Thermal and Rheological Properties of Juices and Syrups during Non-centrifugal Sugar Cane (Jaggery) Production

Abstract

This work focused on the physicochemical characterization of sugarcane juices and syrups obtained during non-centrifugal cane sugar (NCCS) production. Samples were collected from two different factories that use steam or combustion gases as heating medium during the open evaporation process. Juices and syrups contained sucrose as the predominant sugar (>90%), followed by reducing sugars (i.e. glucose and fructose), and the sugars profile remained invariable during processing. Viscosities of the solutions ranged from 1.4 and 165.8 mPa s, and a large dependence on temperature and solids content was observed. Heat capacities of the liquid mixtures ranged from 2.4 to 3.8 kJ/kgK, and the densities were barely constant, ranging from 1.12 to 1.35 g/ml. The thermal conductivity of the liquid solutions was in between 0.26 and 0.46 W/mK. Correlations were obtained for all properties as function of temperature, and the sugars concentration or the solids content (i.e. °Brix). A comparison with reported data, and models for juices, syrups, and sucrose solutions, as well as with predictive equations for saccharides mixtures is presented. Regressed equations enabled to estimate heat transfer coefficients of the boiling liquid during the concentration process. Convective heat transfer coefficients around 160-290 W/m2K were estimated for nucleate boiling. Comparatively, values around 70-200 W/m2K were estimated for film boiling conditions.