Scallop Muscle Research Articles

COMPARISON OF DOMOIC ACID CONCENTRATION IN KING SCALLOPS, PECTEN MAXIMUS FROM SEABED AND SUSPENDED CULTURE SYSTEMS

Abstract Domoic acid (DA) the toxin responsible for amnesic shellfish poisoning (ASP) has proven problematic for king scallop Pecten maximus fisheries and aquaculture in Ireland. Toxin concentration in hepatopancreas of individual scallops and composite samples of gonad and adductor muscle of scallops suspended from a submerged longline, 2 m beneath the water surface and on a seabed site, 12–15 m beneath the suspended scallops were monitored from February 2003 to February 2004 at an aquaculture site in Clew Bay, Ireland. DA concentration in hepatopancreas of scallops from the seabed and longline peaked in April 2003, individual concentrations reaching 1037.1 μg·g−1 and 1212.6 μg·g−1 respectively. No statistically significant differences were exhibited between DA concentration in hepatopancreas of seabed and longline scallops except on 1 of the 10 sampling occasions. Slow depuration of DA toxin from hepatopancreas occurred from April 2003 to June 2003 and the concentration remained relatively stable from J...

Calcium regulates scallop muscle by changing myosin flexibility

Muscle myosins are molecular motors that convert the chemical free energy available from ATP hydrolysis into mechanical displacement of actin filaments, bringing about muscle contraction. Myosin cross-bridges exert force on actin filaments during a cycle of attached and detached states that are coupled to each round of ATP hydrolysis. Contraction and ATPase activity of the striated adductor muscle of scallop is controlled by calcium ion binding to myosin. This mechanism of the so-called "thick filament regulation" is quite different to vertebrate striated muscle which is switched on and off via "thin filament regulation" whereby calcium ions bind to regulatory proteins associated with the actin filaments. We have used an optically based single molecule technique to measure the angular disposition adopted by the two myosin heads whilst bound to actin in the presence and absence of calcium ions. This has allowed us to directly observe the movement of individual myosin heads in aqueous solution at room temperature in real time. We address the issue of how scallop striated muscle myosin might be regulated by calcium and have interpreted our results in terms of the structures of smooth muscle myosin that also exhibit thick filament regulation.

Effects of Rearing Conditions on Oxidation-Reduction Potential Change and ATP Degradation of Live and Dead Scallops (Pecten yessonensis)

The possibility of using oxidation-reduction potential (ORP) as freshness index for scallops (Pecten yessoensis) was investigated. Scallops were divided into three groups and subjected to different rearing conditions : rearing at higher-than-optimum temperatures (at 15-18°C) with aeration, rearing in seawater but without aeration, or removal from seawater and live storage in air at 10°C. The ORP and pH of the adductor muscle of live scallops during rearing were measured at regular time intervals for 24h. Then the adductor muscle in each sample was removed from the valves and stored at 0°C. Changes in ORP, K value, ATP degradation, and D-lactic acid content during storage were monitored. The results showed that live scallops had a reductive characteristic in terms of ORP, which varied between 0.16-0.19V and a pH range from 6.2-7.0. However, ORP generally increased towards a more oxidative state under all the rearing conditions tested. ORP also increased with K value and approached its maximum when K value exceeded 25%. Regardless of rearing conditions, the ORP range that indicates the reasonable freshness of scallops for sashimi was 0.166-0.215V. The postmortem ATP content was highest in the scallops reared in seawater while the fastest ATP degradation observed in the live scallops stored in air. D-lactic acid accumulation during storage was lowest in the samples reared in seawater with aeration. The absence of oxygen supply during rearing promotes enhanced ATP degradation and D-lactic accumulation.

