Characterisation of myoglobin from sardine (Sardinella gibbosa) dark muscle

Myoglobin from the dark muscle of sardine (Sardinella gibbosa) with the molecular weight of 15.3 kDa was isolated and characterised. The different myoglobin derivatives exhibited varying thermal unfolding characteristics. Deoxymyoglobin showed a single distinct endothermic peak at 74.5 °C, whereas two transition temperatures were noticeable for oxymyoglobin (64.5 and 78.4 °C) and metmyoglobin (59.0 and 76.0 °C). The spectrum of deoxymyoglobin and oxymyoglobin had absorption bands at 739, 630, 575, 500 and 405 nm, while the disappearance of the peak at 575 nm was found in the spectrum of metmyoglobin. The soret peak of all derivatives was noticeable at 405 nm. The autoxidation of myoglobin became greater at very acidic or alkaline conditions as evidenced by the formation of metmyoglobin, the changes in tryptophan fluorescence intensity as well as the disappearance of soret absorption. The higher temperature, particularly above 40 °C, and the longer incubation time induced the higher metmyoglobin formation as well as the conformational changes.     

Structural changes in sardine (Sardina pilchardus) muscle during iced storage: Investigation by DRIFT spectroscopy

Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy has been used for the first time to evaluate the postmortem changes in structure of components from sardine muscle in relation to quality loss. Sardines (Sardina pilchardus) were stored in ice for up to thirteen days. The spectroscopic study was focussed on the structural changes produced on the lipids and proteins.     

Effect of chitosan edible coating on the quality of double filleted Indian oil sardine (Sardinella longiceps) during chilled storage

The effectiveness of edible chitosan coating (1 and 2%) on the quality changes of Indian oil sardine (Sardinella longiceps) in iced condition was assessed. The chitosan prepared in the study had higher degree of deacetylation (83%). Edible coating with chitosan was effective in inhibiting bacterial growth and reduced the formation of volatile bases and oxidation products significantly. The muscle pH increased with the storage period for all the samples. On the day of sensory rejection for untreated samples, the formation of total volatile base nitrogen and trimethylamine nitrogen was less by 14.9 and 26.1% for 1% chitosan treated sardine and 32.7 and 49% for 2% chitosan treated samples respectively. The chitosan coating improved the water holding capacity, drip loss and textural properties significantly compared to untreated sample. The eating quality was maintained up to ∼8 and 10 days for 1 and 2% chitosan treated sardine respectively, compared to only 5 days for untreated samples.     

Pink discoloration and quality changes of squid (Loligo formosana) during iced storage

Pink discoloration and quality changes of squid (6-10 squids/kg) with and without deskinning during iced storage at different squid/ice ratios (1:1 and 1:2, w/w) for 16 days were investigated. The increases in a* and b*-values of squid mantle were observed with increasing storage time (p < 0.05), indicating the formation of pink color on the mantle. The increase was more pronounced in squid without deskinning with a squid/ice ratio of 1:1 (p < 0.05). No changes in a*-value were observed in deskinned squid throughout the storage, regardless of squid/ice ratio (p > 0.05). However, the slight increase in b*-value was found in the squid with deskinning during the storage. Psychrophilic bacteria counts of squid increased continuously as the storage time increased. Coincidental increases in total volatile base (TVB), trimethylamine (TMA) and ammonia contents were observed during the storage. The rates of increase were greater in the samples with a squid/ice ratio of 1:1 than those found in the samples kept in ice with a squid/ice ratio of 1:2. Pink discoloration, psychrophilic bacteria count, TVB and TMA contents were much lowered when the squid without deskinning was treated with 0.1 g/100 mL sodium azide (NaN₃) prior to storage, suggesting that microbial growth was associated with those changes. Therefore, deskinning together with icing using a sufficient amount of ice as well as the use of safe antimicrobial agent could be a means to lower the pink discoloration and retard the losses in quality of squid stored in ice.     

