Maria E. Paredi

Postmortem Changes in the Adductor Muscle of Scallop (Chlamys tehuelchus) in Chilled and Frozen Storage

Abstract The effects of freezing and frozen storage on the biochemical properties of scallop adductor muscles stored at 2-4EC were investigated. Glycogen content fell 40% in the first 12 hr of chilled storage and decreased slowly thereafter. ATP content increased for a short time after death and then decreased slowly. Glycogen and ATP degradation was accompanied by a decrease in both pH and 260/250 absorbance ratio of scallop muscle extracts. A significant increase (p < 0.05) in the hypoxanthine (Hx) content was also observed in chilled stored adductor muscles. Adductor muscles showed a significant decrease (p < 0.05) in the 260/250 absorbance ratio of extracts and an increase in the Hx level after freezing. An increase in Hx content was observed during frozen storage of adductor muscles frozen immediately after processing. Expressible juice increased with freezing and frozen storage of the muscles. The results shown in this paper indicate a rapid loss of quality in scallop adductor muscles during storage at 2-4. Freezing and frozen storage enhanced the quality deterioration of the muscles.

Post mortem changes in glycogen, ATP, hypoxanthine and 260250 absorbance ratio in extracts of adductor muscles from Aulacomya ater ater (Molina) at different biological conditions

1. 1. Post mortem changes in glycogen, ATP, hypoxanthine levels and 260250 absorbance ratio in extracts of adductor muscles from Aulacomya in different biological condition, were investigated. 2. 2. Glycogen and ATP levels were higher in muscles from specimens in good biological condition. The rate of decrease of both glycogen and ATP was not dependent on the biological condition of Aulacomya. 3. 3. The 260250 absorbance ratio values in muscle extracts from specimens in poor biological condition were significantly lower (P < 0.05 at 0 and 24 hr; P < 0.01 at 48, 72, 96 and 120 hr of storage) than in those from specimens in good condition. 4. 4. Irrespective of the biological condition, hypoxanthine levels remained unchanged for 72 hr of storage and increased thereafter.

A chemical assessment of freshness in stored adductor muscle from scallops

The postmortem catabolism of adenosine triphosphate (ATP) in cold-stored adductor muscles from scallops (Zygochlamys patagonica) was studied. Changes in the pH of stored muscles were also studied. The ATP content increased for a short time after death and afterwards decreased up to 24 hr of storage. Thereafter, the nucleotide level remained unchanged up to the end of storage. The ADP content slightly decreased up to 48 hr and after that remained unchanged. The AMP slowly accumulated to around 15% of the total nucleotide concentration when the ATP decreased. Small amounts of IMP were detected in all samples. Conversely, adenosine (Ado) was not detected. Inosine (HxR) increased slightly after 48 hr of storage and hypoxanthine (Hx) increased significantly after 24 hr. The 260/250 absorbance ratio of muscle extracts and the pH of stored muscles fell sharply up to 24 hr and then decreased slowly up to the end of storage. The hypoxanthine concentration and the 260/250 absorbance ratio could be reliable indicators of storage age in adductor muscles from scallops.

Thermal behavior of myofibrillar proteins from the adductor muscles of scallops: a differential scanning calorimetric study (DSC)

Muscles and different proteins obtained from scallops (Chlamys tehuelchus and Zygochlamys patagonica) were analyzed. In both species of scallop, the thermograms of striated and smooth muscles showed two endothermic transitions. The Tmax values corresponding to striated and smooth muscles from C. tehuelchus were 53.2, 79.0oC and 52.7, 78.0 oC, respectively. The Tmax corresponding to striated and smooth muscles of Z. patagonica were 55.0, 79.2oC and 54.7, 78.7oC, respectively. No significant differences were observed between the thermal transitions of myofibrils and actomyosin of both types of muscles from both species of scallop. Irrespective of the species, the thermal stability decreased when the pH of the muscles was increased. The increase in ionic strength greatly affected Tmax, the DH total and the DH of the first transition. A significant decrease in DH total and DH corresponding to both transitions was observed, particularly in the striated muscles of Zygochlamys patagonica. These results indicate a major sensitivity of the adductor muscles of Zygochlamys to changes in the chemical environment.

Physicochemical and Biochemical Properties of Actomyosin from Striated Adductor Muscles of Scallop (Zygochlamys patagonica) Stored at 2-4°C

ABSTRACT Actomyosin was partially purified from cold stored adductor muscles. During two days of storage the reduced viscosity and Mg2+-ATPase activity decreased about 30 and 50%, respectively. These changes were due neither to actomyosin dissociation nor to fragmentation of the major component of the complex. A gradual decrease in both parameters was observed thereafter up to the end of storage. Relative percentage of myosin and myosin/actin ratio significantly decreased (p < 0.01) and that of actin increased (p < 0.01) after the second day. These changes were related to a decrease in myosin heavy chain and could explain the slow decrease in reduced viscosity and ATPase activity after the second day. Expressible moisture accompanied the protein denaturation during storage.

Influence of the Capture Method on the Physicochemical and Functional Properties of Myofibrillar Proteins of Fin from Frozen, Stored Squid (Illex argentinus)

ABSTRACT The physicochemical and functional properties of actomyosin from fins of frozen, stored squid caught either by jigging machines (AME1) or by trawling (AME2) were investigated. At time 0 SDS-PAGE, 10% of AMEl and AME2 showed the characteristic polypeptide bands of myofibrillar proteins and two components of 155 kDa and 55 kDa. Both the degradation of the myosin heavy chain and an increase in the 155-kDa component occurred earlier in AME2. Irrespective of the capture method used, no significant changes in protein solubility and a decrease (P < 0.05) in reduced viscosity were observed in both AMEl and AME2. Surface hydrophobicity (SoANS) of AMEl increased (P < 0.05) during the first month of storage and remained unchanged thereafter. The SoANS of AME2 was unchanged. The initial value of SoANS of AME2 was higher than that of AMEl. The emulsion activity index and the emulsion stability of AME2 increased (P < 0.05) during the first month of storage, whereas the emulsion activity index and emulsion stability of AMEl remained unchanged during the frozen storage period. These results indicate that the capture method influences the rate of autolysis and the functional properties of myofibrillar proteins of fin from frozen, stored squid.