High concentration and yield production of mannose from acai (Euterpe oleracea Mart.) seeds via mannanase-catalyzed hydrolysis

The acai seed corresponds to approximately 85% of the fruit's weight and represents similar to 1.1 million metric tons of residue yearly accumulated in the Amazon region, resulting in an acute environmental and urban problem. To extract the highest value from this residue, this study aimed to evaluate its chemical composition to determine the appropriate applications and to develop conversion methods. First, mannan was confirmed as the major component of mature seeds, corresponding to 80% of the seed's total carbohydrates and about 50% of its dry weight. To convert this high mannan content into mannose, a sequential process of dilute-acid and enzymatic hydrolysis was evaluated. Among different dilute-H2SO4 hydrolysis conditions, 3%-acid for 60-min at 121 degrees C resulted in a 30% mannan hydrolysis yield and 41.7 g/L of mannose. Because similar to 70% mannan remained in the seed, a mannanase-catalyzed hydrolysis was sequentially performed with 2-20% seed concentration, reaching 146.3 g/L of mannose and a 96.8% yield with 20% solids. As far as we know, this is the highest reported concentration of mannose produced from a residue. Thus, this work provides fundamental data for achieving high concentrations and yields of mannose from acai seeds, which could add commercial value to the seeds and improve the whole acai productive chain.