Effects of the addition of spleen of skipjack tuna (Katsuwonus pelamis) on the liquefaction and characteristics of fish sauce made from sardine (Sardinella gibbosa)

The effects of the addition of spleen of skipjack tuna (Katsuwonus pelamis), at levels of 0%, 10% and 20%, on the liquefaction and characteristics of fish sauce produced from the sardine (Sardinella gibbosa) with different salt concentrations (15%, 20% and 25%) were monitored during fermentation for 180 days. Fish sauces prepared from sardine with spleen supplementation contained greater total nitrogen, amino nitrogen, formaldehyde nitrogen and ammonia nitrogen than did those without spleen addition throughout the fermentation. The rate of liquefaction was dependent on the amount of spleen added. Reduction of salt content accelerated the hydrolysis of fish protein during fermentation. The liquefaction rate of the lower salt-treated samples was generally faster than were those treated with higher salt content. Among all treatments, sardine with 25% spleen and 15% salt added exhibited the greatest protein hydrolysis, particularly at the early stages, suggesting the combined effects of autolysis and spleen proteinase. The greater liquefaction was coincidental with the development of browning as well as the increase in redness of liquid formed. An acceptability test revealed that the samples were different in colour, aroma, taste and overall acceptance (p < 0.05). Fish sauce samples containing 20% salt, without and with 10% spleen addition had similar acceptabilities to commercial fish sauce. Therefore, the addition of spleen, as well as salt reduction, can accelerate the liquefaction of sardine for fish sauce production.     

Vibrational spectroscopic analysis of hake (Merluccius merluccius L.) lipids during frozen storage

Vibrational spectroscopy (mid FTIR and FT-Raman) was used to monitor lipids extracted from hake fillets during frozen storage. Kramer shear resistance was used as a marker of texture changes and lipid damage was also investigated by following the development of conjugated dienes and free fatty acids by spectrophotometric methods. Results show that the intensity of the free fatty acid carboxylic ν(CO) band measured by ATR-FTIR spectroscopy can be used for monitoring the development of lipid hydrolysis in hake lipids. Changes in the Raman ν(CC) stretching region (1658 cm⁻¹ band), partially attributed to conjugated dienes development, were the only observed spectroscopic alterations related to lipid oxidation of hake lipids during frozen storage at −10 °C. The high correlation of free fatty acids with instrumental texture and the disappearance of the ν_as(PO₂⁻) band are consistent with membrane lipid hydrolysis being one of the factors directly related with toughening of lean fish flesh.     

Changes in physico-chemical properties and gel-forming ability of lizardfish (Saurida tumbil) during post-mortem storage in ice

Changes in physico-chemical properties and gel-forming ability of lizardfish muscle (Saurida tumbil), stored in ice, were investigated up to 15 days. Heading and eviscerating, prior to iced storage, retarded myosin heavy chain degradation and formaldehyde formation. Additionally, denaturation of myosin and troponin was slightly impeded as monitored by the lower decrease in Ca²⁺-ATPase and lower increase in Mg²⁺–EGTA-ATPase, respectively. Gel-forming ability of surimi, prepared under different setting and/or heating conditions, decreased as storage time increased (P<0.05). However, superior breaking force and deformation of surimi gel, from headed/eviscerated fish, to that from whole fish was observed throughout the storage. Whiteness of surimi gel from headed/eviscerated fish was much higher than that from whole fish, especially when the storage time increased. Therefore, storage time and pretreatment were found to be crucial factors, determining the changes in physico-chemical properties and gel-forming ability of lizardfish during iced storage.     

Characteristics and gel properties of muscles from sardine (Sardinella gibbosa) and mackerel (Rastrelliger kanagurta) caught in Thailand

Dark and ordinary muscle from sardine (Sardinella gibbosa) and mackerel (Rastrelliger kanagurta) were characterized. Lipid and myoglobin contents were higher in dark muscle than in ordinary muscle of both species, and higher contents of both constituents were found in sardine muscle than mackerel muscle. The extractable myoglobin contents in sardine dark and ordinary muscle were 14.27 and 2.18 mg/g, while mackerel dark and ordinary muscle contained 4.88 and 1.37 mg myoglobin/g sample, respectively. Alkali-soluble protein and stroma contents were greater in dark muscle than ordinary muscle. Mackerel muscle comprised a higher content of non-protein nitrogenous compounds than sardine muscle. The effect of washing conditions on the myoglobin extractability was investigated. A large amount of myoglobin was removed in the first washing cycle and only a small amount was removed in the second washing cycle. The highest removal of myoglobin from sardine (32.10–46.55%) and from mackerel muscle (103.20–313.66%) was achieved when the mince was washed with 0.2% NaCl and 0.5% NaCl, respectively. Washing media showed the marked effect on the color, expressible drip and textural properties of sardine and mackerel mince gels. The breaking force of directly heated and kamaboko gels from both sardine and mackerel mince washed with NaCl solution was higher than that of unwashed mince and water washed mince. However, no difference in deformation was observed. Washing also resulted in increased whiteness and lowered expressible moisture. In general, sardine surimi showed the superior gel-forming ability and whiteness to mackerel surimi.     

