Utilisation of mango seed husk for the production of phenolic compounds and glucose with C1184 enzyme preparation reveals the role of glucuronoyl esters in lignin–carbohydrate linkages in biomass recalcitrance

This study assessed mango seed husk (MSH) fractions for producing glucose and phenolic compounds using commercial enzymes. We focused on cleaving lignin-carbohydrate linkages, specifically feruloyl and glucuronoyl esters, to decrease biomass recalcitrance and enhance product extraction. For saccharification studies, we used Sigma's C1184 cellulase from Aspergillus niger. Characterisation results of ground MSH using phloroglucinol and scanning electron microscopy revealed that it could be separated into a fine fraction, containing less lignin and cellulose fibres with parallel orientation, and a coarse fraction, with higher lignin content and cellulose fibres at an angled orientation. Activity assays and zymogram analysis of the C1184 preparation prior to saccharification studies revealed diverse CAZyme activities associated with distinct proteins, with xylanolytic activity dominating. Saccharification studies with ground MSH found that the C1184 preparation supplemented with feruloyl or glucuronoyl esterases was suitable for extracting phenolic compounds (0.4-1.7% w/w) from MSH while converting up to 20% of the total biomass as glucose. Interestingly, when replacing 50% (w/w) of the C1184 preparation with glucuronoyl esterase, glucose release nearly doubled from both MSH fractions. Additionally, phenolics attached to carbohydrates may be less condensed in the fine fraction, as all three esterases released three-to-five times more phenolics from the fine fraction compared to the coarse fraction with higher lignin content. Saccharification trials with alkali-pretreated ground MSH showed that the C1184 preparation supplemented with β-glucosidase produced low glucose levels (170-250 mg/g dry biomass) from the substrate after 24 h, even at 50 mg/g biomass protein loading. Overall, this work advances our understanding of the importance of lignin-carbohydrate linkages formed via glucuronoyl esters in biomass recalcitrance. Furthermore, our study corroborates the potential of MSH as a valuable feedstock for producing value-added products in the biorefinery sector.