Structural Evidence for Non-canonical Binding of Ca2+ to a Canonical EF-hand of a Conventional Myosin

We have previously identified a single inhibitory Ca2+-binding site in the first EF-hand of the essential light chain of Physarum conventional myosin (Farkas, L., Malnasi-Csizmadia, A., Nakamura, A., Kohama, K., and Nyitray, L. (2003) J. Biol. Chem. 278, 27399-27405). As a general rule, conformation of the EF-hand-containing domains in the calmodulin family is "closed" in the absence and "open" in the presence of bound cations; a notable exception is the unusual Ca2+-bound closed domain in the essential light chain of the Ca2+-activated scallop muscle myosin. Here we have reported the 1.8 A resolution structure of the regulatory domain (RD) of Physarum myosin II in which Ca2+ is bound to a canonical EF-hand that is also in a closed state. The 12th position of the EF-hand loop, which normally provides a bidentate ligand for Ca2+ in the open state, is too far in the structure to participate in coordination of the ion. The structure includes a second Ca2+ that only mediates crystal contacts. To reveal the mechanism behind the regulatory effect of Ca2+, we compared conformational flexibilities of the liganded and unliganded RD. Our working hypothesis, i.e. the modulatory effect of Ca2+ on conformational flexibility of RD, is in line with the observed suppression of hydrogen-deuterium exchange rate in the Ca2+-bound form, as well as with results of molecular dynamics calculations. Based on this evidence, we concluded that Ca2+-induced change in structural dynamics of RD is a major factor in Ca2+-mediated regulation of Physarum myosin II activity.

Effects of microbial growth on the preservation of scallop muscle in a vital state

Adductor muscles dissected from live scallop Patinopecten yessoensis were stored in oxygenated artificial sea water. The initial muscle adenosine triphosphate (ATP) level, approximately 7.5 μmol/g, remained longer at 5°C than at either 0 or 10°C. The pH of sea water, decreased continuously and the consumption of dissolved oxygen increased even after muscle ATP was almost exhausted. The number of viable microbes, measured as colony-forming units (c.f.u.) in the muscle, increased to reach a plateau at approximately 107–108 c.f.u./g, while muscle ATP remained at high levels. After this time, muscle ATP sharply decreased. Antibiotics or sorbate added into the oxygenated sea water effectively inhibited both the growth of microbes and the decrease in the pH of sea water. Under these conditions, the retention period of muscle ATP was greatly extended. Thus, it seems most likely that scallop adductor muscle cells are suffocated by the limitation of oxygen supply caused by aerobic microbes grown on the surface of muscle tissue.

Physico-chemical and functional properties of myofibrillar proteins from different species of molluscs

The physico-chemical and functional properties of myofibrillar proteins from scallop ( Zygochlamys patagonica), bivalve molluscs ( Aulacomya ater ater), and squid ( Illex argentinus) were investigated. Actomyosins were studied by SDS-PAGE, Mg 2+-(Ca 2+-dependent) ATPase activity, reduced viscosity, and surface hydrophobicity determinations. The emulsion capacity (EC) of both soluble protein extracts and actomyosins was also determined. Densitometric analysis of the SDS-PAGE 10% gels showed that in comparison with the actomyosin from striated muscle of scallop, the actomyosins of Aulacomya, squid, and smooth plus striated muscle of scallop have a significant higher relative percentage of paramyosin and a lower relative percentage of myosin. The reduced viscosity of actomyosin from both striated and smooth plus striated adductor muscle of scallop was significantly lower than that of squid and Aulacomya. No significant differences were observed in the enzymatic activity of the actomyosins analysed. Surface hydrophobicity and EC of actomyosin from striated muscle of Aulacomya were lower than those corresponding to actomyosin of the other species. The highest values of EC were observed in extracts of squid mantle. In addition, the EC of the extracts was significantly higher than the EC of their respective actomyosins.

