Stevioside1) is natural non-caloric sweetener from Stevia rebaudiana BERTONI, which has been used for a long time in Paraguay and Brazil. Purified stevioside is an odorless powder approximately 250 to 300-fold sweeter than sucrose, and is composed of steviol, a diterpenic hydroxy carboxylic acid and three glucose molecules. At present, stevioside is widely used as a non-caloric sugar substitute, and in various kinds of drinks and food products in many countries. In Japan alone, approximately 200 t of S. rebaudiana extract are consumed each year. Stevioside has been subjected to various assessments for safety, and to date, no serious toxic effects have been reported. 2,3) Stevioside and the crude extract of S. rebaudiana have been determined as non-mutagenic in many bacterial test systems, such as some test strains of Salmonella typhimurium, Escherichia coli, and Bacillus subtillis, either in the presence or absence of metabolic activation, which is mostly derived from the rat liver S9 fraction. 4) However, it is known that stevioside is converted to its aglycone, steviol, by intestinal bacteria when orally administered to rats. 5) Pezzuto et al. 6) demonstrated that steviol causes a dose-dependent positive response in the forward mutation assay using S. typthimurium TM677 in the presence of a metabolic activation system (Aroclor-induced rat liver S9 fraction).Recently Suttajit et al. 7) showed that stevioside, at a high dosage (50 mg/plate), possesses a weak mutagenic activity S9 fraction. Since this observed mutagenic effect could be caused by the impurities present in stevioside. Matsui et al. 8) examined seven mutagenicity tests using bacteria (reverse mutation assay, forward mutation assay, umn test and rec assay), cultured mammalian cells (chromosomal aberration test and gene mutation assay), and mice (micronucleus test). Consequently, the aglycone, steviol, was shown to produce dose-related positive responses with the same mutagenicity, i.e. forward mutation assay using S. typhimurium TM677, and chromosomal aberration test using Chinese hamster lung fibroblast cell (CHL) line, and gene mutation assay using CHL. Herein, we wish to identify the genuine mutagenic active substance that is mutagenic toward S. typhimurium in the absence of S9 in steviol derivatives. The present paper describes the mutagenicity (forward mutation assay) studies, which were carried out with steviol and several of its oxidative derivatives.We report that steviol (2), steviol-16a,17-epoxide (3), 15-hydroxy-steviol (4), 15-oxo-steviol (5), steviol methyl ester (6), 16-oxo-steviol methyl ester (7), 3,16-seco-13-oxo-steviol methyl ester (8), 3,16-seco-13-hydroxy-steviol methyl ester (9), and steviol methyl ester 8,13-lactone (10) are mutagenic toward S. typhimurium strain TM677, in the presence of a 9000ϫg supernatant fraction (S9) obtained from the liver of Aroclor 1254-pretreated rats. While only steviol methyl ester 8,13-lactone (10) showed mutagenicity toward the same strain in the presence and in the absence of S9, it is int...

The linear thermal expansion, AC susceptibility and magnetostriction have been measured on a single crystal of HoA12. Our results clearly show two phase transitions associated, respectively, with establishment of magnetic order and with spontaneous spin reorientation. The critical exponent ySR of the susceptibility for l-3 TSR has been determined. From magnetostriction measurements along the major symmetry directions of the crystal, we have obtained the possible deformation modes compatible with the point symmetry of the cubic crystal structure. A complete study of the magnetoelastic behaviour has allowed us to determine the reduced magnetoelastic coupling coefficients M : / C y , M i / C ' , M f / C " (I = 4,6)and D"/C".Themodelusedisbasedonasingle-ionorigin for the crystal electric field interaction of the rare-earth ion, and we have taken into account the spontaneous reorientation of the magnetic moment in the molecular field, which represents the exchange interaction.

We have developed a super-resolution read-only memory (ROM) disc with a high readout stability using a zinc oxide (ZnO) thin film. Applying the reversible and repeatable change in the optical constants of ZnO induced by heat, we can successfully confirm super-resolution effects that can read out a small mark beyond the optical diffraction limit. By realizing this characteristic in a ROM disc, we obtained a linear bit density twofold higher than that of a conventional disc in the blue-laser optical system. To clarify the origin of ZnO super resolution, we performed two types of test: a test to compare ZnO super-resolution characteristics using blue- and red-laser optical systems, and a test to determine the relationship between the absorption edges of semiconductor films with various energy band gaps and readout laser wavelength.

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Energy-gap-induced super-resolution (EG-SR) technology has been developed for high-density optical discs with a high readout stability using a zinc oxide (ZnO) thin film. ZnO film indicated a thermal change in optical properties. By applying these effects to a read-only-memory (ROM) disc, we obtained a linear bit density twofold that of conventional ROM discs in our experimental optical pickup system with a 404-nm-wavelength laser and a 0.85-numerical-aperture (NA) objective lens. In this study, we report an optical disc technology that enables super-resolution readout of data pits in a dual-layer structure by employing a transparent ZnO super-resolution functional film.