Potential of fluorescence fingerprints for fish meat authentication: Differences in freshness evaluation in white and dark meat at frozen state.

As dark meat has a faster deterioration rate and its unintentional mixing occurs during processing, it is crucial to know the status and freshness indicators of dark meat to ensure fishery product quality. In this method, fluorescence fingerprints (FFs) was applied as a rapid and noninvasive quality authentication method to determine differences between white and dark meat in the evaluation of freshness indicators at frozen state. Spotted mackerel (Scomber australasicus) fish chunks with different postmortem conditions (0-40 h ice stored) were obtained and frozen. A new generation of fluorescence spectrophotometer (F-7100) was used to acquire FFs of the frozen fish chunks (containing white and dark meat). Adenosine triphosphate metabolites and pH were determined in both white and dark meat using their relevant biochemical methods. Higher K-values in dark meat might be attributed to a higher accumulation rate of inosine (HxR) in dark meat than in white meat. The pH decrease rate in white meat was higher than that in dark meat during postmortem ice storage periods of fish. Principal component analysis of FFs spectra demonstrated clear discrimination (PC1 + PC2 = 91.7%) between white and dark meat of frozen fish due to the influence of freshness parameters based on the fluorescence features of fish meat. Furthermore, partial least squares regression validation models revealed that freshness indicators of white meat could be predicted more accurately at the frozen state than those of dark meat. This method could be applied during the processing of fishery products, thereby facilitating quality control activities and making it a promising authentication tool for the fisheries industries.

Effects of tyndallization temperature on the sterility and quality of kamaboko.

In this study, kamaboko gels were tyndallized at various temperatures and sterilization efficiency and impact on quality parameters were assessed. The microbiological, physical, and chemical properties of kamaboko gels were determined throughout the tyndallization process. Superior sterilization efficiency was achieved by tyndallization at a higher temperature; and the combination of heat-induced germination and thermal inactivation of spores was proposed as the main reason. The process had minimal effect on the color of gels. While tyndallized gels heated at 80 °C possessed superior physical properties, all gels showed impaired quality with the progress of heating cycles. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) revealed that the cause of alterations in quality differed depending on the processing temperature. This study suggests that the sterility of products could be improved by increasing the processing temperature, time or number of heating cycle.

The influence of processing sequence and frozen storage on the seasoned alaska pollack (Theragra chalcogramma) roe product quality.

The quality of seasoned products of Alaska pollack (Theragra chalcogramma) roe declined dramatically during frozen storage. This research investigated the effects of processing sequence and frozen storage period on seasoned Alaska pollack roe product quality. In addition, the relationship between mechanical properties and protein composition of ovary membrane and eggshell was discussed. The seasoned roe product made by the Seasoning-Frozen storage process showed higher mechanical property values, better surface color and more stable protein composition. The results clarified that this process allowed endogenous transglutaminase to act before it had been denatured and effectively prevented protein degradation during frozen storage. The retardation of protein degradation was probably attributed to cryoprotective effects from components in seasoning solution.

Rapid noninvasive monitoring of freshness variation in frozen shrimp using multidimensional fluorescence imaging coupled with chemometrics.