Benefits of closed area protection for a population of scallops

Despite the current interest in using closed areas for fisheries management, few studies have actually examined the benefits for invertebrate fisheries such as scallops. This study details the dynamics of a population of great scallops Pecten maximus (L.), within a closed area and an adjacent fished area off the Isle of Man, over a 14 yr period (1989 to 2003). Scallop densities were very low in both areas when the closed area was set up, but increased at an accelerated rate over time within the closed area. Scallop densities also increased on the adjacent fishing ground, but not to the same extent. Consequently, the density of scallops above the minimum legal landing size (110 mm SL) was more than 7 times higher in the closed area than in the fished area by 2003. There was also a shift towards much older and larger scallops in the closed area and, correspondingly, lower estimates of total mortality. Experimental dredging of 2 plots within the closed area confirmed that fishing drove these differences in population dynamics and structure. These patterns of scallop density, age and size structure resulted in the exploitable biomass (adductor muscle and gonad) of scallops being nearly 11 times higher in the closed area than in the fished area by 2003, and the reproductive biomass was 12.5 times higher. This is significant for fisheries management because the build up of high densities of large P. maximus individuals enhanced local reproductive potential and therefore the likelihood of export of larvae to the surrounding fishing grounds. Along with these direct benefits of closed area protection, juvenile scallops had higher survival and individual growth rates in the closed area, apparently in response to reduced fishing disturbance. Although juvenile scallops are not subject to direct removal by fishing, protection during this critical phase therefore appeared to assist the recovery of the closed area population. In summary, this study joins a growing number indicating that the use of closed areas offers a range of benefits over more traditional methods of managing fisheries. Fisheries for relatively sedentary and long-lived species such as P. maximus appear to be particularly suitable for this type of management.

Two Novel Thio-Arsenosugars in Scallops Identified with HPLC - ICPMS and HPLC - ESMS

Environmental Context. A new group of arsenic compounds, namely thio-arsenosugars, has recently been discovered in some marine samples, including seafood products. We do not yet understand how these arsenic compounds are produced by living organisms, nor do we know their implications for human health. Their unusual chromatographic properties are the reason that they are difficult to detect by existing methods. We present a new method for finding these thio-arsenosugars, and we also report two new thio-arsenosugars. Abstract. Two new thio-arsenosugars were identified in aqueous and methanol extracts from the gonad and the muscle of the great scallop by using high-performance liquid chromatography–inductively coupled plasma mass spectrometry (HPLC–ICPMS) and HPLC–electrospray ionization mass spectrometry (ESMS). The gonad of the scallops contained thio-arsenosugar–sulfonate [0.067 mg (As) kg−1; dry mass ± 3.7%] and thio-arsenosugar–sulfate [0.267 mg (As) kg−1; dry mass ± 1.2%]. The muscle also contained both thio-arsenosugar–sulfonate [0.030 mg (As) kg−1; dry mass ± 2.6%] and thio-arsenosugar–sulfate [0.200 mg (As) kg−1; dry mass ± 2.6%]. Methanol increased the extraction efficiency threefold for the two thio-arsenosugars as compared to water. Fresh and freeze-dried samples from both parts of the scallop showed no significant difference with respect to the concentration of the two thio-arsenosugars. In order to confirm the presence of the thio-arsenosugars, a new method for their determination with HPLC–ESMS was developed. Under optimized conditions [Hamilton PRP-X100; 150 by 1.0 mm; 20 mM NH4HCO3 with 55% (v/v) methanol at pH 10.3] we succeeded in determining the pseudomolecular ions of thio-arsenosugar–glycerol, thio-arsenosugar–phosphate, thio-arsenosugar–sulfonate, and thio-arsenosugar–sulfate at concentrations less than 5 µg (As) dm−3 in standard solutions and real samples.

