Abstract:

Papain is a natural sulfhydryl protease of removing aging skin and eliminating melanin, which has skin whitening and skin rejuvenation effects. This enzyme needs to be stored at appropriate temperature, humidity and pH, otherwise it will easy lose its activity during cosmetics processing because of improper operation. Compared with free enzyme, immobilized enzyme can maintain its high efficiency and specific catalytic activity. The commonly used methods of immobilization are cross-linking and embedding. Polyacrylamide （PAM） is a linear water-soluble macromolecule with good biocompatibility and harmless to skin without irritation. It is suitable for cosmetics and commonly used as cosmetics thickener. By PAM gel embedding method, a kind of papain biological membrane with good stability and high enzyme activity could be successfully synthesized. The SEM results showed that the optimal cross-linked structure of the biological membrane was obtained when the concentration and addition amount of aluminum ions was 1.2 mol/L, and 500 μL, and the reaction time was 10 h. It is found that the enzyme activity of the skin-whitening cosmetics containing this kind of biomaterial is three times higher than that of the enzyme-containing cosmetics because of the protection from PAM gel. However, the enzyme activity in the formula of cosmetics containing biological membrane was not as good as that of biological membrane, so the influencing factors of biological membrane stability need further study. It was found that small-molecule moisturizers such as glycerine, propanediol, carbamide and sorbitol did not affect the structure of the biological membrane with embedded enzyme. The sodium hyaluronate with high molecular weight could intertwine with the PAM, making the papain-embedding biological membrane wrap more tightly, resulting in a reduced contact area between the enzyme and the substrate. It was found that PAM would interact with the emulsifiers like Tween20, Tween60, Tween80, APG0814 or M68 and induce encapsulation and sedimentation, thus destroying the stable structure of the enzyme embedded in biological membrane. It is concluded that papain-embedding biological membrane is suitable for the formulation of water-based cosmetics containing small-molecule moisturizers.

Key words: papain, enzyme activity, polyacrylamide, gel embedding, skin whitening