Shrimp is one of the most delicious and popular food commodities worldwide due to its exceptional taste and characteristics. Freshness is considered as a key factor for shrimp consumers because freshness has a significant relationship with taste and shelf-life of shrimp. However, post-mortem metabolism of shrimp differs from that of fish as they are highly susceptible to post-harvest quality loss, and it is hard to distinguish the freshness variation of shrimp at frozen state instantly. Thus, instant monitoring of frozen shrimp freshness is challenging for the seafood and aquaculture industries and a reliable, expeditious, and noninvasive technique to estimate shrimp quality is in high demand. Accordingly, this study aimed to visualize changes in post-mortem freshness of frozen shrimp using multidimensional fluorescence imaging. Live coonstripe shrimp (Pandalus hypsinotus) were harvested and instantly killed by beheading, cooled on ice for 0, 6, 24, 48, 72 and 96 h (n = 8), followed by processing into frozen peeled deveined shrimp product and stored at -60 °C. 50% of frozen shrimp were analyzed for excitation-emission matrix (EEM), ATP-related compounds, and pH using a fiber optic supported fluorescence spectrophotometer (F-7100), high performance liquid chromatography (HPLC) and pH meter, respectively at each time point (n = 4). Then, fluorescence images were obtained from the remaining 50% of frozen shrimp (n = 4) by computer vision method equipped with a charge-coupled device (CCD) camera, MAX-303 xenon light source for an excitation light (Ex. 330 nm), and an automatic filter changer for emission band-pass filters (Em. 380-610 nm at 10 nm intervals). Chemical analysis of frozen shrimp revealed that K-value and pH of shrimp increased from 1.61 to 66.56% and 6.49-7.31, respectively, during storage on ice. Repeated partial least squares regression (PLSR) models of EEM for K-value prediction suggested an efficient excitation wavelength (330 nm) and its corresponding emission wavelengths (380-610 nm) to produce fluorescence images. Spatial-temporal changes of K-value and pH were visualized successfully in frozen shrimp by fluorescence imaging. K-value visualization was then validated effectively using another group of frozen shrimp (0-72 h ice stored) with different killing method (super chilling) and the prediction accuracy was R2 = 0.80. This novel approach using a CCD camera coupled with EEM provides a state-of-the-art authentication method for practical assessment of frozen seafood freshness.

A novel and simple non-thermal procedure for preparing low-pH-induced surimi gel from Alaska pollock (Theragra chalcogramma) using glucose oxidase.

The aim of this study was to develop a novel and simple non-thermal method for preparing a low-pH-induced surimi gel from Alaska pollock (Theragra chalcogramma). To this end, effect of glucose oxidase (GOD) on gelation properties of the surimi with added 5% glucose was investigated. The surimi containing glucose was blended with 0%-3.0% GOD and incubated for 15 h at 4 °C. The pH of the surimi gel with 1.0% GOD decreased to 4.6 after the incubation. The addition of 1.0% GOD was the optimum to elevate breaking force and breaking deformation of the surimi gel. Surface hydrophobicity and disulfide bond contents that are involved in the formation of protein gel network in the surimi increased with an increase in GOD concentration. These results indicate that the addition of 1.0% GOD significantly enhances low-pH-induced gelation of surimi because GOD catalyzes the oxidative reaction of glucose resulting in lowering of the pH.

Changes in quality properties and tissue histology of lightly salted tuna meat subjected to multiple freeze-thaw cycles.

The influence of various freeze-thaw cycles on the physicochemical and histological properties of lightly salted tuna meat was studied. Enhanced water-holding capacity and springiness were obtained in the salted samples even after repeated freezing-thawing, which was ascribed to the modifications in tissue microstructure, ice crystal morphology, and protein properties. Intracellular and spherical ice crystals were observed in the salted meat, rather than the extracellular and large ice columns in the unsalted counterparts. Proteins in the salted meat were more sensitive to the stresses imposed by freezing-thawing and would form hydrophobic interactions more readily. Excessive freeze-thaw cycles accelerated the discoloration of salted meat, probably due to the decreased oxidative stability by salt. The overall quality properties of lightly salted tuna meat could be better maintained when subjected to no more than three freeze-thaw cycles.

Texture enhancement of salted Alaska pollock (Theragra chalcogramma) roe using microbial transglutaminase.

The aim of our study was to improve the texture quality of salted Alaska pollock (Theragra chalcogramma) roe product using microbial transglutaminase (MTGase). Thus, the effect of 0-1.0% MTGase on the physical properties of the salted roe was assessed. Endogenous TGase activity in the roe, which contributes to improving its texture, decreased at -20 °C during frozen storage. Mechanical properties of the salted roe, such as roe firmness and egg breaking strength, were improved using MTGase, the optimum concentration of which was 0.5%. Protein polymerizations using SDS-PAGE and decreasing of protein solubilities in SDS-urea solution were observed in the salted roe with MTGase. Therefore, the texture of salted Alaska pollock roe can be significantly enhanced by adding 0.5% MTGase because of catalyzing protein crosslinking. Additionally, this study most likely indicates that MTGase can be used to improve the texture of aquatic processed foods at low temperatures, especially 5 °C.

