Synthesis and degradation of adenosine triphosphate in cod (Gadus morhua) at subzero temperatures

This study has demonstrated that the extraction step is very important when analysing ATP and its degradation products. An important factor is whether the sample is fresh, frozen or thawed when homogenised since thawing of the sample will lead to rapid loss of ATP. During frozen storage it was found that ATP in cod (Gadus morhua) was stable at −40 °C in small samples for at least 12 weeks. At −20 °C it was found that ATP content increases initially and thereafter falls. It was demonstrated that degradation of ATP in small samples occurs faster at 0 °C than at −2 and −5 °C. Furthermore, it was found that in whole cod ATP could be synthesised at a significant rate at −7 °C. © 1999 Society of Chemical Industry     

The effects of various salt concentrations during brine curing of cod (Gadus morhua)

The method used for salting of cod (Gadus morhua) is believed to influence the quality and characteristics of the final product. In recent years an initial brine salting for 1–4 days has preceded dry salting; this increases both the weight yield and quality of the final product. After removal from the brine, dry salting is followed by packaging and storage. The effect of the salt concentration in the brine has been a matter of controversy, with some indication that higher weight yield and quality may be obtained by using lower salt concentrations than by using a fully saturated brine solution. Therefore to test this hypothesis, the effect of different brine salting methods was studied; traditional brine salting, maintaining a constant brine concentration and increasing the salt concentration gradually during brining. The results indicated that the effect on weight yield, chemical composition and water holding capacity of the salted or rehydrated cod were not significant. Altering salt concentration of the brine, by adding salt during brining, did not result in any significant improvements in weight yield, either after the salting process or after the rehydration. The overall quality was increased by using a lower salt concentration of 16° Bau compared with 20 and 24° Bau.     

Influence of collagenous material during frozen storage when added to minced cod (Gadus morhua)

The influence of added purified collagenous material from skin on minced fish during frozen storage is studied with a view to improving the sensory quality of the frozen product. The base material used was minced cod muscle, thawed and fresh, to which collagenous material was added in varying proportions. Following purification, the collagenous material was prepared in four different ways (frozen, pre-solubilized/frozen, freeze-dried and pre-solubilized/freeze-dried) for stabilization before addition to the fish mince. This collagenous material was found to have a positive effect on water-holding ability and to improve the sensory properties of the fish mince during frozen storage.     

Acid-induced gelation of natural actomyosin from Atlantic cod (Gadus morhua) and burbot (Lota lota)

The acid-induced gelation of natural actomyosin (NAM) from burbot (Lota lota) and Atlantic cod (Gardus morhua) added with d-gluconic acid-δ-lactone (GDL) during incubation at room temperature (22–23 °C) for 48 h was investigated. During acidification, pH values of both NAMs reached 4.6 within 48 h. Both NAMs underwent aggregation during acidification as evidenced by increases in turbidity and particle size, especially after 6 h of incubation. The decreases in Ca²⁺-ATPase activity and salt solubility of both NAMs were observed during incubation. Decreases in total sulphydryl content with the concomitant increases in disulphide bond content of NAM from both species were also noticeable. Additionally, surface hydrophobicity of NAM increased, suggesting the conformational changes in NAM induced by acidification. The storage modulus (G′) values increased with increasing incubation time and G′ development was greater in Atlantic cod NAM, compared with burbot NAM. Differential scanning calorimetry (DSC) revealed that T_max and enthalpy of myosin peak shifted to the lower values and endothermic peak of actin completely disappeared. In general, gel development was more pronounced in Atlantic cod NAM, compared with the burbot counterpart. As visualised by transmission electron microscopy, network strands of aggregates from Atlantic cod were finer and more uniform than those of the burbot counterpart. Acid-induced gelation of NAM from both fish species therefore involved both denaturation and aggregation processes. However, gelation varied with fish species and had an impact on the resulting gels.     

Lipid and autoxidative changes in cold stored cod (Gadus morhua)

A study of lipid changes during the frozen storage of cod confirms that the major change is that of lipolysis. Oxidation is extremely slow and occurs primarily in the phospholipid fraction. Nevertheless, sufficient oxidation takes place during cold storage to reduce the acceptability of the fish primarily through the production of hept-cis-4-enal. The mechanism whereby hept-cis-4-enal occurs is discussed.     

Proteolytic activity in cod (Gadus morhua) muscle during salt curing

The proteolytic activity of alkaline and acidic proteases in muscle from cod (Gadus morhua) was determined during salt curing. Proteolytic activity was determined for cod muscle that was either ice-stored or frozen-stored before it was subjected to three different salt treatments. The activity of the proteases chymotrypsin, trypsin, collagenase, elastase and cathepsin B/L was determined by the use of different fluorogenic substrates, while the total activity of acidic proteases was determined using haemoglobin as a substrate. The results indicated that the activity of the chymotrypsin, trypsin, collagenase and elastase was stimulated with increasing salt concentration, but seemed to decline again as the salt curing proceeded. Haemoglobin-hydrolysing activities, however, seemed to decrease with increasing concentration of salt in the muscle tissue.     

