An unusual reversible sol-gel transition phenomenon in organogels and its application for enzyme immobilization in gelatin membranes

An unusual phenomenon is observed for gelatin solutions (1.7-6.8%) in the m icroemulsion system of 0.3 M bis(2-ethylhexyl)sulfosuccinate sodium salt in isooctane and 14.5% distilled water. Highly viscous gels obtained at tempe ratures above 30 degrees C become free-flowing liquids at low temperatures (5-10 degrees C). This reversible temperature-dependent sol-gel transition phenomenon is used to immobilize several enzymes, such as lipase from Candi da rugosa, alcohol dehydrogenase from baker's yeast, mandelonitrile lyase f rom Sorghum bicolor, and horseradish peroxidase in the gelatin matrix by so lubilizing the enzyme in a microemulsion-based gelatin solution at low temp erature (<5 degrees C) and then cross-linking with glutaraldehyde. The enzy mes retain 70-80% of their activity after immobilization and can be used in biotransformations in organic solvents without any changes in enantioselec tivity. This work provides a unique low-temperature technique for enzyme im mobilization in a biocompatible gelatin matrix with a great flexibility of size and shape.