Surfactant-mediated hydrothermal pretreatment of Ryegrass followed by enzymatic saccharification for polyhydroxyalkanoate production

Abstract

Lignocellulosic biomass from non-food crops is an attractive renewable source of sugars. These sugars can be used as feedstock for the microbial production of different industrially relevant compounds. Delignification of lignocellulosic biomass is a major challenge in sugar extraction. In the present study, ryegrass biomass (non-food), which is high in carbohydrates, was pre-treated with the anionic surfactant sodium dodecyl sulphate (SDS) for effective delignification. Enzymatic hydrolysis of the pre-treated biomass led to the extraction of high sugar levels compared with the raw biomass. Furthermore, these sugars were used for the production of poly-hydroxyalkanoates (PHA), which is an alternative to synthetic polymers. Ryegrass treated with 1% SDS solution at 180°C showed the maximum delignification. This pre-treated biomass was characterised by TGA, FTIR and SEM and showed successful lignin removal. Enzymatic hydrolysis of the resultant pre-treated biomass showed 87% conversion into sugars and was used as a carbon source for the production of medium chain length (mcl) PHAs using two Pseudomonas strains. Both strains accumulated approximately 30% of their cell dry weight in mcl-PHAs. Hence, this study shows for the first time that surfactant pretreatment is effective for lignin solubilisation; this process increased the biomass surface area and improved enzyme actions, resulting in higher sugar extraction.