J. Gen. Appl. Microbiol., 53, 201–205 (2007)

propane units, is an agglutination element in the cell wall of vascular plants. These units are referred to as guaiacyl (a), syringyl (b), and p-hydroxyphenyl, (c) phenyl-propane units (Fig. 1). They are connected in three-dimensional space by C–C and C–O–C bonds. Softwood lignin consists of (a), hardwood lignin of (a) and (b), and herb lignin of (a), (b) and (c). Lignin is taken up as a “dietary fiber” when vegetables and fruits are consumed. It is thought that dietary fiber is useful for the prevention of some diseases (such as cancer) although most is excreted without being digested. To clarify the influence of dietary fiber on an organism, it is important to examine the relationship between the dietary fiber and enterobacteria. It has been reported that cellulose, hemicellulose, and pectin, components of dietary fiber other than lignin, are metabolized by enterobacteria (Van Soest, 1978). On the other hand, it has also been reported that ferulic acid, a model compound of lignin, is metabolized by Enterobacter and Escherichia (Grbić-Galić, 1986). From the results of various reports, it can be stated that the various influences of many components of dietary fiber (other than lignin) on enterobacteria differ. For example, it is reported that guar gum and pectin (both components of dietary fiber) do not influence the status of intestinal bacterial flora (Drasar and Jenkins, 1976; Drasar et al., 1976). The antibacterial activity against Klebsiella pneumoniae, Pseudomonas aeruginosa, E. coli, and Staphylococcus aureus was found in a dietary fiber, chitosan, but not in cellulose or pectin (Nelson et al., 1994). On the other hand, there is a report on the lack of antibacterial activity of pectin (ElNakeeb and Yousef, 1970). In respect to the influence of lignin on enterobacteria, it is reported that woody lignin shows antibacterial activity against Klebsiella pneumoniae, Pseudomonas aeruginosa, E. coli, Staphylococcus aureus (Nelson et al., 1994). The suppressive effect of isoeugenol, a model compound of lignin, and wood lignin extracts (alkali extracts of wood) have also been found to act against Candia albicans and E. coli (Oh-hara et al., 1990; Zemek et al., 1979). However, the influence of herb lignin, which is eaten as a food, on intestinal bacterial flora has not been reported. In this study, the influence on the growth of enterobacteria of lignin extracted from rice bran and the effect of enterobacteria on rice bran lignin were investigated. Effect of herb lignin on the growth of enterobacteria