Effect of bleeding on lipid oxidation and quality changes of Asian seabass (Lates calcarifer) muscle during iced storage

Lipid oxidation, microbial load and fishy odour development in the slices of bled and un-bled Asian seabass during 15 days of iced storage were comparatively investigated. Bled samples showed the lower peroxide value (PV) and thiobarbituric acid-reactive substances (TBARS) throughout the storage period (P < 0.05). Bleeding effectively lowered the total haem and non-haem iron contents in Asian seabass slices. The release of non-haem iron was pronounced in the un-bled samples during the storage. Solid phase micro-extraction coupled with gas chromatography and mass spectrometric (SPME-GCMS) analysis revealed that the bled samples stored in ice for 15 days contained the lower amount of volatile compounds. Heptanal, the major volatile compound detected in the un-bled samples, was four-fold higher than that of bled counterparts. The contents of aldehydic compounds, including hexanal, octanal, nonanal and nonenal were also higher in the former. Bled samples had the lower fishy odour, compared with the un-bled counterparts during storage (P < 0.05). The lower total viable counts (TVC) and psychrophilic bacterial counts (PBC) were observed in the bled samples, in comparison with the un-bled ones (P < 0.05). Thus, bleeding was a potential means in retarding lipid oxidation, fishy odour development, and microbial growth of Asian seabass slices during storage in ice.     

Lipid oxidation and fishy odour development in protein hydrolysate from Nile tilapia (Oreochromis niloticus) muscle as affected by freshness and antioxidants

Lipid oxidation and fishy odour development in protein hydrolysate from fresh and ice-stored Nile tilapia (Oreochromis niloticus) were investigated. During iced storage of 18 days, heme iron content decreased with a concomitant increase in non-heme iron content (P < 0.05). Peroxide value (PV) and thiobarbituric acid reactive substances (TBARS) values increased. Phospholipid content decreased with a corresponding increase in free fatty acid content. The results suggested that lipid hydrolysis and oxidation took place during storage. When protein hydrolysates were produced from fresh and 18 days ice-stored Nile tilapia muscle, higher lipid oxidation and fishy odour/flavour along with higher amount volatile compounds were obtained in hydrolysate for unfresh sample (P < 0.05). However, the addition of mixed antioxidants during hydrolysis process markedly lowered lipid oxidation, b^∗, ΔC^∗, ΔE^∗ values, fishy odour/flavour as well as the formation of volatile compounds in the resulting hydrolysates prepared from both fresh and unfresh samples. Therefore, hydrolysate from Nile tilapia muscle with reduced fishy odour and lighter colour could be prepared by using fresh fish and incorporation of mixed antioxidants during hydrolysis.     

Quality loss during the frozen storage of sea salmon (Pseudopercis semifasciata). Effect of rosemary (Rosmarinus officinalis L.) extract

Lipid and protein alterations during the frozen storage (−11 °C) were analyzed in minced sea salmon muscles to evaluate the effect of the application of rosemary extract (200 and 500 mg/kg). Lipid oxidation reached maximum TBA values between 3 and 4 months of storage in untreated muscles. The main polyunsaturated fatty acids affected were 22:6-ω3, 22:5-ω3 and 20:4-ω6 acids. Phospholipid hydrolysis was also detected. Rosemary extract reduced lipid oxidation for 6 months (500 mg/kg, muscle with 10.8 g/kg lipids) or 3 months (200 mg/kg, muscle with 5.3 g/kg lipids). Myofibrillar proteins showed a decrease of extractability (80%) after 2 months of storage. Myosin denaturation was evident by DSC at 3 months, while myosin and actin peaks disappeared at 6 months. A diminution of extractable polypeptides of high molecular weight was recorded by SDS-PAGE after 3 months. The available lysine content suffered a reduction starting at 3 months of storage, suggesting some interaction involving the free amino groups of lysine. Fluorescent compounds' determination did not show changes due to the interaction of lipid oxidation products and proteins, while protein alterations could not be reduced by the rosemary extract. Furthermore, the antioxidant reduced the loss of red color in the muscle.     

