Emiko Okazaki

Total mercury and methylmercury levels in commercially important fishes in Japan

The distribution of mercury in the muscle and other tissues was determined in 23 species of fishes and invertebrates. This study reveals species-specific patterns of mercury accumulation in the muscle of tuna and alfonsino. Consistently high levels of total mercury were found in Beryx splendens (0.78±0.56 μg/g), Atlantic Thunnus thynnus (0.42±0.06 μg/g), Pacific T. thynnus (0.59±0.34 μg/g), Thunnus obesus (0.98±0.34 μg/g), Makaira nigricans (0.56±0.05 μg/g), Tetraptrus audax (0.51±0.08 μg/g), and Xiphias gladius (0.47±0.24 μg/g). Other fish species had lower levels of total mercury or methylmercury in muscle than the maximum permitted level of mercury in fish in Japan (0.4 μg/g). Total mercury and methylmercury levels in the muscles of T. thynnus, T. obesus, and B. splendens were closely correlated with body weight.

Isolation and characterization of acid-soluble collagen from the scales of marine fishes from Japan and Vietnam

Acid-soluble collagen (ASC) was successfully extracted from the scales of lizard fish (Saurida spp.) and horse mackerel (Trachurus japonicus) from Japan and Vietnam and grey mullet (Mugil cephalis), flying fish (Cypselurus melanurus) and yellowback seabream (Dentex tumifrons) from Japan. ASC yields were about 0.43-1.5% (on a dry weight basis), depending on the species. The SDS-PAGE profile showed that the ASCs were type I collagens, and consisted of two different α chains, α1 and α2, as well as a β component. ASC of horse mackerel from Vietnam contained a higher imino acid level than that from Japan. ASC denaturation temperature (Td) ranged from 26 to 29 °C, depending on fish species and imino acid content (p<0.01). Maximal solubility of individual collagens was observed at pHs 1-3. Collagen solubility decreased sharply at NaCl concentrations >0.4M, regardless of fish type.

Distinct regional profiles of trace element content in muscle of Japanese eel Anguilla japonica from Japan, Taiwan, and China

Trace element distribution patterns were examined in Japanese eel from five Asian regions for the purpose of identifying the elements and patterns that could be used to determine provenance. Distinctive patterns were found in eels from the Japanese prefectures of Miyazaki, Kagawa, and Shizuoka, and from Taiwan and China. The levels of six trace elements, selenium, mercury, copper, manganese, zinc, and arsenic, in muscle tissue varied among eels of different origins, and factorial analysis of the elemental patterns showed that Factor 1 was attributable to selenium and mercury levels and Factor 2 to zinc and copper levels. Multivariate analysis showed that the patterns of elemental composition in fish muscle were mainly differentiated by these two factors.

Stability of the Physical Properties of Plasticized Edible Films from Squid (Todarodes pacificus) Mantle Muscle during Storage

UNLABELLED Edible films from squid mantle muscle plasticized with different plasticizers were stored at 25 °C, 50% RH before the determination of physical properties. The results showed that tensile strength significantly increased (P < 0.05) upon the storage time, especially for the film plasticized with glucose, while there was no significant change (P ≥ 0.05) in elongation at break of all plasticized films. Water vapor permeability of glucose-plasticized film significantly decreased (P < 0.05) during storage, while there was only a slight change in those with glycerol, sorbitol, and fructose. Redness and yellowness of the films became significantly higher (P < 0.05) during storage, especially for the films plasticized with fructose and glucose. SDS-PAGE and protein solubility in SDS solution showed a possibility of protein aggregation throughout the storage. From these results, it is suggested that the changes in physical properties of the films were caused by the progress of Maillard reaction. PRACTICAL APPLICATION In this study, squid mantle muscle was used as an edible film-forming material. By mixing with Na-citrate, squid mantle muscle possessed the ability to form transparent films with an excellent UV barrier property. Glycerol was found to be the most effective and stable plasticizer for the films. Edible films represent an option for the utilization of discarded squid during the fishing process.

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.