Relationship among pH, generation of free amino acids, and Maillard browning of dried Japanese common squid Todarodes pacificus meat.

Relationship among pH, generation of free amino acids (FAAs), and Maillard browning was investigated in Japanese common squid during air drying at 40 °C to prevent its discoloration. In the surface color measurement, increase in the b* value which is an indicator for Maillard browning of the dried squid was mitigated at pH 4.0-6.0 and accelerated at pH 7.5-9.0. Adjusting the pH to 5.5 effectively suppressed increasing of the b* value (p < 0.05). Arginine (Arg) generation involved in the Maillard reaction, was inhibited in the dried squid at pH 5.5 (p < 0.05). Maillard reactivities between ribose and amino acids were lower at pH 4.0 than at pH 5.5 (p < 0.05). These results indicate that browning of the dried squid is significantly suppressed at pH 5.5. Moreover, suppression of Arg generation is more effective than weakening of Maillard reactivity between ribose and Arg, in mitigating Maillard browning of the dried squid at an acidic pH.

Expeditious prediction of post-mortem changes in frozen fish meat using three-dimensional fluorescence fingerprints.

The present study was conducted to characterize fluorophores in the fish body using three-dimensional fluorescence fingerprints (3D-FFs) and to utilize these 3D-FFs obtained from frozen horse mackerel (Trachurus japonicus) fillets to predict early post-mortem changes. Alive fish were sacrificed instantly, preserved in ice until 2 days, and then filleted, vacuum packed, and frozen. Subsequently, 3D-FFs of the frozen fillets were acquired using F-7000 aided with a fiber probe. Post-mortem freshness changes were tracked by measuring adenylate energy charge (AEC) values and nicotinamide adenine dinucleotide (NAD and NADH) content. Partial least squares regression models for predicting AEC values and NADH content in frozen fish meat showed good fittings, with R2 of 0.90 and 0.85, by utilizing eight and five excitation wavelengths, respectively, based on their fluorescence features acquired from standard fluorophores. This novel approach of 3D-FFs could be utilized as an efficient technique for at-line monitoring of frozen fish quality.

Changes in protein properties and tissue histology of tuna meat as affected by salting and subsequent freezing.

The effects of salting and subsequent freezing on the physicochemical and histological properties of frozen-thawed tuna meat were investigated. Salting facilitated the microstructural recovery as indicated by the decrease or disappearance of intracellular holes. The yield of the 0.5 M and 1 M salted samples increased by 20% which was evaluated by the mass ratio of products to raw material. Morphological transformation from ice columns to spherical or ellipsoidal ice crystals was tentatively attributed to the extraction/solubilization of myofibrillar proteins, contributing to increased water-holding capacity. However, increased thawing loss and centrifuging loss after thawing were observed in the 2 M and 3 M salted samples with large ice crystals and enlarged extracellular spaces. These modifications were closely associated with the changes in protein properties. In conclusion, enhanced water-holding capacity, high yield, and good freezing stability can be achieved by optimal salting.

Effect of pH and heating conditions on the properties of Alaska pollock (Theragra chalcogramma) surimi gel fortified with fish oil.

