Sugar and value-added products derived from retentate concentrate of sugarcane juice

Abstract

Retentate is a by-product of the membrane clarification of sugarcane juice process and contains high sucrose concentration which is not recovered during sugar manufacturing. The lack of cost-effective treatment of retentate produced by membrane clarification is one of the main issues that hinder adoption of membrane technology in the sugar industry. The present work evaluates retentate composition and uses the information to explore effective approaches for retentate utilization. Compositional analysis revealed that the insoluble components was 6.25% of the retentate in which 48% was organics, and 52% was inorganics. Sucrose (14.9%) was the dominant component followed by reducing sugars (0.62%). Significant amounts polysaccharides (2%) and proteins (0.5%) were present in the retentate, far higher than those present in mixed juice. Lipophilic compounds (e.g., fatty acids, octacosanol, stigmasterol and β-sitosterol) were accumulated in the retentate (3.56% based on the dry substance), while the phenolic compounds content (equivalent to 1.1 mg gallic acid·g−1) was similar to that in mixed juice. Based on the retentate composition, it is proposed that a multifaceted approach can be used to harness various products from sugarcane retentate concentrate. As the carbohydrate component is the highest component in the retentate, two approaches were evaluated to add value, namely sugar recovery via the carbonation process and production of oleaginous yeast biomass from the retentate by a R. glutinis strain. Carbonation clarification was effective to clarify retentate, and it was estimated that 71.2% of sucrose can be recovered using typical sugar manufacturing processes. Biolipid derived has the potential for biodiesel production and the biomass residue had the potential to be used as a valuable feed supplement. A preliminary comparative economic analysis was conducted with the two approaches considering the value of the final products (i.e., sugar and biolipid/biodiesel) and their operating costs.