wide range of textures. Raw and cooked fillets were analyzed for texture using Kramer and Warner-Bratzler shear cells and a puncture device. Apparent viscosity, dimethylamine and protein solubility were also measured. Principal Component Analysis indicated three factors accounted for 86.5% of the variance. Four clusters were found, ranging from excellent quality (low texture, high viscosity) to very poor (high texture, low viscosity). Parameters required for classification were viscosity, maximum force from Kramer and maximum force and energy from the puncture test.     

Development of a Quality Index Method for Frozen Hake (M. capensis and M. paradoxus)

A quality index method (QIM) consisting of 9 parameters with a total of 17 sensory points was developed for frozen hake (M. capensis and M. paradoxus). The score sheet was divided into 2 parts. The 1st, including 7 parameters with up to 13 sensory points, was directly related to loss of quality during storage at ?20 °C. Multivariate analysis confirmed the relevance of these parameters for prediction of storage time. The 2nd part contained 2 additional parameters scoring up to 4 sensory points. These parameters are commercially important but not directly linked to storage time.     

Influence of Thermal Treatment on Gelation of Actomyosin from Different Myosystems

We analyzed the influence of temperature and heating time on rheological properties, and types of proteins involved in the gelation process of natural actomyosin from pork, chicken, and hake. At low temperatures (40–50°C) hake gels were stiffer than chicken or pork gels (due to setting); at higher temperatures (60°C), actomyosin from all three formed gels with similar rheological characteristics. Types of protein in the different fractions (analyzed by electrophoresis) were consonant with the rheological behavior of the AM gels for each heat treatment and species.     

Gelling Properties of Actomyosin from Pre- and Post-Spawning Hake (Merluccius hubbsi)

The biochemical properties and the characteristics of heat-induced gelation of natural actomyosin (NAM) from pre- and post-spawning hake were studied. Mg²⁺ ATPase activity, reduced viscosity and myosin/actin mole ratio of NAM from post-spawning fish were higher than those of pre-spawning ones. Gelation of both actomyosin at 10 mg mL^?1 of protein concentration was optimal at 60°C and pH 6.0. The highest rigidity was reached at 0.40M and 0.44M KCl with NAM from pre and post-spawning hake, respectively. Irrespective of heating temperature, ionic strength conditions and at pH range 5.5–7.5, rigidity of post-spawning hake NAM gels was higher than those of pre-spawning fish. Scanning electron micrographs of pre- and post-spawning hake NAM showed “actin-type” and “myosin-type” ultrastructures, respectively.     

Effect of frozen storage of hake,sardine and mixed minces on natural actomyosin extracted in salt solutions

Natural actomyosin extracted in salt solutions from mixtures of hake and sardine minces (3:1; 1:1 and 1:3 w/w) stored frozen for up to 1 year differed in the amount extracted and in the characteristics of the extracts. In the mixed minces the amount of natural actomyosin extracted decreased during frozen storage at a higher rate than that theoretically corresponding to the amount of hake in the mixes. With increasing storage time and proportion of sardine a lower percentage of myosin heavy chain and actin was observed by electrophoresis. An increased size of aggregates was also observed by electrophoresis and transmission electron microscopy. The stability of emulsions was enhanced when aggregates appeared in the extracts. The decrease in the amount of natural actomyosin extracted does not explain the changes observed in the texture of the minces during frozen storage. This may indicate that the size of the aggregates unextractable in salt solutions, independently of the type of bonds that bind the proteins in the aggregates, plays an important role in the textural changes observed. Copyright © 2003 Society of Chemical Industry     

Biochemical and Functional Properties of Myofibrils from Preand Post-Spawned Hake (Merluccius hubbsi Marini) Stored on Ice

Enzymatic activities assayed at beginning of storage in myofibrils from post-spawned hake were 3 X those in myofibrils from pre-spawned hake. Ca²⁺ sensitivity of myofibrils from pre-spawned hake was 40% less than that of myofibrils from post-spawned hake. The profiles of SDS-PAGE gels of pre-spawned myofibrils at beginning of storage showed a partially denatured myosin heavy chain, and polypeptide bands under myosin heavy chain. They probably represent proteolytic fragments produced by degradation of MHC in vivo. No proteolysis was detected in myofibrils during storage. These results help predict functional properties of fish proteins and changes during storage.     

