Production of Polyhydroxybutyrate from Ralstonia eutropha H-16 Using Makgeolli Lees Enzymatic Hydrolysate

The objective of this study was to investigate the potential use of waste Makgeolli lees (ML), a by-product of Makgeolli production, as a feedstock for biorefinery production of polyhydroxybutyrate (PHB). ML enzymatic hydrolysate (MLEH) was prepared from ML subjected to liquefaction with amylase and subsequent saccharification with glucoamylase. Since MLEH contains glucose (81 g/L) and protein (39 g/L) among other elements, it was used as the carbon source for PHB production by Ralstonia eutropha H-16. After flask incubation with MLEH, the obtained biomass and PHB content were 10.03 g/L and 34%, respectively, which were higher than the contents obtained when using glucose as the sole carbon source. However, batch fermentation resulted in low PHB accumulation despite suitable cell growth being observed, and these results were thought to be due to the unbalanced C/N ratio. To control the C/N ratio to 20:1, sterile glucose solution was added twice in the fed-batch fermentation with MLEH, and we could obtained dry cell weight and PHB of 36.9 g/L and 24.1 g/L, respectively. Therefore, this study demonstrated the potential use of waste ML as a feedstock for industrial PHB production, which has the important advantage of reduced production cost.