Effect of meat washing on the development of impact odorants in fish miso prepared from spotted mackerel

BACKGROUND Miso, a fermented soybean paste prepared using koji (rice malt inoculated with Aspergillus oryzae) has been commonly used as a traditional seasoning for several centuries in East Asian countries. A miso-like fermented product was prepared using washed and unwashed meats of spotted mackerel (Scomber australasicus) with improved food functionality and aroma attributes. The evolution of aroma-active volatiles was further evaluated during the early stages of maturation. RESULTS The newly developed fermented product was rich in flavor. The product was found to contain 98 volatile compounds, including aldehydes, alcohols, esters, ketones, furans, sulfur- and nitrogen-containing compounds, aromatics, and acids. Koji enzymes efficiently hydrolyzed protein and carbohydrate substrates in both the unwashed and washed fish meats. Significantly higher enzyme activities were observed when the unwashed meat was used as a raw material rather than when washed meat was used. The substrate specificity of koji enzymes plays an important role in the formation of volatile compounds. CONCLUSION The results confirmed that meat washing can reduce the levels of certain aldehydes, ketones, and nitrogen-containing compounds, and can thereby provide a pleasant aroma by reducing fishy odor in the finished product.

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.

Effects of Koji Fermented Phenolic Compounds on the Oxidative Stability of Fish Miso

UNLABELLED In the present study, Aspergillus oryzae-inoculated koji inhibited lipid oxidation in fermented fish paste rich in polyunsaturated fatty acids following a long fermentation period. The fermentation of koji by A. oryzae liberated several bioactive phenolic compounds, including kojic acid and ferulic acid, which were the most abundant. A linear correlation between several phenolic compounds and their bioactive properties, including their radical-scavenging activity, reducing power, metal-chelating activity, and ability to inhibit linoleic acid oxidation was observed. This suggested an important role of koji phenolics in the oxidative stability of fermented fish paste. The activities of different carbohydrate-cleaving enzymes, including α-amylase, cellulase, and β-glucosidase, were positively correlated with the liberation of several phenolic compounds through koji fermentation. Thus, the application of koji offers a novel strategy to enhance the oxidative stability of newly developed fermented fish miso. PRACTICAL APPLICATION Application of traditional Japanese koji fermentation technique to develop an aroma enriched fish meat bases seasoning has been established. Aspergillus oryzae-inoculated koji releases several carbohydrate-cleaving enzymes, including α-amylase, cellulose, and β-glucosidase, which led to the liberation of several phenolic compounds during fermentation. Improvement of oxidative stability of the fermented fish meat paste by koji phenolics suggests a useful strategy to uplift the value of different trash fish meat-based seasoning through proper utilization of the present technique.

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.

Fish and Related Products

This chapter provides a summary of studies on seafood quality evaluation using near-infrared (NIR) spectroscopy and presents the future prospects for this method. NIR spectroscopy is applied to determine the chemical composition in minced raw fish samples used to make fishmeal. One of the groups of researchers investigated the utility of NIR spectroscopy as a means to quantify the diet of seals via analysis of feces. Five of the six calibrations could accurately and precisely quantify how much of a given dietary component the seal had eaten the previous day from an NIR scan of the feces. NIR spectroscopy is therefore potentially a viable way to quantify seal diets. NIR spectroscopy is also successfully employed to determine moisture and sodium chloride in cured, and cold smoked Atlantic salmon. NIR reflectance spectroscopy in the spectral range of 1000–2500 nm was also measured directly for brine from barrel-salted herring, to investigate the potential of NIR as a rapid method to determine the protein content. A partial least squares (PLS) regression model between selected regions of the NIR spectra and the protein content yielded a correlation coefficient of 0.93, and a prediction error of 0.25 g/100 g. A nondestructive visible/NIR spectroscopy technique is proposed to investigate whether fish have been frozen-thawed. Compared with dry extract spectroscopy by infrared reflection (DESIR), no extraction is needed, and no wastes are produced in visible/NIR (Vis/NIR) spectroscopy using a fiber-optic probe, which would be an eco-friendly instrumental technique.