To improve the quality and functionality of emulsified surimi gels, the effect of pH and heating conditions on the properties of surimi gel fortified with fish oil was investigated. Results showed that pH conditions influenced the solubility and emulsifying properties of surimi proteins and that the gel properties were associated with the protein properties. Under direct heating, the highest gel strength was achieved at pH 8.0, in which condition the solubility was significantly higher than others. Higher emulsifying stability resulted in enhanced gel strength relative to that of the control group. However, the changes in the gel strength were not consistent under two-step heating. In addition, the expressible moisture and oil content were found to vary depending on the pH values under both heating conditions. The corresponding changes in expressible moisture and oil content could be attributed to the high protein solubility and emulsifying properties of surimi proteins. Analysis of the dynamic rheological properties of the resulting surimi paste revealed that the gelation properties varied depending on the pH conditions during the heating process. In addition, the temperatures of myosin cross-linking changed according to the structure of surimi proteins, which in turn varied depending on the pH conditions. PRACTICAL APPLICATIONS: To improve the functionality of surimi-based product, the fish oil was added to prepare surimi gel. pH and heating conditions play important roles in the gelation of fish proteins. Therefore, this study investigated the effect of combined pH and heating condition on the property of surimi gel fortified with fish oil. The emulsified surimi gel with fine texture was obtained at pH of 8-8.5; moreover, heating conditions (direct heating and two-step heating) also influenced texture of emulsified surimi gel. These results provide the evidence to produce the emulsified surimi-based product with the high gel strength, water- and oil-holding capacity.

The effect of organic salts on the browning of dried squid products processed by air-drying.

To control discoloration of dried Japanese common squid (Todarodes pacificus) product, influence of 0-1% organic salts, including sodium gluconate (Na-gluconate), sodium citrate (Na-citrate), sodium phytate (Na-phytate), sodium benzoate (Na-benzoate) and sodium tartrate (Na-tartrate), on Maillard browning in the squid meat during air-drying was investigated. Changes in surface color of the dried squid were mitigated by the addition of organic salts. Organic salts also showed inhibitory effects on autolysis and generation of free amino acids (FAAs), especially arginine, in both the dried squid meat and the model solution. Moreover, Maillard reaction degree of the dried squid was decreased by using organic salts. The addition of 1% Na-citrate or 1% Na-phytate well suppressed the browning of the dried squid (p < 0.05). The results indicated that organic salts having strong chelating ability, including Na-citrate and Na-phytate, can prevent the browning of the dried squid product by inhibiting the generation of FAAs.

Effect of emulsifying stability of myofibrillar protein on the gel properties of emulsified surimi gel.

Several kinds of emulsified surimi gels were prepared from different quality levels of Alaska Pollack surimi, and the relationship between the emulsifying stability (ES) of myofibrillar protein and the properties of the emulsified surimi gels was investigated. Fish oil emulsified into surimi gels enhanced the breaking strength, but this was decreased by denaturation of the surimi protein, and the rate of enhanced gel-forming ability with emulsification decreased with decreasing ES. Expressible drip also decreased with emulsification; however, increasing amounts of lipid in the expressible drip were separated out from the gel upon protein denaturation of the source surimi. Scanning electron microscopy revealed that the shape of fish oil particles became irregular and some voids caused by oil leakage were observed with increasing storage period of source surimi. The results suggested that improvement in gel properties of the emulsified surimi gels was correlated with ES as well as the level of protein denaturation.

Influence of Various Phenolic Compounds on Properties of Gelatin Film Prepared from Horse Mackerel Trachurus japonicus Scales.

Influence of various phenolic compounds on physical properties and antioxidant activity of gelatin film from horse mackerel Trachurus japonicus scales was investigated. Tensile strength (TS) of the film was enhanced whereas elongation at break was declined by adding 1% to 5% phenolic compounds. Rutin was the most effective to improve the TS compared to the other tested phenolic compounds including ferulic acid, caffeic acid, gallic acid, and catechin. Gelatin films with the phenolic compounds showed the excellent UV barrier properties. FTIR spectra exhibited that wavenumber of amide-A band of films decreased with formation of hydrogen bonding between amino groups of gelatin and hydroxyl groups of the phenolic compounds. Gelatin film incorporated with rutin which has the largest number of hydroxyl groups among the tested compounds demonstrated the lowest wavenumber for the amide-A peak. It is indicated that hydroxyl groups contained in the phenolic compounds contribute to formation of hydrogen bonds involved in improvement of the mechanical properties of the films. The incorporation of the phenolic compounds with gelatin films also led to the increasing of total phenolic contents and DPPH radical scavenging activities. Thus, it is concluded that phenolic compounds can promote the quality of gelatin film. PRACTICAL APPLICATION: Properties of gelatin film derived from horse mackerel scales can be improved by adding of phenolic compounds. Phenolic compounds containing a large number of hydroxyl groups should be selected to enhance physical properties of the gelatin film. A biodegradable film prepared from horse mackerel gelatin incorporated with phenolic compounds, which has good physical properties and antioxidant properties, can solve environmental problems caused by synthetic plastic materials.

