Hiroo Ogawa

Influence of pH and temperature on the ultraviolet-absorbing properties of porphyra-334

Mycosporine-like amino acids (MAA) are a class of small, water-soluble ultraviolet (UV)-absorbing compounds composed of aminocyclohexenone or aminocycloheximine rings with nitrogen or imino alcohol substitutes. Their absorption maxima are from 310 to 360 nm. They have been reported in green, red and brown algae from torrid zones, temperate zones and polar regions. Approximately 20 MAA have been identified in marine organisms since the 1960s. As natural UV-absorbing compounds with high molar extinction coefficients, MAAs have potential commercial applications in suncare products, such as cosmetics for skin protection, and in the protection of non-biological materials, such as photostabilizing additives in the plastic, paint and varnish industries. Porphyra-334 is one kind of MAA widely distributed among marine algae. It has a maximum absorption at 334 nm (ε = 4.23 × 10). Porphyra334 has potential commercial applications. Most of the studies on MAA are concerned with environmental control (mainly light, salinity and temperature) of production of MAA and their physiological roles. There are few reports on the stability of MAA in different conditions. The lack of basic studies limits the use of MAA. The present study investigates the stability of porphyra-334 solution using the UV absorption spectra under various environments of pH and temperature. Commercial products of Porphyra yezoensis harvested from the Ariake Sea in Saga Prefecture, Japan were used. Dried nori was stored at −20°C until used. Porphyra-334 was extracted and purified based on Takano et al. Porphyra-334 was identified by comparing the absorption spectrum and retention time reported by Klisch and Häder. pH of purified porphyra-334 aqueous solution was adjusted with 0.1 M HCl and 0.1 M NaOH to give pH values of 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 8.0, 9.0, 10.0, 11.0, 12.0 and 13.0. After pH adjustment, the porphyra-334 solutions were sealed in airtight containers with N2 and maintained at room temperature or in 40, 60 and 80°C water baths in darkness. The absorption spectra of porphyra-334 solutions were measured every 2 or 4 h in the range 200– 400 nm using a spectrophotometer (Hitachi, U-

Comparison of horse mackerel and tilapia surimi gel based on rheological and 1H NMR relaxation properties

Horse mackerel and tilapia surimi were subjected to six different heat and pressure treatments in order to compare gelation characteristics of easy- and difficult-setting gels, that is, temperature dependence, by observing rheological properties and microscopic molecular mobility. The stress-relaxation and proton spin-spin relaxation time (1H T2) of water were measured for all treated gels. Horse mackerel gel demonstrated higher elasticity, large distribution of the stress-relaxation process, and smaller water 1H T2 than tilapia in both heat and pressure treatments. The water 1H T2 was steeply increased in the pressure treatment at around 294 MPa for both fishes. In contrast, the 1H T2 rarely changed in the heat treatment in spite of the considerable change in rheological properties. From the experimental results, it is considered that the gelation of horse mackerel (easy setting) surimi is induced by highly unfolding are re-aggregation of protein, which contributes to the formation of a strong network structure compared with tilapia in both heat and pressure treatments, and that pressure treatments hardly improve the gel strength of tilapia (difficult setting) surimi. The water 1H T2 measurement was used effectively in order to study gelation characteristics of easy- and difficult-setting fish through observing its molecular dynamics.

The isolation of prophyra-334 from marine algae and its UV-absorption behavior

Prophyra-334 was prepared by methanol extraction and HPLC methods from marine algae (dried laver). It is a sunscreen compound that has good absorption of ultraviolet radiations in the wavelength ranges of 200–400 nm. The absorption maximum wavelength of prophyra-334 is at 334 nm, so defined the name. The molar extinction coefficient (ε) of prophyra-334 in aqueous solution at 334 nm wavelength is 4.23×104. The absorption of prophyra-334 in organic solvents differs in aqueous solutions. In polar organic solvents, the absorption maximum wavelength of prophyra-334 has a slight shift toward longer wavelength compared with that in pure water. On the contrary, in inert non-polar organic solvents, the absorption maximum wavelength and the shape of absorption spectra of prophyra-334 are changed. The effects of organic solvents on prophyra-334 stability suggested that: (1) the absorbance of prophyra-334 in water is generally constant at temperature of 60°C in 24 h, meaning that prophyra-334 is quite stable in water; (2) the absorbance of prophyra-334 in ethanol and hexane decreases at the same condition. The stability of prophyra-334 in organic solvents is less than that in aqueous solution. In benzene, the prophyra-334 is very instable.

