Extraction of Ziziphus lotus fruit syrups: effect of enzymatic extraction and temperature on their rheological and chemical properties

Fruit syrups are attracting increasing interest in the food industry. Ziziphus lotus fruit syrups were elaborated through the traditional and enzymatic methods with 30, 50 and 70° Brix. A chemical analysis revealed that Ziziphus lotus fruit powder and syrups present a potential source of energy through their relatively higher content of carbohydrates. Rheological oscillatory tests showed that syrups of 30°Brix demonstrate a viscous type of behaviour, the 70°Brix syrups possess an elastic behaviour, while the 50°Brix syrups present a mixed behaviour over the temperature range of 20 to 80°C. These syrups did not demonstrate any thixotropy or time dependence of viscosity. The complex viscosity was described successfully with a mathematical model that incorporates both independent variables, with an Arrhenius-type dependence on temperature, with an activation energy of 21.94 kJ mol-1 for the whole Brix range. The flow behaviour evaluation of the 30 and 50°Brix showed that these are shear-thinning fluids, tending to Newtonian fluids at higher temperatures. The dynamic viscosity was well described by the power law and the dependence of its parameters on temperature was adequately described by a Turian approach. The syrups of Ziziphus lotus fruit demonstrated a potential for further beneficial research with a view to obtaining a commercial food product.