UV-Absorbing and Emulsifying Property of Cinnamic Acid-Conjugated Gelatin

Gelatin-cinnamic acid conjugates (Gel-CAs) with Gel/CA molar ratio of 1:1, 1:3.8, and 1:10.7 were prepared as a UV-absorbing emulsifier. Tensiometric and fluorescence spectroscopic study indicated that Gel-CAs were less surface active than Gel. However, Gel-CAs could act as a potent emulsifier in the preparation of mineral oil-in-water emulsion. The oil droplets of the emulsions were stable in terms of their size at room temperature under dark condition during the storage period (1 week). The emulsions stabilized with Gel-CA (1:10.7) were a little but not markedly subjected to the droplet size change by 60-minute UV irradiation (254 nm, 6 W), and the emulsions prepared using Gel-CA (1:1) and Gel-CA (1:3.8) were stable against the UV irradiation. The molar extinction coefficient at 280 nm of CA residue of Gel-CAs, 12,600 M-1 cm(-1), was almost the same as that of free CA, indicating that CA can be conjugated to Gel without the loss of its photochromic property. And the molar extinction coefficient of CA residue of Gel-CAs was much higher when they were contained in emulsions as an emulsifier. Since Gel-CAs could act as not only an emulsifier but also a UV-absorbing agent, they can be used as a UV-absorbing emulsifier.