Program

[Objective] Around 2400 fish species are estimated to inhabit the bathyal zone, which is defined as the one deeper than 200 m. There seems be a tremendous amount of underutilized fish species, which could be used as food, pharmaceuticals, animal feeds, and so on. In order to estimate the availability of these species for human consumption, it is essential to characterize their nutritional components and functional substances for more species.
[Materials & methods] More than thirty species were collected from the catch of drag net fishing in Suruga Bay, Shizuoka Pref. The specimens were transported to the laboratory in ice water, and stored at -80C after cleaning and filleting. Edible parts (ordinary muscle in most species) were the major targets for this study. Inedible parts were weighed to estimate the yield. Proximate composition was measured by the official methods. Free amino acid composition was determined by the conventional chromatography techniques. Protein components of muscle water-soluble fractions were analyzed electrophoretically.
[Results & discussion] The yield for the edible part varied from 37 to 72%. While the water content tended to be high (>80% for a few species) for most species, it varied greatly depending on the species. This was also true for the protein (>10% for some species) and lipid content (<10% for several species). Some oily species contain not a small amount of wax ester which would cause keriorrhea when ingested beyond the acceptable amount of flesh. Some species were rich in taurine and anserine, both of which would show health promoting functions. Protein patterns were quite species-specific, and degradation was recognized in some species, indicative of quality deterioration during storage. These data suggest that not a few species are available for human consumption. The safety and possibility of utilization other than food and pharmaceuticals will also be discussed.

Fish processing yields a wide variety of fish by-products such as scales, head, skin, viscera and roes. Among them, roes are rich in nutritious materials of fat, mineral and protein. In this experiment, we investigated the physico-chemical and functional properties of roe protein concentrate from Spanish mackerel (Scomberomorus commersonii); to apply the roe protein concentrate to produce infant food product through replacing of skim milk. Roes protein concentrate was prepared by defatting process using ethanol, isopropyl alcohol and ethanol-isopropyl alcohol (1:1) for 1, 2, 3, 4 cycles extraction. Defatting process using isopropyl alcohol for 4 cycles extraction yielded 11.50% of roe protein concentrate, contained protein and fat of 76.43% and 2.97%, respectively; possessing characteristics of water absorption (346.79%), oil absorption (340.47%), bulk density (0.35%) and protein digestibility (90.30%). The highest and lowest content of essential amino acids was found in leucine (66.01 mg/g protein) and methionine (21.65 mg/g protein). Replacing of 10% roe protein concentrate to skim milk, obtained the best infant food formulation that contained protein and protein digestibility of 17.83% and 83.99%, respectively. Leucine and lysine were found as major essential amino acids of infant food of 118.30 and 83.30 mg/g protein, respectively.

The concentration of collagen determined by the biuret method is usually lower than its true value, due to the collagen’s triple helix structure. In order to obtain more accurate measurement results, the conditions for the determination of collagen concentration by biuret method were studied. The collagen extracted from the calf tendon was employed as the raw material. The collagen solutions were heated at 40℃ for 5min, 15min and 30min, respectively. The same operations were also performed at 60℃ and 80℃, respectively. Then the absorbance of the samples was measured by using biuret method. The results showed the sample heated at 40℃ for 5min had the highest absorbance value, which increased 50% than that of the unheated one. With the increase of heating temperature and extension of heating time, the absorbance values gradually decreased. It was in accordance with the degradation of collagen molecules showed on SDS-PAGE pattern. The collagen concentrations were also determined by the Lowery method. The results indicated that the Lowery method was more accurate for determination of collagen from calf tendon compared to the biuret method. However, there was little difference in accuracy between the Lowery and the modified biuret methods for the determination of collagen from fish skin. Therefore, the modified biuret method was more applicable for fish collagen due to its simplicity of operation.

Threadfin bream (Nemipterus virgatus) is one of the most important commercial fishery species in Japan and Southeast Asia, and it has been widely used as a raw material for surimi productions. However, the surimi of threadfin bream is susceptible to modori phenomenon which is due to the presence of the endogenous proteases. Furthermore, the activity of the endogenous proteases is always affected by spawning. In this study, we investigated the effect of spawning on endogenous proteases in the muscle of threadfin bream.
Threadfin bream was sampled in the spawning period of July and the November, respectively. The characterization of autolysis was investigated using various protease inhibitors. The protease activities of sarcoplasmic and myofibrillar fractions were measured using various fluorogenic synthetic substrates. The gelatinolytic activity of sarcoplasmic fraction was determined by gelatin zymography. The results were concluded as follows: (1) Threadfin bream possessed a higher autolysis activity in abdominal muscle during spawning period. (2) The main working protease in the autolysis process was a serine protease. (3) It was confirmed by substrate specificity and inhibitory properties that the main working protease in sarcoplasmic fraction was trypsin-type serine proteinase. (4) The serine proteinase of 50 kDa in sarcoplasmic fraction possessed an especially high gelatinolytic activity. (5) The activity of myofibril-bound serine proteinase (MBSP) was detected in myofibrillar fraction.