Cooperative effect of relative humidity and glucose concentration on improved solubility of shellfish muscle protein by the Maillard reaction

: Myofibrillar protein (Mf) of scallop muscle was reacted with various concentrations of glucose at 50°C and different relative humidities (RH 5–95%), and the change in solubility of Mf in low- and high-ionic-strength media was investigated. When the lyophilized Mf-glucose mixture (Mf : glucose = 1 : 18) was reacted at RH 5% and RH 35%, the solubility of Mf in 0.1 M NaCl increased markedly and almost equaled the solubility in 0.5 M NaCl. However, the improvement of the solubility in 0.1 M NaCl diminished at RH 65% and almost disappeared at RH 95%. The suppression of the solubility at RH 65% and RH 95% was mainly caused by the loss of the intrinsic salt-solubility of myosin, regardless of the degree of the Maillard reaction. The loss of the salt-solubility of myosin during the reaction with glucose was effectively suppressed by controlling the relative humidity at less than 35% and increasing the glucose concentration to more than 0.08 mol/g H2O. These results indicate that the improvement of the solubility of Mf in a low-ionic-strength medium by the Maillard reaction with glucose is closely related to the salt-solubility of myosin, and the relative humidity and the glucose concentration are important factors in suppressing myosin heat denaturation.

Binding of glycolytic enzymes in adductor muscle of Iceland scallop Chlamys islandica is altered by reproductive status

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 268:141-149 (2004) - doi:10.3354/meps268141 Binding of glycolytic enzymes in adductor muscle of Iceland scallop Chlamys islandica is altered by reproductive status Katherina Brokordt1,2, Helga Guderley1,* 1Département de Biologie and Quebec-Océan (Le Groupe Interinstitutionnel de Recherches Océanographique du Québec), Université Laval, Quebec City, Quebec G1K 7P4, Canada 2Present address: Departamento de Ecología, Pontificia Universidad Católica de Chile, Alameda 340, Santiago, Chile *Corresponding author. Email: helga.guderley@bio.ulaval.ca ABSTRACT: During gonad growth and spawning by the Iceland scallop Chlamys islandica, muscle glycogen levels decrease in parallel with the activities of several glycolytic enzymes, including glycogen phosphorylase (GP), pyruvate kinase (PK) and octopine dehydrogenase (ODH), even though muscle protein concentrations remain unchanged. These parallel changes suggested that binding of glycolytic enzymes to glycogen influences their activities. Decreases in the amount of glycogen in the muscle would reduce the number of binding sites for these enzymes and decrease measurable activities or accelerate their degradation. We tested this hypothesis by evaluating the impact of reproductive status on the activity and intracellular distribution of GP, PK and ODH in adductor muscle of inactive Iceland scallops. Glycogen, but not protein, levels decreased markedly during gonad maturation and spawning. GP and ODH activities decreased in parallel with glycogen, while PK activity did not change. GP showed the highest binding both to glycogen (9 to 19.5% of activity bound) and to the particulate fraction (37 to 53%). As the units of GP bound per mg glycogen did not change with maturation and spawning, the total units of GP bound to glycogen decreased with maturation and spawning in females and males. For the enzymes measured, more activity was bound to the particulate fraction than to glycogen. The units of ODH bound to glycogen and to the particulate fraction decreased during maturation and spawning in females. Within a reproductive state and within a cellular fraction, the relative activities of the glycolytic enzymes (ODH/GP and PK/GP) were quite similar, suggesting conservation of the stoichiometry of glycolytic enzyme capacities in a given cellular fraction. Enzyme-binding to the particulate fraction of scallop adductor muscle shifts with long-term physiological change. Our results are compatible with the interpretation that the intracellular localization of enzymes influences their rates of synthesis and degradation. KEY WORDS: Enzyme-binding · Glycogen · Glycogen particles · Glycolytic enzymes · Scallops · Reproduction · Reproductive cost · Chlamys islandica Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 268. Online publication date: March 09, 2004 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2004 Inter-Research.

