Lipase production by Yarrowia lipolytica with soybean hulls in tray and packed-bed bioreactors : experimental studies and process modeling

Abstract

This study aimed at lipase production by Yarrowia lipolytica in solid-state fermentation (SSF) of soybean hulls. Defined and complex media were tested as supplementation for lipase production in tray and packed-bed bioreactor (PBB). With the temperature, lipase and protease data acquired from PBB fermentations, energy and mass balance equations were implemented aiming at the mathematical process description. Also, a computational routine to process soybean hull images was developed for particle diameter determination. The results from medium supplementation investigation indicated that lipase production was higher with complex media and reached 1.35 kU L−1 with the medium containing yeast extract, bactopeptone and soybean oil (YPO). In this case, the bed temperature in the PBB reached 35 °C, which may have influenced protease and lipase production. Size distribution models were fitted to the data obtained with the digital image processing routine, and the equivalent diameter was better described by the Sigmoid model. Finally, simulations were performed and the Nusselt number (Nu) values smaller then those calculated with single sphere correlations were required in the simulation. A parameter sensitivity analysis indicated that the inlet water activity (aw0 ) had the most relevant influence on the model, Therefore, these two parameters were estimated. The value for Nu was 3.96×10−4 ± 7.33×10−5 , while aw0 presented no statistical significance. The final simulation results were consistent with experimental data in terms of peak temperatures and lipase production.