Microbial and sensory changes during refrigerated storage of desalted cod (Gadus morhua) preserved by combined methods

Water blanching and the use of additives (potassium sorbate and citric acid) combined with different types of packaging (air, vacuum "VP" and modified atmosphere packaging "MAP": 60% CO(2), 30% N(2) and 10% O(2)), were studied as new methods of preservation of chilled desalted cod. Microbial counts and total volatile basic nitrogen (TVB-N) analyses were carried out during a period of 42 days on all samples stored at 4 degrees C. No Aeromonas or sulphite-reducing Clostridium were isolated from any of the analysed samples. The lowest microbial counts of mesophilic, psychrotrophic, Pseudomonas, moulds and yeasts, were found in samples with additives in all kinds of packaging. These samples in VP or MAP maintained an excellent microbial quality throughout the 42 days of storage, with mesophilic and psychrotrophic counts always below 4 log CFU/g. Counts of the four microorganisms above-mentioned in blanched samples packaged with air, exceeded 5 log CFU/g on days 21-28, so it became necessary to use VP or MAP to maintain these microorganisms at an acceptable level for the entire storage period. TVB-N contents were low in samples with additives, regardless of the kind of packaging, as well as in blanched samples packaged in VP and MAP, never reaching 25 mg/100 g. Since there were no significant differences either in microbial growth or in TVB-N between samples in VP and MAP, a sensory analysis was performed only in desalted cod submitted to the two treatments (blanching and additives) combined with VP, both in raw and cooked samples. The results of this analysis showed that the addition of potassium sorbate and citric acid did not alter the typical organoleptic features of desalted cod. The sensory characteristics of both blanched samples and those with additives in VP showed no change during the period of the study.     

Quantitative and qualitative changes in added phosphates in cod (Gadus morhua) during salting,storage and rehydration

Phosphate blend can be used in salted cod processing to improve yields, water holding capacity and appearance of the final product. However, added phosphates are gradually degraded during processing and storage, leading to changes in functional properties of phosphates. The objective of the study was to monitor the quantitative and qualitative changes in added phosphates in cod during salting, storage and rehydration using ion chromatography (IC) and spectrophotometric analysis. The phosphates diffused into the fish muscle during brining but the phosphate content (mg P₂O₅/g sample) decreased again as liquid drained away from the muscle in the following dry salting step. Changes during six months storage of the dry salted products were minor. Further losses were observed during rehydration where the phosphates were washed out to levels lower than in the raw material.The advantage of the IC method was the ability to separate and determine different soluble phosphate species in the fish muscle. The IC results showed that pyrophosphate (P₂O₇) and triphosphate (P₃O₁₀) were partly degraded into orthophosphate (PO₄) during the storage period. Lower values were obtained for the total phosphate content by IC than with the spectrophotometric method, which explained by difference is sample preparation.     

超高压对鳙鱼肌动球蛋白物化特性的影响

研究不同超高压条件（100、300、500 MPa,保压15、30、45 min）下鳙鱼肌动球蛋白物化特性的改变。结果表明,随着压力和时间的增加,鳙鱼肌动球蛋白的溶解度降低,浊度基本呈上升的趋势,表明肌动球蛋白发生了聚集变性。SDS-PAGE显示超高压引起肌动球蛋白发生交联聚集形成了大分子物质。超高压处理后鳙鱼的Ca²⁺-ATP酶(Ca²⁺-ATPase)活性消失,表明肌动球蛋白发生了变性。随着压力的增加和加压时间的延长,肌动球蛋白的表面疏水性增加,表明超高压使蛋白氨基酸的疏水性基团暴露。随着压力的增大,肌动球蛋白的总巯基含量减少,二硫键含量升高,表明肌动球蛋白中的巯基发生氧化,形成了二硫键。鳙鱼肌动球蛋白上述物化特性的改变证明超高压诱导使其构象发生了改变。      

The effect of slaughter method on the quality of rainbow trout (Salmo gairdneri) during storage on ice

Rainbow trout ( Salmo gairdneri ) were stunned by electrocution, exposure to elevated concentrations of carbon dioxide and by a blow to the head, and subsequently bled. The fish were stored ungutted in ice for up to 15 days, and the changes in the textural properties of the flesh of the fish were measured by a sensory panel and with a texturometer. Parallel changes in the concentrations of spoilage-related biochemical constituents, in water-holding capacity and in bacterial counts were also determined. Slaughter by electrocution and by carbon dioxide narcotization led to a greater initial production of lactic acid and a slightly reduced pH, compared with slaughter by a blow to the head. No significant differences were found in the values of the other indices of quality, either immediately after death or during post-mortem storage.     

Precursors of the volatile sulphides in spoiling north sea cod (Gadus morhua)

Quantitative analyses of the free sulphur amino acids, cyst(e)ine, methionine, taurine and glutathione in the muscle of spoiling chill-stored cod, showed that the concentrations of cyst(e)ine and methionine increased until the twelfth day of storage before decreasing rapidly. Only the disappearance of methionine and cyst(e)ine could be correlated with the production of volatile sulphides in the flesh. Taurine, the principal sulphur amino acid present appeared resistant to both microbial and autolytic enzymes, whilst glutathione disappeared before the onset of active bacterial spoilage. The importance of these compounds as odour and/or flavour precursors in white fish is dssed.     

