HYGROSCOPIC PROPERTIES OF ORANGE PULP AND PEEL

Abstract

This contribution addresses the hygroscopic properties of orange pulp and peel (OPP), an agro-industrial by-product used for pectinase and phytase production by solid-state fermentation (SSF). Experiments were carried out using the static gravimetric method and the modified Halsey model best fitted to the experimental data. Bates and Watts curvature measurements, Box parameter bias estimation and residual analysis were performed in order to validate the model and the estimated parameters. Desorption experiments were also carried out and the results showed that drying took place even at high air relative humidity. The results presented are fundamental for water transfer modeling in SSF in fixed bed bioreactors.Practical ApplicationsThe current work addresses the hygroscopic properties of OPP, a solid waste rich in pectin, which can be used as substrate in SSF for the synthesis of pectinases and phytases. Thermal sorption isotherms (TSI) and water desorption kinetics (WDK) were investigated, both of the key information required for the fermentation process, either on simulation or in the laboratory. Usually, the moisture content of the solid phase in SSF is far above its moisture equilibrium content, and since the microbial metabolism is strongly affected by the moisture content, knowledge of TSI and WDK are mandatory. Experimental information was gathered and TSI nonlinear models were applied and special care was taken for the parameter estimation, applying specific tools to assess nonlinearity problems. The work therefore possesses significant new information, particularly interesting for engineers dealing with design and scaling-up of SSF bioreactors and with nonlinear regression estimation.