QUANTITATIVE CHANGES IN WHOLE MYOFIBRILS AND MYOFIBRILLAR PROTEINS DURING FROZEN STORAGE OF TRUE COD

The extractability of whole myofibrils from true cod decreased more rapidly during frozen storage at −40°C than did the extractability of the component myofibrillar proteins. There was a 95% decrease in extractable myofibrils after 6 months in storage, but only a 23% decrease in extractable myofibrillar proteins.     

COLLAGEN IN THE TISSUES OF SQUID ILLEX ARGENTINUS AND LOLIGO PATAGONICA - CONTENTS AND SOLUBILITY

Collagen was isolated from the skin, connective tissue sheets, and mantle muscle of squid Illex argentinus and Loligo patagonica, by extracting all soluble noncollagenous material. The tissues and the collagen isolates were characterized by determining the total nitrogen, hydroxyproline, and solubility. The contents of hydroxyproline in the collagen isolate of skin, membranes, and muscle of Illex were 5.3, 8.0, and 4.4% dry matter and of Loligo 6.1, 7.4, and 4.9%, respectively. The collagen contents in these tissues were in Illex 4.9, 7.8, and 1.0; in Loligo 3.4, 4.9, and 0.3%, respectively, in the wet material. Collagen preparations obtained from the skin, membranes, and mantle muscle of Loligo yielded, respectively, 9%, 4%, and 8% collagen soluble in citrate buffer. For Illex squid the solubilities were 41%, 6%, and 21%, respectively.     

PROTEOLYTIC ACTIVITY OF CRUDE ENZYME EXTRACTS OF SQUID ILLEX ARGENTINUS LIVER

The extract obtained from the acetone powder of frozen stored squid liver had optimum proteolytic activity against hemoglobin at pH 2.6 to 4.0. About 90% of the activity at pH 3.0 was inhibited by pepstatin and about 15% was inhibited by phenylmethanesulfonyl fluoride or iodoacetamide. The activity was increased by dithiothreitol and cysteine by about 55 and 40%, respectively. At pH 3 the enzyme extract had a temperature optimum of 45 to 50C; at 5C the activity was about 15% of that at 45 to 50C. At pH 7 the optimum activity was at about 45C. Heating of the extract without substrate at pH 3 and 7 caused a rapid decrease in proteolytic activity above 35 and 30C, respectively. A water extract of the liver was used to treat isolated bovine myofibrils at pH 5.5 and 0C. After 20 h a fragment of slightly lower m.w. than that of the myosin heavy chain was detected. After treatment at pH 7 and 0C, little degradation of the myofibrillar proteins was evident. At 20C the myofibrils were hydrolyzed to several products.     

PHYSICOCHEMICAL AND BIOCHEMICAL CHANGES IN WHOLE LIZARDFISH (SAURIDA MICROPECTORALIS) MUSCLES AND FILLETS DURING FROZEN STORAGE

The physicochemical and biochemical changes in whole lizardfish (Saurida micropectoralis) muscles and its fillets kept in air and under vacuum during frozen storage at ?20C for 24 weeks were investigated. The formaldehyde (FA) and dimethylamine contents increased with a concomitant decrease in trimethylamine‐ N‐oxide (TMAO) content as the storage time increased (P < 0.05). The Ca²⁺–adenosine 5′‐triphosphatase activity continuously decreased with a coincidental decrease in salt‐soluble fraction. The disulfide bonds were increasingly formed throughout the storage (P < 0.05). The surface hydrophobicity increased and reached the maximum at week 12 with a subsequent decrease up to the end of storage. In general, the higher changes were observed in samples kept under vacuum than those kept in air. With the same atmosphere used, the whole fish showed slightly higher changes than the fillets. A marked increase in TMAO demethylase (TMAOase) activities was observed up to 12 weeks, followed by the continuous decrease up to 24 weeks of storage. The produced FA might play an important role in inducing protein denaturation and/or aggregation in lizardfish. The TMAOase activity as well as the FA formation could be reduced to some extent with the removal of internal organs and storage in the presence of oxygen. However, a detrimental effect of oxygen, especially on the promotion of lipid oxidation, would be an obstacle.     

POSTMORTEM CHANGES IN MYOFIBRILLAR PROTEINS OF GOAT SKELETAL MUSCLES

Postmortem changes at 5C in myofibrillar proteins of longissimus dorsi (LD), biceps femoris (BF), semimembranosus (SM) and semitendinosus (ST) muscles and myofibrillar structure of LD muscle of goat were investigated. Muscle samples were immediately collected after killing, and from carcasses stored at 5C for 3, 6, 9, 12 and 20 days. The sodium dodecyl sulfate‐polyacrylamide gel electrophoresis of myofibrils indicated the appearance of a 30 kDa component, depending on the type of the muscles. A new 55 kDa component appeared in BF and SM muscles during postmortem. Titin I and nebulin also disappeared during storage. The disappearance of titin 1 and nebulin and the appearance of a 30 kDa component were confirmed by Western blot analysis. The Transmission Electron Microscopy studies showed that after 3 days postmortem, Z‐disks stayed unaltered. After 6 days postmortem, a little ultrastructural alteration was observed, and at 12 days postmortem a considerable degradation of Z‐disk ultrastructure was shown. The Z‐disk degradation, which results in the fragmentation of myofibrils and the appearance of 30 kDa components, is the major change observed in goat skeletal muscles during postmortem.     