The influence of proteases on the browning of dried squid products processed by air-drying.

To clarify why mantle meat from Japanese common squid (Todarodes pacificus) dried products discolor dramatically when processed by air-drying, the role of endogenous protease(s) on browning during the processing of dried squid products was studied. The involvement of endogenous protease(s) in the generation of Free Amino Acids (FAAs) participating in the Maillard reaction was characterized. The browning and myosin heavy chain degradation during air-drying were obviously mitigated by the addition of metalloprotease inhibitors, especially EGTA and 1,10-phenanthroline, followed by serine proteinase inhibitor, especially PMSF. The amount of total FAAs in dried products increased by only 0.17% with the addition of 1,10-phenanthroline and 5.0% with added EGTA. In autolysis models, protein autolysis was almost completely inhibited by 1,10-phenanthroline. The addition of, 1,10-phenanthroline inhibited the increase in total FAAs including arginine (Arg), followed by EGTA and PMSF. The results indicated that endogenous metalloproteases and serine proteases might influence the generation of FAAs including Arg, and contribute to product discoloration during air-drying.

High Arachidonic Acid Levels in the Tissues of Herbivorous Fish Species (Siganus fuscescens, Calotomus japonicus and Kyphosus bigibbus).

The lipid and fatty acid compositions in the various organs (muscle, liver, other viscera) and stomach contents of three common herbivorous fish species in Japan, Siganus fuscescens, Calotomus japonicus and Kyphosus bigibbus, were examined to explore the stable 20:4n-6 (arachidonic acid, ARA) sources. Triacylglycerol (TAG), phosphatidylethanolamine (PtdEtn), and phosphatidylcholine (PtdCho) were the dominant lipid classes, while the major FA contents were 16:0, 18:1n-9, 16:1n-7, 14:0, 18:0, 18:1n-7, and some PUFA, including ARA, 20:5n-3 (eicosapentaenoic acid, EPA), 22:5n-3 (docosapentaenoic acid, DPA), and 22:6n-3 (docosahexaenoic acid, DHA). The amounts of these fatty acids were varied among species and their lipid classes. Phospholipids contained higher levels of PUFA than TAG. However, ARA in both phospholipids and TAG was markedly present in the muscle and viscera of all specimens, particularly in C. japonicus and K. bigibbus. Moreover, their ARA levels were higher than the levels of DHA and EPA. The observed high ARA level is unusual in marine fish and might be characteristic of herbivorous fish. Furthermore, ARA was the dominant PUFA in the stomach contents of the three species, suggesting that the high ARA level originated from their food sources. The above indicates that these three herbivorous fishes are ARA-rich marine foods and have potential utilization as stable ARA resources.

Textural improvement of salt-reduced Alaska pollack (Theragra chalcogramma) roe product by CaCl2.

