Production of green juice with an intensive thermo-mechanical fractionation process. Part II: Effect of processing conditions on the liquid fraction properties

The thermally assisted mechanical dewatering (TAMD) process proved to be efficient to dewater various biomasses. The main idea of this process is to supply heat by conduction through the press walls during the wet fractionation. Applied to spinach leaves, this process led to energy saving but also to a larger amount of green juice. In order to optimize the TAMD process and to evaluate the valorisation potential of the liquid fraction produced, the physico-chemical characteristics of the green juice were investigated.In addition to conventional characterisation methods, an analysis method specific to Rubisco protein (ribulose-1,5-bisphosphate carboxylase/oxygenase) has been developed in the present work. The method enables detection and quantification of Rubisco in green juice samples by using size exclusion chromatographic principles (HPLC SEC).Global methods showed that cut degree of the biomass leaves has an effect on the liquid fraction produced. Indeed, nitrogen content, green and white proteins contents are higher when leaves are finely cut.The investigation of temperature processing effect on juice characteristics by applying the different characterisation methods leads to:-At high temperature (90 °C), low nitrogen and fractionated proteins contents in juice, which means that an enriched press cake is produced.-At medium temperature (50 °C), higher nitrogen content in juice, which means that a polypeptides-rich liquid I produced.-At low temperature (30 °C), HPLC SEC method developed revealed that TAMD process produced a green juice containing biomolecules of high added value such as Rubisco protein.