Yukinori Nozaki

Effect of trehalose on the gel-forming ability, state of water and myofibril denaturation of horse mackerel Trachurus japonicus surimi during frozen storage

The cryoprotective effects of trehalose on fish myofibrillar protein were compared with those of sucrose, glucose and sorbitol. The frozen surimi with trehalose exhibited significantly higher Ca2+-ATPase activity through-out the storage periods, resulting in higher gel-forming ability than that of without trehalose. The amount of unfrozen water was significantly increased in the surimi upon addition of trehalose at any concentrations tested. The findings suggest that trehalose constructed bound water molecules in protein structure, consequently suppressed freeze-induced denaturation of protein and maintained gel-forming ability. An addition of 5.0% to 7.5% concentration of trehalose showed threshold behavior to increase the amount of unfrozen water and to prevent freeze-induced denaturation of protein. The effects of trehalose were almost similar to those of other sugars.

Effect of chitin hydrolysate on the denaturation of lizard fish myofibrillar protein and the state of water during frozen storage

Abstract We investigated the effect of chitin hydrolysate made from crustacean shells and cephalopod cartilage on the denaturation and state of water in lizard fish myofibrillar protein (Mf) during frozen storage at −25 °C for 120 days. The chitin hydrolysate (2.5–12.5 g dry weight) was added to 100 g of the Mf, and the changes in the Mf Ca–ATPase activity and the amount of unfrozen water in the Mf were examined during frozen storage. The addition of chitin hydrolysate markedly decreased the inactivation rate of the Mf Ca–ATPase. The amount of unfrozen water in the Mf increased upon the addition of chitin hydrolysate, and then decreased gradually during frozen storage. On the other hand, the amount of unfrozen water in the control dropped drastically during the initial period of frozen storage. At a concentration of over 5.0%, chitin hydrolysates completely suppressed the inactivation of the Ca–ATPase and maximized unfrozen water in Mf. These results suggest that chitin hydrolysates suppress the denaturation of Mf through enhancement of the interaction between the hydration sphere of the Mf and equatorial OH groups of chitin hydrolysate.

Effect of shrimp head protein hydrolysates on the state of water and denaturation of fish myofibrils during dehydration

To utilize fisheries waste products as food materials with functional properties, shrimp head protein hydrolysates (SHPH) from three species of shrimp, that is, Northern pink shrimp (Pandalus eous). Endeavour shrimp (Metapenaeus endeavouri) and Black tiger shrimp (Penaeus monodon), were produced by enzymatic hydrolysis using endopeptidase derived from Bacillus subtilis and exopeptidase derived from Aspergillus oryzae at a level of 0.1% (w/w). SHPH were rich in protein (90–91%) and amino acids (71–84%) but little fat (0.01–0.02%). The average molecular weight of SHPH was 300–1400. The effect of 5% SHPH (dry basis) addition on the state of water and denaturation of lizard fish myofibrils (Mf) during the dehydration process was evaluated by the desorption isotherm and the Ca-ATPase activity, and compared with the effect of sodium glutamate (Na-Glu). SHPH decreased the water activity and the Ca-ATPase inactivation, and increased monolayer sorbed water and multilayer sorbed water of Mf, although these effects of SHPH were smaller than those of Na-Glu. These findings suggest that the SHPH suppressed dehydration-induced denaturation of myofibrillar protein by stabilizing the hydrated water surrounding myofibrils.

Preservation of resting eggs of the euryhaline rotifer Brachionus plicatilis O. F. Müller by canning

Recent research has indicated that the hatchability of mass-produced rotifer (Brachionus plicatilis) resting eggs (stored in sea water in the dark at 4°C) gradually decreases due to bacterial infection of the porous egg surface. We investigated whether lyophilization as well as a canning treatment could solve the problem of bacterial infection of resting eggs. The canning method preserves eggs in a dry form, after lyophilization at −40°C. The resting eggs were packed in cans under various pressures: 21, 34, 48, 61, 75, 88 and 101 kPa. The viability of the canned resting eggs was tested by hatching experiments done 6 and 12 months after canning and storage at 5°C. When partial pressures were less than 88 kPa, percent hatching after 6 months ranged between 16 and 20%, similar to that of uncanned eggs (19% hatching), but significantly lower (9 and 11%, P<0.01) at 88 and 101 kpa. Even after 12 months, percent hatching remained at 35% when canning was at 61 kpa. Lyophilization and canning at partial pressure lower than 88 kPa could therefore preserve resting eggs, and hatchability was maintained. Canned eggs that were treated with NaC1O (1 mg 1−1) or NFS-Na (5 mg 1−1) showed a significantly higher percent hatching (68% and 80%, respectively, each P<0.05) than untreated eggs.