Changes in heme proteins and lipids associated with off-odour of seabass (Lates calcarifer) and red tilapia (Oreochromis mossambicus × O. niloticus) during iced storage

Changes in heme proteins and lipids associated with off-odour development in seabass (Lates calcarifer) and red tilapia (Oreochromis mossambicus × O. niloticus) muscles during 15 days of iced storage were studied. Fresh seabass contained the higher contents of myoglobin and heme iron, compared with red tilapia (P < 0.05). An increase in metmyoglobin proportion was observed during storage. After 3 days of storage, a decreased heme iron content and a concomitant increase in non-heme iron content were noticeable in both fish (p < 0.05). Oxidation of myoglobin and released non-heme iron were associated with lipid oxidation. The increases in oxidation products and free fatty acids were observed as the storage time progressed. Fishy and rancid odours were detected at day 6 of storage for both fish and a higher intensity was found in seabass muscle. Thus, the off-odour in fish muscle was mostly governed by lipid oxidation and species specific.     

Changes in composition of lipids,free amino acids and organic acids in rice-bran-fermented- sardine (Etrumeus teres) during processing and subsequent storage

Changes in composition of lipids, free amino acids and organic acids in rice-bran-fermented sardine—one of the traditional marine products of Japan—were investigated. The moisture content decreased rapidly during pre-curing and then slowly during rice bran fermentation. The salt content of the finished product was about 234 g kg⁻¹ on a dry weight basis. The pH decreased from 6.1 in the raw sardine to 5.3 in the finished product. Total volatile basic nitrogen increased up to 1.0 g kg⁻¹ after 2 months of rice bran fermentation and then remained almost unchanged. Most free amino acids except histidine and taurine increased during rice bran fermentation. The histamine content increased to 0.75 g kg⁻¹ at 2 months of rice bran fermentation and subsequently decreased gradually. Certain polyamines also accumulated on relatively lower levels. Lactic acid (8.14 g kg⁻¹ at 2 months of rice bran fermentation) was a prominent organic acid produced during processing. Considerable decompositions of triglyceride and phospholipids occurred accompanied by production and accumulation of a correspondingly high concentration of free fatty acids. The peroxide value and the amount of thiobarbituric acid reactive substances in the extracted total lipids decreased gradually during rice bran fermentation. It was concluded that lipid oxidation was restricted during rice bran fermentation although remarkable proteolysis occurred. The present traditional manufacturing process seems to be applicable to the technology of processing and subsequent preservation of fish products in the developing countries.     

Changes in lipids and their contribution to the taste of migaki-nishin (dried herring fillet) during drying

This study was conducted to investigate the changes in lipids and their effect on the taste of migaki-nishin during drying. Lipid was extracted from herring fillets following different drying stages to measure the degree of lipid oxidation and changes in lipid composition, and fatty acid profile. Peroxide value, carbonyl value and acid value of the lipids were significantly increased (P < 0.05) during the drying period. Marked increase in free fatty acids, with decreases in triglyceride and phospholipid content were observed in proportion to drying time and this result suggested that hydrolysis was induced by lipases and phospholipases. The decreases in polyunsaturated fatty acids (PUFAs), especially eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), were observed in the total lipids and phospholipid fraction. In addition, significant increase in PUFAs especially DHA was found in the free fatty acid fraction. Sensory evaluation showed that an addition of DHA to mentsuyu significantly (P < 0.05) enhances the intensities of thickness, mouthfulness and continuity. These results suggest that during drying period lipid oxidation was not only occurred but also lipolysis predominantly released DHA, which might have a contribution to kokumi enhancement of migaki-nishin.     

Enzymatic oxidative activity in sardine (Sardina pilchardus) and herring (Clupea harengus) during chilling and correlation with quality

 Enzymatic oxidative activity of two fatty fish species, sardine (Sardina pilchardus) and herring (Clupea harengus), was studied during chilled storage. Lipoxygenase enzyme activity was isolated and tested by measuring the hydroperoxides produced after induced oxidation of arachidonic and docosahexaenoic fatty acids. The most abundant degradation products of the hydroperoxides formed were 12- and 16-hydroxy acids which were detected by HPLC. Lipoxygenases were concentrated in the skin tissue of fish, and were active for up to 48 h of chilled storage. The pro-oxidative activity due to haem proteins continued for longer than that due to lipoxygenase. Trends of fluorescent formation resulting from interaction between oxidation products and biological amino constituents were compared with the pro-oxidative activities to establish correlations with quality loss during chilling. Received: 29 December 1998 / Revised version: 14 March 1999     

Endogenous proteinases in true sardine (Sardinops melanostictus)

