Akira Okamoto

Influence of storage temperatures and killing procedures on post‐mortem changes in the muscle of horse mackerel caught near Nagasaki Prefecture, Japan

The effect of storage temperature (0, 5, 10, and 15°C) and killing procedure (instant, struggled, temperature shocked, and spinal cord destruction killing) on post-mortem changes in the muscle of the horse mackerel caught near Nagasaki, Japan, was investigated. Temporal changes in adenosine triphosphate (ATP), inosine monophosphate (IMP), and lactic acid concentrations were slowest at 10°C storage temperature. The increase in K-values was slower at 10°C and below than at 15°C storage temperature. In addition, 10°C storage temperature was most suitable for maintaining a constant breaking strength value of the muscle. Regarding the effect of killing procedure, temporal changes in ATP, IMP, and lactic acid concentrations were slowest then killed by spinal cord destruction. The increase in K-value and the decrease in breaking strength were also slowest in the spinal cord destruction group. From these results, it was considered that storage at 10°C temperature and spinal cord destruction killing procedure were most effective in delaying post-mortem change in the horse mackerel.

Differences in free amino acid composition between testis and ovary of sea urchin Anthocidaris crassispina during gonadal development

For the purpose of clarifying the differences of taste components between the testis and ovary of the sea urchin Anthocidaris crassispina, variations in free amino acid composition in gonadal extract during gonadal development were investigated using chemical and histopathological methods. Sea urchins were collected at Iki Island, Nagasaki, Japan between 30 April and 5 June 2003, and maturation stages and the free amino acid compositions were determined. The sweet amino acids threonine (Thr), glycine (Gly), and alanine (Ala), the umami amino acid glutamic acid (Glu), and the bitter amino acids lysine (Lys) and arginine (Arg) were the main constituents accounting for more than 80% of total free amino acids. In the testis and ovary, Gly levels were the highest among them and increased with gonadal development. The other free amino acids consisted mainly of bitter amino acids and either showed no variation or decreased with gonadal development. These variations in free amino acid composition were observed more clearly in the ovary than the testis. These findings indicate the possibility of differences in the flavor of sea urchin gonad by sex and gonadal development stages.

Characteristics of burnt meat in cultured yellowtail Seriola quinqueradiata

In order to understand the characteristics of burnt meat in cultured yellowtail Seriola quinqueradiata, fish were kept at two different temperatures (13 and 30°C) and slaughtered by either spinal cord destruction (SCD) or suffocation in air (SA). Early postmortem changes during storage at 32°C were analyzed by rheological, biochemical, and histological methods. The burnt meat (with lightness parameter, L*≥55) was observed at 1-h storage in the SA 30°C group, at 2 h in SCD 30°C, and at 4 h in SA 13°C; meat was normal for the SCD 13°C group until 6h of storage. Breaking strength scores were higher for the normal meat (200 g/cm2) than burnt meat (70 g/cm2) at 4 h of storage. Expressible water content was higher for the burnt meat than for the normal meat. Adenosine triphosphate concentrations for the SCD groups were higher than for the SA counterparts. Moreover, pH decrease was much faster in the 30°C groups, showing pH 5.6 at 2 h of storage. A negative correlation between the pH and lactic acid contents in muscle (P<0.001) was found. Histological analysis evidenced a larger pericellular area (40%) in the burnt samples than in the normal samples (16%). It was confirmed that a higher fish-keeping water temperature and a stressful slaughter method (faster glycolytic process) were determinative factors that influence the occurrence of burnt muscle in yellowtail, and that the effect of the former is larger than the latter.

Quality aspect of fish sauce prepared from underutilized fatty Japanese anchovy and rabbit fish

To explore the potential utility of underutilized fish in the fish sauce industry, fish sauces were prepared from both raw and heat-induced meat of Japanese anchovy Engraulis japonica and rabbit fish Siganus fuscescens using wheat malt, and their quality aspects and sensory properties were assessed. Proximate composition of the fish meat represents protein as the major component (16.0–17.8%), other than moisture. Analyses of free amino acids, peptides including oligopeptides, and organic acids contents in fish sauces revealed suitability of both raw and heat-induced meat of the selected species in commercial fish sauce production. The variations in taste of raw meat fish sauces were species-specific, but the taste of fish sauces from heat-induced meat were similar.

