Studies on the Composition of Lignin Isolated from Orchard Grass Hay Cut at Four Stages of Maturity and from the Corresponding Feces

Abstract

Lignin has been reported by a number of workers to be indigestible (7, 9, 13, 14, 16, 17, 20, 39). Other reports indicate that varying amounts of lignin may be digested or broken down in the ruminant digestive tract (4, 8, 10, 11, 18, 22, 23, 28). Since the chemical structure of lignin has not been established, it is not feasible to isolate or determine a product of uniform composition from different materials. Certain characteristics of crude lignin preparations vary considerably, depending upon the material from which it is isolated and the method used for its isolation. Extensive studies have been made of the characteristics of lignin isolated from various woods, but only limited studies have been reported on lignin prepared from forage plants important in animal feeding. Phillips et al. (34) found 4.34 per cent nitrogen in the lignin obtained from oat plants 7 days old, which decreased to 1.26 per cent nitrogen in the lignin from plants 84 days old. Bondi and Meyer (4) reported from 1.18 to 1.63 per cent nitrogen in the lignin from four grass species and from 2.92 to 3.36 per cent nitrogen in the lignin from four legumes. The lignin isolated from the corresponding feces had slightly higher nitrogen contents. They also showed that the lignin nitrogen was resistant to hydrolysis by strong acid (5 h r H2S04), by weak acid (0.5 N HC1), and by pepsin added to the weak acid. These results led these investigators to conclude that the nitrogen in crude lignin preparations was not present as protein nitrogen. Furthermore, the digestive enzymes of the ruminant did not reduce the nitrogen content of the lignin. Norman and Jenkins (26) believed that protein degradation products following the treatment of plant material with strong acid resulted in high lignin yields rather than protein per se. Paloheimo (27), Waksman and Stevens (41), Phillips (29), and DeMan and DeHeus (12) have corrected crude lignin values by deducting the nitrogen content multiplied by the factor 6.25. Phillips (30) later felt that, because there was not a constant relation between the amount of protein added to samples for the determination of lignin and the size of the error involved, the apparent lignin values should not be corrected but the per cent of nitrogen in the lignin should be reported. Thomas and Armstrong (40) found amino acids in the hydrolysates from crude lignin and proposed that the factor 6.25 for converting lignin nitrogen to protein was valid. DeMan and DcHeus (12) found the tyz'osine and the tryptophane nitrogen in the lignin isolated from Lolium perenne was in agree-