From açaí (Euterpe oleracea Mart.) waste to mannose and mannanoligosaccharides: a one-step process for recalcitrant mannan depolymerization using dilute oxalic acid

Abstract

Açaí seeds are an abundant agroindustrial residue from the Brazilian Amazon region and comprise a rich source of linear mannan polysaccharide, which offers high potential for valorization into bioactive mannose and mannanoligosaccharides. This work optimizes mannose production from açaí seeds using dilute oxalic acid as a safer and greener alternative to sulfuric acid. Experiments were performed to analyze the effects of hydrolysis temperature, time and acid concentration, achieving a maximum mannose yield of 83% when employing 6.0% w/w oxalic acid at 177 °C for 15 min. This is the highest mannose yield ever reported for a one-step hydrolysis of recalcitrant linear mannan using an organic acid. In addition to mannose, this process coproduces mannanoligosaccharides in 9.6% yield. Furthermore, the economic viability of this novel process is demonstrated on an industrial scale via process simulation and techno-economic analysis of a biorefinery processing 6000 kg h⁻¹ of açaí seeds. The simulated process considered oxalic acid recovery and recycling by chromatography, avoiding the use of a base for hydrolysate neutralization and the generation of salt waste, thus minimizing the environmental impacts of the process. The techno-economic analysis revealed a high profitability for a mannose selling price of US$ 10 per kg, resulting in a net present value of US$ 188 million and a payback period of 2.5 years after startup. Therefore, this work provides significant advances in mannose production, offering an efficient and economically viable one-step hydrolysis process that reduces waste, uses renewable raw materials and less harmful chemicals, and has the potential to contribute to a circular bioeconomy in the Amazon region.