Monolignol Potential and Insights into Direct Depolymerization of Fruit and Nutshell Remains for High Value Sustainable Aromatics

Abstract The inedible parts of nuts and stone fruits are low-cost and lignin-rich feedstock for more sustainable production of aromatic chemicals in comparison with the agricultural and forestry residues. However, the depolymerization performances on those food-related biomass remains unclear, owing to the broad physicochemical variations from the edible parts of the fruits and plant species. In this study, the monomer production potentials of ten major fruit and nutshell biomass were investigated with comprehensive numerical information derived from instrumental analysis, such as plant cell wall chemical compositions, syringyl/guaiacyl (S/G) ratios, and contents of lignin substructure linkages (β-O-4, β-β, β-5). A standardized one-pot reductive catalytic fractionation (RCF) process was applied to benchmark the monomer yields, and the results were statistically analyzed using Mantel’s test and Pearson correlations. Among all the tested biomass, mango endocarp provided the highest monolignol yields of 37.1% per dry substrates, respectively. Positive S-lignin (70-84%) resulted in higher monomer yield mainly due to more cleavable β-O-4 linkages and less condensed C-C linkages. Strong positive relationships were identified between β-O-4 and S-lignin and between β-5 and G-lignin. The analytical, numerical, and experimental results of this study shed lights to process design of lignin-first biorefinery in food-processing industries and waste management works.