QUALITY CHANGES OF BLUE CRAB (CALLINECTES SAPIDUS) MEAT DURING FROZEN STORAGE

The aim of the investigation was to determine the quality changes of blue crab (Callinectes sapidus) meat during frozen storage. Blue crabs were obtained directly from fishing boats in the Gulf of Antalya, Turkey and immediately transferred to the laboratory alive. Whole crabs were placed into polyethylene polyamide (PE/PA) pouches, shrunk and stored at ?18C for 10 months. The main changes that take place in blue crabmeat were investigated by means of sensory assessments (odor, appearance), chemical analyses (total volatile bases (TVB‐N), trimethylamine (TMA‐N)) and physical measurements (pH). TVB‐N, TMA‐N values and pH were significantly (P < 0.01) different following frozen storage. Moreover, it was observed that the differences in odor values were significant (P < 0.05), while appearance values were not. All of the measurements indicated that blue crabmeat kept its good quality at ?18C for 10 months.     

NUTRITIONAL ESTIMATION OF CHANGES IN MINERAL CONTENT DURING FROZEN STORAGE OF WHITE ASPARAGUS

Nine essential elements (copper, iron, zinc, manganese, calcium, magnesium, sodium potassium and phosphorous) were determined in white asparagus (Asparagus officinalis, L.) by flame atomic absorption spectrophotometry in order to examine the possible variations in mineral content caused by frozen storage at ?18C for 45 and 90 days. Statistically significant differences were determined during frozen storage for all the mineral elements investigated, except for Ca, Mg, Na and P which did not exhibit any significant differences (p>0.05) and, together with Zn, showed no significant modifications under frozen storage. A diminution in Cu, Fe, Mn and K concentrations was observed during the frozen storage time. Statistically significant differences were established between thicknesses of the asparagus spear in the content of Cu, Fe, Zn, Ca, Na and K and it was seen that the thickness of the asparagus did not fit any specific model. Between portions, all the elements studied displayed statistically significant differences in their concentrations, except for Ca and K (p>0.05) and, for all the minerals elements analyzed, the highest levels were found in the apical portion of the asparagus spear, except for Na with a higher content in the basal portion. White asparagus is an adequate food source of mineral elements, except for Na, and frozen storage does not cause any great variations in the percentages of mineral RDAs (Recommended Dietary Allowances) supplied.     

CHANGES IN PROXIMATE COMPOSITION OF THORNBACK RAY (RAJA CLAVATA, L. 1758) SURIMI DURING WASHING AND FROZEN STORAGE

The effects of frozen storage of surimi produced from thornback ray and the washing of mince on the chemical composition were investigated. The crude ash content which was initially found as 1.38% in raw thornback ray decreased approximately 12 and 80% after the first and second washing, respectively. After the third washing, crude ash content increased to 207% of the amount in the second washing because of addition of salt to the last washing water. The crude protein content of mince also decreased approximately to 28 and 20% after the first and second washing, respectively. After the third washing, the decrease in the lipid levels was approximately 30%. At the end of 6 months of frozen storage at − 23.8  ±  2C, dry matter, crude ash and crude protein contents increased in a greater ratio in surimi containing 4% sorbitol, 4% sucrose and 0.3% Na-tripolyphosphate than surimi prepared with 8% sorbitol and 0.3% Na-tripolyphosphate.

PRACTICAL APPLICATIONS

In the present study, the effects of frozen storage of surimi produced from thornback ray and the washing of mince on the chemical composition were investigated. Washing procedure significantly decreased crude ash, crude protein and crude fat content of mince. There were significant differences in moisture, crude ash, and crude protein contents during the 6 months storage period of frozen surimi obtained by using different cryoprotectant mixtures. The folding test scores were highest in fresh surimi and during the first two months of storage. Thornback ray can be used for the production of surimi.     

EFFECT OF IN SITU FORMALDEHYDE PRODUCTION ON SOLUBILITY AND CROSS-LINKING OF PROTEINS OF MINCED RED HAKE MUSCLE DURING FROZEN STORAGE

Three forms of minced red hake muscle representing whole-mince, mince with the low molecular weight fraction removed (reconstituted-minced) and mince with low and high molecular weight soluble fractions removed (washed-minced) were stored frozen with added Fe⁺² and ascorbate (trimethylamine oxide (TMAO) was added when necessary). The production of DMA and free formaldehyde was measured as were the decreases in water-soluble and salt-soluble proteins and TMAO as a function of increasing concentrations of ascorbate. Dimethylamine (DMA) production and loss of overall protein extractability were greatest in minced muscle, followed by reconstituted-minced muscle, and least in washed-minced muscle. The minced muscle lost water-soluble proteins, however, less rapidly than the reconstituted-minced muscle. The percentage of formaldehyde that was bound was highest in the minced, next in the reconstituted-minced and least in the washed-minced muscle. This supports earlier data and indicates that formaldehyde reacts with both the small molecular weight fraction and the water-soluble proteins as well as the contractile proteins. Loss of protein extractability in all samples appeared to be heavily dependent on hydrophobic interactions. Disulfide interactions appeared to occur to some extent in the reconstituted-minced and washed-minced muscle but were a minor factor with the minced muscle samples. Surface hydrophobicity of the proteins was inversely related to their extractability. In the sample of minced muscle with the highest concentration of added ascorbate where approximately 79% of the proteins became inextractable, some 2% of the muscle proteins were covalently linked in polymers with molecular weights greater than that of the myosin heavy chains. The data indicate that cross-linking of protein components occurs as well as hydrolysis of a considerable amount of the protein.