Improvement of the extraction procedure for hyaluronan from fish eyeball and the molecular characterization

The object of this study was to improve the isolation procedure of hyaluronan and to compare characteristics of hyaluronan from the eyeball of bigeye tuna Thunnus obesus with other sources. General sources of hyaluronan are from Streptococcus zooepidemicus and rooster comb. Hyaluronan can be also obtained from the vitreous of fish eyes. Pure hyaluronan of higher molecular weight was obtained by the following improved extraction procedure: the frozen vitreous of a tuna eyeball was used to avoid contamination with blood, muscle tissue, and other factors; extracting was carried out over a long time period under cold conditions; cetylpyridinium chloride was used in order to separate mucopolysaccharides containing hyaluronan in the initial procedure without the process of removing fat and protein by reagents. The hyaluronan obtained was characterized by gel permeation chromatography, dynamic light scattering measurements, and viscometry. The characteristics of hyaluronan from tuna eyeballs were similar to those from other sources. However, the viscosity was lower. The possible reason could be ascribed to the wide distribution of molecular size in the vitreous humor of fish eye.

Effect of solvent transfer in agar gels on stress relaxation under large deformation.

We measured stress relaxation, volume of exuded water, and spatial distribution of stress in agar gels under large deformation. Gels with smaller sample size and lower concentration exuded water faster and had shorter stress relaxation time. Gels with the storage time of 3 days exuded more water and had shorter stress relaxation time than gels with the storage time of 1 day, and this tendency was remarkable for low-concentration gels. Examination of the spatial distribution of stress in a cylindrical gel under large deformation showed that the outer part of the gel had smaller stress than the inner part at an early stage, and the area with small stress gradually extended into the inner part. This result indicates that the inhomogeneity of water content caused by water exudation from the gel surface induces the stress distribution in the gel.

Applicability of the modified mooney-rivlin equation on rheological analysis of fish-meat gel

Rheological properties of fish-meat gels were investigated according to the modified Mooney-Rivlin equation and the three-element model representing large and small deformation theories, respectively. The Mooney-Rivlin equation was developed considering directly the volume change with the strain for characterizing rheological property of fish-meat gel. The results led to the conclusion that using the modified large-deformation equation considering volume, changes of samples were more useful to investigate effectively the mechanical behavior of fish-meat gels. The volume changes of fish-meat gel with the, strain resulted that fish-meat gel kept the linearity under about 0.2–0.3 compression strain in stress-strain relation. The stress-relaxation test of fish-meat gel was performed under the strain of 0.25 in the compression process. The elastic moduli and viscosity were decreased with the moisture contents of the gels. These results indicated the same trend as the results according to the modified Mooney-Rivlin equation. Comparing the results according to the large and small deformation theories led to the proportional relationships between the elastic modulus values and the Mooney-Rivlin constants, C1 and C2.

Thermal and rheological properties of pressurized carp meat

Abstract In order to make clear the thermal and rheological changes in meat from high pressure treatment, we discussed volume changes, enthalpy changes from measurement of DSC, molecular weight changes from SDS-PAGE, and dynamic viscoelastic measurement on the pressurized samples. Carp meat was pressurized from 98MPa to 490MPa for 13h at 1°C. Although pressurized meat paste under 294MPa produced a gel by heating, meat paste pressurized at not less than 392MPa gave a brittle structure. A comparison of the results from other measurements suggested that there was a similar denaturation mechanism in both heating and pressurizing treatments.