Enhanced degradation of caffeine by immobilized cells of Pseudomonas sp. in agar–agar matrix using statistical approach

Previously, we isolated caffeine degrading Pseudomonas strain from soil of coffee plantation area, which could utilize caffeine as sole carbon and nitrogen source and could tolerate caffeine up to 20 g/L. In this study, caffeine degradation by immobilized cells of this strain was investigated. Various matrices were considered and agar–agar was chosen based on degradation rate (0.08 g/(L h)), bead stability and reusability. Further, immobilization parameters, viz., bead size (mm), agar–agar concentration % (w/v) and cell concentration (g/L) were optimized using central composite design. The optimal conditions of cell concentration, agar–agar concentration and bead size were 7.8 g/L, 5% (w/v) and 6.2 mm. Under optimal conditions, caffeine degradation rate was found to 0.15 g/(L h), which closely agrees with the model predicted values. This is the first report on caffeine degradation at high concentrations (10 g/L) by immobilized cells of Pseudomonas sp. Immobilization efficiency was 80%. Damköhler number is very much higher than 1, suggesting that mass transfer is the rate limiting process.