Biomass Potential of Alkaline-Pretreated <i>Perilla frutescens</i> Residues and Isolation of their Degrading Bacteria

<i>Perilla frutescens</i> is a popular aromatic edible plant. The amount of <i>Perilla</i> residues produced by food or pharmaceutical industry is increasing because of the high demand for this plant. At present, most <i>Perilla</i> 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 <i>Perilla</i> 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 <i>Perilla</i> residues was 0.25 M NaOH at 121 °C for 60 min. The lignin and total sugar contents of the alkaline-pretreated <i>Perilla</i> residues were comparable to those reported for grain straw. These results suggest that alkaline-pretreated <i>Perilla</i> residues have high potential as biomass. With dual aims to reduce the volume of <i>Perilla</i> residues and to effectively use this resource, bacteria capable of decomposing <i>Perilla</i> 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 <i>Klebsiella aerogenes</i> or <i>Raoultella ornithinolytica</i> with both cellulase and xylanase activities. Strain SW8 grew well at 25-35 °C with <i>Perilla</i> seed shells as the sole carbon source. Strain SW8 was identified as a useful bacterium to reduce the volume of, and effectively utilize, <i>Perilla</i> residues.