180 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS ß x m O ß 2 3 4 5 6 7 pH Figure 3. pH dependence of viscosity of Gs aqueous solution (1.0 wt%, 20øC). Table I Gelling behaviors of G derivatives H3Ci,•C OO R 3 CH3 (• H3 '• 3 )-o o H i COO R 2 OH OH R1 R2 R3 gel-formation H H H /3 ++ K(H} H(K} H /3 ++ K K H /3 - K K K /3 - K(H} H (K} CH3 /• - K salt of G Pentaacetate /3 K salt of Glycyrrhetin o• J-

PROPERTIES OF or- AND [3-GLYCYRRHIZINS 181 • 6 3 0 • -g lycy rrhet i n d, -g l y cy rrh e t i n ! ,+ / \ ß , I I •,•ø o 1 2 Shear stress (dyne/cm 2 )X10 -4 Figure 4. Flow curves of gels (10 wt%), Cone-plate viscometer, 30øC, 0-30 rpm. was used. The sample was frozen in a sample-holder using liquid N2 and cracked. Its surface was etched in vacuo at about - 80 - - 90øC. The structure of the frozen gel was directly observed with the microscope. RHEOLOGICAL MEASUREMENTS Flow curves of the gels were obtained with a Cone-plate Viscometer (B.E.E. Co., Ltd.) at 20øC. Maximal shear rate and sweep time were 500 sec-• and two min, respectively. The viscosities of or- and [3-G solutions were measured at 20øC, 24 hr after their prepa- ration. A Brookfield Viscometer (Seiki Kogyo Laboratory, rotor No. 1 and 3, 12 rpm) was used for [3-G. A Ubbelohde's Viscometer (Shibata Kagaku Kiki Kogyo) was uti- lized for ot-G. SOLUBILIZATION TEST Ten grams of ethanol solutions of solubilizates (0.5 wt%) were added to 90 g of ot-G aqueous solutions of various concentrations (all of which were adjusted to pH 4.5 with V3o M phosphate buffer). The mixtures were shaken ten times, left standing for 24 hr at 30øC, and subjected to the measurement of transmittance on a Hitachi Recording Spec- trophotometer, Model EPS-3T. Appraisal of the solubilizing ability of ot-G was based on the transmittance of the resulting quaternary systems at 450 nm, at which wave- length the solubilizates have little optical absorption. EMULSIFICATION TEST Emulsions were prepared by the following procedure. To 70 g of the aqueous solution