Hygroscopic Properties of Orange Pulp and Peel

Abstract

AbstractThis 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 modifiedHalsey model best fitted to the experimental data.Bates andWatts 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 inSSFin fixed bed bioreactors.Practical ApplicationsThe current work addresses the hygroscopic properties ofOPP, a solid waste rich in pectin, which can be used as substrate inSSFfor 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 inSSFis far above its moisture equilibrium content, and since the microbial metabolism is strongly affected by the moisture content, knowledge ofTSIandWDKare mandatory. Experimental information was gathered andTSInonlinear 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 ofSSFbioreactors and with nonlinear regression estimation.