Extraction and intensive conversion of lignocellulose from oil palm solid waste into lignin monomer by the combination of hydrothermal pretreatment and biological treatment

Abstract Empty fruit bunches from palm oil production contain lignin, which can be a source of valuable aromatic chemicals such as protocatechuic acid. In this study, empty fruit bunches were utilized in the hydrothermal pretreatment at different temperatures (100–200 °C) to produce liquid fractions containing depolymerized lignin such as single aromatic chemicals. The liquid fractions then underwent microbial processing by a mutant, ∆pcaHG Rhodococcus jostii RHA1 for six days to produce protocatechuic acid. Hydrothermal pretreatment temperature influenced the types of single aromatic chemicals produced and the sum of area of the single aromatic chemicals in both ethyl acetate extracts and TMS derivatives. The single aromatic chemicals obtained at 160 °C, 180 °C, and 200 °C act as precursors to accumulate protocatechuic acid by ∆pcaHG Rhodococcus jostii RHA1 on the third day of incubation. The role of single aromatic chemicals that acted as either precursors or inhibitors of protocatechuic acid was discussed.