Docosahexaenoic acid levels in the lipids of spotted mackerel Scomber australasicus

The lipid and FA compositions of various organs and of the stomach contents of Scomber australasicus were analyzed. DHA was characteristically the major FA of all the major lipid classes of all organs except for liver TAG. The mean DHA contents of the various organs accounted for more than 17% of the total FA (TFA), whereas those in the stomach contents, originating from the prey, fluctuated and were generally low. In particular, the DHA levels in the TAG from all organs of S. australasicus accounted for up to 17% of TFA, even though it is a neutral depot lipid. S. australasicus contained markedly high levels of DHA, even though it is a small-sized Scombridae species, and its high levels of DHA were close to those in large-sized highly migratory tuna species. Furthermore, DHA levels in its muscle TAG were consistently high, compared with those in the visceral TAG, which might be directly influenced by the prey lipids. These phenomena suggest that long-distance migration has a close relationship with high accumulation of DHA in fish tissues, since S. australasicus is reported to migrate in offshore water, similar to highly migratory tuna species. Additionally, the physiological selective accumulation of DHA in the muscle during migration is caused by in vivo metabolism of FA in the vascular system, suggesting that DHA is poorly used as a source of migration energy, though it is provided abundantly through the prey lipids.

Year-round high arachidonic acid levels in herbivorous rabbit fish Siganus fuscescens tissues

To identify a stable resource of 20∶4 n−6 (arachidonic acid, AA) in marine fish tissues, the lipid profiles of Siganus fuscescens organs (muscle, liver, and other viscera) and stomach contents were examined throughout the year. Crude total lipid (TL) contents in respective organs showed seasonal variations and were high in winter and low in summer. The main FA in TL were 16∶0, 18∶0, 16∶1n−7, 18∶1n−9, AA, and 22∶6n−3 (DHA). These FA were those generally observed in marine fish lipids, except for comparatively high levels of AA. In TL of muscle and liver, AA showed relatively high values during the period from late May to August (muscle, 4.6–13.1%; liver, 4.5–9.1%), compared with other seasons (muscle, 4.3–9.5%; liver, 3.6–8.4%). The AA levels in TL of other viscera and stomach contents fluctuated (other viscera, 2.0–10.7%; stomach contents, 7.6–26.7%). Regardless of the fishing season, each organ contained a higher level of AA in polar lipids (PL) than in neutral lipids. It was concluded that the fish contain comparatively high levels of AA in their TL throughout the year, and they accumulate AA characteristically in their tissue PL, probably from dietary food sources. Moreover, it was suggested that S. fuscescens has potential utility as a natural marine source of nutritional lipids, because the fish contain comparatively high levels of DHA and AA.

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.

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.

Headspace Volatiles along with Other Instrumental and Sensory Analyses as Indices of Maturation of Horse Mackerel Miso

Development of aroma-active compounds during fermentation in the preparation of fermented fish-meat paste product (fish miso) from horse mackerel meat was quantitatively determined and characterized by olfactometric and organoleptic assessments. The critical ripening time was estimated by quantitative and/or qualitative analyses of volatile compounds, peptides, amino acids, product color, and total phenolics of the fish miso matrix throughout fermentation. The results confirmed that the application of koji for the fermentation of horse mackerel meat to produce fish miso significantly reduced the fishy off odor and promoted the development of highly acceptable fish miso with a nutty, cheesy, and fruity aroma. Ethyl acetate, ethyl heptanoate, ethyl decanoate, 2-methylpropanal, 3-methylbutanal, 2,3-butanedione, dimethyl trisulfide, and 3-(methylthio) propanal were identified as key odor-active compounds in fish miso prepared from horse mackerel meat. Among the volatiles, 2-methylpropanal, 3-methylbutanal, and 2,3-butanedione were identified to serve as potential indicators of the maturation of fish miso. Amino acid content could also be a potential indicator of maturation of protein-rich, fermented products such as fish miso. In addition, surface color analysis of fish miso revealed a high correlation between sensory attributes and color components. Specifically, r and b values were considered potential indicators of maturation. Practical Application: Variability is a major drawback in fermented products such as fish miso and it requires establishing the optimum ripening time, defined as that providing the aroma attributes qualitatively and quantitatively mostly appreciated by consumers. We have carried out this work for comprehensive determination of the critical ripening time by applying several instrumental and sensory tools including quantitative and/or qualitative analysis of volatile compounds, peptides, amino acids, product color, and total phenolics of the fish miso matrix throughout the fermentation period. The outcome of the present study can be efficiently applied for detection of maturation in similar types of fermented product for large-scale production.

Year‐round gelation characteristic of bassy chub Kyphosus lembus meat

Year-round change in gelation of bassy chub (Kyphosus lembus) meat, collected from October 2001 to September 2002 off the coast of Nagasaki, was investigated. The fish meat exhibited a similar high gel-forming ability for all seasons, including pre- and post-spawning seasons. Freshwater washing of the meat did not improve its gel-forming ability. It was concluded that bassy chub meat could be used for thermal gel production in all seasons.