BIOCHEMICAL PROPERTIES OF ACTOMYOSIN AND EXPRESSIBLE MOISTURE OF FROZEN STORED ADDUCTOR MUSCLES OF PATAGONIAN SCALLOP (ZYGOCHLAMYS PATAGONICA)

The biochemical properties of actomyosin and the expressible moisture of frozen stored adductor muscles of scallop (Zygochlamys patagonica) were investigated. After freezing (zero time of storage) both the enzymatic activity and the reduced viscosity of actomyosin remained unchanged with respect to those corresponding to actomyosin from unfrozen muscles. Both parameters significantly decreased (P 0.01) were observed in the relative percentages of myosin, actin, and in the myosin/actin ratio up to 4 months of storage. Thereafter myosin significantly decreased (P < 0.01) up to the end of storage. The decrease in the biochemical properties of actomyosin was accompanied by a loss in the water holding capacity of the muscles.

Thermal gelation of salted paste from scallop striated adductor muscle

: Salted muscle paste containing 60–100 mg protein/g paste and 0.5 M NaCl at pH 7.0 was prepared from fresh scallop striated adductor muscle and its heat-induced gelling characteristics were examined in order to produce invertebrate kamaboko-like foods. The heating of the paste to 90°C formed a weak gel. The setting effect on the gelation of the paste was introduced by incubation at 25°C for up to 4 h and was greatly strengthened by the addition of 10 mM Ca2+ due to the activation of an endogenous transglutaminase that preferentially cross-linked myosin heavy chains, but not actin and paramyosin. As a result, the texture of the gel produced by a two-step heating method was almost the same as that of a commercial fish kamaboko. It was also observed that the thermal gelation profile of scallop muscle paste was similar to that of fish myosin, rather than that of actomyosin, by means of a dynamic rheological measurement. Paramyosin also contributed to a characteristic increase in the G′ (storage modulus) value over the thermal gelation process and raised the G′′ (loss modulus) value around 65°C. The G′′ increase resulted in a slightly rigid texture of heated scallop gel. Isolated paramyosin demonstrated a characteristic thermal gelation profile showing a two-step increase in G′ and G′′ values, independent of Ca2+ concentration. The higher NaCl and protein concentrations were required to produce stronger and more elastic gels.

Interactions of the two heads of scallop (Argopecten irradians) heavy meromyosin with actin: influence of calcium and nucleotides.

We recently proposed a co-operative model for the influence of calcium and ADP on scallop ( Argopecten irradians ) muscle heavy meromyosin (scHMM), in which scHMM exists in two conformations (designated 'off' and 'on'), and calcium and ADP are allosteric effectors of the equilibrium between the off and on conformations [Nyitrai, Szent-Gyorgyi and Geeves (2002) Biochem. J. 365, 19-30]. Here we examine the influence of actin on scHMM. In the absence of nucleotide, both heads of scHMM bind very tightly to actin, independent of the presence of calcium. In the absence of calcium, ADP dissociates scHMM from actin completely, and little evidence of ternary complex formation can be found (actin affinity >20 microM). The off state of scHMM therefore does not interact with actin. In the presence of calcium, ADP and actin lower each other's affinity for scHMM by 30-50-fold, although both heads remain strongly attached to actin (actin affinity 0.17 microM). Detailed analysis suggests that the second head contributes far more to the overall binding energy than is the case for mammalian skeletal muscle HMM. This is consistent with a different stereochemical relationship between the two heads in scallop and mammalian HMM molecules.

Food safety implications of the distribution of azaspiracids in the tissue compartments of scallops (Pecten maximus)

Azaspiracids, a new class of shellfish toxins, have been implicated in several recent incidents of human intoxications following the consumption of mussels (Mytilus edulis). A study was undertaken to examine the distribution of azaspiracid poisoning (AZP) toxins in scallops (Pecten maximus) and individual shellfish were dissected into five tissue fractions for the determination of toxin composition. Separation of the predominant azaspiracids, AZA1-3, was achieved using reversed-phase liquid chromatography with detection by positive electrospray multiple tandem mass spectrometry. The AZP toxin composition was determined in the adductor muscle (meat), gonad (roe), hepatopancreas (digestive glands), mantle and gill of scallops. Substantial differences in the AZP toxin levels between tissue compartments were observed and toxins were concentrated predominantly, about 85%, in the hepatopancreas. There was also a significant variation in the total toxin levels between individual scallops from the same sample batch and the RSD was 60% (n = 9). Interestingly, although all three AZP toxins were present in phytoplankton and mussels, AZA3 was not detected in the scallop samples examined. It was concluded that to improve food safety, only the adductor muscle and gonad of scallops should be permitted for sale to the public.