Cryoprotectants Affect Physical Properties of Restructured Trout During Frozen Storage

ABSTRACT: Cryoprotectants other than sucrose/sorbitol were evaluated to reduce the sweetness of restructured trout products during frozen storage. Bacterial growth, lipid oxidation, thaw loss, cook yield, color, and texture were evaluated after 1 d, 3 mo, and 6 mo of storage at-20 °C. Sucrose/sorbitol, trehalose, andtrehalose/sorbitol at 8% equally exhibited a cryoprotective action and minimized thaw loss and texture changes, whereas sodium lactate did not at 2% during 6 mo of frozen storage. Raw, carbohydrate-treated products had less L * values than the control and sodium lactate products. After cooking, no difference in L * value was observed. Cryoprotectants and frozen storage time did not affect bacterial growth and lipid oxidation of raw products.     

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。     

Protein Concentration, pH and Ionic Strength Affect Apparent Viscosity of Actomyosin

Response surface methodology was used to compare effects of NaCl protein concentration, and pH on apparent viscosity (ζapp) of natural actomyosin from hake, pork and chicken muscle. Models for the three species had R² of 0.921, 0.915 and 0.814 (P<0.01) for chicken, pork and hake, respectively. Protein concentration and pH increased qapp, whereas higher ionic strength decreased it and had less influence. Interactions occurred between protein concentration and pH. Models did not reveal inter-species differences (P<0.05). However, analysis of variance of regression coefficients for each variable showed some differences due to pH.     

Comparison of gilthead sea bream (Sparus aurata) and hake (Merluccius merluccius) muscle proteins during iced and frozen storage

Gilthead sea bream (Sparus aurata) and hake (Merluccius merluccius) muscle behave differently during storage, whether in ice or deep frozen. Rapid changes have been observed in the texture of hake muscle during frozen storage, while gilthead sea bream has proved to be more stable. In order to ascertain the role of muscle proteins in the changes observed during storage, parameters related to protein functionality and the properties of extracted natural actomyosin (NAM) were studied initially and during storage in ice or at ?20 °C. Initially, the parameters related to functionality had higher values in hake muscle and extracted NAM than in gilthead sea bream. At the end of iced storage (22 days), less myosin heavy chain (MHC) and actin were extracted from hake, but there was practically no change in gilthead sea bream. This decrease was not accompanied by lower Ca²⁺‐ATPase activity. Freezing produced no drastic changes, with lower values for gilthead sea bream. However, this species was more stable after 1 year, except for the Ca²⁺‐ATPase activity of NAM. This suggests that the changes that hake proteins underwent during storage particularly affected properties related to aggregation, whereas in gilthead sea bream the changes hardly affected the formation of soluble or insoluble aggregates but did affect the active sites of myosin. © 2002 Society of Chemical Industry     

虾夷扇贝贝糜冻藏过程中部分理化性质的变化

研究虾夷扇贝贝糜在不同温度冻藏过程中(－18℃和－35℃)肌动球蛋白的盐溶性、Ca2+-ATPase和Ca2+-Mg2+-ATPase活性及活性巯基与总巯基含量的变化。结果显示：－18℃条件下冻藏5个月时,贝糜蛋白已严重变性,其各指标值分别降至新鲜样品的11.28%、20.31%、30.36%、68.49%和83.67%。－35℃条件下冻藏10个月时,相应指标分别降至新鲜样品的60.01%、45.25%、48.17%、82.80%和88.71%。两种冻藏温度条件下,贝糜的各个指标均随冻藏时间的延长而呈下降趋势,且－35℃冻藏时,各指标值相对于－18℃冻藏时下降幅度较小,表明－35℃冻藏效果优于－18℃冻藏。     

Influence of Gonadal Stage of Hake (Merluccius Hubbsi Marini) on Biochemical Properties of Myofibrils Stored at 2 to 4 °C

ABSTRACT: The influence of the gonadal stage of hake on the biochemical properties of myofibrils stored at 2 to 4 °C was studied. At 0 time and during storage, both Mg²⁺-Ca²⁺-ATPase activity and Ca²⁺ sensitivity of myofibrils from post-spawned hake were significantly higher (p < 0.01) than those of pre-spawned fish. The profiles of SDS-PAGE gels of unstored and stored myofibrils from pre-spawned hake showed a partially denatured myosin heavy chain. The actin-myosin ratio in myofibrils from pre-spawned hake was significantly lower (p < 0.01) than the ratio in post-spawned hake. Irrespective of the gonadal condition of fish, no changes in the myosin-actin ratio of stored myofibrils were observed.