Characterisation of the autolytic profile of true sardine (Sardinops melanostictus) indicated the involvement of heat-activated proteinases, active at both acidic and alkaline pH values. Autolytic activity decreased with increasing NaCl concentration (0–30%). When crude proteolytic activity in true sardine was studied, two activity peaks were observed, at pH 3.5 and 9.0. Crude proteinase extracts exhibited the highest activity at 55 °C and 60 °C when assayed at pH 3.5 and 9.0, respectively. The pH 3.5 peak activity was effectively inhibited by pepstatin A, while the pH 9.0 peak activity was mostly inhibited by soybean trypsin inhibitor, PMSF and TLCK, suggesting that the various proteinases were present in true sardine. The enzymes were stable for up to 8 h at 55 °C. The activities were also stable at a pH range of 2.0–4.0 and still retained high activity toward hemoglobin after incubation at pH 3.5 for 8 h. Activities of the crude extract continuously decreased as NaCl concentration increased. ATP showed no effect on enzyme activity, while CaCl₂ and MgCl₂ activated the proteinase activity. The results implied that pepsin is a predominant enzyme responsible for autolysis in true sardine during fish sauce fermentation.     

The use of a tea polyphenol dip to extend the shelf life of silver carp (Hypophthalmicthys molitrix) during storage in ice

The effects of a tea polyphenols (TP) dip treatment on quality changes of silver carp (Hypophthalmicthys molitrix) during iced storage were examined over a period of 35 days. TP (0.2%, w/v) solution was used for the dip treatment. The control and the treated fish samples were analysed periodically for microbiological (total viable count), chemical (pH, TVB-N, TBA, K-value), and sensory characteristics. The results indicated that the effect of the TP dip treatment on the fish samples was to enable the good quality characteristics to be retained for longer and to extend the shelf life during the iced storage.     

Retardation of haemoglobin-mediated lipid oxidation of Asian sea bass muscle by tannic acid during iced storage

Lipid oxidation mediated by haemoglobin from tilapia was monitored in washed Asian sea bass mince with and without added tannic acid (200 and 400 ppm) during 10 days of iced storage. Control samples (without tannic acid) had the highest peroxide value (PV) within the first 2 days and possessed the greater amount of thiobarbituric acid-reactive substances (TBARS) throughout the storage of 10 days (p < 0.05). With addition of tannic acid, the lipid oxidation of washed Asian sea bass mince was retarded, especially when the higher level (400 ppm) was used, as evidenced by lowered PV and TBARS. The retarded formation of volatile lipid oxidation products in the samples with added 400 ppm tannic acid was found. Sensory analysis revealed that samples with added 400 ppm tannic acid possessed lower fishy odour score, compared with the control sample and that with added 200 ppm tannic acid (p < 0.05).     

Influence of frozen storage on aptitude of sardine and dolphinfish for cold-smoking process

Stability of dolphinfish (Coryphaena hippurus) and sardines (Sardina pilchardus) of different fat content (lean and fatty sardines) during frozen storage and its suitability for cold-smoking throughout storage were evaluated in order to overcome seasonal and excess catches of these species. Dolphinfish showed a relative stability regarding protein functionality (protein solubility, apparent viscosity, water and lipid holding capacity), lipid oxidation and total volatile basic nitrogen (TVBN) accumulation, which led to high acceptability ratings of the resulting smoked product throughout frozen storage (340 days). However, both lean and fatty sardines showed a marked loss of protein functionality, which coincided with the accumulation of oxidation products and TVBN. Freezing of raw muscle may become a valuable preservation method for the smoking industry to overcome the short caught period of dolphinfish in the Balearic Islands and to make use of excess catches of both, lean and fatty sardine. High quality smoked products may be obtained from the frozen muscle during approximately twelve, four and two months of frozen storage for Dolphinfish, lean and fatty sardine, respectively.     

卵形鲳鲹在冰藏过程中鲜度变化研究

研究了卵形鲳鲹在冰藏过程中的鲜度变化。采用挥发性盐基氮（TVB-N）值、K值、Ca2+-ATPase活性、硫代巴比妥酸（TBA）值、菌落总数作为鲜度指标,研究其在冰藏过程中随时间的变化趋势。结果表明,以上指标皆与冰藏时间有很好的相关性,综合分析以上指标可得到卵形鲳鲹在冰藏过程中的鲜度变化。结合各鲜度指标,在冰藏5d内卵形鲳鲹处于一级鲜度范围,其TVB-N小于20mg/100g,K值小于20%,Ca2+-ATPase活性大于2.4μmolPi/mgprot/h,TBA值小于0.40mg/100g;15d后卵形鲳鲹TVB-N值大于30mg/100g,K值大于40%,Ca2+-ATPase活性小于1.0μmolPi/mgprot/h,TBA值大于0.55mg/100g,菌落总数小于106CFU/g,冰藏卵形鲳鲹的货架期为14～15d。