NMR structural study of troponin C C-terminal domain complexed with troponin I fragment from Akazara scallop.

Scallop muscle has been demonstrated to possess both myosin-linked and actin-linked systems1-3 (Fig. 1), even though molluscan muscles were known to be regulated only by the myosin-linked regulatory system mediated through Ca2+-binding to myosin light chains4-6. Recently, the physiological significance of the coexistence of the two systems in scallop adductor muscle was investigated using CDTA-treated scallop myofibrils1. Actin-linked (Troponin-linked) system has been well known as the regulatory system in the muscle contraction of vertebrate striated muscles7. It is regulated by troponin in a Ca2+ dependent manner. Troponin contains three distinct components, i.e., a Ca2+ binding component (TnC), an inhibitory component troponin I (Tnl), and a tropomyosin-binding component troponin T (TnT). TnC contains two independent Ca2+ binding domains, each of which consists of two EF-hand motifs8. Vertebrate striated muscle TnCs bind three or four Ca2+ ions in a molecule and act as the Ca2+ sensor of muscle contraction associated with the binding and release of one or two Ca2+ ion(s) in the N-terminal domain9, 10, 11. The N-terminal domain has, thus, been called the regulatory domain and contains one or two low affinity Ca2+-binding sites (Sites I and II)12. On the other hand, the C-terminal domain has been called the structural domain and contains two high-affinity sites (Sites III and IV). They also bind Mg2+ and are called as Ca2+/Mg2+ sites.

ENVIRONMENTAL MANAGEMENT IN THE BASS STRAIT NORTHERN FIELDS 3D SEISMIC SURVEY

The Northern Fields 3D seismic survey in Bass Strait was a large survey of 4,000 km2, carried out between the months of October 2001 to July 2002. The program attracted interest from various groups regarding the possible impacts of the survey on fisheries and cetaceans (whales and dolphins).The survey was the first to operate in eastern Bass Strait after the Environment Australia Guidelines for Minimising Acoustic Disturbance to Whales, came into force, in September 2001.The Northern Fields program was conducted in accordance with a method statement for the mitigation of impacts to cetaceans, developed by Esso to meet the requirements of Australian environmental legislation and acknowledge environmental best practice. The program utilised teams of three whale watchers who maintained a continuous rotational watch of two observers throughout the day. This proved to be a reliable element of the program and was one of several key learnings that may assist other companies in developing comprehensive and cost-effective mitigation strategies for future surveys.Concerns raised by the fishing industry and some conservation groups about the potentially detrimental impact of seismic sources on commercial scallop larvae and fish populations were effectively addressed by avoiding commercial scallop areas during spawning periods. A controlled, in-situ study of scallops exposed to the acoustic source completed during the program conclusively demonstrated no significant variation in scallop mortality or muscle strength.Observation data collected during this survey provided a sample of the cetacean population in Eastern Bass Strait during a large part of the annual migration cycle. These observations, which may be relevant to the planning and execution of future seismic surveys in the region, are discussed. The findings also provide valuable information for continued research into the distribution and conservation of whales and dolphins in Bass Strait.

Coordination of the two heads of myosin during muscle contraction.

