Biomass Potential of Alkaline-Pretreated Perilla frutescens Residues and Isolation of their Degrading Bacteria

Abstract

Perilla frutescens is a popular aromatic edible plant. The amount of Perilla residues produced by food or pharmaceutical industry is increasing because of the high demand for this plant. At present, most Perilla residues are incinerated, but there is increasing interest in using these materials as a biomass resource. In this study, an alkaline pretreatment to remove lignin from Perilla residues was optimized, and the ash, lignin, and total sugar contents of the treated materials were determined to evaluate their biomass potential. The optimum alkaline pretreatment for Perilla residues was 0.25 M NaOH at 121 °C for 60 min. The lignin and total sugar contents of the alkaline-pretreated Perilla residues were comparable to those reported for grain straw. These results suggest that alkaline-pretreated Perilla residues have high potential as biomass. With dual aims to reduce the volume of Perilla residues and to effectively use this resource, bacteria capable of decomposing Perilla seed shells after alkaline pretreatment were isolated from environmental samples. A total of 66 strains of degraders were isolated, of which one strain (strain SW8) was identified as Klebsiella aerogenes or Raoultella ornithinolytica with both cellulase and xylanase activities. Strain SW8 grew well at 25-35 °C with Perilla seed shells as the sole carbon source. Strain SW8 was identified as a useful bacterium to reduce the volume of, and effectively utilize, Perilla residues.