Salt-reduced Alaska pollack roe benefits public health by decreasing NaCl intake; however, it has a poor texture with low breaking strength. This study addresses the feasibility of NaCl reduction in salted roe products, with focusing on the improvement of breaking strength using CaCl2. Salted roe products were prepared by immersing Alaska pollack roe in either NaCl solutions (3.5, 7.0, 15.0, 20.0, and 25.0%) or 7.0% NaCl solutions with added CaCl2 (0.0, 0.5, 1.0, 2.0, and 3.0%). Breaking strength, moisture and salt contents, eggshell protein composition of the salted roe products, as well as total endogenous transglutaminase (TGase) activity in various NaCl and CaCl2 concentrations were analyzed. CaCl2 addition enhanced eggshell protein crosslinking and breaking strength of the salt-reduced roe products. An acyl transfer reaction catalyzed by calcium-dependent TGase may be responsible for the eggshell protein crosslinking and improved texture. Thus, we successfully developed a salt-reduced Alaska roe product using CaCl2.

Freshness estimation of intact frozen fish using fluorescence spectroscopy and chemometrics of excitation-emission matrix.

The current study attempted to provide a convenient, non-invasive and time-saving method to estimate the freshness of intact horse mackerel (Trachurus japonicus) fish in a frozen state using autofluorescence spectroscopy in tandem with multivariate analysis of fluorescence excitation-emission matrices (EEM). The extracted fluorescence data from different freshness conditions were pretreated, masked and reorganized to resolve fish fluorescence spectra from overlapping signals and scattering profiles for detecting and characterizing freshness changes. The real freshness values of the examined fish samples were then traditionally determined by the hard chemical analysis using the high performance liquid chromatography (HPLC) method and expressed as K-values. The fluorescence EEM data and the real freshness values were modeled using partial least square (PLS) regression and a novel algorithm was proposed to identify the ideal combinations of excitation and emission wavelengths being used as perfect predictors. The results revealed that freshness of frozen fish could be accurately predicted with R(2) of 0.89 and root mean square error estimated by cross validation (RMSECV) of 9.66%. This work substantially demonstrated that the autofluorescence spectroscopy associated with the proposed technical approaches has a high potential in non-destructive sensing of fish freshness in the frozen state.

Properties of gelatin film from horse mackerel (Trachurus japonicus) scale.

Optimal conditions for extracting gelatin and preparing gelatin film from horse mackerel scale, such as extraction temperature and time, as well as the protein concentration of film-forming solutions were investigated. Yields of extracted gelatin at 70 °C, 80 °C, and 90 °C for 15 min to 3 h were 1.08% to 3.45%, depending on the extraction conditions. Among the various extraction times and temperatures, the film from gelatin extracted at 70 °C for 1 h showed the highest tensile strength and elongation at break. Horse mackerel scale gelatin film showed the greatly low water vapor permeability (WVP) compared with mammalian or fish gelatin films, maybe due to its containing a slightly higher level of hydrophobic amino acids (total 653 residues per 1000 residues) than that of mammalian, cold-water fish and warm-water fish gelatins. Gelatin films from different preparation conditions showed excellent UV barrier properties at wavelength of 200 nm, although the films were transparent at visible wavelength. As a consequence, it can be suggested that gelatin film from horse mackerel scale extracted at 70 °C for 1 h can be applied to food packaging material due to its lowest WVP value and excellent UV barrier properties.

Mechanism study of high browning degree of mantle muscle meat from Japanese common squid Todarodes pacificus during air-drying.

Mantle meat from the Japanese common squid (Todarodes pacificus) browns more than other squid meats during air-drying. The factors contributing to the browning of Japanese common squid, long-finned squid (Photololigo edulis) and bigfin reef squid (Sepioteuthis lessoniana) were studied in boiled and raw meat both before and after air-drying. Dried raw meat from the Japanese common squid browned more than dried boiled meat (b(∗) value, from 4.7 to 28.5). The results from SDS-PAGE showed significant degradation of myosin heavy chain (MHC) suggesting that protease activity in raw Japanese common squid meat was higher than in the other two species. The concentration of arginine (1932.0mg/100g) and ribose (28.8µmol/g) in Japanese common squid meat was higher than in the other two species. These results suggest that high protease activity and high concentrations of arginine and ribose increase the browning discoloration of Japanese common squid during air-drying.