Fish fillet and whole fish with skin on, but without scales, are important in the market of fish processing industries. Descaling by hand is a very labour-intensive operation and although descaling machines are available, they have not proven to be satisfactory. In many cases, the machine-descaling process must be repeated, but even then remaining scale requires manual removal. Therefore, much of the flesh and skin are lost, and the process appears to be uneconomical. Mechanical descaling of some fish species such as canned sardine (Sardinella gibbosa) is a difficult task due to high liability of soft muscle damage. An enzymatic process has been developed to remove the scales in a very gentle manner in order to yield a product of superior quality compared to the corresponding mechanically descaled product. The objective of this research was to remove fish scale by using tuna protease. The protease was extracted from tuna viscera by stirring with 0.2 M acetic acid at 4ºC for 3 h, then centrifuge at 6,000 xg for 30 min. The crude extract was protease activity and soluble protein determination and enzyme characterization. The protease specific activity was 0.84 U/mg protein. Temperature optimum and stability of protease were 50 and 0-10ºC, respectively, where as pH optimum and stability of protease were 2.0. Crude extraction was applied to 1 inch square, whole fish skin and whole fish for 6 h at 4 and 25 ºC. Degree of hydrolysis, enzyme efficiency and sensory evaluation were determined. Descaling by tuna protease at 25 ºC was faster than 4 ºC. The result shown in satisfactory with no remaining scale for 2 h crude extract treatment at 25 ºC and the flesh was accepted by panelists. This protease can applied with various fish species in fish processing industries.

Mytilus edulis is a kind of marine shellfish in the coastal area and generally considered to be nutritional food. The bioactivity polypeptides are widely applied in many kinds of food products. However, the low stability of proteins and peptides in liquid system is generally restricted the development of products. In this study, a variety of bioactivity polypeptide hydrolysates were obtained by enzymatic of Mytilus edulis with trypsin. The hydrolysates mixture enriched peptides were prepared, and the effects of four polysaccharides on the stability of Mytilus edulis enzymatic hydrolysate, indicating by protein precipitation rate, particle size and ζ-potential, were investigated. Results showed that the mixed system will be more stable when added 1 mg/mL CMC-Na or xanthan gum at pH 8 when the total protein content is 10 mg/mL, which can effectively prevent disposition of protein in the hydrolysate. The particle size and ζ-potential were proved to be closely correlated with the stability of Mytilus edulis enzymatic hydrolysate. The smaller the particle size, the larger ζ-potential absolute value ，the higher the density of the distribution, and the more stable the system. This study provides some theoretical data and practical technology for the research and development of the proteins from Mytilus edulis in food industry.

Unlike postmortem changes of ATP related compounds in fish muscle, AMP is temporarily accumulated in postmortem muscle of white leg shrimp ( Litopenaeus vanamei ), and then gradually degrades to IMP. Our previous study demonstrated that optimum temperature for accumulation of IMP was in the range from 20℃ to 30℃, resulting in umami enhancement of this shrimp. However, the mechanism is still unclear. The objective of the present study was to elucidate why IMP was accumulated at 20-30℃ in terms of enzymatic activity of muscle homogenate prepared from white leg shrimp.
Frozen white leg shrimp muscle was homogenized in 20mM Tris-maleate ( pH7.0 ) containing 0.1M KCl and the homogenate was dialyzed against the same buffer for enzymatic assay. The homogenate had degradation activities of AMP, IMP and adenosine. The degradation activity levels of AMP and Adenosine were almost the same and was significantly higher than that of IMP. Degradation activity level of AMP in muscle homogenate of white leg shrimp at 0℃was about 1/150,000 of that of red seabream, in which AMP wasn’t accumulated, suggesting that this very low AMP degradation activity caused temporary accumulation of AMP in muscle of white leg shrimp. On the other hand, the initial rates of AMP degradation at 0℃ sigmoidally rose with the increase in substrate concentration. The relationship between initial rates of AMP degradation and substrate concentration changed to hyperbolic type at 20-30℃.
These results suggested that temperature-dependent enzymatic activity of AMP degradation strongly affected IMP accumulation in postmortem muscle of white leg shrimp.