Can Lignin Be Accurately Measured?

too simplistic (Sarkanen and Ludwig, 1971), and there are now many examples showing that other phenolics Foragesserve animportant rolein providingnutrients toruminants besides the cinnamyl alcohols can be incorporated into while providing positive benefits to the environment. Forage cell wall digestibility is incomplete because of several structural features within lignins (as reviewed by Sederoff et al., 1999). From a the wall, but digestion is mostly inversely correlated with the amount functional point of view, lignins impart strength to cell of lignification that has occurred during cell wall development. Lignin walls, facilitate water transport, and impede the degrais a hydrophobic polymer formed through enzyme-mediated radical dation of wall polysaccharides, thus acting as a major coupling of monolignols, mainly coniferyl and sinapyl alcohols. The lineof defenseagainstpathogens, insects,and otherherpolymerishighlyresistanttodegradationandgenerallypassesthrough bivores. the ruminant unmodified. Though lignin is resistant to degradation, It is important, no matter which definition you prefer, it is not easily quantified within various types of forages. Numerous to be able to determine the concentration of lignin methods have been developed over the years to measure lignin levels within a wide range of cell wall types. Since lignin is in different plant species. Most frequently used among workers infairly resistant to both chemical and biological degradavolved with forage development or utilization are the acid detergent, Klason, and permanganate lignin methods. More recently, acetyl bro- tion, one would think that it would be relatively easy midehasreceivedattentionasapossiblelignindeterminationmethod. to measure (Sarkanen and Ludwig, 1971). Lignin has The acetyl bromide method is dependent on determining the ab- been defined, at least in general chemical terms, for sorbance of the extract in which all the lignin of a sample has been 50 yr and several well-defined procedures to quantify dissolved. Each of these methods gives different lignin values for the lignin in plant tissues have been developed and apsame type of forage sample. For example, acid detergent, Klason, proved as AOAC (Association of Analytical Communipermanganate, and acetyl bromide lignin methods give quite different ties International formerly Association of Official Anavalues for alfalfa stems: 93, 145, 158, and 135 g lignin kg 1