Cryoprotective effects of shrimp head protein hydrolysate on gel forming ability and protein denaturation of lizardfish surimi during frozen storage

The effects of shrimp head protein hydrolysate (SHPH) from three species of shrimp (northern pink shrimp [Pandalus eous], endeavour shrimp [Metapenaeus endeavouri], black tiger shrimp [Penaeus monodon]) on gel forming ability and protein denaturation of lizardfish surimi during frozen storage at −25°C were evaluated. The quality of lizardfish surimi with 5% (dried matter) of any of the three SHPH or sodium glutamate (Na-Glu) was examined in terms of gel strength, whiteness, Ca-ATPase activity and the amount of unfrozen water, comparing with those of surimi without additive as the control. The residual Ca-ATPase activity and gel strength of surimi with SHPH were higher than those of the control throughout 180 days of frozen storage, regardless of shrimp species. The highest effect was found in surimi with Na-Glu. The gel strength and Ca-ATPase activity found a high positive correlation. The addition of SHPH to surimi also increased the amount of unfrozen water by approximately 1.29–1.36 fold higher than the control, however kamaboko gels of the control was significantly whiter. From these results, freeze-induced denaturation of lizardfish muscle protein could be lessened by the addition of SHPH, resulting in a high gel strength and Ca-ATPase activity.

Effect of starvation on lipid metabolism and stability of DHA content of lipids in horse mackerel (Trachurus japonicus) tissues

For the purpose of characterizing the effect of starvation on 22∶6n−3 (DHA) content in marine fish tissues, horse mackerel (Trachurus japonicus) were reared in a tank containing filtered, sterilized seawater under nonfeeding conditions for 107 d (survival rate of the fish was 96.5%). The crude total lipids (TL) of ordinary dorsal muscle, dorsal skin, and viscera of the starved individuals were separated into classes on silicic acid columns, and the constituents of the TL were quantified by gravimetric recovery from column chromatography. The TL, initially>85% TAG in dorsal muscle, and even more in skin lipids, decreased dramatically within the first 44 d of starvation, and then decreased more gradually during the remainder of the test period, whereas the visceral TL decreased more slowly. The percentages of both saturated and monoenoic FA in the muscle TL also decreased somewhat, but those of DHA increased significantly in muscle during the test periods. Decreases in PE and PC initially were much smaller than TAG, but DHA levels remained high in both PE and PC. These findings indicate that all of the FA in the depot lipids of horse mackerel tissues are easily metabolized for energy production during starvation, but DHA in muscle lipids of the starved fish was maintained at a consistently high level, indicating that starvation did not affect DHA stability in phospholipids. The findings suggest that preservation of DHA in cell membrane lipid PE and PC is necessary for self-protection functions in starving fish.

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.

Occurrence of two distinct molecular species of cathepsin B in carp Cyprinus carpio

We purified cathepsins B1 and B2 from the ordinary muscle of carp Cyprinus carpio. The N-terminal amino acid sequences (12 residues) of 29 kDa bands of cathepsins B1 and B2 are the same and showed high homology of 75% and 83%, respectively, with the heavy chain of rat and human cathepsins B. Based on conserved sequences of other cathepsins B and the N-terminal amino acid sequences of 29 kDa bands, we cloned carp cathepsin B cDNA. The nucleotide sequence of carp cathepsin B cDNA consists of 1470 bp including a 993 bp open reading frame, encoding a deduced protein of 330 amino acids. The deduced amino acid sequence of carp cathepsin B has similarity of 80% to rainbow trout cathepsin B and of 76–78% to other vertebrate cathepsins B. The sequence of its isoform was also determined during molecular cloning, which has 94.8% similarity with first cloned cathepsin B. They are completely same in N-terminal amino acid sequence of heavy chain, active sife and potential N-glycosylation site. This indicates there are at least two kinds of cathepsin B functioning in vivo in carp.

Effect of Amino Acid Addition on the Isosteric Sorption Heat during Dehydration of Fish Myofibrils.

To elucidate the suppressive effects of amino acid on the denaturation of fish myofibrils during dehydration, the water activity and the sorption water content of white croaker myofibrils in the presence of various amino acids at different temperatures were examined, and isosteric sorption heat was calculated on the basis of the Clausius Clapeyron equation.Isosteric sorption heat of the myofibrils increased with the addition of amino acids such as Na-Asp, Na-Glu, Lys, and Ala. It was suggested that amino acids enhance isosteric sorption heat of myofibrillar proteins during dehydration and consequently suppress the dehydro-denaturation of them.

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.