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 microemulsion system of 0.3 M bis(2-ethylhexyl)sulfosuccinate sodium salt in isooctane and 14.5% distilled water. Highly viscous gels obtained at temperatures above 30 degreesC become free-flowing liquids at low temperatures (5-10 degreesC). This reversible temperature-dependent sol-gel transition phenomenon is used to immobilize several enzymes, such as lipase from Candida rugosa, alcohol dehydrogenase from baker's yeast, mandelonitrile lyase from Sorghum bicolor, and horseradish peroxidase in the gelatin matrix by solubilizing the enzyme in a microemulsion-based gelatin solution at low temperature (<5 degreesC) and then cross-linking with glutaraldehyde. The enzymes retain 70-80% of their activity after immobilization and can be used in biotransformations in organic solvents without any changes in enantioselectivity. This work provides a unique low-temperature technique for enzyme immobilization in a biocompatible gelatin matrix with a great flexibility of size and shape.