We have used luminescence resonance energy transfer between regulatory light chains (RLC) to detect structural changes within the dimeric myosin molecule in contracting muscle fibers. Fully functional scallop muscle fibers were prepared such that each myosin molecule contained a terbium-labeled (luminescent donor) RLC on one head and a rhodamine-labeled (acceptor) RLC on the other. Time-resolved luminescence energy transfer between the two heads increased upon the transition from relaxation (ATP) to contraction (ATP plus Ca) and increased further in rigor (no ATP). Combined with experiments on mutant RLCs labeled specifically at other sites, these results support a model in which the force-generating weak-to-strong transition causes one myosin LC domain to tilt through a 30 degrees angle toward the other, thus acting as a coordinated lever arm.

Molecular Dynamics Simulation of Site-Directed Spin Labeling: Experimental Validation in Muscle Fibers

We have developed a computational molecular dynamics technique to simulate the motions of spin labels bound to the regulatory domain of scallop myosin. These calculations were then directly compared with site-directed spin labeling experimental results obtained by preparing seven single-cysteine mutants of the smooth muscle (chicken gizzard) myosin regulatory light chain and performing electron paramagnetic resonance experiments on these spin-labeled regulatory light chains in functional scallop muscle fibers. We determined molecular dynamics simulation conditions necessary for obtaining a convergent orientational trajectory of the spin label, and from these trajectories we then calculated correlation times, orientational distributions, and order parameters. Simulated order parameters closely match those determined experimentally, validating our molecular dynamics modeling technique, and demonstrating our ability to predict preferred sites for labeling by computer simulation. In several cases, more than one rotational mode was observed within the 14-ns trajectory, suggesting that the spin label samples several local energy minima. This study uses molecular dynamics simulations of an experimental system to explore and enhance the site-directed spin labeling technique.

Volatile Compounds Recovered by Solid‐Phase Microextraction from Fresh Adductor Muscle and Total Lipids of Sea Scallop (Placopecten magellanicus) from Georges Bank (Nova Scotia)

ABSTRACT: The volatile compounds of the adductor muscle of the sea scallop Placopecten magellanicus were recovered by solid‐phase microextraction using both polydimethylsiloxane and polydimethylsiloxane/divinylbenzene‐coated fibers. Gas chromatography/mass spectrometry revealed the presence of 34 compounds, including 7 long‐chain alcohols, 6 aldehydes, and 6 ketones. Two sulfur‐containing volatiles were also identified. Six aldehydes, 3 alkanes, and 3 alcohols were tentatively identified from the total lipid fraction. The profiles obtained with the 2 fibers was different because of polarity and polymer differences. The fatty‐acid compositions of the total lipid and of the phospholipid class were determined. Phospholipids with 95% of the total lipid are potentially a source of fatty‐acid oxidation products.

Thermal denaturation of myofibrillar proteins of striated and smooth adductor muscles of scallop (Zygochlamys patagonica). A differential scanning calorimetric study.

Denaturation of proteins from striated and smooth muscles of scallop (Zygochlamys patagonica) was studied with differential scanning calorimetry (DSC) by monitoring maximum temperatures of transition and denaturation enthalpies. DSC thermograms of both striated and smooth whole muscles showed two transitions: Tmax 55.0, 79.2 degrees C; and Tmax 54.7, 78.7 degrees C, respectively. The DSC thermograms of myofibrils and actomyosin were similar to those corresponding to their respective whole muscles. As pH and ionic strength increased, the thermal stability of whole muscles decreased. The pH increase (5.0-8.0) significantly (p < 0.01) decreased the denaturation enthalpies (deltaH total, deltaH peakI, and deltaH peakII) of whole striated muscles. A significant decrease (p < 0.05) in the deltaH total and the deltaH peakI was also observed in DSC thermograms of smooth muscles at pH 8.0. Denaturation enthalpies (deltaH total and deltaH peakI) significantly decreased (p < 0.01) when the ionic strength increased from 0.05 to 0.5 in both types of muscles. Striated muscles were more affected than smooth muscles by changes in the chemical environment.