Freezing and frozen storage of actomyosin from different species

A comparative study was made of the influence of freezing (–24°C) and frozen storage (–12°C) on the functional properties (viscosity, solubility) and physico-chemical characteristics (aliphatic and aromatic hydrophobicity, ATPase activity) of actomyosin (AM) from myosystems (chicken and hake) of differing freezing and frozen stability. The difference in functional behaviour between chicken and hake AM as a consequence of freezing and frozen storage suggests that, for hake AM, denaturation and aggregation occur essentially through direct aggregation of AM molecules to produce AM aggregates, whereas in chicken proteins, AM first dissociates into myosin and actin to produce myosin and myosin-actin aggregates.     

Biochemical and physicochemical properties of actomyosin from pre- and post-spawned flounder (Paralichtys patagonicus) stored on ice

The biochemical and physicochemical properties of actomyosin from pre- and post-spawned flounder stored on ice were studied. Irrespective of the gonadal condition of the fish, a gradual decrease in reduced viscosity, Mg²⁺ATPase and Mg²⁺Ca²⁺ATPase activities of actomyosin was observed. A similar decrease in the Mg²⁺ EGTA ATPase activity of actomyosin from post-spawned flounder was also observed. The decrease in enzymatic activities was accompanied by an increase in surface hydrophobicity of the protein. No signs of proteolysis of the major components of the actomyosin complex were detected. The relative percentage of myosin decreased and that of actin increased in actomyosin from pre- and post-spawned flounder stored on ice. These changes occur earlier in actomyosin from prespawned flounder. The results of this paper indicate that actomyosin from flounder denatured during fish storage on ice and suggest that this denaturation is due to structural and conformational changes in myosin which led to aggregation of this protein.     

Properties of Trypsin from the Pyloric Ceca of Atlantic Cod (Gadus morhua)

Trypsin (EC 3.4.21.4) was isolated from the pyloric ceca of Atlantic cod and purified to homogeneity by affinity chromatography. The enzyme catalyzed the hydrolysis of benzoyl arginine p-nitroanilide (BAPA, pH 8.2 and 25°C) such that V_max was 250 BAPA units per micromole trypsin and K_m was 1.48 mM. For the hydrolysis of tosyl arginine methyl ester (TAME, pH 8.1 and 25°C), V_max was 18.2 × 10³ TAME units/micromole trypsin, and K_m 0.22 mM. The pH and temperature optima with BAPA substrate were 7.5 and 40°C, respectively. Atlantic cod trypsin was most active and stable at alkaline pH. The enzyme was heat labile, losing more than 50% of its activity after incubation at 50°C for 30 min. Amino acid analysis of Atlantic cod trypsin revealed that the enzyme was rich in residues such as serine, glycine, glutamate and aspartate, but poor in basic amino acid residues compared to trypsins from warm blooded animals.     

提取温度与提取时间对真鳕鱼骨明胶理化性质的影响

以真鳕鱼骨为原料,对其明胶的理化性质进行了研究。提取温度分别设置为45和70℃,不同提取温度的提取时间分别设置为4和8h。热水抽提后冷冻干燥,得到4种明胶样品,并对其化学组成及理化性质进行研究。结果表明,随着提取温度的升高和提取时间的延长,样品凝胶强度、乳化性和乳化稳定性随之下降,而其浊度和起泡性能则有所上升。红外光谱分析显示,70℃提取制备的明胶样品其酰胺I吸收峰强度要弱于45℃提取的样品,这说明提取温度的升高会导致样品分子结构无序程度的增加。在扫描电镜观察下,高温制备的凝胶结构排列无规则且具有大量孔洞。      

Thermal properties and heat-induced aggregation of natural actomyosin extracted from goatfish (Mulloidichthys martinicus) muscle as influenced by iced storage

Thermal properties and aggregation of natural actomyosin (NAM) extracted from fresh and 9 days ice-stored goatfish were comparatively studied. Myosin of fresh goatfish had the higher thermal stability than that of ice-stored counterpart as indicated by the higher maximum transition temperature (T_max). Additionally, the thermal inactivation rate constant (K_D) of Ca²⁺-ATPase in NAM from fresh goatfish was lower than that of ice-stored counterpart when incubated at the temperature range of 20–40 °C, indicating the lower thermal stability of the latter NAM. NAM from fresh goatfish exhibited the higher turbidity, surface hydrophobicity and disulfide bond formation than did NAM of iced-stored sample when heated at temperature from 35 to 75 °C, suggesting the higher extent of aggregation of the former. However, goatfish NAM showed the lower extent of heat-induced aggregation than did bigeye snapper NAM. As visualized by transmission electron microscopy, network strands of aggregates from bigeye snapper NAM were finer and more uniform than those from goatfish. NAM from goatfish stored in ice showed the lower extent of heat-induced aggregation than did NAM from fresh counterpart. Therefore, heat-induced aggregation of goatfish muscle proteins was governed by freshness.