Influence of Mechanochemical Pretreatment on the Bioavailability of Mannan from Macauba Seed Cake

Macauba seed cake, a carbohydrate-rich biomass from seed mechanical oil extraction, is a promising feedstock for sustainable biorefinery applications. In this study, seed cake polysaccharides were characterized, and a mechanochemical pretreatment using planetary ball milling was applied as a chemical-free strategy to overcome biomass recalcitrance. The effects of dry grinding at different times (30, 60, 120, 180, and 240 min) were evaluated through ¹³C solid-state nuclear magnetic resonance, X-ray diffraction, and mid-infrared FTIR spectroscopy. The characterization of macauba seed cake confirmed it to be a rich source of d-mannose (44%). Solid-state ¹³C CPMAS NMR proved to be highly sensitive for monitoring mannan I polymorphs and revealed progressive amorphization during the pretreatment. Ball milling significantly reduced mannan crystallinity (from 26.6% in untreated biomass to 1.2% after 120 min and 2.4% after 180 min of pretreatment), promoted polymorphic transformations, and induced structural modifications in the polysaccharide functional groups. These structural changes improved polysaccharide bioavailability, leading to improved enzymatic hydrolysis by mannanases produced from Aspergillus niger. Saccharification yields, using 20 IU of mannanases per gram of dry biomass, reached up to 76.8% mannose release after 120 min of milling, confirming the strong correlation among crystallinity reduction, amorphization of mannan I, and enzymatic digestibility. Overall, macauba seed cake was validated as a promising feedstock for mannose recovery and other reducing sugars. To our knowledge, this is the first report of mannose production from macauba seed cake via ball milling and enzymatic hydrolysis and the first to demonstrate solid-state NMR as a tool to track amorphization in mannan-rich biomasses.